Insights into the mechanism of plasma pretreatment-enhanced ammonia decomposition kinetics from a lattice-mediated perspective

Abstract

Fe, Co, Ni and other transition metal-based catalysts are widely applied in the catalysis field due to their unique d-orbital electronic configurations. However, transition metal/oxide catalysts face challenges such as metal particle aggregation and insufficient intrinsic activity during thermocatalytic ammonia decomposition reaction (ADR), which significantly limits their practical applications. Herein, we propose a high-energy ammonia plasma pretreatment strategy to disperse aggregated metal particles and introduce nitrogen-containing intermediates (such as NH and NH₂) into the catalyst lattice. This approach is designed to increase the exposure of active sites and regulate the dehydrogenation and NN recombination pathways in the ADR via NH_x groups within the catalyst. The regulation method introduced NH and NH₂ intermediates, significantly enhancing the catalyst's ammonia decomposition performance. Results demonstrated that at 650℃ under a gas hourly space velocity (GHSV) of 9552 h⁻¹, the ammonia plasma-pretreated catalyst (Ni/Al₂O₃-PT) exhibited an 11 % higher conversion rate compared to the untreated Ni/Al₂O₃ achieving a hydrogen production rate of 6.59 mmol·g⁻¹_cat·min⁻¹ (versus 5.97 mmol·g⁻¹_cat·min⁻¹ for Ni/Al₂O₃). When the GHSV was increased to 19104 h⁻¹ at 550℃, Ni/Al₂O₃-PT showed a 16 % higher conversion rate than Ni/Al₂O₃. Long-term stability tests conducted over 50 h confirmed the excellent operational stability of the Ni/Al₂O₃-PT catalyst. Our work presented an efficient solution to the challenges of transition metal-based catalysts while providing a theoretical framework for novel catalyst design through a lattice-mediated intermediate evolution model.