Effect of the nature of the support, operating and pretreatment conditions on the catalytic performance of supported Ni catalysts for the selective methanation of CO

The catalytic activity of supported Ni (5 wt.%) catalysts for the selective methanation of CO in the presence of excess CO2 has been investigated with respect to the nature of the support, operating and pretreatment conditions employed. It has been found that catalytic activity of Ni depends appreciably on the nature of the support. The specific reaction rate (TOF) for CO hydrogenation increases by 2 order of magnitude in the order of Ni/CeO2 < Ni/Al2O3 < Ni/YSZ < Ni/ZrO2 < Ni/TiO2. The effect of the nature of the support is less pronounced for the CO2 hydrogenation with specific activity being one order of magnitude higher when Ni is supported on ZrO2 compared to CeO2, whereas Ni/TiO2, Ni/YSZ and Ni/Al2O3 exhibit intermediate performance. Results provide evidences that the performance of 5%Ni/TiO2 catalysts can be improved by optimizing operating and/or pretreatment conditions. In particular, catalytic activity for both CO and CO2 hydrogenation reactions can be increased with decreasing the gas hourly space velocity. The improvement is lower for the CO2 methanation, thus, expanding the temperature window for the selective methanation of CO. It has been found that increase of the in situ reduction temperature or time prior to catalytic performance tests results in an increase of the CO2 methanation reaction rate, whereas CO hydrogenation remains practically unaffected. DRIFT results showed that the relative population of reactive surface species (Ni carbonyls) for the CO methanation reaction are not affected by varying pretreatment conditions. However, population of reactive surface species (formates) for the CO2 methanation increases under prolonged reduction of catalyst. Therefore, mild in situ reduction conditions of Ni/TiO2 catalyst are required in order the selective methanation of CO to be operable in a wide temperature range.