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

Diffuse reflectance spectroscopy has been used to investigate structural modification of mazzite zeolite subjected to calcination, acid leaching and acetylacetone treatments. Extra-framework aluminium species, formed upon expulsion of aluminium from the framework, are detected by DRS because they are involved in aluminium-oxygen charge transfer transitions. Impregnation of the calcined ammonium-exchanged and acid leached samples with ethanolic acetylacetone will convert the broadened 260-280 nm band of extra-framework aluminium with distorted symmetry to a distinct well-defined 285 nm band. The appearance of this band is due to the transformation of the aluminium atoms with a different coordination number to structures with highly ordered octahedral symmetry. Washing the acetylacetone treated samples with hot ethanol leads to extraction of some of the complexed aluminium. The presence of an extracted aluminium triacetylacetonate complex in the eluant is verified by the same spectrophotometer used in its conventional mode. This suggests 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.