Methanation Of Carbon Di-Oxides Over Ordered Mesoporous Alumina Supported Ni Catalysts

The carbon-rich fossil fuels consumption is the largest proportion in the energy consumption of the world.As a result,a large amount of carbon dioxide is released into the atmosphere,causing a series of environmental problems,such as global warming,glacier melting,sea level rise and so on.Therefore,it is urgent to reduce the concentration of CO₂ in the atmosphere.In the process of CO₂ methanation,Ni-based catalysts tend to be deposited with carbon and Ni nanoparticles in the active phase may aggregate into larger particles,which result in decreased CO₂ conversion and product selectivity.On the basis of an in-depth understanding on the mechanism of carbon dioxide methanation,this thesis investigates the application of different carriers Ni and rear earth elements promoters loading amounts for carbon dioxide methanation from the perspectives of controlling the pore size of mesoporous carriers,as well as the content of the Ni and rear earth elements promoters.The main contents are as follows:1.Ordered mesoporous alumina carrier are prepared using the evaporation induced self-assembly method?EISA?for the loading of different content of Ni catalyst?i.e.,the molar ratio of Ni/Al?,toward the catalyic carbon dioxide methanation reaction.The samples are characterized with XRD,BET,H₂-TPR,CO₂-TPD and TEM for the analysis of the structure reactivity of the catalysts.The results showed that increasing the molar ratio of Ni/Al could significantly increase the methanation activity of CO₂,while the increases of the molar ratio of Ni/Al and the methanation are not linear.2.On the bass of the first part of work,we explored the influence of the addition of rare earth on the catalytic performance of the catalyst.Ce was fist chosen to added into the catalyst,for the investigation of the content of additives on the catalytic performance of the catalyst by adjusting the content of Ce,namely n _Ce/n _Al.The results showed that the addition of Ce additive to the 10Ni/OMA catalyst significantly increased the alkalinity of 10Ni/OMA,which also promoted the adsorption of CO₂ on the surface of the catalyst,thus improved the activity of the catalyst.When n _Ce/n_Al=0.05,the performance of the catalyst is the best.Excessive Ce were added to the 10Ni/OMA catalyst,leads to the cera covered the active phase of Ni on the surface,which results in a decrease in the activity of Ni compared to the surface area.The influence of different rare earth auxiliaries?Ce,La,Nd,Y?on the methanation activity of 10Ni/OMA catalyst CO₂ was also investigated.The results showed that the activity sequence of the modified catalyst follows the order:5Ce-10Ni/OMA?29?5Nd-10Ni/OMA?29?5Y-10Ni/OMA?29?5 La-10Ni/OMA.3.Controlling the pore effect of ordered mesostructure is one of the effective strategies to improve the activity and stability of the catalysts.The 5Ce-10Ni/OMA,5Ce-10Ni/?-Al₂O₃ and 5Ce-10Ni/NPA catalysts were prepared to study the influence of carrier structure and morphology on catalyst activity.The activity sequences of the catalyst toward the methanation of CO₂ is as follows:5Ce-10Ni/OMA?29?5Ce-10Ni/?-Al₂O₃?29?5Ce-10Ni/NPA.In the 5Ce-10Ni/OMA catalyst,TEM results show that the ordered mesoporous catalyst could control the active metal nanoparticles as well as prevent the metal particles from sintering.Moreover,high specific surface area can form highly dispersed active metals,which can obtain high catalytic activity.