• TABLE OF CONTENTS
HIDE
 Front Cover
 Acknowledgement
 Table of Contents
 List of Tables
 List of Figures
 Introduction
 Literature review
 Experimental
 Catalyst preparation and nitrogen...
 Summary
 Appendix: Tables of numerical...
 Bibliography
 Bibliographical sketch
 Back Cover














Title: Preparation and adsorptive properties of thorium oxide
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Permanent Link: http://ufdc.ufl.edu/UF00098221/00001
 Material Information
Title: Preparation and adsorptive properties of thorium oxide
Physical Description: viii, 189 l. : illus. ; 28 cm.
Language: English
Creator: Davis, Burtron H., 1934-
Publisher: s.n.
Place of Publication: Gainesville
Publication Date: 1965
Copyright Date: 1965
 Subjects
Subject: Thorium oxide   ( lcsh )
Chemistry thesis Ph. D
Dissertations, Academic -- Chemistry -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Thesis: Thesis - University of Florida.
Bibliography: Bibliography: l. 183-188.
General Note: Manuscript copy.
General Note: Vita.
 Record Information
Bibliographic ID: UF00098221
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 000424015
oclc - 11069284
notis - ACH2420

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Table of Contents
    Front Cover
        Page i
    Acknowledgement
        Page ii
    Table of Contents
        Page iii
        Page iv
    List of Tables
        Page v
    List of Figures
        Page vi
        Page vii
        Page viii
    Introduction
        Page 1
        Page 2
        Page 3
    Literature review
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
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        Page 15
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        Page 22
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        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
    Experimental
        Page 35
        Page 36
        Page 37
        Page 38
    Catalyst preparation and nitrogen B. E. T. surface area
        Page 39
        Page 40
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    Summary
        Page 159
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    Appendix: Tables of numerical data
        Page 162
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    Bibliography
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    Bibliographical sketch
        Page 189
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    Back Cover
        Page 191
Full Text








PREPARATION AND ADSORPTIVE

PROPERTIES OF THORIUM OXIDE



















By

BURTRON H. DAVIS


A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY












UNIVERSITY OF FLORIDA

June, 1965












ACKNOWLEDGMENTS


The assistance of the author's committee chairman,

Dr. Wallace S. Brey, Jr., in completing the work reported

here is gratefully acknowledged. Even more appreciated,

however, has been his influence on the author's over-all

outlook.

The author would like to acknowledge the financial

support received from the Atomic Energy Commission during

the course of this investigation.

Thanks are also extended to Mrs. Thyra Johnston for

typing the manuscript.













TABLE OF CONTENTS


ACKNOWLEDGMENTS . . .. . . . . . .

LIST OF TABLES. . . . . .. . . . .

LIST OF FIGURES . . . . . . . . . .

Chapter


I


II

I


I. INTRODUCTION . . . . . . . . .

:I. LITERATURE REVIEW . . . . . . .

A. Thoria Preparation Methods Described for
Catalytic Reaction Studies. . . . .

B. Preparation of Thoria from Thorium Oxalate.

C. Thermal Decomposition of Thorium Nitrate
Hydrate . . . . . . . . .

D. Chemistry of Aqueous Thorium Salt Solutions

E. Colloidal Thoria . . . . . .

F. X-Ray Investigations of Thoria. . . .

G. Studies of Adsorption on Thoria . . .

H. Nuclear Magnetic Resonance Studies of
Materials Adsorbed on Solids. . . . .

I. EXPERIMENTAL . . . . . . . . .

:V. CATALYST PREPARATION AND NITROGEN B.E.T.
SURFACE AREA . . . . . . . . .

V. PRESENTATION AND DISCUSSION OF RESULTS . .

A. General . . . . . . . . .

B. Oxalate Catalysts . . . . . . .


Page

ii

v

vi



1

4


4

6


15

14

21

26

28


33
35


39

68

68

74


iii










C. Preparation of Thoria by Thermal
Decomposition of Thorium Nitrate Hydrate 78

D. Preparation of Thoria from Thorium-
Oxalate-Hydroxide. . . . . . ... 79

E. Preparation of Thoria from the
Precipitated Hydroxide . . . . . 81

F. Preparation of Catalysts from Colloidal
Thoria . . . . . . . . . 99

G. Discussion of a Possible Reaction Path for
the Precipitation of Thoria. . . .. 104

H. Precipitation of Thoria from a Mixed
Solvent System . . . . . . .. 112

I. Average Crystallite Size from X-Ray Line
Broadening . . . . . . . .. 114

J. Sintering of Thoria Catalysts. . . ... 120

K. Water Adsorption on Thoria . . . . 122

L. N.M.R. Line Width of Water Adsorbed on
Thoria . . . . . . . . . 137

M. Temperature Dependence of Line Width of
Water Adsorbed on Thoria . . . ... 153

VI. SUMIrARY . ................... 159

APPENDIX . . . . . . . . ... . . 162

BIBLIOGRAPHY . . . . . . . .... . 183

BIOGRAPHICAL SKETCH. . . . . . . . . 189


Chapter


Page












LIST OF TABLES


Table Page

1. Water B.E.T. Surface Areas . . . . .. 165

2. Average Crystallite Size as Determined by
X-ray Line Broadening. . . . . . ... 165

3. Loss of Surface Area by Prolonged Heating. . 168

4. Adsorption of Nitrogen by Thorium Oxide. 169

5. Water Adsorption Isotherms . . . . 170

6. Summary of N.M.R. Samples. . . . . . 172

7. Dependence of Line Width on Surface Coverage 173

8. Temperature Dependence of Line Width . . 177

9. Apparent Activation Energies of Processes
Contributing to the Spin-Spin Relaxation of
Water on Thorium Oxide . . . . .. 181

10. Change in Line Width of Water Adsorbed on
Thoria after Standing Several Weeks at a Given
Surface Coverage . . . . . ... 182












LIST OF FIGURES


Figure Page

1. Concentration of various thorium species for
increasing degree of hydrolysis . . ... 18

2. The (Th(OH)2+2)n chain viewed along [010]
(left) and from the side (right). ..... . 19

3. Nitrogen adsorption isotherm at the boiling
point of nitrogen for catalyst 12-B . . .. .71

4. Plot of P/V vs. P for the Langmuir isotherm for
catalyst series 25. . . . . . . . 72

5. Plot of the linear form of the B.E.T. equation
for catalyst 13-E . . . . . . . 75

6. Plot of surface area vs. average crystallite
size for catalyst series 7 and 21 ...... 77

7. Effect of washing catalyst precipitate on
surface area. . . . . . . . . 83

8. Plot of the nitrogen and water surface area vs.
thorium concentration for catalyst series 9 . 86

9. Plot of nitrogen surface area vs. amount of
ammonium hydroxide added to standard amount of
thorium solution to prepare catalyst series 11. 88

10. Effect of activation conditions on thorium
oxide surface area. ....... . . 93

11. Effect of final pH of thorium solution on the
oxide surface area. . . . . . .. 96

12. Possible structure of [Th(OH)2(N03)2]n. ... 109

13. Plot of average crystallite size as determined
by x-ray line broadening vs. surface area . 115

14. Effect of activation temperature on the average
crystallite size for catalyst series 12 . . 117
vi








Figure Page

15. Plot of crystallite size vs. surface area for
catalyst series 25 . . . . . . .. 119

16. Effect of extended heating periods on the
nitrogen 3.E.T. surface area of thorium oxide. 121

17. Nitrogen surface area vs. water surface area
for oxalate catalysts. . . . . . . 125

18. Nitrogen surface area vs. water surface area
for catalyst series 11, 14, and 21 . . .. .126

19. Plot of nitrogen surface area vs. water
surface area for catalyst series 9 ..... 127

20. Water adsorption isotherm for catalyst 21-B. 133

21. Water adsorption isotherm at 230C for oxalate
catalysts. . . . . . . . . . 135

22. Plot of n.m.r. line width vs. surface coverage
for Th-1.. . . . .. ... . . . 140

23. Plot of n.m.r. line width vs. surface coverage
based on water B.E.T. monoTayer. . . ... 142

24. n.m.r. Line width dependence on surface
coverage based on water B.E.T. monolayer for
oxalate catalysts. . . . . . . ... 144

25. Plot of line width for oxalate catalysts vs.
surface coverage based on water B.E.T.
monolayer. . . . . . . . . . 145

26. n.m.r. Line width vs. surface coverage based
on water B.E.T. monolayer for hydroxide
catalysts . . . . . . . . . 147

27. n.m.r. Line width vs. surface coverage based
on nitrogen B.E.T. nonolayer for hydroxide
catalysts. . . . . . . . . .. 148

28. Spectrum of H20 and D20 adsorbed on catalyst
21-0 . . . . . . . . . . 150

29. Log line width vs. reciprocal temperature for
water adsorbed on Th-5. Surface coverages are
based on water B.E.T. monolayer. . . .. .156


vii









Figure

50. Log of the line width vs. reciprocal
temperature for 0.56 monolayer of water
adsorbed on catalyst 22-B . . . . .


viii












CHAPTER I


INTRODUCTION


The nature of hetereogeneous catalysis is such that

the investigation of this topic lends itself to two general

methods of attack; one is the study of the reaction course

by measurement of its kinetics, products produced, relative

amounts of products produced, radio-isotope distribution in

products from labeled reactants, etc., while the other

approach is to study the nature of the catalytic material

itself in order to elucidate the structure of the catalytic

surface.

Numerous studies have been made employing the study

of the reaction and these studies have shed considerable

light on the reaction path. However for a material to serve

as a catalytic material it is necessary for the reactant to

be in contact with the catalytic material at some stage of

the reaction. Thus any complete description of the reaction

path must present the "structure" of the reactant-catalyst

species. This then requires a knowledge of the structure

of the catalytic surface.

The structure of the catalytic material is determined

to a great extent or even completely by the preparation and

pretreatment of the catalytic material. Yet one encounters








2

all too frequently in the literature detailed studies of

catalytic reactions using a catalyst prepared by "the

thermal decomposition of the metallic salt" or "a sample

of thoria of ordinary reagent grade and unknown history."

This last quote appeared in the literature in 1950 so meager

description of catalytic material is not restricted to the

pioneering studies.

Thorium oxide has been widely studied as a dehy-

dration-dehydrogenation catalyst for alcohols since the

pioneering work of Sabatier and Maihle (1). This catalyst

has been found to give dehydration almost exclusively by

some investigators (1) while others have found the catalyst

to produce both dehydration and dehydrogenation, the amount

of each reaction depending on the particular thoria catalyst

used (2). In addition to the dehydration-dehydrogenation

properties, a recent investigation by Legg (3) has shown

that this catalyst is able to cause condensation of some

n-alcohols to yield either a symmetrical secondary alcohol

or ketone. Many of the catalysts which yielded the above

contradictory results were prepared by "the same method."

The present investigation was undertaken to study the

effect of the various parameters of the thoria catalyst

preparation by noting the effect of a given parameter on

some physical property of the catalyst. Certainly one

physical property which would be related in some manner to









catalytic activity of a material is the surface area. Thus

the effect of various parameters of the preparation was

determined by a measurement of the surface area by the

B.E.T. method (4) using nitrogen at its boiling point as

the adsorbent. This method for surface area measurements

is not without criticism, some of which will be discussed

in more detail in Chapter V; however it has given very re-

producible results when employed by different workers and

is much more convenient and rapid than measuring the

catalytic activity itself.

Lawson (5) obtained n.m.r. results for materials

adsorbed on thoria which appeared to depend upon the

catalyst preparation. Thus another area of the present

study was to be an n.m.r. study of water adsorbed on thoria

samples whose method of preparation led to reproducible

nitrogen surface areas. In this study it is desirable to

be able to obtain the water surface coverage without

resorting to an assumption as to the area occupied by a

water molecule since this area may vary for different

samples (6). Therefore measurement of surface areas for

several catalysts was done to obtain the amount of water

for a monolayer coverage independent of the nitrogen surface

area.












CHAPTER II


LITERATURE REVIEW

A. Thoria Preparation Methods Described for Catalytic
Reaction Studies


The preparation of catalytic materials was reviewed

by Ciapetta and Plank (7) and by Griffith and Marsh (8); in

addition the latter authors give a general discussion of

catalyst evaluation. The literature contains thousands of

recipes for specific catalyst preparations and numerous new

ones appear in the literature each year. Catalyst prepa-

ration directions are usually given, more or less completely,

in the literature for catalytic reaction studies.

Unfortunately these descriptions are very incomplete for

thoria. Most of the preparation procedures given for thoria

preparation merely state that the catalyst was prepared by

thermal decomposition of a thorium salt or precipitation

from a dilute solution. Very few of the descriptions are

given in sufficient detail so that a similar material could

be prepared with any degree of confidence; hence these

preparative methods will not be discussed here.

One reaction study which presents a detailed

description of a thoria preparation is that of Kistler,

Swann, and Appel (9). These authors prepared thorium










hydroxide front the nitrate by precipitation with excess

ammonia, washed free of electrolytes, and then peptized the

hydroxide at 900C by the addition of thorium nitrate. They

obtained a yellow-orange sol. They dialyzed this sol and

then concentrated it by vacuum evaporation. They then

added sufficient citric acid to cause gel formation on

standing; the amount needed was learned from past experience.

The gel was first washed with acetone, then with methanol.

Then the gel was heated in an autoclave nearly filled with

methanol to a point above the critical temperature of the

alcohol. After the critical temperature was reached the

alcohol was slowly bled from the autoclave. This catalyst

was more active for the formation of ketones from acids

than three other catalysts; however the descriptions of the

preparation procedures for the comparison thoria catalysts

were very meager.

Later Kearby and Swann (10) used a variation of the

preceding catalyst preparation but found this catalyst to

be much less active for the dehydration-dehydrogenation of

ethyl alcohol than the one described in the last paragraph.

Dissertations by Legg (5), Moreland (11), and Schmidt

(12) contain discussions of various thoria catalyst prepa-

rations used for the dehydration-dehydrogenation of alcohols

which had appeared in the literature. In addition Moreland

studied the effect of catalyst preparation by the










precipitation method on the dehydration-dehydrogenation of

ethanol in a batch reactor.

The use of thorium oxide as a breeder fuel in nuclear

reactors has motivated numerous studies concerning the

preparation of thorium oxide. However the goal of these

studies was the preparation of high density thoria instead

of high surface area thoria; hence this area of preparation

studies will not be considered here.

B. Preparation of Thoria from Thorium Oxalate

There have been several studies of the thermal

decomposition of thorium oxalate hydrate but few of these

studies have been directed toward the examination of the

thoria which results from the decomposition.

