Boosting CO oxidation via cu-induced defects: Engineered rare-earth phosphate catalysts for the synergistic removal of NOx and CO.

Coke oven flue gas contains two major pollutants, NOx and CO, whose simultaneous removal remains a considerable challenge. While CO-selective catalytic reduction (CO-SCR) is a potential solution, its sensitivity to O2 severely hinders its efficiency. Therefore, an alternative and promising approach is to synergistically couple CO oxidation with the selective catalytic reduction of NO using NH3 (NH3-SCR). In this paper, building on efficient Ce0.75La0.25PO4 for NOx removal, y%Cu/Ce0.75La0.25PO4-xAl2O3 catalysts were synthesized via ultrasonic-assisted impregnation and hydrothermal methods. The findings indicate that Cu modification dramatically enhanced performance: CO removal efficiency surged by over 75% compared to the Cu-free catalyst between 280 and 320 °C while maintaining above 80% NOx removal. Furthermore, the 4 wt% Cu catalyst outperformed CO-SCR systems in simultaneous CO and NOx abatement. Characterization revealed that the composite support's larger specific surface area improved active component dispersion. Cu introduction fostered strong support-metal interaction and charge transfer (Cu2++Ce3+↔Cu++Ce4+), generating abundant defects (oxygen vacancies, lattice distortions). The optimal 4 wt% Cu catalyst uniquely possessed the most medium-strength acid sites and superior redox properties, enabling synergistic NOx/CO removal. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) identified the CO oxidation pathway via the Mars-van Krevelen mechanism, while NH3-SCR proceeded via combined Langmuir-Hinshelwood and Eley-Rideal mechanisms.