PNNL

Abstract

The adsorption of NO2 was investigated and compared on Na- and Ba-Y,FAU zeolites both in the absence and presence of adsorbed water using FTIR and TPD techniques. The same ionic NOx species (NO?, NO?:NO2, NO3-), formed by the disproportionation of NO2, were observed to form on both materials under dry conditions at room temperature. The thermal stabilities of these species, however, were vastly different on the two materials. Room temperature evacuation was sufficient to decompose the NO?NO2 adduct in Na-Y, while this species was stable up to 350K over Ba-Y. The adsorbed NO? was also much more stable over Ba-Y than on Na-Y. Water significantly affected the adsorbed NOx species on both materials. In the presence of water the IR signatures of adsorbed NO+ were eliminated from both catalysts, however it did not affect the IR feature of the NO?NO2 species on Ba-Y. In the TPD spectra the NO2 desorption peak shifted from 350K to 520K on Na-Y pre-exposed to water. In Ba-Y the high temperature NO2 desorption feature of ~470K shifted to ~620K as a result of adsorption on the water containing sample, while the low temperature peak remained unchanged.