Development Of High Performance Cu-based Catalyst For RWGS Reaction

The extensive use of fossil energy leads to the wanton emission of CO₂,which eventually can lead to serious environmental problems.The resource utilization of CO₂hydrogenation is an effective way to solve this problem,and the key to this technology is the design and preparation of highly active CO₂ hydrogenation catalysts.In this paper,supported Cu/γ-Al₂O₃ catalysts were designed and prepared,and the relationship between the physicochemical properties of catalysts and the CO₂ hydrogenation performance were investigated.The physicochemical properties of Cu/γ-Al₂O₃ catalysts were studied by XRD,TEM/HRTEM,H₂-TPR,CO₂-TPD,H₂-TPD and Quasi in-situ XPS.The influence of Cu loading and promoter on CO₂ hydrogenation performance was examined.The main conclusions are as follows:1.Supported Cu/γ-Al₂O₃ catalysts were obtained by the wet impregnation method,the Cu~0 species were the active components of the RWGS reaction and the selectivity of Cu/γ-Al₂O₃ catalysts for CO was 100%.The Cu/γ-Al₂O₃ catalyst with a Cu loading of 12%showed the best CO₂ reaction rate,which could reach 1.855×10^-5 mol/g_cat/s at400°C.A suitable Cu loading（12%）can provide a moderate specific surface area（260.3 m~2/g）to the catalyst,while it can improve the homogeneity of the mesoporous structure in the Cu/γ-Al₂O₃ catalyst to increase the content of active Cu~0 species.Cu loading can regulate the crystallinity of active Cu~0 species,and Cu~0 species with low crystallinity are conducive to the formation of more CO₂ hydrogenation active sites,which can improve the CO₂ hydrogenation ability of Cu/γ-Al₂O₃ catalysts.The grinding method effectively improved the content and dispersion of Cu~0 species on the surface of Cu/γ-Al₂O₃ catalysts,which were conducive to the formation of active sites for CO₂ hydrogenation,so the CO₂ reaction rate of the corresponding catalysts can reach 2.124×10^-5 mol/g_cat/s.2.The Ce O₂,La₂O₃ and Zr O₂ promoters can increase the dispersion of Cu O species in the Cu O/γ-Al₂O₃ precursor,which decrease the crystallinity of Cu~0 species.And the Cu~0 species with low crystallinity are conducive to the formation of more CO₂hydrogenation active sites in the catalyst.In addition,the Cu~0-La O_x and Cu~0-Ce O_xinterfaces formed in La-Cu Al catalyst and Ce-Cu Al catalyst,which can enhance the CO₂ adsorption performance of catalysts.The Ce-O-Cu solid solution in Ce-Cu Al catalyst can increase the dispersity of Cu~0 species.At the reaction temperature of 400°C,the CO₂ reaction rates of La-Cu Al,Ce-Cu Al and Zr-Cu Al catalysts were as follows:2.268×10^-5 mol/g_cat/s,2.519×10^-5 mol/g_cat/s,and 1.782×10^-5 mol/g_cat/s,respectively.However,the Mg Al₂O₃ spinel was formed by the chemical reaction between Mg O and Al₂O₃ support,which can inhibit the formation of CO₂ hydrogenation active sites.In addition,the acidic promoter of In₂O₃ reduced the number of Lewis base centers on the surface ofγ-Al₂O₃ support,which weakened the CO₂ chemisorption properties of In-Cu Al catalysts.At the reaction temperature of 400°C,the CO₂ reaction rates of Mg-Cu Al and In-Cu Al catalysts were 1.462×10^-5 mol/g_cat/s and 0.514×10^-5 mol/g_cat/s.3.The high Ce O₂ content contributes to the electron transfer between Ce O₂ species and Cu~0 species in the catalysts,which can improve the H₂ adsorption performance of the corresponding catalysts.The number of oxygen vacancies on the catalyst surface increased with the increment of Ce O₂ content,which contributes to the efficient adsorption and activation of CO₂ molecules.When the reaction temperature is 400°C,the CO₂ reaction rate of the 10Cu11Ce Al catalyst can reach 2.473×10^-5 mol/g_cat/s.However,the change of the Ce O₂ species loading sequence would result in the aggregation of Cu~0 species or coating by Ce O₂ species.The formation of Cu~0 species with large grain size would inhibit the generation of CO₂ hydrogenation active sites,which can decrease the CO₂ adsorption performance of the corresponding catalysts.When the reaction temperature is 400°C,the CO₂ reaction rates of 9Ce/10Cu Al and10Cu/9Ce Al catalysts were only 2.289×10^-5 and 1.968×10^-5 mol/g_cat/s.