LOW-TEMPERATURE CONVERSION OF NOX TO N-2 BY ZEOLITE-FIXED AMMONIUM-IONS

The selective catalytic reduction (SCR) of NOx in oxygen excess is rep orted to proceed with good efficiency by NH4+ ions fixed to zeolites a t temperatures as low as 373 K. The reaction starts with almost comple te reduction of NOx to N-2 under consumption of NH4+ ions thereby conv erting the zeolite into its H+ form. The consumed NH4+ ions can easily be replenished at reaction temperature by admission of gaseous ammoni a. A key step of the reaction sequence is the oxidation of NO to NO2 b y O-2 which is catalyzed by the zeolite. Both properties of the zeolit e, namely, its storage capacity for NH3 (in the form of NH4+ ions) and its oxidation capability for NO allow the abatement of NOx in exhaust gases at low temperatures and in the presence of oxygen without perma nent addition of a reductant. This process is named catalytic low temp erature conversion (CLTC) of NOx. (C) 1998 Elsevier Science B.V.