Carbon Dioxide Hydrogenation To Methanol On Differently Morphological CeO₂-supported Cu-Ni Catalysts

Fossil resources are the material basis of modern industry and civilization,but their recycling cycle is long and its use will bring a series of environmental problems.The catalytic conversion of carbon dioxide to methanol is significant for solving environmental problems and coping with energy crisis.Therefore,the cerium oxide supported copper-nickel alloy catalyst was prepared and applied to the carbon dioxide hydrogenation to methanol.The main work and results are as follows:1.The cerium oxide nanotubes were prepared by precipitation-hydrothermal method.Then a series of Cu-Ni/CeO₂ nanotube catalysts were prepared by impregnation method.The effects of different Cu-Ni alloy ratios on carbon dioxide hydrogenation to methanol were studied.The characterization results show that regular CeO₂ nanotubes are perfectly formed with a tube diameter of about 30-50 nm and Cu-Ni alloy is well dispersed on CeO₂ nanotube without nanotube morphology change.There is a synergistic effect between Ni and Cu,promoting the bimetallic Cu-Ni dispersion,reducibility,CO adsorption and hydrogenation.Additionally,a strong interaction is observed between Cu-Ni alloy and CeO₂,and it contributes to partial reduction of Ce⁴⁺to Ce³⁺and formation of oxygen vacancies which adsorb and activate CO₂.When exploring the optimal ratio of Cu-Ni alloy,the activity test results show that with the increase of Ni/?Cu+Ni? ratio,the CO₂ conversion and the CH₃OH STY increase first and then decrease,and reaches a maximum when Ni/?The Cu+Ni?ratio is 2/3.The results also show that temperature and pressure have a greater impact on the reaction.After preliminary optimization of the reaction conditions,CO₂ conversion was 17.8%,and CH₃OH STY was 18.1 mmol/(g_cat·h).In addition,changes in space-time rate have no greateffect on CO₂ hydrogenation to methanol,and the catalysts still exhibit excellent performance in a wide range of space velocity(6000-18000 h^-1).2.Three kinds of morphlogical cerium oxides?nanorods?NR?,nanospheres?NS? and nanoparticles?NP??were prepared by solvothermal method and precipitation,and then a series of Cu-Ni/CeO₂ catalysts were prepared by impregnation method The effects of the morphology of cerium oxide CO₂hydrogenation to methanol were studied.Characterization results show that perfectly formed and well-defined 1Cu2Ni/CeO₂-NR is enclosed by the exposed?110?and?100?facets,while 1Cu2Ni/CeO₂-NS with the diameter of 10-20 nm and irregularly formed 1Cu2Ni/CeO₂-NP expose?111?plane.The?110?and?100?facets possess lower energy than the?111?facet and CO₂ is more easily absorbed and activated on the?100?and?110?facets.The morphology of CeO₂ not only has great effect on exposed facets,but also on the formation of surface oxygen vacancies.Oxygen vacancies are mainly generated from the reduction of Ce⁴⁺to Ce³⁺.Besides,Cu or/and Ni can also replace cerium,along with formation of oxygen vacancies.All catalysts have oxygen vacancies,while 1Cu2Ni/CeO₂-NR possesses the most oxygen vacancies among all three catalysts.Moreover,catalytic tests show that 1Cu2Ni/CeO₂-NR exhibits the best catalytic performance during the reaction of CO₂ hydrogenation to methanol,because the CeO2 in the catalyst exposes the low energy?100?facets and the catalyst has the most oxygen vacancies.