In summary, we have comprehensively

In summary, we have comprehensively investigated the COmethanation on a series of Ni/Al2O3 catalysts synthesized bythe impregnation method for the production of SNG. It isfound that the physicochemical properties of NiO species in thecatalyst are strongly dependent on the nature of the support,the loading of NiO, the calcination temperature, and theexistence of MgO additive. In general, a large surface area ofAl2O3 support and a relatively strong interaction between NiOand Al2O3 promote the formation of small NiO particles andmore reducible β-type NiO species, which result in highcatalytic activity, strong resistance to the carbon deposition, andgood thermal stability. Particularly, a moderate NiO loading(20 wt %) and a relatively low calcination temperature (400°C) can produce a high density of reducible NiO on the S4Al2O3 support. In this catalyst, after the activation, relativelysmall-sized and highly active Ni0 particles are generated.Moreover, the addition of MgO (2 wt %) is proved to be anefficient measure to enhance the resistance to the carbondeposition, thus significantly increasing the stability of the Nicatalyst. Other conditions proved to enhance CO conversionand CH4 selectivity include running the reaction at a relativelylow GHSV of 30 000 mL/g·h, at a high pressure of 3.0 MPa,and a molar ratio of H2/CO more than 3:1. In addition,dilution of catalyst with quartz sand is favorable for COmethanation. The lifetime test shows that the synthesized 20 wt% NiO-2 wt % MgO/S4 catalyst calcined at 400 °C is highlyactive, thermally stable, and resistant to carbon deposition dueto its moderate interaction between NiO and Al2O3 supportand high density of reducible NiO. This work would thereforebe important for developing highly efficient Ni catalyst andmethanation process for SNG production and providesscientific understanding to the CO methanation reaction.