Enhanced ammonia synthesis performance of a ceria-supported bimetallic catalyst by changing Co and Mo segregation

Abstract

The development of a Co–Mo bimetallic catalyst played a crucial role in ammonia synthesis. However, its underlying mechanism is not well understood and the optimal catalyst has yet to be obtained. Herein, we designed two methane-treated ceria-supported Co–Mo bimetallic catalysts with different dispersions and segregations of Mo and Co species by changing the order of addition of Mo and Co species. There is the segregation of Mo and Co species on the surface of the catalyst with the subsequent addition of Co and Mo species (Mo/Co–C), leading to a higher proportion of low oxidation states of Mo species as well as a larger amount of exposed Mo and Co species, oxygen vacancies and concentration of Ce³⁺. As a result, there is a larger amount of nitrogen and hydrogen species adsorbed on Mo/Co–C, and the migration and exchange of the adsorbed hydrogen species are also boosted. Mo/Co–C shows 1.7 times higher ammonia synthesis activity and a superior pressure effect in ammonia synthesis than its counterpart obtained by the simultaneous addition of Co and Mo species. These findings are essential for the further development of bimetallic catalysts.