Unravelling the Effects of Layered Supports on Ru Nanoparticles for Enhancing N2 Reduction in Photocatalytic Ammonia Synthesis

Abstract Harnessing the vast supply of solar energy as the driving force to produce ammonia from abundant nitrogen gas and water is beneficial for both relieving energy demands and developing sustainable chemical industry. Bulk carbon nitride (B-g-C3N4), exfoliated carbon nitride (E-g-C3N4) and graphite (g-C) supported Ru-K catalysts, denoted as Ru-K/B-g-C3N4, Ru-K/E-g-C3N4 and Ru-K/g-C, respectively, with the layered materials serving both as supports and light harvesters, were designed for photocatalytic ammonia synthesis. It was discovered that, besides the light harvesting properties of the catalysts which played roles in photocatalytic reactions, the structure of the supports influenced greatly the preferential locations of Ru species, which further exerted effects on the N2 activation process and ultimately impacted the ammonia production rate. The fine Ru nanoparticles uniformly and randomly dispersed on the monolayered E-g-C3N4 did not provide outstanding activity in ammonia photosynthesis; in contrast, Ru nanoparticles at the step edges of bulk g-C3N4 exhibited lower overall barriers for N2 activation and a much enhanced photocatalytic ammonia synthesis rate due to the synergy effects between metal and support as confirmed by density functional theory (DFT) calculations. The discovery of the relationship between reactivity and support geometry in this study will be important in guiding the rational predesign of efficient photocatalysts.