Participation of surface bicarbonate, formate and methoxy species in the carbon dioxide methanation catalyzed by ZrO2-supported Ni

- ZrO2-supported nickel is active for CO2 methanation at atmospheric pressure.
- CO2 is activated on the support in the form of bicarbonate and carbonate species.
- H2 is dissociated on Ni particles and spills over to the support.
- Bicarbonate species are hydrogenated on ZrO2 to give formate and methoxy species.
- Formate and methoxy species are intermediates to the formation of methane.

ZrO2-supported Ni samples were prepared by an impregnation method and tested as catalysts for CO2 methanation. Infrared spectra recorded during catalysis show that CO2 was initially adsorbed in the form of carbonate and bicarbonate species bonded to sites of the support. The data indicate that bicarbonates were hydrogenated to give surface formate species, which reacted with H2 at increasing temperature and led to the formation of methane, as evidenced by changes in the mass spectral signal of methane in the effluent gases from a flow reactor/DRIFT cell. No surface carbonyls were observed during the reaction. Separate experiments in which the catalysts were tested for the hydrogenation of methanol and formic acid also show their activity towards methane formation. In both cases, surface methoxy species bonded to Lewis acid sites of ZrO2 were identified. Our results indicate a bifunctional character of the ZrO2-supported Ni catalysts for CO2 methanation, with the CO2 being activated on sites of the support and the role of Ni consisting on providing sites for hydrogen adsorption and dissociation.

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