Time-resolved in situ Raman spectroscopy of working catalysts:: sulfated and tungstated zirconia
Time-resolved in situ Raman spectroscopy of working catalysts:: sulfated and tungstated zirconia
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DOI：
10.1002/jrs.815
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发表时间：
2002-05-01
影响因子：
2.5
通讯作者：
Knözinger, H
中科院分区：
文献类型：
--
作者：
Kuba, S;Knözinger, H
本文给出了硫酸化和钨酸化氧化锆催化剂在正戊烷异构化反应中的原位拉曼光谱，并对实验结果进行了讨论。描述了用于该应用的特制的原位拉曼池。讨论了合适的实验参数，即激光功率和激光波长的选择。在实验过程中，催化剂的活性和选择性的同时测定了在线气相色谱。硫酸化氧化锆催化剂在反应过程中在硫酸盐区域显示出结构变化。最初存在的两种不同类型的硫酸盐物质之一在反应过程中被侵蚀，可能是由于还原为H2S。活性显示出典型的诱导期，随后是快速失活。没有观察到焦炭形成。由于发生快速失活，焦炭形成不能是催化剂失活的唯一原因。钨酸盐催化剂在反应开始后随着运行时间（TOS）的增加显示出强烈的变暗。这导致催化剂带消失。然而，可以观察到由1590 cm（-1）处的宽带指示的焦炭形成。由于暗化对拉曼强度有很强的影响，因此不能正确地获得所观察到的谱带的时间演化。我们提出了一种新的方法来纠正的影响变暗。激光等离子体谱线强度的变化决定了催化剂漫反射率的变化。基于沃茨提出的将样品的拉曼强度与漫反射率相关联的近似方程，获得了光谱的校正因子。在强度校正之后，光谱表明大部分焦炭在反应的最初几分钟内形成，随后是使用TOS的恒定形成速率。版权所有（C）2002约翰威利父子有限公司
The spectra of time-dependent in situ Raman experiments on sulfated and tungstated zirconia catalysts during the isomerization reaction of n-pentane are presented and discussed. A purpose-made in situ Raman cell which was used for this application is described. The choice of appropriate experimental parameters, namely laser power and laser wavelength, is discussed. During the experiments the activity and selectivity of the catalysts were determined simultaneously by on-line gas chromatography. The sulfated zirconia catalyst shows structural changes in the sulfate region during the reaction. One of two different types of initially present sulfate species is eroded during the reaction, presumably due to a reduction to H2S. The activity shows a typical induction period followed by a fast deactivation. No coke formation is observed. Since fast deactivation occurs, coke formation cannot be the only reason for the deactivation of the catalyst. The tungstated catalyst shows strong darkening after initiation of the reaction with increasing time-on-stream (TOS). This leads to the disappearance of the catalyst bands. However, coke formation indicated by a broad band at 1590 cm(-1) can be observed. Since darkening has a strong effect on Raman intensities, the time evolution of the observed bands is not obtained correctly. We propose a new method to correct for the effect of the darkening. The change of the diffuse reflectance of the catalyst is determined by the variation of the intensity of laser plasma lines. Based on an approximate equation proposed by Waters which correlates the Raman intensities and the diffuse reflectance of a sample, a correction factor for the spectra is obtained. After the intensity correction the spectra indicate that most of the coke is formed in the first few minutes of the reaction followed by a constant formation rate with TOS. Copyright (C) 2002 John Wiley Sons, Ltd.