Mechanistic study of the effect of chlorine on selective CO methanation over Ni alumina-based catalysts

•We clarified the controlling factor for the selective CO methanation.•CO2 hydrogenation over Ni/Al2O3 catalyst was significantly suppressed by chlorine.•Dissociation of CO2 on the catalyst was suppressed by chlorine.•Chlorine adsorbed on Ni site diminished the formation of carboxylate species.•The controlling factor for the selectivity should be the presence of chlorine on Ni.

The effect of residual chlorine of alumina-supported Ni catalysts on the selective CO methanation reaction was investigated. By chloride addition to the catalyst, CO2 methanation and the reverse water gas-shift reaction were significantly suppressed in the course of the reaction. FTIR measurements for CO2 adsorption on a series of modified catalysts with various chlorine-containing additives revealed that chlorine suppressed the dissociation of CO2 on the catalyst surface, which led to the formation of adsorbed CO species. The FTIR results combined with TPD measurements for CO2 desorption indicates that chlorine adsorbed on Ni metal diminished the formation of carboxylate species on the same surface under flowing CO2 conditions. Through the present study, the controlling factor for the selective methanation of CO by chlorine was clarified in high CO2 concentration-containing hydrogen rich gas.

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