| Abstract
| - The pretreatment conditions (temperature, medium) have a strong influence on the N2O decomposition activityof Fe−ZSM-5 catalysts (J. Jia et al., J. Catal. 2002, 210, 453). We used X-ray absorption spectroscopy tofollow in situ the structural changes of the iron oxide clusters in an Fe−ZSM-5 sample, which was preparedby chemical vapor deposition of FeCl3, during different pretreatments and during N2O decomposition. Reductivepretreatment in H2 always decreased the Fe−Fe coordination number; i.e., it broke the iron oxide clustersinto smaller units by removing bridging oxygen atoms. When reduction was carried out at low temperatures(673 K), this process was reversed during reoxidation by N2O. When reduction was carried out at hightemperatures (873 K), the smaller fragments were stabilized by forming strong bonds to the zeolite matrixand did not agglomerate during reoxidation. An analysis of the Fe−O coordination numbers showed thattemperatures above 673 K are required to dehydroxylate the iron oxide clusters. Reduction at 673 K did notsignificantly change the Fe−O coordination number because the oxygen remained adsorbed on the iron clusterin the form of H2O (or as a hydroxy group). This is an important result because the degree of (de)hydroxylationof the iron oxide clusters has implications on their catalytic activity. During N2O decomposition the catalystwas in a fully oxidized state. The EXAFS spectra of the samples before and after reaction with N2O wereidentical, indicating that only a very small concentration of sites, which is not detectable by EXAFS, isresponsible for the N2O decomposition activity.
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