Some aspects about the nature of surface species on Pt-based and MFI-based catalysts for the selective catalytic reduction of NO by propene under lean-burn condition

The nature of surface species for the selective catalytic reduction of NO by propene under lean-burn condition is relatively investigated on Pt/Al2O3 and Co-ZSM-5 catalysts. An experimental set of three continuous steps including adsorption, temperature programmed desorption (TPD) and temperature programmed oxidation (TPO) is performed to observe the particular behavior of surface species on both catalysts. The surface species on Pt/Al2O3 are almost totally released during TPD step, whereas those on Co-ZSM-5 are necessarily removed by the oxidizing gas on TPO step. It is suggested that the different nature of surface species on both catalysts should possibly play an important role on the reaction mechanism pathway. For Co-ZSM-5 catalyst, the surface species, which are formed by the interaction of NO, propene and oxygen, are distinctly assigned as the intermediate species in the NO reduction mechanism. On the other hand, for Pt/Al2O3 catalyst, the observation of several surface species and the investigation about their reactivities indicate that several reaction mechanisms are simultaneously proceeded at the same operating condition.