A literature proposal that the reduction of nitrous oxide by carbon monoxide over rhodium catalysts proceeds by cleavage of the N-N bond has been tested through the use of (NNO)-N-15-N-14 as the reactant. The results disprove the suggestion in that (NN)-N-14-N-15 is the dominant product at temperatures from 336 degrees C to 356 degrees C with nitrous oxide conversions from 26% to >99%. Little, if any, N-14(2) and N-15(2) is formed, in contrast with the 25% of each expected for the model. Results for the corresponding reaction of (NNO)-N-15-N-14 with H-2 are even more clear-cut in demonstrating the absence of N-N bond cleavage. The activity of the Rh/SiO2 used here for the N2O/CO system fell within the rather wide of values reported in the literature for other Rh catalysts. However, activity for the reduction of N2O by H-2 was approximately five times higher than the only previous result in the literature, that for a Rh/Al2O3 catalyst. (C) 2010 Elsevier Inc. All rights reserved.