Spectroscopic evidence for the mode of action of alkali promoters in Pt-catalyzed de-NOx chemistry

The interaction of NO with sodium-dosed Pt(Na)/γ-Al2O3 catalysts was studied by means of diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). With increasing sodium loading, pronounced and progressive red shifts of the NO stretching frequency associated with molecular NO adsorbed on the Pt component were observed. This decrease in ν(NO) correlates with enhancement of NO dissociation at higher temperatures on Na-promoted Pt catalysts under conditions where clean Pt is almost ineffective. These spectroscopic observations provide a clear and consistent explanation for the recently reported very strong promotion by alkalis of the performance of supported Pt catalysts in de-NOx chemistry [I.V. Yentekakis, M. Konsolakis, R.M. Lambert, N. Macleod, L. Nalbandian, Appl. Catal. B 22 (1999) 123; I.V. Yentekakis, V. Tellou, G. Botzolaki, I.A. Rapakousios, Appl. Catal. B 56 (2005) 229].