The preparation, characterization and catalytic activity of a new sold acid catalyst system

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Title:
The preparation, characterization and catalytic activity of a new sold acid catalyst system
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xv, 203 leaves : ill. ; 28 cm.
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English
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Getty, Edward E., 1962-
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Subjects / Keywords:
Catalysis   ( lcsh )
Heterogeneous catalysis   ( lcsh )
Superacids   ( lcsh )
Aluminum chloride   ( lcsh )
Chemistry thesis Ph. D
Dissertations, Academic -- Chemistry -- UF
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bibliography   ( marcgt )
non-fiction   ( marcgt )

Notes

Thesis:
Thesis (Ph. D.)--University of Florida, 1988.
Bibliography:
Includes bibliographical references.
Statement of Responsibility:
by Edward E. Getty.
General Note:
Typescript.
General Note:
Vita.

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University of Florida
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All applicable rights reserved by the source institution and holding location.
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Full Text











'TE PREPARATION, CHARACTERIZATION AND
CATALYTIC ACTIVITY OF A NEW SOLID ACID CATALYST SYSTEM















By

EDEARD E. GETTY


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DECGEE OF
DOCTOR OF PHIIDSOPHY

UNIVERSITY OF FIORIDA

1988

3'OF F LIBRAR!F



































To my parents















ACKNOWLEDGEMENIS


I would like to express my gratitude to Professor Russell S.

Drago for his support and encouragement over the past four years.

Doc made my years in graduate school very enjoyable both in the lab

and on the tennis court. I would also like to thank Ruth Drago for

making Florida seem like a home.

I would like to thank all the members of the Drago group for

their support over the last four your years. I would especially

like to thank Mark Barnes, Jerry Grunewald, Larry Chamusco, and Ngai

Wong for their friendship and help. A special thank you goes to

Alan Goldstein for his comradeship and support.

I am deeply indebted to my wife, Cindy, for all her love and

devotion during our time in graduate school. She has shown me that

there is more to life than work. I will love her always.


iii










TABLE OF CONTENTS


ACENOWLEDGMENT ............................................. iii

TABLE OF NTENTS........................................... iv

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

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

ABSTRA ... ...... ..... ....................................... xiv

CHAPTERS

I. INTROD[TION ..................................... 1

II. REACTION OF HYDR CARBONS............................. 3

2.1 Bakground..................................... 3

2.2 Experimental................................... 9

Reagents.......................................... 9

Instrumentation ................................... 11

Fixed Bed Flow Reactor.............................. 13

Preparation of a Silica Gel Catalyst Doped with
Aluminum Chloride Using Carbon Tetrachloride as
a Solvent...................................... 14

Preparation of an Alumina Catalyst Doped with
Aluminum Chloride Using Carbon Tetrachloride as
a Solvent....................................... 15

Preparation of a High-Silica Zeolite Doped with
Aluminum Chloride Using Carbon Tetrachloride as
a Solvent ....................................... 18

Preparation of a Y-Zeolite Catalyst Doped with
Aluminum Chloride Using Carbon Tetrachloride as
a Solvent....................................... 18

Preparation of a Boron Oxide Catalyst Doped with
Aluminum Chloride Using Carbon Tetrachloride as
a Solvent..................................... 19









Preparation of a Titanium Dioxide Catalyst Doped
with Aluminum Chloride Using Carbon
Tetrachloride as a Solvent..................... 20

Preparation of a Magnesium Oxide Catalyst Doped
with Aluminum Chloride Using Carbon
Tetrachloride as a Solvent....................... 20

Preparation of a Silica Gel Catalyst Doped with
Aluminum Chloride Using Chloroform as a Solvent. 21

Preparation of a Silica Gel Catalyst Doped with
Aluminum Chloride Using Methylene Chloride as a
Solvent ........................................ 22

Preparation of a Silica Gel Catalyst Doped with
Aluminum Chloride Using 1,2-Dichloroethane as a
Solvent ........................................ 22

Preparation of a Silica Gel Catalyst Doped with
Aluminum Chloride Using n-Hexane as a Solvent... 23

Preparation of a Silica Gel Catalyst Doped with
Aluminum Chloride Using Cycldhexane as a Solvent 24

Preparation of a Silica Gel Catalyst Doped with
Aluminum Chloride Using Benzene as a Solvent.... 24

Preparation of a Silica Gel Catalyst Doped with
Aluminum Chloride by Vapor Deposition........... 25

Preparation of a Palladium (II) Chloride-Aluminum
Chloride Doped Catalyst Using Carbon
Tetrachloride as a Solvent...................... 25

Preparation of a Rhodium (III) Chloride-Aluminum
Chloride Doped Catalyst Using Carbon
Tetrachloride as a Solvent .................... 26

Procedure for the Adsorption of Pyridine onto
Supports and Solid Acid Catalysts for the
Characterization of Acid Sites................. 26

Procedure for the Spin Trapping of Radicals on
Solid Acid Catalysts Using MPO ................. 27

2.3 Results and Discussion............................ 28

Preparation of a New Solid Acid Catalyst.......... 28










Characterization of the New Solid Acid Catalysts
by the Infrared Spectroscopy of Adsorbed
Pyridine ........................................ 33

Characterization of a New Solid Acid Catalyst by
27A1 and 29Si Solid-State Magic Angle Spinning
(AS) FTr NR Spectroscopy ..................... 44

Characterization of the Radical on the Catalyst
Surface........................................ 59

Titration of Strong Acid Sites with Pyridine...... 64

Catalytic Cracking of Hydrocarbons by a New Solid
Catalyst System............................... .. 65

Reaction of an Aluminum Chloride Treated Silica
Gel with Various Straight Chained Hydrocarbons
in a Fixed Bed Flow Reactor..................... 65

Reactions of Various Aluminum Chloride
Functionalized Inorganic Oxides with
Hydrocarbons in a Batch Reactor................ 90

Reactions of Hydrocarbon Substrates with an
Improved Solid Acid Catalyst in a Syringe Pump
Flow Reactor................................... 113

Other Acid Catalyzed Reactions Involving
Hydrocarbons and Solid Acid Catalysts........... 122

2.4 Summary............................................ 134

III. REACTION OF CHLRINATED HYDROCARBONS.................. 137

3.1 Background ................ ..................... 137

3.2 Experimental...................................... 140

Reagents....................................... 140

Preparation of a Palladium (II) Chloride-Aluminum
Chloride Doped Catalyst Using Carbon
Tetrachloride as a Solvent..................... 142

Preparation of a Rhodium (III) Chloride-Aluminum
Chloride Doped Silica Gel Catalyst Using Carbon
Tetrachloride as a Solvent...................... 143









Preparation of a Dipotassium Palladium (II)
Chloride-Aluminum Chloride Doped Catalyst Using
Carbon Tetrachloride as a Solvent............... 143

Preparation of a Ruthenium (III) Chloride Doped
Catalyst Using Carbon Tetrachloride as a Solvent 144

Preparation of a Copper (II) Chloride-Aluminum
Chloride Doped Catalyst Using Carbon
Tetrachloride as a Solvent..................... 144

Preparation of a Cobalt (II) Chloride-Aluminum
Chloride Doped Catalyst Using Carbon
Tetrachloride as a Solvent.............. ..... .. 145

Preparation of a Iron (III) Chloride-Aluminum
Chloride Doped Catalyst Using Carbon
Tetrachloride as a Solvent..................... 146

3.3 Results and Discussion.......... ................... 146

Hydrogenation of C-C1 Bonds...................... 146

Hydrodechlorination of Carbon Tetrachloride at
High Conversion Rates......................... 178

Homogeneous Hydrodechlorination of Carbon
Tetrachloride ............................... 181

3.4 Summary....................... ................ 189

IV. N ION ......................... ................... 193

REFERENCES................................................. 197

BIOGRAPHICAL SKETCH.......................................... 203


vii









LIST OF TABLES


TABLE
NUMBER Title Page

2-1 Infrared Shift Data for Pyridine Adsorbed onto
A1C12-X Catalysts............................... 39

2-2 Products Obtained by Cracking Isbutane. .......... 89

2-3 Activities for Different AlC12-Functionalized
Su orts................................... .... 93

2-4 Activities for AlCl2-SiO2 Catalysts Prepared in
Different Solvents............................. 96

2-5 Product Distribution for Catalysts with Varying
Percent of Aluminum Chloride on Silicon
Dioxide........................................ 99

2-6 Activities for Catalysts with Varying Percents of
Aluminum Chloride on Silicon Dioxide ........... 100

2-7 Product Distribution for Catalysts with Varying
Surface Areas Using 50 wt% Aluminum Chloride
on Silicon Dioxide............................. 102

2-8 Activities for Catalysts with Varying Surface
Areas Using 50 wt% Aluminum Chloride on
Silicon Dioxide................................ 102

2-9 Product Distribution for the 50 wt% Aluminum
Chloride on Silicon Dioxide Under Various
Experimental Conditions ........................ 106

2-10 Activities for the Catalyst with 50 wt% Aluminum
Chloride on Silicon Dioxide under Various
Experimental Conditions ....................... 107

2-11 Activities for AC12-SiO2 Catalyst in Different
Solvents and Different Tenperatures............. 108

2-12 Product Distributions for AlCl2-SiO2 Catalyst in
Different Solvents and Different Temperatures... 109

2-13 Activities for AlC12-SiO2 Catalyst at Different
Feed Percents in Carbon Tetrachloride at 100 C
and 25 psig H2 ................................. 111

2-14 Product Distributions for AlC12-SiO2 Catalyst at
Different Feed Percents in Carbon Tetrachloride
at 100l C and 25 psig H2 ........................ 112

viii









LIST OF BABIES
(Cont'd)

Table
Number Page

3-1 Product Distribution for Pd(II)A1C12-Si2 Catalyst
at 90C with H2 and OCl4....................... 148

3-2 Product Distribution for a 3% Palladium-on-
Charcoal Catalyst at 90C with H2 and CC14...... 149









LIST OF FIGURES


Figure
Number Figure Title Page

2-1 The A1 Bending Modes for Pyridinev............... 7

2-2 An EPR Spectrum of a Heterogeneous Acid Catalyst
Before Ocmplete Reaction....................... 16

2-3 An EPR Spectrum of a Heterogeneous Acid Catalyst
After complete Reaction ........................ 17

2-4 Infrared Spectrum of SiO2 Dried at 200C........... 30

2-5 Infrared Spectrum of SiO After Pyridine
Adsorption and Evacuation at Roon Temperature... 31

2-6 Infrared Spectrum of SiO After Pyridine
Adsorption and Evacuation at 150*C.............. 32

