Characterization of Calcined FAPO-5

Abstract

FAPO-5 samples were synthesized according to a patent method and characterized by chemical analysis, differential thermal analysis, scanning and transmission electron microscopy, electron spin resonance, X-ray diffraction, Mössbauer spectroscopy and magnetic susceptibility measurements. The as-synthesized material contains about 70% of Fe(III) and about 30% of Fe(II) with structures similar to those of the Fe(III)- and Fe(II)-phosphates. K + impurities are enriched in cracked sphere-shaped particles, whilst the K + -free particles exhibit a hexagonal leaf-type morphology. Calcination at 973 K of the as-synthesized molecular sieve finally yields three different iron phases as identified by Mössbauer spectroscopy, i.e. α-Fe 2 O 3 (25%), Fe(III)-phosphate clusters (40%) which are probably occluded within the calcined FAPO-5, and Fe(III) (35%) in a site with tetracoordination and high structural symmetry. According to X-ray diffraction studies the latter phase corresponds to AlPO 4 -tridymite, with Al(III) being partially substituted by Fe(III).