Ti3+ Tuning the Ratio of Cu+/Cu0 in the Ultrafine Cu Nanoparticles for Boosting the Hydrogenation Reaction

Abstract Hydrogenation of diesters to diols is a vital process for chemical industry. The inexpensive Cu+/Cu0‐based catalysts are highly active for the hydrogenation of esters, however, how to efficiently tune the ratio of Cu+/Cu0 and stabilize the Cu+ is a great challenge. In this work, it is demonstrated that doped Ti ions can tune the ratio of Cu+/Cu0 and stabilize the Cu+ by the TiOCu bonds in Ti‐doped SiO2 supported Cu nanoparticle (Cu/Ti–SiO2) catalysts for the high conversion of dimethyl adipate to 1,6‐hexanediol. In the synthesis of the catalysts, the Ti4+OCu2+ bonds promote the reduction of Cu2+ to Cu+ by forming Ti3+OVCu+ (OV: oxygen vacancy) bonds and the amount of Ti doping can tune the ratio of Cu+/Cu0. In the catalytic reaction, the O vacancy activates CO in the ester by forming new Ti3+δORCu1+δ bonds (OR: reactant oxygen), and Cu0 activates hydrogen. After the products are desorbed, the Ti3+δORCu1+δ bonds return to the initial state of Ti3+OVCu+ bonds. The reversible TiOCu bonds greatly improve the activity and stability of the Cu/Ti–SiO2 catalysts. When the content of Ti is controlled at 0.4 wt%, the conversion and selectivity can reach 100% and 98.8%, respectively, and remain stable for 260 h without performance degradation.