2-7 Infrared Spectrum of ACl2-SiO2 Dried at 200C .... 34

2-8 Infrared Spectrum of AC12-SiO2 After Pyridine
Adsorption and Evacuation at Room Temperature... 36

2-9 Infrared Spectrum of A1C12-SiO2 After Pyridine
Adsorption and Evacuation at 150C.............. 37

2-10 Infrared Spectrum of AC12-Si02 After Pyridine
Adsorption and Evacuation at 300"C ............. 38

2-11 An 27Al Solid-State NMR of an AlC12-SiO2 Catalyst
Prepared in the Presence of H20................ 46

2-12 A 29Si Solid-State NMR of an A1C12-SiO2 Catalyst
Prepared in the Presence of H20.................. 47

2-13 An 27Al Solid-State NMR of an Active AlCl2-SiO2
Catalyst Prepared in the Absence of H20......... 49

2-14 An 27Al Solid-State NMR of an ACl2-SiO2 Catalyst
Prepared with a 690 m2/gram Surface Area Silica
Gel......................... ................... 51

2-15 A 29Si Solid-State NMR of an AlCl2-SiO2 Catalyst
Prepared with a 690 nm/gram Surface Area Silica
Gel....... ..................................... 52

2-16 An 27Al Solid-State NMR of an ACl2-SiO2 Catalyst
Prepared with 100 wt% of Aluminum Chloride...... 54










LIST OF FIGURES
(Cont'd)
Figure
Number Figure Title Page

2-17 A 29Si Solid-State NMR of an AlCl2-SiO2 Catalyst
Prepared with 100 wt% of Aluminum Chloride...... 55

2-18 An 27Al Solid-State NMR of an AlC12-SiO2 Catalyst
After Reaction with n-Pentane.................. 57

2-19 A 29Si Solid-State NMR of an AlCl2-SiO2 Catalyst
After Reaction with n-Pentane.................. 58

2-20 Radical on AlC12-SiO2 Spin Trapped Using EMPO
in Toluene...................................... 60

2-21 EPR Simulation of Radical on ACl2-SiO2 ........... 61

2-22 GC Chrcmatogram from the Reaction of n-Pentane
with a Solid Acid Catalyst at Fast Flow Rates... 67

2-23 GC Chrcmatogram from the Reaction of n-Pentane
with a Solid Acid Catalyst at Slow Flow Rates... 68

2-24 Activity Curves for the Reaction of n-Pentane with
a Solid Acid Catalyst at 175C.................. 69

2-25 GC Chrcmatogram from the Reaction of n-Heptane
with a Solid Acid Catalyst at 175C............. 72

2-26 Mass Intensity Report for Propane................. 73

2-27 Mass Intensity Report for Isobutane.............. 74

2-28 Mass Intensity Report for n-Butane................ 75

2-29 Mass Intensity Report for Isopentane ............. 76

2-30 Mass Intensity Report for n-Pentane.............. 77

2-31 Activity Curves for the Reaction of n-Heptane with
a Solid Acid Catalyst at 175C.................. 78

2-32 A Simplified Scheme for the Cracking of n-Heptane. 80

2-33 A Mechanism for the Catalytic Cracking of
Hydrocarbons in the Presence of C14 ............ 85

2-34 GC Chrcmatogram from the Cracking of Resid with a
Solid Acid Catalyst at 175C.................... 91
I eeooooolooooeeooeooo.









LIST OF FIGURES
(Cont'd)

Figure
Number Figure Title Page

2-35 Major Products from the Reaction of n-Hexadecane
with a Solid Acid Catalyst at 175C........... 116

2-36 GC-FTIR Chrmnatogram of the Product Stream from
the Reaction of a Pd(II)C12AlCl2-Si02 Catalyst
with n-Hexdecane at 175*C...................... 118

2-37 Major Products from the Reaction of n-Hexadecane
with a Pd(II)C12A1C12-Si02 Catalyst at 175C.... 119

2-38 COmparison of the A1CI2- and Pd(II)C2A1C12-Si02
Catalysts....................................... 120

2-39 Infrared Spectrum of Purified Neat 1-Hexne....... 124

2-40 Infrared Spectrum of Polymerized 1-Hexene......... 125

2-41 Pregas Sample for the Alkylative Condensation of
Methane by a Solid Acid Catalyst................ 129

2-42 Post Gas Sample for the Alkylative Condensation of
Methane by a Solid Acid Catalyst at 175C....... 130

2-43 Post Gas Sample for the Cracking of n-Pentane
at 175C....................................... 132

3-1 Plot of Activity vs Time for the Reaction of
Pd(II)Cl2AlCl2-Si02 Catalyst with C14 and
H2 at 90C........................... .......... 152

3-2 Comparison of the Product Distributions for the
Reaction of Various Catalysts with OC14 at 1000C 159

3-3 GC-FIIR Chromatogram of the Product Stream from
the Reaction of a Pd(II)Cl2AlCl2-Si02 Catalyst
with 1,2-Dichloroethane at 175C............... 161

3-4 Infrared Spectrum of Vinyl Chloride with EPA Vapor
Phase Library Best Matches.................... 163

3-5 Product Distribution from the Reaction of 1,2-
Dichloroethane with Pd(II)C12A1Cl2-Si2
Catalyst at 100'C and a Flow Rate of 1ml/2.4 sec 164


xii









LIST OF FIGURES
(Cont'd)
Figure
Number Figure Title Page

3-6 Product Distribution frmn the Reaction of 1,2-
Dichloroethane with Pd(II) C12AC12-SiO2
(Type II) Catalyst at 100C and Various Addition
Times .......................................... 165

3-7 Product Distribution from the Reaction of 1,2-
Dicfloroethane with Pd(II) C2A1Cl2-SiO2
{Type II) Catalyst at Various Temperatures...... 166

3-8 Product Distribution from the Reaction of 1,2-
Dichloroethane with Rh(III)C13AlCl2-SiO2
Catalyst at Various Temperatures............... 168

3-9 Product Distribution from the Reaction of 1,2-
Dichloroethane with Ru(III)C13AClC2-SiO2
Catalyst at Various Temperatures............... 170

3-10 Product Distribution fran the Reaction of 1,2-
Dichloroethane with K2Pd(II)Cl4AlC12-SiO2
Catalyst at Various Temperatures............... 171

3-11 Product Distribution from the Reaction of 1,2-
Dichloroethane with Pd(II)Cl2AlCl2-SiO2 (Type I}
Catalyst at Various Temperatures ............... 172

3-12 OCnparison of all Catalysts Reacted with 1,2-
Dichloroethane at 100C ........................ 173

3-13 Camparison of the PdC12 and K2PdC14 Doped Solid
Acid Catalysts (Type I)......................... 174

3-14 COmparison of the PdC12 Doped Acid Catalysts
Prepared by Method I and Method II.............. 175

3-15 Product Distribution for the Reaction of 1,2-
Dichloroethane with AlCl2-SiO2 catalyst at
Various Reaction Temperatures........ ......... 177


xiii















Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

THE PREPARATION, CHARACTERIZATION AND
CATALYTIC ACTIVITY OF A NEW SOLID ACID CATALYST SYSTEM

By

Edward E. Getty

December 1988

Chairman: Russell S. Drago
Major Department: Chemistry

The preparation and use of solid strong acid catalysts and

superacids are active areas of research. Solid acids and superacids

are reported to exhibit extremely high catalytic activities for

reactions such as isamerization, cracking, hydrocracking,

dehydration, alkylation, acylation, conversion of methanol to

gasoline, and so forth. Recent research in this area has focused on

the preparation of stronger solid acids and their characterization.

Advantages of solid acid catalysts over liquid acid catalysts

include ease of separation from reaction mixture and high

selectivity or specific activity.

A series of novel solid strong acids has been prepared by

treatment of inorganic oxides by Lewis acids. The method of

creating or enhancing the number of tetrahedral aluminum centers on

inorganic oxides has led to a series of novel solid acid catalysts

which displays an increased acidity over the supports alone.


xiv









Investigations of acid sites by the infrared spectroscopy of

adsorbed pyridine, calorimetric titrations and solid-state nuclear

magnetic resonance on a series of new solid acid catalysts will be

discussed. This new solid acid catalyst system exhibits high

catalytic activity and selectivity for cracking reactions under

relatively mild conditions. In addition to the reactions of

hydrocarbons, the reactions of various polychlorinated molecules

have been studied.















CHAPTER I
INTRODUCTICN



Since the introduction of amorphous silica-alumina solid acids

over 40 years ago, catalytic cracking has become one of the world's

most important processes for the refining of petroleum. [1] The

popularity of the catalytic cracking process results from its

flexibility in treating a variety of feedstocks used in refinery

processes. [1-3] Temperatures of 450-550 C and pressures of 1-2 atm

are typical reaction conditions. [2] Amorphous silica-aluminas and

zeolites are the most common catalysts used and recent trends in

catalytic cracking research are aimed at enhancing the acidity of

these catalysts. [4]

The preparation and use of strong solid acids and superacids as

catalysts are active areas of research.[4,5] These materials

exhibit extremely high catalytic activity for reactions such as

iscmerization, cracking, hydrocracking, dehydration, alkylation,

acylation, conversion of methanol to gasoline, and so forth. [4,5]

Advantages of solid acid catalysts over liquid acid catalysts

include ease of separation from reaction mixture and high

selectivity or specific activity. [4]

In view of the higher activity of tetrahedral aluminum Lewis

acids than octahedral Lewis acids, we are interested in preparing

solids containing stable tetrahedral aluminum sites. As a result

1









2

of this research a new solid, strong acid catalyst system is

reported which exhibits high catalytic activity and selectivity for

catalytic cracking reactions under relatively mild conditions. In

the following chapters the synthesis, characterization, and

catalytic activity for these new solid acid catalyst systems are

reported.

The synthesis, characterization, and catalytic activity of

these catalysts for the catalytic cracking of hydrocarbons is

discussed in Chapter II. The synthesis and catalytic activity of

various solid acid catalysts doped with metals is discussed in

Chapter III. In addition to cracking, the dehydrochlorination and

hydrodechlorination of various polychlorinated hydrocarbons is

reported.















