RESUMO
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.