Ultraviolet Raman spectroscopy characterization of coke formation in zeolites
Ultraviolet Raman spectroscopy characterization of coke formation in zeolites
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DOI：
10.1016/s0920-5861(96)00120-4
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发表时间：
1997-01-17
期刊：
影响因子：
5.3
通讯作者：
Stair, PC
中科院分区：
文献类型：
--
作者：
Li, C;Stair, PC
用紫外(UV)拉曼光谱研究了在300~773K温度范围内丙烯存在下ZSM-5和USY分子筛的结焦情况。在紫外拉曼光谱中，完全避免了正常拉曼光谱中始终存在的强荧光背景。两种分子筛在1390附近、1600附近和3000 cm(-1)附近有三组紫外拉曼谱带，这些谱带在结焦的不同阶段有明显的不同。在室温下，两种沸石分子筛中均形成了吸附的丙烯，表现出相似的光谱特征。在高温下，两种沸石的结焦行为有很大的不同。例如，在773K时，ZSM-5中的焦炭物种主要是聚烯烃和芳香族物种，而USY分子筛中的焦炭物种主要是聚芳烃和优势石墨物种。ZSM-5分子筛在773K下吹扫也能脱除大部分焦炭，而USY中的焦炭很稳定，只有在773K以上的氧气中才能脱除。ZSM-5和USY分子筛结焦的差异可能是由于两种分子筛的孔结构和酸性不同所致。
Ultraviolet (UV) Raman spectroscopy has been used to characterize coke formation in ZSM-5 and USY zeolites under propene at temperatures from 300K to 773K. The strong fluorescence background always present with normal Raman spectra is completely avoided in UV Raman spectra. Three groups of UV Raman bands near similar to 1390, similar to 1600 and similar to 3000 cm(-1) regions were detected for the two zeolites, and these bands varied significantly at different stages of coke formation. At room temperature, adsorbed propene was formed in the two zeolites and showed similar spectra. At elevated temperatures, the coke formation behavior in the two zeolites is quite different. For example, at 773K the coke species in ZSM-5 are mainly polyolefinic and aromatic species, but polyaromatic and pregraphite species are predominant in USY. The major portion of coke species formed in ZSM-5 can be removed even by He purging at 773K while the coke species in USY are very stable and can only be removed in O-2 flow at temperatures above 773K. The difference in coke formation in ZSM-5 and USY is likely due to the different pore structure and acidity of the two zeolites.