Thermal Evolution of 4- and 5-fold Coordinated Al-Sites in Aluminum Hydroxide Fluorides with Low Fluorination Degree
Thermal Evolution of 4- and 5-fold Coordinated Al-Sites in Aluminum Hydroxide Fluorides with Low Fluorination Degree
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DOI：
10.1021/acs.jpcc.6b01191
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发表时间：
2016-04
影响因子：
3.7
通讯作者：
Lukas Ahrem;G. Scholz;R. Bertram;E. Kemnitz
中科院分区：
文献类型：
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作者：
Lukas Ahrem;G. Scholz;R. Bertram;E. Kemnitz
采用一种改进的氟化溶胶-凝胶合成方法合成了纯的、无定形的氢氧化铝氟化物，其具有非常低的且易于调节的结晶度，以及可控的表面积。对它们的热行为的仔细研究表明，这些氢氧化铝氟化物已经在非常低的温度下进行脱羟基反应（即，低于80 ° C），这与所有结晶氢氧化铝（氟化铝）相相反。27Al和19F MAS NMR实验明确表明，这种脱羟基作用与局部结构的剧烈重组有关，并导致亚配位Al物种的显着进化。发现在高温下煅烧的样品AlF 0.25（OH）2.75的5倍（AlV）和4倍（AlIV）配位Al位点的最大强度分别为约45%和54%。调查还表明，相对强度的AlIV-和AlV-物种基本上取决于结晶度。
A modified approach of the fluorolytic sol–gel synthesis was used to synthesize pure, amorphous aluminum hydroxide fluorides with very low and easily adjustable fluorination degrees, as well as controllable surface areas. The careful investigation of their thermal behavior revealed that these aluminum hydroxide fluorides undergo dehydroxylation reactions already at very low temperatures (i.e., below 80 °C), which is in contrast to all crystalline aluminum hydroxide (fluoride) phases. 27Al and 19F MAS NMR experiments unambiguously demonstrated that this dehydroxylation is clearly linked to a drastic reorganization of local structures and leads to a remarkable evolution of subcoordinated Al-species. A maximum intensity of about 45% for 5-fold (AlV) and 54% for 4-fold (AlIV) coordinated Al-sites was found for sample AlF0.25(OH)2.75, calcined at elevated temperatures. The investigations also revealed that the relative intensity of AlIV- and AlV-species essentially depends on the fluorination degree.