<%BANNER%>

Effects of Composition and Preparation on Heterogeneous Catalysts for Para-Hydrogen Induced Nuclear Polarization

Permanent Link: http://ufdc.ufl.edu/UFE0045606/00001

Material Information

Title: Effects of Composition and Preparation on Heterogeneous Catalysts for Para-Hydrogen Induced Nuclear Polarization
Physical Description: 1 online resource (52 p.)
Language: english
Creator: Li, Quanning
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2013

Subjects

Subjects / Keywords: catalyst -- dispersion -- heterogeneous -- infrared -- phip -- preparation
Chemical Engineering -- Dissertations, Academic -- UF
Genre: Chemical Engineering thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: In modern industry, heterogeneous catalysts such as titanium dioxide and aluminum oxide supported platinum and iridium have become increasingly essential to the selectivity and the extent of desired heterogeneous reactions. The scale of influence of a given catalyst on a corresponding reaction can be determined by a number of factors including its crystal structure, type of chemical bond between the metal and the reacting molecules,catalyst dispersion, the composition of supported metal, etc. We have designed dozens of catalysts, applied different conditions to the preparation processes individually and used state-of-the-art experimental technologies to test their actual properties and performances. The two most basic methods we have used when preparing heterogeneous catalysts are precipitation and impregnation (also known as incipient wetness). For this thesis, it will be mainly focusing on the properties and performances of catalysts prepared by precipitation method when different conditions are applied and the disparity between properties and performances of catalysts prepared by precipitation and impregnation respectively. We will discuss emphatically about the dispersion and crystal size of catalyst, which are of central importance in evaluating the performance of heterogeneous catalysis. We will also discuss details on the information of bond type and metal structure of Pt/TiO2 catalyst revealed by infrared spectroscopy analysis.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Quanning Li.
Thesis: Thesis (M.S.)--University of Florida, 2013.
Local: Adviser: Hagelin, Helena Ae.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2015-05-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2013
System ID: UFE0045606:00001

Permanent Link: http://ufdc.ufl.edu/UFE0045606/00001

Material Information

Title: Effects of Composition and Preparation on Heterogeneous Catalysts for Para-Hydrogen Induced Nuclear Polarization
Physical Description: 1 online resource (52 p.)
Language: english
Creator: Li, Quanning
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2013

Subjects

Subjects / Keywords: catalyst -- dispersion -- heterogeneous -- infrared -- phip -- preparation
Chemical Engineering -- Dissertations, Academic -- UF
Genre: Chemical Engineering thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: In modern industry, heterogeneous catalysts such as titanium dioxide and aluminum oxide supported platinum and iridium have become increasingly essential to the selectivity and the extent of desired heterogeneous reactions. The scale of influence of a given catalyst on a corresponding reaction can be determined by a number of factors including its crystal structure, type of chemical bond between the metal and the reacting molecules,catalyst dispersion, the composition of supported metal, etc. We have designed dozens of catalysts, applied different conditions to the preparation processes individually and used state-of-the-art experimental technologies to test their actual properties and performances. The two most basic methods we have used when preparing heterogeneous catalysts are precipitation and impregnation (also known as incipient wetness). For this thesis, it will be mainly focusing on the properties and performances of catalysts prepared by precipitation method when different conditions are applied and the disparity between properties and performances of catalysts prepared by precipitation and impregnation respectively. We will discuss emphatically about the dispersion and crystal size of catalyst, which are of central importance in evaluating the performance of heterogeneous catalysis. We will also discuss details on the information of bond type and metal structure of Pt/TiO2 catalyst revealed by infrared spectroscopy analysis.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Quanning Li.
Thesis: Thesis (M.S.)--University of Florida, 2013.
Local: Adviser: Hagelin, Helena Ae.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2015-05-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2013
System ID: UFE0045606:00001


This item has the following downloads:


Full Text

PAGE 1

1 EFFECTS OF COMPOSITION AND PREPARATION ON HETEROGENEOUS CATALYST FOR PARA HYDROGEN INDUCED NUCLEAR POLARIZATION By QUANNING LI A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR TH E DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2013

PAGE 2

2 2013 Quanning Li

PAGE 3

3 To Tao, Wei, Grace, and my family

PAGE 4

4 ACKNOWLEDGMENTS There are a lot of people having helped me during the time of my research. First of all, I thank my academic advisor, Dr. Helena Hagelin Weaver, for giving me the hard won opportunity to do research work in her group. Her technical instructions, easy going temper and great toleranc e have encouraged and benefited me a lot. My committee member, Dr. Peng Jiang, is also interested in my research and has also provided me valuable suggestions. I thank Dr. William Lear for his fruitful collaboration when I was working on Fuel Cell Project in the Solar Park. I am extremely grateful to Wei Cheng, Ph.D. candidate of Department of Chemical Engineering at the University of Florida and a worthy friend of mine, for all the guidance and assistance full of patience and responsibility. I also want to acknowledge my g roup members Luke Neal, Haibin Zheng, Trenton Elkins, and Justin Dodson for all having offered me much important assistance all the time. I also thank Sydni Credle, hearted hel p she provided to me in the Solar Park. Finally, on a personal point, I particularly want to thank my parents for all the financial and mental support with tremendous resolution throughout all my years of studying. I thank my girlfriend Tao Li for the beau tiful mind and strong courage she has ever made me feel. I thank all those friends that I have ever met during my career of studying abroad you guys are unbelievable

PAGE 5

5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 7 LIST OF FIGURES ................................ ................................ ................................ .......... 8 ABSTRACT ................................ ................................ ................................ ..................... 9 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 11 Heterogeneous Catalyst ................................ ................................ ......................... 11 Nuclear Magnetic Resonance Technology ................................ ............................. 12 Para hydrogen Induced Polarization ................................ ................................ ....... 12 Catalyst Support ................................ ................................ ................................ ..... 13 Aluminum Oxide ................................ ................................ ............................... 13 Titanium Oxide ................................ ................................ ................................ 14 Preparation Me thod ................................ ................................ ................................ 14 Precipitation ................................ ................................ ................................ ...... 15 Impregnation ................................ ................................ ................................ .... 15 Calcination ................................ ................................ ................................ .............. 15 2 EXPERIMENTAL METHODS ................................ ................................ ................. 17 Precipitation ................................ ................................ ................................ ............ 17 Measuring Support and Precursor ................................ ................................ .... 17 Titration and Overnight Aging ................................ ................................ ........... 17 Filtering and Washing ................................ ................................ ....................... 18 Drying and Calcination ................................ ................................ ..................... 19 Impregnation ................................ ................................ ................................ ........... 19 Carbon Monoxide Adsorption on Heterogeneous Catalysts ................................ ... 20 Hydrogen Treatment ................................ ................................ ........................ 20 Measuring the Dispersion and Crystallite Size ................................ ................. 21 Infrared Spectrum Analysis ................................ ................................ ..................... 21 Hydrogen Treatment and Collecting Background ................................ ............. 22 Collecting Sample Spectrum and Heat Treatment ................................ ........... 23 3 RESULTS AND DISCUSSIONS ................................ ................................ ............. 27 Effects of Different Precipitation Conditions on Pt/TiO 2 Catalyst ............................ 27 Discussion of Pt/TiO 2 Catalyst Preparation ................................ ...................... 27 Effects of Metal Composition ................................ ................................ ............ 29 Effects of pH Value for Titration ................................ ................................ ........ 30

