Identification and estimation of extra-framework aluminium in acidic mazzite by diffuse reflectance spectroscopy

Diffuse reflectance spectroscopy has been used to investigate structural mo dification of mazzite zeolite subjected to calcination, acid leaching and a cetylacetone treatments. Extra-framework aluminium species, formed upon exp ulsion of aluminium from the framework, are detected by DRS because they ar e involved in aluminium-oxygen charge transfer transitions. Impregnation of the calcined ammonium-exchanged and acid leached samples with ethanolic ac etylacetone will convert the broadened 260-280 nm band of extra-framework a luminium with distorted symmetry to a distinct well-defined 285 nm band. Th e appearance of this band is due to the transformation of the aluminium ato ms with a different coordination number to structures with highly ordered o ctahedral symmetry. Washing the acetylacetone treated samples with hot etha nol leads to extraction of some of the complexed aluminium. The presence of an extracted aluminium triacetylacetonate complex in the eluant is verifie d by the same spectrophotometer used in its conventional mode. This suggest s that a dual DR and UV-VIS spectrophotometry is an appropriate approach to study such topics. (C) 2001 Elsevier Science B.V. All rights reserved.