Fast pyrolysis of biomass produces bio-oil suitable for use as transportation fuel after an appropriate upgrade step to increase the heating value, lower the viscosity and improve the long-term stability. This upgrade can be accomplished by reducing the oxygen content through hydrotreatment over heterogeneous catalysts. While hydrodeoxygenation (HDO) of bio-oil is an emerging technology, hydrotreating for the removal of sulfur from petroleum products (HDS) has matured over decades and detailed knowledge regarding the catalyst structure, active sites and reaction mechanism are available. Both hydrotreating processes show similarities on the macroscopic scale and the identification of atomic-scale catalytic reactivity descriptors may speed up the discovery of novel HDO catalysts from existing knowledge of HDS chemistry.Using density functional theory (DFT) we have investigated the HDO mechanism of acetaldehyde and furan as surrogate molecules for the over 400 different oxygenated species in biomass-derived pyrolysis oil on RuO2(110), which is the oxygen analogue of the most active HDS catalyst RuS2. As additional catalysts systems we considered MoO3(010) for HDO of furan, and Ru(0001), TiO2(110), Ru-doped TiO2(110), 1 ML RuO2/TiO2(110), and Ru10/TiO2 for HDO of acetaldehyde. The surface structure of metal-sulfides and metal-oxides under reaction conditions and the role of surface vacancies as active sites during both, HDS and HDO, are discussed. Our results indicate that metallic Ru favors C-C bond scission and leads to catalyst coking, while oxygen vacancy sites on metal-oxides are active for C-O bond scission. The oxygen vacancy formation energy may be used as a descriptor for HDO activity. A more detailed understanding of the HDO mechanism on metal-oxide catalysts and by drawing parallels to the related and well-studied HDS catalysis, new and efficient materials for HDO can be developed faster and ultimately lead to an increased utilization of biofuels.

From hydrodesulfurization to hydrodeoxygenation: What are the similarities at the atomic-scale?

247th National Meeting (2014)

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