Schwermetallausgetauschte Zeolithe als Katalysatoren für die Selektivoxidation

Transition Metal Zeolites as Catalysts for the Partial Oxidation of Methanol Zeolites containing cations of the 4th period of the periodical system from Ti to Cu have been prepared by ion exchange of a NaY zeolite in aqueous solutions. Structural and surface chemical properties of the zeolites were characterized by adsorption, DTA, thermogastitrimetry, x-ray, ESR, IR, and UV-V is spectroscopy. It could be shown that both localization and coordination state of transition metal ions is fairly different and depends on the thermal treatment of the zeolites. By exchanging sodium ions the acidic properties as well as the ability of the zeolites to interact with H₂O or CO₂ is changed and depends on the kind of transition metal ion. VO and Cr exchanged zeolites proved to be selective catalysts for the oxidative dehydrogenation of methanol to formaldehyde with a maximum selectivity of 70%. It is concluded that in contrast to oxides where a redox mechanism is assumed the reaction on zeolites occurs via an associative mechanism.