Synthesis Of Cold Plasma Surface-Modified Nickel-Based Catalysts And Study On The Stability Of Reforming Reactions

In recent years,the issue of global warming has become a major environmental issue,so the disposal or utilization of the greenhouse gases carbon dioxide（CO₂）and methane（CH₄）has become a top priority.The methane carbon dioxide reforming（DRM）reaction not only reduces both methane and carbon dioxide greenhouse gases at the same time,but the resulting syngas（H₂ and CO）can be further synthesized into other chemicals.However,the DRM reaction is a highly endothermic process accompanied by a large number of side reactions,which will inevitably lead to catalyst sintering and carbon deposition caused by CH₄ cracking and CO disproportionation.The high cost of noble metal catalysts limits its industrial application.Non-precious metal nickel-based catalysts are the most commonly used catalyst systems for this reaction.Its reforming activity is comparable to that of noble metal catalysts,but it is difficult to achieve industrialization due to sintering and carbon deposition.Therefore,it has become very important to develop nickel-based catalysts with high activity and activity to improve their anti-coking properties.Aiming at the problem that supported nickel-based catalysts are prone to deactivation due to carbon deposition during sintering and agglomeration during calcination and high-temperature reactions,this study uses molecular sieve MCM-41 with high specific surface area and high stability as the carrier.Firstly,introduces surfactants,improve the dispersion of metallic nickel and regulate the interaction between the metal and the carrier;then introduce the cold plasma technology to modify the catalyst,and investigate the influence of plasma treatment time,power and atmosphere factors to reduce the particle size of metallic nickel,enhance the interaction between the metal-support,thereby enhancing the catalytic performance of the catalyst;finally,through the joint action of surfactants and plasma technology,a small particle size and highly dispersed Ni-based catalyst is prepared to obtain DRM catalysts with high stability and strong resistance to carbon deposition.First,three different surfactants（P123,TPAOH,SDBS）were selected to modify the 10%Ni/MCM-41 catalyst to adjust the structure of the catalyst and apply it to the methane carbon dioxide reforming reaction.The stability test investigated the reforming catalytic performance of the catalyst,and deeply analyzed the structure-activity relationship between the metal-support in the modified catalyst.The addition of surfactant can effectively control the texture of the catalyst,and the modified catalyst has a smaller pore volume,which comes from more Ni species entering the pores of MCM-41.Compared with the catalyst NM-C,the initial activity of the catalyst prepared by surfactant-assisted impregnation was significantly improved.At 750°C,compared with the catalyst NM-C,the CH₄ and CO₂conversion rates of the catalyst NM-P123-C were increased by 21.4%,14.6%,respectively.After reacting at 750°C for 10 h,the final CH₄ conversions of catalysts NM-P123-C,NM-TPAOH,and NM-SDBS-C remained at 80.6%,72.3%,and 61.4%,respectively,which were lower than the initial activity7.8%,17.2%and 26%;the CO₂ conversion rate decreased by4.7%,14.2%and 21.4%,respectively.It can be seen that the stability of the catalyst after P123 modification is relatively best.The law of carbon deposition is:NM-P123-C（2.3%）<NM-TPAOH-C（4.27%）<NM-SDBS-C（12.55%）<NM-C（37.40%）,that is,after P123modification,the catalyst produces the least amount of carbon deposition and has the best resistance to carbon deposition.Then,10%Ni/MCM-41 catalysts were prepared by radio frequency discharge cold plasma,the effects of plasma treatment time,power and atmosphere on the structure and properties of the catalysts were investigated,and the reforming catalytic performance of the catalysts was investigated by stability tests.The initial conversion rates of CH₄ and CO₂ of the catalyst NM-PN0.5h were 78.8%and 85.7%.When the treatment time was between 1.5and 3 h,the initial conversion rates of CH₄ and CO₂ remained above 87.7%and 87.5%.After10 hours of reaction,the conversion rates of CH₄ and CO₂ of catalyst NM-PN2h were relatively the highest,which remained at about 81.7%and 84.9%,respectively,and there was no obvious carbon deposition.The CH₄ and CO₂ conversion trends of catalysts NM-PN50w and NM-PN100w are generally similar,and the values are similar.When the plasma processing power is 150w-250w,the CH₄ and CO₂ conversion rates of the catalysts are generally similar and the specific processing power is 50w-100w catalyst has high conversion rate,and catalyst NM-PN200w has relatively the highest CO yield.Compared with the base catalyst NM-C,the CH₄ and CO₂ conversions of the catalysts treated with different plasma atmospheres were improved.Among them,the NM-PN stability of the catalyst treated with N₂ atmosphere for 2h was better than that of the catalyst treated with H₂ atmosphere for 2h,while the NM-PN-PH stability of the catalyst treated with N₂ for 1h and H₂ for 1h was between the two.The catalyst NM-PAr of the stability is relatively the worst.Finally,catalyst precursors were prepared by P123-assisted impregnation,and then catalysts（NM-P123-PN）were prepared by N₂ radio frequency discharge plasma for different treatment times to reduce the particle size of nickel,and the stability and coking resistance of the catalyst in the CH₄/CO₂ reforming reaction under the action of P123 and N₂ radio frequency discharge plasma were further discussed.The initial conversions of CH₄ and CO₂of the catalyst NM-P123-PN2h were 90.80%and 89.60%,respectively.After 10 hours of reaction at 750°C,the conversions of CH₄ and CO₂ remained at 88.10%and 88.50%,respectively,which were relatively stable among all catalysts.