OXIDATION CATALYSIS WITH SEMI-INORGANIC ZEOLITE-BASED MN CATALYSTS

The chelation of zeolite-exchanged Mn2+ by N-containing ligands gives rise to a whole class of heterogeneous liquid phase oxidation catalyst s. Bi-, tri- or tetradentate ligands can be used. A high degree of met al complexation is required to avoid side reactions due to the presenc e of zeolite-coordinated manganous ions. Applied physico-chemical tech niques include IR, ESR and electronic spectroscopy. Oxidation-resistan t chelands, e.g. with aromatic pyridine groups, are employed to ensure long-term catalyst stability. Use of hydrogen peroxide is most succes sful in combination with 2,2'-bipyridine (bpy) or 1,4,7-trimethyl-1,4, 7-triazacyclononane (tmtacn); with both systems double bond oxidation proceeds with high selectivity. Olefin oxidations with other oxidants, e.g. tert-butylhydroperoxide (tBuOOH) or iodosylbenzene, are less sel ective or slower. Alkane oxidation with tBuOOH is possible with variou s tetradentate diimine ligands. A principal effect of the zeolite matr ix is that formation of Mn clusters is impeded in comparison with solu tion chemistry. Other effects of the zeolite matrix include modulation of the acid strength and suppression of side reactions, such as allyl ic oxidation of olefins or formation of isomerized epoxides.