Insight on photocatalytic oxidation of high concentration NO over BiOCl/Bi2WO6 under visible light

The exhaust gas from an SCR (Selective Catalytic Reduction) unit still has about 100 ppm NO. BiOX/Bi2WO6 catalysts were fabricated by a one-step ultrasound-assisted method and employed for photocatalytic oxidation of NO under visible light. The bandgap energy of BiOX (Cl, Br, I)/Bi2WO6 were estimated to be 2.65 eV, 2.35 eV, and 1.75 eV, respectively. Photocurrent density and EIS curves revealed that BiOCl/Bi2WO6 had the optimal charge transfer velocity. Simulated NO removal experiments of BiOX/Bi2WO6 catalysts were carried out in a fixed bed reactor, 20–30% NO (100 ppm inlet) removal rate was achieved under visible light while promoting by H2O vapor, and the maximum NO removal rate is up to 31% on BiOCl/Bi2WO6. The fitted L-H model revealed that NO oxidation followed two-centered adsorption, and scavenger experiments confirm that the main ROS (Reactive Oxygen Species) was •OH. In situ DRIFT spectra revealed that there were bridging nitrates, monodentate and bridging nitrites, and other intermediates formed on the BiOCl/Bi2WO6, these species can be scrubbed by seawater to regenerate the catalyst. The NO photocatalytic oxidation pathway was proposed. Good activity and stability of BiOCl/Bi2WO6 provide a new approach for scale-up application of NO oxidation under visible light.