The role of organic nitrogen-containing compounds as intermediates of the HC-assisted SCR of NOx has been investigated. For this purpose, homogeneous NO, O-2 and NO2 interactions with C3H6 were first studied. Then, the catalytic interaction of C3H6 was investigated over NOx-pretreated Ce0.68Zr0.32O2 samples. The obtained results, together with a critical review of the literature data, lead to the conclusion that R-NOx compounds are intermediates of the deNO(x) process. However, it is suggested that these products are not directly involved in the formation of N-2. R-NOx species result from the interaction of ad-NOx species and C3H6, and decomposed to NO and oxygenates. These oxygenates are thought to act as reductants of adsorbed oxygen species left from NO decomposition to N-2 to restore the corresponding catalytic sites. A link between much of the intermediates already reported in the literature (NO2, ad-NOx, R-NOx and CxHyOz), over a wide variety of catalytic materials and reductants, is established and provides new arguments in favor of a deNO(x) decomposition mechanism. Consequently, much of the results reported in the literature might be reasonably understood in light of an in-depth decomposition mechanism, which describes the role of each intermediate. Finally, this work shows that Ce0.68Zr0.32O2 includes the three catalytic functions required to allow deNO(x) to occur. (C) 2004 Elsevier B.V. All rights reserved.