Transient analysis of the release and reduction of NOx using a Pt/Ba/Al2O3 catalyst

The release and reduction of NOx in a NOx storage-reduction (NSR) catalyst were studied with a transient reaction analysis in the millisecond range, which was made possible by the combination of pulsed injection of gases and time resolved time-of-flight mass spectrometry. After an O2 pulse and a subsequent NO pulse were injected into a pellet of the Pt/Ba/Al2O3 catalyst, the time profiles of several gas products, NO, N2, NH3 and H2O, were obtained as a result of the release and reduction of NOx caused by H2 injection. Comparing the time profiles in another analysis, which were obtained using a model catalyst consisting of a flat 5 nmPt/Ba(NO3)2/cordierite plate, the release and reduction of NOx on Pt/Ba/Al2O3 catalyst that stored NOx took the following two steps; in the first step NO molecules were released from Ba and in the second step the released NO was reduced into N2 by H2 pulse injection. When this H2 pulse was injected in a large amount, NO was reduced to NH3 instead of N2. A only small amount of H2O was detected because of the strong affinity for alumina support. We can analyze the NOx regeneration process to separate two steps of the NOx release and reduction by a detailed analysis of the time profiles using a two-step reaction model. From the result of the analysis, it is found that the rate constant for NOx release increased as temperature increase.