Alkane Conversion on Platinum-based Catalysts PDF Download

Author: Duygu Gerceker
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Languages : en
Pages : 381

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Book Description
Heterogeneous catalysis has contributed to human civilization in an overwhelming manner by allowing the development of efficient processes to transform natural resources into fuels and chemicals. Currently, dwindling fossil fuel resources and alarming level of environmental issues have entailed a search for the development of novel catalysts to be used in more sustainable processes that have lower carbon footprint. Recent advancements in computing technologies coupled with the progress in electronic structure calculation methods yielded density functional theory (DFT) calculations as a powerful tool in computational catalysis. Combined with experimental and characterization efforts, atomic-level understanding of the catalyst structure and reaction mechanisms obtained through DFT calculations can be employed in novel catalyst design with improved properties. In this dissertation, a combined theoretical and experimental approach is presented to study Pt-based catalysts for conversion of light alkanes. A rigorous understanding of atomic-scale properties of the catalyst is paramount for developing novel catalysts that would provide more efficient transformation of light alkanes derived from shale gas. By using extensive DFT calculations, reaction kinetics measurements, catalyst characterization techniques and microkinetic modeling, Pt and Pt-based bimetallic catalysts are investigated for reaction mechanism, structure-activity relationship, and product selectivity in ethylene production from ethane and methane. First, the Pt catalyst is examined to understand ethane dehydrogenation mechanism and origins of coking that curtails its activity and stability. It is observed that the under-coordinated atoms at the step edge significantly contribute to the strong binding of the reaction intermediates and catalyze coke formation reactions. Then, various Pt-based bimetallic catalyst systems such as Pt-Sn, Pt-Zn, Pt-Pb, are studied by extensive DFT calculations coupled with ethane dehydrogenation reaction kinetics studies to identify the promotional effect of the addition of the second metal. It is observed that notably stepped sites of the catalyst surfaces become less active towards catalyzing deep dehydrogenation reaction due to geometric effects of alloying that decreased the binding strength of the reactants. For a further understanding of the reaction mechanism, a mean-field microkinetic model is also implemented for Pt and Pt-Sn catalysts. Following, DFT calculations for complete ethane dehydrogenation network are performed on Pt-Ir and Pt-Au catalysts to evaluate the reaction mechanism and promotional effects. Next, a descriptor-based approach to predict novel ethane dehydrogenation catalysts is presented using available DFT calculations and microkinetic modeling. As a complementary to the studies with using ethane as the feed, a study on non-oxidative methane conversion to ethylene and aromatics over Pt and Pt-Sn catalysts is also presented. It is demonstrated that Pt-Sn catalysts can be promising candidates for the reaction due to their comparable activity and selectivity with the state-of-the-art catalysts. Finally, a summary of the presented work is given, together with suggestions for future work.