The removal of the extra-framework aluminum species without destroying the micropore structure and extraction of the species can be achieved by employing complexing agents. The effect of the acetylacetone as a chelating agent for extraction of extra-framework aluminum from zeolite L was investigated by means of diffuse reflectance spectroscopy. The treatment of the as-synthesized zeolite L with acetylacetone at room temperature does not produce any extra-framework aluminum species as evidenced by diffuse reflectance spectra (DRS). However, acetylacetone reacts with extra-framework aluminum species that are formed upon thermal treatment or acid leaching of zeolite L. Removal of aluminum acetylacetone complexes out of the zeolite crystal can be achieved by several successive washing up steps by hot ethanol. DRS monitoring was used to control removal of extra-framework aluminum species because amount and distribution of these species are correlated with catalytic activity and selectivity of zeolites. (C) 2004 Elsevier B.V. All rights reserved.