Modified Harrick reaction cell for in situ/operando fiber optics diffuse reflectance UV–visible spectroscopic characterization of catalysts

[Display omitted] •Modified reaction cell for rapid in situ UV–vis characterization of catalysts.•New dome design for in situ/operando fiber optics diffuse reflectance measurements.•Reaction cell with average residence time of 4–12 s.•Reaction cell + spectrometer designed for UV–vis spectral sampling in seconds.•Modified cell characterizes gold catalysts via novel gas adsorption transients. UV–visible (UV–vis) spectroscopy is a common, powerful, and affordable technique for the characterization of heterogeneous catalysts. Here, we present an improved design of the commercial ubiquitous Harrick Scientific high temperature reaction cell for use in diffuse reflectance (DR) UV–vis spectroscopy with fiber optics at very close proximity of a catalyst sample and with high time resolution. The cell possesses significant dead volume which was reduced by a homemade compact dome and by volume reduction of cell void space with simple addition of glass beads, thereby, enabling faster transfer of gases. The cell was also improved by adding a second thermocouple to directly monitor the temperature of the catalyst bed via the outlet port without requiring any additional machining. This modified design and the use of an optical fiber DR probe in conjunction with a miniature concave-CCD combination based spectrometer allowed fast acquisition of in situ UV–vis spectra in the order of seconds and at temperatures up to about 500 °C. It is also shown that, unlike probes used in tubular reactors, expensive high temperature DR probes are not required in this design. The flow dynamics of the reaction setup were followed by an analysis of residence time distributions (RTD) via pulse experiments of Ar, O2, H2, CO, and CO2 as analyzed online by mass spectrometry (MS). These tests enabled a rigorous analysis of the fluid dynamics of the modified cell showing average gas residence times (after correcting for transfer lines and MS contributions) of ∼13 s at gas flow rates of 45 cm3/min (or ∼4 s at gas flow rates of 120 cm3/min) and a fluid behavior that could be approximately described by a CSTR reactor model. The RTD method is of general application and can be easily implemented to other reaction cells to rigorously determine gas mean residence times and distribution, regardless of setup and transfer lines design, provided that a reaction cell bypass line is added to the system. A thermal analysis indicated that significant heat losses due to radiation, conduction, and convection contr