N 2 O decomposition catalyzed by oxidized Fe clusters localized in the micropores of Fe/ZSM-5 has been studied using the DFT approach and a binuclear cluster model of the active site. Three different reaction routes were found, depending on temperature and water pressure. The results show that below 200 °C the binuclear cluster is hydroxylated and is probably inactive. Above this temperature and up to 500 °C the catalytic site has the [HO-Fe-O-Fe-OH] 2+ structure, and above 500 °C the site is predominantly [Fe-O-Fe] 2+ . The reaction paths on the latter two forms of the site are similar. N 2 O dissociates on each of the Fe ions with subsequent oxygen recombination and desorption. Some of the side reactions including NO formation are also considered.

Cluster model quantum chemical calculations have been performed to compare stabilization energies (E st) of Zn2+ ions in four-, five-, and six-membered zeolitic rings. E st was evaluated as energy of the reaction Zn2+/Z + H2 ⇒ 2H+/Z + Zn0. It was found that E st substantially decreases in the series six-, five-, and four-membered ring, and this trend is essential to the understanding of the comparative adsorption ability and reactivity of Zn2+ in cationic sites of different zeolites. This conclusion was proved in calculations of the heterolytic dissociation of ethane. The molecular structure of active sites in ZnHY and ZnHZSM-5 zeolites and the question of the stability of small intrazeolite zinc oxide species are discussed.

The coordination and electronic structure of monatomic Pt species in mordenite have been investigated by scalar−relativistic density functional model cluster calculations using CO molecules as a probe. It was found that anchoring a Pt−CO moiety by the protons of one or two acidic hydroxyl groups increases the CO stretching frequency compared to that of free Pt−CO, but leaves the frequency still smaller than that of a free CO molecule, in line with experiment. The results for various molecular model complexes support the hypothesis that the platinum species in mordenite are electron-deficient. An alternative model comprising “naked” protons interacting with Pt−CO moieties can be ruled out since the calculated CO frequency is too large. The dependence of the CO stretching frequency on the acidity of the Brønsted groups and on the electronic charge of the Pt species is discussed.

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Tetrahedral and octahedral palladium clusters with an entrapped proton, [Pd,H] + and [Pd,H] + , were considered as models of electron-deficient palladium species encaged in a zeolite matrix. Density functional studies employing a gradient-corrected exchange-correlation potential have been carried out on the bare and protonated Pd, and Pd, clusters as well as on their complexes with a CO molecule adsorbed at the three-fold hollow position. In line with the experimental data it is found that the protonation of palladium clusters leads to a reduced CO adsorption energy and an increased vibrational frequency of the adsorbed CO. The protonation energies of the clusters Pd, and Pd, were calculated to 9.4 eV and 9.9 eV, respectively. These large values are comparable to the proton affinity of such a strong base as NH, (calc. 9.2eV) and support the hypothesis that, as a result of the interaction of the guest metal particles with zeolitic protons, electron-deficient [Pd,H,IX+ species are formed.

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