Catalytic NH3/H2 co-combustion: A strategy for efficient and clean NH3 combustion

Abstract

Ammonia (NH₃) is a promising carbon-free fuel; however, its substantial nitrogen oxide emissions and low reactivity hinder its practical applications. These limitations can be addressed by enhancing NH₃ reactivity and nitrogen (N₂) selectivity via the addition of hydrogen (H₂) and use of catalysts. This study presents an investigation on the catalytic co-combustion of NH₃ and H₂ (NH₃/H₂ co-combustion) as a novel strategy for achieving an efficient and clean NH₃ combustion, providing valuable insights into the key design parameters for developing high-performance catalysts. Mechanistic studies using Chemkin-Pro demonstrated that the H₂ addition promotes radical-driven pathways, facilitating NH₃ activation and accelerating N₂ formation. A noble metal catalyst (1 wt% Pd/Al₂O₃) and three metal oxide catalysts (CuO, Mn₂O₃, and CeO₂) were evaluated for their catalytic performance in NH₃/H₂ co-combustion. Among the tested catalysts, CuO demonstrated superior catalytic performance, achieving 100 % NH₃ and H₂ conversion with nearly 100 % N₂ selectivity at 550 °C–800 °C, which was attributed to its enriched surface-adsorbed oxygen species and superior redox property. A comparative analysis of catalytic NH₃ combustion and NH₃/H₂ co-combustion further elucidated the role of H₂, revealing that it exerted a minimal influence on NH₃ conversion but considerably improved the N₂ selectivity of metal oxide catalysts.