Abstract:

The development of high-performance catalysts play curial role in the field of CO₂ hydrogenation to methanol，however，the formation conditions of crystal phases of catalyst precursors and their corresponding relationships with catalytic performances remain unclear.A series of Cu/ZnO/Al₂O₃ catalysts synthesized at different precipitation temperatures were prepared by co-precipitation method.The prepared catalysts were characterized by XRD，SEM，BET，H₂-TPR and CO₂-TPD.Meanwhile，the catalytic performances of the prepared catalysts in CO₂ hydrogenation to methanol was also investigated in the fixed bed setup.The results indicated that the precipitation temperature had significant effects on the crystal structure，microstructure and interaction of Cu-ZnO species.Low temperature precipitation was conducive to the formation of aurichalcite phase of catalyst precursors and smaller crystalline size.Higher precipitation temperature was conducive to the formation of malachite phase and generating more Cu-O-Zn sites in the catalyst，which were regarded as the active sites for CO₂ hydrogenation to methanol.The catalytic performance of Cu/ZnO/Al₂O₃ catalyst for hydrogenation of carbon dioxide to methanol was probably determined by the catalyst crystalline size and copper-zinc interface.The optimal precipitation temperature was 70 ℃ within the scope of this investigation.Under the reaction conditions of 240 ℃，5 MPa，GHSV of 10 000 mL/（g·h），and feed gas composition of V（CO₂）∶V（H₂）∶V（N₂）=23.5∶70.5∶6（volume ratio），CZA-70 catalyst，which was prepared at optimal precipitation temperature，showed 23.8% of CO₂ conversion，60.9% of methanol selectivity and 0.48 g/（g·h） of methanol space time yield.

Key words: hydrogenation of carbon dioxide, Cu/ZnO/Al₂O₃ catalyst, co-precipitation method, methanol