Beckett and Winfield (13) employed thermograms and

electrical conductivity to study the decomposition of thorium

oxalate hexahydrate. They found that ThO2 may appear at

temperatures as low as 2000C. Thorium carbonate concentra-

tion reached a maximum at approximately 3000C and was only

0.075 mole/mole of thorium oxide. By chemical analysis they

found that only the dihydrate was present at 1800C. Between

180 and 2900C not only water but also CO and CO2 was lost.

Extensive decomposition of the oxalate began at 295C and

was practically isothermal. When the oxalate decomposition

was complete there was still about one-half mole of water

remaining in the thoria.









Winfield (14) in an earlier study found that a thoria

catalyst active for the dehydration of 2,3-butanediol was

obtained by the thermal decomposition of thorium oxalate

prepared from thorium nitrate only if the thorium oxalate

had been washed sufficiently to remove traces of the

nitrate ion. In this publication the author also reported

that the thoria from the thermal decomposition of the

oxalate was a much more active catalyst than the ones pre-

pared by ignition of the thorium nitrate or by ignition of

"hydroxide" precipitated from a salt solution; indeed these

latter two preparations gave very inactive catalysts.

Winfield (15) also found that thoria prepared from

washed thorium oxalate by ignition at 4000C for six hours

had a B.E.T. surface area of 24.3 2/g when measured using

nitrogen at liquid oxgen temperature. From water adsorption

isotherms, using a value of o = 10.6 A2 for water, the

author calculated a surface area of 56 m2/g for this same

catalyst.

D'Eye and Sellman (16) thermally decomposed thorium

oxalate dihydrate in an air atmosphere. They found that

the anhydrous oxalate is formed by heating to a temperature

of 2700C. At 3200C they found CO and CO2 to be liberated

in a ratio slightly greater than unity; after five hours at

5200C they increased the temperature to 420C and the ratio

CO:CO2 decreased to approximately 0.3. The total mass of CO










and CO2 exceeded theory; they proposed disproportionation

of CO to C and CO2 followed by air oxidation of the C at

4200C to CO2.

Padmanabhan, Saraiya and Sundaram (17) performed a

differential thermal analysis (D.T.A.) on thorium oxalate

dihydrate. They obtained endothermic peaks at approximately

1600 and 2700C which they attributed to successive loss of

the water of hydration. They obtained an exothermic peak at

roughly 5900C. Wendlandt, George, and Horton (18) performed

the same experiment with thorium oxalate hexahydrate. They

also obtained the first two endothermic peaks and attributed

these to the initial loss of four molecules of water of

hydration, followed by the loss of two more molecules of

water of hydration. However these authors obtained an

endothermic peak at 3850C and a broad exothermic peak at

about 5600C.

Claudel, Perrin, and Trambouze (19) have explained

the above D.T.A. results as being due to the experimental

conditions. With a sample packed tightly in the sample

holder they obtained three endothermic peaks at 1520, 3000,

and 5790C. They interpreted these peaks to correspond to

the removal of four molecules of water, one molecule of

water, and removal of the last molecule of water of hydration

simultaneously with the decomposition of the thorium oxalate,

respectively. However, when they did not pack the sample










tightly and passed a current of air through the sample during

decomposition they obtained not only an endothermic peak at

3640 but also an exothermic peak at 42600. They attributed

the three endothermic peaks to the actual decomposition of

the thorium oxalate hexahydrate and the exothermic peak to

catalytic oxidation of carbon monoxide which is an exothermic

reaction.

Claudel et al. (20) followed the thermal decomposition

of the hydrates of thorium nitrate and oxalate by the

simultaneous thermograviometric, D.T.A., and emanation

methods. They concluded that thorium nitrate decomposed by

successive loss of a water of hydration and then decomposi-

tion of the thorium nitrate. They found the decomposition

reaction of anhydrous thorium oxalate to be a complex

reaction. The D.T.A. curve has two peaks which they

attributed to the formation of two-or three-dimensional

structures through an intermediate Th(CO3)2 phase. The

curve for the emanation has two peaks corresponding to those

for the D.T.A.; in addition it has a peak for the initial

thorium oxalate decomposition.

Bobtelsky and Ben-Bassat (21) studied the titration

and precipitation of thorium as the oxalate from a solution

of the nitrate. They observed that precipitation did not

occur until the ratio Th:0x (Ox represents oxalate anion)

was unity. Further addition of oxalate induced bonding










between the soluble thorium-oxalate complexes, or bonding

of the soluble oxalate complex with oxalate ions or with

other anions in the solution and the formation of cyclic

compounds which are insoluble. In acid solutions, that is,

pH less than ca. 5, the authors supposed the simple Th+4

ion and Ox~ ion form soluble structures; the compounds with

stoichiometrical formula [ThOx] +2, [Th2Ox+2, and [Th Ox5]+2

were postulated to have the structures

F +2 -+2 Ox = Th +2

Th Ox ,and Ox = Th

00C Th = Ox Ox
Ox = Th


respectively. At a pH of approximately 7 the thorium exists
I I
as -Th-O-Th- The free valences are saturated by oxalate
I I
ions, by other hydrated thorium ions, or other anions, for

example, nitrate ions. The authors proposed a reaction

scheme for neutral solutions as follows. The soluble

compounds Th4nOxn, Th nOxn, and Th2nOxn can be presented by

structures such as shown below (n is an integer which could

not be determined by the experimental procedures used; it

is used here to indicate that these formulas are merely

basic units of a larger structure)









I I
-Th Ox -Th-
I I
0 O
I I
-Th- Th-

(Th:Ox = 4:1)


I
- Th -

0
I
-Th-
I


x- T
Ox Th-


-Th-


0 0
I I
-Th- Ox -Th-
I I
(Th:0x = 5:1)


The addition of more oxalate to these soluble oxalate com-

plexes result in the formation of ring structures such as


-Th Ox Th-
I I
Th2nOxn as 0 0
S Ox
-Th-- Ox-- Th-
I I


Th3nOx2n as


i| I
-Th Ox Th Ox Th-
I I I
or 0 0 0
I I I
-Th- -Th- Ox- Th-
I I I


I I I
-Th Ox Th Ox Th-
I I I
O 0 O

-Th Ox Th Ox Th-
I I i


These authors feel that the course of the reaction depends

primarily on the structure of the soluble compounds which

are formed quantitatively in the solution before the begin-

ning of the initial precipitation.

Rombau and Peltier (22) patented a method of prepara-

tion of thorium oxide which involved heating thorium oxalate

in concentrated ammonium hydroxide, washing, then adjusting

the pH of the aqueous suspension of the solid to approximately

2.5, and finally increasing the pH to a predetermined value.

They found that the oxide catalyst formed by thermal

decomposition at 8000C had the highest surface area when the

final pH was adjusted to 6.0. The solid that had a


and










composition of Th:0x = 2:1 gave a higher surface area

material than a solid of the composition Th:0x = 1:1 when

the final pH was 6.0 for both materials.

Allred, Buxton, and McBride (23) studied the effect

the temperature of the thorium nitrate solution, from which

the thorium oxalate was precipitated with oxalic acid, had

on the properties of the oxide obtained after thermal

decomposition. The material precipitated at increasing

temperatures yielded oxides of increasing particle size;

however, no change was noted in the particle size or shape

with an increase of decomposition temperature from 400 to

9000C. Material from the oxalate precipitated at 100C gave

a cubical shaped particle with an edge-to-thickness ratio

of about 3:2; and those from the 1000C material were plate-

lets with edge-to-thickness ratio 6:1. For decomposition

temperatures above 6000C, the material precipitated at 40C

produced the solid of highest surface area. The crystallite

size as determined by X-ray line broadening was apparently

determined by the firing temperature. The authors felt they

had obtained a fundamental relationship between the surface

area, S, and the crystallite size, D, which was S =

(6/pD)(1/F) where p is the density and (1/F) is a packing

factor indicative of the relative crystallite surface area

unavailable for nitrogen adsorption in the B.E.T. surface

area measurement.










C. Thermal Decomoosition of Thorium Nitrate Hydrate

The thermal decomposition of thorium nitrate hydrate

has been investigated by Claudel and Trambouze (24). They

observed that below 2240C the loss of weight when heated at

a rate of 20/minute was greater under vacuum than at atmos-

pheric pressure; at this temperature the weight-loss curves

intersected; and above this temperature the weight loss of

the sample heated at atmospheric pressure was larger. They

explained this by proposing that at atmospheric pressure

the thorium is hydrolyzed by the water of hydration and that

the thoria formed from the hydrolysis acts to provide nuclei

for de-nitration. They propose that above 224AC the

reaction occurring at atmospheric pressure is

Th(NO3) -4ThO2 + 4 NO2 + 02

while under vacuum these two reactions occur (both slower

than the above reaction)

Th(NO ) -ThO(N03)2 + 2 NO2 + 02

1
ThO(NO )2 -ThO2 + 2 NO2 + Z 02

Veron (25) found that the thermal decomposition of

thorium nitrate hydrate yielded thoria with a surface area

(nitrogen B.E.T.) of 55 m2/g at 600C, 29 m2/g at 700C, and

10 m2/g at 9000C.










Winfield (14) found that catalysts prepared by the

thermal decomposition of thorium nitrate at 8000C for 50

minutes or by heating successively for 90 minutes at 2700C,

70 minutes at 4000C, and finally 10 minutes at 4500C, were

inactive for dehydration of 2,3-butanediol.

D. Chemistry of Aqueous Thorium Salt Solutions

There have been numerous investigations of aqueous

thorium salt solutions. These investigations have been

undertaken for a variety of motives; one of the most

frequent reasons has been for the development of analytical

gravimetric procedures where a precipitate of small surface

is desirable. There is a general agreement that, while the

thorium species Th+ may be present at low pH, more complex

species are formed as the OH- concentration is increased

and these species formed are polynuclear thorium complexes.

It is the structure and composition of these species that

causes controversy. Indeed different workers, studying the

same system and obtaining nearly identical experimental

results, have proposed quite different polynuclear species

as being involved in the equilibria at various pH values.

Thus a complete literature survey of thorium ions in

solution will not be attempted; but only a few of the more

recent publications will be discussed.

Schaal and Faucherre (26) made pH measurements on

partially neutralized thorium nitrate and thorium perchlorate










solutions of various concentrations. From these measure-

ments they concluded that the tetramer Th 08+8 was resent

over a considerable range of hydrolysis. Souchay (27)

obtained evidence for this tetramer in his measurements on

the freezing point depressions of thorium nitrate solutions.

Kraus and Holmberg (28) made studies of the change in

emf when a known amount of thorium nitrate or perchlorate

(with sufficient supporting electrolyte to maintain its

concentration at 1 M) was added to solutions at various pH.

This change in pH enabled the calculation of the degree of

hydrolysis of the thorium species. They concluded that at

low pH the principal uncomplexed species of Th(IV) was Th+4

(this species is hydrated, that is, Th(H20)x+ and they

felt that the coordination number should be eight). They

back-titrated solutions with initial hydroxyl number

n = ca. 2 (i.e., n = ca. 2 for the reaction Th+4 + 2n H20 =

Th(OH) n+4-n + n H+) and found that equilibrium is rapidly

established. This is in marked contrast to two other

members of the same "rare-earth" group, Pu(IV) and U(IV);

both of these form polymeric materials for n = ca. 0.5 and

only depolymerize slowly. Hydrolysis of Th(IV) became

appreciable near a pH 3. They made'no attempt to explain

the hydrolyzed species in the region n > ca. 0.5 but state

only that a large number of species will have to be con-

sidered in this region. They assumed the following reactions










to treat the data in the region n < 0.5 and calculated

equilibrium constants for these reactions.

Th4 + 4 H20 = Th(OH)22 + 2 H 3 K = 5.(10-8)

2 Th4 + 4 H20 = Th(OH)4 + 2 H3 0 K = 2.6(10-5)

Hietanen (29) performed potentiometric titrations by

adding NaOH to thorium perchlorate in 1 M C10,~ solution.

He continued the titration until precipitation; at this

point the potential began to drift. For thorium concen-

tration of 20 mM a visible precipitate formed at a pH 3.8-

3.9; for the concentration 2 mM the solution became opaque

at pH 4.7 but the emf became irregular at a pH 3.8. The

author concluded that all complexes formed in appreciable
+4+n
amounts can be written in the form Th(Th(OH))n++n No

n value predominated and no upper limit was found for n but

it must be considerably greater than six. A good approxi-

mation to the experimental data was obtained if it was

assumed that all successive steps in the reaction

Th(Th(OH) )2+4+n + Th+4- Th(Th(OH) )++n + 3 H

had the same equilibrium constant; K = 10-7 .

Hietanen and Sillen (30) studied the hydrolysis of

Th in 0.5 or 0.7 M solutions using chiefly the Cl of

thorium chloride as the ionic medium and limiting themselves

to small degrees of hydrolysis. In addition to the species









Th(Th(OH ) 4n found in the preceding publication they
found evidence for the complexes Th2(OH)2+6 and Th20H+7.

Lefebvre (51) has utilized the pH values from the
titrations of Kraus (28) and apparently others and employed

a method for calculation which he has called "surface
potentiometric titrations." This method derived its name

not because of a titration involving solid surfaces but
from the fact that he related the pH (or pA) change to the

area under a plot of pH versus the concentration of the H+

ion (or A ion). He found that for a value of n (n = number
of hydroxyl groups per thorium atom) less than 0.5 the

assumption of Hietanen (29) is not valid and that his
proposed species is not present in this area. For the

region for n ( 0.5 one has the equilibrium

a Th4 + 2 OH = Th(OH)2+4 a-2

and a varies between one and two, that is, the ratio of the

species Th(H)2+2 and Th2(0H)2+6 varies between one and two.
In the range 0.5 < n < 2 Lefebvre found only the species
Th(OH)2+2, Th2(OH)2+6, and Th5(OH)12+8; thus he found only
a single complex of the type proposed by Hietanen (29) of
the general structure Th(Th(OH) )+4+n Lefebvre then
considers the region n > 2. Here the experimental data are
not sufficiently accurate, because of the discontinuity of
the potential as one approaches the precipitation point, for
exact interpretation. However if the species Th5(OH)12+8 is











precipitated the equivalence point should be at n = 2.4,

whereas precipitation occurs near n = 3. This shows that

the pentacondensed species must disappear as n is increased

toward three. The author feels that as one approached

n= 3 there exists in solution the species Th7(OH)x (where x

has any value between 18 and 21) whose concentration becomes

noticeable at n = 2 and increases rapidly as n approaches

three. The following figure presents the results of the

author's calculations.



