A novel fluoride-doped aluminium oxide catalyst with tunable Brønsted and Lewis acidity,Catalysis Science & Technology

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A novel fluoride-doped aluminium oxide catalyst with tunable Brønsted and Lewis acidity
Catalysis Science & Technology ( IF 4.4 ) Pub Date : 2018-01-09 00:00:00 , DOI: 10.1039/c7cy02257c
Lukas Ahrem _{1,

2,

3,

4} , Jakob Wolf _{1,

2,

3,

4} , Gudrun Scholz _{1,

2,

3,

4} , Erhard Kemnitz _{1,

2,

3,

4}

Affiliation

The fluorination of transition aluminas has long been used to modify their properties and tune their catalytic performance. In this study, the preparation of a novel F-doped Al₂O₃ catalyst is demonstrated. The introduced two-step synthesis route enabled adjustment of the amount of fluoride and thus control of the characteristic properties of the catalyst. Structural investigation by XRD, ¹⁹F and ²⁷Al MAS NMR revealed the formation of an F-doped Al₂O₃ phase at high temperatures (700 °C). This new phase shows high similarity to common transition aluminium oxides like γ-Al₂O₃. Contrary to other fluorinated alumina, in this phase fluoride is finely distributed throughout the bulk and surface of the sample. Surface characterisation methods like nitrogen and pyridine adsorption and NH₃-TPD revealed a vital influence of fluoride doping for catalytic purposes. This is evidenced by the increased acidic strength and the introduction of strong Brønsted acid sites. Different from other systems, these Brønsted acid sites are formed despite the absence of a proton-rich atmosphere. The high catalytic potential of this new F-doped Al₂O₃ is additionally demonstrated in a catalytic test reaction which is the cyclisation of citronellal to isopulegol, a key step in the synthetic production of menthol.

中文翻译：

具有可调的Brønsted和Lewis酸度的新型氟化物掺杂氧化铝催化剂

过渡氧化铝的氟化长期以来一直用于改变其性能并调整其催化性能。在这项研究中，证明了新型F掺杂Al ₂ O ₃催化剂的制备。引入的两步合成路线使得能够调节氟化物的量，从而控制催化剂的特性。通过XRD，¹⁹ F和²⁷ Al MAS NMR进行的结构研究表明，在高温（700°C）下会形成F掺杂的Al ₂ O ₃相。这个新阶段显示高相似共同过渡氧化铝等的γ-Al ₂ ö ₃。与其他氟化氧化铝相反，在此相中，氟化物精细地分布在整个样品和整个样品表面。诸如氮和吡啶吸附以及NH ₃ -TPD的表面表征方法揭示了氟化物掺杂对催化目的的重要影响。增强的酸强度和强力的布朗斯台德酸位的引入证明了这一点。与其他系统不同，尽管没有富质子的气氛，但仍形成了这些布朗斯台德酸位。这种新的F掺杂的Al ₂ O ₃的高催化潜力在催化测试反应中得到了进一步证明，该反应是香茅醛向异薄荷醇的环化反应，这是薄荷醇合成生产中的关键步骤。

更新日期：2018-01-09

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