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Evidence for a strong polarization of n-hexane in zeolite H-ZSM-5 by FT-IR and solid-state NMR spectroscopy
Microporous and Mesoporous Materials ( IF 4.8 ) Pub Date : 2018-06-30 , DOI: 10.1016/j.micromeso.2018.06.054
Mariusz Gackowski , Jerzy Podobiński , Michael Hunger

The adsorption and interaction of n-hexane in acidic zeolites were investigated via the adsorbate-induced shifts of the FT-IR bands (Δν˜) and 1H MAS NMR signals (Δδ) of acidic bridging OH groups (Si(OH)Al) in H-mordenite, H-Beta, 10H,Na-Y, 86H,Na-Y, H-ZSM-5, and US-Y. The plot of the experimentally determined Δν˜ values as a function of Δδ shows a linear correlation. In a subsequent step, the influences of the average electronegativity Sav of the individual zeolites under study and the deprotonation energy ΔpA of their acidic hydroxyl protons on Δν˜ and Δδ were investigated. The individual Sav values were calculated via the geometric average of all element electronegativities of the zeolite framework, while the ΔpA values were obtained via an evaluation of the CO-induced shifts of the FT-IR bands of Si(OH)Al groups compared with that of SiOH groups and using an empirical relationship. In the plots of the Δν˜/Sav and Δν˜pA ratios as a function of Δδ/Sav and ΔδpA, respectively, the data sets of all zeolites under study are closely arranged, excluding that of H-ZSM-5. This finding indicates that n-hexane adsorbed on zeolite ZSM-5 is not exclusively involved in the interaction with acidic Si(OH)Al groups, but is also influenced by the zeolite framework. The 13C solid-state NMR shifts of n-hexane adsorbed on the zeolites hint at a polarization of this alkane especially in the 10-ring pores of zeolite H-ZSM-5. This polarization of n-hexane in H-ZSM-5 is important for the reactivity of this alkane in heterogeneously catalyzed reactions.



中文翻译:

FT-IR和固态NMR光谱证明H-ZSM-5沸石中正己烷发生强极化

通过吸附剂诱导的FT-IR谱带位移(ΔΔ)研究了正己烷在酸性沸石中的吸附和相互作用ν)和1个ħMAS NMR信号(Δ δ)酸性的桥接的OH团(Si(OH)的Al)中H-丝光沸石,H-β,10H,的Na-Y,86H,的Na-Y,H-ZSM-5,和US-Y。实验确定的Δ的图ν值Δ的函数δ示出了线性关系。在随后的步骤中,平均电的影响š AV所研究的个体沸石和去质子化的能量Δ p上Δ它们的酸性羟基质子的ν和Δ δ进行了调查。各个小号AV值经由沸石框架的所有元素电负性的几何平均计算,而Δ p分别通过Si的FT-IR谱带(OH)的Al基团中的CO诱导的移位的评价获得的值与SiOH基团比较,并使用经验关系。在Δ的图中ν/ S av和Δνp比率为Δ的函数δ /小号AV和Δ δp分别在研究的所有沸石的数据集紧密排列,但不包括H-ZSM-5的。该发现表明吸附在沸石ZSM-5上的正己烷不仅仅参与与酸性Si(OH)Al基团的相互作用,而且还受到沸石骨架的影响。吸附在沸石上的正己烷的13 C固态NMR位移暗示了该烷烃的极化,特别是在沸石H-ZSM-5的10环孔中。H-ZSM-5中正己烷的这种极化对于这种烷烃在非均相催化反应中的反应性很重要。

更新日期:2018-06-30
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