PAGE 6

6 Effects of Calcination Temperature ................................ ................................ .. 30 Comparison of Different Catalysts Prepared by Precipitation ................................ 31 Comparison of Different Preparation Methods for Pt/TiO 2 Cata lyst ........................ 31 Result of Infrared Spectroscopy Analysis for Pt/TiO 2 Catalyst ................................ 32 Peak Position ................................ ................................ ................................ ... 32 Heat Resistanc e of Pt/TiO 2 Catalyst ................................ ................................ 33 4 CONCLUSIONS ................................ ................................ ................................ ..... 48 LIST OF REFERENCES ................................ ................................ ............................... 49 BIOGRAPHICAL SKETCH ................................ ................................ ............................ 52

PAGE 7

7 LIST OF TABLES Table page 2 1 L ist of preparation conditions of heterogeneous catalysts ................................ .. 24 2 2 L ist of titration conditions to be checked before pulse titration ........................... 24 3 1 Dispersion and particle size of different type s of catalysts under the identical precipitation condition ................................ ................................ ......................... 35 3 2 Dispersion and particle size of Pt/TiO 2 catalysts using different preparation methods and Pt precursors when calcined at 450 ................................ .......... 35 3 3 Dispersion and particle size of CA T009, CAT011, and CAT015 ......................... 35 3 4 Parameters of goodness of Gaussian fit for infrared spectrums of CAT009, CAT011, and CAT015 when p urging helium for 20 minutes after CO adsorption ................................ ................................ ................................ ........... 35 3 5 Peak positions of carbon monoxide adsorption on different kinds of Pt CO bond types and Pt crystal structures ................................ ................................ ... 36 3 6 Parameters of goodness of Gaussian fit for infrared spectrums of heat treatment of CAT 015 ................................ ................................ .......................... 36

PAGE 8

8 LIST OF FIGURES Figure page 2 1 Quantachrome ChemBET 3000 TPR/TPD ................................ ......................... 24 2 2 ChemBET 3000 chemisorption measurement ................................ .................... 25 2 3 Fourier transfer infrared spectroscopy experiment instruments .......................... 26 3 1 Diagram of relation between metal dispersion and particle size ......................... 37 3 2 Diagram of general relationship between supersaturated state and perti nent parameters ................................ ................................ ................................ ......... 37 3 3 I nfluence of Pt composition on dispersion D and particle size d at different calcination temperature ................................ ................................ ...................... 38 3 4 Influence of different fin al pH value for titration on dispersion D and particle size d when platinum composition is 0.5% ................................ ......................... 39 3 5 Influence of differen t calcination temperature on dispersion D and particle size d when platinum composition is 0.5%, 0.75 %, and 1.0% respectively ........ 40 3 6 FT IR spectrum of carbon monoxide adsorbed on CAT009 (0.5% Pt on TiO 2 final pH = 8, calcined at 450 ) surface ................................ ............................. 41 3 7 FT IR spectrum of carbon monoxide adsorbed on CAT011 (1.0% Pt on TiO 2 final pH = 7, calcined at 450 ) surface ................................ ............................. 42 3 8 FT IR spectrum of carbon monoxide adsorbed on CAT015 (0.75% Pt on TiO 2 final pH = 8, calcined at 450 ) surface ................................ .................... 43 3 9 FT IR spectrum of carbon monoxide adsorbed on CAT009 (0.5% Pt on TiO 2 final pH = 8, calcined at 450 ) surface after Gaussian peak fitting ................... 44 3 10 FT IR spectrum of carbon monoxide adsorbed on CAT011 (1.0% Pt on TiO 2 final pH = 7, calcined at 450 ) surface after Gaussian peak fitting ................... 45 3 11 FT IR spectrum of carbon monoxide adsorbed on CAT015 (0.75% Pt on TiO 2 final pH = 8, calcined at 450 ) surface after Gaussian peak fitting .......... 46 3 12 Gaussian fitting version of FT IR spectrum of carbon monoxide adsorbed on CAT015 (0.75% Pt on TiO 2 final pH = 8, calcined at 450 ) surface heat treatment ................................ ................................ ................................ ............ 47

PAGE 9

9 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science EFFECTS OF COMPOSITION AND PREPARATION ON HETEROGENEOUS CATALYST FOR PARA HYDROGEN INDUCED NUCLEAR POLARIZATION By Quanning Li May 2013 Chair: Helena E. Hagelin Weaver Major: Chemical Engineering In modern industry, he terogeneous catalysts such as titanium dioxide and aluminum oxide supported platinum and iridium have become increasingly essential to the selectivity and the extent of desired heterogene ous reacti ons. The scale of influence of a given catalyst on a corresponding reaction can be determined by a number of factors including it s crystal structure, type of chemical bond between the metal and the reacting molecules, catalyst dispersion, the composition o f supported metal, etc. We have designed dozens of catalysts, applied different conditions to the preparation processes individually and used state of the art experimental technologies to test their actual properties and performances. The two most basic me thods we have used when preparing heterogeneous catalysts are precipitation and impregnation (also known as incipient wetness ) For this thesis, it will be mainly focusing on the properties and performances of catalysts prepared by precipitation method when different conditions are applied and the disparity between properties and performances of catalysts p repared by precipitation and impregnation respectively.

PAGE 10

10 We will discuss emphatically about the dispersion a nd crystal s ize of catalyst, which are of central importance in evaluating the performance of hetero geneous catalysis We will also discuss details on the information of bond type and metal structure of Pt/TiO 2 catalyst revealed by infrared spectroscopy an alysis.

PAGE 11

11 CHAPTER 1 INTRODUCTION Heterogeneous Catalyst In modern industry, h eterogeneous catalysts such as titanium dioxide and aluminum oxide supported pla t inum and i r idium have become increasingly essential to many aspects of chemical processes where surface reactions are involved When being exploited properly and thoroughly, heterogeneous catalysts can bring tremendous i mprovement and enhancement to the controlling of s electivity and extent of desired heterogeneous reactions. However, despite being studied for several decades, the elaboration of even the most simple structured hydrocarbon, like ethylene and acetylene remains a complicated and burdensome issue. Numerous potential reactions on the surface are the major obstacles f or scientists and researchers on the path to deep and comprehensive understand ing of the mechanisms of heterogeneous reactions. Now we are aware that the existence of carbon deposits, reactants, intermediates and pr oducts on the surface can influence hydrogenation activity and selectivity to some extent More importantly, the presence of co adsorbed species can frequently have unex pectedly positive effects, which results in the beneficial modifications for selectivity of reaction pathways or product formation [1, 2]. The powerful and productive working of heterogeneous catalysts also depends on many other factor s, including the chem ical properties of the metal, pore structure or morphology of the support ing oxide metal particle shape and size and metal compositi on [3 6]. In this thesis, the main focus is the effects of preparation methods and different conditions on PHIP over heter ogeneous catalyst s

