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Novel electropositivelly-promotedcatalytic materials for efficient nitrogen oxide emission control: A DRIFTS-aidedstudy of the role of promoter

Matsouka Vasiliki, Konsolakis Michail, Yentekakis Ioannis.V.

Πλήρης Εγγραφή

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Περίληψη

In the present study the technique of the in situ diffuse reflectance infrared Fouriertransform spectroscopy (DRIFTS) is used in order to explore the effect of electropositivepromoters, such as sodium, on the surface chemistry and catalytic behavior of Pt/γ-Al2O3catalysts during the NO reduction by C3H6. It was found that under steady-state reactionconditions the surface of un-promoted catalysts is mainly covered by carbon containing species(hydrocarbon fragments, formates, acetates, cyanides), whereas that of Na-promoted catalysts ispredominantly covered by NOx ad-species, carbonyls and isocyanates, implying the significanteffect of Na promoter on the nature of adsorbed species. To further elucidate the role of Napromoteron the nature and the reactivity of adsorbed species, the transient response of IRspectra under the cycle: NO→He→C3H6→NO, is also investigated over both un-promoted andNa-promoted catalysts. The results indicate that interaction of propene with NOx pre-adsorbedspecies (mainly nitrates) over un-promoted Pt/Al2O3 catalysts results in the formation of stronglybonded carboxylates and cyanide species, which are inactive towards NO. On the opposite, NOadsorption 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 thesespecies isocyanates are very active towards NO, leading to the formation of the gas phasereaction products (i.e., N2, N2O, CO2, H2O). The present results demonstrate that the excellentcatalytic performance of sodium modified Pt/Al2O3 catalysts during the NO reduction bypropene, can be interpreted based on the significant modifications induced by the electropositivepromoter on the catalyst’s surface chemistry

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