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首页> 美国卫生研究院文献>Wiley-Blackwell Online Open >On the Role of Acidity in Bulk and Nanosheet TMFI (T=Al3+ Ga3+ Fe3+ B3+) Zeolites in the Methanol‐to‐Hydrocarbons Reaction
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On the Role of Acidity in Bulk and Nanosheet TMFI (T=Al3+ Ga3+ Fe3+ B3+) Zeolites in the Methanol‐to‐Hydrocarbons Reaction

机译：关于酸度在块状和纳米片T MFI（T = Al3 +Ga3 +Fe3 +B3 +）分子筛在甲醇制烃反应中的作用

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摘要

The influence of framework substituents (Al3+, Ga3+, Fe3+ and B3+) and morphology (bulk vs. nanometer‐sized sheets) of MFI zeolites on the acidity and catalytic performance in the methanol‐to‐hydrocarbons (MTH) reaction was investigated. The Brønsted acid density and strength decreased in the order Al(OH)Si>Ga(OH)Si>Fe(OH)Si≫B(OH)Si. Pyridine 15N NMR spectra confirmed the differences in the Brønsted and Lewis acid strengths but also provided evidence for site heterogeneity in the Brønsted acid sites. Owing to the lower efficiency with which tervalent ions can be inserted into the zeolite framework, sheet‐like zeolites exhibited lower acidity than bulk zeolites. The sheet‐like Al‐containing MFI zeolite exhibited the greatest longevity as a MTH catalyst, outperforming its bulk [Al]MFI counterpart. Although the lower acidity of bulk [Ga]MFI led to a better catalytic performance than bulk [Al]MFI, the sheet‐like [Ga]MFI sample was found to be nearly inactive owing to lower and heterogeneous Brønsted acidity. All Fe‐ and B‐substituted zeolite samples displayed very low catalytic performance owing to their weak acidity. Based on the product distribution, the MTH reaction was found to be dominated by the olefins‐based catalytic cycle. The small contribution of the aromatics‐based catalytic cycle was larger for bulk zeolite than for sheet‐like zeolite, indicating that shorter residence time of aromatics can explain the lower tendency toward coking and enhanced catalyst longevity.
机译：骨架取代基（Al 3 + ，Ga 3 + ，Fe 3 + 和B 3 + 的影响）研究了MFI沸石的形态和结构（相对于纳米片的体形），研究了其在甲醇制烃（MTH）反应中的酸度和催化性能。布朗斯台德酸的密度和强度按Al（OH）Si> Ga（OH）Si> Fe（OH）Si≫B（OH）Si的顺序降低。吡啶的 15 N NMR光谱证实了布朗斯台德和路易斯酸强度的差异，但也为布朗斯台德酸位点的位点异质性提供了证据。由于三价离子可插入沸石骨架的效率较低，因此片状沸石的酸度低于块状沸石。片状含铝MFI沸石作为MTH催化剂具有最长的使用寿命，胜过其体积较大的[Al] MFI对应物。尽管[Ga] MFI的较低酸度比[Al] MFI的具有更好的催化性能，但片状[Ga] MFI样品由于较低的和不均匀的布朗斯台德酸度而几乎没有活性。所有的Fe和B取代的沸石样品由于其弱酸性而显示出非常低的催化性能。根据产物分布，发现MTH反应主要受基于烯烃的催化循环的影响。块状沸石对芳烃基催化循环的微小贡献要比片状沸石大，这表明芳烃的较短停留时间可以解释较低的焦化趋势和延长的催化剂寿命。

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