Preparation Of Cu-ZnO-ZrO₂ By Solvothermal Method And Its Catalytic Performance For CO₂ Hydrogenation

For decades,the burning of fossil fuels has emitted a large amount of carbon dioxide,which has caused global warming and climate change,threatening the sustainable development of our society.With the increasing awareness of reducing carbon dioxide emissions and resource utilization,the carbon dioxide hydrogenation to synthesize methanol has received more and more attention.Because methanol is an important basic raw material for the chemical industry,carbon dioxide hydrogenation to synthesize methanol can not only realize the reuse of carbon resources,but also play a key role in the sustainable development of society.Solvothermal method has been widely used in the preparation of inorganic materials,because it can greatly enhance the dissolution and dispersion process of reactants and the chemical reaction activity,so that the reaction can occur at a lower temperature.And it can form metastable phase that cannot be obtained under conventional conditions due to the particularity of the chemical environment of the system.Therefore,the product prepared by the solvothermal method has higher purity and uniformity.However,this method has not been reported for the preparation of Cu-based catalysts so far to our best knowledge.In this paper,the Cu-Zn O-Zr O₂ catalysts were prepared by the solvothermal method and studied for the methanol synthesis from CO₂ hydrogenation.The effects of solvothermal temperature,solvothermal time and different solvents on the catalytic performance of the Cu-Zn O-Zr O₂ catalysts were investigated.The following results were obtained.1.Effect of the solvothermal temperature on the Cu-Zn O-Zr O₂ catalystsWhen the solvothermal time was fixed and the solvothermal temperature was changed,the results indicate that the CO₂ conversion and CH₃OH yield of the Cu-Zn O-Zr O₂ catalysts exhibit volcanic trend with the increase of solvothermal temperature.When the solvothermal temperature was 180°C,tetragonal zirconium dioxide（t-Zr O₂）appeared in the catalyst,and the Cu-based catalyst supported by t-Zr O₂ showed higher activity.By correlating with the characterization results of the catalyst,it is found that the difference in the activity of Cu-Zn O-Zr O₂ catalysts is mainly ascribed to their different adsorption capacity for H₂ resulted from discrepant S_Cu.2.Effect of the solvothermal time on the Cu-Zn O-Zr O₂ catalystsUnder certain solvothermal temperature conditions,with the extension of the solvothermal time,the catalytic performance of the Cu-Zn O-Zr O₂ catalyst first increases and then decreases.When the solvothermal time was 3 h and 6 h,t-Zr O₂ appeared in the catalyst.It proves once again that the Cu-based catalyst supported by t-Zr O₂ shows higher activity.Among them,when the solvothermal time is 6 h,the Cu-Zn O-Zr O₂ catalyst has the largest S_Cu and CH₃OH yield,and also adsorbs more CO₂,indicating that the activity of the the Cu-Zn O-Zr O₂ catalyst prepared under this condition in the CO₂ hydrogenation to methanol is also related to the adsorption capacity for H₂ and CO₂.3.Effect of different saturated monoalcohols on the Cu-Zn O-Zr O₂ catalystsThe effects of different saturated monoalcohols as solvents on the performance of Cu-Zn O-Zr O₂ catalysts were studied.For saturated monohydric fatty alcohols that are homologous to each other,the methanol solvent with a large dielectric constant,the precursor is precipitated in a smaller particle state during the solvothermal reaction;the resulting catalyst has the smallest particle size of the active component and the largest S_Cu.The relationship between the S_Cu and the adsorption capacity for H₂ as well as CO₂ conversion and the adsorption capacity for H₂ were studied.It was found that there is a good linear correlation,indicating that the catalytic performance of the Cu-Zn O-Zr O₂ catalyst used in CO₂ hydrogenation to methanol is mainly affected by S_Cu.