Role of MgO and CaO promoters in Ni-catalyzed hydrogenation reactions of CO and carbon

Abstract The roles of Mg and Ca promoters in Ni-catalyzed hydrogasification of carbon were investigated with emphasis on nickel dispersion and nickel-carbon interactions during gasification. The dispersion of nickel on carbon, which was estimated by means of XRD, H 2 -TPD, and CO methanation test, was (Ni + Mg)a(Ni + Ca)>Ni. The increased dispersions of nickel by the Mg and Ca added were found to result in the enhanced NiC interaction, which was monitored through the desorption of CO from oxygen remaining on carbon, and, therefore, in the promotions of Ni-catalyzed lower-temperature gasification at 400 ≈ 700°C. The Ca promoter was likely to give surface CaO(OOO) species upon heating up to 550°C and release CO 2 above ≈650°C. The CO 2 released is efficiently converted by the nickel adjacent to CaO into CO to create Ni(OC species above 700°C, resulting in acceleration of Ni-catalyzed gasification above 700°C. In situ oxygen transfer to Ni/C during reaction is the most important role played by the Ca promoter.