A transient kinetic study of the mechanism of the NO+H2 reaction over Pt/SiO2 catalysts -: 2.: Characteristic features of SSITKA profiles

SSITKA profiles obtained for the NO+H-2 reaction on a 5% Pt/SiO2 catalyst at low temperatures are analysed in an attempt to gain insight into the reaction mechanism at the molecular level, specifically for the formation of N-2, N2O, and NH3. Three different analyses are introduced which give information about the nature of the reaction network and the final intermediates on the Pt surface under reaction conditions. These are (a) the initial distribution of isotopic molecules of product (IDIMP), (b) the temporal redistribution of isotopic molecules of product (TRIMP), and (c) the semilogarithmic plot of (<(alpha)over bar>) versus time. The first two analyses (IDIMP and TRIMP) are discussed in terms of "types of production" of two atom labelled product molecules. We also introduce the integral characteristics of a reaction mechanism, i.e., the coefficient of percolation (C-PE) and the coefficient of production (CPR) The conclusions, along with the experimental data, are used to develop a reaction mechanism for the formation of N-2, N2O, and NH3 from Pt catalysts in the NO + H-2 reaction. (C) 1999 Academic Press.