Study On Preparation, Characterization And Catalytic Performance Of Ni Based On Mesoporous SiO₂Methanation Catalysts

Basic energy landscape of China is characterized by " rich in coal, poor in oil and natural gas". Coal to Synthetic Natural Gas can not only realize the clean use of coal resources, but also meet the constant demand for natural gas in China. Syngas methanation is one of the key processes and the development of methanation catalyst is the key of this technique.In this paper, the methanation catalyst with nickel as the active component were prepared by the impregnation method and hydrothermal synthesis method, respectively, and its catalytic activity, high temperature performance and carbon performance were tested in a fixed bed reactor. The effect of Mo on structures and properties of catalysts were also studied and the better methanation catalyst was selected. At last, methanation kinetics based on Ni-0.5%Mo-SiO2catalyst was studied.The nickel based catalysts with different nickel content were prepared by the impregnation method with MCM-41, Al2O3and SiO2as the supports. The catalysts were characterized using XRD, BET, TG and H2-TPR and the results showed that the Ni particle size could obviously affect the catalytic performances of the catalysts and Ni/MCM-41showed better catalytic performance. The effect of Ni content on the catalytic performance of Ni/MCM-41was investigated and it was found that the catalytic activity of Ni/MCM-41increased with Ni loading increasing and kept stable with the Ni loading of above10mol%.10%Ni/MCM-41showed a high CO conversion of100%and a CH4yield of95%at350℃under1.5MPa and12000ml·h-1·g-1with a3:1molar ratio of H2to CO and it also exhibited excellent catalytic activity and stability in the catalytic stability test.Several Ni-Mo based catalysts with Mo content from1mol%to7mol%were prepared by the impregnation method with MCM-41as the support and the effect of Mo content on the catalyst activity was investigated. The addition of MoO3could obviously improve the activity of Ni/MCM-41at250℃. Ni-3%Mo/MCM-41showed the best activity with a CO conversion of100%and a CH4selectivity of94%at350℃under1.0MPa and12000ml/g/h with a3:1molar ratio of H2to CO. Compared with Ni/MCM-41, Ni-Mo/MCM-41showed higher resistance to sintering and no decrease in the catalytic activity after calcination at700℃for2h. In the100h stability test, CO conversion and CH4selectivity obtained on Ni-3%Mo/MCM-41maintained at about100%and89%, respectively, suggesting an excellent catalytic stability of this catalyst. The catalysts were characterized by different technologies, and the results showed that electron transfer from MoO3to metal nickel was the main cause of activity improvement of Ni-Mo/MCM-41at250℃. The addition of MoO3could enhance the interaction between metal nickel and the support in the way of Ni-Mo alloy, which inhibited the catalyst sintering.Several nickel incorporated MCM-41catalysts with a nickel molar content from1%to10%were prepared by a hydrothermal synthesis method, and characterized by FTIR, ICP, XRD, H2-TPR, TG-DTA and TEM. The results showed that mesoporous structure of MCM-41still maintained well when Ni molar content was up to10%.10%Ni-MCM-41showed the best catalytic activity with a high CO conversion of almost100%, and a CH4yield of96%at350℃with3:1molar ratio of H2to CO under1.0Mpa and12000ml/h/g. Compared with10%Ni/MCM-41,10%Ni-MCM-41showed a higher resistance to sintering and no decrease in catalytic activity after calcination at700℃for2h. In the100h stability test, CO conversion and CH4yield obtained on10%Ni-MCM-41maintained at about100%and82%, respectively, suggesting an excellent catalytic stability. The results of XRD, H2-TPR and TG-DTA showed that there was a strong interaction between the Ni species and the support, which inhibited the catalyst sintering.Several Ni incorporated SiO2catalysts with MoO3molar content in range of0.5%to5.0%were prepared by the hydrothermal synthesis method. MoO3can significantly improve the activity of Ni-SiO2due to electron transfer from MoO3to Ni species, while excessive MoO3(>3.0mol%) will reduce the catalyst activity due to partial coverage of active metal by MoO3and formation of Ni-Mo alloy. Ni-0.5%Mo-SiO2achieves the best activity with100%CO conversion and about99%CH4yield at400℃,2.0MPa and12000mL/g/h. The results of TG and TPR show that MoO3can inhibit carbon deposition of Ni-SiO2and excessive MoO3(>1.0mol%) will weaken the interaction between metal Ni and the support. The results of XRD, TPR and TG show that catalyst sintering rather than carbon deposition leads to catalyst deactivation in catalytic stability and thermal stability tests.Based on the Ni-0.5%Mo-SiO2catalyst, the intrinsic kinetics of CO methanation reaction were measured in a differential reactor at250～450℃and0.1～1.5MPa.The measured kinetics experimental data of methanation reaction is proved reliable. Hyperbolic functional was adopted as the reaction kinetics model and the best fitting model was obtained after several model fitting. The results of residual test, statistical testing and Arrhenius relationship test model showed that the kinetics model fits well and the residual distribution is reasonable. It can truly reflect the response characteristics of the catalyst. The dynamic expression is:...