PAGE 12

12 Nuclear Magnetic Resonance Technology Nuclear Magnetic Resonance or NMR, is a physical phenomenon in which magnetic nuclei absorb and release electromagnetic radiation in a magnetic field By applying NMR Technology, it is an effective method to solve various kinds of physical, chemical and biological problems including nano porous systems and transport phenomena. However with its comparative ly low sensitivity dominated by the unobviousness of the interaction between the nuclear spins and the applied magnetic field conventional NMR signals can only be obtained on samples with rather small spin energy level and extremely weak polarization of nuclear spins [ 6, 7 ] Para hydrogen Induced Polarization Para hydrogen induced nuclear polariza tion, or PHIP [8, 9] by exploiting the quantum mechanical properties of the spin isomers of H 2 in hydrogenation reactions, is a widely acknowledged means for the study of homogeneous and heterogeneous hydrogenation. It has been recently recognized to a hi gh status for the reason that it offers an efficient mode to tackle the sensitivity issue of NMR with dramatic results [ 10 ] PHIP provides prominent enhance ments of NMR signals for nuclei of up to five orders of magnitude in magnetic fields of modern NMR spectrometers and even much higher enhancements in low and ultra low magnetic fields [ 11 ] The amplified signals make it possible to observe transient reaction intermediates that may exist but coul d not be detected when equipped with conventional NMR devices and the information acquired can be useful to deeply investigate the kinetics of heterogeneous hydrogenation catalysis There are two variants of PHIP divided basically according to their diffe rent reaction conditions [ 12 ] : (1) PASADENA (P ara Hydrogen and Synthesis Allow

PAGE 13

13 Dramatically E nha nced Nuclear A lignment), in which hydrogenation and NMR detection of the sample is entirely carried out at high magnetic field, leading to significantly enhance d anti phase multiplets, and (2) AL TADENA (Adiabatic Longitudinal T ransport After dissociation Engenders Nuclear A lignment), in which hydrogenation is initially carried out at low magnetic field followed by being transport ed t o high er field for NMR detecti on. In addition to be ing applied to amplify the NMR signals, PHIP is also increasingly utilized in the field of Magnetic Resonance I maging (MRI) [ 13 ] where hyperpolarized procedures are advantageous for its inexpensiveness and conciseness. In recent days, PHIP technology has been successfully adopt ed as a remarkable tool to observe and control the chemical processes in all kinds of micro scaled reactors [ 14 ] Catalyst Support In chemistry, a catalyst support or carrier, is the material and one indispensabl e composition of supported catalyst usually a solid with a high surface area, to which a catalyst is affixed. S upport enables a catalyst to have suitable shape, size and mechanical strength, meeting the operational requirements of chemical reactors. S uppo rt disperses active components throughout the surface of support to obtain higher specific surface area and improve the catalytic efficiency of active components per unit mass. Support also prevents active components fr om sintering or agglomerating during reactions and increases the heat resistance of catalyst. Typical supports include vario us kinds of carbon, alumina, titania, and silica. Aluminum Oxide Alum inum o xide is confirmed in term s of being easily manipulated to produce optimum texture properties. With developed process accumulated on the hydrothermal

PAGE 14

14 treatment of hydrous alumina, catalyst manufacturers are able to produce supports with controlled pore shapes and sizes However, alu minum oxide always leads to undesirable side reactions and catalyst deactivation due to its natural acidity, which, on the other hand, has been proven not always a negative influence on heterogeneous catalysis in certain situations. Titanium Oxide Titaniu m oxide support has only evolved in recent decades as a reducible support. It is observed to have much more dramatic electron transfer effect, in which electrons are moved to or from the active components as a result of electron accepting or donating sites on the support This effect, combining with the strong metal support interaction (SMSI) effect of titanium oxide, provide titanium oxide supported catalyst distinct properties such as high activity, good heat and toxicity resistance, and strong acidity an d alkalinity tolerance. Preparation Method Although catalyst possesses its natural catalytic properties inside, it is the successful preparation methods and favorable conditions that give it the possible ultimate output. The reactivity of heterogeneous catalysts and nanomaterial based catalysts occurs at the atom s urface. Consequently tremendous effort is made to maximize the surface area of a catalyst by distributing it over the support. Dispersion of precursors on high s urface area supports is carried out by one of the following methods: (1) precipitation, (2) impregnation, (3) adsorption, (4) ion exchange. Each approach has its own advantages and disadvantages. This thesis will discuss more details on the first two metho ds.

PAGE 15

15 Precipitation In this method, the aim is to achieve a reacti on where metal salt solution (which means platinum and iridium precursor in this experiment) and support powders or particle s mix together to form metal hydroxide on support. Support powders o r particles dried in advance to remove pore moisture, are stirred with sufficient amount of precursor solution long enough to ensure that pores are appropriately saturated with uniform solution. Adequate volume of alkali ne solution is immediately added in to the slurry usually using titration, to enforce precipitation Then the titrated slurry is filtered and washed repeatedly to remove alkali ions and other anions in it to acquire more purified colloidal. Impregnation pregnation is the most direct and simplest methods ever used in deposition. The aim is to fill the pores with precursor solution with calculated (or to be more precisely determined preliminarily tested) concentration to yield desired metal compos i tion Support, typically in the form of particle or small pellet, is also dried in advance to remove pore moisture. Fill the pores and moisten the surface of particl es or pellets by precursor solution before drying to crystallize the metal on the pore surface wh ich should be slow enough to form uniform deposits. Calcination Calcination is the further heat treatment after drying during chemically bounded water and carbon monoxide is eliminated and pore size is redistributed. It is also useful for generating active phase for catalyst, surface conditioning and stabilizing mechanical properties. Trying different calcination temperature is a tentative way to recognize the

PAGE 16

16 distribution form of active component and degree that chemical bonds of water and CO 2 break down.

PAGE 17

17 CHAPTER 2 E XPERIMENTAL METHODS Precipitation In this experiment, we set the total theoretical mass of every single catal yst a s 2 g regardless of the composition of the catalyst. Note that the total mass means the combined mass of the support and the mass of metal component from the precursor rather than the mass of precursor itself, and the loading means the ratio of mass of metal to mass of catalyst. Here, we take CAT023 as an example for describing this preparation method throughout this chapter, it s detailed preparation conditions are shown in Table 2 1 Measur ing Support and Precursor Find a dry and clean 200 mL beaker and put a magnetic stirring bar in it, add slightly less than 100 mL DI water into the beaker. Place the beaker on top of a magneti c stirring machine and set it at a proper speed. Use analytica l balance to weigh 1.980 0.001 g grinded TiO 2 in a weighing boat, then mix the TiO 2 slowly into the beaker to form some uniform slurry. Continue stirring the slurry for at least 30 minutes to make it really stable. After 30 minutes, use analytical balance again to weigh 0.053 0.001 g Pt Precursor H 2 PtCl 6 6H 2 O in a weighing boat, note that it is mandatory to use sp atula f or the weighing of any precursor when scraping it out of reagent bottle. Dissolve the precursor in a few drops of DI water and when the whole solution become relatively uniform, pour it into the slurry beaker drop by drop very gently and cautiously. Titrat ion and Overnight Aging Find another clean beaker and weigh about 0.1 g solid NaOH, dissolve the NaOH in about 100 mL DI water and pour the solution into a 100 mL burette for titration.

