Study of cumene oxidation over zirconia-, titania- and alumina-based complex oxides obtained by sol-gel methods: activity-structure relationships
✍ Scribed by Yu.V. Maksimov; I.P. Suzdalev; M.V. Tsodikov; V.Ya. Kugel; O.V. Bukhtenko; E.V. Slivinsky; J.A. Navio
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 834 KB
- Volume
- 105
- Category
- Article
- ISSN
- 1381-1169
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✦ Synopsis
Activity-structure relationships have been studied in the low temperature liquid phase cumene oxidation over Fe-O/Zr&, Fe-O/TiO? and Fe-0/A1203 complex oxides obtained by sol-gel methods. The study has been carried out by the measurements of overall kinetics, product distribution and by X-ray diffraction and MCissbauer spectroscopic methods. Kinetic study in the presence of homogeneous initiator (azo-bis-diazobutyrorkile) has led to the conclusion that the active surface of complex oxides participates in chain initiation most probably via R--H bond rupture. Three groups of complex oxides are described: ( 1) two-phase polycrystalline zirconia-based catalysts showing high activity at low iron loading; (2) one-phase pokrystalline zirconia-and titania-based catalysts exhibiting either activity drop at some critical iron content (zirconia) or monotonic activity dependence (Mania) on iron loading; (3) amorphous alumina-based catalysts containing y-fenic oxide clusters and showing monotone activity dependence. Electronically excited terminal Fe=0 groups related to the surface FeO, polyhedra and ironcontaining species located at the interface have been suggested as active centers acquiring the anion-radical behavior. When comparing thermodynamically stable titania (anatase) with metastable one-phase zirconia (cubic or tetragonal) as host matrices, the suggestion was introduced that greater activity of zirconia-based catalysts is due to more energy transfer from the host matrix to the particular active center.
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