Using periodic density functional theory (DFT) we have explored the hydrodeoxygenation (HDO) pathways of acetaldehyde, a surrogate molecule for some of the over 400 different oxygenates from biomass fast pyrolysis, on metallic Ru(0001), pure oxide catalysts (RuO2(110), TiO2(110)), and modified oxide catalysts (1 ML RuO2/TiO2(110), Ru-doped TiO2(110), Ru10/TiO2(110)). The binding energies of possible surface intermediates and the activation energies of a large number of different elementary steps, including the preference for C-H, C-O, and C-C bond scission reactions, were investigated. Kinetic Monte Carlo simulations with DFT derived input parameters were used to predict surface activity, selectivity, and the location of the active site. On the metallic Ru(0001) surface, C-C scission rather than C-O scission and the deposition of carbon on the surface at the end of the catalytic cycle is the preferred pathway. For RuO2(110), 1 ML RuO2/TiO2(110), and TiO2(110) we first derived constrained thermodynamic phase diagrams under typical HDO conditions, which indicate that these surfaces are partially reduced and exhibit bridging hydroxyl groups. Upon further hydrogen adsorption the surface hydroxyl groups can be removed as water and surface oxygen vacancies are formed. These vacancies not only play an important role for acetaldehyde adsorption, but are also beneficial for the preferential activation of C-O scission over C-C scission in acetaldehyde, leading to the desired product ethylene. Ethanol is predicted as the primary, competing by-product on these oxide surfaces. The highest selectivity for ethylene is predicted for TiO2(110), however, the dissociation of gas-phase hydrogen and the formation of bridging hydroxyl groups, the precursor to the formation of a required oxygen vacancy, is highly activated in comparison to the remaining oxide surfaces. In best agreement with experimental observations is a mechanism involving facile hydrogen spill-over from the Ru nanocluster in the Ru10/TiO2(110) system and acetaldehyde HDO on the TiO2(110) surface.

First-principles investigation of the active site and the reaction mechanism of acetaldehyde hydrodeoxygenation over Ru/TiO<sub>2</sub>

247th National Meeting (2014)

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First-principles investigation of the active site and the reaction mechanism of acetaldehyde hydrodeoxygenation over Ru/TiO2

First-principles investigation of the active site and the reaction mechanism of acetaldehyde hydrodeoxygenation over Ru/TiO₂