PAGE 18

18 Set the titration speed at around 0.5 pH / min and especially more slo wly when the pH is approaching 11, the expected maximum value before the first overnight aging. After the pH value reaches 11, stop titrating momentarily but keep stirring the slurry. After holding it for about 15 minutes, the pH value will drop down to ar ound 10.80 due to the gradually mixing process of the titrated slurry. Resume titrate the slurry back to 11 and hold it for another 1 or 2 hours and then titrate it all the way up to around 0.2 more than 11. Keep stirring the slurry till almost the same ti me next day as the first overnight aging. Use a piece of labeled parafilm to cover the top of the beaker to prevent any impurity in air from falling into the slurry. When the overnight a ging is sufficiently long the next day, find a clean beaker and pour a bout 80 mL DI water into it. Use pipette to measure exactly 200 L acetic acid, press it into the DI water, mix them uniformly and pour the solution into the burette for the second titration. Apply the exactly same titrating strategy for the first time onl y except change the titration destination down to approximately 7 this time. After the titration, keep stirring the slurry till almost the same time next day as the second overnight aging. Filtering and Washing After the second overnight aging, filter the slurry till the filtrate is perfect ly clean. Discard the filtrate and use a sp atula to scratch the filter cake out of the filter paper. Place the scratched filter cake into a new clean beaker with the previous magnetic stirring bar, add about 100 mL DI wat er into th e new beaker and start the overnight rinsing for the cleaner slurry. Filter the slurry the next day and place the filter cake in a crucible.

PAGE 19

19 Drying and Calcination Put the crucible containing the filter cake into an oven that has been set to 105 and take it out the next day. We may obtain a post drying recovery yield of CAT023 by weighing all the dried material in the crucible. Use mortar and pestle to grind the dried material into particles as small as possible, place all the small particles back to the crucible and put it back to the oven whi ch has been pre heated up to 350 for calcination. Take it out 3 hours later and we may again get a post calc ination recovery yield of CAT023 by weighing the material in the crucible. Preserve all the particles in a small labeled reagent bottle and we have successfully com pleted the preparation of CAT023 Impregnation In this experiment, we set the total theoretical mass of every single catalyst as 2 g as well as in the precipitation method. Here, we ta ke ICAT001 as an example for describing this preparation method throughout this chapter, its detailed preparation conditions are shown in Table 2 1. Use analytical balance to weigh 1.990 0.001 g grinded TiO 2 in a clean crucible 0.026 0.001 g Pt Precur sor H 2 PtCl 6 6H 2 O in a small beaker. Add 1080 L DI water to dissolve the precursor and keep stirring the solution for several minutes so that the solution can be stable and uniform. Use micro pipette tip to add the precursor solution in the crucible and ke ep stirring the TiO 2 pellets with a spatula in the meantime to ensure that all the solution is dispersed onto the surface of the TiO 2 pellets as evenly as possible.

PAGE 20

20 Set the temperature of oven at 80 and place the crucible in it for ca. 1 hour with additi onal momentary stirring every 10 minutes approximately. After 1 hour 80 drying, set the oven temperature at 105 and start to dry the catalyst overnight. The following preparation steps are exactly the same as those for CAT023 using precipitation method. Carbon Monoxide Adsorption on Heterogeneous Catalysts This test enable s us to realize how much the dispersion and the c rystallite size of the active metal of the catalyst are by chemisorption measurements Here, the instrument we mainly use is called ChemBET 3000, as it is shown in Figure 2 1. It is working by titrating a certain amount of adsorbent gas as CO, NH 3 o r H 2 into a flow of inert gas, letting the gas be absorbed onto the surface of the catalyst sample until the surface is saturated and measuring the amount of unabsorbed titrating gas using a thermal conductivity detector (Figure 2 2) [15 ]. Hydrogen Treatm ent Use an alytical balance to measure 0.09 0 0.010 g sample of catal yst and feed the sample into a U tube with a ball of quartz wool blocking the outlet of the U tube. Connect the U tube to the analysis station of ChemBET 3000 letting the furnace cover u p the middle and bottom part of U tube control panel Immerse the cold trap on right side of the machine in an ice water bath the temperatur e from room temperature to 170 (which is experimentally the ideal reduction temperature for Pt/TiO 2 ) at a heating rate of 20 / min. After the temperature reaches 170 switch purging gas to 5% hydrogen in nitrogen to reduce the sample for

PAGE 21

21 about 30 minutes at 170 After that, switch back to helium for chemical desorption of hydroge n for about 30 minutes at 170 and then d ecrease the temperature naturally to room temperature When the temperature is below 100 dismantle the furnace and immerse the U tube in a water bath of room temperature. Note that the temperature of hydrogen treatment for iridium catalysts would be much higher than that for platinum catalysts. The accurate condition can be measured through an experiment on ChemBE T called temperature programmed reduction (TPR) to find the most appropriate and efficient reducing temperature for Ir. We have tested a series of reducing temperatures for Ir/TiO 2 and Ir/Al 2 O 3 catalysts and it appears that 300 and 350 are apparently the best option respectively Measuring the Dispersion and Crystallite Size Switch on the calibration gas control, connect CO gas line to the calibration titration port located at the bottom of right side of the machine and open the line to st abilize the calibration gas flow for no less than 30 minutes. Use the 130 L injection loop Check the detector parameters shown in Table 2 2 every 15 minutes and start to run the pulse titration as long as the calibration gas flow is stable. Collect 6 to 8 data for crystallite size of the catalyst sample. Infrared Spectrum Analysis Fourier transform infrared spectroscopy (FT IR) by measuring how well light is absorbed on t he surface of a chosen sample at each wavelength, is a basic technique to obtain infrared spectrum of absorption, emission, photoconductivity or Raman scat tering of a gas, liquid or solid In our experiment, we introduce this technique to analyze the c ryst al structure of Pt and bond type of CO and Pt on catalyst surface. The

PAGE 22

22 instrument we use for this analysis is called Nicolet 6700 FT IR spectrometer shown in Figure 2 3. Hydrogen Treatment and Collecting Background It is required to cool the detector with liquid nitrogen for at least 20 minutes before any spectrum is collected. We also need to purge nitrogen gas into the Praying Mantis TM in advance for 30 minutes. Use accessories in sa mpling accessory kit to load the sample cup with pure grinded KBr powder s as reference material. After aligning the Praying Mantis TM to optimize the performance of the instrument by maximizing the signal on the detector collect a pure KBr background spectrum. To determine whether the background spectrum is reliable collect another sample spectrum immediately after the background spectrum and as long as the sample spectrum only fluctuates within 100.00 2.00 % by reflectance, the background is good to use. Replace the pure KBr powders with catalyst sample composed of 90% KBr and 10% catalyst which has pre mixed and well grinded before being loaded in to the sample cup. Set the temperature controller to the desired reduction temperature (like 170 for Pt/TiO 2 catalysts) and switch purging gas to 5% hydrogen in nitrogen to red uce the sample for about 30 minutes at that temperature After that, switc h back to helium for chemi cal desorption of hydrogen for about 30 minutes at the reduction temperature and then dec rease the temperature naturally to room temperature When the temperature falls almost down to room temperature, collect another background spectrum of hydrogen treated sample and examine its reliability by applying the same rule of previous background s pectrum

