Design And Preparation Of Supported Ni Catalysts And Their Catalytic Performance For Methanation

In recent years,China's economy has advanced by leaps and bounds and GDP has grown rapidly.At the same time,energy consumption has also increased.China's energy structure is rich in coal,low in oil and gas.However,relatively backward coal mining,processing and processing technologies waste a lot of resources and seriously pollute the environment.The conversion efficiency of coal-to-natural gas(SNG)process is high,which is an important way for the clean utilization of coal and an important direction for the development of modern clean energy.The key step of coal-based synthetic natural gas is CO methanation,and the core of the technology is methanation catalyst.At present,domestic industrial methanation catalysts are still immature.In recent years,research on high-efficiency methanation catalysts has attracted much attention.In this paper,the design and preparation of supported Ni-based methanation catalysts are studied.Firstly,several conventional carriers were compared.Three kinds of methanation catalysts,20Ni/Al₂O₃,20Ni/TiO₂ and 20Ni/SiO2 were prepared using Al₂O₃,TiO₂ and SiO2,as supports by the same volume impregnation method.Through the activity evaluation,it is found that the Al₂O₃ carrier has a large active interval,excellent thermal stability,excellent CH4 selectivity and the highest yield;the TiO₂ carrier has the highest CO conversion rate,up to 99.9%,and the low temperature activity is excellent;The performance of the SiO2 carrier is the worst,and the CO conversion rate and CH4 yield are inferior to the other two carriers.The xNi/Al₂O₃ catalyst was prepared by using equal volume impregnation method to load different amounts of nickel.Then,the xNi/TiO₂ catalyst was prepared by using equal volume impregnation method to load different amounts of nickel.The effect of Ni loading on the methanation performance of the catalyst was examined.According to the results of activity evaluation,it was found that the performance of the two catalysts with a Ni loading of 20%by weight was better.Combined with BET,SEM,XRD,thermogravimetric analysis and other characterizations,it was found that too little Ni loading of the active component,the active center is insufficient.When Ni loading is excessive,NiO particles tend to agglomerate and block the pores of the catalyst,and it is easy to deposit carbon and coke during use.Using 20Ni/TiO₂ as the research standard,alkaline earth metals(Ca,Mg),transition metals(Mn),rare earth metals(La,Ce)were added respectively,and the effects of the type and amount of additives on the methanation performance of the catalyst 20Ni/TiO₂ were investigated.A series of cocatalyst modified catalysts 20Ni/xM-TiO₂ were designed and prepared by the same volume multiple impregnation method.Through activity evaluation and SEM,XRD,thermogravimetric analysis and other characterizations,the results show that the proper addition of these five cocatalysts can increase the activity of 20Ni/TiO₂ to varying degrees and extend its service life.Among them,Mn and Ca co-catalysts reduce the optimal activity temperature of the catalyst and expand the active temperature range.When examining the effect of the amount of co-catalyst added on the methanation performance of the catalyst,it was found that the optimal amount of each additive was different,The optimal amount of each additive is respectively 10%Ca,2%Mg,8%Mn,8%La,and 6%Ce.The reduction temperature and mode are screened to the selected catalyst.Each catalyst was set at 400?,500?,and 600? for isothermal reduction and programmed temperature reduction,and then the methanation catalytic performance was compared at the optimal reaction temperature.It was found that the catalyst 20Ni/10Ca-TiO₂ is suitable for isothermal reduction at 500?;the catalyst 20Ni/2Mg-TiO₂ is suitable for isothermal reduction at 400?;the catalyst 20Ni/8Mn-TiO₂ is suitable for temperature-programmed reduction at 400?;20Ni/8La-TiO₂ is suitable for temperature-programmed reduction at 600?;catalyst 20Ni/6Ce-TiO₂ is suitable for temperature-programmed reduction at 500?.The TG-DTA analysis of several catalysts after the activity test showed that the additives Ca and La increased the amount of carbon deposits,the additives Mg and Mn could inhibit the formation of carbon deposits,and the additive Ce had no significant effect on the carbon deposits.The excellent physical and chemical properties of zirconium dioxide have potential for development in terms of catalyst support.A high specific surface area porous ZrO₂ support material was designed and prepared by the precipitation method,and the preparation process conditions were determined by orthogonal experiments.The sample was characterized by SEM,XRD,BET and other means,and the results showed that its fine particle size,loose surface and specific surface area could reach 214m2/g,which met the basic requirements of the carrier material.The crystallization kinetics of the precipitation process was measured by the conductivity method.The results show that the nucleation rate of the precipitation process is much higher than the crystal growth rate,and the nucleation is almost completed at the instant of mixing.It can be considered that the nucleation of the zirconium hydroxide crystals was only one nucleation during the experiment,and was not caused by the secondary nucleation.Therefore,the resulting product particles are small and have a large specific surface area.After evaluating the activity of the xNi/ZrO₂ catalyst,it was found that as the Ni loading increased,the selectivity of CH4 changed irregularly,but the CO conversion rate and CH4 yield showed a regular increase trend.The 40Ni/ZrO₂ catalyst with 40%Ni loading has the best comprehensive activity.Based on the 40Ni/ZrO₂ catalyst,three additives,Ce,Ca,and Mn,were added to study the effects of the additives and their additions on the catalyst activity.It was found that the activity of the catalyst added with Ce was increased,and the conversion of CO and the yield of CH4 were improved,but the effect of the amount of addition was not great.In comparison,40Ni/2Ce-ZrO₂ with an addition amount of 2%wt is slightly better than other ratios;The activity of the catalyst with the addition of Ca increased significantly,especially at low temperatures.Compared with the catalyst without additives,the CO conversion rate,CH4 yield,and CH4 selectivity increased significantly,but its high temperature activity was relatively poor.Judging from the above,40Ni/4Ca-ZrO₂ with an added amount of 4%wt is better than other ratios;The catalyst with the aid of Mn increased its high-temperature activity significantly.Compared with the catalyst without the aid of Additives,the CO conversion,CH4 yield,and CH4 selectivity increased significantly at high temperatures.There were also differences in the amounts added.40Ni/6Mn-ZrO₂ with an added amount of 6%wt is superior to other ratios.Comparing the three cocatalysts,Ca increased the low-temperature activity of the 40Ni/ZrO₂ catalyst,Mn increased the high-temperature activity of the 40Ni/ZrO₂ catalyst,and the effect of Ce was not as obvious as the other two.Finally,Three composite carriers of Al₂O₃-ZrO₂,CeO2-ZrO₂ and CaO-ZrO₂ were prepared by co-precipitation method.The methanation catalytic performance of three composite carriers of Al₂O₃-ZrO₂,CeO2-ZrO₂ and CaO-ZrO₂ at different ratios was preliminarily investigated-The results showed that the activity of Al₂O₃-ZrO₂,CeO2-ZrO₂ composite carriers was higher than that of a single ZrO₂ carrier,but CaO-ZrO₂ did not show any superiority.In comparison,9CeO2-ZrO₂ has better performance in a variety of different ratios.