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Indexed by:期刊论文

Date of Publication:2013-03-21

Journal:JOURNAL OF PHYSICAL CHEMISTRY C

Included Journals:SCIE、EI、Scopus

Volume:117

Issue:11

Page Number:5848-5854

ISSN No.:1932-7447

Abstract:In the present work, multinuclear solid-state NMR techniques together with power X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to monitor the crystallization process of aluminophosphate AlPO4-11 molecular sieves in 1-ethyl-3-methylimidazolium bromide ([emim]Br) ionic liquids (LLs). The local environments of the selected solid samples were probed by one-dimensional Al-27, P-31, and F-19 MAS NMR experiments, and more information was obtained from two-dimensional Al-27 -> P-31 heteronuclear correlation (HETCOR) and Al-27 triple-quantum MAS (3QMAS) experiments. It is found that a large amount of amorphous aluminophosphates was formed with the F-Al-oct-O-P-par and Al-tet-O-P-par structures in the initial stage of aging. With increasing crystallization time, the partially condensed framework phosphorus species disappeared gradually and became fully condensed. Meanwhile, the octahedral Al was transformed into the pentahedra] and tetrahedral Al species with the structures of F-Al-penta-O-P-ful and Al-tet-O-P-ful in the AlPO4-11 frameworks. During the crystallization process, [emim] cations acting as the structure-directing agents were occluded into the channels, and F- anions were connected with pentahedral Al in the final AlPO4-11 phase. All of these findings can allow proposing a possible formation mechanism for the synthesis of AlPO4-11 in ionic liquids.