PAGE 23

23 Collecting Sample Spectrum and Heat Treatmen t Open CO gas line to purge CO for adsorption for 7 to 8 minutes, then switch to helium to purge out redundant CO that cannot be adsorbed onto catalyst surface collect three sample spectrums at purging time equals to 5, 10, and 20 minutes, respectively. Af ter that, set temperature controller to 105 and collect sample spectrum after temperature reaches 105 then decrease temperature back down to room temperature to collect another sample spectrum these two spectrums constitute a data group of heat treat ment, the goal of which is to detect the extent of damage that increasing t emperature causes on chemi cal desorption bond. We collect four data gro ups for heat treatment of CAT023 they are 105 / 25 150 / 25 200 / 25 250 / 25 respectively

PAGE 24

24 Table 2 1. L ist of preparation conditions of heterogeneous catalysts Catalyst number Composition Precursor Method Titrating condition Calcination temperature CAT001 0.5% Pt on TiO 2 H 2 PtCl 6 6H 2 O Precipitation pH : 11 450 CAT002 1.0% Pt on Al 2 O 3 H 2 PtCl 6 6H 2 O Precipitation pH : 11 7 450 CAT008 0.5% Pt on TiO 2 H 2 PtCl 6 6H 2 O Precipitation pH : 11 10 450 CAT009 0.5% Pt on TiO 2 H 2 PtCl 6 6H 2 O Precipitation pH : 11 8 450 CAT011 1.0% Pt on TiO 2 H 2 PtCl 6 6H 2 O Precipitation pH: 11 7 450 CAT015 0.75% Pt on TiO 2 H 2 PtCl 6 6H 2 O Precipitation pH: 11 8 450 CAT018 1.0% Ir on TiO 2 H 2 IrCl 6 6H 2 O Precipitation pH: 11 7 350 CAT022 1.0% Ir on Al 2 O 3 H 2 IrCl 6 6H 2 O Precipitation pH: 11 7 350/450 CAT023 1.0% Pt on TiO 2 H 2 PtCl 6 6H 2 O Precipitation pH: 11 7 350/450 CAT026 0.75% Pt on TiO 2 H 2 PtCl 6 6H 2 O Precipitation pH: 11 7 350/450 CAT029 0.5% Pt on TiO 2 H 2 PtCl 6 6H 2 O Precipitation pH: 11 7 350/450 ICAT001 0.5% Pt on TiO 2 H 2 PtCl 6 6H 2 O Impregnation 450 ICAT002 0.5% Pt on TiO 2 Pt(NH 2 ) 4 (OH) 2 x H 2 O Impregnation 450 ICAT003 3.0% Pt on TiO 2 Pt(NH 2 ) 4 (OH) 2 x H 2 O Impregnation 450 Table 2 2. L ist of titration conditions to be checked before pulse titration Name of item Set value Controlling knob TCD reading ( 0 Zero adjust Current ( I B ) ( 150 Current ( I B ) TCD reading ( attenuation=16) 0 Detector zero Figure 2 1 Quantac hrome ChemBET 3000 TPR/TPD

PAGE 25

25 Figure 2 2. ChemBET 3 0 00 chemisorption measurement

PAGE 26

26 A) B) C) Figure 2 3. Fourier transfer infrared spectroscopy experiment instruments including A) Thermo Scientific Nicol et 6700 FT IR s pectrometer B) Praying Mantis sample compartment and associated alignment tools C) high temperature reaction chamber

PAGE 27

27 CHAPTER 3 RESULTS AND DISC USSIONS For each metal, t he mean diameter or particle size, d ( ) of metal crystallite and its dispersion D ( the ratio of number of surface atoms N S to number of total atoms N T ) (%) have a certain universal relationship [16 17 ] High dispersions can be obtained by inducing metal atoms dispersed uniformly onto support to form monolayers or by achieving very small crystallite. Within a region of particle size from 10 to 100 t he platinum dispersion can be estimated with a given particle size by the following equation : D = D S / D T = 9.44 / d (3 1) A more intuitional image is provided in Figure 3 1. Effects of Different Precipitation Conditions on Pt/TiO 2 Catalyst The effects of different preparation conditions on Pt/TiO 2 catalyst including different metal composition, different pH value for titration, and different calcination temperature, will be discussed orderly and specifically. Discussion of Pt/TiO 2 Catalyst Preparation The titanium oxide we use as catalyst support o ccurs as a white, amorphous, and odorless powder that has a solubility of less than 0.25% in water. It can form a suspension that has a pH value of ca. 5 when certain amount of TiO 2 powder is added into water. The pH is lowered by small amount of aqueous s olution of Pt precursor H 2 PtCl 6 6H 2 O, which is ionized into H + and PtCl 6 2 A ser ies of hydrolysis indicated in Equation 3 2 through Equation 3 7 from the original PtCl 6 2 will start once the aqueous sol ution of Pt precursor is formed [18, 19, 20] : PtCl 6 2 + OH = Pt(OH)Cl 5 2 +Cl (3 2)

PAGE 28

28 Pt(OH)Cl 5 2 + OH = Pt(OH) 2 Cl 4 2 +Cl (3 3) Pt(OH) 2 Cl 4 2 + OH = Pt(OH) 3 Cl 3 2 +Cl (3 4) Pt(OH) 3 Cl 3 2 + OH = Pt(OH) 4 Cl 2 2 +Cl (3 5) Pt(OH) 4 Cl 2 2 + OH = Pt(OH) 5 Cl 2 +Cl (3 6) Pt(OH) 5 Cl 1 2 + OH = Pt(OH) 6 2 +Cl (3 7) Obviously, as pH of the suspension increases, anions containing Pt tend to combine with the growing number of OH and react to lose more chloride, obtaining a higher composition of Pt. During this process, pH keeps dropping down slowly as long as OH is co nstantly consumed if no more alkaline solution is added. This is the main reason that we need the first overnight aging to stabilize the suspension system. This overnight progress is also efficient for Pt anions to be dissolved uniformly to create a favora ble environment for the following precipitation during which deposition should be happening at the entire surface of support Precipitation develops in three phases which are super saturation, nucleation, and growth sequentially The term super saturation refers to a state where a certain type of solution is containing more dissolved substance than the amou nt it could dissolve. Figure 3 2 shows the general relationship between supersaturated state and pertinent parameters. From the figure we can see the sol ubility curve is a function of pH value and temperature. Any minor disturbance may cause precipitation to the system within the supersaturated area. In order to prevent the precipitation from developing too fast or causing severe agglomeration, it is prefe rable to settle the parameters not too far away from the solubility curve but still within supersaturated area. This operation can be easily carried out by setting the real precipitation pH value slightly higher than the pH

