Hydrogenation of diesters to diols is 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, we demonstrate 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 nanoparticles (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 hours without performance degradation.

Ti3+ tuning the ratio of Cu+/Cu0 in the ultrafine Cu nanoparticles for boosting the hydrogenation reaction

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