Co/CeO2 and Ni/CeO2 catalysts for ethanol steam reforming: Effect of the cobalt/nickel dispersion on catalysts properties

Abstract

The Co/CeO2 and Ni/CeO2 catalysts were obtained by impregnation method with using different active phase precursors, different impregnation solvents and in presence of organic additive in order to improve cobalt/nickel dispersion and metal-support interaction. An addition of citric acid to precursor metal salt solution allowed to obtain their better dispersion and smaller metal particle size of Co/CeO2 and Ni/CeO2 samples. Whereas catalysts obtained from ammonia solution exhibited the largest size of metal particles. The key step for steam reforming of ethanol at 420 °C over both Co/CeO2 and Ni/CeO2 catalysts is ethanol dehydrogenation which occurs preferentially on cobalt/nickel terrace sites. But efficiency to cleavage C─C bond is favored by the edge/steps sites. Because nucleation of carbon requires relative large domains of flat terraces or larger ensemble sizes, the terrace atoms are involved in the catalyst deactivation under SRE conditions. Whereas the increase in fraction of edge and corner, i.e. better dispersion and strong metal-oxide interactions between metal and ceria could enhance the transfer of oxygen and thus improve the oxidation of carbon formed on the catalysts surface under SRE conditions. Catalytic performance of Ni/CeO2 catalysts in SRE reaction depends on the nickel crystallite size. Whereas catalytic performance of Co/CeO2 catalysts in SRE reaction is related to combination of cobalt crystallite size dependence and the oxidation state of the cobalt nanoparticles.