PAGE 29

29 where the solubility curve stand s for. The best precipitation pH value for Ti(OH) 4 is presumably around 8 [21, 22] Even after washing and filtering, there is definitely large amount of water in the hydrogel, which can be removed by drying under a certain temperature. The temperature mus t be carefully controlled at 105 in order to achieve desired high er porosity Calcination temperature is an essential factor to the surface structure of the catalyst. When calcined higher than ca. 400 the crystallite size of TiO 2 powder increases dramatically [23] which can be a remarkable damage to the cat alytic activity of the catalyst [24] At excessively high temperature, nanoparticles tend to agglomerate or sinter and form large amount of over grown clusters which remain intact afterwards [25 ] In this experiment, we choose two representative temperature s, 350 and 450 to illustrate how seriously calcination temperature can affect properties of catalysts. Effects of Metal Composition It can be seen from Table 2 1 that CAT 029 CAT 026, and C AT023 have complete ly identical preparation conditions except that their apparent platinum composition are respectively 0.5%, 0.75%, and 1.0% In the experiment, we examined the average crystallite size and dispersion of the three catal ysts on ChemBET 3000 Figure 3 3 shows the result of the test. It can be observed that when calcined at 350 t he dispersion of Pt/TiO 2 catalyst yields its highest value when the metal composition is around 0.75%, whereas at 450 the dispersion increases along with the rise of metal composition. Based on Figure 3 3 we may deduct that when making cata lyst planned to be calcined at 3 50

PAGE 30

30 precisely controlling the metal composition at a certain point will probably result to a notable improvement of dispersion Contrarily, to achieve an ideal dispersion of Pt/TiO 2 catalyst calcined at 450 more controlling on other preparation conditions instead of metal composition needs to be taken into account. Effects of pH Value for Titration It can be seen from Table 2 1 that CAT 001 CAT 008, CAT009, and CA T029 have complete ly identical preparation conditions except that their precipitation pH values before the second overnight aging are respectively 11, 10, 8, and 7 In the experiment, we examined the average crystallite size and disp ersion of the three catal ysts on ChemBET 3000. Figure 3 4 shows the result of the test. It can be observed that for Pt/TiO 2 with 0.5% loading of Pt, the most favorable pH value for precipitation is somewhere around 8 10 The dispersion become s tremendously worse once pH is lower than 8 or higher than 10 Figure 3 4 serves as a perfect example of how sensitive pH value for precipitation is to the properties of catalysts. Effects of Calcination Temperature It can be seen from Table 2 1 that CAT 02 9 CAT 026, and CAT023 were all calcined at both 350 and 450 which makes it convenient to compare the effect of different calcination temperature on Pt/TiO 2 catalysts of 0.5%, 0.75%, and 1.0% loading, respectively Figure 3 5 shows the result of CO ads orption test for the three catalysts using different calcination temperatures. It can be observed that for the 0.5% Pt catalyst, both 350 and 450 calcination yield similarly low dispersion, which is perhaps the evidence that ca lcination temperature is not a decisive, but an insignificant condition for the preparation of Pt/TiO 2

PAGE 31

31 catalyst at this metal composition. The 0.75% Pt catalyst, on the other hand, is dramatically affected by different calcination temperatures on its dispersion. In the process of making Pt/TiO 2 catalyst at this metal composition, carefully controlling the calcination temperature at 350 is a crucial step to obtain a high dispersion. For the 1.0% Pt catalyst, the dispersion of those calcined at 350 is also much higher than the dispersion of those calcined at 450 However, compared to the 0.75% Pt c atalyst, calcination temperature plays a less prominent role in the whole preparation process of 1.0% Pt catalyst Comparison of Different Catalysts Prepared by Precipitation Four ki nds of catalysts which have different metal/support combinations will be discussed in details. Now we choose CAT 023 CAT 002 CAT 018 and CAT 022 as examples from Table 2 1 since their metal percentage are equal and that they all experienced exactly identica l precipitation procedures and partially identically calcination temperature. Table 3 1 shows the dispersion and particle size of those different types of catalysts under the identical precipitation condition Compared to a 50% or even higher theoretical d ispersion achieved by silica supported i ridium catalyst [26] Ir/TiO 2 and Ir/Al 2 O 3 can barely reach such high dispersion under the same preparation method. The favorable preparation method for supported iridium catalyst is still under further development. Comparison of Different Preparation Methods for Pt/TiO 2 Catalyst In this part, we will compare how different preparation methods, precipitation and impr egnation, influence the properties of Pt/TiO 2 catalyst We choose CAT029, ICAT001, ICAT002, and ICAT003 as examples from Table 2 1 for comparison.

PAGE 32

32 Table 3 2 shows the dispersion and particle size of those Pt/TiO 2 catalysts using different preparation methods and Pt precursors. It can be seen that two preparation methods obtain closely similar dispersions whe n Pt composition is 0.5% and calcination temperature is 450 Pt(NH 2 ) 4 (OH) 2 x H 2 O is an apparently better Pt precursor if impregnation method is applied. Result of Infrared Spectroscopy Analysis for Pt/TiO 2 Catalyst Among all the catalysts analyzed by FT I R experiment, we found that the data of CAT009, CAT011, and CAT015 (the preparation conditions are shown in Table 2 1) is much more comprehensive and representative to demonstrate the surface structure of Pt/TiO 2 catalyst. Table 3 3 shows the result s for C O adsorption test for the three catalysts. Peak Position Shown in Figure 3 6 through Figure 3 8 are infrared spectrums of CAT009, CAT011, and CAT015 in the wavelength region from 2300 cm 1 to 1400 cm 1 where the vast majority of informative adsorption peaks should appear. It is possible to apply Gaussian f it ting f unction to all the IR spectrum curves in order to dissociate individual peaks from the initial synthetic peak [27] Figure 3 9 through Figure 3 11 show the Gaussian fitted diagrams of CAT009, C AT011, and CAT015 unveiling individual peaks of the spectrums all collected when purging helium for 20 minutes after CO adsorption. Table 3 4 shows several parameters displaying the goodness of Gaussian. The more the value of R square is close to 1, the le ss the deviation of the fitting is. Tremendous efforts have already been involved into the exploration of correlation among Pt CO bond type, Pt crystal structure, and peak position. By referring to several

PAGE 33

33 previous literatures and documents, we are able to summarize all the useful information about peak positions shown in Table 3 5 [ 28 37 ] From the reference peak positions, it can be deducted that Pt(111) and Pt(100) are the basic type of metal structure for the case that platinum composition is 0.75% and 1.0% [ 29, 32, 38 40] where as Pt(100) is the dominant metal structure when platinum composition is 0.5% [29, 30, 32, 33, 41] For any metal loading, linear bond is the only one bond ty pe that can be clearly observed [42 43 ] There are certain possibilitie s that other metal structure types also appear at a relatively low ratio compared to the major structure types due to the potential experimental errors and fitting in accuracy [31, 41] However, all the speculations must be proven by further collection of i nfrared spectrums and more suitable curve fitting functions or other more precise data compiling methods. Other bond types like bridge bond and three fold bond are ev en more difficult to be accurately observed as a result that considerable noises have disturbed the region where adsorption peaks of such bond types would always appear. Heat Resistance of Pt/TiO 2 Catalyst As the rise of temperature, chemical desorption will occur on the surface where carbon monoxide has been adso rbed by platinum atoms [44] Because of the theoretical reason that peak area is a decisive indicator for the quantity of its corresponding bond type and metal structure, the impact of temperature increase on CO adsorption can be interpreted by how much th e area of a certain peak decreases as shown in Figure 3 12 and Table 3 6. T he initial curve of Figure 3 12 D) is not even fittable by Gaussian fitting for the faraway from one R square value which implies that the heat resistance of

PAGE 34

34 Pt/TiO 2 catalyst has b een largely diminished due to the high temperature leading to the chemical desorption of CO molecules.

