Geometry-Dependent Electronic Structure for Enhanced Ammonia Synthesis: From Nanoparticle to Nanosheet and Metallene.

Developing highly effective catalysts for ammonia (NH3) synthesis under mild conditions remains a challenging task. The active metals employed in catalysts are predominantly presented as zero-dimensional nanoparticles, which limits their capacity to fully exploit atoms and electrons, resulting in unsatisfactory activity. Herein, we present triangular Ru nanosheet that features a two-dimensional structure characterized by a hexagonal close-packed atomic arrangement. The thickness of the Ru nanosheet is further tailored down to angstrom level, yielding Ru metallene. In contrast to Ru nanoparticles or regular nanosheet, our studies demonstrate that the unique geometric configuration of Ru metallene substantially stabilizes metallic Ru0 active sites enriched with abundant 4d electrons. Therefore, atomically thin Ru metallene delivers a high NH3 synthesis rate of 70.7 mmol gcat-1 h-1 at 400 °C and 1 MPa, surpassing Ru nanoparticles or nanosheets. This synthetic approach is broadly applicable to other transition metals (e.g., Fe and Mo). This work provides a new route for angstrom-level geometric engineering for NH3 synthesis catalysts.