Ferrisilicate Molecular Sieve

Abstract

Ferrisilicate molecular sieves of the ZSM-5 type, having SiO₂ /Fe₂ O₃ mole ratios ranging from 20 to 400, are prepared by adding a silica source and a quaternary ammonium salt in that order to an acedified solution of an iron (III) compound, crystallizing the resulting gel to form a ferrisilicate molecular sieve, and thermally treating the molecular sieve with nitrogen, air and/or steam at 300° to 700° C. Preferred thermal treatment comprises treating with nitrogen first, then with air or steam. Thermally treated molecular sieves contain iron both in and outside the crystal framework; most of the non-framework iron is dispersed as very finely divided iron oxides or internal surfaces. Molecular sieves are useful as catalysts in Fischer-Tropsch and other iron oxide-catalyzed reactions.