THE INCORPORATION OF IRON IONS IN ALPO4-5 MOLECULAR-SIEVES AFTER MICROWAVE SYNTHESIS STUDIED BY EPR AND MOSSBAUER-SPECTROSCOPY

FeAPO-5 samples with up to 3 mol% Fe were synthesized by microwave cry stallization from Fe(II)- and Fe(III)containing gels. The samples were studied as-synthesized and during thermal treatment in air, N-2 and N H3 using in situ EPR and Mossbauer spectroscopy. The iron ions are mai nly incorporated in lattice positions substituting for aluminium. Duri ng calcination, Fe(II) is easily oxidized to Fe(III). The Fe(III) ions in both the as-synthesized and rehydrated calcined samples are locate d on the inner pore surface. They have octahedral symmetry coordinatin g to framework oxygen atoms and ligand molecules in the pores as well. The non-framework ligands are released on calcination leaving behind tetrahedral Fe(III). Structural changes of the iron coordination spher e caused by adsorption/desorption processes are reversible. (C) 1998 E lsevier Science B.V.