Preparation,Characterization And CO₂ Hydrogenation Performance Of Ni-Based And Mo-Based Catalysts

In the research and development system of green low carbon technology,CO₂ methanation and RWGS reaction are effective methods to achieve low CO₂emission and recycling.Ni-based catalyst shows excellent catalytic activity in CO₂methanation,but it is easy to agglomerate and sinter during the reaction,resulting in deactivation of the catalyst;Although Mo-based catalysts have high CO selectivity in RWGS reaction,they often require high reaction temperature（600°C）and low CO₂conversion.In order to solve the above problems,Co was introduced into Ni-based catalyst to construct Co-Ni alloy catalyst in this work,and its catalytic activity in CO₂methanation was improved;Additives and supports were added to the bimetallic Mo-based catalyst,which improved the CO₂ conversion and CO selectivity in the RWGS reaction at relatively low reaction temperature.The following are the main tasks:（1）The water talc precursors(Ni₃Al-LDH,Co₃Al-LDH and Co_xNi_3-xAl-LDH with different Co/Ni molar ratios)were prepared by hydrothermal method.The precursors were reduced at high temperature in hydrogen atmosphere to obtain Ni₃/Al O_x,Co₃/Al O_x and Co_xNi_3-x/Al O_x catalysts with different Co/Ni molar ratios.Characterization and activity evaluation of these catalysts for CO₂ methanation.The results showed that Co and Ni formed Co-Ni alloy in Co_xNi_3-x/Al O_x catalyst,and the Co-Ni alloy in Co_1.5Ni_1.5/Al O_x catalyst had higher dispersion and reduction.In addition,the catalyst also has the advantages of sintering resistance and agglomeration resistance.The Co_1.5Ni_1.5/Al O_x catalyst exhibits the best catalytic performance with excellent CO₂conversion（96.0%）and CH₄ selectivity（99.8%）at relatively low reaction temperature（250°C）.（2）CA-Co₃Mo₃N and Ni₂Mo₃N catalysts were prepared by sol-gel method and coprecipitation method respectively.The CA-Co₃Mo₃N and Ni₂Mo₃N catalysts were optimized by adding rare earth additives（La and Ce）.The above catalysts were characterized and the RWGS reaction activity was evaluated.The results show that the addition of La and Ce makes the particle size of the catalyst smaller and more active sites for CO₂ adsorption.Comparing the catalytic activities of La and Ce,it was found that the effect of La promoter was better,and the catalytic activity of La_0.15-Ni₂Mo₃N was better than that of La_0.15-CA-Co₃Mo₃N.At 1.0MPa and 400°C,the CO₂ conversion and CO selectivity of La_0.15-Ni₂Mo₃N catalyst were 46.8%and 69.2%,respectively,which were higher than those of Ni₂Mo₃N catalyst.（3）Ni₂Mo₃N/γ-Al₂O₃ catalysts with different loadings were prepared by equal volume impregnation method,and the catalysts were characterized and the RWGS reaction activity was evaluated.The results showed that the CO₂ conversion of15wt.%Ni₂Mo N/γ-Al₂O₃ at 400°C was basically equivalent to that of Ni₂Mo₃N catalyst,while the CO selectivity was greatly improved.In order to further improve the CO₂conversion,15wt.%La_0.15-Ni₂Mo₃N catalyst with smaller particle size was loaded onγ-Al₂O₃ support by the same method.The results showed that at 400°C,the CO₂conversion and CO selectivity of the catalyst were 39.7%and 92.3%,which were higher than those of the 15wt.%Ni₂Mo₃N/γ-Al₂O₃ catalyst.