Catalytic upgrade of bio-oil to fuels and chemicals requires the selective reduction of its 10-40 wt% oxygen content.1 Ruthenium supported on titania (Ru/TiO2) has recently evolved as one of the better performing catalysts for such hydrodeoxygenation (HDO) processes. Commonly proposed HDO mechanisms on oxide containing materials invoke oxygen vacancy sites as catalytically active sites, but the mechanism of their formation remains disputed. To address this question, we use first-principles kinetic Monte Carlo (kMC) simulations to investigate the HDO reaction of m-cresol over TiO2(110) in the presence and absence of Ru, with particular focus on the Ru/TiO2 interface. To eliminate the strong effect of Lewis acid-base pairs on adsorbate-adsorbate interactions as illustrated by Metiu et al.2, we extract pairwise interaction parameters from a series of co-adsorbed configurations that do not exhibit any electronic artifacts on rutile TiO2(110). Our kMC results show that the presence of Ru nanoparticles substantially increases the reduction rate of the TiO2(110) surface attributed to H spillover and a facile, heterolytic H2 cleavage pathway across the Ru/TiO2 interface. We also qualitatively reproduce experimental results for water adsorption on TiO2(110).3 Under HDO reaction conditions over Ru/TiO2, the Arrhenius plot exhibits two kinetic regimes at low and high temperatures, corresponding to a coverage transition occurring at around 550 K. The presence of added water in the feed impedes this reaction pathway though vacancies by rapid water dissociation on vacancies, resulting in two hydroxyl groups. Alternatively, we propose proton-assisted HDO reactions occurring at the interface. Overall, our detailed simulation is capable of capturing coverage effects and mechanistic changes in response to variations in temperature or feed composition, including the addition of water to the feed. To our knowledge, there exist no comparable model with the ability to discriminate between metal, oxide and interfacial activity, and assign a dominant catalytic role to each component. The ability to generate such detailed fundamental insight can be leveraged for the future design of multifunctional catalysts with unprecedented selectivity advantages.

First-principles kinetic Monte Carlo study of biomass conversion over titania supported ruthenium catalyst

2019 Fall National Meeting

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