Collaborative Research: Selective Oxidation Catalysis on Oxides Containing Pores of Molecular Dimensions

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Our modern standard of living depends upon the fuels that are needed for our transportation, and the chemicals that are used to make many of the materials of our many consumer products. These fuels and chemicals are predominantly derived from the conversion of fossil fuels into value-added chemicals and materials via catalytic reactions. Thus, the environmental footprint of our lifestyles can be significantly reduced with more efficient use and conversion of these raw materials. One example of a catalytic upgrading reaction is the conversion of shale gas to bulk chemical and fuel precursors. Conversion of the short, saturated hydrocarbon molecules (light alkanes) within shale gas to alkenes leads to a more reactive, and thus more valuable, chemical intermediate. This conversion involves the removal of hydrogen atoms and insertion of a more reactive carbon-carbon double bond. To perform this conversion at low temperatures requires use of a catalyst, and one such example is a mixed metal oxide catalyst. The objective of this project is to understand how the size and shape of pores within the mixed metal oxide may be engineered to more selectivity catalyze the oxidative alkane to alkene reaction. This project will probe the role of micropores in ordered bulk transition metal oxide catalysts in the selective hydrocarbon oxidation of small alkanes and alkanols. Ordered M1 phase mixed oxides contain one dimensional pores that are similar in size to the kinetic diameters of the reactants; examples include M1 phase mixed oxides of Mo V, Te and Nb and octahedral molecular sieves of Mn oxides. The project will correlate the oxidation rate ratios of linear versus branched alkanes to cycloalkanes to pore dimension, with consideration of pore sizes that exhibit size exclusivity. Kinetic and density functional theory (DFT) will probe selectivity with variations in pore geometry, reactant geometry, and surface reactivity. It is anticipated van der Walls stabilizations and steric hindrance may limit conversion to secondary byproducts, which may enhance selectivity by bypassing the thermodynamic driving forces for secondary oxidation reactions to secondary byproducts. Planned education and outreach activities will promote understanding of heterogeneous catalysis and its role in meeting the challenges of sustainable chemical production and energy efficiency. These activities will target students from underprivileged backgrounds, with an aim to increase their retention in science and engineering fields.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.