Influences of the confinement effect and acid strength of zeolite on the mechanisms of Methanol-to-Olefins conversion over H-ZSM-5: A theoretical study of alkenes-based cycle
Influences of the confinement effect and acid strength of zeolite on the mechanisms of Methanol-to-Olefins conversion over H-ZSM-5: A theoretical study of alkenes-based cycle
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沸石的限域效应和酸强度对 H-ZSM-5 甲醇转化为烯烃机理的影响：基于烯烃循环的理论研究
DOI：
10.1016/j.micromeso.2016.05.029
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发表时间：
2016-09
影响因子：
5.2
通讯作者：
Liu, Zhongmin
中科院分区：
文献类型：
--
作者：
Zhang, Mozhi;Zheng, Anmin;Deng, Feng;Liu, Zhongmin
酸性沸石催化剂上的甲醇转化为烯烃（MTO）已成为生产轻质烯烃的最重要的非石化途径。 H-ZSM-5 沸石的“双循环”机制（即基于烯烃的循环和基于芳烃的循环）已被普遍接受用于甲醇转化生成烯烃。然而，催化性能与催化剂的限域效应/酸强度之间的关系仍不清楚。在此，通过密度泛函理论（DFT）计算深入讨论了基于烯烃的循环中涉及的甲基化、异构化和裂解过程。计算结果预测，沸石骨架的范德华（vdW）相互作用可以显着稳定过渡态，从而减少活化势垒。而且酸的强度也可以增强反应活性。然而，随着酸强度的增加，基于烯烃的循环中所有基本步骤的催化反应活性都可以不同程度地提高。此外，乙烯的形成、转化以及乙烯形成的前驱体需要较高的能量。并且增加酸强度可以急剧降低裂解反应乙烯形成的活化势垒，表明乙烯形成可能需要较强的酸强度。
Methanol-to-Olefins (MTO) conversion over acidic zeolite catalysts has become the most important non-petrochemical route for the production of light olefins. The ‘dual-cycle’ mechanism (i.e., alkenes-based cycle and aromatics-based cycle) over H-ZSM-5 zeolite has been generally accepted for olefins generation from methanol conversion. However, the relationship between the catalytic performance and the confinement effect/acid strength of the catalyst is still unclear. Herein, the methylation, isomerization and cracking processes involved in the alkenes-based cycle are discussed in-depth by density functional theory (DFT) calculations. The calculation results predicted that the transition states can be considerably stabilized by the van der Waals (vdW) interactions from the zeolite framework, resulting in the reduction of the activation barriers. And acid strength can also enhance the reaction activities. However, the catalytic reactivity of all elementary steps in the alkenes-based cycle can be improved at a different degree with increasing the acid strength. In addition, the ethene formation, transformation and the precursor of ethene formation need higher energy. And increasing acid strength can sharply decrease the activation barriers of ethene formation of cracking reaction, indicating that ethene formation may need strong acid strength.
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影响因子：
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作者：
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DOI：
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DOI：
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期刊：
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