Investigation Of Modification Of Catalyst Cuo-ZnO-Al₂O₃for Methanol Synthesis From CO₂Catalytic Hydrogenation

CO2emission causes the huge waste of carbon resource and environmental problem, leading to the greenhouse effect and ozone depletion, and result in the worse harmonious relationship between nature and human being. As a branch of C1chemistry, methanol synthesis from CO2hydrogenation has been considered an issue, while CO2conversion was found to be too poor to exceed30%because of both intrinsic inertia of CO2and thermodynamics. In this present work, the Cu-based catalyst CuO-ZnO-Al2O3was prepared by co-precipitation method, using oxalate as precipitant, and CuO-ZnO-Al2O3was promoted with the single component promoter such as MgO, TiO2, CaO, etc. and the multicomponent promoter such as MgO-TiO2, MgO-SiO2, TiO2-SiO2, etc. in dosages range of2-8wt.%. The catalytic evaluation was performed using a fixed-bed reactor, results showed that most of the CO2conversions on the promoted catalysts were higher than that on the one unpromoted. For catalyst CuO-ZnO-Al2O3, the catalytic evaluation results showed that XCO2=15.81%, SCH3OH=23.31%and YCH3OH=3.69%under the conditions of P=2.6MPa, t=260℃, SV=3600h-1and H2:CO2=3:1(volume ratio), however it showed the higher CO2conversion and the higher methanol selectivity on the promoted catalysts than that on the one without promoter under the same conditions. Especially, the CO2conversion and methanol selectivity could reach40.70%and41.17%on the catalyst2wt.%TiO2-SiO2/CuO-ZnO-Al2O3, respectively. But the addition should be at the optimal dosage, however the excessive promoter would decrease the CO2conversion and methanol selectivity. In this present work, XRD, FT-IR, H2-TPR, H2-TPD, NH3-TPD, CO2-TPD, BET and SEM characterizations were performed, it was found that most of the promoters enhanced the dispersion of CuO in the catalyst body, modulated the acidity of the surface of the catalyst, meanwhile synergistic effect produced between the promoters, and most of these modifications improved the adsorption capacity/strength of CO2or H2on the surface of the catalyst.In this work, the effect of pre-treatment condition (calcination temperature) on the catalytic performance, and the effect of reaction conditions such as temperature, pressure, space velocity and the ratio of H2/CO2on the reaction were investigated either. Take the catalyst2wt.%MgO/CuO-ZnO-Al2O3as example, testing results showed that the calcination temperature played an important role on the crystals of CuO and ZnO in the catalyst body, hence the performance of the catalyst in the reaction, it was found also that the catalyst calcined at550℃showed the higher catalytic performance with CO2conversion of29.80%and methanol selectivity of34.52%under the conditions of P=2.6MPa, t=260℃, SV=3600h-1and H2:CO2=3:1(volume ratio). The catalyst which was pre-treated at too high or too low temperature can not exhibit the well performance. Too low temperature can not run the catalyst, while too high would inhibit the formation of methanol, the optimal temperature was found to be at260℃under the conditions of P=2.6MPa, SV=3600h-1, H2:CO2=3:1(volume ratio). CO2conversion increased with the increase in H2/CO2while decreased with the increase in flow rate.