The critical role of La/Ce composition in Ni/Ce1-yLayOx catalysts: Optimizing oxygen vacancies and metal-support interactions for ammonia decomposition

Abstract

As a carbon-free hydrogen carrier, ammonia requires efficient decomposition catalysts to enable its practical use in hydrogen energy applications. In this study, a series of Ce_1-yLa_yO_x oxides with varying La/Ce molar ratios were synthesized via a citric acid method and utilized as supports for Ni-based NH₃ decomposition catalysts. The La/Ce molar ratio significantly influenced the catalytic performance, with Ni/Ce_0.5La_0.5O_x exhibiting the highest catalytic activity, achieving nearly 100 % ammonia conversion at 540 ℃ (GHSV= 9000 mL g_cat⁻¹ h⁻¹) and 600 ℃ (GHSV = 30000 mL g_cat⁻¹ h⁻¹). Various characterizations demonstrated that optimal La/Ce ratio promoted uniform dispersion of Ni nanoparticles (4.6 nm), maximizing available active sites for NH₃ adsorption. Moreover, the Ce_0.5La_0.5O_x support enriched the catalyst surface with high Ce³⁺ species and oxygen vacancies, facilitating electron transfer to Ni species. These electron-enriched Ni species significantly enhanced the cleavage of Ni-N bonds and facilitated the recombination of N adatoms, thereby boosting the overall reaction rate. This work provided fundamental insights into the critical role of metal-support electron transfer in optimizing catalytic performance for efficient ammonia decomposition, offering valuable guidance for the design of advanced hydrogen production catalysts.