Ozone oxidation of nitric oxide: Promoting effect of phosphorus and inhibitory effect of phosphoric acid

This work presents experimental and density functional theory theoretical methods to carry out the catalytic role and reaction mechanism of phosphorus (P-4) for liquid phase catalytic oxidation nitric oxide. Meanwhile, it carries out the promoting effect of phosphorus and inhibitory effect of phosphoric acid in the ozone oxidation of nitric oxide. The work reveals the significant involvement of P-4 in facilitating the NO catalytic oxidation process by generating O-3. Meanwhile, the presence of phosphoric acid (H3PO4) hindered the NO catalytic removal process. The calculation results highlight that P-4 promoted the formation of O-3 and favoured the oxidation pathway (oxidation-hydration, NO -> NO2 -> HNO3). During the liquid-phase NO catalytic removal process, O-2 and NO dissolved into the solution, where O-2 exhibited preferential adsorbed on P-4, promoting the O-3 formation. Subsequently, O-3 first oxidized NO to NO2. Then, HNO2 and HNO3 were generated under the hydration reaction of NO2 and H2O. Next, O-3 further oxidized the generated HNO2 to HNO3, realizing the complete oxidation of NO. The hydration step of NO2 was identified as the key step in the O-3 oxidation processes. Furthermore, the generation of H3PO4 led to the consumption of P-4 and inhibited the NO removal process. O-3 played the crucial role in liquid phase NO oxidation.