CHAPTER II
REAC IN OF HYERCARBNS



2.1 BACKGROUND



Since the introduction of acid-treated clays and amorphous

silica-alumina solid acids as cracking catalysts in the late 1930s,

catalytic cracking has became the most important process for the

refining of crude petroleum in the world. [1-3] In 1985 the

petroleum industry bought 370 million lbs of catalytic cracking

catalysts at a cost of 250 million dollars. The projected use of

catalytic cracking catalysts in 1990 is expected to increase to 405

million lbs which is worth 275 million dollars. [6] Because of the

large volumes of solid acid cracking catalysts used and the

importance of the petroleum refining process, a large amount of

research has been conducted in the area of solid acid and superacid

catalysis. [1-6]

Currently, the preparation and use of strong acid catalysts and

superacids are active areas of research. These materials exhibit

extremely high catalytic activity for reactions such as

ismnerization, cracking, hydrocracking, dehydration, alkylation,

acylation, conversion of methanol to gasoline, and so forth. [5]

Because of the reported advantages of solid acid catalysts[4],









4
recent research has focused on the preparation and

characterization[2,4,5] of stronger solid acids.

Many attempts have been made to use metal halides as

homogeneous acid catalysts and one of the most frequently studied

inorganic Lewis acid metal halides is aluminum chloride. Aluminum

chloride was even tested commercially but was abandoned because of

technical difficulties such as corrosion, separation of phases,

difficulty in the recovery of the catalyst and the formation of high

molecular weight hydrocarbons. [2,3] As a result recent research has

focused on the anchoring of homogeneous acid catalysts onto

inorganic oxides for use as solid acid catalysts. [2-7]

Many patents have been issued for the treatment of inorganic

oxides with aluminum chloride. [8-15] the most coamon method of

treating hydroxylated inorganic oxides with aluminum chloride is by

vapor deposition. [4,8-14] The vapor deposition is conducted by

passing the vapors of aluminum chloride through the inorganic oxide

using a carrier gas such as helium[7,9,10,12,14] or sublimation of

the aluminum chloride from a mixture of the inorganic oxide and

aluminum chloride. [11,14] An alternative to the vapor deposition of

the aluminum chloride is the reaction of aluminum chloride and the

inorganic oxide in a chlorinated or hydrocarbon solvent. [8]

Past attenpts[8] conducted on this reaction have employed

solvents other than carbon tetrachloride (00C4). It has been

determined that chloroform (CHC13), methylene chloride (C12C12),

ethylene dichloride (C1Q2a2Cl) and saturated hydrocarbons (to name









5
a few) do not produce a solid acid catalyst with the properties

described for the reaction employing C014. [15]

In each of these cases (except CC14) aluminum chloride is

evolved from the catalyst surface with time and only short term

activity results. [4,8-14] This is in contrast to what has been

found for the inorganic oxides treated with aluminum chloride in

C014 by the procedure reported here. [15]

Since it is known that the catalytic properties of these

amorphous silica-alumina catalysts arises from the acidity[1-3] many

methods have been developed to characterize the acidity of these

catalysts. [1-3,16-25] Using changes in the infrared spectra of

adsorbed basic molecules on solid acids to determine the nature and

strength of the acid sites present has been practiced

extensively. [16-27] Same of the early work in this area was

performed by E. Parry in the early 1960's. [16] In this method,

pyridine is allowed to interact with the solid acid surface and

changes in the infrared adsorptions in the 1400 cm-1 to 1700 cm-1

region for pyridine are measured. When pyridine is adsorbed on an

acid site which has protonic character, infrared adsorptions

indicative of pyridinium ion are observed at 1485-1500 cm-1, 1540

cm-1, -1620 cm-1 and -1640 cm-1. [16-18] The infrared band at 1540

cmi- involves the A1 bending mode for pyridinium ion including the

C-N-C as well as the N+-H bending motion. [21-24] Since the 1540 cm"

1 band is not present for pyridine bound to other Lewis acid sites,

it is used along with the other bands to characterize protonic

(Bronsted) sites. [16] When pyridine is adsorbed on a non-protonic









6

(Lewis) acid the infrared adsorptions indicative of coordinately

bound pyridine are observed at 1447-1460 cam-, 1488-1503 ncm-, -1580

cam- and 1600-1635 cm-1. [21-24] The infrared band in the 1447-1460

cm-1 region involves the A1 bending mode, C-N-C, and is used to

characterize coordinatively bonded pyridine, Figure 2-1. As the

Lewis acid strength of the acid site increases the band is

reported[16] to shift to higher frequencies.

Extensive research has been conducted on the vibrational

spectra of benzene and pyridine. The assignments of the frequencies

have been reported in the literature. [27,28]

The use of solid-state Magic-Angle-Spinning (MAS) NMR

spectroscopy as a spectroscopic tool to characterize heterogeneous

catalysts has bee widely documented. [29-33] A large amount of work

has focused on the 27Al and 29Si solid-state MAS NMR spectra of

silica-aluminas, aluminosilicates and zeolites.[29] By the use of

27Al and 29Si MAS NMR spectroscopy it has been shown that 4-

coordinate and 6-coordinate aluminum exhibit different chemical

shifts with large enough separation that they can be distinguished

even if they coexist in the same sample. [29,30]

It has been generally accepted that 4-coordinate aluminum, such

as that in zeolites, has a chemical shift in the 50-65 ppn region

relative to an Al3+(aq) standard. [30] A chemical shift of 58 ppm

relative to a Al3+(aq) standard has been observed for zeolitic

aluminum centers generated by the reaction of aluminum chloride with

ZSM-5 zeolite by vapor phase deposition. [33] The chemical shift for


















































Figure 2-1. The A1 Bending Modes for Pyridine.









8
framework Al in gaima-A1203 has been reported to occur at 50 ppm

relative to an Al3+(aq) standard. [33] The 27Al NMR of an aqueous

Al(NO3)3 solution is the reference for all our 27Al MAS NMR work.

Since the reference is a 6-coordinate octahedral complex, a peak

between 50 and 100 ppm down field from Al3+(aq) would be expected if

the aluminum chloride has retained its tetrahedral geometry. The

chemical shift for aluminum chlorohydrate is reported[31] to be 62.8

ppn versus Al3+(aq) which would be near the peak expected for a

surface-bound chloroaluminum species formed by the reaction of

aluminum chloride and a hydroxylated inorganic oxide, [8-14] Equation

2-1.


/ /
/ -0-H /-0-H
/\ /\
/ o / \ l
/I/ // \/
/ -0-H / -0-Al
/ -0-H / --H \
/ --H + Al2C16 -- > / --H C + 3 HC (2-1)
/ -0-H / -0\
/ -0-H / -0-Al-Cl
I\ /\ /
// //
/ /


The chemical shift for Al2C16 in solution has been reported to occur

at 91-105 ppm and the chemical shift for A1C14" has been reported to

occur at 100-110 ppm depending on the solvent. [32]

When aluminum chloride reacts with an inorganic oxide (such as

silica gel), tetrahedral aluminum centers are formed on the oxide

surface. [8-14,34] These tetrahedral aluminum centers should have

properties similar to free aluminum chloride and hence should have









9
similar catalytic activity. It can be determined using solid-state

MAS NMR if the aluminum chloride that is reacted with an inorganic

oxide has retained its tetrahedral conformation. Furthermore, the
27Al chemical shifts for A12C16 and AlC14- are much higher than for

the oxycdloroaluminum species. It should be easy to distinguish the

A12C16 and AlC14" species from surface bound oxyaluminum species by
27A1 MAS NMR.

The following chapter is concerned with the preparation of

aluminum chloride treated inorganic oxides by a previously

unreported method. [15] The characterization by Infrared and NMR

spectroscopy as well as an in depth study of the catalytic activity

of the aluminum chloride treated supports is discussed to support

the claim that a new solid, strong acid has been discovered with

this new method of preparation.



2.2 EXPERMENTAL


Reagents

All metal halides were used as purchased unless otherwise

stated. The palladium (II) chloride (WPCl2) and rhodium (II)

chloride (RhCl3) were purchased from Aldrich Chemical Company

(Aldrich). Aluminum chloride (Al2C16) with a purity of 99.997% was

purchased from Alfa Products. The iron (III) chloride (FeC3) and

antimony (V) chloride (SbCl5) were purchased from AESAR. All

solvents were purchased from Fisher Scientific Co. (Fisher) except

tetrachloroethylene which was purchased from Eastman Kodak Co.









10

(Kodak), n-dodecane and n-hexadecane which were purchased from Alfa

Products. Carbon tetrachloride, chloroform and methylene chloride

were dried over phosphorous (V) oxide (Fisher). Benzene was dried

by distillation over calcium hydride. Cyclohexane and chloroform

(containing ethanol as a stabilizer) were purified by passage

through an activated alumina column. Tetrachloroethane, n-pentane,

n-hexane, n-heptane, n-dodecane, n-hexadecane and cumene were used

as purchased. Gold label (99+%) pyridine was purchased from Aldrich

and was used without further purification. All solvents were stored

over 4A molecular sieves (Davison Chemical). The gaseous reactants

methane, dimethyl ether, propylene, propane, isobutane, technical

grade hydrogen chloride (99.0%), and C.P. Grade carbon monoxide

(99.5%) were purchased from Matheson. Hydrogen, helium, argon and

nitrogen were supplies by Airco and Liquid Air. The semiconductor-

grade hydrogen chloride (99.995%) was purchased from Air Products.

The supports used for the preparation of the catalysts are silicon

dioxide (SiO2), alumina (A1203), high-silica zeolite (silicalite),

Y-zeolite (IZ-Y82), boron oxide (B203), titanium dioxide (Tio2) and

magnesium oxide (MgO). All support materials were used as purchased

unless otherwise stated. For the silicon dioxide supports the

primary material was Davison Grade #62 silicon dioxide (donated by

W.R. Grace Co.) with a surface area of 340 m2/gram, pore volume of

1.1 cnm/gram and a mess size of 60-200. [35] The three types of

silicon dioxide support materials used for surface area dependence

studies were purchased from AESAR. All three supports are 60-325

mesh size with surface areas of 215 m2/gram, 420 m2/gram, 690









11
m2/gram and pore volumes of 1.0 cm3/gram, 0.8 cm3/gram and 0.4

can/gram, respectively. The alumina support, acid Brockman Activity

I (80-120 mesh), had a surface area of 180 m2/gram. [35] A high-

silica zeolite which was donated by Union Carbide had a surface area

of 400 m2/gram and a pore volume of 0.19 cn3/gram. The Y-zeolite

was a Linde LZ-Y82 molecular sieve purchased from Alfa Products and

is used c'mnercially as a fluid catalytic cracking (FCC) catalyst.

The boron oxide was purchased from AESAR and had a mesh size of 60.

