Hydrogen-Reduced LaNiO3 for Ammonia Synthesis

Abstract

In this study, oxygen-deficient LaNiO3–x was synthesized through noncontact reduction using hydrogen released from CaH2, and its catalytic performance for thermocatalytic ammonia synthesis was evaluated. The reduction process removes lattice oxygen without detectable hydride incorporation, generating electron-rich oxygen-vacancy sites in the nickelate lattice. These vacancies facilitate N2 activation and, at the same time, promote the migration and exsolution of lattice Ni under ammonia synthesis conditions. The resulting catalyst evolves into a defect-rich oxide-supported Ni system, in which oxygen vacancies mainly contribute to N2 activation and defect-assisted Ni exsolution, while exsolved Ni nanoparticles provide metallic sites for H2 activation and subsequent hydrogenation. This coupled defect–metal interaction, rather than the simple coexistence of oxygen vacancies and Ni nanoparticles, accounts for the enhanced catalytic activity and durability. The present work therefore highlights defect-assisted metal exsolution as an effective strategy for constructing bifunctional perovskite-derived catalysts for ammonia synthesis under relatively mild conditions.