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

Hydrogenation of diesters to diols is a vital process for chemical industry. The inexpensive Cu+/Cu-0-based catalysts are highly active for the hydrogenation of esters, however, how to efficiently tune the ratio of Cu+/Cu-0 and stabilize the Cu+ is a great challenge. In this work, it is demonstrated that doped Ti ions can tune the ratio of Cu+/Cu-0 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+-O-V-Cu+ (O-V: oxygen vacancy) bonds and the amount of Ti doping can tune the ratio of Cu+/Cu-0. In the catalytic reaction, the O vacancy activates C(sic)O in the ester by forming new Ti-3+(delta)-O-R-Cu-1+(delta) bonds (O-R: reactant oxygen), and Cu-0 activates hydrogen. After the products are desorbed, the Ti-3+(delta)-O-R-Cu-1+(delta) bonds return to the initial state of Ti3+-O-V-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.

Automated summary

This study demonstrates a method to tune the ratio of Cu+/Cu-0 and stabilize Cu+ in Cu/Ti-SiO2 catalysts, promoting the efficient hydrogenation of esters. Reversible Ti-O-Cu bonds greatly enhance the activity and stability of the catalysts, achieving high conversion and selectivity with long-term stability.