Study On Stability Of Alkaline-earth Oxide Modified Ni-based Catalysts For CO Methanation

Natural gas is widely used as a clean and efficient energy.Methanation reaction of syngas from coal for the production of SNG(substitute natural gas)is considered as an efficient methond for the use of coal,and can also solve the shortage of natural gas in China.Development of high-performance methanation catalyst is one of the core technologies in the coal to SNG.Ni-basesd catalyst has been investigated in the CO methanation on account of its low cost and high catalytic activity.Aiming to improve the hydrothermal stability and resistance to carbon deposition of supported Ni catalysts,the relation between the performance and structure of Ni/Al2O3,Ni-Fe/La2O3-Al2O3 and the alkaline-earth oxides modified catalysts were studied via the techniques such as N2-physisorption,XRD,H2-TPR,O2-TPO,UV-Vis DRS,SEM,TEM.The main results are as follows:(1)A series of Ni/Al2O3 catalysts modified with 3 wt.%alkaline-earth oxide(MgO,CaO,SrO,BaO)were prepared by co-precipitation.Among them,Ni/SrO-Al2O3 sample showed a better catalytic activity and hydrothermal stability for CO methanation.This is due to a smaller size of Ni metal crystallite in Ni/SrO-Al2O3 sample,and the introduction of SrO can also weaken the strong metal-support interaction.(2)SrO promoter trends to combine with Al2O3 to form SrAl2O4.In the Ni/5SrO-Al2O3 catalyst with 5 wt.%SrO,SrAl2O4 subcrystalline is highly dispersed on support,which leads to well-dispersed Ni metal and support,a larger surface area and an improvement in hydrothermal stability.The CO was conversed completely at 350 ?over Ni/5SrO-Al2O3-HT catalyst,which suffered from hydrothermal treatment at 800 ? for 20 h in a stream of H2O(g)/H2=2:1,GHSV 120,000 mL·h-1·g-1.Furthermore,Ni/5SrO-Al2O3 showed better stability at 700 ? in a feed gas of low H2/CO molar ratio(H2/CO=2:1).The deactivation of Ni/5SrO-Al2O3 is related to the amount of C? and C?carbon species on the surface.(3)MgO doped Ni-Fe/La2O3-Al2O3 catalysts were prepared by impregnation.Compared to unmodified Ni-Fe/La2O3-Al2O3 catalysts,the catalyst modified by 5 wt.%MgO showed better catalytic activity and hydrothermal stability for CO methanation.It also exhibited excellent resistance to coke deposition.This is maybe related to a decrease in surface acidity of catalyst after doping with MgO.