Transition Metal Exchanged Zeolites : Physical and Catalytic Properties

Abstract

Catalysis by transition metal compounds in solution or supported on solids is an active field of research of considerable interest. It is worthwile to recall that transition metal ions were found active and selective for a great number of reactions among them, oxidation of ethylene to acetaldehyde, hydroformylation of olefins to aldehydes, carbonylation and homologation of alcohols, hydrogenation and isomerisation of olefins, oligomerisation and cyclodimerisation of olefins, water gas shift reaction ... etc. In recent years a new area of research developed which consisted to anchor or immobilize to a solid support a soluble transition metal complex to produce a potential active and selective new type of heterogeneous catalyst. In addition it is thought that relationship between homogeneous and heterogeneous catalysis may be found through the studies of such heterogeneized catalysts. Several distinct ways for “heterogeneizing homogeneous catalysts” have been proposed. One approach was to anchor the soluble metal complex to an oxide surface either through surface oxygen bond resulting from the reaction of the metal ligands with hydroxyl groups, or by ligand exchange with functionalized oxide surface. An alternative means for converting homogeneous metal complexes into heterogeneous catalysts is to introduce the active complex into the intercrystal space of a layer lattice silicate by exchanging the Na+ cations of the layer silicate by cationic transition metal ions.