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Abstract

In-situ UV/VIS/near-IR diffuse reflectance spectroscopy can be carried out on catalysts with a suitable microreactor at temperatures up to 673 K. The experimental difficulties in the application of such a reactor at higher temperatures could be solved as follows:
Integrating sphere and reactor are connected by a ceramic part of high reflectivity and low thermal conductivity, i.e. the integrating sphere is enlarged. The signal/noise ratio increases by a factor of 2.
The standard IR-detector was replaced by a temperature-stabilized version. In addition watercooling jackets were mounted at the integrating sphere. The signal/noise ratio in the near-IR region was thus improved by a factor of 2-3 with a very good reproducibility of measurements.
To overcome an alteration of catalyst spectra by thermal radiation, a series of reference spectra of quartz powder (SiO2) were recorded at several temperatures. These spectra are used to correct the catalyst spectra by dividing catalyst and SiO2 spectra.