1.0
Th*4

Th5(OH)12
Th7(OH)x

0.5


Th2(O H) 2
ThTh(OH(OH) )



1.0 2.0 3.0
n




Fig. 1.-Concentration of various thorium species for
increasing degree of hydrolysis. (Redrawn from J. Chim.
Phys. 55, 227 (1958)).









Lundgren and Sillen (32) determined the structure of
Th(OH)2CrO H20 by X-ray diffraction. The positions of the
Th and Cr atoms were determined by means of the intensities
of the X-ray reflection. The positions of the oxygens were
obtained by assuming the Cr04_ group was a regular tetra-
hedron with Cr at the center, and assuming that the 0-0 and
Th-0 bonds have their minimum distances as determined in
previous crystal structures. The data led the authors to
conclude that the structure of the crystal contained
infinite strings of (Th(OH)2+2)n and finite Cr4O and water
+2
groups. The (Th(OH)22 ) strings contain almost parallel
rows of OH- groups. The Th atoms are situated on alternate
sides of the OH- "ribbon" in such a way that every Th is in
contact with four OH (forming almost a square) and every
OH- is in contact with two Th atoms. The Th-O-Th bond
length is 2.4 A. The chain structure is shown below.







oo 5 10 A
0 0
Th OH


Fig. 2.-The (Th(OH)2+2)n chain viewed along [010]
(left) and from the side (right). (Redrawn from Arkiv.
Kemi. 1, 277 (1949)).










Lundgren (33) made an X-ray study for Th(OH)2SO4.

The only plausible structure that the author could obtain

to satisfy the X-ray intensities was very similar to that

given above for Th(OH)2CrO4H20. Again the long zigzag

chain of composition (Th(OH)2+2 )n held together by sulphate

ions was proposed.

Larsen and Brown (34) investigated thorium nitrate

solutions in dilute nitric and perchloric acids and in pure

water by the X-ray radial distribution method using Waser-

Schonaker formalism involving pair interaction. They found

no indication of the Th-Th bonding indicative of metal ion

hydrolysis and polymerization. The radial distribution

peaks could be interpreted in the terms of the average

features of a distorted antiprism. It was proposed that

two nitrate ions are coordinated as bidentate ligands to a

central thorium ion with the remaining positions being

occupied by water molecules.

Matijevic et al. (35) have investigated the coagula-

tion of silver iodide sols by dilute thorium nitrate

solutions at various pH values. At low pH the amount of

thorium nitrate required for coagulation agrees with the

value calculated by the Schulze-Hardy rule for four-valent

counterions. At pH of four the amount of thorium ions

required for coagulation increases rapidly until at a pH -7

where it leveled off again at a much higher thorium









concentration. The amount of thorium at pH 7 or higher

required for coagulation is just that which is calculated

for a trivalent counterion. These authors proposed this

trivalent species was Th(OH)+3. At the highest pH range

the amount of thorium required dropped sharply suggesting

an ion whose valence was even greater than four.

E. Colloidal Thoria

Colloidal thoria sols were prepared over one hundred

years ago, for example by Bahr (36), and many methods of

preparation have been employed since that time. Two common

methods of preparation are considered below. Blitz (37)

dialyzed a 14 per cent by weight solution of thorium nitrate

and obtained a dilute, water-clear thoria sol containing a

small amount of nitrate ion. The sol was determined to be

positively charged by electropheresis, presumably because

of adsorption of Th+4 or H+ ions. Electrolysis of the sol

caused the particles to be precipitated at the cathode.

hIller (38) prepared a more concentrated sol containing

approximately 150 g thorium hydroxide per liter. First the

thorium was precipitated from the nitrate solution by addi-

tion of base. The precipitate was washed thoroughly and

then the mixture brought to a boil. A solution of thorium

nitrate (200 g thorium nitrate/liter) was added one ml at a

time at five minute intervals. After the addition of about

10.5 ml thorium nitrate solution the solution cleared and










had a slightly opaque or turbulent appearance. According to

MIuller the solid resulting from the evaporation to dryness

of this sol is soluble in water whereas the sol prepared

according to Blitz's procedure gave an insoluble solid.

A more recent study of colloidal thoria was made by

Chun, Wadsworth, and Olson (39). One colloid was prepared

by adding thorium nitrate solution to "thorium hydroxide"

which had been calcined at 3000C for five hours. Another

sol was prepared by treating thorium oxide (from the thermal

decomposition of the oxalate) with nitric acid, then repeated

drying and slurrying in water to obtain a stable sol. Aging

studies were then made on 100 ml samples (not stirred while

aging) of various concentrations and pH. The particle

growth was followed by measuring the decrease of turbidity

with time. The sol from "thorium hydroxide" initially had

cubic crystallites approximately 30 A diameter and rather

uniform in size; the other sol was cubic and 80 A in diameter

but appeared polydisperse. The electron micrographs indi-

cated the samples were isotropic. The optimum temperature

for particle growth was 800C; essentially no growth occurred

at the boiling temperature, at room temperature there was

slow particle growth. X-ray studies showed that the crystal-

lite size did not increase, thus particle growth was due to

aggregation of crystallites. If particles that were aged

in thorium nitrate or potassium nitrate solutions were dried










at 80-900C and redispersed by adding water the turbidity

measurements showed particles essentially the same size as

before aging. The initial particle size and rate of growth

varied inversely with the thorium concentration; the particle

growth also varied inversely with the electrolyte concentra-

tion. There was no growth of particles for the 0.2 H sols.

Dobry-Duclaux, Guinand, and Mathieu-Sicand (40)

reported filamentous inorganic macromolecules were formed

when dilute thorium chloride solutions were hydrolyzed or

treated with dilute ammonium hydroxide to incipient

precipitation. Electron microscope studies revealed some

spheres and filaments from 150 to 2500 A in length and not

over 18 A thick. Molecular weights of 175,000 and 960,000

were calculated from diffusion experiments but these values

are smaller than required for the chain lengths given above.

They found that after dialysis the value of n for the compound

( -Th(OH)20- )n Th(OH)3 Cl varied from 6 to 45 for one series

and from 7 to 50 for another one.
Hentz and Tyree (41) performed light scattering

experiments on solutions of thorium-hydroxide-perchlorate

with the OH:Th ratio from zero to three. The hydrous oxide

was precipitated from a dilute nitrate solution and then

washed until the supernatant liquid reached a pH 7-8. This

ThO2 was then dissolved in sufficient perchloric acid to

give the desired composition of Th(OH)n(C10)x and these










solutions were used as stock solutions; all solutions were

clear except the one with n = 5 and this one was turbid even

after standing three weeks. Aliquots of these stock solutions

were diluted to 100 ml to give final concentrations of Th

from 0.01 to 0.1 M. All experimental solutions were clear.

In none of the series did the degree of polymerization appear

to be appreciably concentration dependent. For hydroxyl

number, n, 0.0 the degree of polymerization was ca. 0.9 and

an unhydrolyzed and uncomplexed species Th(H20)n+4 was

therefore indicated. For n = 1.0 a mononuclear species with

+1 charge was indicated, and the ion Th(OH)(Cl04)2+1 was

suggested. The results at hydroxyl numbers 1.6 and 2.0

indicated the presence of small hydrolytic aggregates with

polymerization numbers near 2.5 and 2.9, respectively. These

data corresponded closely to the near-neutral species

Th2(0H)4(C104)4 at n = 1.6 and Th (OH)6(C104)6 at n = 2.0;

these species have the low charges required for concentration

independence for the light scattering experiment. Extremely

large aggregates were found at hydroxyl number 5.0. The

data indicated a zero charge and polymeric species containing

approximately 140-150 thorium atoms per solute particle.

They ruled out the possibility of colloidal species at

conditions of incipient precipitation because of (a) the

constancy of the turbidity of the solutions over repeated

ultrafine filtrations; (b) the absence of any dissymmetry of










the scattering particles; and (c) the fact that the refrac-

tive index increment was found unchanged when measured before

and after all other measurements and operations. The

measurements at all concentrations appeared to be equilibrium

values although extremely slow processes could not be ruled

out.

Zhukov, Onosov, and Kazantsev (42) studied the

hydrolysis of thorium ions by adsorption by cation-exchange

resins. The sorptive capacity of a KU-1 resin, y, was 2.20

meq/g dry resin. The adsorbability of thorium, x, increased

from 1.8 at pH 0.3 to 9.05 meq Th+4/g at pH 3.6. At high pH

at the beginning of precipitation the experimental results

agree with the compound (Th(CH)4Th)n+4 where n = (x/y) 1.

Anderson (43) calculated the -potentials from the

measured electrophoretic mobility. Adsorption isotherms

were calculated from the --potential by means of the diffuse

double layer theory. The thoria was prepared by heating

thorium oxalate (precipitated from the nitrate solution at

700C) at 105C for 12 hours, 20 hours at 4000C, and 70

hours at 9000C. The electrophoretic mobility was studied

at different pH values by using NaOH to adjust the pH. The

pH effect was complicated and the author found it necessary

to postulate the existence of two pH-dependent dissociation

processes schematically visualized as








26


OH
O~ OTh

>Th'-OOOH hTh
SOH
Th _0- T


+ H'


(low pH) (high pH)

The Cl- ion had a higher adsorbability than the NO ion.

The interpretation of the data for the addition of a thorium

nitrate solution to the aqueous suspension of thoria was

very complicated because there was hydrolysis of the thorium

ion. In spite of the hydrolyzed complex the high adsorption

of the thorium complex ion was apparent. The maximum value

of a the electrokinetic surface charge density, in throium

nitrate corresponds to a surface almost saturated (according

to a Langmuir surface) with positive charge; upon further

increase in concentration marked anion adsorption occurred

giving a sharp decrease in the value of -

F. X-Ray Investigations of Thoria

Some earlier investigators (44) believed that meta

as well as ordinary thorium oxide existed because of the

relative ease of solution in acid of some thoria when the

sample had been heated to temperatures around 6000C. How-

ever Levi and Reiva (45) found from an X-Ray study that the

meta oxide had the same crystal lattice dimensions before









and after peptization and that while the meta oxide is more

finely sub-divided than the ordinary oxide there was no

further sub-division of the individual crystalline granules

in the meta oxide.

Winfield (15) found by X-ray examination of thoria

prepared from the oxalate at 3500C a "super lattice," also

cubic, with a unit cell double the normal thorium oxide

dimensions and which corresponded to the thorium oxalate

lattice. Infield concluded that the "porous" lattice of

the active thoria was stabilized by the presence of water

in "holes" and that removal of this water at higher

temperatures led to partial collapse to normal thoria dis-

tances (the X-ray lines also became sharper as the sample

was heated to 500C).

Draper and Killigan (46) made X-ray diffraction powder

pictures of many thoria samples from the Oak Ridge National

Laboratories. They observed that, in addition to the

standard lines characteristic of cubical thoria, there were

present on nearly all of the negatives additional weak lines

at positions corresponding to inter-plane spacings larger

than those attributable to thoria. Re-examination of several

X-ray diffraction patterns taken previously at the Oak Ridge

National Laboratories showed these faint lines on all photo-

graphs examined. The lines were present for samples heat

treated over a wide range of temperatures, heat treated in










an oxidizing or reducing atmosphere, and samples from various

thorium salts. However these lines were not present when

the thoria was examined using monochromatix X-radiation from

an NaC1 crystal nor were these lines present in electron

diffraction patterns obtained for the samples. Thus these

authors attributed the faint lines to the fact that they

were using X-radiation that was not monochromatic.

Chun, Wadsworth, and Olson (39) obtained lines at

29 = 16.80, 19.70, and 27.90 as well as the strong thoria

peaks at 27.50, 45.780, and 54.200 from an X-ray diffraction

pattern for colloidal thoria samples aged at pH 0.6 and 1.1

at 900C. They did not attempt to explain the data in this

publication.

G. Studies of Adsorotion on Thoria

Chun, Wadsworth, and Olson (47) determined the

dehydration kinetics and equilibrium water vapor adsorption

by thoria gel prepared from thoria obtained by thermal

decomposition of the oxalate similar to the method given in

reference 39. Before study the gel was dried at 90C for

16 hours. Dehydration rates were measured under isothermal

conditions by flushing with dry nitrogen. From room tempera-

ture to 130C, a first order dehydration mechanism was found.

The enthalpy and entropy was calculated from the rate data

on the basis of the absolute reaction rate theory equation.

AF was calculated from AH and AS'; its value was not zero









until a temperature of 1370C was reached. These authors

concluded that the water is adsorbed by hydrogen bonding to

OH NO etc., groups and that this water is thermo-

dynamically more stable than liquid water because of its

higher entropy in the gel state.

Pearce and Alvarado (48) prepared a thoria catalyst

by precipitation from a dilute thorium nitrate solution with

ammonium hydroxide, boiling the solution to expel excess

ammonia, decanting off the precipitating liquid, and washing

eight times. The solid was dried at 1200C for 18 hours,

ground and dried at 2500C for 24 hours, re-ground and dried

at 2500C for 10 more hours. Adsorption isotherms were

measured for ethanol, acetic acid, water, and ethyl acetate

at 99.40C. All adsorption isotherms fit the Freundlich

equation (49) except acetic acid. The thoria gel was

evacuated at 1000C before running the isotherm.

Hoover and Rideal (50) made a study of the adsorption

of nitrogen, hydrogen, ethylene, and ethanol on thoria. The

thoria was prepared by precipitation from a hot, dilute

thorium nitrate solution with ammonium hydroxide, washing

the precipitate free of electrolytes and drying at 1200C.,

The pressure versus volume adsorbed plots for nitrogen and

hydrogen at both 00 and 1000C were nearly straight lines.

The adsorption curves for ethanol had discontinuities at

both 52.3 and 1000C measurements. Using the Kelvin equation










(49) these discontinuities corresponded to average radii of

5.2 and 14 A. However, they attributed the first break to

completion of the adsorption on an active portion of the

surface.

Winfield (15) measured water adsorption isotherms on

thoria prepared by the thermal decomposition of washed

thorium oxalate at 4000C for six hours. The sample was de-

gassed at 2700C for four to six hours before measuring an

isotherm. The author found that the Harkins-Jura equation

for a condensed film (49) loglO(P/Po) = 0.162 1.19/m2 (m

is the number of millimoles of water adsorbed/gram, P is the

pressure, and Po is the saturation pressure at the tempera-

ture) described the isotherm at high relative pressures.

Using this equation a surface area of 95 m2/g was calculated.

