Using Fiber Bragg Grating Sensors to Quantify Temperature Non‐Uniformities in Plasmonic Catalyst Beds under Illumination

Abstract

Distinguishing between photothermal and non‐thermal contributions is essential in plasmon catalysis. Use of a tailored optical temperature sensor based on fiber Bragg gratings enabled us to obtain an accurate temperature map of an illuminated plasmonic catalyst bed with high spatiotemporal resolution. Its importance for quantification of the photothermal and non‐thermal contributions to plasmon catalysis is demonstrated using a Ru/Al2O3 catalyst. Upon illumination with LEDs, we measured temperature differences exceeding 50 °C in the top 0.5 mm of the catalyst bed. Furthermore, we discovered differences between the surface temperature and the temperature obtained via conventional thermocouple measurements underneath the catalyst bed exceeding 200 °C at 2.6 W cm−2 light intensity. This demonstrates that accurate multi‐point temperature measurements are a prerequisite for a correct interpretation of catalysis results of light‐powered chemical reactions obtained with plasmonic catalysts.

Comparing the Performance of Supported Ru Nanocatalysts Prepared by Chemical Reduction of RuCl3 and Thermal Decomposition of Ru3(CO)12 in the Sunlight-Powered Sabatier Reaction

“…They observed that the activity of the catalyst upon sunlight illumination increased superlinearly with a higher loading of metal in the catalyst. This effect was attributed to collective photothermal heating, which was further supported by continuous flow experiments [34] and multipoint temperature measurements inside the illuminated catalyst bed [35].…”

Photothermal nonlinearity in plasmon-assisted photocatalysis

“…In particular, the sample in ref. 51 consisted mostly of high-emissivity alumina (in contrast to ref. 17 where the amount of alumina was small and instead the sample consisted of additional materials with lower emissivities; see discussion in ref.…”

“…In contrast to these experiments which were characterized by low-emissivity samples, a recent experimental work 51 employed a high-emissivity sample. In particular, the sample in ref.…”

“…Finally, in addition to the above, for very high temperatures and/or systems having high emissivity, the thermal emission will cause a further decrease in the temperature rise, resulting in an even stronger photothermal nonlinearity. 51…”

“…This indicates that, on the one hand, further experimental study of the emissivity of the catalyst sample at high temperatures is required, while on the other hand accounting for the thermal emission properly requires a more comprehensive model. In contrast to these experiments which were characterized by low-emissivity samples, a recent experimental work 51 employed a high-emissivity sample. In particular, the sample in ref.…”