Correct me if I'm wrong, but planes look like a bad target for this fuel substitute : for 1 kg of CO2 emitted, estimates give a ~2 (or worse, 2.7 - 4) factor of radiative forcing (the potential for climate warming), due to the water vapor released at high altitudes.
You'd have to capture 2 or 3 times more fuel that you'd burn in the sky for this to be "net zero climate", which is a better metric than "net zero carbon".
You seem to be right about the forcing of water being much higher [1], but CO2 has a nasty property as opposed to water: it stays in the atmosphere for much longer and contributes to warming for much longer than the water does. If temperatures get really bad in future, we can limit burning fuels and all the excess water will fall back down to oceans in few years. CO2 won't do such thing as fast. So even if we can't decrease forcing due to aviation burning fuel, it makes sense to make aviation use CO2 neutral fuels to keep the concentration of CO2 low.
Contrary to what I said above, it seems the effect of jet exhaust water is more complicated and hard to evaluate... the problem is that unless there is enough water for condensation, water molecule is lighter than oxygen or nitrogen molecule, which means the high altitude vapor isn't likely to fall down quickly.
You'd have to capture 2 or 3 times more fuel that you'd burn in the sky for this to be "net zero climate", which is a better metric than "net zero carbon".