Tinnemans Stan J, Kox Marianne H F, Sletering Marco W, Nijhuis T A Xander, Visser Tom, Weckhuysen Bert M
Inorganic Chemistry and Catalysis, Department of Chemistry, Utrecht University, The Netherlands.
Phys Chem Chem Phys. 2006 May 28;8(20):2413-20. doi: 10.1039/b602311h. Epub 2006 Apr 19.
In continuation of our previous work on the applicability of the G(R(infinity)) correction factor for the quantification of Raman spectra of coke during propane dehydrogenation experiments (Phys. Chem. Chem. Phys., 2005, 7, 211), research has been carried out on the potential of this correction factor for the quantification of supported metal oxides during reduction experiments. For this purpose, supported chromium oxide catalysts have been studied by combined in situ Raman and UV-Vis spectroscopy during temperature programmed reduction experiments with hydrogen as reducing agent. The goal was to quantify on-line the amount of Cr(6+) in a reactor based on the measured in situ Raman spectra. During these experiments, a significant temperature effect was observed, which has been investigated in more detail with a thermal imaging technique. The results revealed a temperature 'on the spot' that can exceed 100 degrees C. It implies that Raman spectroscopy can have a considerable effect on the local reaction conditions and explains observed inconsistencies between the in situ UV-Vis and Raman data. In order to minimize this heating effect, reduction of the laser power, mathematical matching of the spectroscopic data, a different cell design and a change in reaction conditions has been evaluated. It is demonstrated that increasing the reactor temperature is the most feasible method to solve the heating problem. Next, it allows the application of in situ Raman spectroscopy in a reliable quantitative way without the need of an internal standard.
延续我们之前关于G(R(∞))校正因子在丙烷脱氢实验中对焦炭拉曼光谱进行定量分析的适用性研究工作（《物理化学化学物理》，2005年，第7卷，211页），现已对该校正因子在还原实验中对负载型金属氧化物进行定量分析的潜力展开研究。为此，在以氢气作为还原剂的程序升温还原实验过程中，通过原位拉曼光谱和紫外-可见光谱联用技术对负载型氧化铬催化剂进行了研究。目标是基于原位拉曼光谱测量在线定量反应器中Cr(6+)的含量。在这些实验过程中，观察到了显著的温度效应，并用热成像技术对其进行了更详细的研究。结果揭示了“现场”温度可能超过100摄氏度。这意味着拉曼光谱可能对局部反应条件产生相当大的影响，并解释了原位紫外-可见光谱和拉曼光谱数据之间观察到的不一致现象。为了将这种加热效应降至最低，已对降低激光功率、光谱数据的数学匹配、不同的样品池设计以及反应条件的改变进行了评估。结果表明，提高反应器温度是解决加热问题最可行的方法。其次，这使得原位拉曼光谱能够以可靠的定量方式应用，而无需内标。
