Role of adsorbed NO in N2O decomposition over iron containing ZSM-5 catalysts at low temperatures
Transient response and temperature-programmed desorption/reaction (TPD/TPR) methods were used to study the formation of adsorbed NOx from N2O and its effect during N2O decomposition to O2 and N2 over FeZSM-5 catalysts at temperatures below 653 K. The reaction proceeds via the atomic oxygen (O)Fe loading from N2O on extraframework active Fe(II) sites followed by its recombination/desorption as the rate-limiting step. The slow formation of surface NOx,ads species was observed from N2O catalyzing the N2O decomposition. This autocatalytic effect was assigned to the formation of NO2,ads species from NOads and (O)Fe leading to facilitation of (O)Fe recombination/desorption. Mononitrosyl Fe2+(NO) and nitro (NO2,ads) species were found by diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) in situ at 603 K when N2O was introduced into NO-containing flow passing through the catalyst. The presence of NOx,ads does not inhibit the surface oxygen loading from N2O at 523 K as observed by transient response. However, the reactivity of (O)Fe toward CO oxidation at low temperatures (<523 K) is drastically diminished. Surface NOx species probably block the sites necessary for CO activation, which are in the vicinity of the loaded atomic oxygen.
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Record created on 2006-06-02, modified on 2016-08-08