A novel ligand protection strategy based on lacunary polyoxometalate to precisely construct CoMoS active sites for hydrodesulfurization

Abstract

Efficient CoMoS catalysts with intimate bimetallic synergy are derived from cobalt-substituted phosphomolybdate and exhibited excellent hydrodesulfurization (HDS) activity. Based on ligand protection strategy, the introduction of pyridine ligands onto the vacancies of the trivacant polyoxometalates (POMs) successfully overcame their low stability and isomerization behavior in solution. Subsequently, Co2+ was anchored in the molecular skeleton of [A-α-PMo9O31(py)3]3− (PMo9-py) to form CoxPMo9-py precursors with high Co/Mo ratios, which enhanced the reducibility of Mo species and transformed them to abundant CoMoS active phase during sulfidation process. The quenching effect of pyridine molecules on the acidic sites of support and carbon deposition generated in the high temperature sulfidation weakened the strong metal-support interactions (SMSI) while improving the dispersion and sulfidation of active metals. Due to the unique structure of CoxPMo9-py, the CoMoS phase with high dispersion, efficient synergy and high concentration was obtained. The combination of POMs precursors and pyridine ligands enabled the S-CoxPMo9-py/Al2O3 catalyst to achieve up to 99.5% conversion of dibenzothiophene (DBT).