They claim the new Rolls Royce engines will run on biofuel.

It's left as an exercise for the reader to figure out how to make biofuels net zero.

I suspect that the "net" qualifier is doing a lot of important work in that statement. Maybe they are planting a gazillion trees, do carbon capture or regrow coral reefs. Could mean anything really. Plant enough trees and you'll theoretically have "net zero emissions" from lighting a lake of crude on fire.

Fuel from carbon-capture or biofuels. Looks like something they intend to do in the future, not necessarily the first prototype. More details here : https://blog.boomsupersonic.com/booms-principles-of-sustaina...

Lots of marketing and gullible fanboys of course.