| RESEARCH |
T. A. (Xander) Nijhuis, a postdoc at Utrecht University, in the Netherlands, who works with chemistry professor Bert M. Weckhuysen, demonstrated the effectiveness of the operando approach by presenting results of recent time-resolved experiments in which Raman spectroscopy, UV-Vis spectroscopy, gas chromatography (GC), and mass spectrometry were used simultaneously to study propane dehydrogenation to propene over alumina-supported chromium oxide catalysts. Catalytic processes of that type are used to produce millions of tons of olefins annually. Nijhuis explained that in industrial plants, propane dehydrogenation causes the catalyst to undergo reduction. At the same time, coke accumulates on the catalyst and deactivates it. The reduced catalyst then becomes oxidized and reactivated by burning the coke in air. The process cycles every 20 to 30 minutes. Using the combination of time-resolved techniques, the Utrecht group was able to correlate the catalyst activity (based on product composition) with the catalyst oxidation state (from UV-Vis spectroscopy) during dehydrogenation and regeneration phases of the catalytic cycle. In addition, using the Raman spectroscopy data, they could monitor coke accumulation on the catalyst and the corresponding disappearance of Cr2O3 spectral features as the coke layer occluded the catalyst surface [Phys. Chem. Chem. Phys, 5, 436 (2003)]. With their ability to continuously monitor the amount of coke on the catalyst and relate the coke coverage to the catalyst's performance, researchers will be able to adjust the cycle times dynamically to optimize the performance of the system, Nijhuis asserted. He added that, in an industrial setting, information of that type could be used to tweak the process parameters to maximize the product output and extend the life of the catalyst. |
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