PAGE 35

35 Table 3 1. Dispersion and particle size of different types of catalysts under the identical precipitation condition Catalyst number Composition 350 Ca lcination 450 Calcination Dispersion Particle s ize Dispersion Particle s ize CAT023 1.0% Pt on TiO 2 54.49% 17.32 30.88% 30.56 CAT002 1.0% Pt on Al 2 O 3 42.61% 22.15 CAT018 1.0% Ir on TiO 2 49.95% 16.53 CAT022 1.0% Ir on Al 2 O 3 14.41% 57.27 30.71% 27.89 Table 3 2. Dispersion and particle size of Pt/TiO 2 catalysts using different preparation methods and Pt precursors when calcined at 450 Catalyst number Composition Precursor Preparation method Dispersion Particle s ize CAT029 0.5% Pt on TiO 2 H 2 PtCl 6 6H 2 O Precipitation 16.25% 58.08 ICAT001 0.5% Pt on TiO 2 H 2 PtCl 6 6H 2 O Impregnation 15.74% 59.96 ICAT002 3.1% Pt on TiO 2 Pt(NH 2 ) 4 (OH) 2 x H 2 O Impregnation 48.30% 19.54 ICAT003 0.5% Pt on TiO 2 Pt(NH 2 ) 4 (OH) 2 x H 2 O Impregnation 31.69% 24.41 Table 3 3. Dispersion and particle size of CAT009, CAT011, and CAT015 Catalyst number Composition Titrating condition Dispersion Particle s ize CAT009 0.5% Pt on TiO 2 pH: 11 8 39.21% 24.07 CAT011 1.0% Pt on TiO 2 pH: 11 7 70.73% 13.34 CAT015 0.75% Pt on TiO 2 pH: 11 8 79.23% 11.91 Table 3 4. Parameters of goodness of Gaussian fit for infrared spectrums of CAT009, CAT011, and CAT015 when purging helium for 20 minutes after CO adsorption CAT009 CAT011 CAT015 Number of terms 2 3 3 SSE 2.289e 06 0.0001974 9.025e 06 R square 0.9951 0.9964 0.9988 Adjusted R square 0.9947 0.9962 0.9987 RMSE 0.000137 0.001272 0.000272 Peak position and peak area 2056 cm 1 0.0805 2060 cm 1 0. 5817 2065 cm 1 0.1185 2035 cm 1 0.2323 2042 cm 1 2.8801 2060 cm 1 0.2045 2010 cm 1 1.2445 2049 cm 1 0.7561

PAGE 36

36 Table 3 5. Peak positions of carbon monoxide adsorption on different kinds of Pt CO bond types and Pt crystal structures Crystal structure Peak position Linear bond Bridge bond Three fold bond Pt(111) 2085; 2094 2110; 2040 2080 1840 1857; 1810 1770 1785 Pt(110) 2075 Pt(100) 2035; 2013 2060 1879; 1800 1870 Pt(210) 2058 Table 3 6. Parameters of goodness of Gaussian fit for infrared spectrums of heat treatment of CAT015 105 150 200 Number of terms 2 3 3 SSE 2.278e 05 1.28e 05 2.335e 05 R square 0.9916 0.985 0.8679 Adjusted R square 0.9913 0.994 0.8593 RMSE 0.0004269 0.0003239 0.0004375 Peak position and peak area 2058 cm 1 0.1732 2056 cm 1 0.0308 2055 cm 1 0. 0204 2044 cm 1 0.5191 2057 cm 1 0.2369 2070 cm 1 0.0467 2025 cm 1 0.1323 2047 cm 1 0.0647

PAGE 37

37 Figure 3 1. Diagram of relation between metal dispersion and particle size Figure 3 2 Diagram of general relationship between supersaturated state and pertinent parameters

PAGE 38

38 A B Figure 3 3 Influence of Pt composition on A) dispersion D and B) particle size d at different calcination temperature

PAGE 39

39 A B Figure 3 4 Influence of different final pH value for titration on A) dispersion D and B) particle size d when platinum composition is 0.5%

PAGE 40

40 A B Figure 3 5 Influence of different calcination temperature on A) dispersion D and B) particle size d when platinum composition is 0.5%, 0.75%, and 1.0% respectively

PAGE 41

41 Figure 3 6 FT I R spectrum of carbon monoxide ad sorbed on CAT009 (0.5% Pt on TiO 2 final pH = 8, calcined at 450 ) surface

PAGE 42

42 Figure 3 7 FT IR spectrum of carbon monoxide adsorbed on CAT011 (1.0% Pt on TiO 2 final pH = 7, calcined at 450 ) surface

PAGE 43

43 Figure 3 8 FT IR spectrum of carbon monoxide adsorbed on CAT015 (0.75% Pt on TiO 2 final pH = 8, calcined at 450 ) surface

PAGE 44

44 Figure 3 9 FT IR spectrum of carbon monoxide adsorbed on CAT009 (0.5% Pt on TiO 2 final pH = 8, calcined at 450 ) surface after Gaussian peak fitting

PAGE 45

45 Figure 3 10 FT IR spectrum of carbon monoxide adsorbed on CAT011 (1.0% Pt on TiO 2 final pH = 7 calcined at 450 ) surface after Gaussian peak fitting

PAGE 46

46 Figure 3 11 FT IR spectrum of carbon monoxide adsorbed on CAT015 (0.75 % Pt on TiO 2 final pH = 8, calcined at 450 ) surface after Gaussian peak fitting

PAGE 47

47 A) B) C) D) Figure 3 12 Gaussian fitting version of FT IR spectrum of carbon monoxide adsorbed on CAT015 (0.75% Pt on TiO 2 final pH = 8, calcined at 450 ) surface after A) no heat treatment B) 105 heat treatment C) 150 heat treatment D) 200 heat treatment

PAGE 48

48 CHAPTER 4 CONCLUSIONS All the research work discussed in this thesis is aimed to improve and strengthen the promoting effects heterogeneous catalysts such as titanium oxide supported platinum are on para hydrogen induced nuclear polarization which is a state of the art technol ogy to examine the nature of many hydrogenation reactions. Through the course of the research, we found that when precipitation pH value is around 8 and calcination temperature is 350 for deposition precipitation method Pt/TiO 2 catalyst is likely to get relatively higher dispersion and smaller particle size, both favorable features for heterogeneous hydrogenation reactions Those Pt/TiO 2 catalysts with 0.75%, metal composition tend to yield higher dispersion than those with 1.0% and even much higher than those with 0.5% metal composition when other preparation conditions are identically applied to each catalyst. Impregnation method is still falling behind precipitation on obtaining higher dispersion for Pt/TiO 2 catalysts that have already explored, fur ther exploration on this method will be carried out soon to find the ideal metal loading and most suitable precursor for impregnation method Pt/Al 2 O 3 catalysts, when calcined at 450 are more likely to produce smaller crystallite particles Better support ing oxides, preparation methods and conditions for iridium catalysts are still under probation till the most effective match is confirmed.

