I have my doubts about practical application, too, but the area of 800 km² need not be a show stopper if these things can be stacked, and that seems likely to me.
Also, if I understand https://www.pnas.org/action/downloadSupplement?doi=10.1073%2... correctly, the catalyst weighed 0.22 mg/cm². That’s 2.2g/m² or 2200kg/km² or less than 2 million kg for 800km². So, I guess the amount of catalyst wouldn’t be a problem either, _if_ it is a perfect catalyst that doesn’t degrade and doesn’t require regular cleaning.
Also, if I understand https://www.pnas.org/action/downloadSupplement?doi=10.1073%2... correctly, the catalyst weighed 0.22 mg/cm². That’s 2.2g/m² or 2200kg/km² or less than 2 million kg for 800km². So, I guess the amount of catalyst wouldn’t be a problem either, _if_ it is a perfect catalyst that doesn’t degrade and doesn’t require regular cleaning.