Highly Active And Selective Carbon Dioxide Hydrogenation Research On Catalysts For Methanol Production

With the continuous development of green renewable energy technologies,the hydrogenation of CO₂ into high-value chemicals and energy carriers has become a research hotspot,which is also a promising way to solve environmental and energy problems.CO₂ hydrogenation to methanol technology can reduce greenhouse gas emissions while realizing hydrogen conversion and energy storage.The core of this process lies in the development of efficient and stable CO₂ hydrogenation to methanol catalyst and process.In this thesis,to transfer CO₂ to methanol catalyst by hydrogenation,a series of Zn-Zr,Cu-In,Cu-Zn-Zr catalysts were designed,prepared and tested.The structure-activity relationship of the catalysts was studied by combining different characterization methods,and the following results were obtained:（1）A series of Zn-Zr metal oxide catalysts were prepared by using different precipitation methods and controlling the p H value of the precipitation.Through the evaluation of CO₂ hydrogenation of Zn-Zr catalyst,the results show that the catalyst prepared by the parallel addition method has the best performance.The reverse addition method is slightly inferior,and the positive addition method was the worst.On the basis of parallel addition,a series of Zn-Zr catalysts were prepared by controlling the p H value of the precipitation.The evaluation results show that in the range of p H=7.2～7.7,the selectivity of CO₂ hydrogenation to methanol over the catalyst exceeds 90%.The highest methanol yield of the catalyst can be obtained at p H=7.7.（2）A series of Cu-In catalysts with different Cu In ratios were designed and prepared by co-precipitation.The evaluation results show that the Cu-In catalyst shows a high CO₂conversion rate in the CO₂ hydrogenation reaction.When the Cu In ratio is 0.2,the CO₂conversion rate reaches 12%,but the methanol selectivity of the Cu-In catalyst is all the same.（3）Based on the research on Zn-Zr and Cu-In catalysts,a series of Cu-Zn-Zr catalysts with different Cu contents were designed and prepared by co-precipitation method.The evaluation results show that the Cu Zn Zr-25 catalyst with Cu content of 25%has the highest specific surface area and the lowest reduction temperature,exhibiting excellent catalytic performance for CO₂ hydrogenation to methanol.Under the reaction conditions of 240℃,3 MPa,V（H₂）/V（CO₂）=3,6000 m L/（g·h）,the CO₂ conversion rate reached 18%,the methanol selectivity remained at 51%,and the methanol yield reached9%,which was significantly higher than that of Cu-In and Zn-Zr catalyst.Combined with BET,XRD,H₂-TPR,XRF characterization results and catalyst evaluation,it is believed that the high selectivity of CO₂ hydrogenation on the catalysts is mainly due to the inhibition ability for water gas shift reaction of the catalysts.The addition of Cu to the catalyst will significantly enhance the performance of the reverse water gas shift reaction,which is not conducive to improving the methanol selectivity.However,the introduction of Cu is conducive to improve the activity of CO₂ conversion,which make it come close to the thermodynamic equilibrium.