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

Screening of various supports reveals that Co catalysts supported on ZrO 2 and Al 2 O 3 show good initial activity for CO 2 methanation. Co/ZrO 2 and Co/Al 2 O 3 catalysts prepared by impregnation with different metal loadings were further examined comparatively. The 10Co/ZrO 2 catalyst showed high activity with CO 2 conversion of 92.5% and CH 4 selectivity of 99.9% without deactivation after 300   h time on stream (TOS). However, the 10Co/Al 2 O 3 catalyst gave a lower CO 2 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), H 2 -TPR(temperature programmed reduction), XPS (X-ray photoelectron spectroscopy), chemisorption of H 2 , CO, CH 4 , CO 2 and NH 3 -TPD (temperature programmed desorption). Re-dispersion of Co species on the ZrO 2 support during reduction by H 2 was observed by STEM/EDS. New Co-Zr phase formed on the Co-ZrO 2 interface was directly observed by TEM for the first time; the Co/ZrO 2 catalyst exhibited high stability with high activity for CO 2 conversion. In situ XRD, H 2 -TPR and XPS results indicate the promoting effect of ZrO 2 on the reduction of Co 3 O 4 to Co metal along with the negative effect of Al 2 O 3 . The oxygen vacancies on the ZrO 2 detected by XPS may help to activate CO 2 and H 2 O and resist deactivation. Co/Al 2 O 3 catalyst deactivates rapidly due to coke deposition and spinel formation.