Cu-Doped Mesoporous Coal Fly Ash for Ammonia-Free Denitration in Cement Kilns: Synergistic Catalytic Mechanism

Abstract

This study proposes a novel strategy to achieve ammonia-free direct NO decomposition in cement pyroprocessing by utilizing Cu-doped modified coal fly ash (Cu-MCFA) as a consumable catalytic additive. This study aims to clarify the synergistic effect between the Fe sites within MCFA and the supported Cu species toward direct NO decomposition. The findings indicate that alkaline–acid modification constructs a mesoporous conduit and exposes intrinsic Fe3+ active sites, while the introduction of Cu alters NO activation. Specifically, Cu doping generates binuclear [Cu–O–Cu]2+ dimers and abundant surface oxygen vacancies. These dimeric centers execute the complete cleavage of the N–O bond via a Langmuir–Hinshelwood bimolecular coupling mechanism, achieving 89% NO conversion and 99% N2 selectivity. In situ DRIFTS revealed that the undoped MCFA can form stable bidentate nitrates, the robust reducibility of Cu sites drives rapid oxygen desorption and averts nitrate accumulation. Furthermore, while incomplete NO decomposition over unpromoted sites leads to massive N2O byproduct emissions, the Cu-driven redox cycle suppresses this pathway. Importantly, leveraging the compositional homology between the CFA substrate and cement raw materials, the exhausted catalyst seamlessly undergoes in situ calcination into cement clinker. This research reveals the potential of utilizing industrial solid waste for efficient denitration, providing a viable pathway for collaborative resource utilization in cement-kiln systems and other energy-intensive industries.