Understanding of the Key Properties of Supported Cu-based Catalysts and Their Influence on Ester Hydrogenolysis

The application of Cr-free Cu-based catalysts in ester hydrogenolysis is a modern environmentally-friendly research approach. The comprehensive study of four supported Cu-based catalysts was performed using 8 wt % of Cu loaded on Al2O3, ZnO, TiO2 and ZrO2 supports by an impregnation method. Using XRD, H2-TPR, BET, pyridine-TPD, CO2-TPD and N2O-RFC methods, the effect of the support on the formation of Cu-nanoparticles was described. Al2O3 was evaluated as the support ensuring the highest nanoparticles dispersion, while Cu nanoparticles in Cu-TiO2 were liable to sintering. The catalysts were tested in dimethyl adipate hydrogenolysis, where the catalyst performance and activity (TOF) were evaluated and Cu-ZrO2 showed the best results. A correlation between the number of acid-base sites and the catalyst selectivity was revealed and the catalyst effect on the formation of various by-products was described. The intrinsic selectivity to hydrogenolysis products was found to decrease with the increasing acid-base character of the supports whereas the selectivity to transesterification and cyclization products increased. The hydrogenolysis activity was not a simple function of the number of the surface copper atoms, but it was affected by the support nature and its properties.