Ag addition to CuO-ZrO2 catalysts promotes methanol synthesis via CO2 hydrogenation

•The effect of adding Ag to CuO-ZrO2 catalysts on the hydrogenation of CO2 to methanol was studied.•Ag addition promoted methanol hydrogenation via CO2 hydrogenation.•Ag addition enhanced methanol selectivity.•Formation of a Ag-Cu alloy on the Ag/CuO-ZrO2 catalyst was identified.•The Ag-Cu alloy can be the main active species for CO2 hydrogenation.

The effect of adding Ag to CuO-ZrO2 catalysts for the hydrogenation of CO2 to methanol was investigated using CuO-ZrO2, Ag/CuO-ZrO2, and Ag/ZrO2. The addition of Ag to CuO-ZrO2 catalysts decreased the specific surface area and also broke its mesostructure. Thus, Ag played a significant role as a sintering aid in the preparation of Ag/CuO-ZrO2 catalysts. We note that the as-prepared Ag/CuO-ZrO2 catalysts contained Ag+ and Zrq+ (q < 4) sites and that the Zrq+ content increased with increasing Ag+ content. Furthermore, the presence of CuO in the Ag/CuO-ZrO2 catalyst appeared to stabilize Ag+ and Zrq+ species under air. Based on H2 chemisorption and powder X-ray diffraction patterns, formation of a Ag-Cu alloy was observed on completely reduced and spent Ag/CuO-ZrO2 catalysts. Completely reduced Ag/CuO-ZrO2 catalysts exhibited a higher methanol production rate (7.5 mL h−1 gcat−1) compared to completely reduced CuO-ZrO2 (6.9 mL h−1 gcat−1) and Ag/ZrO2 catalysts (2.2 mL h−1 gcat−1) under the following reaction conditions: CO2/H2/N2 = 1/3/1, catalyst loading = 500 mg, W/Ftotal = 1000 mgcat s mL−1, reaction temperature = 230 °C, pressure = 10 bar.

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