Impacts of metal loading in Ni/attapulgite on distribution of the alkalinity sites and reaction intermediates in CO2 methanation reaction

Both metal sites and alkaline sites are essential parameters for a catalyst used in methanation of CO2. This study investigated the impacts of the relative abundance of metal sites and alkaline sites on the catalytic performances of nickel-based catalyst with attapulgite, a natural mineral, as the support. The results showed that the increase of nickel loading to attapulgite significantly decreased the abundance of alkaline sites, remarkably enhanced the catalytic activity, and suppressed the formation of CO. The in situ DRIFTS characterization of the CO2 methanation indicated that the alkaline sites favored formation of the oxygen-containing reaction intermediates such as CO∗, –OH, ∗CO2, formate, carbonate and bicarbonate species. In comparison, metallic nickel species promoted their further hydrogenation to form CH4. Besides the absorption/activation of ∗CO2 was more preferable on surface of metallic nickel, but not on the alkaline sites. The availability of the alkaline sites was not as important as the metallic nickel species for preparation of an efficient catalyst for CO2 methanation.