Ammonia Abatement via Selective Oxidation over Electron-Deficient Copper Catalysts

Abstract

Selective catalytic ammonia-to-dinitrogen oxidation (NH₃-SCO) is highly promising for the abatement of NH₃ emissions from flue gas purification devices. However, there is still a lack of high-performance and cost-effective NH₃-SCO catalysts for real applications. Here, highly dispersed, electron-deficient Cu-based catalysts were fabricated using nitrogen-doped carbon nanotubes (NCNT) as support. In NH₃-SCO catalysis, the Cu/NCNT outperformed Cu supported on N-free CNTs (Cu/OCNT) and on other types of supports (<i>i.e.,</i> activated carbon, Al₂O₃, and zeolite) in terms of activity, selectivity to the desired product N₂, and H₂O resistance. Besides, Cu/NCNT demonstrated a better structural stability against oxidation and a higher NH₃ storage capacity (in the presence of H₂O vapor) than Cu/OCNT. <i>Quasi in situ</i> X-ray photoelectron spectroscopy revealed that the surface N species facilitated electron transfer from Cu to the NCNT support, resulting in electron-deficient Cu catalysts with superior redox properties, which are essential for NH₃-SCO catalysis. By temperature-programmed surface reaction studies and systematic kinetic measurements, we unveiled that the NH₃-SCO reaction over Cu/NCNT proceeded via the internal selective catalytic reaction (<i>i</i>-SCR) route; <i>i.e.</i>, NH₃ was oxidized first to NO, which then reacted with NH₃ and O₂ to form N₂ and H₂O. This study paves a new route for the design of highly active, H₂O-tolerant, and low-cost Cu catalysts for the abatement of slip NH₃ from stationary emissions via selective oxidation to N₂.