NO reduction with H2 in the presence of excess O2 over Pd/MFI catalyst

The NO SCR (selective catalytic reduction) activity with H2 in the presence of excess O2 was investigated over Pd/MFI catalyst prepared by sublimation method. With GHSV=90 000 h−1, a very high steady-state conversion of NO to N2 (70%) is achieved at 100 °C. Significant reorganizations take place inside the catalyst upon its first contact with all reactants and products at the reaction temperature. Pd0, which has a significant role in the NO–H2–O2 reaction, is possibly the active site for NO reduction. The formation of Pd-β hydride deactivates the catalyst for NO reduction. Throughout the entire NO–H2–O2 reaction, no N2O or NO2 is formed; N2 is the only N-containing product. The presence of O2 inhibits the formation of undesirable NH3. The rate of the NO+H2 reaction is fast or comparable to that of the H2+O2 reaction. The oxidation of Pd0 and subsequent agglomeration of PdO are responsible for the decreased NO reduction activity at high temperature.