Together photo‐ and thermal energy promote catalytic reactions in a synergetic way. However, how light cooperates with thermal energy is still unclear. Here, C−H bond rupture within HCOOH* was determined to be the rate‐determining step, with adsorbed CO* as the most abundant surface intermediate under both thermal and photothermal reaction conditions, as confirmed by kinetic isotopic effects and in‐situ FTIR characterizations. Clear evidence of kinetically relevant consistency was found under both thermal and photothermal HCOOH decomposition reactions over a Pd/LaCrO3/C3N4 composite. More information can be found in the Research Article by H. Zhang et al. (DOI: 10.1002/chem.202104623).

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Photo-thermal catalysis has been an attractive alternative strategy to promote chemical reactions for years, however, how light cooperates with thermal energy is still unclear. We meet this demand by exploring reaction mechanism via pressure dependency studies as well as H/D exchange experiments with HCOOH decomposition as a probe over a palladium nanoparticle (Pd n ) and isolated Pd (Pd 1 ) decorated LaCrO 3 /C 3 N 4 composite catalyst, in which the H 2 formation rate shows a first-order dependence on HCOOH and inverse first-order dependence on CO partial pressures no matter the reaction was driven by thermal or photothermal energy. Additionally, negligible kinetic isotopic effects (KIEs: k H /k D ) were determined under both dark and light conditions at 1.04 and 1.18 when the HCOOH was replaced by HCOOD. Besides, when the reactant HCOOH was further replaced by DCOOD, the KIE values of 1.55 (dark) and 1.92 (light) were obtained, which indicates that the HCOOH decomposition follows kinetically relevant (KR) of CÀ H bond rupture within HCOOH molecule under both thermal and photo-thermal reaction conditions and the catalytic surface was found to be densely covered by CO based on the pressure dependency studies as well as the in situ Fourier transform infrared spectroscopy (FTIR) analysis. Clearly, the HCOOH decomposition driven by thermal and photo-thermal energy follows the same reaction mechanism. Nevertheless, light induced hot electrons and the derived thermal effect do cause the enhancement of the reaction activity in some circumstances compared with bare thermal catalysis, which clarifies the confusion on cooperation mechanism of photo and thermal energies from the kinetic perspective. Hot electrons induced by photo-illumination was confirmed by in situ FTIR CO chemisorption with ~10 cm À 1 redshift identified of the CO feature once light was introduced. Meanwhile, the photo thermal reaction system suffers from severe electron-hole re-combination at high reaction temperatures and make the thermal effect of photo irradiation dominant with respect to the effect at low reaction temperatures. This research provides insight to the mechanism on how photothermal reaction works and draws attention to the photothermal reaction process in boosting catalytic activity.

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