Bayer AG donated the hydroxylated titanium dioxide (surface area 200

m2/gram) and the magnesium oxide was purchased from Fisher. 5,5-

dimethyl-l-pyrroline-l-oxide (EMPO) which is a diamagnetic spin

trapping agent was purchased from Aldrich. Other reactants used for

cracking reactions were activated carbon (Curtin, MCB) and resid

(FHC-353 donated by Amoco) which is a mixture of high molecular

weight hydrocarbons obtained from the distillation of heavy crude

oil. Manomers used for polymerization reactions were isobutane

(Matheson), styrene (Fisher), methyl methacrylate (Fisher),

methacrylate (Fisher), vinyl acetate (Aldrich), ethyl vinyl ether

(Aldrich) and epichlorchydrin (Kodak). Purification of monomers

ware conducted by literature methods.


Instrumentation

All air and water sensitive manipulations were performed in a

Vacuum Atmosphere Company model HE-43-2 inert atmosphere box or in

an Aldrich inert atmosphere glove bag. All syntheses were conducted

under a nitrogen or argon atmosphere and one atmosphere pressure.









12

Routine GC analysis for hydrocarbon products were performed on a

model 940 FID Varian gas chromatograph equipped with a Hewlett-

Packard 3390A integrator and a 1/8 inch by 8 foot stainless steel

Porapak Q (100-120 mesh) column or a 1/8 inch by 6 foot stainless

steel Hayesep Q (80-100 mesh) column. Routine GC analysis for

chlorinated hydrocarbons were performed on a model 3700 TCD Varian

gas chromatograph equipped with a Hewlett-Packard 3390A integrator

and a 1/8 inch by 8 foot Porapak Q (100-120 mesh) column. The GC

FIIR was performed on a Nicolet 5DXB FTIR spectrometer equipped with

a Nicolet GC interface and a Hewlett-Packard 5890A gas chromatograph

using a 1.5 micron thick DB 130m fused silica capillary column that

was 30 meters in length. EPR spectra were obtained from a Bruker

ER200D-SRC spectraneter equipped with a variable temperature unit,

ER 022 signal channel controller, ER 001 time base controller, ER

031M field controller, ER 082 power supply and ER 040XR microwave

bridge. GC mass spectranetry was performed by Dr. Roy King of the

Microanalytical Laboratory, University of Florida, Gainesville,

Florida. Gas samples were analyzed on a AEI MS 30 mass spectrometer

with a IDITOS DS55 data station. The system was connected to a PYE

Unicam 104 gas chrmaatograph equipped with a 1/4 inch by 5 foot

glass Porapak Q (100-120 mesh) column. Solid-state magic angle

spinning (MAS) nuclear magnetic resonance spectra were collected by

Dr. W. S. Brey of the University of Florida, Gainesville, Florida,

on a Nicolet NT-300 300 mHz wide-bore superconducting FT-NMR

spectrometer. Infrared spectra were obtained as mulls on a nicolet

5DXB FP-IR spectrometer using KBr plates. All solid-liquid phase









13

cracking reactions and polymerizations were carried out in 250 mL or

500 mL Parr pressure bottles equipped with a brass or stainless

steel swagelok pressure heads and neoprene stoppers. [36]



Fixed Bed Flow Reactor

A fixed-bed flow reactor was constructed as described by Keith

Weiss and reported in his Ph.D. Dissertation. [35] The reactor was

modified by placing a hydrocarbon bubbler after the reactant gas

bubblers and before the catalyst zone to allow the addition of a

hydrocarbon substrate. The modified reactor allowed the

experimenter to saturate the reactant and carrier gases with any

liquid hydrocarbon substrate that has an appreciable vapor pressure.

The flow rates of the individual gases were controlled by teflon

needle valves. Hydrogen and helium were passed through mineral oil

bubblers whereas the HC1 was bubbled through sulfuric acid. The

gases were allowed to mix and pass through bubbler which contained a

hydrocarbon/carbon tetrachloride mixture. This gas mixture was then

allowed to flow through a catalyst which was supported on a glass

frit. The catalyst zone was heated by a Thermolyne Briskheat

flexible electric heat tape controlled by an Omega Engineering, Inc.

digital temperature controller, model CN 310 equipped with a J-Type

thermocouple. Pregas and post gas samples for GC analysis could be

obtained through sample ports before and after the catalyst zone.

Overall flow rates for the reactor system were monitored by a

calibrated bubble flow meter. The entire reactor was constructed of

glass and was custom built by glass blowers Rudy Schroschein and









14

Dick Moshier at the glass shop, University of Florida, Gainesville,

Florida.

This reactor was further modified using a syringe pump to

deliver liquid reactants to the catalyst in place of a hydrocarbon

or hydrocarbon/carbon tetrachloride bubbler. [37] A preheater zone

was added to the system to ensure proper mixing and heating of all

reactants before they were contacted with the catalyst. Typically

only one gas was used as a carrier gas and/or reactant gas. The gas

flow rate was regulated by a calibrated rotoflow meter purchased

from Gilmont Instruments, Inc.



Preparation of a Silica Gel Catalyst Doped with Aluminum Chloride
Using Carbon Tetrachloride as a Solvent

In a 250 mL 3-neck round bottom flask equipped with a reflux

condenser and a teflon coated magnetic stir bar was placed 10.20

grams of silica gel (washed with 1M HC1 and dried under vacuum at

800C for 72 hrs) and 150 mL of carbon tetrachloride (dried over 4 A

sieves). After purging the system with nitrogen (N2), 5.10 grams of

anhydrous aluminum chloride (A12C16) was added and the mixture was

allowed to stir at reflux under a N2 atmosphere for 1-5 days in the

absence of light.

After approximately 1 hour the mixture developed a purple

color. This color continued to increase in intensity until the

mixture was black in appearance (-8 hours).

After 5 days the reaction mixture was filtered under an N2

atmosphere. The filtrate was colorless and the resulting solid

product obtained was burgundy in color and was utilized as the









15

catalyst material for the cracking experiments described later in

this chapter. The catalyst was water-sensitive and turned white on

exposure to moisture.

The catalyst gave an EPR signal indicative of a free-radical

with a g value of 2.012, Figure 2-2. If after the purple color

first appears, to approximately 1 days, the mixture is filtered, the

catalyst obtained will show an EPR signal which is very broad and

has a g value of 2.06, Figure 2-3.



Prearation of an Alumina Catalyst Doped with Aluminum Chloride
Using Carbon Tetrachloride as a Solvent

In a 250 mL 3-neck round bottom flask equipped with a reflux

condenser and a teflon coated magnetic stir bar was placed 15.0

grams of alumina (dried at 150 C) and 175 mL of carbon tetrachloride

(dried over 4 A sieves). After purging the system with nitrogen

(N2), 7.5 grams of anhydrous aluminum chloride (Al2C16) was added

and the mixture was allowed to stir at reflux under a N2 atmosphere

for 2 days in the absence of light.

After approximately 1 hour the mixture developed a purple

color. This color continued to increase in intensity until the

mixture was black in appearance.

After 2 days the reaction mixture was filtered under an N2

atmosphere. The filtrate had a slight red color and the resulting

solid product obtained was purple in appearance.

The catalyst was water-sensitive and turned white on exposure

to moisture. The catalyst gave a sharp EPR signal, similar to

Figure 2-3, indicative of a free-radical with a g value of 2.012.























2.0/


2300
















Figure 2-2.


3300


B/Gauss


An EPR Spectrum of a Heterogeneous Acid Catalyst
Before Ocnplete Reaction.






















2.0/


I
2300















Figure 2-3.


3300
I/Gauss


An EPR Spectrum of a Heterogeneous Acid Catalyst
After Complete Reaction.


4300









18

Preparation of a High-Silica Zeolite Catalyst Doped with Aluminum
Chloride Usinc Carbon Tetrachloride as a Solvent

In a 250 mL 3-neck round bottom flask equipped with a reflux

condenser and a teflon coated magnetic stir bar was placed 10.0

grams of zeolite (dried at 2500C under vacuum) and 150 mL of carbon

tetrachloride (dried over 4 A sieves). After purging the system

with nitrogen (N2), 5.0 grams of anhydrous aluminum chloride

(A12C16) was added and the mixture was allowed to stir at reflux
under a N2 atmosphere for 5 days in the absence of light.

After approximately 1 hour the mixture developed a bright

yellow color. After 2 days the reaction mixture was filtered under

an N2 atmosphere. The filtrate had a slight yellow color and the

resulting solid product obtained was bright yellow in appearance.

The catalyst was water-sensitive and turned white on exposure

to moisture. The catalyst gave a sharp EPR signal, similar to

Figure 2-3, indicative of a free-radical with a g value of 2.012.



Preparation of a Y-Zeolite Catalyst Doped with Aluminum Chloride
Using Carbon Tetrachloride as a Solvent

In a 250 mL 3-neck round bottom flask equipped with a reflux

condenser and a teflon coated magnetic stir bar was placed 23.9

grams of zeolite (dried at 300*C under vacuum) and 250 mL of carbon

tetrachloride (dried over 4 A sieves). After purging the system

with nitrogen (N2), 13.29 grams of anhydrous aluminum chloride

(Al2C16) was added and the mixture was allowed to stir at reflux

under a N2 atmosphere for 2 days in the absence of light.









19

After approximately 1 hour the mixture developed a tan color.

After 2 days the reaction mixture was filtered under an N2

atmosphere. The filtrate had a pale brown color and the resulting

solid product obtained was tan in appearance. The catalyst was

water-sensitive and turned white on exposure to moisture.



Preparation of a Boron Oxide Catalyst Doped with Aluminum Chloride
Usin Carbon Tetrachloride as a Solvent

In a 250 mL 3-neck round bottom flask equipped with a reflux

condenser and a teflon coated magnetic stir bar was placed 15.0

grams of boron oxide (dried at 80"C under vacuum) and 250 mL of

carbon tetrachloride (dried over 4 A sieves). After purging the

system with nitrogen (N2), 7.50 grams of anhydrous aluminum chloride

(A12C16) was added and the mixture was allowed to stir at reflux

under a N2 atmosphere for 3 days in the absence of light.

After approximately 1 hour the mixture developed a purple

color. This color continued to increase in intensity until the

mixture was black in appearance.

After 3 days the reaction mixture was filtered under an N2

atmosphere. The filtrate was colorless and the resulting solid

product obtained was black in color.

The catalyst was water-sensitive and turned white on exposure

to moisture. The catalyst gave a sharp ER signal, similar to

Figure 2-3, indicative of a free-radical with a g value of 2.012.









