Synthesis of AlPO4-34 and its large single crystal by partially substituting framework fluorine with oxygen species |
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Authors: | Chenguang Wang Jinxiong Wu Mingchang Hu Niu Li Naijia Guan Shouhe Xiang |
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Affiliation: | 1. Institute of New Catalytic Material Science, Key Laboratory of Advanced Energy Materials Chemistry, Ministry of Education, College of Chemistry, Nankai University, Tianjin, China
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Abstract: | AlPO4-34 is a fluorine containing aluminophosphate with two fluorine atoms located in the bridge of two octahedrally coordinated Al atoms of a 4-ring. It has a unit cell composition (C4H10NO+)2 (AlPO4)6F2 ? with the stoichiometric value of Al:P:F being 3:3:1 (F/Al?=?0.33) and to be named as AlPO4-34F. The presence of fluorine in the reacting gels favors the formation of AlPO4-34 structure, but hinders the growth of its large crystals. In present work, a seesaw effect between organic template and hydrofluoric acid on the crystallization of AlPO4-34 has been found and used to synthesize AlPO4-34 with F/Al in the framework lower than 0.33. Large single crystal of AlPO4-34 has been prepared from a gel having the molar ratio of HF/Al2O3?=?0.125. Single crystals refinement has shown that the unit cell formula of the AlPO4-34 is (C4H10NO+)2(AlPO4)6F 1.18 ? (OH) 0.82 ? (H2O)0.5. The molar ratio of Al:P:F:Ob is 3:3:0.59:0.41 with 40% fluoride ions being substituted by oxygen species (Ob: oxygen atoms in the bridges of Al?CO?CAl). Ion chromatography analysis has confirmed the partial substitution of fluorine by oxygen. It was named as AlPO4-34P. Thermal analyses have shown that oxygen species in the bridge position of two octahedrally coordinated Al atoms are more instable than fluoride ions. Under heating, the AlPO4-34P will transform to chabazite structure at a temperature lower than AlPO4-34F. |
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