ZrO2 support imparts superior activity and stability of Co catalysts for CO2 methanation

Screening of various supports reveals that Co catalysts supported on ZrO2 and Al2O3 show good initial activity for CO2 methanation. Co/ZrO2 and Co/Al2O3 catalysts prepared by impregnation with different metal loadings were further examined comparatively. The 10Co/ZrO2 catalyst showed high activity with CO2 conversion of 92.5% and CH4 selectivity of 99.9% without deactivation after 300 h time on stream (TOS). However, the 10Co/Al2O3 catalyst gave a lower CO2 conversion of 77.8% which decreased to 38.6% after 300 h TOS. The catalysts were characterized by STEM/EDS (scanning transmission electron microscopy/energy-dispersive X-ray spectroscopy), in situ XRD(X-ray diffractometer), H2-TPR(temperature programmed reduction), XPS (X-ray photoelectron spectroscopy), chemisorption of H2, CO, CH4, CO2 and NH3-TPD (temperature programmed desorption). Re-dispersion of Co species on the ZrO2 support during reduction by H2 was observed by STEM/EDS. New Co-Zr phase formed on the Co-ZrO2 interface was directly observed by TEM for the first time; the Co/ZrO2 catalyst exhibited high stability with high activity for CO2 conversion. In situ XRD, H2-TPR and XPS results indicate the promoting effect of ZrO2 on the reduction of Co3O4 to Co metal along with the negative effect of Al2O3. The oxygen vacancies on the ZrO2 detected by XPS may help to activate CO2 and H2O and resist deactivation. Co/Al2O3 catalyst deactivates rapidly due to coke deposition and spinel formation.