Activity enhancement of ceria-supported Co-Mo bimetallic catalysts by tuning reducibility and metal enrichment

The development of efficient oxides-supported bimetallic catalysts is critical for ammonia synthesis or other catalytic reactions. Herein, the design of ceria-supported Co-Mo bimetallic catalysts with different properties is performed by changing Mo addition to enhance the ammonia synthesis activities. It is found that the reduction of ceria and molybdenum oxide would be boosted by Co species, but the reduction of the bimetallic catalyst would be inhibited by the aggregated molybdenum oxide for the catalyst with Co and Mo simultaneous addition. On the contrary, this ill effect of molybdenum oxide on the reduction of the bimetallic catalyst can be effectively alleviated by the subsequent addition of Mo species to ceria-supported Co catalyst, resulting in enhancement of the proportion of Co metal, Ce3+ and low-valent Mo species, as well as surface enrichment of Co species. In such cases, the amount of the adsorbed hydrogen and nitrogen species would increase, and hydrogen species preferentially desorbs following a pathway of H2 formation. As a result, the catalyst obtained by the separate addition of Co and Mo shows 2.5-fold more active than its counterpart with the simultaneous addition of Co and Mo species. These findings provide a valuable insight in designing reducible oxide-supported bimetallic catalysts in ammonia synthesis or other hydrogen-involved reactions.