The B.E.T. equation in the range of P/Po = 0.05 to 0.35

represented the experimental points with a probable error of

about 2 per cent. The value E1 where E is the heat

of liquification of water and E1 is the average heat of

adsorption of the first monolayer, calculated from the B.E.T.

equation was 3.3 kcal/mole. The water surface area was

56 m2/g using a = 10.6 A2/water molecule; the nitrogen

surface area was only 24.3 m2/g.

Draper and Milligan (46) measured water adsorption

and desorption isotherms for several thoria samples prepared

from thorium oxalate calcined at 8000C. They observed that









adsorption was very slow; periods of over fifty hours were

required to reach equilibrium. They always found some

irreversibly adsorbed water after the adsorption-desorption

run. These samples were subjected to four adsorption-

desorption runs, the thoria was left under high water pres-

sures for as long as a month for the last two runs. All

samples showed an increase of irreversibly adsorbed water

after each run; this increase was attributed to some slow

aging process. One possible explanation of the slow ad-

sorption equilibrium proposed by the authors was that the

thoria had a plate-like structure and diffusion of the

adsorbate vapor between the plates was slow. A calculation

of pore-size distribution using the Kelvin equation for the

desorption curves in the region of hysteresis (P/Po ca. 0.35)

indicated a large number of pores with 10 A radius. Water

surface areas were calculated to be 10 to 20 m 2/g; nitrogen

surface areas for catalysts prepared similarly are about

10 m2/g. Adsorption isotherms were run at higher temperatures

(175 to 2750) after evacuation at 7000C; however the amount

of adsorption was not very large. Heats of adsorption

estimated from these curves are of the order of 20 kcal/mole,

suggesting that chemisorption may be occurring. Samples were

observed with an electron microscope but the information

obtained was limited by the inability to disperse the oxide

so that the individual smaller particles could be observed.










Oblad, Weller, and Mills (51) measured the reversible

adsorption of water on thoria, obtained by calcining thorium

oxalate at 6500C, by passing a nitrogen .stream with the

desired pressure of water vapor over the thoria sample. The

sorption experiments were done at 5930, 5380, and 4820C;

then the thoria was heated to 7600C and the sorptions run at

7040, 6490, and 5930C. The surface area (nitrogen B.E.T.)

was 30 m2/g initially; after heating to 7600C and concluding

the adsorptions the surface area was 12 m2/g. The highest

heat of adsorption measured was 40 kcal/mole.

Holmes and Secoy (52) measured the heats of immersion

for the thoria-water system. Thoria samples were obtained

by calcination of thorium oxalate at 6500, 8000, 10000, and

12000C for four hours. The heat of immersion increased with

outgassing temperature. Thus they concluded that they were

removing progressively more strongly chemisorbed water as

well as physically adsorbed gases with increased outgassing

temperatures. The heat of immersion increased with in-

creasing specific surface area (water monolayer was estimated

from the measured nitrogen surface areas). The dehydration

of surface hydroxyl groups appeared to be a reversible

process. They observed a "slow heat of immersion," that is,

heat was evolved for as long as 90 minutes after immersion;

they proposed that this was due to slow diffusion of water

into the porous structure of the thorium oxide particle.










Both physical and chemical adsorption have been

widely investigated. The theory of adsorption in general

has been treated in several review articles (53) and books

(54). Therefore even an incomplete survey of the literature

on these topics will not be presented in this section.

H. Nuclear Magnetic Resonance Studies of Materials
Adsorbed on Solids

The general theory of nuclear magnetic resonance has

been presented at various levels ofelegance in the past

few years (55). Both Neikam (6) and Lawson (5) have re-

viewed the literature dealing with n.m.r. studies of

adsorbate-solid systems. However special mention should be

made of a series of publications by workers at the Field

Research Laboratory of Socony Mobil Oil Company, Incorporated,

who have made both theoretical and experimental spin echo

studies of water adsorbed on silica gel catalysts (56). From

measurements made at room temperature they have been able to

observe relaxation times corresponding to two distinct ad-

sorbed phases. They felt that this two phase system

distinguished protons in the water adsorbed in and water

adsorbed on the monomolecular layer. Temperature studies

from 1930 to 3740K were made for these silica samples for

various surface coverages. No change of state was indicated

near the freezing point of water. The motional phenomena as

revealed by relaxation measurements were different for the










two environmental states. The state with the longer relaxa-

tion time, state a, exhibited very rapid motion as deduced

by both T, and T2; the activation energy for this motion

was approximately 7 kcal/mole. The low temperature study

indicated that the other state (shorter relaxation time,

state b) has a very rapid motion as indicated by T1 and a

slow motion as indicated by T2. They found that nuclear

transfer occurred more slowly than the above motions. At

room temperature the effective activation energy for nuclear

transfers was about 4.9 kcal/mole; it decreased at higher

temperatures and apparently increased somewhat at lower

temperatures.

Brey and Lawson (57) made measurements of the average

T1 and average T2 for water, alcohols, and butylamine

adsorbed on various thoria samples as a function of surface

coverage and as a function of temperature at particular

surface coverages. Their work will be discussed more

completely in Chapter V.












CHAPTER III


The catalyst preparation methods used for this

investigation varied widely. In addition the catalyst

preparation methods are a major part of the study; thus the

catalyst preparations will be described in a separate

chapter.

The nitrogen 3.5.T. surface areas were determined by

a previously described method (11,58). The catalyst sample

was evacuated for two hours at 2000C; the sample weight was

not corrected for the loss due to removal of adsorbed

materials.

Water 3.2.T. surface areas and water adsorption iso-

therms were measured by directly weighing on an analytical

balance the amount of water adsorbed at each pressure. The

sample, 2-4 g, was placed in a 50 ml Erlenmeyer flask to

which a stopcock had been attached. The sample tube was

attached to the adsorption apparatus by a standard taper

joint. The sample was evacuated at an elevated temperature,

usually 4000C for a four hour period. At each point on the

isotherm, after constant pressure readings indicated that

equilibrium had been established, the cock was closed, the










bulb removed, grease removed from the joint and the bulb

weighed. The pressure was measured by a Zimmerli gauge.

No correction was used for the unadsorbed water vapor present

in the sample bulb. The adsorption temperature was not

controlled precisely; the adsorption temperature was 230C +

20C.

The average crystallite size of the catalyst was

estimated from the width of the X-ray diffraction line for

the (111) crystal plane. The line width was obtained with

a Norelco recording diffractometer using copper K~ radiation

with a nickel filter. The samples were ground to pass

through a 400 mesh screen and packed into a shallow sample

holder. Crystallite size was calculated using the Scherrer

equation (59):

L = kL/j cos 9

where L is the average crystallite dimension perpendicular

to the (111) plane which produced the diffraction, k is a

constant assumed to be equal to unity (see reference 59 for
2 2 2
a discussion of this), and 2 = B b where B is the

measured half-width at half-maximum intensity and b is the

corresponding value for crystalline ThO2 (crystalline ThO2

for these measurements reported for this study was thoria

which had been heated at 12000C).

The magnetic resonance spectra in this study were

obtained from a Model 4300-2 Varian Associates spectrometer










operated at a frequency of 56.4 or 60.0 megacycles. The

spectra were recorded as the derivative of the absorption

signal. The spectrum was recorded at least four times, in

most cases the spectrum was recorded six or more times; in

all cases the average values of these spectra are recorded

in the tables. An exception to this was -or catalyst 21-P

where the line widths were recorded one or more times at

different rates of increasing the static magnetic field.

However the line-widths recorded for the line-width versus

surface coverages were the average of six or more measure-

ments.

The power level from the transmitter was kept several

decibels below that power which gave saturation for the

sample. The amplitude of the sweep field used to modulate

the static magnetic field as it was being varied through

resonance was controlled in order to minimize artificial

broadening. The lowest value of the modulation field that

would give a measurable signal was used to record the spec-

trum.

The temperature dependence of the line width was

studied using a Varian Model V-4340 variable temperature

probe unit. The temperature was controlled by regulating

the flow rate of nitrogen gas passing through a copper coil

immersed in a liquid nitrogen bath. The temperature of the

sample was determined by a thermocouple located on the sample










container wall. The thermocouple reading was correlated to

temperature by comparing the emf of the thermocouple cn the

sample holder wall to the emf of a thermocouple placed in

the sample cavity in an empty sample tube.

A more complete description of the :2: experimental

procedure and the determination of T1 and T2 is presented

in Lawson's dissertation (5).

The NXR catalyst sample, approximately two grams, was

placed in a thin walled 2iR tube commercially available from

Varian. This tube was attached to a vacuum stopcock fitted

with a standard taper joint. A small piece of glass wool

was placed above the catalyst sample to prevent the catalyst

fines from being pumped from the sample tube when the tube

was evacuated. Each 1KR sample was evacuated and heated to

4000C under vacuum and held at this temperature for four

hours. The sample was then removed from the vacuum system,

grease cleaned from the joint, and the sample tube weighed

on an analytical balance. This weight was used to calculate

surface coverages. Water was added in roughly four milli-

gram increments and the nmr signal recorded after each

addition until the NXR line width became narrow (about 300

cps); after this a larger amount of water was added each

time. At least one day was allowed to elapse between

adsorption of the water and recording the XTiR spectrum.












CHAPTER IV


CATALYST P3RPARATI OI: AD -. ::'?02: B .T. SU?3rACE A:c ,


The different catalyst activation methods will be

described before explaining the catalyst preparation pro-

cedures. ..ost of the catalysts were activated by heating

at 6000C under vacuum for four hours. To accomplish this

the catalyst material, previously dried at 1000C, was placed

in a Vycor tube and the tube connected to a vacuum system

by a standard -taper joint. The catalyst was evacuated

continuously during the activation; the pressure was

approximately 0.5-2.0 microns. The activation tube was

placed in a furnace and the furnace temperature kept at

6000C by a h.Feelco temperature regulator. The furnace

temperature reached 400C in approximately fifteen minutes

and 6000C in about 30 minutes; this heat-up tine was taken

to be a part of the four hour activation period.

The catalysts activated in air were placed in either

a Vycor or porcelain boat which was then placed in a 24 mm

Vycor tube. This tube was placed in a 10 inch lon- furnace.

The furnace temperature was controlled by a Tnheelco tempera-

ture regulator. For the first few activations by this

method, air, to aid in the oxidation and to carry away

decomposition products, was forced through the tube by a

59










blower; this caused the temperature to fluctuate so greatly

that no effort was made to force air over subsequent

catalysts during their activation. In addition to this

activation method some catalysts were activated in air by

placing the material in a porcelain dish in a Hevi Duty

Electric muffle furnace. This furnace could not be heated

to the activation temperature nearly as rapidly as could

the 10 inch furnace.

Some of the catalysts were activated in a water vapor

atmosphere. The sample was placed in a porcelain boat in

the Vycor tube which was in the 10 inch furnace. In addi-

tion to this furnace a six inch pre-heater furnace was

placed in front of the main furnace. Steam was generated by

boiling water in a flask with a side arm. The main furnace

was heated to approximately 100C and the pre-heater was

heated to 2500C before beginning the activation. After the

water in the distillation flask was boiling steadily the

flask was connected to the Vycor tube and the temperature

of the main furnace, which had been heated to 1000C before

connecting the steam generator, was increased to 6000C as

rapidly as possible. The activation time was four hours and

the activation was considered to begin when the temperature

of the main furnace was increased above 1000C.

Many of the catalysts had certain steps of their

preparation in common. Unless it is stated to the contrary









under the catalyst series preparation the following conditions

were used for the catalyst preparations:

(a) The thorium hydroxide* prepared by precipitation

was dried at approximately 11000 for 12-24 hours (longer if

necessary to obtain a "dry" solid).

(b) Catalysts were activated for four hours at 6000C

under vacuum.

(c) Wash procedure employed for precipitated catalyst

series from series 4 through 13 was: 200 nl distilled water

was added to the precipitate, the mixture was stirred for

about five minutes with a mechanical stirrer to obtain a

slurry, the precipitate was allowed to settle, and then the

liquid was siphoned off. This procedure was repeated until

the desired amount of washing was accomplished. At pH

below about 7.0 the precipitate began to settle so slowly

that some of the very small particles were lost when the

liquid was siphoned off.

Therefore a modification of the above procedure was

used for the precipitated catalyst series 14 and all subse-

quent precipitated series. Instead of allowing the gel to

settle after stirring the wash water was removed by vacuum


The precipitate obtained by adding base to a thorium
solution will be referred to as thorium hydroxide even though
this material is not a hydroxide in the ordinary sense; many
authors consider the precipitated material to be hydrous
thorium oxide.










filtration using Whatman '42 filter paper. This filter

paper retained all visible thoria precipitate except for

some of the catalysts prepared by precipitation at the

lowest pH values at which precipitation occurred.

(d) The solid Th(TO3)4-4 H20 is very hygroscopic and

it is unlikely that the material used in these studies had

this formula; the water content was probably greater than

given by this formula. However this formula weight was used

for the calculations unless it is stated that the thorium

content was determined gravimetrically. The thorium nitrate

used was the Fisher Certified Reagent grade obtained from

the Fisher Scientific Company.

(e) The ammonium hydroxide was Baker and Adamson,

reagent grade, containing 28-30 per cent T!3 and was used

as received unless stated otherwise for the particular

catalyst preparation.

A. Catalyst 3

Eighty grams of Th(NO3)4 4 H20 was dissolved in 1000

ml distilled water. One hundred ml concentrated ammonium

hydroxide was added rapidly to the stirred (by hand rather

than by the mechanical stirrer) solution. The gel was

divided into equal portions and the washing was done by

putting 100 ml water on the precipitate filter cake and

allowing to filter by gravity. The nitrate test was by the

standard brown ring test (60). The following results were

obtained:







1 43


Catalyst Wash, ml Final pH NKO- Test Surface Area*

3-A 50 9 Positive 0.52, 0.i4
3-3 100 8 Positive 9.4
5-C 150 8 Positive 7.95, 7.13
5-D 200 7 Positive 10.7
3-E 500 6-7 Hegative 6.75, 6.05
3-F 1000 5-6 Negative 14.3
3-H None -- 7.1
3-I Yone -- 2.1


B, Catalyst 4

Sixty g of Th(. 03)~4 H20 was dissolved in 750 ml of

distilled water. One hundred ml aliquots of this solution

were removed and precipitation was effected by dumping 10 ml

of the concentrated ammonium hydroxide into the stirred (by

hand) solution. Each catalyst was washed with 1000 ml of

distilled water by adding 200 ml portions on top of the

filter cake of thorium hydroxide and allowing to filter by

gravity. The surface areas for these catalysts were:

Catalyst Surface Area

4-A 10.9
4-B 16.7
4-C 17.6
4-D 22.3
4-3 21.7
4-F 16.8
4-G 21.7

Eighty g of Th(TO03)-4 H20 was dissolved in 1000 ml distilled

water and the hydroxid. was precipitated by dumping: 100 ml

concentrated ammonium hydroxide into the solution which was

stirred with a mechanical stirrer. The surface areas were:


*All surface areas in this chapter have units of
-2 /g.










