Copper-Based Catalysts Confined in Carbon Nanocage Reactors for Condensed Ester Hydrogenation: Tuning Copper Species by Confined SiO2 and Methanol Resistance

Hydrogenation of aliphatic esters to natural alcohols is an important strategy for the efficient utilization of biomass-derived oils. The synthesis of highly active copper (Cu)-based catalysts is a challenge for condensed-phase ester hydrogenation due to the difficulties in controlling active sites and catalyst deactivation. Here, a copper-based catalyst confined in a carbon nanocage reactor was successfully designed and prepared. The copper catalyst with 56 wt % SiO2 exhibited the best performance because of the optimum proportion of Cu+ and Cu0 sites and high dispersion. The interaction between SiO2 and Cu particles contributes to the formation of Cu+ species, which is the key site for the adsorption of carbonyl groups. Meanwhile, the confinement effect of the carbon nanocages effectively inhibited the agglomeration of the copper particles. The catalysts exhibited not only excellent thermal stability but also superior methanol resistance in comparison with the Cu/SiO2 catalyst. On the basis of the density functional theory (DFT) calculations results, methanol resistance should be attributed to the fewer hydroxyl groups on the catalyst surface, which increase the activation barrier for the dissociation of silica, allowing the stable holding of the copper species in the methanol solvent.