Preparation And Catalytic Performance Of ZrO₂ Nanosheets Supported Nickel Catalysts In CO₂ Methanation

The continuous use of global fossil fuels has led to a rapid increase in the concentration of CO₂ in the atmosphere,and further caused the global climate change,which becomes a major challenge for human society today.Subsequently,the effective utilization of CO₂ has increasingly attracted people’s attention.A large amount of hydrogen released by electrolyzing water through electricity generated from renewable resources such as wind energy and solar energy was used to react with excess CO₂ to produced methane（CO₂methanation）,which can not only effectively reduce CO₂ emissions,but also ease the supply and demand of natural gas.Therefore,it has attracted the attention of researchers.With the increase of the conversion rate,the thermal effect is gradually obvious due to CO₂methanation reaction with strong exothermic phenomenon,which will cause the sintering and agglomeration of the catalyst and even occurrence of the reverse reaction of water vapor transformation.This will lead to the reduction of CH₄ selectivity by producing CO,and the formation of surface carbon through disproportionation reaction of CO.Considering the above mentioned,the reaction condition with low temperature and high pressure is beneficial to CO₂ methanation.Therefore,the research focus of CO₂ methanation is to develop low temperature and high efficiency catalysts.Noticeably,various preparation methods and additives were used to prepare catalysts in order to control the particle size and dispersion of active metal components and increase the interaction between metal and support,to improve catalytic activity of CO₂ methanation.The specific research contents are as follows:（1）ZrO₂ nanosheets were synthesized by hydrothermal method,Ni/ZrO₂-IMP and Niy/ZrO₂-ALD catalysts were further prepared by impregnation method and atomic layer deposition（ALD）method,respectively,for CO₂ methanation.The reaction results showed that the supported catalyst prepared by ALD method has higher catalytic performance,it can be considered that Niy/ZrO₂-ALD catalyst surface Ni particle size is smaller,more uniform distribution,and can expose more active sites,thereby promoting the catalytic performance of CO₂ methanation;（2）The Niy/ZrO₂-ALD catalysts prepared with different ALD cycles（60-80）were tested in CO₂ methanation under the reaction conditions of P=0.5 MPa,H₂/CO₂=4 and WHSV=12000 mL·g^-1·h^-1.The results showed that the catalytic activity first increased and then decreased with the increase of the number of ALD cycles.The catalyst prepared with ALD cycles exhibited the highest activity,with CO₂ conversion and CH₄ selectivity of 98.5%and 94.3%,respectively at 360℃;（3）The Mo₂C-Ni/ZrO₂ catalysts with different Mo/Ni molar ratios were prepared by mechanical mixing method and investigated in CO₂ methanation under the conditions of P=0.5 MPa,H₂/CO₂=4,WHSV=15000 mL·g^-1·h^-1.The catalyst with Mo:Ni=1:2 showed the best activity with the CO₂ conversion and CH₄ selectivity of 97.7%and 96.2%,respectively at 360℃,significantly higher than Ni/ZrO₂ catalysts;（4）The characterization results of Mo₂C-Ni/ZrO₂ catalysts showed that the strong interaction between Ni and Mo₂C constructed the Ni-Mo₂C interface,which promoted the dispersion of Ni species,reduced the size of Ni particles,and then exposed more active sites,thus significantly improved the catalytic activity in CO₂ methanation.