The behavior of the NO-H-2 reaction over Rh(533) was studied in situ using fast x-ray photoelectron spectroscopy. The high energy resolution achieved by using synchrotron light allowed us to distinguish five surface species by analyzing the line shape and energy positions of the N 1s and O 1s photoelectron spectra. It was established that there are three nitrogen species, labeled NO, N(I) and N(II). The species NO and N(I) are attributed to adsorbed NO and atomic nitrogen, respectively. The nitrogen species N(TI) might be attributed to atomic nitrogen adsorbed at step sites or to an NHx species. The short measurement time for the spectra opens the possibility of studying the reaction more dynamically.