Methanation of CO2 over alumina supported nickel or cobalt catalysts: Effects of the coordination between metal and support on formation of the reaction intermediates

This study focused on the potential coordination between nickel or cobalt and alumina in Ni/Al2O3 and Co/Al2O3 catalysts and the impacts on their catalytic performances in methanation of CO2. The results exhibited that Co/Al2O3 catalyst was far more active than Ni/Al2O3 catalyst, due to the varied reaction intermediates formed in methanation. The DRIFTS results of methanation of CO2 exhibited that, over bare alumina, bicarbonate, formate and carbonate were the main intermediate species, which could be formed at even 80 degrees C. Over unsupported Ni catalyst, the formaldehyde species (H2CO*) and CO* species were dominated. Over the Ni/Al2O3 catalyst, however, the reaction intermediates formed were determined by alumina and accumulated on surface of the catalysts. The coordination effects between nickel and alumina in Ni/Al2O3 were thus not remarkable in terms of enhancing catalytic activity when compared to that in Co/Al2O3 catalyst. Over unsupported Co catalyst and the bare alumina, the reaction intermediates formed were roughly similar. Nevertheless, the combination of Co and alumina in Co/Al2O3 catalyst could effectively facilitate the conversion of bicarbonate, formate and carbonate species. CO2 could be activated over metallic cobalt sites, which could migrate and integrate with the hydroxyl group in alumina to form bicarbonate and further to formate and CO* species, and be further hydrogenated over cobalt sites to CH4. Such a coordination between alumina and cobalt species promoted the catalytic performances. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.