This study focuses on the comparison of de-NO, mechanisms and surface physical properties between Pt-impregnated MCM-41 and Pt-impregnated MCM-48 with different framework dimensions. In the de-NOx, reaction, NO reduction occurred from 250 C with reducing reagent (propylene) combustion in both the catalysts. The conversion reached a maximum (60%) at 300 degrees C, however, in the case of Pt/MCM-41, while it was enhanced and kept at a high temperature of 550 degrees C without any conversion decrease in Pt/MCM-48. This result could be attributed to the differences in structural dimension, surface acidity, adsorption abilities of the reducing agent and NO, and the different Pt-active species on MCM-41 and MCM-48. The adsorption ability for NO, the reducing agent (propylene), and NH3 definitely increased on Pt/MCM-48 compared with Pt/MCM-41. The XPS and XRD results suggest that the PtO and PtO2 had a role as active species on Pt/MCM-48, while only the PtO was active on Pt/MCM-41. The results of the physical properties mentioned and of in situ IR spectra suggested that the de-NOx reaction in Pt/MCM-41 progressed by partial oxidation and reduction for the reducing agent and NO, respectively. This resulted in the production of NCO and CxHyO2* intermediates. In contrast, the complete oxidation and reduction of these occurred on Pt/MCM-48. (c) 2005 Elsevier B.V. All rights reserved.