Catalytic activity of Cu/ZnO catalysts mediated by MgO promoter in hydrogenation of methyl acetate to ethanol

Hydrogenation of methyl acetate is a key step in ethanol synthesis from dimethyl ether carbonylation and Cu-based catalysts are widely studied. We report here that the hydrogenation activity of Cu/ZnO catalysts can be enhanced by the addition of MgO promoter. The evolution of crystal phases during coprecipitation and the physicochemical properties of calcined and reduced catalysts by X-ray diffraction (XRD), thermogravimetric (TG)-mass spectrometry (MS), Brunauer-Emmett-Teller (BET), transmission electron microscopy (TEM), N2O titration, in situ CO-Fourier transform infrared spectroscopy (FTIR) and H-2-temperature programmed reduction (H-2-TPR) reveal that the promoter effect likely lies in the presence of Mg2+. A proper amount of Mg2+ mediates the precipitation process of Cu and Zn, leading to preferable formation of aurichalcite (CuxZn1-x)(5)(CO3)(2)(OH)(6) crystal phase and a small amount of basic carbonates such as hydrozincite Zn-5(CO3)(2)(OH)(6) and malachite Cu2CO3(OH)(2). The presence of aurichalcite strengthens the interaction between Cu and Zn species, and thus enhances the dispersity of Cu-0 species and helps generation of Cu+ species on reduced catalysts. Furthermore, the performance of Cu/ZnO catalysts exhibits an optimal dependence on the Mg loading, i.e., 17.5%. However, too much Mg2+ in the precipitation liquid prohibits formation of aurichalcite but enhances formation of basic nitrates, leading to a dramatically reduced hydrogenation activity. These findings may find applications for optimization of other Cu-based catalysts in a wider range of hydrogenation reactions. (C) 2021 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.