Improved experimental setup for in situ UV-vis-NIR spectroscopy under catalytic conditions

Abstract

A commercial UV-vis-NIR spectrometer (Lambda 9, PerkinElmer) equipped with an integrating sphere was supplemented with a construction to measure in situ diffuse reflectance spectra from room temperature to 723 K in the range from 250 to 2500 nm. The new construction was compared to a previously developed setup, which features a highly reflecting ceramic spacer that bridges the 12 mm between the integrating sphere and microreactor. In the new construction, the catalyst bed is in the isothermal zone of a tubular furnace and the 120 mm space between the optical quartz window of the microreactor and the integrating sphere are bridged with a specially formed light conductor made of quartz. Improvements include a stable position of the powder bed, a smaller bed volume (ca. 0.27 cm3), a reduction of thermal radiation, and a higher signal level and thus better signal-to-noise-ratio. The performance of the setup is demonstrated by two examples, (i) spectra recorded at 723 K during the activation of a zirconia sample, and (ii) spectra recorded during n-pentane isomerization over sulfated zirconia at room temperature with simultaneous gas phase analysis.