Podkolzin-PhD_Thesis

Podkolzin-PhD_Thesis - Reactivity of light hydrocarbons...

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SG Podkolzin - JAD Catalysis Group - University of WI-Madison 1 Reactivity of light hydrocarbons over noble metal catalysts S. G. Podkolzin
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SG Podkolzin - JAD Catalysis Group - University o 2 Scope of Work System Catalysts: Pt and Pd, alloys with Sn, Au. Gases: H 2 , CO, CO 2 , C 2 -C 4 hydrocarbons. Reactions: Selective hydrogenation, hydrogen exchange, dehydrogenation (coking), hydrogenolysis (cracking), dimerization. Commercial: Stability against gum formation (FCC, Pyrolysis), production of poly-grade olefins. Results Experimental characterization of surface chemistry; Selection of quantum chemical methods and model development; Developing of molecular simulations. Application Comprehensive model for reactivity of light hydrocarbons over noble- metal catalysts. Methodology for developing molecular simulations for solid-fluid interfaces.
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SG Podkolzin - JAD Catalysis Group - University o 3 Selective Hydrogenation Project evolution: Commercial reactions CH CH CH 2 =CH 2 CH 3 -CH 3 CH 2 =CH-CH=CH 2 C 3 H 6 =CH 2 C 3 H 7 -CH 3 Complete hydrogenation is very fast Some catalysts give almost 100% selectivity Selective catalysts also have high activity Traditional explanation : heats of adsorption of the original HC are much higher than those of the partially hydrogenated product. Group’s strength : Calorimetry: perfect method for testing catalysts. Measure heats and predict performance. 10-100x
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SG Podkolzin - JAD Catalysis Group - University o 4 C 4 Kinetics and Calorimetry on Pt, Pd CH 2 =CH-CH=CH 2 C 3 H 6 =CH 2 Referenc e catalysts Activity, TOF Selectivity, % Pt 0.01-0.1 40-60 80-100 Butene 0 40 80 120 160 200 0.00 0.02 0.04 0.06 0.08 0.10 0.12 Coverage, ML -ΔH, kJ/mol  Pt Pd Butadiene 0 40 80 120 160 200 240 0.00 0.05 0.10 0.15 0.20 Coverage, ML Pt Pd Butadiene adsorbs stronger than butene (as expected) Heats on Pt and Pd are similar C 4 hydrocarbons disproportionate on adsorption, producing gas- phase butane Pd is more active and selective than Pt
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SG Podkolzin - JAD Catalysis Group - University o 5 Levels of Model Complexity A* + B* C Power law: rate = k P α a P β b no information about catalytic surface Langmuir-Hinshelwood (Mean Field Approximation): average surface concentrations, Langmuir adsorption, energetics are invariable, competitive or non-competitive model. Molecular simulation: Chemical species and their geometries; Potential Energy Surface vs. traditional adsorption site; Local concentrations as a function of lateral interactions, steric effects, reaction rates; Dependence of energetics and geometries on local surroundings 2 ( ) (1 + ) a b a b a a b b k K K P P rate K P K P = + Consistency Simplicity
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SG Podkolzin - JAD Catalysis Group - University o 6 Goal: Unified surface chemistry for description of reactivity Why now : computational resources Why us:
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Podkolzin-PhD_Thesis - Reactivity of light hydrocarbons...

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