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|Type:||Artigo de periódico|
|Title:||Static crystallization of zeolites MCM-22 and MCM-49|
|Abstract:||Zeolites MCM-22 and MCM-49, with SiO2/Al2O3 molar ratios (SARs) of 30 and 50, were prepared under static conditions using silica, sodium aluminate and hexamethyleneimine. An aging step before the hydrothermal treatment made it possible to obtain good-quality MCM-22 under these reaction conditions. No aging step during gel preparation gave rise to MCM-49. The aging step probably provides the reaction mixture with nuclei that grow in the static hydrothermal crystallization and whose formation conditions are extremely specific. The physico-chemical characteristics of these materials compare well with those for the same zeolites prepared under stirring, except for the morphology of the particles. The MCM-22 samples with SAR = 30 are cylindrical particles with a depression in the center, while those with SAR = 50 are spheres with a crack along the centerline. MCM-49, with SAR = 30, crystallizes as hollow cylinders with approximately the same dimensions as MCM-22 having the same SAR. (C) 1999 Elsevier Science B.V. All rights reserved.|
|Editor:||Elsevier Science Bv|
|Appears in Collections:||Artigos e Materiais de Revistas Científicas - Unicamp|
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