Synthesis And Performance Of Ni-M Bimetallic Catalysts For Methanation

The production of SNG(substitute natural gas)from coal is very essential according to the growing demand of natueral gas and the energy structure in China.Furthermore,the development of efficient methanation catalyst is one of the core techniques in the coal-to-SNG route.Nickel-based catalyst has been widely used in the CO methanation reaction because of its low cost and high catalytic properties,but its catalytic activity at low temperature and hydrothermal stability still need to be further improved.In this paper,the nickel-based catalyst and Ni-M(M=Co?Cr?Fe)bimetallic catalysts were prepared,using Al2O3 as the support.The catalytic activity for CO methanation was investigated in the fixed-bed reactor.And the physicochemical properties of the catalysts were investigated via the XRD?N2-physisorption?H2-TPR?UV-vis DRS?Raman and TEM techniques.The main results are as follows:(1)Compared with impregnation method,the Ni/Al2O3 catalyst prepared by coprecipitation exhibits the relatively high catalytic activity and hydrothermal stability for CO methanation,which could be due to the optimized texture,higher Ni dispersion,appropriate interaction between nickel metal and aluminum oxide support.(2)The sample with Ni/Co molar ratio of 8:2 shows better catalytic activity in the methanation of CO.In which,the synergistic effect between Ni and Co is advantageous to the reduction of the catalyst.Besides,the addition of a moderate amount of Co can improve the texture properties of catalyst,promote the dispersion of active component in catalyst,and increase the number of active sites of the bimetallic catalyst.(3)For the Ni-Cr/Al2O3 bimetallic catalysts modfied by different content of Cr,the formation of chromate species changs the interaction between metal Ni and carrier in the catalysts,thus improves the CO methanation activity of the catalysts at low temperature.The results show that the catalyst with Ni/Cr molar ratio of 9:1 has the better CO methanation catalytic activity.In addition,the addition of the second metal component Cr obviously inhibits the aggregation of metallic Ni grains in the high temperature steam atmosphere,thereby strengthens the hydrothermal stability of the catalyst.(4)The study indicates that the catalyst with Ni/Fe molar ratio of 8:2 shows better CO methanation catalytic activity,it can be attributed to the formation of Ni-Fe alloy.Meanwhile,the hydrothermal stability of Ni-Fe/Al2O3 catalyst is worse than Ni/Al2O3 sample.In orde to improve its stability,the Ni-Fe bimetallic catalyst is modified by La2O3 with varied contents.The results revealed that the 5 wt%La2O3-doping remarkably improves the texture of the Ni-Fe catalyst,and inhibits the phase transformation from ?-Al2O3 to ?-Al2O3 and the growth of Ni-Fe grain in the process of hydrothermal aging treatment.In general,the Ni8Fe2/5La2O3-Al2O3 catalyst displays excellent catalytic activity and hydrothermal stability.It also shows better sulfur-resistance in this work.