Reaction–Thermal Coupling in Bifunctional Monolithic Catalysts: Simultaneous CO Oxidation and NOx Removal for Sintering Flue Gas Purification

Abstract Achieving synergistic pollution reduction and carbon mitigation is a key strategy for the iron and steel industry in response to the carbon peaking and carbon neutrality targets. To realize low-energy denitration of sintering flue gas, this work develops a bifunctional catalyst that harvests exothermic heat from CO oxidation to satisfy the thermal demand for NOx reduction. A coupled heat-mass transfer-reaction model is established to optimize the structured catalyst geometry and evaluate its adaptability to flue gas parameters. Results indicate that in situ heat release from CO oxidation significantly promotes low-temperature SCR kinetics and mass transfer, enabling over 85% conversion without external heat. Excessive temperature rise deteriorates NO conversion owing to suppressed NH3 adsorption, verifying that the synergistic effect is strongly temperature window-dependent. The reaction is mainly confined within a 0.2 mm near-wall thin layer. Increasing pore width can enhance mass transfer, yet internal diffusion limitation is largely eliminated beyond 20 nm, leading to a pronounced reduction in marginal benefits. The bifunctional catalyst presents favorable adaptability to flue gas conditions, with synergistic performance governed by the matching of inlet temperature and CO concentration. Compared with the conventional blast furnace gas supplementary heating scheme, the proposed catalytic self-sustaining heating strategy reduces operating costs by more than 90% and nearly eliminates extra carbon emissions. This work reveals the reaction–thermal synergistic mechanism at the reactor scale, providing a promising technical route for low-carbon sintering flue gas purification.