Selective Production of C₃ Polyols from Cellulose over Hydrogen Spillover Promoted Pd–Mo/TiO₂ Catalyst with Adjacent Lewis Acid Pairs

Abstract

The use of cellulose as a substitute for fossil resources has gained significant attention due to the depletion of nonrenewable energy sources and the increasing potential environmental crisis. The selective hydrogenolysis of cellulose to C 3 polyols, namely, 1,2-propanediol and glycerol, is one of the attractive biomass depolymerization and utilization pathways. However, coordinating sugar isomerization and retro-aldol condensation remains a challenge. In this paper, we manipulate the hydrogen spillover behavior of the Pd−Mo/TiO 2 catalyst by tuning the density and aggregation states of Mo/Pd species to promote the yield of C 3 polyols in the one-pot cellulose hydrogenolysis reaction. The optimal Pd−Mo/TiO 2 catalyst realizes a ∼50% C 3 polyol yield with the total polyol yield approaching 70%, surpassing the performances of known heterogeneous catalysts. We demonstrate that the strong hydrogen spillover on the Pd/TiO 2 facilitates the reduction of MoO X and enhances the formation of continuous oxygen vacancies on Ti−O−Mo sites as adjacent Lewis acid pairs that serve as the adsorption sites for the tridentate complex of hexose and efficiently catalyze the isomerization and subsequent retro-aldol condensation steps. The acceleration of glucose → fructose isomerization and inhibition of undesirable condensation account for the high product yield.