The processes needed for light hydrocarbon conversion from natural gas into more valuable energy carriers and chemically relevant species is limited by their need for extreme synthetic conditions, making it infeasible to scale into industrial processes. Catalysts can be used to aid in these conversions; however, an efficient catalyst for selective oxidation under mild conditions has yet to be found. Materials comprising of just a few isolated metal centers have shown promise for these conversions, due to their structural and electronic isolation, thereby allowing the system to be directly tuned to produce a desired reaction. We plan to exploit this phenomena by utilizing small metal cluster catalysts supported on metal-organic frameworks (MOFs), which can be prepared by atomic layer deposition (ALD), with the goal to optimize a catalyst to selectivity oxidize ethane to ethanol.<br/><br/>The broad focus of this work is to learn how to screen or design catalysts on the atomic scale. At this scale the catalysts would consist of small clusters composed of only a few metal atoms. Methods traditionally used for catalytic screening and design are generally well-established for extended metal surfaces, however this is not the case for atomic level catalytic screening and design. At the atomic level the descriptors for catalytic activity are likely to be different, and the linear relationships found for extended systems might not be held. The goal is to try and answer questions about how catalysis is governed on this scale. This could include how the catalysts work at the atomic level and what descriptors describe catalytic activity and how they differ from surface models. Also, how the reaction mechanism might differ at the atomic-level and how this affects the selectivity of the reaction will be investigated.<br/><br/>In this work, we employ simplified gas phase metal (+1) and (+2) hydroxide complexes, which we use to screen for activity and selectivity in ethane oxidation to ethanol/ethene. We apply methods normally used for catalyst screening on extended metal surfaces in order to determine if such methods apply at the atomic scale. Microkinetic models as implemented in the python package CatMAP are used to determine the activities and selectivities of various transition metal hydroxide catalysts. We search for descriptors of catalytic activity and uncover overall design clues that could potentially lead to further increases in activity and selectivity for these catalysts.

Screening for activity and selectivity in small metal-based oxidation catalysts

251st National Meeting (2016)

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