Strong acidity of silanol groups of zeolite beta: Evidence from the studies by IR spectroscopy of adsorbed CO and 1H MAS NMR
Strong acidity of silanol groups of zeolite beta: Evidence from the studies by IR spectroscopy of adsorbed CO and 1H MAS NMR
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DOI：
10.1016/j.micromeso.2009.12.025
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发表时间：
2010-06-01
影响因子：
5.2
通讯作者：
Stepanov, Alexander G.
中科院分区：
文献类型：
--
作者：
Gabrienko, Anton A.;Danilova, Irina G.;Stepanov, Alexander G.
用H-1 MASNMR和CO吸附红外光谱对酸型沸石和Zn、Ga改性β沸石的酸性OH基团进行了表征。结果表明，OH基在3740 cm（-1）处有一个振动带，其酸性与OH基在3610 cm（-1）处有一个振动带的酸性相似，这是根据吸附CO时OH振动的低频位移值（Δ nu（OH/CO）= 300 cm（-1））确定的。IR波段3740 cm（-1）对应于ca. 2.1 ppm。信号为2.1 ppm的OH基团参与与甲烷-d（4）的H/D交换，类似于信号为4.0-5.1 ppm的酸性OH基团。在H-1 MAS NMR中2.1ppm处和在IR中3740 cm（-1）处的信号归因于沸石的断裂结构的强酸性硅醇基团。在1.8 ppm和3745 cm（-1）处具有信号的硅烷醇是弱酸性的（Δ nu（OH/CO）= 85 cm（-1）），并且不参与H/D交换。用Zn负载沸石提供强酸性SiOHAl基团的浓度的显著降低，而这些基团的量在用Ga负载沸石时不降低。(C)2009 Elsevier Inc. All rights reserved.
Acidic OH groups of acid-form and Zn and Ga-modified zeolite beta (BEA) have been characterized with H-1 MAS NMR and by IR spectroscopy of adsorbed carbon monoxide. It is demonstrated that OH groups, which exhibit a vibration band at 3740 cm(-1), reveal acidity, which is similar to that of the OH groups with the band at 3610 cm(-1) according to the value of the low frequency shift of OH vibrations with adsorbed CO (Delta nu(OH/CO) = 300 cm(-1)). The IR band 3740 cm(-1) corresponds to the signal at ca. 2.1 ppm in H-1 MAS NMR spectrum. The OH groups with signal 2.1 ppm are involved in H/D exchange with methane-d(4) similar to acidic OH groups with the signals 4.0-5.1 ppm. The signals at 2.1 ppm in H-1 MAS NMR and at 3740 cm(-1) in IR are attributed to the strongly acidic silanol groups of the faulted structure of the zeolite. The silanols with the signals at 1.8 ppm and 3745 cm(-1) are weakly acidic (Delta nu(OH/CO) = 85 cm(-1)) and are not involved in the H/D exchange. Loading of the zeolite with Zn affords a notable decrease of the concentration of strongly acidic SiOHAl groups, whereas the quantity of these groups does not decrease upon loading the zeolite with Ga. (C) 2009 Elsevier Inc. All rights reserved.