Methylation of benzene with methanol over HZSM-11 and HZSM-5: A density functional theory study
Methylation of benzene with methanol over HZSM-11 and HZSM-5: A density functional theory study
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DOI：
10.1016/j.molcata.2016.07.051
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发表时间：
2016-12
影响因子：
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通讯作者：
Z. Wen;Daqiang Yang;He Xuan;Yunsheng Li;Xuedong Zhu
中科院分区：
文献类型：
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作者：
Z. Wen;Daqiang Yang;He Xuan;Yunsheng Li;Xuedong Zhu
通过使用密度泛函理论（一种计算量子力学建模方法），计算了 HZSM-11 和 HZSM-5 的布朗斯台德酸位。从气体分子在这些沸石上的估计吸附能可以看出，与 HZSM-11 相比，HZSM-5 可能存在更强的客主相互作用。对甲醇苯甲基化的协同和逐步路径的研究表明，协同路径中计算的苯甲基化能垒为 HZSM-11 的 129 kJ/mol 和 HZSM-5 的 149 kJ/mol。在逐步途径的情况下，HZSM-11 上甲氧基形成和苯甲基化所达到的能垒分别为 153 kJ/mol 和 93 kJ/mol（HZSM-5 上分别为 149 kJ/mol 和 97 kJ/mol）。在两种沸石上获得的能量值相似，与其类似的拓扑结构非常一致。甲烷是由分子内质子从环碳转移到甲苯离子中甲基的碳上形成的，类似于烃池机制。 HZSM-11 和 HZSM-5 上甲烷形成的能垒经计算分别为 92 和 101 kJ/mol。甲烷脱甲基化形成的C6H5+物质可能被吸附在酸性位点上，导致催化剂失活。烷烃的形成也是间接降低催化剂反应活性的一个重要因素。
By using density functional theory, a computational quantum mechanical modelling method, the Brønsted acid sites of both HZSM-11 and HZSM-5 were calculated. From the estimated adsorption energies of gas molecules on these zeolites, it can be seen that there may exist stronger guest-host interactions in HZSM-5 when compared to that in HZSM-11. Investigation of concerted and stepwise pathways for benzene methylation by methanol showed that the energy barriers of benzene methylation calculated in concerted pathway are 129 kJ/mol for HZSM-11 and 149 kJ/mol for HZSM-5. In the case of stepwise pathway, the achieved energy barriers of formation of the methoxy group and benzene methylation over HZSM-11 are 153 and 93 kJ/mol (vs. 149 and 97 kJ/mol over HZSM-5), respectively. The energy values obtained over both zeolites are similar, in good agreement with their analogous topologies. Methane is formed by an intramolecular proton transfer from the ring carbon to the carbon of methyl group in the toluenium ion, which is similar to hydrocarbon pool mechanism. The energy barriers for the methane formation over HZSM-11 and HZSM-5 were calculated as being 92 and 101 kJ/mol, respectively. C6H5+species, which can be formed by the demethylation of methane, may be adsorbed on the acid sites, leading to the catalyst deactivation. The formation of alkane is also due to a significant factor that indirectly decreases the reactivity of catalyst.