Enhanced activity of Cu/SiO2 and Cu/ZrO2 catalysts in dimethyl adipate hydrogenolysis

According to green chemistry principles, the process of ester hydrogenolysis is not sustainable. It is catalysed by Adkins CuCr2O3 catalyst that brings some environmental risks. Therefore, a design of new environmentally-friendly hydrogenolysis catalysts is highly desired. We investigated eight catalysts prepared using two methods - incipient wetness impregnation (IWI) and chemisorption-hydrolysis (CH) - with a combination of two types of supports - ZrO2 and two types of SiO2. The preparation method affects significantly the dispersion of the resulting copper phase in case of SiO2, and CH is essential to obtain very small and active Cu particles. On the other hand, when ZrO2 is used, the most critical aspect is its specific surface area, and a highly dispersed copper phase is formed on the high specific surface area sample, both for CH and IWI preparation methods. All eight prepared catalysts were investigated in dimethyl adipate hydrogenolysis to compare their activity and selectivity. Nice correlation between support – synthesis method – activity was found. ZrO2-based catalysts and CH resulted in more active catalysts compared to SiO2-based ones and IWI. Interestingly, Cu/SiO2 catalyst prepared by CH was more selective to the main reaction product hexane-1,6-diol due to the presence of acid sites. In this paper, the catalyst hydrogenolysis activity was increased twice, compared to our previous experiments using Cu/ZnO prepared by deposition-precipitation.