20

Preparation of a Titanium Dioxide Catalyst Doped with Aluminum
Chloride Using Carbon Tetrachloride as a Solvent

In a 500 mL 1-neck round bottom flask equipped with a reflux

condenser and a teflon coated magnetic stir bar was placed 30.0

grams of titanium dioxide and 300 mL of carbon tetrachloride (dried

over 4 A sieves). After purging the system with nitrogen (N2), 15.0

grams of anhydrous aluminum chloride (Al2C16) was added and the

mixture was allowed to stir at reflux under a N2 atmosphere for 3

days.

After approximately 1 hour the mixture developed a slight pink

color which gradually increase in intensity until the mixture was

peach in color.

After 3 days the reaction mixture was filtered under an N2

atmosphere. The filtrate was colorless and the resulting solid

product obtained was peach in appearance.

The catalyst was water-sensitive and turned white on exposure

to moisture. The catalyst gave a sharp EPR signal, similar to

Figure 2-3, indicative of a free-radical with a g value of 2.013.



Prearation of a Magnesium Oxide Catalyst Doped with Aluminum
Chloride Using Carbon Tetrachloride as a Solvent

In a 250 mL 1-neck round bottom flask equipped with a reflux

condenser and a teflon coated magnetic stir bar was placed 15.0

grams of magnesium oxide and 150 mL of carbon tetrachloride (dried

over 4 A sieves). After purging the system with nitrogen (N2), 7.5

gram of anhydrous aluminum chloride (A12C16) was added and the









21

mixture was allowed to stir at reflux under a N2 atmosphere for 3

days.

After approximately 1 hour the mixture developed a slight pink

color which gradually increase in intensity until the mixture was

bright pink in color.

After 3 days the reaction mixture was filtered under an N2

atmosphere. The filtrate was colorless and the resulting solid

product obtained was pink in appearance.

The catalyst was water-sensitive and turned white on exposure

to moisture.



Preparation of a Silica Gel Catalyst Doped with Aluminum Chloride
Using Chloroform as a Solvent

In a 250 mL 3-neck round bottom flask equipped with a reflux

condenser and a teflon coated magnetic stir bar was placed 10.20

grams of silica gel (washed with IM HC1 and dried under vacuum at

80*C for 72 hrs) and 150 mL of chloroform (dried over 4 A sieves).

After purging the system with nitrogen (N2), 5.10 grams of anhydrous

aluminum chloride (A12C16) was added and the mixture was allowed to

stir at reflux under a N2 atmosphere for 5 days.

After approximately 1 hour the mixture developed a purple

color. This color continued to increase in intensity until the

mixture was black in appearance.

After 5 days the reaction mixture was filtered under an N2

atmosphere. The filtrate was colorless and the resulting solid

product obtained was burgundy in color.









22

The catalyst was water-sensitive and turned white on exposure

to moisture. The catalyst gave a sharp EPR signal, similar to

Figure 2-3, indicative of a free-radical with a g value of 2.012.



Preparation of a Silica Gel Catalyst Doped with Aluminum Chloride
Using Methvlene Chloride as a Solvent

In a 500 mL 1-neck round bottom flask equipped with a reflux

condenser and a teflon coated magnetic stir bar was placed 10.16

grams of silica gel and 200 mL of methylene chloride (dried over 4

A sieves). After purging the system with nitrogen (N2), 5.07 grams

of anhydrous aluminum chloride (A12C16) was added and the mixture

was allowed to stir at reflux under a N2 atmosphere for 5 days.

After 5 days the light purple reaction mixture was filtered

under an N2 atmosphere. The filtrate was colorless and the

resulting solid product obtained was light purple in appearance.

The catalyst was water-sensitive and turned white on exposure

to moisture. The catalyst gave a sharp EPR signal, similar to

Figure 2-3, indicative of a free-radical with a g value of 2.012.



Preparation of a Silica Gel Catalyst Doped with Aluminum Chloride
Using 1.2-Dichloroethane as a Solvent

In a 250 mL 3-neck round bottom flask equipped with a reflux

condenser and a teflon coated magnetic stir bar was placed 5.00

grams of silica gel (washed with IM HC1 and dried under vacuum at

80'C for 72 hrs) and 175 mL of 1,2-dichloroethane (dried over 4 A

sieves). After purging the system with nitrogen (N2), 2.50 grams of









23

anhydrous aluminum chloride (A12C16) was added and the mixture was

allowed to stir at reflux under a N2 atmosphere for 5 days.

After approximately 1 hour the mixture developed a purple

color. This color continued to increase in intensity until the

mixture was black in appearance.

After 5 days the reaction mixture was filtered under an N2

atmosphere. The filtrate was colorless and the resulting solid

product obtained was burgundy in color.

The catalyst was water-sensitive and turned white on exposure

to moisture. The catalyst gave a sharp EPR signal, similar to

Figure 2-3, indicative of a free-radical with a g value of 2.012.



Preparation of a Silica Gel Catalyst oped with Aluminum Chloride
Usina n-Hexane as a Solvent

In a 500 mL 1-neck round bottom flask equipped with a reflux

condenser and a teflon coated magnetic stir bar was placed 10.16

grams of silica gel and 200 mL of n-hexane (dried over 4 A sieves).

After purging the system with nitrogen (N2), 5.07 grams of anhydrous

aluminum chloride (A12C16) was added and the mixture was allowed to

stir at reflux under a N2 atmosphere for 3 days.

After 3 days the bright yellow reaction mixture was filtered

under an N2 atmosphere. The filtrate was colorless and the

resulting solid product obtained was yellow in appearance.

The catalyst was water-sensitive and turned white on exposure

to moisture. The catalyst gave a sharp EPR signal, similar to

Figure 2-3, indicative of a free-radical with a g value of 2.011.









24

Preparation of a Silica Gel Catalyst Doped with Aluminum Chloride
Using Cyclohexane as a Solvent

In a 250 mL 3-neck round bottom flask equipped with a reflux

condenser and a teflon coated magnetic stir bar was placed 5.00

grams of silica gel (washed with 1M HC1 and dried under vacuum at

80C for 72 hrs) and 175 mL of cyclobexane (dried over 4 A sieves).

After purging the system with nitrogen (N2), 2.50 grams of anhydrous

aluminum chloride (A12C16) was added and the mixture was allowed to

stir at reflux under a N2 atmosphere for 16 hours.

After 16 hours the reaction mixture was filtered under an N2

atmosphere. The filtrate was colorless and the resulting solid

product obtained was light yellow in color.

The catalyst was water-sensitive and turned white on exposure

to moisture. The catalyst gave a sharp EPR signal, similar to

Figure 2-3, indicative of a free-radical with a g value of 2.012.



Preparation of a Silica Gel Catalyst Doped with Aluminum Chloride
Using Benzene as a Solvent

In a 1000 mL 3-neck round bottom flask equipped with a reflux

condenser and a teflon coated magnetic stir bar was placed 100 grams

of silica gel (washed with IM HC1 and dried under vacuum at 80*C for

72 hrs) and 750 mL of benzene (dried over 4 A sieves). After

purging the system with nitrogen (N2), 50 grams of anhydrous

aluminum chloride (A12C16) was added and the mixture was allowed to

stir at reflux under a N2 atmosphere for 2 days.

After 2 days the reaction mixture was filtered under an N2









25

atmosphere. The filtrate was colorless and the resulting solid

product obtained was black in color.

The catalyst was water-sensitive and turned white on exposure

to moisture. The catalyst gave a sharp EPR signal, similar to

Figure 2-3, indicative of a free-radical with a g value of 2.012.



Preparation of a Silica Gel Catalyst Doped with Aluminum Chloride by
Vapor DeDosition

In a sublimation apparatus 3 grams of aluminum chloride and 5

grams of silicon dioxide (washed with 1M HC1 and dried under vacuum

at 80"C for 72 hrs) were physically mixed and heated under vacuum at

240C to sublimed the aluminum chloride through the support. After

all of the aluminum chloride was removed from the sample the support

was heated to 3500C to remove any excess aluminum chloride.

The same procedure was also repeated using alumina as the

support material.



Preparation of a Palladium (II) Chloride-Aluminum Chloride Doped
Catalyst Using Carbon Tetrachloride as a Solvent

In a 200 mL 3-neck round bottom flask equipped with a reflux

condenser and a teflon coated magnetic stir bar was placed 5.0 grams

of silica gel (washed with IM HC1 and dried under vacuum at 80C for

72 hrs), 0.06 grams palladium (II) chloride (PdC12) and 100 mL of

carbon tetrachloride (dried over 4 A sieves). The reaction mixture

was stirred and heated at reflux under a nitrogen (N2) atmosphere

for 6 hours. Next 2.61 grams of anhydrous aluminum chloride









26

(A12C16) was added and the mixture was allowed to stir at reflux
under a N2 atmosphere for 2 days.

After 2 days the reaction mixture was filtered under an N2

atmosphere. The filtrate was colorless and the resulting solid

product obtained was orange in color.

The catalyst was water-sensitive and turned light peach on

exposure to moisture.



Preparation of a Rhodium (III) Chloride-Aluminum Chloride Doped
Silica Gel Catalyst Using Carbon Tetrachloride as a Solvent

In a 200 mL 3-neck round bottom flask equipped with a reflux

ondenser and a teflon coated magnetic stir bar was placed 9.0 grams

of a 2% rhodium (III) chloride (RhCl3) on silica gel (prepared as

above for palladium), 5.0 grams aluminum chloride, and 150 mL of

carbon tetradhloride (dried over 4 A sieves) .The reaction mixture

was allowed to stir at reflux under a N2 atmosphere for 24 hours.

After 24 hours the reaction mixture was filtered under an N2

atmosphere. The filtrate was colorless and the resulting solid

product obtained was orange in color.

The catalyst was water-sensitive and turned light orange on

exposure to moisture.



Procedure for the Adsorption of Pyridine onto Supports and Solid
Acid Catalysts for the Characterization of Acid Sites

The infrared spectra of pyridine on solid acid catalysts has

long been used for characterization of the acid sites on solid acid

catalysts.[16,17,20-25] The procedure used to adsorb and desorb









27

pyridine was similar to that reported previously[16,17] with the

exception that our samples were in powder form and not in pressed

wafers. This meant that quantitative infrared measurements of the

acid site concentrations could not be performed and only a

qualitative determination of the nature of the acid sites could be

made. Support and catalysts samples were dried at 200C for 8 hours

under vacuum prior to the adsorption experiments. Pyridine vapors

were be contacted with the catalyst at room temperature for 2 to 3

hours and then the catalyst was placed under vacuum to remove any

excess pyridine (2-3 hours). A sample of the support or catalyst

was removed and a fluorolube mull prepared. An IR spectrum was

obtained in the region from 1700 cm-1 to 1400 an-1 in order to

characterize the type of acid sites present. The sample was then

evacuated at 150'C, 225'C and 300C for 2 to 3 hours at each

temperature. An IR spectrum was obtained after evacuation at each

temperature. The results of these experiments are discussed in a

later section.