Catalyst Surface Area

4-K 29.6
4-L 31.6
4-K? 27.9

C. Catalyst 5

Catalysts 5- -3, and -C were prepared from a solu-

tion of 8 g of thorium nitrate tetrahydrate per 100 ml water;

the remaining catalysts were precipitated from a solution of

70 g thorium nitrate tetrahydrate per liter of solution.

The method of precipitation and washing was as follows (100

ml thorium solution was used for each catalyst):

5-A Precipitated by adding 10 ml concentrated ammonium
hydroxide in approximately three minutes and washed
with 800 ml of water.

5-B Precipitated by slowly adding 10 ml concentrated
ammonium hydroxide to the stirred solution in about
one hour and washed with 600 ml water.

5-C Slowly precipitated by adding just enough concentrated
ammonium hydroxide to the stirred solution in 15 minutes
to cause the thick gel formation (see discussion section'
and washed with 200 ml water.

5-D Same as 5-C except washed with 400 ml water.

5-E A portion of the catalyst 5-D precipitate was washed
with 200 ml of dilute ammonium hydroxide (5 ml concen-
trated ammonium hydroxide in 195 ml of water) and then
washed with 1800 ml water.

5-F Precipitated by dumping 10 ml concentrated ammonium
hydroxide into the thorium solution and then the slurry
was stirred for one hour; the precipitate was washed
with 1000 ml water.

5-G Precipitated by adding dropwise in four minutes 10 ml
concentrated ammonium hydroxide and washed with 100 ml
water.










5-1, 5-H Enough concentrated ammonium hydroxide was added
to cause thick gel formation; washed with 400 ml water.

5-J Ten ml concentrated ammonium hydroxide was added in 50
minutes and washed with 1000 ml water.

5-K Ten ml concentrated ammonium hydroxide was added in 25
minutes and washed with 1000 ml water.

Catalyst Surface Area Catalyst Surface Area

5-A 2.6 5-G 7.5
5-3 0.6 5-H 1.0
5-C 15.0 5-I 4.0
5-D 28.6 5-J 0.5
5-E 0.8 5-K 0.9
5-F 24.2


D. Catalyst 7


These catalysts were prepared from thorium oxalate

which was precipitated from an acid solution with oxalic

acid (61). The precipitation was carried out at approxi-

mately 50C in a solution approximately 1 N in nitric acid

by the addition of a 5-10 per cent excess of an oxalic acid

solution over a 10 minute period. The catalysts prepared

from washed thorium oxalate were prepared from the same

thorium oxalate as the other catalysts below except that

the thorium oxalate was washed ten times with distilled

water.

7-A Thorium oxalate was thermally decomposed by heating
under vacuum by slowly increasing the temperature in
1000C increments each hour to 6000C and held at this
temperature for six hours. The catalyst was very
black after this treatment.

7-B About 3.5 g of catalyst 7-A was placed in about 200 ml
distilled water and heated at 700C for two and one-half
hours. The catalyst was then dried at 1100C.










7-C Thorium oxalate was placed in a porcelain dish and put
in a 18 mm Vycor tube. The temperature was increased
by increments as follows: kept at 10000 for one hour,
then increased by 1000C increments each 30 minutes until
6000C was reached. The temperature was kept at 6000C
for six hours.

7-3 Thorium oxalate was placed in the boat in the Vycor
tube and the temperature increased to 6000C as rapidly
as the furnace could attain this temperature and then
heated at 6000C for six hours.

7-F Prepared the same as 7-E; after solid cooled to room
temperature it was heated in 200 ml water for three
hours at 70-800C. The surface area was determined
after drying at 1000C; then sample was heated to 600C
for two hours.

7-G Thorium format was prepared from thorium nitrate and
formic acid by preparing a concentrated solution of
these compounds and the water was allowed to slowly
evaporate. The thorium format crystals were then
recovered from the saturated solution and dried at 50C.
This thorium format was thermally decomposed the same
as was 7-E.

7-H The furnace was heated to 6000C and then the boat con-
taining the thorium oxalate was placed in the furnace
as rapidly as possible. The temperature dropped to
5000C but rapidly increased to 6000C. The sample was
heated at this temperature for six hours.

7-I Thorium oxalate which had been washed with de-ionized
water was thermally decomposed by the same method as
was used for catalyst 7-H.

7-J Thorium oxalate was heated from room temperature to
6000C; then heated at this temperature for six hours.

7-K Washed thorium oxalate was heated from room temperature
to 6000C then was heated at this temperature for six
hours.

7-L Washed thorium oxalate was heated at 9700C for four
hours.

7-YI Three g of thorium oxalate and 0.075 g of ammonium
nitrate were mixed together by grinding; the mixture
was placed in a boat and heated at 6000C for four hours.










7-N Thorium oxalate was heated to 60000 in air and heated
at this temperature for four hours. The surface area
was determined; then the catalyst was heated in dis-
tilled water at 800C for four hours and re-heated at
6000C for two and one-half hours.

7-0 Three g of washed thorium oxalate and 0.3 g of ammonium
nitrate were mixed by grinding; the mixture was heated
at 6000C in air for four hours.

7-P Washed thorium oxalate was heated in air at 6000C for
four hours.

7-R A mixture of 2.6 g washed thorium oxalate and 0.63 g
ammonium nitrate was heated at 6000C for four hours in
air.

7-S A mixture of 4.1 g washed thorium oxalate and 0.01 g
ammonium nitrate was heated at 6000C for four hours in
air.

7-T A mixture of 3 g washed thorium oxalate and 0.074 g
ammonium nitrate was heated at 60000 for four hours in
air.

7-U Pills were prepared from unwashed thorium oxalate by
compressing under 90,000 p.s.i. and these pills were
heated to 6000C in a stream of oxygen, then they were
heated for four hours at 6000C under vacuum.


7-V Same as 7-U except pills were heated
6000C rather than oxygen.

7-W Same as 7-U except pills were heated
vacuum.


Catalyst
7-A
7-B
7-C
7-E
7-F


7-G
7-H

7-J
7-K
7-L
*Surface
drying at
**Surface
drying at


Surface Area
17.7
21.6
18.1
29.9
37.4*
30.6
55.2
15.8
33.0
12.2
2.3


Catalyst
7-M
7-N1T
7-0
7-P
7-R
7-S
7-T
7-U
7-V
7-W


under nitrogen to


to 6000C under


Surface Area
38.9
37.8**
27.8
18.0
34.5
14.0
25.6
16.8
1.8
1.5


area after heating at 6000C a second time; after
1100C the surface area was 35.4.
area after heating to 6000C a second time; after
1100C the surface area was 38.4.










E. Catalyst 8

Forty g Th(NO3)4*4 H20 was dissolved in 500 ml of

distilled water and precipitated by dumping 50 ml concen-

trated ammonium hydroxide into the stirred (mechanical)

solution. The precipitate was filtered and divided into

six equal portions and washed as follows:

Catalyst NO- Test Ml Wash M1 Wash/g pH Surface
Th(NO 3)44 H20 Area

8-A Positive 200 30 9 1.05
8-B Positive 400 60 9 13.0
8-C Positive 600 90 9 13.3
8-D Positive 1000 150 7-8 22.1
8-E Uncertain 1200 180 5 20.4
8-F Uncertain 1400 210 5 22.8

F. Catalyst.9

Sixty-five g Th(N03)4.4 H20 was dissolved in enough
water to give 375 ml of solution. Aliquots of this solution

were then diluted as described below and each aliquot was

precipitated by dumping into the stirred solution 10 ml of

concentrated ammonium hydroxide.
Catalyst Dilution Resulting M1 Wash Surface
Molarity Area

9-A None 0.30 1800 34.8
9-3 37.5 to 75 0.15 1800 28.6
9-C 37.5 to 137 0.08 1800 18.6
9-D 37.5 to 188 0.06 1800 9.3
9-3 37.5 to 375 0.03 1800 1.1
9-F 37.5 to 750 0.015 2000 1.0
9-G 37.5 to 1500 0.0075 2200 1.1

The following catalysts were prepared by the same procedure

as given above except a stock solution of 60 g Th(N03)4 4 H20









was dissolved in enough water to make 60 ml of solution.

Catalyst Dilution Resulting M1 Wash Surface
Molarity Area
9-K None 1.8 1200 15.9
9-L 10 to 15 1.35 1200 22.0
9-M 10 to 20 0.90 1200 27.4
9-N 10 to 30 0.60 1200 31.2
9-0 10 to 40 0.45 1200 33.5

9-H No dilution, heated to 70C before precipi-
tation, washed with 400 ml acetone. 2.9
9-I Dilution was 37.5 ml to 75 ml, precipitated
at 700C, mixture heated at 700C for one
hour, and washed with 1200 ml water. 32.5
9-J Same as 9-I except the hour heating period
was eliminated from the procedure. 25.2


G. Catalyst 10

Forty g of Th(N03)4*4 H20 was dissolved to make 500 ml

stock solution which was used to prepare the following

catalysts.

10-A One-half ml of concentrated ammonium hydroxide was
slowly added to 100 ml of the stock solution; then
precipitation was completed by dumping 10 ml concen-
trated ammonium hydroxide into the mixture; washed
with 1400 ml water.

10-B Same as 10-A except one ml of concentrated ammonium
hydroxide was added slowly before the rapid precipi-
tation.

10-C Same as 10-A except two ml of concentrated ammonium
hydroxide was added slowly before the rapid precipi-
tation.

10-D Same as 10-A except three ml of concentrated ammonium
hydroxide was added slowly before the rapid precipita-
tion.










Catalyst

10-A
10-B
10-C
10-D


Surface Area

27.7
30.5
23.4
9.9


H. Catalyst 11

One hundred ml aliquots of a stock solution of 40 g

of Th(N 03)*4 H20 per 500 ml were precipitated by dumping

the amount of concentrated ammonium hydroxide indicated be-

low into the stirred thorium solution.

Catalyst M1 Ammonium Hydroxide M1 Wash Surface Area

11-A 7 1200 24.4
11-B 5 1200 8.3
11-C 15 1600 39.4
11-D 20 1600 38.2
11-E 30 2800 41.2
11-F 50 3000 37.6
11-G 100 3000 41.7

I. Catalyst 12

One hundred sixty-six g Th(N03)4 4 H20 was dissolved

in enough water to make one liter of solution. The thoria

was precipitated by dumping 200 ml concentrated ammonium

hydroxide into the solution. It was necessary to divide the

gel into two equal portions before washing due to the bulk

of the precipitate. Each portion was washed twelve times

with 600 ml portions of water. The catalysts were prepared

by activation as described below.







51
Catalyst Surface
Area
12-A 6000C under vacuum for four hours 37.8
12-B 4000C 1" "t 65.9
12-C 5000C f" "t 53.5
12-D 7000C 18.9
12-E 8000C 0.9
12-F 6000C in air for four hours 31.0
12-G 4000C "t 57.0
12-H 5000C f" 49.5
12-I 7000C t"" 3.5
12-J 6000C under water vapor for four hours 28.6
12-K 40000C 60.8
12-L 5000C 42.7
12-M 7000C 11.8
12-N 9000C "t 0.5
12-0 8000C 1.1
12-P 5000C It i 40.5
12-Q 6000C under vacuum for four hours 27.8


J. Catalyst 13

The thorium hydroxide was prepared by dumping 200 ml

of concentrated ammonium hydroxide into 1000 ml of a solution

containing 166 g Th(N03)4 4 H20. The precipitate was divided

into six equal portions and washed with the amount of water

shown below.

Catalyst M1 Wash Water M1 Wash/g Th(NO )4*4 H20 Surface
Area

13-A 200 24 13.7
15-3 400 48 31.4
13-C 500 60 31.8
13-D 600 72 38.8
13-E 800 96 33.8
13-F 1600 192 31.3

K. Catalyst 14

Eighty grams of Th(NO3)4 4 H20 was dissolved in enough

water to make 350 ml of solution. This was precipitated by










dumping 200 ml of concentrated ammonium hydroxide into the

stirred solution. The precipitate was collected by filtra-

tion, then 300 ml of water was added to the solid. This

mixture was stirred for 10 minutes and two aliquots, con-

taining as nearly as possible 1/9t and 1/8t of the total

thorium, respectively, was removed from the slurry while

stirring. The remaining thoria precipitate was collected

by filtration and then placed in 400 ml water and the

mixture again slurried by stirring for 10 minutes. This

time an aliquot was removed which contained 1/7b of the

remaining thorium since two samples were removed from the

first washing. This washing and removing aliquots was

continued until all of the precipitate was washed.

Catalyst Total Water Ml Wash/g Th(NO )4.4 H20 Surface
Added Area

14-A 300 3.8 1.0
14-3 300 3.8 1.0
14-C 700 10.2 28.9
14-D 1100 18.1 36.2
14-E 1500 27.6 44.4
14-F 1900 39.7 42.1
14-G 2300 56.4 38.4
14-H* 2700 32.0
14-I* 3100 33.4
*Heated 15 hours instead of 4 hours.

L. Catalyst 16

These catalysts were prepared by precipitating dif-

ferent concentrations of thorium nitrate solutions with 1.14

times the theoretical amount of ammonium hydroxide by dumping










the required amount of ammonium hydroxide into the stirred

thorium solution. The thorium nitrate concentration was

determined by precipitating the thorium as the oxalate and

igniting the thorium oxalate at 10000C for 24 hours.

Catalyst Thorium Concentration, M M1 Wash Surface
Water Area

16-A 0.282 600 <0.5
16-B 0.217 800 -0.5
16-D 0.0575 800 0.5
16-H 0.0199 800 w0.5
16-J 0.0121 800 <0.5


M. Catalyst 17

17-A Eighty ml of a 0.282 M thorium nitrate solution (thorium
concentration determined by precipitation as the oxalate
for this series of catalysts) was diluted to 800 ml and
the thorium precipitated by adding 250 ml 0.286 M
ammonium hydroxide over a 5 minute period. After 220 ml
was added the solution was merely cloudy; there was
complete precipitation after the addition of 250 ml of
ammonium hydroxide. Precipitate was washed with 200 ml
of water.

