Design,Preparation Of Graphene-copper Composite Catalysts And Application For Methanol Synthesis From CO₂ Hydrogenation

The emission reduction of greenhouse gas CO2 is a hotspot worldwide.CO2 hydrogenation to methanol has attracted interest of both academic and industrial cycles.The research focuses on developing efficient catalysts and understanding relevant mechanisms to improve CO2 conversion and methanol selectivity.The preparation,characterization and catalytic activity of graphene composite copper-based catalysts for CO2 hydrogenation were conducted considering of high surface area and good conductivity of graphene.Effects of compositing methods on the properties of catalysts were first investigated.Co-precipitation,impregnation and solvothermal synthesis were employed for compositing graphene with traditional Cu-ZnO/Al2O3(CZA).With graphene compositing,the reduction temperature of catalysts was decreased and the CO2 absorption enhanced.The composite catalyst by co-precipitation showed the best catalytic activity for CO2 hydrogenation.At typical evaluation conditions(Ha/CO2=3,W/F=10g·h·mol-1,250℃,3MPa),the methanol selectivity and yield were increased by 6.10%and 0.77%,respectively.For G/CZA by co-precipitation,there existed an appropriate amount of graphene in terms of improving CO2 conversion and methanol selectivity.This was attributed to that the graphene compositing promoted the interaction between Cu with ZnO and Al2O3,improved the reducibility,increased the surface area and Cu dispersion of the catalysts.When the content of graphene was 13%,the CO2 conversion was 17.1%,the methanol selectivity and yield were 43.9%and 7.51%,respectively,at typical evaluation conditions.Appropriate amount of graphene oxide(GO)composite with CZA improved much the catalytic activity toward CO2 hydrogenation.When the content of GO was 4%,the surface area and dispersion of Cu were 20.7 m2·g-1 and 3.05%,increased by 7.30 m2·g-1 and 1.07%,respectively,compared with CZA.The CO2 conversion was 19.4%and the methanol yield was 7.64%at typical evaluation conditions.For Cu-ZnO/ZrO2(CZZ)catalyst with ZrO2 replacement of Al2O3,the Cu dispersion was increased by 2.12%The CO2 conversion,the selectivity and the yield of methanol increased by 4.10%,11.7%and 3.61%,respectively.The composite GO/CZZ catalyst showed lower reduction temperature and higher Cu dispersion.When the content of GO was 10%,the catalyst had maximum Cu dispersion of 4.99%.The CO2 conversion,the selectivity and yield of methanol were 21.8%,51.7%and 11.3%,respectively.