Deactivation of Cu-ZSM-5 during selective catalytic reduction of NO by propane under wet conditions

The presence of H2O in the feed during NO reduction over Cu-ZSM-5 caused kinetic inhibition together with reversible and irreversible deactivation. These phenomena were sensitive to the operating conditions. Kinetic inhibition had small characteristic times and was associated with competition for active sites between H2O and the reactants. Slow recovery of activity after H2O removal from the feed after long runs characterized reversible deactivation, probably caused by solid state rearrangements in the catalyst. Irreversible deactivation had a quasi-sigmoidal character, with a maximum rate occurring after more than 15 h on stream. Neither structural changes or dealumination of the zeolite were detected. Temperature programmed reduction showed that the state of Cu cations changed significantly during the diverse treatments. Bands associated with Cu2+, Cu+ and CuO were observed in different ratios, as well as a band at 593 that could not be associated with any Particular species. In spite of those changes the state of Cu species did not correlate well with the activity of the catalysts.