Mechanistic insights into heterogeneously catalyzed methane reactions




Brush, Adrianna

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Catalysts play an exceptionally important role in our society. Most synthetic materials rely on a catalyst at some point during their production, and the efficiency improvements due to catalysts are key to achieving the goal of sustainable human existence. Methane reactions have become important due to methane’s increasing source for energy and as a chemical feedstock. Understanding the mechanisms involved in catalyzed methane reactions will help direct future catalyst research. In this dissertation, we investigate mechanistic aspects of methane reactions over heterogeneous catalysts. Using model studies, we explore the surface structures and mechanism of O-H bond dissociation of methanol, a methane derivative, coadsorbed with hydrogen on Au(111). Using a classical catalyst reactor, methane reforming reactions and methane dissociation over molybdenum carbide based catalysts were investigated. We determined that Ni/Mo₂C will simultaneously catalyze the Dry Methane Reforming and Steam Methane Reforming reactions, with the resulting syn-gas ratio (H₂:CO) capable of being “tuned” from 0.9 to 3.0 by adjusting the ratio of H₂O:CO₂ in the reactant oxidant mixture. With an interest in developing transient techniques, we developed a novel apparatus capable of utilizing isotopically labeled gases more efficiently than current designs for Steady State Isotopic Transient Kinetic Analysis (SSITKA) experiments. This more efficient design allows more experiments to be performed. Using this apparatus, we investigated the methane dissociation mechanism over commercial Mo₂C. We found that carbon exchange did not occur between the methane and the Mo₂C carbide carbon, in contradiction to previous studies’ findings. Further, the dissociation of methane over Mo₂C was determined to involve a single C-H bond dissociation. This dissertation provides insights into the mechanisms behind heterogeneously catalyzed methane reactions, particularly methane reforming reactions over Mo₂C based catalysts. In addition, valuable isotopic experimental techniques, such as SSITKA, can benefit from the efficiency improvements offered by the Pulse Injection Apparatus, facilitating more robust investigations into catalytic mechanisms and kinetics


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