Study On Structure Of Effects Of Ni/MCF Catalyst And Properties Of Protective/Sacrificial Graphitic Coating For Carbon Dioxide Reforming Of Methane

The rapid development of economy is accompanied by serious pollution and enormous carbon dioxide emissions.In 2020,"double-carbon"target has been put by China,that is,strive to peak carbon dioxide emissions by 2030 and achieve carbon neutrality by 2060.Studies show that chemical capture and utilization of carbon dioxide can accelerate the realization of"dual carbon"goal.The carbon dioxide reforming of methane（CRM）can efficiently convert two main greenhouse gases,methane and carbon dioxide,into syngas（H₂:CO=1:1）,a important industrial raw material,under the conditions of catalysts and high temperature,so as to solve the problems of environment and energy.Nickel-based catalysts are the most used catalysts for CRM,which have high catalytic activity,but the active component sintering and catalyst carbon deposition can easily lead to catalyst deactivation.The nanoparticle size of the active metal,the metal-support interaction and the overall structure of the catalyst have significant effects on the catalytic performance.Therefore,controlling the particle size of active metal and enhancing the interaction of metal-support become the key to prepare catalyst with high activity and stability.In this thesis,the structure of nickel-based catalyst was designed and modified to improve the stability of the catalyst for carbon deposition and sintering of CRM.In the first part of this thesis,mesoporous foam silica（MCF）was synthesized as support,10%Ni/MCF,10%Ni@C/MCF and 10%Ni/MCF@C were prepared by impregnation method.A series of characterizations show that the localized catalysts10%Ni@C/MCF and 10%Ni/MCF@C have smaller Ni nanoparticles and stronger metal-support interactions than those of 10%Ni/MCF,because of the introduction of protective graphitic coating.The results of catalysts performance tests show that Ni@C/MCF has higher catalytic activity and stability,which the limited strategy not only improves the nickel dispersion but also effectively improves the anti-sintering and anti-carbon deposition capacity of the catalyst.In the second part,the study of graphite-carbon confinement effect was extended to the high loading catalysts,so as to solve the practical problems of agglomeration and sintering of active metals under high metal loading.The 10%Ni@C/MCF,20%Ni@C/MCF and 30%Ni@C/MCF catalysts were prepared by impregnation method and their structure-activity relationships were studied by instrumental analysis.XRD and STEM characterizations of the catalysts before the reaction showed that the size of metal nickel nanoparticles were relatively stable with the increase of catalyst loading.The performance test results of the catalyst showed that there was no obvious sintering and carbon deposition after the reaction of the catalyst with high loading.The results show that the graphite confining strategy can alleviate the sintering and carbon deposition problems of metal catalysts with high loading.In the third part,30%Ni/MCF-ROR catalyst was prepared by oxidization and rereduction treatment on the basis of 30%Ni@C/MCF,and the influences of ROR treatment catalyst on CRM have been explored.A series of characterizations show that ROR treated catalyst has lower metal nickel nanoparticles than those of30%Ni/MCF catalyst by common impregnation method,which improves the metal-support interaction.Stability tests proved that 30%Ni/MCF-ROR had better stability and showed excellent activity and stability at both low and high temperatures.The results show that the graphite carbon protective layer can inhibit the metal sintering at high temperature during the catalyst synthesis process,and the subsequent ROR treatment of the carbonized catalyst can sacrifice the protective layer and generate new active sites during the intense oxidation process,which enhances the performance of the catalyst.