It is well-established that combining noble and oxophilic metals can improve activity and selectivity in a number of chemical processes, including hydrogenation of carboxylic acids. A number of catalyst formulations have been proposed, including bulk alloys, near-surface alloys, and metal-metal oxide interfaces. Yet, the precise structure of the catalytic sites and their corresponding selectivity-altering function remains elusive. In this work, we investigated several monometallic and bimetallic catalysts for the selective reduction of propionic acid (PA) to 1-propanol (1-PrOH), identifying RuSn, synthesized by sequential deposition of Ru and Sn, as the top performer. RuSn characterization with extended X-ray absorption fine structure spectroscopy revealed the existence of near-surface Ru0Sn0bimetallic phase and small SnOxdomains, a catalyst formulation we refer to as inverse bimetallic. These experimentally-proposed structures were examined with density functional theory to elucidate the observed selectivity differences. We find that only selective hydrogenation is energetically feasible on SnOx/Ru with SnOxclusters facilitating C-OH scission, while Ru sites enable hydrogen dissociation, even in the presence of Sn0. Intrinsic barriers suggest that RuSn alloy and SnOxincrease the resistance to reaction paths leading to side products and catalyst deactivation. Computationally-predicted reactivity of Ru-supported SnOxdomains was further supported by inhibiting hydrogenation with phenylphosphonic acid, thus differentiating it from purely alloyed bimetallic particles. Overall, this work proposes inverse bimetallic sites as working catalysts for selective hydrogenation processes and describes how each catalytic part may be tuned in the future.

Inverse bimetallic catalysts for selective reduction of propionic acid

2019 Spring National Meeting

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