Novel electropositivelly-promoted catalytic materials for efficient nitrogen oxide emission control: A DRIFTS-aided study of the role of promoter

Summarization: In the present study the technique of the in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) is used in order to explore the effect of electropositive promoters, such as sodium, on the surface chemistry and catalytic behavior of Pt/γ-Al2O3 catalysts during the NO reduction by C3H6. It was found that under steady-state reaction conditions the surface of un-promoted catalysts is mainly covered by carbon containing species (hydrocarbon fragments, formates, acetates, cyanides), whereas that of Na-promoted catalysts is predominantly covered by NOx ad-species, carbonyls and isocyanates, implying the significant effect of Na promoter on the nature of adsorbed species. To further elucidate the role of Napromoter on the nature and the reactivity of adsorbed species, the transient response of IR spectra under the cycle: NO→He→C3H6→NO, is also investigated over both un-promoted and Na-promoted catalysts. The results indicate that interaction of propene with NOx pre-adsorbed species (mainly nitrates) over un-promoted Pt/Al2O3 catalysts results in the formation of strongly bonded carboxylates and cyanide species, which are inactive towards NO. On the opposite, NO adsorption over Na-promoted catalysts favours the formation of nitro/nitrite and nitrosyl species, which are highly active towards propene, leading to the formation of enolic species (R-CH=CO), organic compounds (CxHyNOz), isocyanates (NCO) and carbonyl (CO) species. Among these species isocyanates are very active towards NO, leading to the formation of the gas phase reaction products (i.e., N2, N2O, CO2, H2O). The present results demonstrate that the excellent catalytic performance of sodium modified Pt/Al2O3 catalysts during the NO reduction by propene, can be interpreted based on the significant modifications induced by the electropositive promoter on the catalyst’s surface chemistryΠαρουσιάστηκε στο: Proc. 2nd International Conference on Hazardous Waste Managemen