(560he) Investigation on Control of Surface Reactivity Towards Carbon, Oxygen, and Hydrogen of Intermetallic Compounds in Wet Reforming of Hydrocarbons and Oxygenates

Authors: 
Song, Y., University of Tennessee
He, Y., University of Tennessee
Laursen, S., University of Tennessee
The heterogeneous catalysis community has long been married to late transition metal catalysts for hydrocarbon reforming despite significant issues with coke formation, catalyst deactivation, and the need for high temperatures and water-rich feed. It is proposed that the focus on late transition metal catalysts has polarized our understanding of the mechanism and that materials that present higher surface reactivity towards O and H and lower towards C may be beneficial in the reaction. It has already been shown by others that the addition of a secondary catalytic element with elevated reactivity towards O can limit coke formation and enhance overall activity. However, the catalyst formulations often produced active portions of the catalyst that could not be effectively characterized, e.g., a surface alloy or off-stoichiometric intermetallic compound.

Our approach is to utilize supported intermetallic compound solid nanoparticles (Ni+Ga/SiO2) with well-defined bulk and surface compositions to build in the favorable properties already demonstrated but also benefit from more stable particles and quite tunable surface chemistry towards C, O, and H. Quantum chemical surface reaction modeling indicated that surface reactivity towards carbon, oxygen, and hydrogen could be tuned via p-block element selection as well as adjustment of the bulk and surface compositions. These features allowed for control of the dissociation of propane and H2O and surface reactions of H-transfer, H2 evolution, and carbon oxidation steps. Experimentally, suits of IMCs with controllable bulk and surface composition as well as particle size were successfully used in the reaction. Significantly improved H2 selectivity and catalyst stability were achieved as well as comparable overall rates of reaction. The selectivity of CO vs. CO2 could also be controlled from a 1:1 H2:CO synthesis gas ratio to a CO-lean H2/CO2 composition. These studies and the new understanding of IMC surface chemistry developed can be extended to aid in the development of small-oxygenate reforming, biomass deoxygenation, and controlled hydrogenation catalysts.

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