Effect of leaching agent in the dealumination of stabilized Y zeolites

X-ray diffraction and Al-27 multiquantum MAS NMR combined with global elemental analysis have been used to identify and quantify extra-framework aluminum (EFAL) in Y zeolites stabilized by steaming followed by EFAL extraction using nitric acid, ammonium hexafluorosilicate (AHFS) or ethylenediaminetetraacetic acid (EDTA). Both the ease of extraction and the type of EFAL extracted are found to vary with the strength and nature of the leaching agent. Polymeric amorphous alumina, removed easily at low concentrations of nitric acid, is extracted progressively with increasing concentrations of other agents. This type of EFAL accounts for less than half of the extra-framework aluminum. Aluminum atoms linked to the zeolite framework in a distorted tetrahedral environment are also removed by acid leaching but are resistant to high concentrations of AHFS and EDTA, whereas isolated cationic EFAL shows the reverse behavior. (C) 2000 Elsevier Science B.V. All rights reserved.