Structure, Nature and Activity of Ga Species for Propane Aromatization in Ga/ZSM-5 Revealed by Solid-state NMR Spectroscopy
Structure, Nature and Activity of Ga Species for Propane Aromatization in Ga/ZSM-5 Revealed by Solid-state NMR Spectroscopy
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固态核磁共振波谱揭示Ga/ZSM-5中Ga物种的结构、性质和丙烷芳构化活性
DOI：
10.7503/cjcu20200474
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发表时间：
2020
影响因子：
1
通讯作者：
Deng Peng
中科院分区：
文献类型：
--
作者：
Zhao Xingling;Qi Guodong;Wang Qiang;Chu Yueying;Gao Wei;Li Shenhui;Xu Jun;Deng Peng
采用不同方法制备了一系列镓改性ZSM-5分子筛。用固体核磁共振（ssNMR）对催化剂的结构和酸性进行了表征。考察了丙烷芳构化反应的催化性能。借助Ga-71 NMR和三甲基膦（TMP）探针1D P-31和2D H-1-P-31 HETCOR NMR，发现物理混合法制备的Ga_2 O_3/ZSM-5样品中只含有Ga物种，具有弱的刘易斯酸性，并且通过浸渍制备的样品（Ga/ZSM-5-ox）和浸渍后还原-氧化处理（Ga/ZSM-5-redox）含有高度分散的镓簇和阳离子Ga物质。离子交换法制备的Ga/ZSM-5-IE催化剂中Ga的存在有利于阳离子物种的形成。分散的镓团簇和阳离子镓都表现出较强的刘易斯酸性。丙烷在Ga改性ZSM-5上的芳构化反应结果表明，Ga的存在形态和酸性对丙烷的芳构化反应有显著影响。芳烃转化率和选择性的顺序为Ga/ZSM-5-IE > Ga/ZSM-5-氧化还原> Ga/ZSM-5-ox > Ga_2 O_3/ZSM-5 > H-ZSM-5。协同活性中心由布朗斯台德酸中心（BAS）和刘易斯酸中心（阳离子）组成。Ga/ZSM-5分子筛上的Ga和分散的Ga物种）通过2D H-1-P-31 HETCOR NMR谱进行了鉴定，并与催化活性进行了关联。
A series of Ga-modified ZSM-5 zeolites were prepared by different methods. The structure and acidity of these catalysts were characterized by solid-state NMR(ssNMR). The catalytic reactions for propane aromatization were also investigated. With the help of Ga-71 NMR and trimethylphosphine (TMP) probe 1D P-31 and 2D H-1-P-31 HETCOR NMR, it was found that the Ga2O3/ZSM-5 sample prepared by physical mixing only contains Ga species with weak Lewis acidity, and the samples prepared by impregnation (Ga/ZSM-5-ox) and impregnation followed by reduction-oxidation treatment (Ga/ZSM-5-redox) contain both highly dispersed gallium clusters and cationic Ga species. Cationic Ga species was favored on Ga/ZSM-5-IE prepared by ion exchange. Both dispersed gallium clusters and cationic Ga exhibited stronger Lewis acidity. The results of propane aromatization over Ga-modified ZSM-5 showed that the speciation and acidity of Ga have significant effect on the propane conversion. The conversion and selectivity to aromatics followed the order of Ga/ZSM-5-IE > Ga/ZSM-5-redox > Ga/ZSM-5-ox > Ga2O3/ZSM-5 > H-ZSM-5. The synergic active sites composed of Bransted acid site(BAS) and Lewis acid sites (cationic. Ga and dispersed Ga species) on Ga/ZSM-5 zeolite were identified by 2D H-1-P-31 HETCOR NMR spectroscopy, which were correlated to the catalytic activity.