Study of promoted Cu/ZnO and Cu/ZrO2 catalysts for dimethyl adipate hydrogenolysis†

Two supports (ZnO, ZrO₂) and four promoters (Al₂O₃, ZnO, CoO_x, NiO) were investigated to design environmentally-friendly Cu-based hydrogenolysis catalysts. Both catalyst characterization and activity in dimethyl adipate hydrogenolysis were described. While ZrO₂ improved the reducibility of CuO nanoparticles, these particles were less stable under reaction conditions. ZnO provided better stabilization and reduced coke formation. CoO_x, used as a promoter, increased the surface availability of dissociated H₂ and stabilized Cu nanoparticles with a high surface area. Conversely, Al₂O₃ or NiO promoters improved neither catalyst performance nor selectivity due to the higher number of acid–base sites. The essential role of ZnO, whether used as support or a single promoter, was attributed to Cu–ZnO synergy that enhanced the activity in dimethyl adipate hydrogenolysis and improved desired selectivity to hexane-1,6-diol. Overall, the hydrogenolysis activity (TOF_H) was 5 times higher for ZnO-supported catalysts.