Procedure for the Spin Trapping of Radicals on Solid Acid Catalysts
Using CMPO

All manipulations were conducted in an inert atmosphere box.

Powder samples of the catalysts were added to quartz EPR tubes that

contained carbon tetrachloride or toluene. An amount of EMPO was

added to this mixture that corresponded to the number of moles of

aluminum chloride contained in the sample. The EPR spectra were

collected in the usual manner. Computer simulations of the spin

trapped radicals were performed using the program QPCW[38,39] as









28
modified by J. Telser[40] and N.M. Wang of the University of

Florida, Gainesville, Florida.


2.3 RESULTS AND DISCUSSION


Preparation of a New Solid Acid Catalyst

As described in the experimental section the catalysts are

prepared by the reaction of the hydroxyl groups of an inorganic

oxide with aluminum chloride (A12C16) in refluxing carbon

tetrachloride (CC14), Equation 2-2. The reaction of aluminum

chloride with silicon


/ /
/ -0-H / --H
/ \ /k\
/ o / \ Cl
II /I/ \/
S-0-H / -0-Al
/ -0-H Reflux / -0-H \
S-0-H + Al2CI6 -> / -O-H C1 + 3 HC1 (2-2)
/ -H CC14, N2 / 0\
/ -0-H / -0-Al-C
/I\ /I\ /
/ / O

/ /

dioxide was monitored by accurately weighing the aluminum chloride

and silicon dioxide before the reaction. When the weight of the

resulting aluminum chloride doped silica gel was subtracted from the

sum of the weights of the starting materials used in the reaction it

was determined that 1.1 moles of hydrogen chloride (HC1) was evolved

for every mole of A1C13 used. This suggests that over 90% of the

chloroaluminum species on the catalyst surface of this support has









29

the composition (-O-)ACl2. Since the average composition is two

chlorides per aluminum and A12C16 would sublime off upon heating

(which does not occur) there is very little (-O-)2AlCl present. A

blank reaction between SiO and CC14 showed no HC1 evolution and the

resulting solid did not have any acidic properties as indicated by

pyridine adsorptions. This result is consistent with literature

reports in that CC14 does not chlorinate the surface of silica gel

below a temperature of 350*C. [41]

Past attenpts[8] conducted on this reaction have employed

solvents other than 0C14. It has been determined that chloroform,

methylene chloride, ethylene dichloride and saturated hydrocarbons

(to name a few) do not product a solid acid catalyst with the

properties described for a solid acid prepared in 0C14. [15] Several

patents have been issued for the treatment of inorganic oxides with

aluminum chloride to form strong acid catalysts. [5,8-14] In each of

these cases aluminum chloride is rapidly evolved from the surface

and only short term activity results.[4,5,8-14] This is in contrast

with what has been found for the aluminum chloride doped inorganic

oxides prepared in 0014.

The new catalysts reported in the experimental section have

been characterized by IR spectroscopy, solid-state MAS NMR

spectroscopy and calorimetric titration. As detailed in latter

sections these aluminum chloride doped inorganic oxides are

catalysts for a wide range of acid catalyzed reactions.












































1700 0 1650 0 1600 0 1550.0 150
WAVENUUBERS (CM-1)


Figure 2-4.


0 1450.0 1400. 0


Infrared Spectrum of SiO2 Dried at 200'C.











































1700 0 1650.0 1600 0 1550 0 150
WAVENUMBERS (CM-1)


Figure 2-5.


Peak List

X- 146. 7 Y= 1 P305
X- 15985 Y= 0 6454






450.0 1400 0


Infrared Spectrum of SiO2 After Pyridine
Adsorption and Evacuation at Roan Temperature.










































1700.0 1650.0 1600.0 1550 0 1500.0
WAVENUUBERS (CU-1)


Figure 2-6.


1450.0 1400 0


Infrared Spectrum of SiO2 After Pyridine
Adsorption and Evacuation at 150*C.









33

Characterization of the New Solid Acid Catalysts by the Infrared
Spectroscopy of Adsorbed Pyridine

Using the procedure outlined in the experimental section a

sample of the silicon dioxide was dried under vacuum at 200*C for 8

hours and three IR spectra were collected. The three IR spectra are

shown in Figures 2-4 to 2-6. The IR spectrum shown in Figure 2-4 is

of the silicon dioxide after drying at 200"C under vacuum. This

relatively featureless spectrum is typical of the inorganic oxides

used. After pyridine is adsorbed onto the silica gel surface and

all excess pyridine is removed by evacuation at room temperature,

two bands that are indicative of hydrogen bonded pyridine appear,

Figure 2-5. The band at 1447 cm-1 is attributed to the interaction

of pyridine with the hydroxyl groups of the silica gel and results

from hydrogen bonding since it is known that unmodified silicon

dioxide has no strong acidic or basic properties. [16,19] This band

is located at 1438 cm-1 for free pyridine. When the silicon dioxide

is evacuated at 150'C all of the adsorbed pyridine is removed

indicating that the pyridine interacts only weakly with the surface

of the support, (see Figure 2-6). The results obtained on the

silicon dioxide material parallel the results obtained by Parry[16]

for silicon dioxide and indicates that the experimental method being

used is valid.

Next a sample of the silicon dioxide doped with A12C16

(A1C13/SiO2) which had been prepared in OC14 was dried at 200C for

8 hours. The infrared spectrum of the dried AlC13/SiO2 is similar

to the IR spectrum of the dried silicon dioxide, Figure 2-7. When

pyridine is adsorbed onto the AlCl3/SiO2 catalyst and evacuated at












































0 1650.0 1600 0 1550 0 1500.0
WAVENUMBERS (CU-1)


Figure 2-7.


1450.0 1400.0


Infrared Spectrum of A1C12-SiO2 Dried at 200C.









35
roma temperature, bands indicative of both Bronsted and Lewis acid

sites are observed, Figure 2-8. The large band at 1540 cm-1 results

from pyridinium ion which is formed by the protonation of pyridine

by Bronsted acid sites. Lewis acid sites are indicated by the

presence of a band at 1449 can-. Since the IR spectrum is obtained

after evacuation at room temperature, there is some hydrogen bonded

pyridine present on the surface and is responsible for the broad

shape of the Lewis acid band. The peak at ~1499cm-1 is a band

present in both Bronsted and Lewis acid bound pyridine and cannot be

used to distinguish between the two types of acid sites[16]. After

evacuation at 1500C, to remove any hydrogen bound pyridine, the peak

for the Lewis acid bound pyridine is centered at 1456 cm-1, Figure

2-9. This is a shift of 18 cm-1 and is comparable to shifts

reported in the literature for solid acid cracking catalysts. [16]

In addition to a shift in the Lewis acid band for pyridine there is

a large amount of Bronsted acid sites present as indicated by the

band at 1540 cm-1. Even after evacuation at 3000C both Bronsted and

Lewis acid sites are present indicating a very strong interaction

between the surface of the solid acid and the adsorbed pyridine,

Figure 2-10. The results for this catalyst are in good agreement

with the data obtained by Parry[16] and other workers in the

area[17] for commercial amorphous silica-aluminas and zeolites. A

summary of the infrared shift data for pyridine adsorbed onto

various aluminum chloride treated inorganic oxides (AlCl2-X; X=

inorganic support) is presented in Table 2-1.
















































0 1550 0 150
WAVENUUBERS (CU-i)


Figure 2-8.


Infrared Spectrum of AlC12-SiO After Pyridine
Adsorption and Evacuation at Room Tenperature.


1. 1554
1 2757
0 7889
1 0347
0 7233
0 7342
1. 1269
1 0317
o 8444


1400 0

















































1700.0 1650.0 1600 0 1550 0 1500.0
WAVENUUBERS (CU-1)


Figure 2-9.


(- 1456 5 Y- 0.7534
L- 1473 4 Y- 0.6716
(- 1487.9 Y- 0.8626
(- 1506.4 Y- 0 5918
- 1539.d Y- 0.7337
c- 1559 1 Y- 0.5572
S1570.5 Y- 0.5213
C- 1576. 2 Y= 0.5357
C- 1616 4 Y- 0 7640
C- 1636 7 Y- 0 7713
(- 1653. 4 Y- 0.6719

1450.0 1400.0


Infrared Spectrum of A1C12-Si After Pyridine
Adsorption and Evacuation at 150*C.




































L&B


Peak List
A- 1456. 7
X- 1472 7
X- 1488 9
X- 1506 5
X- 1521 9
X 1527 3
X- 1540 4
XI 1616. 4
X 1624 0
X 1636. 7
X- 1653 4


1700 0 1650 0 1600 0 1550 0 1500 0
WAVENUMBERS (CU-1)


Figure 2-10.


1450 3 1400.0


Infrared Spectrum of A1C12-SiO After Pyridine
Adsorption and Evacuation at 300'C.


0 6387
0.5848
O 6799
0. 5408
0 5240
0.5226
0. 5826
0 6401
0 6183
0. 6612
0 6108









39

Table 2-1. Infrared Shift Data for Pyridine Adsorbed onto
A1C12-X Catalysts.


X SOLVEN- SHIFT OF IEWIS BAND*

SiO2 OC14 18.0

A1203 1C4 15.2
Silicalite*** CC14 18.1

B203 CC14 18.1

TiO2 CC14 14.1

MgO Cl14 7.8

Si2 CHC13 9.3

SiO2 CH2C12 8.6

SiO2 CH14 8.9

SiO2 C6H6 8.3

* This solvent was used to prepare the catalyst.

** This shift is measured after pumping at 150-C on the sample
exposed to pyridine. The free pyridine band occurs at
1438.5 cn"1.

*** A high silica zeolite.









40

As seen in Table 2-1 the acid treated SiO2, silicalite and B203

supports resulted in the largest shifts for the Lewis acid band.

Alumina and titanium dioxide exhibited shifts in an intermediate

range with magnesium oxide resulting in the lowest shift. The

frequency shifts listed are after evacuation at 150 C to remove any

weakly hydrogen bound pyridine. The low shift for MgO is not

unexpected due to the fact that magnesium oxide is basic[19] and the

resulting material formed from reacting a strong acid with a base

would result in a product that is weakly acidic in nature. Even

though the shift in the Lewis acid band for the MgO catalyst issmall

and in the range that would normally represent hydrogen bonded

pyridine, the band is still present after evacuation at 150C and

considered to arise form a Lewis acid-base interaction.

