The organic–inorganic dual anchoring strategy based on organic chelators and lacunary polyoxometalates for the preparation of efficient CoWS hydrodesulfurization catalysts

Abstract

Designing catalysts with bimetallic intimate synergistic effects to enhance catalytic activity has always been a focused problem for hydrodesulfurization (HDS) systems. Efficient HDS catalysts with abundant CoWS active phases were prepared through novel organic–inorganic ligand dual anchoring strategy based on the organic chelating agents and lacunary polyoxometalates (POMs). Citric acid (CA) chelating agent and Co2+ promoter are pre-coordinated in the impregnating solution, the trivacant Keggin [SiW9O34]10- (SiW9) POMs attract the promoter through the nucleophilic oxygen groups at the vacant sites to form the CA-Co@SiW9 “sandwich-like” structure, which allows the organic chelator-promoter-active center to be intimate interaction in a single molecule, thus achieving atomic-scale Co-W proximity on the precursor. In the subsequent sulfidation process, CA delayed the reduction temperature of cobalt species, enabling more Co promoter to be anchored at the edge sites of WS2 clusters to form abundant CoWS active phases, which fully exerted the bimetallic intimate synergism in the HDS reaction. Furthermore, the carbon deposits generated from CA carbonation acted as secondary support weakening the interaction of active metals with Al2O3 support and increasing the sulfidation degree as well as the dispersion of active metals. As a result, the S-Co(CA)W/Al2O3 catalyst achieves a remarkable turnover frequencies (TOF) value of 1.24 × 10-3 s−1 in HDS reaction of dibenzothiophene (DBT). This dual anchoring method based on POMs inorganic ligand and organic chelator ligand provides a new idea for designing novel HDS catalysts.