Methane Interaction with Zn2+-Exchanged Zeolite H-ZSM-5: Study of Adsorption and Mobility by One- and Two-Dimensional Variable-Temperature 1H Solid-State NMR
Methane Interaction with Zn2+-Exchanged Zeolite H-ZSM-5: Study of Adsorption and Mobility by One- and Two-Dimensional Variable-Temperature 1H Solid-State NMR
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甲烷与 Zn2 交换沸石 H-ZSM-5 的相互作用：通过一维和二维变温 1H 固态 NMR 研究吸附和迁移率
DOI：
10.1021/acs.jpcc.5b04028
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发表时间：
2015
影响因子：
3.7
通讯作者：
A.G. Stepanov
中科院分区：
文献类型：
--
作者：
M.V. Luzgin;D. Freude;J. Haase;A.G. Stepanov
与母体沸石相比，质子被金属阳离子（全部或部分）取代的酸性沸石在低碳烷烃转化催化反应中表现出更高的活性。烷烃在金属阳离子上的吸附是烷烃与沸石活性位相互作用的第一阶段，研究其在金属阳离子上的吸附对于理解低碳烷烃在含金属沸石上的活化机理具有重要意义。用变温1H魔角自旋核磁共振（1HMASNMR）研究了333-463 K温度范围内，甲烷在不同Zn ~（2+）含量的Zn ~（2+）交换H-ZSM-5分子筛（Zn ~（2+）/H-ZSM-5）及H-ZSM-5分子筛上的吸附行为。在两种Zn 2 +/H-ZSM-5沸石样品中，不同中心（酸桥OH基团和Zn 2+阳离子）的吸附焓（ΔHads）已被确定为OH基团为−18.6 ± 0.4 kJ mol-1，Zn 2+阳离子为−10.9至−11.7 kJ mol-1。二维1H MAS交换NMR实验揭示了吸附态甲烷分子与气相甲烷分子在353-463 K之间的化学交换，有效速率常数为10-60 s-1.随着Zn ~（2+）含量的增加，交换速率降低，交换反应的表观活化能（Ea）由H-ZSM-5沸石的13 kJ mol ~（-1）增加到Zn ~（2+）分别取代50%和85%酸性质子的样品的20和23 kJ mol ~（-1）。Ea的变化与不含Zn 2+阳离子的样品被解释在内部传输障碍，可以存在于晶体的基本构件之间的交叉点和/或晶体共生体之间的晶体中的我们的沸石样品。额外的传输障碍可以从位于晶体表面上的沸石孔系统的入口处的庞大的Zn 2+阳离子产生。
Acidic zeolites in which protons are substituted (completely or in part) by metal cations demonstrate higher activity in catalytic reaction of light alkanes conversion in comparison with parent zeolites. The study of alkane adsorption on metal cationic species as the first stage of alkane interaction with the active sites of zeolites is crucial for understanding the mechanism of light alkane activation on metal-containing zeolites. By using variable-temperature1H magic-angle spinning nuclear magnetic resonance (1H MAS NMR), the adsorption of methane on Zn2+-exchanged H-ZSM-5 zeolites (Zn2+/H-ZSM-5) with different Zn2+content, as well as on source H-ZSM-5, has been studied at 333–463 K. The enthalpy of adsorption (ΔHads) on different centers, acid-bridged OH groups and Zn2+cations, has been determined to be −18.6 ± 0.4 kJ mol–1for OH groups and from −10.9 to −11.7 kJ mol–1for Zn2+cations of both Zn2+/H-ZSM-5 zeolite samples studied. Two-dimensional1H MAS exchange NMR experiments revealed the chemical exchange between the adsorbed and gas-phase methane molecules at 353–463 K with the effective rate constant of 10–60 s–1. The increase of Zn2+content leads to a decrease of the exchange rate, whereas the apparent activation energy (Ea) of the exchange increases from 13 kJ mol–1for H-ZSM-5 zeolite to 20 and 23 kJ mol–1for the samples, in which 50% and 85% of acid protons, respectively, were substituted by Zn2+cations. Variation ofEafor samples with and without Zn2+cations was interpreted in terms of internal transport barriers that can exist at the intersections between the elementary building blocks of the crystals and/or between the crystal intergrowths in crystals of our zeolite samples. Additional transport barriers can arise from the bulky Zn2+cations, located at the entrances of the zeolite pore system on the crystal surface.
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DOI：
10.1016/s0167-2991(07)80800-7
发表时间：
2007
期刊：
Studies in Surface Science and Catalysis
影响因子：
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作者：
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通讯作者：
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影响因子：
7.4
作者：
FERGUSON, DB;HAW, JF
通讯作者：
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DOI：
10.1039/ft9918701935
发表时间：
1991
期刊：
Journal of the Chemical Society, Faraday Transactions
影响因子：
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作者：
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DOI：
10.1016/s0166-9834(00)82708-6
发表时间：
1985
期刊：
Applied Catalysis
影响因子：
--
作者：
A. Tungler;M. Ács;T. Máthé;E. Fogassy;Z. Bende;J. Petró
通讯作者：
J. Petró
影响因子：
2.9
作者：
Gédéon, A;Favre, DE;Chmelka, BF
通讯作者：
Chmelka, BF