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|Type:||Artigo de periódico|
|Title:||Synthesis And Characterization Of Tubular Aluminophosphate Mesoporous Materias Containing Framework Magnesium|
|Abstract:||A series of aluminophosphates (and magnesium-aluminophosphates based on tubular molecular sieves have been synthesized using cetyltrimethylammonium bromide (CTAB) as structure-directing agent in the presence of tetramethylammonium hydroxide, at room temperature and under hydrothermal synthesis, using molar ratios of CTAB/A1 = 0.5 and 1.0, and 0 ≤= (=MgO/A12O3) ≤0.015 in the gel composition. The hexagonal mesostructure of the assynthesized aluminophosphates and magnesium-aluminophosphates was evidenced by two defined diffractions in the range between 20 = 2° and 5°, and was obtained regardless of the amount of magnesium added to the synthesis mixture. The usual processes for removal of structure-directing agent, i.e. calcination and Soxhlet extraction with azeotropic solutions, both resulted in framework collapse, possibly due to the poor polymerization of the inorganic matrix. An alternative procedure was performed by extracting CTAB using a solution of ethanol/n-butylamine, which showed to be efficient in extracting the majority of the organic part, without destruction of the mesostructure. After extraction, the samples exhibited only the characteristic low angle peak, typical of tubular materials, whose structure remained after further calcination. Elemental analyses confirmed the presence of magnesium in these materials. The 31P nuclear magnetic resonance spectra of calcined sample confirmed the better condensation of the sample after thermal treatment, compared to the as-synthesized materials. The transmission electron microscopy image showed disordered arrays of tubes. These results indicates that thermally stable mesoporous magnesium-aluminophosphate materials can be obtained by using alkaline extraction and calcination as post-synthesis treatment. © 2001 Elsevier Science B.V. All rights reserved.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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