Promoting effect of alkaline earth metals on Ni/CeO2 catalysts for ammonia decomposition reaction

Abstract

Ni-based catalysts, as non-noble metal alternatives, are widely regarded for their potential in ammonia decomposition for hydrogen production. However, their performance at low temperatures is suboptimal, necessitating the addition of promoters and a clear understanding of their mechanisms to enhance catalytic activity. In this study, we have successfully improved the low-temperature ammonia decomposition performance of Ni/CeO₂ by incorporating alkaline earth metals and conducted a comprehensive analysis of the underlying structural and electronic effects. The findings reveal that alkaline earth metals can enhance the basicity of the catalyst and increase electron density around the active metal sites, thereby facilitating the rate-determining step of recombination and desorption of N atom. Moreover, the presence of alkaline earth metals disrupts hydrogen adsorption stability on the catalysts, effectively mitigating the impact of hydrogen inhibition. Based on systematic kinetic experiments, a kinetic model was developed that accurately captures the hydrogen inhibition effect for Ni/CeO₂ catalysts. The insights into the promotional mechanisms of alkaline earth metals offer theoretical guidance for the development of highly active and cost-effective catalysts for ammonia decomposition.