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Inverse Bimetallic RuSn Catalyst for Selective Carboxylic Acid Reduction

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journal contribution
posted on 12.11.2019, 16:38 by Vassili Vorotnikov, Todd R. Eaton, Amy E. Settle, Kellene Orton, Evan C. Wegener, Ce Yang, Jeffrey T. Miller, Gregg T. Beckham, Derek R. Vardon
Inverse bimetallic catalysts (IBCs), synthesized by sequential deposition of noble and oxophilic metals, offer potential reactivity enhancements to various reactions, including the reduction of carboxylic acids for renewable fuels and chemicals. Here, we demonstrate that an IBC comprising RuSn exhibits high selectivity for propionic acid reduction to 1-propanol, while Ru alone results in cracking. On RuSn, X-ray absorption spectroscopy identified Ru0 nanoparticles with a near-surface bimetallic Ru0Sn0 alloy and small SnOx domains. Corresponding model surfaces were examined with density functional theory to elucidate the observed selectivity difference. Only selective hydrogenation is predicted to be favorable on SnOx/Ru, with the SnOx clusters facilitating C–OH scission and Ru enabling hydrogen activation. Intrinsic barriers along nonselective pathways suggest that the RuSn alloy and SnOx resist cracking. SnOx/Ru hydrogenation activity was supported experimentally by inhibiting hydrogenation with phenylphosphonic acid, differentiating the system from fully alloyed RuSn metallic nanoparticles. Overall, this work demonstrates a plausible mechanism for selective reduction of carboxylic acids and proposes a roadmap for rational design of IBCs.