METHYL HALIDE REACTIONS ON MULTIFUNCTIONAL METAL-EXCHANGED ZEOLITE CATALYSTS
METHYL HALIDE REACTIONS ON MULTIFUNCTIONAL METAL-EXCHANGED ZEOLITE CATALYSTS
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DOI：
10.1021/ja00093a040
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发表时间：
1994-07
影响因子：
15
通讯作者：
D. K. Murray;T. Howard;Patrick W. Goguen;T. Krawietz;J. F. Haw
中科院分区：
文献类型：
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作者：
D. K. Murray;T. Howard;Patrick W. Goguen;T. Krawietz;J. F. Haw
沸石骨架中由作为氢氧化物和/或氧化物的二价金属阳离子和阴离子位点组成的近端位点对于卤代甲烷转化为乙烯非常活跃。这些研究进一步支持了先前报道的沸石骨架和卤化物离去基团稳定性的影响（J. Am. Chem. SOC. 1993,115,4732-4741），并证明了二价金属位点的多种作用。碱性沸石 CsX 在低至 498 K 的温度下将碘甲烷转化为碳氢化合物，而该反应在多功能催化剂 ZnX 上于 248 K 开始。活性的顺序 Zn2+ > Cd2+ 和 Mgz+ > Ba2+ 表明路易斯酸度是这些作用之一。 CuY 沸石对于乙烯的形成具有很强的选择性。通过原位 13C 固态 NMR、使用流通池的原位 FT’IR 光谱以及传统的流动反应器研究了这些反应。 ZnZSM-5 的活性位点也用 1H 固态NMR 进行了探测。第一个中间体是骨架结合的甲氧基。该物质的 I3C NMR 和 FTIR 性质已被关联，并且表明该物质与甲醇制汽油化学过程中观察到的物质非常相似或相同。提出了卤代甲烷在 Zn 和 Mg 沸石上反应的详细机制，其中包括金属的几种明确作用。
Proximal sites consisting of a divalent metal cation as a hydroxide and/or oxide and an anion site in the zeolite framework are very active for the conversion of methyl halides to ethylene. These studies further support the effects of zeolite framework and halide leaving-group stability reported previously (J. Am. Chem. SOC. 1993,115,4732-4741) and demonstrate multiple roles for divalent metal sites. Whereas the basic zeolite CsX converted methyl iodide to hydrocarbons at temperatures as low as 498 K, this reaction commenced at 248 K on the multifunctional catalyst ZnX. The orders of activity Zn2+ > Cd2+ and Mgz+ > Ba2+ suggest that Lewis acidity is one of these roles. Zeolite CuY is very selective for ethylene formation. These reactions were studied by in situ 13C solid-state NMR, by in situ FT’IR spectroscopy with a flow cell, and with conventional flow reactors. The active sites of ZnZSM-5 were also probed with IH solid-stateNMR. The first intermediate is a framework-bound methoxy group. The I3C NMR and FTIR properties of this species have been correlated, and it is shown that this species is very similar or identical to that observed during methanol to gasoline chemistry. A detailed mechanism is proposed for the reaction of methyl halides on Zn and Mg zeolites that includes several explicit roles for the metal.