Controllable design of phosphorus-doped cobalt sulfide for catalytic conversion of cellulose to methyl levulinate: The importance of Co3+/Co2+ ratio

The development of efficient and recyclable heterogeneous catalysts for the catalytic conversion of cellulose into high-value platform chemicals has garnered significant attention. Cobalt sulfide, recognized for its earth-abundance and recyclability, has emerged as a promising catalyst for the production of methyl levulinate (ML) from cellulose, albeit with a noted disparity in catalytic performance when compared to conventional homogeneous catalysts. In this study, various phosphorus-doped cobalt sulfides (CoSxP2-x) were employed to enhance the production of ML from cellulose, with a particular focus on the sulfide-phosphorus ratio. Notably, an optimal ML yield of 48.9 wt% and a complete conversion of cellulose were achieved at a sulfide-to-phosphorus ratio of 1:1. Comprehensive characterization of the synthesized CoSxP2-x materials revealed that CoS1.00P1.00 exhibited distinctive properties, such as the presence of ternary acid sites and the lowest Co3+/Co2+ ratio among the series. Density functional theory (DFT) calculations elucidated that the bound electrons within the P-Co bonds were activated by the synergistic effects among Co, P, and S atoms, thereby diminishing the free energy barrier for the adsorption of reaction intermediates.