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1 Wiadomości Chemiczne

1 2009

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Sita molekularne modyfikowane metalami przejściowymi jako katalizatory utleniania węglowodorów

Nowińska K., Held A., Kowalska J.

Wiadomości Chemiczne

2009

[Z] 63, 3-4

233-268

The development of a one-stage procedure for hydrocarbons oxidation to produce oxygen bearing products is still a challenging task for chemical technology. In the presented paper, the recent achievements in heterogeneous oxidation of benzene to phenol and propene to propylene oxide, as well as an oxidative functionalization of light paraffins have been demonstrated. The successful use of molecular sieves modified with transition metal cations as catalysts for oxidation reactions, performed in the presence of nitrous oxide as an oxidant has been shown. One-stage benzene to phenol hydroxylation was developed and commercialised on the base of iron modified high silica zeolites as catalysts and N_2O as an oxidant. However, structure of the active iron complex and mechanism of the oxidation reaction are still under debate. The most important ideas are presented in the paper. Panov and co-workers [5, 10, 29] underline the role of binuclear iron complex accommodated on ion-exchangeable centres in zeolite channels which easily undergo autoreducion at high temperature and subsequent reoxidation as a result of contact with N2O. Ryder and Bell [35, 36] indicate (FeO_2)+ complex as responsible for benzene hydroxylation, while Hensen and co-workers [37, 38] claim, that not only iron but also aluminium cation is involved in active centre leading to formation of Fe-O-Al complex. Oxidation of light paraffins over N_2O/Fe-ZSM-5 system results in oxydehydrogenation of alkanes and formation of olefins [68, 72, 80]. The possible mechanisms of N_2O decomposition in the presence of alkanes and ODH products, developed in the literature [58, 80-82], are presented. Propylene epoxidation, performed over transition metal cations (iron, vanadium and mixed system) modified molecular sieves, is also presented. Mainly all-silica mesoporous molecular sieves [91, 93, 94] and amorphous silica [7, 95, 96] characterised with very low acidity, show suitable properties as matrices for accomodation of transition metal cations.