Untersuchungen an oxidischen Katalysatoren. XVI. Über Zusammensetzung und Struktur dotierter Zinkoxidkatalysatoren

Studies on Oxide Catalysts. XVI. Composition and Structure of Doped Zinc Oxide Catalysts Analytical, x-ray, textural, IR-spectroscopic, and MÖSSBAUER investigations of zinc oxide catalysts doped with Li₂O, Ga₂O₃ and Fe₂O₃ were conducted in order to reveal relations between electronic and catalytic properties. The mixtures ZnO/Li₂CO₃, ZnO/Ga₂O₃, ZnO/Fe₂O₃, and ZnO/⁵⁷Fe(NO₃)₃, after the thermal pretreatment, always exist in the state of a polyphase solid system. In the ZnO/Li₂O system, only a very small part of the added lithium oxide is incorporated into the zinc oxide lattice by substitution. A second part of the Li₂O volatizes during the thermal pretreatment, and the greater part of it exists in the state of a separate solid phase in the catalyst and can be washed out by water. During the pretreatment, according to its temperature and duration, two-phase systems (ZnO, ZnMe₂O₄) or three-phase systems (ZnO, ZnMe₂O₄, Me₂O₃) are formed in the solid systems ZnO/Ga₂O₃ and ZnO/Fe₂O₃. For the reaction of both oxides forming a spinel, an electronic model is proposed.