CO₂ Hydrogenation Over Copper-Based Catalysts Prepared By Cold Plasma

The use of fossil fuels has brought prosperity to human society,but it has also increased the content of CO₂ in the atmosphere.In recent years,large amount of CO₂emissions seriously interferes with the Earth’s natural carbon cycle,causing problems such as global warming,ocean acidification,sea level rise,and climate change.The conversion of CO₂ into methanol is a sustainable technical means in line with the"methanol economy"and has considerable prospects.Cu-based catalyst is a classic CO₂ methanol synthesis catalyst that has been used for a long time and has proven performance.The optimization of Cu-based catalysts has attracted the attention of academia and industry,driven by the current rapidly growing CO₂ synthesis methanol industry.As a green and efficient preparation method,cold plasma has been widely used in the field of catalyst preparation.In this paper,the cold plasma was used to successfully prepare Cu-based catalysts and explore its performance in the reaction of CO₂ to methanol.In this paper,Cu-Zn precursors supported on activated carbon were prepared by simple cold plasma decomposition of Cu-Zn precursors at room temperature and used for CO₂ hydrogenation of methanol.Compared with the traditional calcination,the Cu/ZnO/C catalyst prepared by the cold plasma has smaller particle size and higher active metal dispersion.Various methods were used to characterize the catalyst.Through XPS characterization,we found that cold plasma can introduce oxygen-containing groups on the surface of activated carbon.The results of H₂-TPR and TEM demonstrate stronger metal interactions in Cu/ZnO/C catalysts prepared by cold plasma.In the catalytic activity evaluation experiment,the Cu/ZnO/C catalyst prepared by cold plasma showed better catalytic performance.It obtained a space-time yield of methanol of 92.5 g_methanol·kg_ca^-1 _t·h^-1 at 260°C,which was about 1.5 times that of the Cu/ZnO/C catalyst prepared by calcination.Through the in situ DRIFTS experiment,the mechanism of CO₂ hydrogenation to methanol occurred on the Cu/ZnO/C catalyst has also been revealed.In addition,Cu/ZnO/CeO₂ and Cu/ZrO₂ catalysts were prepared by cold plasma in this thesis.After a series of characterizations,it was found that cold plasma can be used to increase the oxygen vacancy content in the catalyst.Compared with the traditional calcination method,the Cu/ZnO/CeO₂ catalyst prepared by plasma and Cu/ZrO₂catalyst both contain more oxygen vacancies.Moreover,the catalyst prepared by plasma has a smaller particle size and a larger specific surface area.In the activity evaluation experiment,the highest STY_methanol achieved by the plasma prepared Cu/ZnO/CeO₂ catalyst and Cu/ZrO₂ catalyst was 162.7 g_methanol·kg_ca^-1 _t·h^-1 and 86.2g_methanol·kg_ca^-1 _t·h^-1,which are 1.5 and 1.2 times that of traditional calcination.The excellent performance of the plasma-produced catalyst is also related to the synergy between the metals in the catalyst.The mechanism of CO₂ hydrogenation to methanol on Cu/ZnO/CeO₂ catalyst is similar to that of Cu/ZnO/C catalyst,indicating that replacing the carrier from activated carbon to CeO₂ will not change the catalytic mechanism of Cu/ZnO-based catalyst.