Facile and direct approach to synthesize nitride based catalysts for ammonia synthesis

Nitride based catalysts have recently emerged as efficient non-precious metal catalysts for ammonia synthesis, overcoming traditional scale-relationship limitations. However, their synthesis is often hindered by high moisture sensitivity, and the use of toxic reagents presents both procedural and environmental challenges. In this study, we introduce an innovative argon plasma sputtering method to tackle the above challenges for the fabrication of nitride based catalysts. This self-created approach enables the direct use of as-prepared catalysts in ammonia synthesis, eliminating the need for additional reduction steps and streamlining the process from synthesis to application, and more importantly, the Ni nanoparticles exhibit smaller sizes (4.04 nm) compared to those produced by chemical vapor deposition, with no aggregation observed after ammonia synthesis. Additionally, a time delay was demonstrated via in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) between nitrogen adsorption and conversion, partially supporting the “dual active site” concept. The rate-determining step of the ammonia synthesis reaction is supposed not to be nitrogen activation but rather the subsequent hydrogenation of nitrogen species or the desorption of NH₃. These findings highlight the advantages of the sputtering method and present a promising and environmentally friendly approach to developing heterogeneous catalysts for ammonia synthesis.