Effect of additive on CuO-ZnO/SBA-15 catalytic performance of CO₂ hydrogenation to methanol

Three kinds of porous catalysts CuO-ZnO/SBA-15 (CZ/SBA-15), CuO-ZnO-MnO₂/SBA-15 (CZM/SBA-15) and CuO-ZnO-ZrO₂/SBA-15 (CZZ/SBA-15) were synthesized by impregnation method with a siliceous framework mesoporous molecular sieve SBA-15. The performance of all catalysts for catalytic hydrogenation of CO₂ to methanol was evaluated on a fixed bed reactor, combined with N₂ adsorption-desorption (BET), X-ray diffraction (XRD), H₂ temperature-programmed reduction (H₂-TPR), temperature programmed desorption (H₂-TPD, CO₂-TPD), N₂O titration, X-ray photoelectron spectroscopy (XPS) and transmission electron microscope (TEM). The results show that the introduction of metal oxide in the catalyst changes the pore size and specific surface area of the SBA-15 molecular sieve support. The CuO-ZnO-MnO₂/SBA-15 and CuO-ZnO-ZrO₂/SBA-15 have high copper dispersion (D_Cu%), large specific surface area (S_Cu), small surface CuO particle size, and easy to be reduced. Compared with the Mn-O cluster, the Zr-O cluster enhances the basic site and improves the methanol selectivity. In addition, CuO-ZnO-ZrO₂/SBA-15 has the highest oxygen vacancy concentration and better catalytic activity among three catalysts. The methanol selectivity of CuO-ZnO-ZrO₂/SBA-15 is 25.02%, which is 28% and 136.9% higher than those of CuO-ZnO/SBA-15 and CuO-ZnO-MnO₂/SBA-15, respectively.