Operando Luminescence Thermometry for Hydrocarbon Conversion Catalysis: Dealing with Dynamic Changes in Catalyst Optical Properties

Luminescence thermometry offers an attractive strategy for temperature sensing of a catalytic process, whereby the temperature-dependent luminescence of a phosphor material embedded in the reactor is excited and recorded remotely. However, changes in the optical properties of the catalyst materials can distort the luminescence recording, resulting in inaccurate temperature sensing. This is particularly problematic in hydrocarbon conversion catalysis due to the buildup of carbon deposits, which color the material and cause fluorescence upon excitation. In this work, we developed operando reflectance-corrected time-gated luminescence thermometry, using a highly dynamic and industrially relevant Pt-Sn-based propane dehydrogenation (PDH) catalyst and an Eu³⁺-based phosphor as a showcase. PDH catalyst materials deactivate via the deposition of carbon, which is subsequently removed by an oxidative regeneration treatment. During these alternating reaction-regeneration processes, the background fluorescence and the color of the catalyst material change continuously. This skews the Eu³⁺ luminescence, leading to temperature-readout artifacts. We solved these problems by rejecting background fluorescence using time-gated detection following pulsed excitation and by correcting for the wavelength-dependent absorption changes of the PDH catalyst. This method offers accurate temperature sensing of the PDH catalyst material and is a step forward in the development of luminescence thermometry for samples with highly dynamic optical properties.