Synthesis, characterization and activity pattern of Cu-ZnO/ZrO2 catalysts in the hydrogenation of carbon dioxide to methanol

A novel synthesis route based on reverse co-precipitation under ultrasound irradiation has led to Cu-ZnO/ZrO2 catalysts (Znat/Cuat, 0-3; ZrO2, 42-44 wt%) with a remarkable development of total surface area (SABET, 120-180 m2/g) and very high dispersion (3-58%) and exposure (MSA 9-63 m2/g) of the active Cu phase. The activity pattern in the hydrogenation of CO2 to CH3OH (TR, 433-533 K; PR, 1.0-3.0 MPa) was addressed in comparison with a commercial Cu-ZnO/Al2O3 methanol synthesis catalyst. Volcano-shaped trends in total and metal surface area signal an optimum zinc loading (Zn/Cu, 0.3-0.7), ensuring higher concentration of active sites and methanol productivity values, whereas the basic relationships among dispersion, reducibility, and TOF indicate a structurally sensitive character of the title reaction and a superior reactivity of poorly dispersed Cu particles. Thermodynamic analysis of the reaction stream revealed that methanol formation proceeds along a parallel path, whereas a stronger "water affinity" accounts for the poorer performance of the conventional alumina-based catalyst compared with zirconia-based ones.