Enhanced ammonia synthesis over barium cerate-supported cobalt catalyst by rare-earth element doping

Abstract

A series of BaCeO₃ doped with various rare-earth elements (REE = Nd, Sm, Gd) were synthesised and used as the supports for cobalt catalysts for ammonia synthesis. The effects of rare-earth dopant type and concentration on the physicochemical properties and catalytic activities were studied using, e.g., XRD, STEM-EDX, and TPD techniques. Catalyst testing revealed that the optimal doping concentration was 10 mol%, regardless of the rare-earth ion. Samarium was identified as the most effective dopant, followed by gadolinium and neodymium. The superior performance of the Co/BaCe_0.9REE_0.1O_3–δ catalysts was due to the incorporation of REE dopant into the BaCeO₃ structure, which increased the electron density, enabling efficient electron transfer from the support to the Co surface. This, in turn, facilitated the N₂ dissociative adsorption, recognised as the rate-determining step (RDS) of ammonia synthesis. In addition, the catalysts were characterised by favourable hydrogen adsorption properties (co-existence of weak and strong adsorption sites), contributing to the effective hydrogen activation under the reaction conditions. This study provides an effective approach for designing cobalt catalysts supported on perovskites, demonstrating their great potential as next-generation catalysts for ammonia synthesis.