Selective catalytic reduction of NO by hydrocarbons in the presence of excess oxygen using Pt/MCM-41 catalysts

The selective catalytic reduction of NO by C3H6 and C3H8 in the presence of 5% O2 over 0.5–2% Pt supported on siliceous MCM-41 has been studied in detail. Pt/MCM-41 shows better activity for NO reduction than Pt/SiO2 and Pt/Al2O3 under the same reaction conditions due to the larger surface area and pore volume of MCM-41. Two types of Pt species having different reduction temperatures (50–200, 350–500 °C, respectively) are formed on Pt/MCM-41. The Pt species having lower reduction temperature is suggested to be responsible for the selective reduction of NO. A redox mechanism is used to explain this behavior. In addition to its high stability in the presence of water vapor, Pt/MCM-41 shows high resistance to SO2 without irreversible deactivation due to its weak interaction with SO2. The activity of Pt/MCM-41 catalyst is found to be improved in the presence of Al species both in the framework or on the surface of MCM-41 support, possibly due to the improvement of the acidity of Pt/MCM-41 by Al species. In situ XRD result indicates that the surface Al-species prevent the active Pt from sintering at high temperature, hence improving the thermal stability of Pt/MCM-41. Having additive Ru species, Pt/Ru/Si-MCM-41 is found to widen the reaction window and decrease the selectivity of the conversion of NO to N2O during the SCR of NO; this is an important finding for overcoming the main shortcoming of Pt-based catalyst.