Comment on "CO₂ Footprint of Thermal Versus Photothermal CO₂ Catalysis"

The previously published report by Wang et al. provides universal equations for evaluating the net CO₂ emission via photothermal/thermal CO₂ hydrogenation reactions in batch and flow reactors, respectively. However, it remains to be discussed whether the original feed amount or feed rate of H₂ should be changed accordingly when the CO₂ reduction rate is selected as the variable to investigate the net CO₂ emission rate of the system. If not, the reaction would not be in accordance with the stoichiometric ratio, which is inconsistent with reality, bringing about the optimistic scenario in the assessment of CO₂ footprint. This work has taken the potential relationship between the original feed amount or feed rate of H₂ and CO₂ conversion rate into account. The effects of CO₂ conversion rate on the net CO₂ emission rate in the photothermal catalytic system are re-examined, the obtained trends exhibit more challenging preconditions to achieve net-zero carbon emission than those in the work by Wang et al. The quantitative results indicate that green hydrogen source is indeed vital for carbon neutrality in photothermal CO₂ catalysis. Here, the viewpoints will be worth considering and be seen as complementary to the proposed carbon emission assessment equations.