Hydrodeoxygenation mechanism of Acetaldehyde on Ru(0001), RuO2(110), and RuO2/TiO2(110) from first-principles investigations

Hydrodeoxygenation (HDO) of acetaldehyde, a surrogate molecule for the ca. 400 oxygenates in bio-oil, is explored on Ru(0001), RuO2(110), and a RuO2/TiO2(110) overlayer surface using periodic density functional theory. Under typical HDO reaction conditions, the oxide surfaces are partially reduced and have bridging hydroxyls. Upon additional hydrogen adsorption, these surfaces form oxygen vacancies, which play a key role for the adsorption of acetaldehyde. Subsequent acetaldehyde isomerization favors C-O scission and leads selectively to the formation of ethylene on both RuO2 and RuO2/TiO2 surfaces. In contrast, decarbonylation (C-C scission) and carbon deposition is more likely to occur on the metallic Ru(0001) surface. Overall, the rutile RuO2 and RuO2/TiO2 surfaces seem more promising for selective C-O bond breaking than the metallic Ru(0001) surface. A more detailed understanding of catalytic differences between metals and metal-oxides for HDO is necessary to develop novel catalysts that can lead to an increased utilization of biofuels.