Ni-sepiolite and Ni-todorokite as efficient CO2 methanation catalysts: Mechanistic insight by operando DRIFTS

The hydrogenation of CO2 to methane was studied on Ni-sepiolite and Ni-todorokite catalysts. Catalytic testing and operando DRIFTS studies revealed the excellent performance of in particular todorokite-based catalysts. The catalytic activity is related to specific reaction pathways depending on the support material. Based on operando DRIFTS studies, different mechanisms are proposed for the methanation reaction. Over Ni-sepiolite catalysts, a dissociative adsorption of CO2 is observed. Linearly and bridged bonded CO on Ni-0 was identified as intermediate. On Ni-todorokite this dissociative mechanism is accompanied by an associative one. Here, carbonate species were identified as additional intermediates, the formation of which is facilitated by the MnOx support. The ability of Ni-todorokite catalysts to activate CO2 via a dissociative as well as an associative mechanism explains their excellent catalytic performance. The influence of the applied preparation method on the catalytic performance was demonstrated for the Ni-sepiolite catalysts.