Operando Luminescence Thermometry of a Solid Catalyst in a Reactor during a High-Temperature Chemical Process

In most catalytic processes, thermal energy is released or consumed locally in a reactor due to the exothermicity or endothermicity of the chemical reactions. This causes the actual operating temperature of the catalyst material to deviate from the reactor temperature, which can lead to underperformance, reduced catalyst stability, or even thermal runaway. Conventional methods to measure the catalyst temperature, with a thermocouple in the reactor oven or in the catalyst bed, suffer from complications because of separation between the sensor and catalyst material, chemical activity of the thermocouple/coating material, added complexity of the setup, and disruption of the reactant flow and heat flow through the catalyst bed. Here, we show the possibilities and challenges of luminescence thermometry as an analytical technique for remote temperature monitoring of the local catalyst temperature in a strongly exothermic high-temperature reaction environment. We observe that the luminescence lifetime depends not only temperature, but also on oxygen concentration, which can introduce a significant systematic error of up to 40 °C in the recorded temperature. In the case of ratiometric luminescence thermometry, this error is strongly reduced to ~5 °C. We use the ratiometric technique to confirm its applicability in the exothermic oxidative coupling of methane (OCM) process at high reaction temperatures, showing an exothermic increase in the local catalyst temperature of up to 100 °C, relative to the constant reactor temperature under inert conditions.