Collect. Czech. Chem. Commun. 1998, 63, 1724-1742

Activities and Stabilities of Redox Molecular Sieve Catalysts in Liquid Phase Oxidations. A Review

Roger A. Sheldon, Isabel W. C. E. Arends and Hans E. B. Lempers

Laboratory of Organic Chemistry and Catalysis, Delft University of Technology, 2628 BL Delft, The Netherlands


The use of redox molecular sieves as heterogeneous catalysts for liquid phase oxidations with H2O2 and alkyl hydroperoxides is reviewed. Emphasis is placed on titanium- and chromium-substituted molecular sieves as examples of catalysts operating via peroxometal and oxometal pathways, respectively. Various titanium-substituted molecular sieves were shown to be stable, heterogeneous catalysts for, e.g., olefin epoxidation, but the remarkable activity of the progenitor of this family of catalysts, titanium-silicalite (TS-1), has not been equalled. The catalytic activity of chromium-substituted molecular sieves was shown to be entirely due to small amounts of homogeneous chromium species leached from the catalyst during reaction. The catalytic activities and stabilities of other materials, including zirconium-substituted hexagonal mesoporous silicas and a vanadium bipyridyl complex encapsulated in zeolite Y, were also tested. They were either unstable (vanadium) towards leaching or showed low activity (zirconium). Attempts to incorporate molybdenum in silicalite were unsuccessful and previously reported activity was shown to be due to the blank reaction. A review with 64 references.

Keywords: Heterogeneous catalysis; Oxidations; Molecular sieves; Zeolites; Metal-complexes; Redox reactions; Titanium; Zirconium; Chromium; Porous materials.