Minimizing Temperature Bias through Reliable Temperature Determination in Gas‐Solid Photothermal Catalytic Reactions

Abstract

Enormous advances in photothermal catalysis have been made over the years, whereas the temperature assessment still remains controversial in the majority of photothermal catalytic systems. Herein, we methodically uncovered the phenomenon of temperature determination bias arising from prominent temperature differences in gas-solid photothermal catalytic systems, which extensively existed yet has been overlooked in most relevant cases. To avoid the interference of temperature bias, we developed a universal protocol for reliable temperature evaluation of gas-solid photothermal catalytic reactions, with emphasis on eliminating the temperature gradient and temperature fluctuation of catalyst layer via optimizing the reaction system. This work presents a functional and credible practice for temperature detection, calling attention to addressing the effects of temperature differences, and reassessing the actual temperature-based performances in gas-solid photothermal catalysis.

Is There a Discernible Photochemical Effect Beyond Heating for Visible Photon-Mediated NH3 Decomposition over Ru/Al2O3?

“…While the results presented here may be considered “negative,” they highlight a few important findings. First, the results demonstrate the effectiveness (and necessity) of using thermocouples in the catalyst bed, at least for small catalyst bed volumes of densely packed particles, to account for light-induced metal nanoparticle heating. ,, Second, comparison of the results presented here to other reports of photocatalysis by metal nanoparticles, where thermocouples were used in the catalyst bed, lends confidence to previous conclusions of inherent photochemical responses for various catalytic systems. Thermocouples have been proposed as less reliable than temperature-sensitive IR cameras to measure catalyst temperatures accurately .…”

“…9 Thus, rigorous assessment of temperature measurement methods (like IR imaging or the use of thermocouples) is essential, and it has been demonstrated that the measured temperature values can strongly differ depending on the method used. 27,28 Further studies are needed that demonstrate reference "cases" where the influence of photon fluxes can be explained entirely through equilibrium heating. 29 Benchmarking setups, measurements, and approaches against such reactions will allow proper assignments of photochemical effects.…”

“…One reaction that has attracted particular attention for photocatalysis by supported metal nanoparticles is NH 3 cracking or decomposition (2 NH 3(g) ⇆ N 2(g) + 3 H 2(g) , Δ H ° = 92 kJ mol –1 ). , NH 3 decomposition is essential for using NH 3 as a liquefiable hydrogen storage molecule to transport green H 2 . − The proposed mechanism of photon flux promotion of catalytic NH 3 decomposition rate is the photochemical-mediated associative desorption of strongly bound N* or H* to produce N 2 or H 2 . , This mechanism has been proposed based on experimental analyses of Cu-based bimetallic nanoparticles (e.g., CuRu and CuFe), where significant differences in photochemical effects were observed as a function of nanoparticle composition (CuRu vs CuFe vs Ru) . Thus, rigorous assessment of temperature measurement methods (like IR imaging or the use of thermocouples) is essential, and it has been demonstrated that the measured temperature values can strongly differ depending on the method used. , Further studies are needed that demonstrate reference “cases” where the influence of photon fluxes can be explained entirely through equilibrium heating . Benchmarking setups, measurements, and approaches against such reactions will allow proper assignments of photochemical effects.…”

“…Thus, the influence of photon fluxes on catalysis by metal nanoparticles is often a combination of energy transfer to adsorbates through photochemical processes and equilibrium heating, which both contribute to the overall energy efficiency . These multiple potential mechanisms have led to “heated” debates on the dominant mechanism. ,− …”

Mechanism of photocatalytic CO2 methanation on ultrafine Rh nanoparticles

“…The catalytic performance was evaluated in a fix-bed reactor using a thin layer of Rh-NP/SiO x -NS composite particles (∼0.7 mm in thickness, ∼7 mg in mass) on a platinum mesh, which can minimize the photothermal effect. 32 The loose packing of the particles favored the isotropic and uniform mass transport of gas flow and heat transfer, ensuring fast dissipation of heat generated from light absorption ( i.e. , photothermal effect) to eliminate significant temperature deviation from the set temperature and temperature gradient in the thin catalyst layer (ESI,† Part II and Table S1).…”