Promoters are indispensable components of Ru-based catalysts to promote N2 activation in ammonia (NH3) synthesis. The rational addition and regulation of promoters play a critical role in affecting the NH3 synthesis rate. In this work, we report a simple method by altering the loading sequence of Ba and Ru species to modulate the Ru-promoter interface, thus significantly boosting the NH3 synthesis rate. The Ba-Ru/GC BM catalyst via the prior loading of Ba rather than Ru over graphitic carbon (GC) exhibits a high NH3 synthesis rate of 18.7 mmol gcat-1 h-1 at 400 °C and 1 MPa, which is 2.5 times that of the Ru-Ba/GC BM catalyst via the conventional prior loading of Ru rather than Ba on GC. Our studies reveal that the prior loading of Ba benefits the high dispersion of the basic Ba promoter over an electron-withdrawing GC support, and then Ba species serve as structural promoters to stabilize Ru with small particle sizes, which exposes more active sites for N2 activation. Additionally, the intimate Ba and Ru interface enables facile electron donation from Ba to Ru sites, thus accelerating N2 dissociation to realize efficient NH3 synthesis. This work provides a simple approach to modulating the Ru-promoter interface and maximizing promoter utilization to enhance NH3 synthesis performance.
Keywords: Ru-promoter interface; ammonia synthesis; loading sequence; particle size; promoter utilization.