Hydrogen H/D Exchange and Activation of C1―n-C4 Alkanes on Ga-Modified Zeolite BEA Studied with 1H Magic Angle Spinning Nuclear Magnetic Resonance in Situ
Hydrogen H/D Exchange and Activation of C1―n-C4 Alkanes on Ga-Modified Zeolite BEA Studied with 1H Magic Angle Spinning Nuclear Magnetic Resonance in Situ
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DOI：
10.1021/jp204398r
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发表时间：
2011-06
影响因子：
3.7
通讯作者：
A. Gabrienko;S. Arzumanov;A. Toktarev;D. Freude;J. Haase;A. Stepanov
中科院分区：
文献类型：
--
作者：
A. Gabrienko;S. Arzumanov;A. Toktarev;D. Freude;J. Haase;A. Stepanov
在423-563 K，用1HMASNMR原位研究了纯酸型沸石H-ZSM-5（H-ZSM-5）和Ga改性沸石H-ZSM-5（Ga/H-ZSM-5）中C1-n-C4烷烃与Bronsted酸中心（BAS）的H/D氢交换动力学。对比分析了H-CH_4和Ga/H-CH_4沸石的交换速率，发现Ga改性H-CH_4沸石后，交换速率显著提高1-2个数量级，交换活化能降低，并出现区域选择性交换C_3-n-C_4烷烃的甲基。这些数据表明Ga对BAS活化烷烃C-H键有明显的促进作用。该效果已被合理化的初步解离吸附烷烃的氧化镓（III）物种内沸石孔形成镓烷基物种，这是进一步参与与邻居BAS交换。在烷烃活化中BAS和Ga物质的参与解释了早期提出的协同效应（Buckles，G.，C.
Kinetics of H/D hydrogen exchange between C1–n-C4 alkanes and Bronsted acid sites (BAS) of both the pure acid-form zeolite BEA (H-BEA) and Ga-modified zeolite BEA (Ga/H-BEA) was monitored by 1H MAS NMR spectroscopy in situ at 423–563 K. Comparative analysis of the rates of the exchange for H-BEA and Ga/H-BEA zeolites reveals a remarkable increase of the rate by 1–2 orders of magnitude, decrease of activation energy, and an appearance of regioselectivity of the exchange into the methyl groups of C3-n-C4 alkanes upon modification of H-BEA zeolite with gallium. These data identify an evident promoting effect of Ga on activation of alkane C–H bonds by BAS. The effect has been rationalized by preliminary dissociative adsorption of alkanes on gallium(III) oxide species inside zeolite pores to form gallium-alkyl species, which are further involved in the exchange with neighbor BAS. Involvement of both BAS and Ga species in alkane activation accounts for earlier suggested synergistic effect (Buckles, G., et al. C...