QUANTITATIVE THERMODYNAMIC UNDERSTANDING OF THE SOLID-LIQUID INTERFACE ...

316 Pages·2013·7.8 MB·English

The Pennsylvania State University
The Graduate School
College of Engineering

QUANTITATIVE THERMODYNAMIC UNDERSTANDING OF THE SOLID-
LIQUID INTERFACE DURING HETEROGENEOUS CATALYST SYNTHESIS

A Dissertation in
Chemical Engineering
by
Jason Michael Binz

© 2013 Jason Michael Binz

Submitted in Partial Fulfillment
of the Requirements
for the Degree of

Doctor of Philosophy

December 2013
The dissertation of Jason Michael Binz was reviewed and approved* by the following:

Robert M. Rioux
Freidrich G. Helfferich Assistant Professor
Dissertation Advisor
Chair of Committee

Darrell Velegol
Distinguished Professor of Chemical Engineering

Themis Matsoukas
Professor of Chemical Engineering

James H. Adair
Professor of Materials Science and Engineering, Bioengineering, and Pharmacology

Andrew Zydney
Walter L. Robb Chair and Professor of Chemical Engineering
Head of the Department of Chemical Engineering

*Signatures are on file in the Graduate School.
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Abstract

We use isothermal titration calorimetry (ITC) to study the binding mechanism
that occurs at the solid-liquid interface during heterogeneous catalyst synthesis. The
study focuses on Pt transition metal complexes (TMC) that adsorb via an electrostatic
interaction onto an oxide support (γ-Al O and SiO ). The electrostatic driving force is
2 3 2
controlled by adjusting the solution pH during synthesis further from its point-of-zero
charge (PZC). γ-Al O was chosen due the amphoteric nature of the surface potential
2 3
(PZC = 7.8), which will allow for a similar pH range to be probed for anion
(chloroplatinic acid (CPA)) and cation (tetraammineplatinum(II) nitrate (TAP))
adsorption. SiO was chosen because it is an acidic support (PZC = 4.4) which will allow
2
a large pH range for TAP adsorption. For all synthesis conditions, we analyze the
thermodynamic parameters (K, ΔG, ΔS, and ΔH) and the binding stoichiometry to
determine the effect of changes in the electrostatic driving force on final catalyst
properties. We correlate the thermodynamics with Pt nanoparticle size and loading
through the use of high-energy x-ray diffraction with a PDF analysis over a temperature
range of 323 – 773 K, determine the final nanoparticle size after reduction at 623 K with
the use of chemisorption, and elemental analysis to determine weight loading. For CPA
and TAP adsorption close the PZC, we observe minimal TMC uptake that exhibit small
exothermic enthalpies, which correlate to larger supported nanoparticles. As the solution
pH is shifted further from the PZC, the supported nanoparticles are smaller with a higher
weight loading and an increased exothermic enthalpy. There is also a large difference
noticed between the adsorption enthalpy for CPA and TAP. We suggest this could be
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due to the formation of covalent bonding between the CPA and surface hydroxyl groups
once CPA is in the diffuse layer or could be associated with larger hydration sheath
interactions between TAP and the surface. We also observe the free energy of adsorption
remains relatively constant through these studies, suggesting there are compensating
entropic contributions associated with interactions between the hydration sheaths and
surface water groups.
We also use ITC to study the adsorption of Rh(OH) nanoparticles onto early
3
transition metal oxides. This study highlights the ability of the ITC to elucidate specific
binding enthalpies from a complex reaction network through the use of the Born-Haber
cycle.

