Influence Of Metal-Support Interaction Of Ni/TiO₂-Al₂O₃ Catalyst For CO₂ Methanation

The metal-support interaction in nickel-aluminum catalysts for CO₂methanation can effectively tune the geometric and electronic structures of the resultant catalysts,by tailoring the adsorption and activation behaviors of reactants,which improve the activity and stability during the reaction.The strong metal-support interaction of Ni catalysts easily results to the formation of inactive nickel-aluminum spinel.The interaction between metal and support was adjusted by a reduction-oxidation-reduction process,in which TiO₂was introduced into Ni catalysts.The effects of metal-support interaction of Ni/TiO₂-Al₂O₃on the performance of CO₂methanation were investigated.In this paper,Ni/Ti₃Al C₂catalysts were prepared by impregnation method with Ti₃Al C₂and nickel nitrate as starting materials under nitrogen atmosphere,and the mechanism for the synthesis was explored,which was proved to follow the process of Ni²⁺→Ni O→Ni.Ni/TiO₂-Al₂O₃catalyst was obtained through the reduction-oxidation-reduction process.For CO₂methanation,the catalytic activity and stability were improved by increasing Ni loading from 5 wt.%to 20 wt.%.For 5 Ni/TiO₂-Al₂O₃catalyst,CO₂conversion and CH₄selectivity reached 68.3%and 78%at 500℃,respectively;whereas CO₂conversion and CH₄selectivity of 20 Ni/TiO₂-Al₂O₃were 77.6%and 97%at 450℃,respectively.The stability test results showed that CO₂conversion and CH₄selectivity of 20 Ni/TiO₂-Al₂O₃remained stable at 66%and 96%at 400℃,respectively;whereas CO₂conversion and CH₄selectivity of 5Ni/TiO₂-Al₂O₃decreased from 28.5%to 18.7%,and from 77.6%to 59.3%,separately.CO₂activation energies of 5 Ni/TiO₂-Al₂O₃and 20 Ni/TiO₂-Al₂O₃were 90.3 k J/mol and 73.0k J/mol,respectively.CO₂reaction orders of 5 Ni/TiO₂-Al₂O₃and 20 Ni/TiO₂-Al₂O₃were 2.73and 2.53,respectively.Carbon deposition of 20 Ni/TiO₂-Al₂O₃catalyst was not obvious after the 72 h of stability test.Therefore,the medium metal-support interaction on 20Ni/TiO₂-Al₂O₃changes coverage and exposure of active Ni sites.The interaction strengthened the geometric and electronic effects on the catalyst structure with the formation of more NiTiO₃species,contributing to an enhanced activity and stability of Ni catalysts in CO₂methanation.