Studies of the selective reduction of nitric oxide by hydrocarbons

The selective reduction of nitric oxide with isobutane in the presence and absence of oxygen has been studied over Cu-ZSM-5-14-114 and compared to the simple decomposition reaction. In the presence of sufficient oxygen, complete combustion of the hydrocarbon was observed, whereas in its absence, acid catalysis accompanied by dehydrogenation associated with coking occurred. The effect of adding nitric oxide to the HC/He stream in the absence of oxygen was small; the conversion to nitrogen was little affected by the hydrocarbon. When oxygen was added, however, the decomposition was complete at 573 K even at high space velocities (e.g., SVH 10⁴) even though the combustion was not. Isobutane (an alkane) was more effective than C₃H₆ (an alkene) for the selective reduction; this is not generally the case. The presence of excess oxygen inhibited aging of the catalyst.