17-B Forty ml of 0.282 M thorium nitrate solution was di-
luted to 400 ml and precipitated by adding in 5 ml
increments a total of 125 ml of 0.286 M ammonium
hydroxide. The precipitate was washed with 200 ml
water.

17-D One hundred thirty ml 0.286 M ammonium hydroxide was
added to a solution of 40 ml 0.282 M thorium nitrate
diluted to 400 ml. Washed with 200 ml water.

17-F One hundred forty ml 0.286 M ammonium hydroxide was
added to a solution of 40 ml 0.282 M thorium nitrate
diluted to 400 ml. Washed with 600 ml water.

17-G Same as 17-F except 40 ml 0.282 M thorium nitrate
was diluted to 800 ml.

17-I Same as 17-F except 40 ml 0.282 M thorium nitrate
was diluted to 150 ml.










17-J Forty ml 0.282 M thorium nitrate was diluted to 1600
ml and 140 ml 0.286 M ammonium hydroxide was added.
This amount of base did not cause precipitation or
even cause the solution to become cloudy; 20 ml of
0.286 M base was then added and precipitation was
complete. Washed with 600 ml water.

17-K Seventeen and one-half ml 0.646 M thorium nitrate
solution was diluted to 400 ml and 127 ml 0.519 M
ammonium hydroxide was slowly added. Washed with
400 ml water.

17-L Thirty-five ml 0.646 M thorium nitrate solution was
diluted to 800 ml and 255 ml 0.519 M ammonium hydroxide
was slowly added. Precipitate was collected and was
added to 200 ml wash water. This mixture could not be
filtered and was dried at 1100C without removal of the
wash water.

Catalyst Surface Area Catalyst Surface Area

17-A 57.2 17-I =0.3
17-B 39.6 17-J -0O.3
17-D < 0.5 17-K < 0.3
17-F 0.5 17-L 39.9
17-G -0.3

N. Catalyst 18

One hundred twenty g Th(N05)4-4 H20 was dissolved in

enough water to make 525 ml solution. The thorium was pre-

cipitated by dumping 300 ml concentrated ammonium hydroxide

into the stirred solution. The precipitate was collected

by filtration, slurried with 400 ml water, and filtered.

A portion of the precipitate corresponding to as nearly

l/91b of the total was removed for catalyst 18-A. The rest

of the precipitate was slurried with 400 ml of water and

the above procedure repeated until all the precipitate

had been used.










Catalyst Ml Wash Water/g Th(N03)4.4 H20


18-A
18-B
18-C
18-D
18-E
18-F
18-G
18-H
18-I


3.33
7.08
11.4
16.3
22.3
29.7
39.4
53.7
84.0


Surface Area

1.0
6.1
33.0
47.3
46.7
44.8
41.6
42.1
39.2


0. Catalyst 20


20-A Fifty ml 0.646 M thorium nitrate was added dropwise
to 480 ml of 0.310 M ammonium hydroxide. Mixture
was heated at 1000C for 10 minutes.

20-B Fifty ml of 0.646 M thorium nitrate was added dropwise
to 480 ml of 0.310 M ammonium hydroxide. Mixture was
heated at 800C for 30 minutes.

20-C Same as 20-B except mixture was not heated after
precipitation.

All three catalysts described above were washed with 800 ml

of a solution containing 12 ml of concentrated ammonium

hydroxide.


Catalyst

20-A
20-B
20-C


Surface Area

23.4
11.7
12.1


P. Catalyst 21


21-A Twenty ml 0.646 M thorium nitrate solution (determined
gravimetrically) was diluted to 400 ml and 140 ml
0.319 M ammonium hydroxide was added. The pH was
6.0-6.1 and precipitation of thorium was not complete.
The precipitate was collected but when the precipitate
was heated to 110C to dry the solid re-dissolved. No
precipitation occurred even after nearly all of the
water was evaporated and the solution was cooled to
room temperature. The solid was collected by evapo-
ration to dryness.











21-B Twenty ml 0.646 M thorium nitrate solution was diluted
to 400 ml and enough 0.519 M ammonium hydroxide was
added to give a final pH of 7.0. The precipitate was
washed with 200 ml water.

21-C Same as 21-B except final pH was 8.5.

21-D Same as 21-B except final pH was 8.4 and 600 ml wash
water was used.

21-E Same as 21-B except final pH was 7.95 and 800 ml wash
water was used.

21-F Twenty-five ml 0.646 M thorium nitrate solution was
diluted to 400 ml and enough 0.519 M ammonium hydroxide
was added to give a final pH of 9.0. Washed with
800 ml water.

21-G Same as 21-F except final pH was 10 and 1000 ml wash
water was used.

21-H A solution of 40 g Th(N0O)4.4 H20 in one liter of water
was precipitated by adding enough ammonium hydroxide to
give a final pH of 7.0. The very thick gel formed at
a pH 5.8. The precipitate was washed twice; first with
800 ml water and then with 500 ml. The precipitate
dissolved when heated at 1000C. The pH of the solution
after dissolving the solid was 3.1. The pH of the
solution was re-adjusted to 7.3 with ammonium hydroxide
and the precipitate collected and dried at 1100C.

21-J Ammonium hydroxide was added to 25 ml of 0.646 M
thorium nitrate solution to give a pH of 9.5; then
nitric acid was added to give a final pH of 6.9.
Precipitate was washed with 200 ml of wash water.

21-K Ammonium hydroxide was added to 25 ml of 0.646 M
thorium nitrate solution to give a pH of 9.3; then
nitric acid was added to give a final pH of 7.9.
Precipitate was washed with 200 ml wash water.

21-L Approximately 4 g of catalyst 21-H solid, dried over-
night at 1100C, was added to 500 ml water and the
mixture was heated at the boiling point for three
hours. The pH was 2.5 at a solution temperature of
ca. 500C. The undissolved solid was collected and
washed with about 500 ml of water while on the filter
pad.










21-M Approximately 4 g of catalyst 21-H solid, dried over-
night at 110C, was added to 300 ml water and the
mixture was heated at the boiling point for three
hours. The pH was 2.9 at a temperature ca. 50C.
Enough ammonium hydroxide was added to give a pH of
7.5 at a solution temperature of ca. 500C.

21-N About 4 g of catalyst 21-H solid, dried at 1100C over-
night was added to 500 ml water and the mixture heated
at the boiling point for three hours. Then 700 ml
water was added and the mixture heated overnight. pH
before mixture was heated overnight was 5.5. After
heating overnight ca. 4 g of thorium nitrate tetra-
hydrate was added during a 15 minute period and the
mixture heated for 48 hours; water was added to keep
the volume at one liter. The pH at the end of the
heating was 3.5. The undissolved solid was collected
by filtration and this solid was used for catalyst 21-N.

21-0 Enough ammonium hydroxide was added to the filtrate
from the preparation of catalyst 21-L (which was
milky in appearance) to increase the pH from the
original 3.5 to a final pH of 7.4.

21-P Enough ammonium hydroxide was added to the filtrate
from the preparation of catalyst 21-N to increase the
pH from the original value of 2.1 to 7.2. The solid
was dried at 850C overnight and the solid redissolved.
Enough ammonium hydroxide was added to this solution
to give a pH of 7.2 and the mixture was heated for
about four hours near the boiling point; then the
precipitate collected by filtration. Solid was dried
at 1000C without dissolving.

Catalyst Surface Area Catalyst Surface Area

21-A 26.8 21-H 90.0
21-B 59.6 21-J <0.5
21-C 0.5 21-K =0.5
21-D -=0.5 21-L 69.5
21-E 0.5 21-M 78.6
21-F 5.88 21-N 69.6
21-G 4.35 21-0 110
21-P 114











Q. Catalyst 22

Thirty g of unwashed thorium oxalate (same as used

for catalyst series 7) was slurried in 400 ml water and 50

ml concentrated ammonium hydroxide was added to this slurry.

The mixture was heated at approximately 900C for about two

hours. The solid was collected and added to a nitric acid

solution whose concentration was such that the final pH was

between 2.5 and 5.0 and a volume about 1500 ml. This mixture

was heated for approximately one and one-half hours. The

mixture was cooled to about 600C and divided into four equal

portions. Each portion was used to prepare one of the four

catalysts given below.

22-A Enough ammonium hydroxide was added to the mixture to
give a final pH of 9.0. The solid was washed with
800 ml water.

22-B Enough ammonium hydroxide was added to the mixture to
obtain a final pH of 6.0; the precipitate was washed
with 600 ml water.

22-C Enough ammonium hydroxide was added to the mixture to
give a final pH of 7.0; solid was washed with 600 ml
water.

22-D Enough ammonium hydroxide was added to the mixture to
give a final pH of 8.0; solid was washed with 800 ml
water.

The four catalysts described above were activated for four

hours at 600C in air; the sample was heated in a Vycor

boat in the 10 inch furnace as described at the beginning

of this chapter.










Twenty g of thorium oxalate was heated in about 200

ml concentrated ammonium hydroxide for about one hour. The

solid was collected and heated for about two hours in a

nitric acid solution at a pH of 2.5. This mixture was then

cooled to about 500C and enough ammonium hydroxide added to

give a final pH of 7.0. The solid was washed four times

with 400 ml of wash water each time. This solid was used

to prepare the catalysts listed below.

22-F Approximately 5 g of the solid was heated at 8000C
in air for eight hours in the small furnace in a
quartz tube.

22-G About 3 g of the solid was heated at 8000C in a
muffle furnace for seven and one-half hours.

22-H About 5 g of the solid was heated at 700C for four
hours in the quartz tube.

Catalyst Surface Area

22-A 46.6
22-B 49.5
22-C 51.5
22-D 48.4
22-F 20.0
22-G 10.7
22-H 16.6

R. Catalyst 25

A rapidly precipitated thorium hydroxide solid was

prepared by dumping 200 ml concentrated ammonium hydroxide

into a solution of 80 g Th(N03)4 4 H20 in 500 ml water.

The slowly precipitated solid was prepared by adding 200 ml

concentrated ammonium hydroxide over an hour period to the

same thorium concentration as was used for the rapidly










precipitated thorium solid. The thick gel formed when about

25 ml of the base had been added. These solids were used to

prepare the following catalysts.

23-B Solid from rapid precipitation was heated at 6000C
under vacuum for four hours; solid was not washed
before activation.

23-C Approximately 7 g of the rapidly precipitated hydroxide
solid was added to 200 ml water and the mixture was
heated at approximately 90C for two hours. The pH
at the end of the heating was 3.8; sufficient ammonium
hydroxide was added to the slurry to obtain a pH of
7.0. The precipitate was washed with 200 ml of water.

23-D Same as 23-C except the slowly precipitated solid was
used. The pH at the end of the heating period was 3.2.

23-E Same as 23-C except was filtered after heating without
adding any base and the solid collected was used as
sample 23-E.

23-F Same as 23-D except was filtered after heating without
adding any base and the solid collected was used as
sample 23-F.

Catalyst Surface Area

25-B Cl.0
23-C 90.6
23-D 86.5
23-E 80.0
23-F 83.6

Attempts were made to prepare a slurry of both the slowly

and the rapidly precipitated hydroxide with a pH of 2.5 by

adding nitric acid without heating the mixture. In both

cases all of the solid dissolved before a pH of 2.5 was

reached.









S. Catalyst 24

24-A Approximately 65 ml of a 30 per cent hydrogen peroxide
solution was added to a solution of 25 ml 0.646 M
thorium nitrate in 200 ml of water. The solid was
collected by filtration and dried in air for three
days, then at 1000C for about 12 hours.

24-B Approximately 8 g Th(N03)4-4 H20 was added to 25 ml of
water and then 500 ml of isopropyl alcohol added to
the solution. Concentrated ammonium hydroxide was
added slowly until the solution became cloudy. Then
approximately 20 ml concentrated ammonium hydroxide
was rapidly added. The precipitate was washed three
times with 500 ml portions of water each time.

A stock solution was prepared by dissolving 40 g

Th(NO3)4 4 H20 in 100 ml of water and this stock solution

was used for catalysts 24-C through 24-G. All catalysts

were precipitated by dumping 10 ml of concentrated ammonium

hydroxide into the stirred mixture of the stock solution and

alcohol.

Catalyst M1 Stock Sol'n M1 Isopropyl Alc. M1 Wash Surface
Water Area

24-C 20 100 600 50.5
24-D 20 250 600 67.0
24-E 20 500 600 62.7
24-F 20 1000 1000 7.6
24-G 20 2000 1000 0.8

A stock solution was prepared by dissolving approximately

20 g Th(NO )4.*4 H20 in the minimum amount of water possible

(approximately 20 ml total solution) and this was used to
prepare the catalysts listed below.

24-H Fifteen ml concentrated ammonium hydroxide was dumped
into a mixture of 4 ml stock solution and 21 ml
dioxane. Washed with 400 ml water.










24-I Fifteen ml concentrated ammonium hydroxide was dumped
into a mixture of 4 ml stock solution, 6 ml water, and
15 ml dioxane. Precipitate was washed with 400 ml
water.

24-J Fifteen ml concentrated ammonium hydroxide was dumped
into a mixture of 4 ml stock solution, 11 ml water,
and 10 ml dioxane. Washed with 400 ml water.

24-K Fifteen ml concentrated ammonium hydroxide was dumped
into a mixture of 4 ml stock solution, 16 ml water,
and 5 ml dioxane. Washed with 400 ml water.

24-L Approximately 4 g Th(N03)4.4 H20 was dissolved in 35
ml dioxane and 15 ml concentrated ammonium hydroxide
was dumped into the solution. Washed with 400 ml
water.

Catalyst Surface Area

24-A 5.2
24-B 75.8
24-H 16.9
24-I 40.5
24-J 37.8
24-K 39.3
24-L 14.6


T. Catalyst 25

25-A About 3 g Th(NO3)4.4 H20 was heated to 6000C rapidly
in the 18 mm Vycor tube in the 10 inch furnace and kept
at this temperature for twenty-four hours.

25-B About 5 g Th(N03)4 4 H20 was heated in the muffle
furnace to 6000C. The furnace temperature was about
1000C when the sample was placed in it; the tempera-
ture was increased to 4000C in about four hours with
the door open; then heated to 6000C with door closed.
Heated at 6000C for twenty-two hours.

25-C Sample of Th(N03)4'4 H20 was placed in the muffle
furnace with the furnace temperature 4000C and the
door left open until the oxides of nitrogen ceased
to be evolved, then heated to 6000C; heated at this
temperature for sixteen hours.









25-D Th(NO0)4 4 H20 was placed in a Vycor boat in a 24 mm
Vycor tube about 12 inches in length and heated as
rapidly to 600C as the furnace could do so (ca. 15
minutes) and heated at this temperature for twenty-
four hours.

