Enhanced activity of CO2 methanation over Ni/CeO2-ZrO2 catalysts: Influence of preparation methods

A series of nickel catalysts supported on CexZr1-xO2(CZ) were prepared by ammonia evaporation (AE), impregnation (IMP) and deposition–precipitation (DP) methods. Their performances for CO2 hydrogenation to methane were investigated at reaction temperatures between 200 and 350 °C. Among the catalysts tested, the Ni/CZ (Ni/CZ-AE) catalyst prepared via AE method gave superior catalytic performance at comparatively lower reaction temperatures. At 275 °C, it can attain a maximum CO2 conversion and methane selectivity of 55% and 99.8%, respectively and it is stable for nearly 70 h reaction time. The better catalytic performance of Ni/CZ-AE is due to the ability of the catalyst to be activated at low temperatures. XPS results for Ni/CZ-AE catalyst shows that some of Ni species are well incorporated into CeO2 lattice of CZ support, resulting in the imbalance of electric charge and lattice distortion of CeO2. Thus, oxygen vacancies can be generated, allowing for adsorption of oxygen species on these vacancies. This finding correlates well with the H2-TPR and CO-TPR results, which demonstrated the shifting of the reduction temperature towards lower temperature ranges than bare CZ support with the incorporation of Ni in Ni/CZ-AE catalyst. DRIFTS experiments for CO2 hydrogenation reaction revealed that the methane formation is via CO free mechanism i.e, formation of carbonates and formate species which are further hydrogenated and decomposed directly to release methane.