Structural Properties and Reactivity Trends of Molybdenum Oxide Catalysts Supported on Zirconia for the Hydrodeoxygenation of Anisole

Abstract

Vapor-phase hydrodeoxygenation (HDO) of anisole was investigated at 593 K and H2 pressures of ≤1 bar over supported MoO3/ZrO2 catalysts with MoO3 loadings ranging from 1 to 36 wt % (i.e., 0.5–23.8 Mo/nm2). Reactivity studies showed that HDO activity increased proportionally with MoO3 coverage up to a monolayer coverage (∼15 wt %) over the ZrO2 surface. Specific rates declined for catalysts with high loadings exceeding the monolayer coverage, because of a decreasing amount of redox-active species, as confirmed by oxygen chemisorption experiments. For low catalyst loadings (1 and 5 wt %), the selectivities toward fully deoxygenated aromatics were 13 and 24% on a C-mol basis, respectively, while at intermediate and high loadings (10–36 wt %), the selectivity was ∼40%. Post-reaction characterization of the spent catalysts using X-ray diffraction and X-ray photoelectron spectroscopy showed that the catalysts with 25 and 36 wt % MoO3 loadings were over-reduced, as evidenced by the prevalence of Mo4+ and Mo3+ ox...