The effect of sulfur dioxide on the activity of modified mordenites in the selective reduction of Nox

The results of a comparative investigation into the activity of modified natural and synthetic mordenites in the selective reduction of NO_x by C₁ and C₃−C₄ hydrocarbons (methane and a propane-butane mixture), the effect of sulfur dioxide on the process, and the acidic characteristics of the mordenites by temperature programmed desorption of ammonia and IR spectroscopy are presented. Sulfur dioxide has practically no effect on the selective reduction of NO_x by C₃−C₄ hydrocarbons at the H forms of synthetic and previously recationized natural mordenites but substantially retards the process at the Cu-, Co-, and Cr-substituted forms and palladium-containing mordenites. The decrease in the concentration of the strong B centers in the transition from the hydrogen to the copper-containing form of the mordenites reduces their activity in selective reduction. Prior recationization of natural mordenites increases their activity, stability, and resistance to the action of sulfur dioxide. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 2, pp. 119–124, March–April, 1999.