A specially designed apparatus employing (1) pulse valves for injection of reactant molecules onto catalysts and (2) a time-of-flight mass spectrometer was used to investigate processes of NO + H-2 reaction using Pt-Al2O3 thin film on Si substrate. First, the planar layer of the catalyst was located in a vacuum chamber and the reactants were supplied onto the surface by pulse valves. This process is considered to involve few consecutive reactions. There, the transient production of N-2 and NH3 Was observed simultaneously, Second, the reactants were supplied into the micro reactor filled with square pieces of planar catalysts spaced with SiC balls. Here, N2O was observed as well as NH3 and N-2. The experiments and the numerical simulation of the NO and H-2 reaction rates clearly elucidated some aspects of NO reduction passes, i.e., while N-2 and NH3 were directly produced from N and H adatoms dissociated from NO and H-2 admolecules, N2O was produced via consecutive process of NO reduction with NH3 molecules which were produced in transient reactions. (C) 2008 Elsevier B.V. All rights reserved.