Matters Arising in -- "Plasmon-driven carbon-fluorine (C(sp^$3$)-F) bond activation with mechanistic insights into hot-carrier-mediated pathways"

TL;DR

This paper critically re-evaluates a recent study claiming hot-electron-driven carbon-fluorine bond activation, demonstrating that the original conclusions are unsupported due to methodological flaws and purely thermal explanations.

Contribution

The authors provide a detailed critique of prior work, showing that the observed effects can be explained without invoking hot electrons, thus challenging previous claims of photocatalytic mechanisms.

Findings

Thermal control experiments do not distinguish thermal from hot-electron effects

Purely thermal calculations explain the observed activation energies

Methodological issues undermine the original claims about hot-electron involvement

Abstract

In a recent paper~[Nature Catalysis 3, 573 (2020)], Robatjazi {\em et al.} demonstrate hydrodefluorination on Al nanocrystals decorated by Pd islands under illumination and under external heating. They conclude that photocatalysis accomplishes the desired transformation \ce{CH3F + D2 -> CH3D + DF} efficiently and selectively due to "hot" electrons, as evidenced by an illumination-induced reduction of the activation energy. Although some of the problems identified in prior work by the same group have been addressed, scrutiny of the data in~[Nature Catalysis 3, 573 (2020)] raises doubts about both the methodology and the central conclusions. First, we show that the thermal control experiments in~[Nature Catalysis 3, 573 (2020)] do not separate thermal from "hot electron" contributions, and therefore any conclusions drawn from these experiments are invalid. We then show that an improved thermal control implies that the activation energy of the reaction does not change, and that an independent purely thermal calculation (based solely on the sample parameters provided in the original manuscript) explains the measured data perfectly. For the sake of completeness, we also address technical problems in the calibration of the thermal camera, an unjustifiable disqualification of some of the measured data, as well as concerning aspects of the rest of the main results, including the mass spectrometry approach used to investigate the selectivity of the reaction, and claims about the stoichiometry and reaction order. All this shows that the burden of proof for involvement of hot electrons has not been met.