The role of oxophilic Mo species in Pt/MgO catalysts as extremely active sites for enhanced hydrodeoxygenation of dibenzofuran

Abstract

Pt/MoO_x/MgO catalysts were prepared with varying Mo coverage and studied for the selective hydrodeoxygenation (HDO) of dibenzofuran (DBF) to biphenyl (BP), aiming at the elucidation of active sites for HDO. Oxophilic Mo species enrich the reducibility of surface Pt and the acidic sites of catalysts, change the product selectivity and then lead to significant improvement of the deoxygenation activity with an excellent HDO reaction rate (1.06 μmol s⁻¹ g⁻¹) on Pt/7MoO_x/MgO compared with that (0.04 μmol s⁻¹ g⁻¹) on Pt/MgO. Moreover, the catalytic performance can be controlled by the MoO_x surface density and varied with the increased MoO_x surface density in a volcano-shape manner, in which at low Mo coverage (<2.27 Mo per nm²), dispersed Mo species are dominant attributed to the active sites, and at further higher Mo coverage (>6.19 Mo per nm²), crystalline MoO₃ particulates may form that is detrimental to the activity. The highest BP yield (100%) was obtained with Pt/7MoO_x/MgO close to Mo coverage of one monolayer. Furthermore, reactivity studies in combination with density functional theory (DFT) calculations for the adsorption of dibenzofuran and H₂ indicate the synergy of Pt species in affording hydrogen species and adjacent MoO_x species in adsorbing/activating C–O bonds suitable for the HDO of DBF.