25-E Sample of Th(N05)4 4 H20 was placed in muffle furnace
at 6000C and was heated at this temperature for
twenty-four hours.

25-F Sample of Th(NO )4.4 H20 was placed in muffle furnace
at 6150C and sample was heated at this temperature for
five hours.

25-G Sample of Th(N 0)4 4 H20 was heated in a Vycor boat
in the 24 mm tube to 2000C, left at this temperature
for approximately 25 minutes; then heated to 2500C
(oxides of nitrogen were given off during this heating
period) and left at this temperature for about 15
minutes; then heated at 3000C for approximately 10
minutes; then the temperature was increased to 6000C
and the sample heated at this temperature for
eighteen hours.

25-H Sample of Th(NO )4 4 H20 was heated in the muffle
furnace, beginning at room temperature and attaining
6000C in about five hours, for a total of fourteen
hours.

25-I Sample of Th(NO3)4.4 H20 was heated to ca. 225C in
air in a Vycor boat in a 24 mm diameter Vycor tube;
heated at this temperature for ca. 20 minutes; then
heated at 3000C for ca. 45 minutes, and then heated
at 6000C for four hours.

25-J Sample of Th(N05)4-4 H20 was heated at 75C for two
hours, then at 1500C for one hour, then at 1800C for
one and one-half hours, then at 2400C for 15 minutes
(decomposition to give oxides of nitrogen during this
period), and then at 6000C for seven hours.

25-K Sample of Th(N03)4.4 H20 was heated under vacuum to
1950C, the temperature dropped back to 1800C quickly
and was kept at this temperature for 15 minutes; then
was heated to 6000C in air and held at this temperature
for four hours.










25-L Prepared by decomposing Th(NO3)4"4 H20 by dropping
the solid into a porcelain dish at red heat. This
catalyst was very bulky for its weight and appeared
very crystalline (see reference 62).

Catalyst Surface Area Catalyst Surface Area

25-A 28.2 25-G 55.5
25-B 14.6 25-H 20.7
25-C 17.1 25-I 58.4
25-D 29.0 25-J 35.4
25-E l<.0 25-K l.0
25-F =0.5 25-L 9.3


U. Catalyst 26

26-A Distilled ammonium hydroxide* was used to precipiate
a solution of 8 g Th(NO3)4 4 H20 in ca. 200 ml of
water. Precipitation was by dumping the base into
the stirred solution. Precipitate was washed six
times with 200 ml portions of water. The solid would
not dissolve in water even after heating at the boil-
ing point for 24 hours. Small portions of thorium
nitrate tetrahydrate were added until about 6 g had
been added; after these additions the solution was
water clear rather than cloudy. Distilled ammonium
hydroxide was added to give a final pH of 6.9. This
solid dissolved when it was heated to 1000C to dry.
About one-half of this solution was used to prepare
catalyst 26-A; the pH of this portion of the solution
was increased to 7.0. This solid dissolved when
dried; the solution was heated to "dryness."

*Baker and Adamson reagent grade concentrated ammonium
hydroxide was vacuum distilled at room temperature; the
distillate was diluted with about five times its volume of
distilled water.

26-B Distilled ammonium hydroxide was added to 30 ml of a
thorium chloride* solution. The solid was washed
four times with ca. 200 ml water each time. This
solid would not acssolve in water after it had been
heated at 1000C overnight even after boiling for 24
hours. Then 25 ml of the thorium chloride solution,
in about 5 ml increments, was added to the boiling
mixture. The solid still would not dissolve. The









26-B (cont'd)

solid material was collected by filtration and was
used for catalyst 26-B.

**Eighty g Th(N03)4.4 H20 was precipitated by addi-
tion of ammonium hydroxide and washed by the siphoning
method used in the earlier catalyst preparations until the
precipitate began to peptize. The solid was then dissolved
in concentrated hydrochloric acid, evaporated to dryness;
the solution in concentrated acid and evaporation process
was repeated two more times. The solid was then dissolved
in enough water to give 500 ml of solution.

26-C The pH of the liquid from catalyst 26-B preparation
was adjusted to 7.5; the solid was washed with 400 ml
of water.

26-J Approximately 10 g Th(N0O)4 4 H20 in 300 ml of water
was precipitated by adding distilled ammonium hydrox-
ide to give a pH of 7.0. The solid was washed with
200 ml of water.

26-K Distilled ammonium hydroxide was added to 1/4t of the
colloidal sol obtained in the preparation of catalyst
26-A to give a final pH of 8.5. Solid was not washed.

26-L Distilled ammonium hydroxide was added to l/4tb of the
colloidal sol obtained in the preparation of catalyst
26-A to give a final pH of 6.5. Solid was not
washed; it dissolved when dried at 1100C.

Fifty ml of the thorium chloride solution** was diluted to

give a volume of 200 ml and then concentrated ammonium hy-

droxide added to give the final pH as shown below.

Catalyst pH M1 Wash Water Surface Area

26-D 5.5 No wash 7.5
26-E 6.5 200 9.1
26-F 7.1 200 19.6
26-G 7.6 400 29.1
26-H 8.5 800 22.0
26-I 10.0 800 2.0










Catalyst Surface Area

26-A -=0.5
26-B 28.6
26-C 38.4
26-J 72.5
26-K 89.4
26-L 76.4


V.. Catalyst 50

Thorium hydroxide was precipitated from a solution

of 80 g Th(N03)4.4 H20 in 500 ml water using a great excess

of concentrated ammonium hydroxide. The sample contained

so much ammonium nitrate that it could not be dried at 1000C.

The sample was put in water and reprecipitated with ammonium

hydroxide. The solid was washed once with 400 ml of water.

It was dried at 1100C. The sample was put in one liter of

water and heated for 48 hours. Most of the material had

not dissolved after this heating. Then 30 ml 0.646 M

thorium nitrate solution was added in 5 ml increments over

a two day period; the mixture was kept at the boiling point

during these additions. Some of the solid still had not

dissolved after this treatment; the mixture was separated

and used to prepare the following catalysts.

30-B The pH of about 1/4t of the solution, after removal
of the insoluble solid, was adjusted from an initial
value of 1.8 to a final value of 7.0 by the addition
of ammonium hydroxide. The solid was not washed.

30-C Same as 30-B except the final pH was 8.5 and solid
was washed with 200 ml of water.







67

30-D Same as 30-B except material was precipitated by
dumping.100 ml concentrated ammonium hydroxide into
the solution; solid was washed with 800 ml of water.

30-E Same as 30-B except final pH was 9.5 and solid was
washed with 200 ml of water.

30-G A portion of the insoluble solid was put in ca. 150 ml
of water and the pH of the suspension adjusted to 6.9.

30-H A portion of the insoluble solid was put in ca. 150 ml
of water and 50 ml concentrated ammonium hydroxide was
added rapidly.

Catalyst Surface Area

50-B 5.0
30-C 62.2
30-D 74.0
30-E 79.5
30-G -1.0
30-H











CHAPTER V


PRESENTATION AND DISCUSSION OF RESULTS

A. General


As indicated in the Introduction much of the study

of heterogeneous catalysis has been, and still is to a

great extent, a poorly defined scientific discipline. One

reason for this is the enormous complexity of a hetero-

geneous solid; indeed the defects present in a so-called

perfect crystal have not been elucidated completely at this

time. In 1954 Emmett wrote, in the preface of volume I of

his series of books "Catalysis" (53c): "In the past,

catalysis has been correctly designated as an art. Those

who have sought to improve catalysts have, accordingly, had

to depend largely on empirical correlations and on a large

measure of intuition in using effectively the mass of

experimental results that have appeared in the literature.

However, within the last thirty years, the art has gradually

been acquiring a considerable coating of scientific

luster . . Though catalysis has not been placed on a

firm scientific foundation, the signs of progress are

numerous and unmistakable."

One reason for little discussion of the catalyst

preparation method in early catalytic studies, such as with









thoria was the belief that the metal oxide, for example,

thoria, had the same properties regardless of the source.

Even after Taylor (63) proposed the heterogeneous nature of

catalysts and Adkins (64) proposed that reactions such as

dehydration were effected by the "porous" structure of the

catalytic material, investigators had no way of measuring

these properties. However, as early as 1925 investigators

began to attempt a measurement of the surface by adsorption

measurements. The first attempts utilized chemisorption and

in a few special cases these were successful, but in general

there was uncertainty as to whether the monolayer was

completed or whether more than a monolayer was adsorbed.

Then in 1958 Brunauer, Emmett, and Teller (4) derived the

B.E.T. equation for multilayer adsorption. This derivation

required assumptions whose justification has been criticized

by many authors (53). However, the equation has been

applicable between relative pressures of about 0.05 to 0.35

for nearly all solids studied to date and has yielded very

reproducible results when employed by different workers in

various laboratories. The B.E.T. method agrees well with

those derived from other viewpoints, for example, Harkins-

Jura method (49). The present situation for the B.E.T.

equation seems to be that while the derivation is not

rigorously correct, the equation provides the best or at

least as good a method for the calculation of the true sur-

face area of a solid as is available at the present time.










In general one would not expect the activity of a

catalyst to be proportional to the surface area. Many

catalytic reactions are believed to be limited to certain

active spots on the surface. Also, for a very porous

material, not all of the surface may be equally accessible

to the reactant. A good correlation is shown by the cata-

lytic activity of chromia-alumina catalysts for the dehydro-

genation of butane (53c); in this case the activity of a

catalyst may be accurately obtained by merely measuring the

surface area. In instances where the reaction takes place

only on certain points, especially where the catalyst is

not a single oxide, the agreement is not as good as in the

above case. However, it has usually been found that the

larger surface area catalysts are more active than the ones

with low surface areas. While Legg (5) did not make reaction

runs over catalysts with a wide range of surface areas, he

did find that the higher surface area thoria, prepared by

precipitation, was more active for the dehydrogenation-de-

hydration of alcohols.

The nitrogen adsorption isotherm for catalyst 12-B

is presented in Figure 3. This isotherm has a shape which

might be interpreted to be a Langmuir isotherm, that is, a

Type I isotherm by Emmett's classification. If this is the

case a plot of P/V versus P should be a straight line with

a slope equal to the monolayer volume, Vm; as seen in Figure

4 this is not the case. Figure 5 is the B.E.T. plot for




























' 0
25 -




-o
< 20 -






E
o
0



E




10 -





5







0.2 0.4 0.6 0.8 1.0
P/Po


Fig. 3.-Nitrogen adsorption isotherm at the boiling point
of nitrogen for catalyst 12-3.













0.85 -



e 25-A
A 25-B
0.75 \ 25-G





0.65 -




U
0.55
E





0.45





0.35





0.25





0.15 II I I
8 16 24 32 40

Pressure, cm

Fig. 4.-Plot of P/V vs. P for the Langmuir isotherm for
catalyst ser-es 25.


















0.030 -





0.025 -
o




0.020 -





0.015 -





0.010 -





0.005 -






0 .05 .10 .15 .20 .25



Fig. 5.-Plot of the linear form of the B.E.T. equation for
catalyst 13-E.










nitrogen adsorption at its boiling point for catalyst 13-E.

The experimental points determine a straight line as pre-

dicted by the B.E.T. theory for multilayer adsorption.

B. Oxalate Catalysts

All catalysts for series 7 were prepared by the

thermal decomposition of thorium oxalate. Thermal decompo-

sition under vacuum does not appear to be a satisfactory

preparation method. The catalyst prepared from the pelleted

material had a very low surface area; the one prepared from

the powder had relatively high area but the catalyst appeared

to be contaminated with carbon. A determination of the CO2

evolved when the catalyst was heated to 950C for a few

minutes in oxygen showed 1.0-1.5 per cent carbon was present;

however, some of this could have been present as the carbo-

nate rather than carbon. These results indicate that, at

least for the un-washed thorium oxalate, the surface areas

produced are higher the more rapidly the sample is heated to

6000C. Also, the washed thorium oxalate produces thoria

whose maximum surface area is only one-half the maximum

surface area obtained from un-washed thorium oxalate.

Thorium format (containing some nitrate) yielded thoria

whose surface area was comparable to the thoria from un-

washed thorium oxalate. It is also noted that the thoria









from un-washed thorium oxalate heated slowly to 6000C, from

un-washed thorium oxalate heated under vacuum to 6000C, and

from the washed thorium oxalate all had approximately the

same surface areas.

It is seen that the addition of ammonium nitrate to

washed thorium oxalate increased the surface area obtained.

Indeed, the addition of 0.63 g ammonium nitrate to 2.6 g of

washed thorium oxalate produced a surface area as large as

that obtained by a similar decomposition of the un-washed

thorium oxalate. The thorium oxalate to which ammonium

nitrate was added should have essentially the same amount

of water present as the washed thorium oxalate; hence it is

not likely that the increased surface area is due to the

water of hydration. Thus it is believed that it is the

ammonium nitrate itself, or more specifically the oxides of

nitrogen, which causes the surface area increase.

It is known that oxides of nitrogen are able to

catalyze oxidations; for example, the oxidation of gaseous

S02, by the formation of intermediate compounds with the

oxygen. Thus it might be possible for the decomposition to

follow a different reaction path in the presence of oxides

of nitrogen.

At the slow rate of heating and heating under vacuum

the ammonium nitrate could vaporize and distill from the

heated portion of the tube before the decomposition tempera-

ture of the thorium oxalate is reached. After heating the










oxalate to which ammonium nitrate had been added, one could

see solid ammonium nitrate condensed on the cooler part of

the reaction tube after the activation was completed. Thus

the slow decomposition, decomposition under vacuum, and

decomposition of the washed oxalate all take place in an

atmosphere with little or no oxides of nitrogen present and

consequently the complete oxidation would be slower than with

the nitrogen oxides present. This still does not explain why

the rapid decomposition leads to a higher surface area; one

possible explanation would be that the slower decomposition

enables the thoria to form more nearly its normal crystal

structure. If this were the case one would expect the low

area catalysts to have larger crystallite sizes; catalysts

7-K and 7-0 fit this pattern but not enough crystallite

sizes have been measured in this series to decide if this

is the case.

