Optimization of Ruthenium Particle Size and Ceria Support for Enhanced Activity of Ru/CeO2 Cluster Catalysts in Ammonia Synthesis Under Mild Conditions

To meet the increasing demand for small-scale NH 3 production, catalysts that work under milder conditions than those of the Haber–Bosch process are essential. In this study, Ru clusters and nanoparticles were impregnated on five different CeO 2 supports to prepare Ru/CeO 2 catalysts for NH 3 synthesis at 400 °C and 0.1 MPa. The basicity of the CeO 2 support and Ru particle size significantly influenced the catalytic activity. The catalytic activity increased with decreasing Ru particle size, reaching the maximum of ~ 200 mmol g Ru −1 h −1 at ~ 1 nm, which is ascribed to a high proportion of unique active sites different from the B 5 -type sites. Our findings demonstrate that Ru cluster catalysts are advantageous over Ru nanoparticle catalysts for NH 3 synthesis. Graphical Abstract