Several catalysts were prepared by methods described in the

patent literature and the results of the pyridine adsorptions are

listed at the bottom of Table 2-1. All patented catalysts that were

used employed silicon dioxide as the support material and solvents

other than OCx4. For each of the solvents used a shift of only 8 or

9 cm-1 was observed after evacuation at 150C. An explanation for

the decrease in frequency shifts upon changing from carbon

tetrachloride to other solvents may be that each of the other

solvents contain reactive hydrogen or are basic molecules. It is

well known that aluminum chloride can react with organic compounds

to form ionic ccuplexes as shown in Equations 2-3 and 2-4. [42] When

solvents such as chloroform, methylene chloride and saturated













2 R-H + Al2C 6 > 2 R+HAIC13 (2-3)

2 R-C1 + A12C16 --> 2 R+AlC14- (2-4)


hydrocarbons are employed, the aluminum chloride can react with the

solvent to form halo organo-aluminum complexes. [42] For solvents

with available hydrogens the reaction that may then take place is

abstraction of a hydride ion from the organic halide generating an

aluminum hydride and a carbonium ion. [43] The carbonium ion may

abstract a hydride ion from another solvent molecule or the support

material forming a neutral species. The aluminum hydride complex

may react with the support material, liberating HC1 and forming a

chloroaluminum hydride complex. This species is less acidic than

the chloroaluminum species formed when pure A12C16 is reacted with

the support material, Equations 2-5 and 2-6. Many other reactions

are possible between the aluminum chloride and the reaction medium.

The point to be made is that in solvents that contain carbon-

hydrogen


/ / o H
/ / /
/-0-H /-0-A1

/ 0 / 0/ Cl
/1 II
H2A12C14 + / -0-H > / -0-H Cl + 2 HC1 (2-5)
/-0-H /-0-H /
/ -0-H -0-Al
/\ /i\ /
/ 0/ O/ H












/ / cl
S-0-H -O-Al

/ o / / Cl

A12C16 + / -0-H -- > /-0-H Cl + 2 HC1 (2-6)
/ -0-H / -0 /
/ --H / --Al

/ o / o C

/ /

bonds reactions involving aluminum-chlorine bonds that result in

the deccuposition of the aluminum chloride into aluminum hydride or

organo-aluminum species that would exhibit lower acidity than

aluminum chloride alone may occur[43,44]. A reason for the decrease

in acidity for the catalyst prepared in benzene is that benzene is a

good -base and would form an acid-base ccnplex with the aluminum

chloride. The complexed aluminum chloride would be a weaker acid

than the free aluminum chloride. On the other hand, a fully

chlorinated solvent such as carbon tetrachloride will undergo an

exchange of chloride ion with aluminum chloride and will result in

no net reaction, Equations 2-7 to 2-9.


2 C130Cl + A12C16 > 2 C13CAlIC4- (2-7)

2 C13C+AlCI4" -> 2 C130C1 + A12Cl6 (2-8)


2 01301 + A12C16 -- > 2 C1300 + A12C16


(2-9)









43

The result of this reaction is that the aluminum chloride is

stabilized in solution by the carbon tetrachloride. Since the

aluminum chloride cannot react with the solvent the aluminum

chloride is forced to react with the hydroxyl groups of the support

material.

The trend for the frequency shifts of the Lewis acid band for

pyridine can be clearly seen in Table 2-1. A neutral support such

as silica gel exhibits the highest shift along with a high silica

zeolite and boron oxide (B203). Acidic supports such as alumina and

titanium dioxide have the next largest shifts and the basic support

magnesium oxide exhibits the lowest frequency shift. An explanation

involving the acidic or basic properties of each support would be

acceptable except that boron oxide is not a neutral support. Boron

oxide has a structure which contains trigonal B03 units and has the

same acidic properties. [45] Because of the acidity associated with

boron oxide it would be expected that boron oxide would exhibit a

frequency shift for Lewis acid bound pyridine similar to that

exhibited by alumina. It should be stated that the same Lewis acid

is used to treat each support and would not be the controlling

factor in determining the frequency shift of the Lewis acid bound

pyridine if the support was not interacting with the acid center.

The shift in the Lewis acid band is a result of an inductive

effect involving the donation of the nitrogen lone pair of the

pyridine to a vacant orbital on a Lewis acid such as aluminum

trichloride (AC13). As electron density is drawn away from the

nitrogen the pW-plT interaction between the ring carbons increases









44

resulting in an increase in the ring bending frequency for pyridine.

It has been previously reported that as the strength of the Lewis

acid increases the Lewis acid band for pyridine will shift to higher

frequencies. [16] This is a direct result of the increased electron

withdrawing strength of the Lewis acid. In the case of the

inorganic oxides treated with aluminum chloride, the strength of the

chloroaluminum center resulting from aluminum chloride should be the

same for each oxide. A difference in the electron withdrawing

strength of the acids would arise from the electronegativity of the

oxides themselves.

Ihe Pauling electronegativity values for each of the elements

in the inorganic oxides are as follows: boron= 2.0, silicon= 1.8,

aluminum= 1.5, titanium= 1.5 and magnesium= 1.2. [46] This trend in

electronegativities (Pauling and Mulliken) correlates with the trend

in the frequency shifts of the Lewis acid bound pyridine and may

contribute to the observed trend in the acid strengths. The trend

in the activities of these materials for the catalytic cracking of

hydrocarbons will be discussed in greater detail in a later section.



Characterization of a New Solid Acid Catalyst by 27Al and 29Si
Solid-State Magic Angle Spiinnin (MAS) FT NMR Sectroscopy

The following discussion is concerned with the solid-state MAS

NMR spectra of the inorganic oxide treated with aluminum chloride as

described in the experimental section of this chapter.

The first material examined was a catalyst which had been

prepared by refluxing SiO2 and A12C16 in CC14 with enough water

present to hydrolyze all the A12C16 in order to determine the









45

spectrum of a deacposed catalyst. If a catalyst were prepared in

the presence of water or a good catalyst is exposed to water, it

would be expected that the aluminum chloride would be hydrolyzed and

form a 6-coordinate aluminum species. The catalyst prepared in the

presence of water (Figure 2-11) shows only one aluminum peak

centered at 0 ppm for the 27Al MAS NMR which is indicative of 6-

coordinate aluminum. Figure 2-12 (which is referenced to MS) shows

the 29Si MAS NMR for the catalyst prepared in the presence of water

and indicates that there is only one type of silicon present which

is the 4-coordinate silicon of silicon dioxide. The broad peak

centered at -110 ppn relative to iMS is consistent with reports in

the literature for the 29Si MAS NMR of silica gels and silicalite

(which is an all silicon zeolite). [29] No other peaks have

developed from the formation of Al-O-Si bonds by the reaction of

aluminum chloride. The aluminum chloride has simply been hydrolyzed

and for the most part is a weakly associated 6-coordinate species on

the SiO2 surface. The slight broadening of the 29Si peak compared

to unmodified SiO2 could be the result of weak association with

these aluminum species. Another factor that will contribute to the

peak broadening is that not all silicons are bonded together by

oxygen bridges (Si-O-Si) in silica gel. On the surface of the

silica gel the silicon dioxide lattice terminates in Si-O-H

(silanol) groups whose chemical shift is approximately 1 ppm

different from that of groups in the bulk lattice. [29]

The next material examined was a catalyst which had been

prepared by refluxing SiO2 and A12C6 in dry CC4 under an N2










































150 100


Figure 2-11.


0 -50 -100 -150 PPM


An 27A1 Solid-State NMR of an AC12-SiO2 Catalyst
Prepared in the Presence of H20.









































50 0 -50 -100


Figure 2-12.


-150 PPM


A 29Si Solid-State NMR of an A1C12-SiO2 Catalyst
Prepared in the Presence of H20.









48

atmosphere. The 27A1 MAS NMR for an active catalyst (before

catalysis) is shown in Figure 2-13. The peak at 0 ppm results from

the presence of 6-coordinate aluminum which formed after the

catalyst was exposed to water vapor in the air during the loading of

the NMR tube. The peak centered at 55 ppn results from 4-coordinate

aluminum, most likely with hydroxide ligands as well as Al-O-Si

bonds. The peak at 55 ppm could also arise fram the formation of

zeolitic aluminum by addition of aluminum into a surface vacancy as

shown in Equation 2-10. [33]



si si
o 0
H H
2 SiOH HOSi + A12C16 -> 2 SiO Al- OSi + 6 HC1 (2-10)
H
0 0
Si Si

The peak at 65 ppm results from Si-O-AlC12 on the silica gel

surface which would be consistent with the value of 62.8 ppm given

for aluminum chlorohydrate with a ratio of Cl/CH of 2.5. [31]

then a high surface area silica gel is treated with aluminum

chloride several types of tetrahedral aluminum centers are formed.

Shown in Figure 2-14 is the 27A1 MAS NMR for a 690 m2/gram silica

gel treated with aluminum chloride. For the high surface area

silica gel three distinct peaks are detected which are at 70, 52 and

23 ppm. The peak at 70 is assigned to a Si-O-AlCl2 species which

was observed for the 340 m2/gram silica gel. The peak at 52 ppm

most likely results from zeolitic or hydroxychloro [Si--AlCl (OH)]










































1


I I

^-^/
^


I


-50 -100 -150


-200 =="


Figure 2-13.


An 27Al Solid-State MR of an Active AlC12-SiO2
Catalyst Prepared in the Absence of H20.


10O


100


1


I '









50

aluminum centers and the peak at 23 ppm probably results from a

chemisorbed 6-coordinate hydroxychloro aluminum species.

This may be explained using the stoidhiometry of the catalyst

preparation reaction. The aluminum chloride treated silica gel is

normally prepared using a silica with a surface area of 340 m2/gram

and a hydroxyl group concentration of approximately 10

mmole/gram. [35,47] Since a 2:1 ratio by weight of inorganic oxide

to aluminum chloride is used there are 7.5 mmole of A1C13 per gram

of support which would yield roughly 80% coverage of the solid

support. If the surface area of the support is doubled a

corresponding increase in the concentration of hydroxyl groups would

occur and the total coverage of the aluminum chloride would decrease

to approximately 40%. This would mean that there would be, on

average, 2.5 hydroxyl groups for every A1C13 molecule used in the

reaction. According to this stoichiometry an average of two Al-C1

bonds would be hydrolyzed by the silica surface for every A1C13

molecule used in the reaction. The resulting 27Al MAS NMR should

then show a significant increase in the number of bands for

hydrolyzed chloroaluminum species as in Figure 2-14.

