Tinnemans S J, Kox M H F, Nijhuis T A, Visser T, Weckhuysen B M
Department of Inorganic Chemistry and Catalysis, Debye Institute, Utrecht University, Utrecht, The Netherlands.
Phys Chem Chem Phys. 2005 Jan 7;7(1):211-6. doi: 10.1039/b414427a.
In continuation to the possibility of using a combined operando Raman/UV-Vis-NIR set-up for conducting qualitative Raman spectroscopy, the possibilities for quantitative Raman spectroscopic measurements of supported metal oxide catalysts under working conditions without the need of an internal standard have been explored. The dehydrogenation of propane over an industrial-like 13 wt% Cr/Al203 catalyst was used as a model system. During reaction, the catalytic solid was continuously monitored by both UV-Vis-NIR and Raman spectroscopy. As the dehydrogenation proceeds, the catalyst gradually darkens due to coke formation and consequently the UV-Vis-NIR diffuse reflectance and Raman scattered signal progressively decrease in intensity. The formation of coke was confirmed with TEOM, TGA and Raman. The measured Raman spectra can be used as a quantitative measure of the amount of carbonaceous deposits at the catalyst surface provided that a correction factor G(R(infinity)) is applied. This factor can be directly calculated from the corresponding UV-Vis-NIR diffuse reflectance spectra. The validity of the approach is compared with one, in which an internal boron nitride standard is added to the catalytic solid. It will be shown that the proposed methodology allows measurement of the amount of carbonaceous deposits on a catalyst material inside a reactor as a function of reaction time and catalyst bed height. As a consequence, an elegant technique for on-line process control of e.g. an industrial propane dehydrogenation reactor emerges.
在继续探讨使用拉曼光谱仪与紫外-可见-近红外光谱仪联用装置进行定性拉曼光谱分析的可能性之后，研究了在无需内标的工作条件下对负载型金属氧化物催化剂进行定量拉曼光谱测量的可能性。以在类工业13 wt% Cr/Al₂O₃催化剂上进行丙烷脱氢反应作为模型体系。在反应过程中，通过紫外-可见-近红外光谱仪和拉曼光谱仪对催化固体进行连续监测。随着脱氢反应的进行，由于积炭的形成，催化剂逐渐变黑，因此紫外-可见-近红外漫反射率和拉曼散射信号的强度逐渐降低。通过热重飞行时间质谱仪（TEOM）、热重分析仪（TGA）和拉曼光谱证实了积炭的形成。如果应用校正因子G(R(∞))，则所测得的拉曼光谱可用于定量测量催化剂表面含碳沉积物的量。该因子可直接从相应的紫外-可见-近红外漫反射光谱中计算得出。将该方法的有效性与另一种方法进行了比较，后者是在催化固体中添加内部氮化硼标准物。结果表明，所提出的方法能够测量反应器内催化剂材料上含碳沉积物的量随反应时间和催化剂床层高度的变化。因此，一种用于例如工业丙烷脱氢反应器在线过程控制的精巧技术应运而生。
