AlPO -5 molecular sieve modified with Cr acac/ 4 3

AlPO4-5 molecular sieve was modified by gas phase reaction with Cr acac.3affording CrrAlPO4-5 material with a chromium content not exceeding 0.2 wt.%. Attachment of Cr species to the external surface of AlPO4-5 is suggested to result from interaction of surface hydroxyl groups with the acac ligands of Cr acac.3, which is too bulky to enter the AlPO4-5 pores. It was shown that the Cr acac.3species which retained their acac ligands predominate on AlPO4-5 surface. These ligands are removed by subsequent thermal treatment in air which simultaneously oxidizes Cr III. ions to give surface-bound Cr VI.oxo-species. q1999 Elsevier Science B.V. All rights reserved