A literature proposal that the reduction of nitrous oxide by carbon monoxide over rhodium catalysts proceeds by cleavage of the Nsingle bondN bond has been tested through the use of ¹⁵N¹⁴NO as the reactant. The results disprove the suggestion in that ¹⁴N¹⁵N is the dominant product at temperatures from 336 °C to 356 °C with nitrous oxide conversions from 26% to >99%. Little, if any, ¹⁴N₂ and ¹⁵N₂ is formed, in contrast with the 25% of each expected for the model. Results for the corresponding reaction of ¹⁵N¹⁴NO with H₂ 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 H₂ was approximately five times higher than the only previous result in the literature, that for a Rh/Al₂O₃ catalyst. Graphical abstract The reduction of ¹⁵N¹⁴NO by carbon monoxide, and also by hydrogen, over a Rh/SiO₂ catalyst yields ¹⁵N¹⁴N as the exclusive nitrogen-containing product. The result rules out a suggestion in the literature that the reduction using carbon monoxide proceeds through cleavage of the nitrogensingle bondnitrogen bond.