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Issue 45, 2010
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Characterization of the gel phases formed in the synthesis of microporous gallophosphate, cloverite

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Abstract

This work examines the formation of a microporous gallophosphate with an extra large pore system, namely cloverite (structure type: CLO) in fluoride medium. The amorphous gallophosphate gel containing the key precursor to cloverite was characterized and its evolution followed by 31P, 71Ga, 19F and 1H MAS NMR and several dipolar-coupling based double-resonance methods including 31P{71Ga} and 19F{71Ga} rotational-echo adiabatic passage double-resonance (REAPDOR), 31P{19F} and 19F{31P} rotational-echo double-resonance (REDOR), and 1H{31P} REDOR and 1H{71Ga} transfer of populations in double-resonance (TRAPDOR). The results indicate that upon mixing the Ga and P sources in the presence of structure directing agent (SDA) and HF, an amorphous oxyfluorinated gallophosphate precursor containing single 4-rings (4Rs) with alternating Ga–O–P linkage forms immediately. The Ga in the 4R is 6-coordinated and the two Ga in the 4R are bridged by a fluorine. Heating quickly converts the 4Rs to double four-membered rings (D4Rs), from which the entire CLO structure is built. The amount of the D4R rapidly increases with increasing heating time. The presence of fluoride ions greatly facilitates the formation of the 4Rs via bridging two Ga sites and the hydrothermal treatment promotes D4Rs via condensation. Interaction between SDA molecule and the phosphorus site in the gel is also probed. Further, the local structure of Ga sites in cloverite is characterized by 71Ga MAS NMR at ultrahigh magnetic field of 21.1 T by obtaining their electric field gradient tensor parameters.

Graphical abstract: Characterization of the gel phases formed in the synthesis of microporous gallophosphate, cloverite

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Publication details

The article was received on 13 Aug 2010, accepted on 11 Sep 2010 and first published on 04 Oct 2010


Article type: Paper
DOI: 10.1039/C0JM02670K
Citation: J. Mater. Chem., 2010,20, 10200-10210
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    Characterization of the gel phases formed in the synthesis of microporous gallophosphate, cloverite

    Z. Yan, C. W. Kirby and Y. Huang, J. Mater. Chem., 2010, 20, 10200
    DOI: 10.1039/C0JM02670K

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