Whatever the mechanism might be for producing high

surface thoria it is evident that the nitrogen compounds

present act to enhance the surface area. This is also evi-

dent from a plot such as that made by McBride et al. (23)

of the surface area versus the average X-ray crystallite

size. The low surface area materials prepared by activation

of washed thorium oxalate, by slow thermal decomposition,

and activation under vacuum gave material which did give a

straight line plot, as shown in Figure 6. Indeed, even a




















120



Catalyst 7 o
Catalyst 21 o
i100l -

E




80






60-






40-






0 \
13
0






20 - -I


01
60 80 100 120 140 160
Average Crystallite Size, Angstrons


Fig. 6.-Plot of surface area vs. average crystallite size
for catalyst series 7 and 21.










catalyst activated by heating slowly at 7000C fitted this

curve. The material from the un-washed oxalate came much

closer to falling on the theoretical curve calculated ac-

cording to the McBride et al. equation than on the curve

defined by those samples for which the nitrogen oxides

probably had little effect.

Some of these catalysts which were heated in water

and then outgassed at 2000C before determining the B.E.T.

surface area had the same area as before heating in water;

re-heating to 6000C under vacuum likewise did not alter the

initial surface area.

C. Preparation of Thoria by Thermal Decomposition
of Thorium Nitrate Hydrate

The preparation of thoria catalysts by the thermal

decomposition of the hydrated thorium nitrate is in agree-

ment with Veron (25). The decomposition under vacuum leads

to a low surface area material while the proper decomposition

in air leads to a high surface area material. This is most

easily explained as has been done by Claudel and Trambouze

(24); that is, some of the water of hydration dissolves the

thorium nitrate. This is further supported by the results

of the present work. It was found that the rate of heating

is very important; indeed, surface areas of less than 1 m /g

were obtained by the very rapid decomposition. Also a slow

rate of heating produced a low area material as indicated by










catalyst 25-B. Apparently this slow rate of heating allowed

too much of the water of hydration to be lost before the

decomposition began; that the loss of water is sufficient to

produce a low area material is demonstrated by catalyst 25-K

which was heated to 2000C under vacuum before decomposition

in air. In addition to the requirement found previously

(25), that the decomposition must take place in air to pro-

duce a high area material, it is found that the rate of

heating is critical. Not enough is known about even the

stoichiometry of the material present when decomposition

occurs to speculate as to the path of the thermal decompo-

sition of the hydrous thorium nitrate.

D. Preparation of Thoria from Thorium-Oxalate-Hydroxide

Thoria samples were prepared by the method patented

by Rombau and Peltier (22). No evidence was noted for a

maximum surface area at a pH of 6; samples precipitated at

pH from 6 to 9 had nearly the same surface area. These

catalysts had higher areas than thoria obtained by the

decomposition of essentially pure hydrated thorium oxalate.

According to Rombau and Peltier the solid prepared as was

done in the present study contains only approximately one-

fourth of the theoretical amount of oxalate required to form

Th(C204)2. Thus the solid has a formula ca. Th2(OH)6(C204).

If it is assumed that the precipitation by oxalate is










reversible, that is, oxalate ions can be replaced by OH

ions and vice versa the solid which is in contact with the

supernatant liquid, then the structure of a solid of this

composition would be

0 0 0
SI I
-0 -Th Ox Th Ox -Th --
1 1 I
O 0 0


I I I
0 0 0


In a basic solution such as was used in the preparation of

these catalysts one should expect the bridging groups to be

oxo instead of ol groups.

This structure does not have thorium present in the

eight coordination state unless water of hydration is

present. However if this plate-like two-dimensional struc-

ture remained after thermal decomposition, it would yield a

structure which could explain water adsorption isotherms

which were obtained for these samples.

The past history of the precipitated solid hydroxide

used for the patented procedure was not stressed by these

authors. However, this study shows that the hydroxide solid

bchaves quite differently than the oxalate'solid and the

past history of the hydroxide is very important in deter-

mining the surface area of the solid obtained.









E. Preparation of Thoria from the Precipitated Hydroxide

Moreland (11) observed that the rate of addition of

base for the precipitation of thorium hydroxide* from the

nitrate solution as well as the amount of washing affected

the surface area of the thoria obtained after activation by

heating at elevated temperatures. Catalyst series 3 shows

that the amount of washing apparently affects the surface

area; however, no conclusions could be made since the

surface area did not change uniformly with washing. Moreland

likewise was not able to obtain a consistent relationship

for the surface area with increased precipitate washing.

Catalyst series 4 shows that the method of washing

for series 5, that is, adding 200 ml portions of water to

the precipitate filter cake, and allowing to filter by

gravity, does not give reproducible results. For catalyst

series 4 a large portion of thoria was precipitated and the

precipitate-supernatant liquid mixture divided into nearly

equal portions and each catalyst washed the same way. After

activation the surface areas were found to range from 10.9

to 22.3 m2/g. The activation method, heating at 6000C under

vacuum for four hours, was found to be quite reproducible;

the surface areas for a thoria sample precipitated, washed,

and dried at 1000C as one batch but then divided into three


See footnote, page 41.










portions and activated separately gave surface areas of 14.9,

15.2, and 14.1 m2/g. Since the catalysts for series 4 were

precipitated together the only variable in their preparation

should have been the washing each one received. The same

procedure was used for three other catalysts except the

washing procedure used was to add 200 ml of wash water, stir

with a mechanical stirrer, allow the precipitate to settle,

and then the liquid siphoned off; this wash procedure was

repeated five times. The surface area for these three

catalysts was 29.6, 31.6, and 27.9 m2/g. It was later found

that an even more reproducible washing method was adding

water, stirring with a mechanical stirrer and filtering,

reslurrying and repeating the procedure.

Catalyst series 5 shows the effect of the rate of

addition of an excess of ammonium hydroxide to the thorium

nitrate solution. All of the catalysts prepared by the slow

addition of a considerable excess of concentrated ammonium

hydroxide have a low surface area. The catalyst prepared

by dumping 10 ml concentrated ammonium hydroxide into the

stirred thorium nitrate had an area of 24.2 m2/g, the area

of the one where the addition of 10 ml of base was over a

four minute period was 7.5 m /g; for the addition over longer

periods, the area was less than 1 m2/g.

The effect of washing can be seen in Figure 7. It

is seen that the surface area of the thoria increases rapidly



























































a \



0 0 o 0 0
U)P C\

i ;/Jv YCJ~ 3~!r S


83



0









CC




o o






-P



b.
(0






C,
4-'
4-'







o o
o 0


















CO
o
*H c3











o
ep












Cl-











during the early stages of precipitate washing. Catalyst

series 8 was washed by dividing the precipitated solid into

six equal portions and washing each portion with different

amounts of water by repeatedly slurrying the solid with

200 ml of wash water, stirring, and siphoning off the wash

water. Series 13 was prepared and washed by the same pro-

cedure as series 8 except the thorium concentration for the

former was 0.27 M while for the latter it was only 0.15.

Catalyst 14 was precipitated from a 0.41 M thorium solution.

The entire precipitate was slurried with 300 ml water and

stirred with a mechanical stirrer for 10 minutes. During

the stirring a portion of the suspension was removed and

the precipitate of this portion collected by filtration,

dried, and activated. The water was siphoned from the re-

maining solid and again slurried with 400 ml water and the

washing cycle repeated. Peptization became noticeable after

washing with a total of 1500 ml of water; the precipitate

removed at this time had the maximum surface area. Catalyst

18 was prepared by precipitation from a solution with the

same thorium concentration as for catalyst 14. However,

instead of siphoning off the wash water after each stirring,

the wash water was removed by filtration; a portion of this

gel was dried and activated; the remaining gel was again

slurried and the washing processes repeated. The agreement

of the results for series 14 and 18 is surprising in view










of the experimental difficulties encountered in making

reproducible washings, that is, siphoning off equal amounts

of water each time, filtering to the same "dryness" each

time, and also removing the same amount of catalyst pre-

cipitate each time since the ml of wash/g was calculated

assuming an equal amount of material was removed each time.

It is also noted that the material for which the

maximum surface is higher requires a smaller amount of

washing to attain this maximum value of surface area. This

indicates a more open structure of the hydroxide precipi-

tate, permitting freer access of the wash water to the

interior of the particles with consequent easier removal of

the excess ions.

These results agree with Moreland's conclusions if

additional stipulations are added. The slow addition of

base produces a low surface area catalyst provided an excess

of base is added. If a sufficient excess is added a great

amount of washing will not yield a catalyst with a surface

area as large as 2-3 m /g. His other conclusion that

washing increases the surface area is supported for the early

stages of washing; prolonged washing will cause a decrease

in surface area, particularly for hydroxides which produce

a high maximum surface area thoria.

In Figure 8 the effect of the thorium nitrate con-

centration on the surface area is shown. All catalysts were

















3 0 0 0
CV .'- 0i 0




)o
,5 /Zu D 'e-J )ejns uQSoji!N p





0






4--
C *:




.- 0
I 4)


0




U U
0 I 0
oo N


Em






0 4-)
0



0 C)
ON
o o




0 5 1


SC o
-J c








4-)


-1-)
0 .
5 0 0 I-
"S. ~ ~ 0 UC
\ ~ ~ C ^
^z rl-P
"S. Qrf









ba Pc
6 /u oEJ sson ~t/










precipitated by the same procedure and washed with the same

amount of water. It is apparent that there is an optimum

thorium concentration at approximately 0.3-0.45 molar. There

was a variable here other than the thorium concentration and

that was the volume of thorium solution precipitated. It

was not practical to precipitate as large a volume of the

concentrated solution as was used for the dilute solutions

due to the amount of thoria involved. Thus the speed and

efficiency of stirring, and hence the rate of precipitation,

probably played a role in determining the thorium concentra-

tion which produced the maximum surface area material. The

figure also shows a plot of the water B.E.T. surface area

versus thorium concentration; these results will be discussed

later.

The effect that the amount of excess ammonium hy-

droxide, used for the rapid precipitation, has on the surface

area is evident from Figure 9. A slight excess produces a

low surface area material, and as the amount of ammonium

hydroxide is increased the surface area rapidly increases

and reaches a maximum value; the addition of a larger excess

of base does not increase the surface area. The catalysts

were all washed until peptization began; the larger quanti-

ties of base used for the precipitation required a greater

amount of wash water to reach this point.











88









O



p 0





O~r4

CO
O4



ZZc
O -
C"








0o .
oo -H

I -P

o o
0
















O 0g
0






S 60 V4




rcd
0 -P












O c O
o 4-'




-H W




- o -P


0 000 0 C









Catalysts 16 and 17 show the effect of addition of

base to produce a stoichiometry of Th(OH)n with n between

3.16 and 4.60. It is noted that the addition of enough base

for n to have a value greater than 3.28 caused complete

thoria precipitation; with the exception of 17-A, 17-3, and

17-L the resulting oxides had a surface area less than 1.0

m2/g. Even when 1.14 times the theoretical amount of base

required to form Th(OH)4 was dumped into the solution, the

low surface area resulted.

From what was learned about preparation of high sur-

face area thoria in the experiments described thus far one

should have expected 17-A to have a low surface area since

the ammonium hydroxide was added slowly. Instead, a higher

surface area catalyst was obtained than for any of the

previous preparations. The result for catalyst 17-B was

even more surprising; the only difference between this

catalyst and 17-A was that all quantities of reagents were

halved. The surface area for 17-B was only about two-thirds

the area obtained for 17-A.

Both 17-K and 17-L should have had a low surface area

if, as indicated by the other catalysts of this series, the

addition of enough base to give the stoichiometry with

n = 3.29 is sufficient to cause low surface material to be

formed. However, when 17-L was washed after collection by

filtration, the precipitate peptized to such an extent that










it could not be recovered by filtration. Thus the solid

was recovered by evaporation of the water at 1100C and, as

will be discussed later, this was probably the reason for

the high surface area.

A phenomenon that was noted with the slow precipita-

tion method was a large increase in viscosity as the base

was added to the thorium solution. The viscosity did not

increase noticeably before incipient precipitation was

reached. Even in the initial stage of precipitation the

viscosity did not increase rapidly. As the precipitation

continued the viscosity increased as might be expected.

However, if one continued to add base to the stirred solu-

tion beyond the amount required for complete precipitation,

a point was reached where the viscosity rapidly increased

and, even with stirring, the mixture appeared to set as a

gel. Either continued stirring or the addition of more

base caused the viscosity to decrease. This increase was

also observed for the rapid precipitation but was not as

pronounced except for the very concentrated thorium solutions.

It was felt that a catalyst prepared from this thick

gel should have a large surface area. Several catalysts

were prepared from the thick gel obtained by precipitating

at various rates and from solutions with a wide range of

thorium concentrations. The point at which the thickest gel

formed was difficult to detect since it was only determined










by ease of stirring and by its appearance. It appeared to

require relatively less base for the more concentrated

thorium solutions. With the exception of two catalysts,

none of the catalysts prepared by adding base to thick gel

formation, washing, and then drying the gel had a surface

area greater than 5 m /g. As learned by catalyst series 21,

these two exceptions were undoubtedly due to stopping the

INL40H addition before thickest gel formation.

Gore and Dhar (65) observed and measured the viscosity

of dilute thorium chloride solutions which had been subjected

to hot dialysis to remove the chloride counter-ions. They

concluded that since the viscosity increased steadily with

purity (that is, as more and more Cl- was removed by di-

alysis) the viscosity increase is related to the decrease

in electric charge.

Another interesting, but unexplained, phenomenon was

the spontaneous explosion of the thoria particles. As the

solid was cooled to room temperature after drying at 100-

1100C the particles would spontaneously explode. Cooling

after activation at 6000C under vacuum did not cause much of

this explosion. However, if the solid was ground even after

standing for a few weeks the explosion of particles would

continue for several minutes after grinding was discontinued.

Shaking the material while sieving was sufficient to










initiate the spontaneous explosions which would continue

for several minutes.

The effect of the activation atmosphere was determined

using catalyst series 12 and the results are presented in

Figure 10. The materials activated under vacuum yield the

highest surface material up to temperatures above 700C;

above this temperature the surface was so small no conclu-

sions could be reached. The activations in air and water

vapor do not seem to follow a general trend. The activation

in water vapor, except for the 5000C activation, seems to

follow the trend of the vacuum activation. One would suspect

that the surface area of the catalysts activated in water

vapor would be smaller than the ones activated at the same

temperature in air if water is the only material that causes

the lower surface area for these activations. This is the

case at 4000 and 700C but at 5000 and 6000C the surface

area is higher for the material activated under water vapor.

The effect of aging the hydrous thorium oxide after

drying at 1000C is shown by catalyst 12. This catalyst

hydroxide was prepared in June, 1963. Catalyst 12-A was

obtained by activating some of this hydroxide at 6000C under

vacuum for four hours a few days after precipitation. Some

of this same hydroxide was stored in a closed bottle for 19

months and then activated at 600C for four hours under

vacuum. The surface area of the material activated shortly




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