Chemical conversion of methane into light olefins involving intermediate CH₃X (X = OH, SH, Cl, and Br) provides an alternative to syngas-based technologies. In this contribution, periodic density functional theory calculations with van der Waals correlation have been performed to achieve a full picture of how the CH₃X methylating agents would affect the catalytic activity of olefin methylation in H-SAPO-34 and other metal-substituted CHA-structured zeotypes. The methylation enthalpy barriers depend strongly on the protonation ability of the methylating agent and how readily the CX bond can be broken. Gibbs free energy calculations indicate that the reactivity of different methylating agents decreases in the trend CH₃OH > CH₃Br ∼ CH₃Cl > CH₃SH. The linear transition state enthalpy scaling relations expressed in terms of adsorption enthalpy of ammonia hold very well for the coupling of propene and tetramethylethene to all the methylating agents. The olefin methylation by CH₃Cl and CH₃Br is much less sensitive to acid strength than that by CH₃OH and CH₃SH. The charge transfer between the organic species and the zeolite framework, and hence the nature of ion-pair interaction, play a key role in determining the sensitivity of the olefin methylation to acid strength.

甲烷化学转化为涉及中间体CH ₃ X（X = OH，SH，Cl和Br）的轻质烯烃的方法可替代基于合成气的技术。在此贡献中，已进行了具有范德华相关性的周期性密度泛函理论计算，以全面了解CH ₃ X甲基化剂如何影响H-SAPO-34和其他金属取代的CHA中烯烃甲基化的催化活性。结构型。甲基化焓屏障在很大程度上取决于甲基化剂的质子化能力以及C X键的断裂容易程度。吉布斯自由能的计算表明，不同的甲基化剂的反应性随CH ₃ OH> CH ₃的趋势而降低。Br〜CH ₃ Cl> CH ₃ SH。对于氨和四甲基乙烯与所有甲基化剂的偶合，以氨的吸附焓表示的线性过渡态焓比例关系非常好。与CH ₃ OH和CH ₃ SH相比，通过CH ₃ Cl和CH ₃ Br进行的烯烃甲基化对酸强度的敏感性要低得多。有机物和沸石骨架之间的电荷转移以及因此离子对相互作用的性质在确定烯烃甲基化对酸强度的敏感性方面起着关键作用。