Degradation Factors of Ni/TiO₂ Catalysts for Selective CO Methanation: Effect of Loss of Residual Cl on Catalyst

Abstract

Accelerated deterioration tests for selective CO methanation over Ni/TiO₂ catalysts were performed to investigate the catalyst degradation factors. The accelerated deterioration test treated the catalyst in the reaction gas flow at the specified temperature (200, 250 or 300 °C) for 24 h. After the accelerated deterioration test, the Ni/TiO₂ selectivity in CO methanation was reduced due to the enhancement of an undesirable reverse water-gas shift reaction. Powder X-ray diffraction found no change in the TiO₂ structure between the fresh and spent catalysts. In-situ X-ray absorption spectroscopy demonstrated that the Ni species reduced by H₂ were present as metallic Ni and remained unchanged in the fresh and spent catalysts. The number of surface Cl species for the spent catalyst was much smaller than that for the fresh catalyst. Therefore, disappearance of surface Cl components during the accelerated deterioration test caused the degradation of Ni/TiO₂ catalysts for selective CO methanation.