Sub-nanometer Ru clusters on Sm2O3 obtained from a room temperature ion adsorption method for ammonia synthesis

Abstract

Transition metal clusters often exhibit unexpected catalytic activities in chemical transformations owing to their unique electronic and geometric structures. Here, we adopt a facile and green approach to prepare highly dispersed sub-nanometer Ru clusters by manipulating adsorption of Ru³⁺ ions from RuCl₃ on the surface of Sm(OH)₃ at room temperature. The sub-nanometer Ru clusters on Sm₂O₃ (Ru/Sm₂O₃) exhibit greatly enhanced catalytic activity in ammonia synthesis relative to that of the Ru nanoparticle counterpart, and an ammonia synthesis rate of 22 570 μmol g⁻¹ h⁻¹ can be achieved at 400 °C under 1.0 MPa. Under reaction conditions, hydrogen induced structure evolution and in situ generation of surface Sm–H species on the Ru/Sm₂O₃ catalyst were identified. Mechanistic investigation indicates that the Sm–H species can promote the dissociation of nitrogen and lead to a much enhanced intrinsic activity of Ru clusters in the Ru/Sm₂O₃ catalyst for ammonia synthesis.