Kinetic oscillations and hysteresis phenomena in the NO+H2 reaction on Rh(111) and Rh(533): Experiments and mathematical modeling

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Abstract
Interesting kinetic phenomena, such as multiple steady states and kinetic oscillations recently found in the NO+H2 reaction over Rh(533) and Rh(111) single crystal surfaces in the 10−6 mbar pressure range have been studied by means of experiments and computer modeling. A mathematical model, consisting of five ordinary differential equations and taking into account the lateral interactions in the adlayer, has been developed for simulating the NO+H2/Rh(533) and NO+H2/Rh(111) reactions. The simulation results make it possible to explain in detail the underlying reasons for the experimentally observed complex dynamic behavior. In particular, the kinetic oscillations and their properties have been reproduced. It was found that accumulation of NHads species, which serves as an intermediate in the pathway of NH3 production, is an important step in the oscillatory mechanism. In addition, the same mathematical model is able to successfully reproduce the experimental data concerning temperature programmed desorption (TPD) spectra, hysteresis phenomena, and the dependence of selectivity upon temperature and reactant partial pressures. Lateral interactions in the adlayer are shown to play a crucial role in the adequate simulation of the experimental observations.