PAGE 49

49 LIST OF REFERENCES [1] G. C. Bond, App l Catal A 149 ( 1997 ) 3 25. [2] G.C. Bond, P.B. Wells, J. Catal 4 (1964) 211 219 [3] I. Lee, F. Zaera, J. Catal 269 (2010), 359 366. [4] L.M. Neal, H.E. Hagelin Weaver, J. Mol. Catal. A 284 (2008), 141 148. [5] L.M. Neal, D. Hernandez, H.E. Hagelin Weaver, J Mol Catal A 307 (2009), 29 36. [6] V.V. Zhivon itko, K.V. Kovtunov, I.E. Beck, A.B. Ayupov, V.I. Bukhtiyarov, I.V. Koptyug, J Phys Chem C 115 (2011) 13386 13391. [7] A. Eichhorn, A. Koch, J. Bargon, J Mol Catal. A 174 (2001), 293 295 [8] C.R. Bowers, D.P. Weitekamp, J A m. Chemical Soc 109 ( 1 987 ), 5541 5542. [9] C.R. Bowers, D.P. Weitekamp, Phys Rev Lett 57 ( 1986 ), 2645 2648. [10] S.B. Duckett, R.E. Mewis, Accounts of Chemical Research 45 (2012), 1247 1257. [11] K.V. Kovtunov, V.V. Zhivonitko, I.V. Skovpin, D.A. Barskiy, I.V. Koptyug, Topics in Current Chem (2012) [12] T. Ratajczyk, T. Gutmann, S. Dillenberger, S. Abdulhussaein, J. Frydel, H. Breitzke, U. Bommerich, T. Trantzschel, J. Bernarding, P.C.M.M. Magusin, G. Buntkowsky, Solid State Nuclear Magnetic Resonance 43 44 (2012), 14 21. [13] E. Terreno, D.D. Castelli, A. Viale, S. Aime, Chem. Rev. 110 (2010) 3019 3042. [14] L. Bouchard, S.R. Burt, S. Anwar, K. V. Kovtunov, I.V. Koptyug, A. Pines, Sci. 319 (2008), 442 445. [15] L. M. Neal, N anoparticle Oxides as Catalyst S upports for the Oxidative Coupling of 4 M ethylpyridine over Palladium, PhD Dissertation, University of Florida, FL, (2008). [16] K.A. Starz, E. Auer, T. Lehmann, R. Zuber, J Power Sources 84 (1999), 167 172. [17] A. Borodzin, M. Bonarowska, Langmuir 13 (1997), 5613 5620. [18] F. Zhang, J. Chen, X. Zhang, W. Gao, R. Jin, N. Guan, Y. Li, Langmuir 20 (2004), 9329 9334. [19] E. Blasius, W. Preetz, R. Schmilt, J. Inorg. Nucl. Chem. 19 ( 1961 ), 115. [20] L.E. Cox, D.G Peters, E.L. Wehry, J. Inorg. Nucl. Chem. 34 ( 1972 ), 297.

PAGE 50

50 [21] J. Hong, W. Chu, M. Chen, X. Wang, T. Zhang, Catal Comm 8 (2007), 593 597. [22] Y. Fovet, J. Gal, F. Toumelin Chemla, Talanta 53 (2001), 1053 1063. [23] Y. Chen C. Lee M. Yeng H. Chiu J Crystal Growth 247 (2003), 363 370. [24] Y. Sakatani, D. G rosso, L. Nicole, C. Boissie`re, G. J. A.A. Soler Illiab C. Sanchez. J. of Materials Chem., 16 (2006), 77 82. [25] K. Nakane, N. Ogata, Photocatalyst Nanofibers Obtained by Calcination of Organic Inorganic Hybrids, Nanofibers Ashok Kumar (Ed.), ISBN: 978 953 7619 86 2, InTech, (2010), 213 226. http://www.intechopen.com/books/nanofibers/photoc atalyst nanofibers obtained by c alcination of organicinorganic hybrids accessed 02/25/13 [26] R. Shibuya, M. Ohshima, H. Kurokawa, H. Miura, Bull. Chem. Soc. Jpn. 83 (2010), 732 734. [27] G.E.A. Swann, S.V. Patwardhan, Clim. Past 7 (2011), 65 74. [28] N.C. Yee, G.S. Chottiner, D.A. Scherson, J. Phys. Chem. B 109 (2005), 7610 7613. [29] Y. Kinomoto, S. Watanabe, M. Takahashi, M. Ito, Surf. Sci. 242 (1991), 538 543. [30] A.E. Morgan, G.A. Somorjai, Surf. Sci. 12 (1968), 405 425. [31] S. Ferrer, H.P. Bonzel, S urf. Sci. 119 (1982), 234 250. [32] A.E. Morgan, G.A. Somorjai, J. Chem. Phys. 51 (1969), 3309 3320. [33] S. Chang, M.J. Weaver, J. Phys. Chem. 94 (1990), 5095 5102. [34] C. Rice, Y. Tong, E. Oldfield, A. Wieckowski, F. Hahn, F. Gloaguen, J. L ge r, C. Lamy J. Phys. Chem. B 104 (2000), 5803 5807. [35] P.A. Thiel, R.J. Behm, P.R. Norton, G. Ertl, Surf. Sci. 121 (1982), L553 L560. [36] T. Iwasita, F. C. Nart, Progress in Surf. Sci. 55 (1997), 271 340. [37] J. Huang, Characterization of Electrochemical Interfa ces by Infrared Spectroscopy, PhD Dissertation, Virginia Polytechnic Institute and State University, VA, (1996). [38] H. J. Krebs, H. Lth, Appl. Phys. 14 (1977), 337 342. [39] H. Froitzheim, H. Hopster, H. Ibach, S. Lehwald, Appl. Phys. 13 (1977), 147 151. [40] G. Ertl, M. Neumann, K.M. Streit, Surf. Sci. 64 (1977), 393 410.

PAGE 51

51 [41] S. Yamagishi, T. Fujimoto, Y. Inada, H. Orita, J. Phys. Chem. B 109 (2005), 8899 8 908. [42] H. Basch, D. Cohen, J. Am. Chem. Soc. 105 (1983), 3856 3860. [43] R.M. Rioux, J. D. Hoefelmeyer, M. Grass, H. Song, K. Niesz, P. Yang, G.A. Somorjai, Langmuir 24 (2008), 198 207. [44] S. Blais, Z. Radovic Hrapovic, G. Jerkiewicz, Langmuir 16 (2000), 4779 4783.

PAGE 52

52 BIOGRAPHICAL SKETCH Quanning (Steve) Li was born in Zibo, Shandong, to Yantong Li and Min Wang in 1987. He was raised in the city of Zhengzhou where he attended Zhengzhou Foreign Language School. After graduating from high school in 2006, he continued his education at China University of Petroleum (East China) where he pursue degree in chemical engineering and t echnology. After graduating from China University of Petroleum (East China) in 2010, he came to Gainesville, Florida one year later and joined Dr. Helena Hagelin f Chemical Engineering at the University of Florida, concentrating on the research of fuel cell and heterogeneous catalyst. Florida in the spring of 2013 and is continuing to pursue his Ph.D. at Co lorado School of Mines