ROLE OF MGO AND CAO PROMOTERS IN NI-CATALYZED HYDROGENATION REACTIONS OF CO AND CARBON

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, H2-TPD, and CO methanation test, was (Ni + Mg)å(Ni + Ca)>Ni. The increased dispersions of nickel by the Mg and Ca added were found to result in the enhanced NiC 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 CO2 above ≈650°C. The CO2 released is efficiently converted by the nickel adjacent to CaO into CO to create Ni(OC 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. © 1992.