Alkylation of Benzene with Methane over ZnZSM-5 Zeolites Studied with Solid-State NMR Spectroscopy
Alkylation of Benzene with Methane over ZnZSM-5 Zeolites Studied with Solid-State NMR Spectroscopy
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用固态核磁共振波谱研究了 ZnZSM-5 沸石上苯与甲烷的烷基化
DOI：
10.1021/jp310872a
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发表时间：
2013-02-28
影响因子：
3.7
通讯作者：
Deng, Feng
中科院分区：
文献类型：
--
作者：
Wang, Xiumei;Xu, Jun;Deng, Feng
采用原位固体核磁共振和气相色谱-质谱联用技术研究了ZnZSM-5分子筛上苯与甲烷在氧化条件下的烷基化反应。实验结果表明，在523-623 K温度范围内，以O-2或N_2O为氧化剂，烷基化反应选择性生成甲苯。使用C-13同位素标记的反应物，甲烷和苯的转化率独立监测，并确定它们各自在反应中的作用。核磁共振谱发现，甲烷首先被活化为甲氧基物种和甲基锌中间体。作为亲电试剂，甲氧基物种的甲基可直接进攻苯环，通过亲电取代反应生成甲苯，而甲基锌物种不直接参与烷基化反应。然而，类似的性质的锌甲基物种（Zn-CH 3）的有机锌化合物允许的锌甲基物种（Zn-CH 3）容易氧化成甲氧基物种。如GC-MS实验所证实的，甲烷专门提供甲苯产物的甲基，而苯提供苯环。实验结果还表明，无论是甲烷还是苯单独都不会产生甲苯。
Alkylation of benzene with methane was studied under oxidization condition over ZnZSM-5 zeolites by using in situ solid-state NMR spectroscopy and GC-MS analysis. The experimental results indicate that the alkylation reaction occurs with selective formation of toluene at ternperatures of 523-623 K using O-2 or N2O as the oxidant. Using C-13 isotope labeled reactants, the conversions of methane and benzene were independently monitored, and their respective role in the reaction was determined. It was found by NMR spectroscopy that methane was first activated into methoxy species and zinc methyl intermediates. As an electrophilic agent, the methyl group of methoxy species could directly attack phenyl ring to produce toluene via electrophilic substitution reaction, while the zinc methyl species was not directly involved in the alkylation reaction. However, the similar nature of zinc methyl species (Zn-CH3) to organozinc compounds allowed the facile oxidization of zinc methyl species (Zn-CH3) into methoxy species. As confirmed by GC-MS experiments, methane exclusively provided the methyl group of toluene product while benzene afforded the phenyl ring. Experimental results also indicated that neither methane nor benzene alone could generate toluene.