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Table of Contents
List of Figures.....................................................................................................................xi
List of Schematics............................................................................................................xvii
List of Tables..................................................................................................................xviii
Acknowledgements............................................................................................................xx
Chapter 1. Introduction........................................................................................................1
1.1 The Importance of Heterogeneous Catalysis....................................................1
1.2 The Science of Heterogeneous Catalyst Synthesis...........................................2
1.2.1 The Selection of the Support and Precursor Material......................5
1.2.2 TMC Deposition onto the Support Surface.....................................7
1.2.3 Thermal Steps of the Catalyst Synthesis Process..........................13
1.2.4 The Effect of Catalyst Synthesis Steps on Nanoparticle
Properties.......................................................................................14
1.3 Understanding the Adsorption Mechanism for the Solid-Liquid
Interface...........................................................................................................17
1.3.1 The Simple Approach to Charged Species at an Interface............18
1.3.2 Basic Stern Model: Improvements to Gouy-Chapman Model to
Account for Hydration and Ion Interactions..................................19
1.4 Development of Physical Adsorption Model Based on Solid-Liquid Interface
Interactions.......................................................................................................23
1.4.1 Correction for the Chemical Interaction Term in the PA Model
Through the Development of Revised Physical Adsorption
Model.............................................................................................25
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1.4.2 Further Simplification of Revised Physical Adsorption Model.....26
1.4.3 Limitations of the Physical Adsorption Models and the Need for
Quantitative Description of TMC Adsorption...............................27
1.5 Summary of the Dissertaion............................................................................27
1.6 References.......................................................................................................29
Chapter 2. Quantification of Strong Electrostatic Adsorption of Platinum Precursors on
Oxide Supports during Heterogeneous Catalyst Synthesis................................................36
2.1 Introduction......................................................................................................36
2.2 Description of the Simplified Revised Physical Adsorption Model................39
2.3 ITC Theory.......................................................................................................44
2.4 Experimental....................................................................................................46
2.4.1 Materials Prepartation......................................................................46
2.4.2 ITC Procedure for Binding TMC to Oxide Supports.......................47
2.4.3 Bulk Uptake Experiments................................................................50
2.4.4 Support Characterization.................................................................50
2.4.5 OH Density Determination via Grignard Titration..........................51
2.5 Results and Discussion....................................................................................53
2.5.1 Comparison of the ITC Experiments to the sRPA Model...............53
2.5.2 ITC Analysis of TMC Adsorption onto Hydroxide Supports..........57
2.6 Conclusion.......................................................................................................89
2.7 References........................................................................................................91
Chapter 3. In-situ Characterization of Platinum Nanoparticle Growth on Oxide Supports
Synthesized via Strong Electrostatic Adsorption by High-Energy X-Ray Diffraction.....95
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3.1 Introduction......................................................................................................95
3.2 Basics of PDF Analysis...................................................................................99
3.3 Experimental..................................................................................................100
3.3.1 Materials Preparation.....................................................................100
3.3.2 High-Energy X-Ray Diffraction Experimental Setup....................101
3.3.3 CO Chemisorption for Particle Size Determination......................102
3.4 Results and Dicsussion..................................................................................103
3.4.1 d-PDF Analysis of CPA Adsorption onto γ-Al O and SiO .........106
2 3 2
3.4.2 d-PDF Analysis of TAP Adsorption onto γ-Al O and SiO .........118
2 3 2
3.5 Conclusion.....................................................................................................128
3.6 References......................................................................................................130
Chapter 4. Study of Interfacial Interactions of Rhodium Hydroxide and Metal
Nanoparticles and Metal Oxide Supports........................................................................135
4.1 The Importance of Heterogeneous Catalysts.................................................135
4.2 Experimental..................................................................................................138
4.2.1 Materials.........................................................................................138
4.2.2 Materials Synthesis.........................................................................138
4.2.3 Deposition of Rhodium Hydroxide Nanoparticles onto Supports..139
4.2.4 Characterization..............................................................................139
4.3 Results and Discussion..................................................................................141
4.3.1 Isothermal Titration Calorimetry....................................................141
4.3.2 Nanoparticle/Support Compositions...............................................144
4.3.3 In-situ TEM in Vacuum..................................................................150
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4.3.4 In-situ TEM in Reducing Atmosphere............................................154
4.3.5 X-Ray Absorption Spectroscopy....................................................158
4.3.6 Pair Distribution Function...............................................................162
4.4 Conclusion.....................................................................................................164
4.5 References......................................................................................................165
Chapter 5. An in-situ High-Throughput Reactor for X-Ray Absorption Spectroscopy at
Low Temperatures...........................................................................................................168
5.1 Introduction....................................................................................................168
5.2 Motivation for Design of Low Temperature X-Ray Absorption Spectroscopy
(XAS) Reactor...............................................................................................171
5.3 The New Multi-Channel Reactor Design......................................................174
5.4 Experimental..................................................................................................183
5.4.1 Catalyst Preparation........................................................................183
5.4.2 Determination of Temperature Uniformity between the Six Sample
Holders of the Reactor.............................................................................185
5.4.3 EXAFS Studies of Pt/SiO Samples to Determine Effect of
2
Temperature on DWF..............................................................................186
5.4.4 Ethylene Hydrogenation Studies.....................................................187
5.5 Results and Discussion..................................................................................188
5.5.1 Temperature Studies.......................................................................188
5.5.2 EXAFS Analysis.............................................................................195
5.5.3 Ethylene Hydrogenation Studies.....................................................199
5.6 Conclusion.....................................................................................................201
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5.7 References......................................................................................................202
Chapter 6. Conclusions and Future Work
6.1 Conclusions of the Dissertation.....................................................................207
6.2 Future Work...................................................................................................210
6.2.1 Characterization of Samples Prepared by SEA utilizing High-Energy
X-Ray Diffraction with PDF Analysis, TEM, Chemisorption, and
Reactivity Studies....................................................................................211
6.2.2 Determination of Uptake Kinetics for Strong Electrostatic
Adsorption................................................................................................216
6.2.3 Ideal Oxide Supports in Order to Accurately Predict Surface OH
Density.....................................................................................................221
6.2.4 Expanded SEA Studies beyond Pt TMCs: Adsorption of Noble and
Base Metals..............................................................................................223
6.2.5 Using ITC to Probe Adsorption Mechanisms beyond Electrostatic
Interactions: Chemical Complementarity and Molecular Recognition...224
6.3 References......................................................................................................228
Appendix A. Thermodynamic Profiles at the Solvated Inorganic-Organic Interface: The
case of Gold-Thiolate Monolayers...................................................................................231
A.1 Introduction...................................................................................................231
A.2 Experimental.................................................................................................232
A.2.1 Materials.........................................................................................232
A.2.2 ITC Experimental Procedure.........................................................233
A.2.3 Solution Calorimetry Experimental Procedure..............................234
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A.2.4 Thermogravimetric Analysis..........................................................235
A.2.4.1 Experimental Procedure..................................................235
A.2.4.2 Results.............................................................................235
A.2.5 Determination of Gold Surface Atom (Au ) Concentration...........237
s
A.2.6 Determination of Coverage (θ)......................................................239
A.2.7 Speciation Diagram for TGA Dissociation....................................240
A.3 Results and Discussion..................................................................................240
A.4 Conclusion....................................................................................................260
A.5 References.....................................................................................................264
Appendix B. MSDS for Alumina and Silica supports.....................................................268
Appendix C. Acronym Definitions..................................................................................294

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