Influence of NOx adsorbed species on component permeation through ZSM-5 membranes

A thin ZSM-5 film was grown on an a-alumina support, resulting in a composite membrane. The membranes were characterized by SEM and adsorption branch n-hexane/helium permporometry. In addition, the permeation of gas mixtures containing NO2, NO, N-2 and argon was evaluated The effect of temperature and gas mixture composition on the component permeation and selectivity was investigated. It was found that NOx permeation through the ZSM-5 membrane was partially surface concentration dependent and was thermally activated. However, transport by gas translational diffusion seemed to dominate at the conditions studied. The presence of various NOx adsorbed species appeared to influence diffusion of NO2 in ZSM-5 and reduced transport of other inert and weakly adsorbed components over a wide temperature range (20-400 degrees C). Strongly adsorbed surface nitrate species formed in the presence of gas phase NOx should be responsible for the reduced transport of these components at the elevated temperature. The findings are of interest for possible applications of ZSM-5 membranes for component separation at high temperature. (C) 2009 Elsevier B.V. All rights reserved