Oxygen Healing and CO 2 /H 2 /Anisole Dissociation on Reduced Molybdenum Oxide Surfaces Studied by Density Functional Theory.

Reduced molybdenum oxides are versatile catalysts for deoxygenation and hydrodeoxygenation reactions. In this work, we have performed spin-polarized DFT calculations to investigate oxygen healing energies on reduced molybdenum oxides (reduced α-MoO 3 , γ-Mo 4 O 11 and MoO 2 ). We find that Mo +4 on MoO 2 (100) is the most active for abstracting an oxygen from the oxygenated compounds. We further explored CO 2 adsorption and dissociation on reduced α-MoO 3 (010) and MoO 2 (100). In comparison to reduced α-MoO 3 (010), CO 2 adsorbs more strongly on MoO 2 (100). We find that CO 2 dissociates on MoO 2 (100) via a two-step process, the overall barrier for which is 0.6 eV. This barrier is 1.7 eV lower than that on reduced α-MoO 3 (010), suggesting a much higher activity for deoxygenation of CO 2 to CO. As H 2 dissociation is shown to be the rate-limiting step for hydrodeoxygenation reactions, we also studied activation barriers for H 2 chemisorption on MoO 2 (100). We find that the chemisorption barriers are 0.7 eV lower than that reported on reduced α-MoO 3 (010). Finally, we have studied the dissociation (C-O cleavage) of anisole (a lignin-based biofuel model compound) on MoO 2 (100). We find that anisole binds very strongly on MoO 2 (100) with an adsorption energy of -1.47 eV. According to Sabatier's principle, strongly adsorbing reactants poison the catalyst surface, which may explain the low activity of MoO 2 observed during experiments for hydrodeoxygenation of anisole.