Synthesis And Modification Of ZnO-ZrO₂ Catalyst And Its Catalytic Performance For CO₂ Hydrogenation To Methanol

Excessive CO2 emissions have led to many environmental problems such as the greenhouse effect.The use of abundant CO2 to produce chemical products or renewable energy will be of great significance.Methanol is a premium fuel and high value-added chemical,and is easily stored and transported.With the increasing demand on it,the catalytic hydrogenation of CO2 to methanol has attracted more researchers’ attention.The development of catalysts with high activity,high selectivity and high methanol yield is the key to the methanol industry.In this paper,the best method for synthesizing ZnO-ZrO2 catalysts has been screened out from co-precipitation,impregnation and solid-state reaction.Then,the effects of precipitation method and ageing time of co-precipitation method on the catalyst were investigated,and the experimental method was optimized.Finally,the catalyst was doped into the additives with different amounts to improve performance.The structure and catalytic performance of the catalyst prepared by different methods are very different.S-ZnZr has more impurities.The ZnO in I-ZnZr was simply dispersed on ZrO2 without further tight bonding.Compared with the former two methods,C-ZnZr has high purity,tight binding of ZnO and ZrO2,rich pore structure and better catalytic activity.The catalytic properties of ZnO-ZrO2 are closely related to its composition,pore structure,interaction between ZnO and ZrO2.Compared with C-ZrO2,the ZnO dispersed on ZrO2 increases the adsorption and dissociation of H2,which contributes to the activation and conversion of CO2.The high specific surface area is beneficial to CO2 conversion,but it is not the decisive factor.The high methanol selectivity of ZnO-ZrO2 is attributed to the strong intermetallic interaction between ZnO and ZrO2.The precipitation method and ageing time of the co-precipitation method have great influences on the catalyst.Catalyst obtained by positive precipitation and non-ageing has better catalytic activity,XCO2 is 9.02%,SCH3OH is 88.49%,and YCH3OH reaches 6.24%.The additives have great influences on the catalyst.The Mg refines and disperses the particles.The introduction of MgO basic sites enhances the CO2 adsorption,which greatly improves XCO2,but reduces SCH3OH.The Cr affects the combination of ZnO and ZrO2.Although XCO2 is improved,SCH3OH is significantly reduced.When the catalyst is doped with a large amount of Al,many micropores belonging to Al2O3 appear.The introduction of acid centers promotes the progress of the hydrogenation reaction.At the same time,the hydrophilicity of Al2O3 affects the SCH3OH The Fe causes the catalyst particles to become larger,the pores to be widened,and the specific surface to be greatly reduced.With the increase of Fe dopidg amount,XCO2 increases,SCH3OH decreases,and YCH3OH maintains a stable value.The catalytic properties was most improved when doped with 3%of Mg.XCO2 is 12.93%;SCH3OH is 81.54%;YCH3OH reaches 10.54%,which is 1.32 times of that of undoped catalyst.The crystal of t-ZrO2 is moderate;metal oxides are tightly bound and have strong interactions;the particles size is concentrated at 25 nm;the particles are highly dispersed,and the BET is 44.128 m2/g.