Boosting N 2 Conversion into NH 3 over Ru Catalysts via Modulating the Ru-Promoter Interface.

Promoters are indispensable components of Ru-based catalysts to promote N 2 activation in ammonia (NH 3 ) synthesis. The rational addition and regulation of promoters play a critical role in affecting the NH 3 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 NH 3 synthesis rate. The Ba-Ru/GC BM catalyst via the prior loading of Ba rather than Ru over graphitic carbon (GC) exhibits a high NH 3 synthesis rate of 18.7 mmol g cat -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 N 2 activation. Additionally, the intimate Ba and Ru interface enables facile electron donation from Ba to Ru sites, thus accelerating N 2 dissociation to realize efficient NH 3 synthesis. This work provides a simple approach to modulating the Ru-promoter interface and maximizing promoter utilization to enhance NH 3 synthesis performance.