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首页> 外文期刊>Microporous and mesoporous materials: The offical journal of the International Zeolite Association >Influence of acid strength on the reactivity of alkane activation on solid acid catalysts: A theoretical calculation study
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Influence of acid strength on the reactivity of alkane activation on solid acid catalysts: A theoretical calculation study

机译:酸强度对固体酸催化剂上烷烃活化反应活性的影响:理论计算研究

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摘要

The influence of Brensted acid strength on the reactivities of alkane activations has been systematically studied by density functional theory (DFT) calculations. Some typical reactions, such as methane hydrogen exchange (C-H bond activation), propane dehydrogenation (C-H bond dissociation and H-H bond formation), and propane cracking (C-C cleavage), were investigated on 8T solid acid models with varying acid strengths from weak-, strong-, to super-acid. According to our calculational results, it was revealed that the activation barriers (E_(act)) of all the reactions decrease linearly, while the rate coefficients (log k) increase linearly with increasing the acid strength, being indicative of the enhancement of reactivities. However, the reactivity of different reactions exhibits different sensitivity to acid strength: the propane cracking is most sensitive to acid strength, while the methane hydrogen exchange reaction is least sensitive to acid strength. On the basis of the natural charge on the organic fragment in the transition state, it was revealed that the sensitivity of the reactivity to acid strength could be related to the ionic character of the transition state. The propane cracking reaction possesses a more ionic transition state (0.913-0.964 |e|), while the methane hydrogen exchange has a less ionic transition state (0.646-0.773 |e|).
机译:布伦斯台德酸强度对烷烃活化反应活性的影响已通过密度泛函理论(DFT)计算进行了系统研究。在8T固体酸模型上研究了一些典型的反应,例如甲烷氢交换(CH键活化),丙烷脱氢(CH键解离和HH键形成)和丙烷裂解(CC裂解),其中弱酸,弱酸,强,超强酸。根据我们的计算结果,发现所有反应的活化能垒(E_(act))线性降低,而速率系数(log k)随着酸强度的增加线性增加,这表明反应性增强。但是,不同反应的反应性对酸强度表现出不同的敏感性:丙烷裂解对酸强度最敏感,而甲烷氢交换反应对酸强度最不敏感。基于过渡态有机片段上的天然电荷,发现反应性对酸强度的敏感性可能与过渡态的离子特性有关。丙烷裂解反应具有更高的离子过渡态(0.913-0.964 | e |),而甲烷氢交换具有更低的离子过渡态(0.646-0.773 | e |)。

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