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Oxygen Healing and CO2/H2 /Anisole Dissociation on Reduced Molybdenum Oxide Surfaces Studied by Density Functional Theory

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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-MoO2 , γ-Mo4O11 and MoO2 ). We find that Mo+4 on MoO2(100) is the most active for abstracting an oxygen from the oxygenated compounds. We further explored CO2 adsorption and dissociation on reduced α-MoO3(010) and MoO2(100). In comparison to reduced α-MoO3(010), CO2 adsorbs more strongly on MoO2(100). We find that CO2 dissociates on MoO2(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-MoO3(010), suggesting a much higher activity for deoxygenation of CO2 to CO. As H2 dissociation is shown to be the rate-limiting step for hydrodeoxygenation reactions , we also studied activation barriers for H2 chemisorption on MoO2(100). We find that the chemisorption barriers are ~0.7 eV lower than that reported on reduced α-MoO3(010). Finally, we have studied the dissociation (C-O cleavage) of anisole (a lignin -based biofuel model compound) on MoO2 (100). We find that anisole binds very strongly on MoO2(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 MoO2 observed during experiments for hydrodeoxygenation of anisole.

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