Techniques to take atmospheric CO₂ and turn it into a fuel provide a climate-friendly alternative to exploiting fossil fuels—they may releases CO₂ back into the air when burned, but there’s no net change. This includes biofuels crops, but can extend to industrial processes that directly involve CO₂. As processes that capture CO₂ from ambient air become more economical, so will the potential value of that CO₂ as a resource for fuels.

There are a few ways to go about making fuel, but all require considerable energy because CO₂ is a stable molecule—reversing the combustion reaction to make a new fuel doesn’t happen for free. But there’s an additional challenge: designing a process tuned to produce the exact type of fuel you want.

One way to do that is with a catalyst—a substance that guides the chemical reactions without being consumed by them. With the help of one catalyst, captured CO₂ plus hydrogen gas might primarily be turned into methane; a different catalyst might shift the primary product towards the larger molecules of liquid fuels.