Shown in Figure 2-15 is the 29Si MAS NMR of the 690 m2/gram

silica gel reacted with aluminum chloride in CC14. In contrast to

Figure 2-12 where only one peak was observed for the 29Si MAS NMR,

there are now at least two distinct peaks centered at -88 and -105

ppm. The peak at -105 ppm is due to the formation of one Si-O-Al

bond per silicon atom on the silica surface and the peak at -88 ppm












































5 0 -50 00 -200

50 0 -50 -100 -150 -200 FF'"


Figure 2-14.


An 27A1 Solid-State NMR of an AC12-SiO2 Catalyst
Prepared with a 690 m2/gram Surface Area Silica
Gel.


150


100


;"









































20 0 -20 -40 -60 -80


Figure 2-15.


-100 -120 -140 PPM


A 29Si Solid-State NMR of an AlCl2-SiO2 Catalyst
Prepared with a 690 m2/gram Surface Area Silica
Gel.









53

is due to the formation of two Si-O-A1 bonds to one silicon center

on the silica surface. These results are consistent with literature

values given for amorphous silica-aluminas, aluminosilicates and

zeolites. [29,30]

The presence of peaks ar -88 and -105 ppn are good evidence for

the incorporation of aluminum chloride onto the silica surface and

supports the fact that the aluminum chloride has actually been

chemically bonded to the solid support. When the catalysts studied

in Figures 2-14 and 2-15 are used in a catalytic cracking reaction

(reported later in this section) low activities are observed. This

may be the result of the increased amount of hydrolyzed

chloroaluminum centers present on the catalyst surface. The

activity that is observed may result from a low number of hydroxy

chloro species and zeolitic aluminum centers which would only show

high activities at high temperatures. [2,3]
The 27A and 29Si MAS NMR spectra of a silica gel support which

has been treated with excess A12C16 (100 wt%) is shown in Figures 2-

16 and 2-17. For the 27Al MAS NMR a large peak at 105 ppm is

observed which results from uncomplexed aluminum chloride and is in

agreement with the shifts reported in the literature for the 27A

solution NMR of A12C16 and AlC4-. [32] Peaks in the 27A MAS NMR

are also observed at 38 and 0 ppn which result from the

hydroxychloro aluminum species discussed earlier. The 29Si MAS NMR

spectrum of the same catalyst exhibits only one peak, resulting from

the framework silicon dioxide[29], indicating that most of the

aluminum chloride is on the support surface as A12C16.












































150 100 50 0 -50


Figure 2-16.


-100 -150 -200 P
-100 -150 -200 RPM


An 27A1 Solid-State NMR of an ACl2-SiO? Catalyst
Prepared with 100 wt% of Aluminum Chloride.







































20 0 -20 -40 -60 -80 -100 -120 -140 PPM


Figure 2-17.


A 29Si Solid-State NMR of an AlC12-SiO2 Catalyst
Prepared with 100 wt% of Aluminum Chloride.









56

The 27A and 29Si MAS NMR spectra of a catalyst after use in a

catalytic cracking reaction are shown in Figures 2-18 and 2-19.

Once again in the 27Al MAS NMR 6-coordinate and 4-coordinate

aluminum centers are present with the 4-coordinate aluminum center

giving a peak at -70 ppm which would indicate the presence of an Si-

O-A1C12 species. The oscillation in the 27Al MAS NMR baseline is

caused by some paramagnetic material (coke) which was deposited on

the catalyst surface during catalysis. The 29Si MAS NMR displays

peaks for the framework silicon dioxide plus the silicon atoms

associated with the formation of one Si-O-Al bond per silicon

center. This indicates that even under catalytic conditions the

tetrahedral chloroaluminum centers are stable and could be

responsible for the catalytically active centers.

From the 27A and 29Si MAS NMR data it has been determined that

the catalyst prepared by reaction of aluminum chloride with

aninorganic oxide results in a solid material which has tetrahedral

chloroaluminum centers. The IR data for adsorbed pyridine indicates

that both Bronsted and Lewis acid sites are present and the

frequency shifts for the Lewis acid bound pyridine are comparable to

those exhibited by conventional cracking catalysts. [16,17] As a

result of these findings the new solid acid catalysts described in

the experimental section of this chapter were used for various

hydrocarbon conversion reactions.

The next section will deal with the characterization of the

radical on the catalyst surface generated during the catalyst
























N



p/vV


400 300 200


100


0 -100 I
o -100O


-200


-300


-400 PPM


Figure 2-18.


An 27A1 Solid-State NMR of an AC12-SiO2 Catalyst
After Reaction with n-Pentane.








































50


Figure 2-19.


0 -50 -100 -150 PPM












A 29Si Solid-State NMR of an A1C12-SiO2 Catalyst
After Reaction with n-Pentane.









59
preparation. The following sections will discuss the solid acids

use as catalytic cracking and polymerization catalysts.


Characterization of the Radical on the Catalyst Surface

It was reported in the experimental section that when the

inorganic oxides treated with aluminum chloride are prepared in

refluxing solvents a free-radical species is formed on the solid

materials with a g value of 2.012. No hyperfine splitting is

observed for the radical signal even at 4 K. In order to identify

the radical species present magnetic susceptibility measurements and

spin trapping experiments have been conducted on the aluminum

chloride treated silicon dioxide made in carbon tetrachloride.

The procedure for the spin trapping experiments using the

diamagnetic spin trapping agent EPO are outlined in the

experimental section of this chapter. Whenever the radical was spin

trapped in carbon tetrachloride no change in the radical signal was

observed indicating that the radical on the surface was not a very

reactive species. If the radical is spin trapped in toluene a

radical is trapped which has the EPR spectrum shown in Figure 2-20.

The signal obtained had a g value of 2.0152 with an observed

nitrogen hyperfine splitting constant of 14.225 gauss and a beta

hydrogen hyperfine splitting constant of 20.275 gauss. The

simulated EPR spectrum shown in Figure 2-21 was obtained using an

EPR simulation program as modified by J. Telser. [38-40] When the

hyperfine splitting constants obtained from the spectrum in Figure

2-20 are compared to literature values[48,49] of known spin trapped















































2300
2300


Figure 2-20.


Radical n AlC12-SiO2 Spin Trapped Using IMEO
in Toluene.


aN aN


3300


I/Gauss


4300















































Figure 2-21. EPR Simulation of Radical on A1C12-SiO2









62

radicals with CMPO, it is found that the EPR spectrum of Figure 2-

20 is for the benzyl radical and not the radical on the surface of

the catalyst. These results suggest that the radical on the surface

is delocalized by the inorganic oxide matrix resulting in a

relatively stable free-radical which is not capable of being spin

trapped by MPO.

It has been reported in the literature that compounds such as

Al2CI6 act as one-electron oxidizing agents towards electron rich

substrates. [43,50,51] A solution of aluminum chloride and

dichlorcnethane is capable of oxidizing any substrate which has a

first (adiabatic) ionization energy below 8 eV. The first

ionization energies for all the solvents used to prepare the

catalyst are well above 8 eV[52] which suggests that the radicals

are not derived from the one-electron oxidation of solvent molecules

which are then adsorbed onto the catalyst surface. Since the first

ionization energies for the elements silicon, aluminum, titanium,

magnesium and boron are 8.3 eV[46,52,53] it is reasonable to

suggest that the radical is derived from the one-electron oxidation

of the support. The radical species generated on the support are

delocalized throughout the inorganic oxide matrix causing the

radical to be unreactive. Because the EER spectrum of the radical

species on aluminum chloride treated silica gel made in refluxing

carbon tetrachloride shows no hyperfine splitting even at 4 K the

radical is most likely oxygen based. The inability to spin trap the

radical, the absence of any radical chemistry in the cracking of

hydrocarbons and the absence of radical initiated polymerizations









63
all support the idea of delocalized radical species on the catalyst

surface. The radical chemistry in the cracking of hydrocarbons and

the radical initiated polymerizations will be discussed later in

this chapter.

Our catalyst is prepared by the reaction of silica gel with

aluminum chloride in a 2:1 ratio by weight. This corresponds to a

4.4:1 mole ratio of silica gel to aluminum chloride. Using this

ratio we have calculated a formula weight of 3977.1 grams/mole

corresponding to a formula unit of Si44088A11oC120. The catalysts

sent for magnetic susceptibility measurements[54] were the catalysts

prepared in carbon tetrachloride and benzene. For the catalyst made

in carbon tetrachloride there were 0.246 unpaired electrons per

formula unit and the catalyst made in benzene had 0.289 unpaired

electrons per formula unit. A second batch of catalyst made in

benzene had 0.142 unpaired electrons per formula unit indicating

that the radicals are not very concentrated and that the radical

concentration does not change significantly when the catalyst

preparation is changed. This also indicates that the radical

concentration does not correlate with catalytic activity. The

catalyst prepared in carbon tetrachloride is a very active acid

cracking catalyst and the catalyst prepared in benzene is about 5

orders of magnitude lower in activity; however, the number of

unpaired electrons per formula unit is approximately the same. The

radical concentration does not correlate with the catalytic activity

of the catalysts.









64

Titration of Strong Acid Sites with Pvridine

A series of calorimetric titrations in addition to the infrared

and NMR studies were performed on several of the solid acid

catalysts. The purpose of the titrations was to measure the

enthalpy of binding of pyridine to the acid sites present on the

catalyst surface. Pyridine was used as the titrant and the

procedure was the same as previously described in the

literature. [55-57]

The first material titrated was the catalyst prepared by

refluxing SiO2 and A12C16 in dry C004 under an N2 atmosphere.

Results from the titrations indicated that the enthalpy of binding

of pyridine to the first 13.6% of the surface acid sites ranged from

48.2 Kcal/mole to 17.1 Kcal/mole. The average enthalpy of binding

measured for the acid sites titrated was 36.0 Kcal/mole. This value

is consistent with the values reported in the literature by other

workers for amorphous silica-alumina, aluminosilicates and

zeolites. [17,18]

The second material was a catalyst prepared by refluxing a

palladium chloride doped silica gel and aluminum chloride in CC14

under an N2 atmosphere. Results from the titrations indicated that

the enthalpy of binding from the first 11.8% of the surface sites

ranged from 45.0 Kcal/mole to 23.9 Kcal/mole. The average enthalpy

of binding measured for the acid sites titrated was 36.5 Kcal/mole.

This indicates that the strength of the acid sites on the catalyst

are not affected by the addition of a metal chloride. This finding

is in agreement with a report in the literature on a palladium