  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.
