Rationalizing Catalytic Performances of Mo/W-(Oxy)Carbides for Hydrodeoxygenation

Hydrodeoxygenation (HDO) reactions are among the most important reactions for the valorization of biomass to value-added chemicals. Transition metal carbides (TMCs) are promising alternative HDO catalysts to platinum group metals. However, it is known that these TMCs have the tendency to partially oxidize themselves in the presence of oxygen or oxygen-containing compounds, which makes it a challenge to identify the nature of the true active site under relevant reaction conditions. In this paper, first, we analyze the surface structure of transition metal oxycarbides (TMOCs), i.e., Mo2COx and W2COx. Further, taking the HDO of n-butyric acid to n-butane with hydrogen as an example, we rationalize the differences in HDO performances of TMOCs as compared to TMCs (Mo2C and W2C) using density functional theory, ab initio molecular dynamics, and microkinetic modelling. It is found that the O* domains on the surface of TMOCs enhance the HDO activity by easing the dissociation of the C-O bond and promoting the hydrogenation reactions, as compared to pure TMCs. Furthermore, microkinetic modelling analysis shows that Mo2COx is a more active and selective catalyst for alkane production compared to Mo2C, W2C, and W2COx. These insights could guide the manipulation of efficient carbide-based HDO catalysts for biomass conversion.