Methanation of carbon monoxide and carbon dioxide on Ni/Al2O3 catalysts: effects of nickel loading

The effects of weight loading on the adsorption and reaction properties of Ni/Al2O3 catalysts were studied for CO and CO2 hydrogenation by temperature-programmed reaction (TPR). The role of the support, which interacts sufficiently strongly with nickel ions during preparation so that reduction to the metal is more difficult, is to create two distinct reaction sites for methanation, i.e. nickel crystallites and less reactive nickel atoms surrounded by oxygens of the alumina lattice. Both sites are present at Ni loadings from 1.8–15%, but the fraction of the less reactive sites is much larger at lower Ni loadings. Methane from both sites is seen in TPR of CO adsorbed at 298 K and of CO2 adsorbed at 473 K. Thus, methanation of CO and of CO2 (following activated adsorption) proceed by the same mechanism on each type of site on Ni/Al2O3. Methane from the more reactive nickel crystallites is not seen in TPR of CO2 adsorbed at 298 K because CO2 adsorption is activated on nickel and because of competition with H2 for these sites.