Atomic layer deposition of Ru nanoclusters on Ba–LaCeOx: a highly efficient catalyst for ammonia synthesis under mild conditions†

Ammonia synthesis has significant implications for global energy and environmental issues, driving the need for highly active catalysts that operate under mild conditions. This study reports the successful deposition of uniform ∼1.0 nm metallic ruthenium (Ru) nanoclusters onto Ba–LaCeO_x particles via atomic layer deposition (ALD). The catalytic performance of the ALD-prepared Ru nanoclusters was assessed for ammonia synthesis and compared with two catalysts produced by conventional incipient wetness impregnation. For the ALD-prepared Ru nanoclusters, a pre-reaction H₂-reduction step induced partial encapsulation of suboxide species on Ru sites due to strong metal–support interactions, limiting Ru nanocluster sintering and maintaining a reduced Ru size of 1.7 nm. The electron donation from the reduced support to Ru sites imparted an electron-rich character, which facilitated the weakening of the NN bond and promoted the rate-determining step of ammonia synthesis. The ALD-Ru catalysts exhibited competitive ammonia synthesis activity under milder conditions, compared to the impregnated catalysts, with a lower requirement for initial reaction temperature. These results highlight the potential of ALD-synthesized Ru nanoclusters as highly efficient catalysts for low-temperature ammonia production, offering a promising avenue for advancing ammonia synthesis technologies.