Simulations of the NO+NH3 and NO+H2 reactions on Pt(100): Steady state and oscillatory kinetics

Abstract

A model for the reactions of NO+NH3 and NO+H2 has been developed for simulating the reduction of NO on Pt(100) in the 10−6 mbar pressure range for temperatures between 300 and 700 K. The model consists of seven ordinary differential equations for describing the coverage changes of six adsorbed species as well as an equation for describing the 1×1⇄hex phase transformation. Simulations of the N2 and H2O reaction rates for both reaction mixtures reproduced the hysteresis effects and the existence range for kinetic oscillations, which were found in the experiments. In addition, the occurrence of the so-called ‘‘surface explosion’’ in both reaction systems is well described by the model. In contrast to the NO+CO reaction on Pt(100), where oscillations may also take place on a pure 1×1 substrate, the 1×1⇄hex phase transition occurs during oscillations for the NO+NH3 and NO+H2 reactions. The transitions between different adsorbate/substrate phases during one oscillatory cycle which are predicted by the model are in agreement with experimental observations made by photoemission electron microscopy (PEEM) for the NO+NH3 reaction. Using values for the constants which were taken from experiments, the model provided quantitative predictions of the absolute reaction rates as well as the relative rates of the competing reaction channels, e.g., N2 and NH3 production in the case of the NO+H2 reaction. The similar dynamical behavior observed in the NO+H2 and NO+NH3 reactions on Pt(100) is attributed to the insensitivity of NO reduction to the source of the hydrogen atoms.

Space-Resolved Profiling Relevant in Heterogeneous Catalysis

“…PEEM typically applies UV light, and when an X-ray source is used for excitation it is called, for clarity, X-ray photoelectron emission microscopy (XPEEM). In the 1990s the great potentials of PEEM have been demonstrated, for example, by monitoring the reaction fronts and their propagation mechanisms during CO oxidation on Pt [96][97][98] and during reactions of NO with H 2 and NH 3 on Pt [99], and the deactivation process during ethylbenzene dehydrogenation over iron oxide catalysts [100]. Synchrotron X-ray based XPEEM has improved the spatial resolution drastically (ca.…”

A kinetic study of NOx reduction over Pt/SiO2 model catalysts with hydrogen as the reducing agent

“…There are several studies of NO reduction with hydrogen over platinum single crystals [4,5] as well as over supported platinum catalysts [6,7]. Earlier studies of NO x storage catalysts have focused on details of the storage period and detailed kinetic models have been constructed by Olsson et al [1,2].…”

“…a 4 ¼ 0:116 and a 7 ¼ 0:118 reduction reactions will therefore not occur in oxygen excess. Nitrogen is the desired product for NO x reduction and different mechanisms for the formation of N 2 have been proposed in the literature[5,7,15]. Mechanisms where hydrogen reacts directly with NO have also been proposed[16].…”

Estudio del Fenómeno Explosión de Superficie en la Reacción NO+CO en Pt(100) por Simulación de Monte Carlo Dinámico

“…El cambio periódico que experimenta la estructura del catalizador causa oscilaciones en la reacción de reducción de NO, por diferentes agentes como CO, H 2 y NH 3 , por ejemplo, en el monocristal de Pt(100), el estado estable cuasi-hexagonal (hex) puede ser reestructurado hacia un estado metaestable 1 1 por efectos de adsorción de las moléculas, y puede reconstruir de manera inversa 1 1 → hex por la desorción de los productos (Imbihl y Ertl, 1995;Lombardo et al, 1993;Fink et al, 1991b). Otro mecanismo que promueve la formación de oscilaciones, en esta reacción, se debe a la gran interacción que existe entre las especies adsorbidas (Slinko et al, 1992).…”