Nickel or iron would be a lot cheaper and could get the job done with some tweaking, good suggestion. I’ve done aromatizations of cyclohexene derivatives with sulfur in the past that have been pretty high yielding too (which is why I mentioned it), and bubbled the hydrogen sulfide gas through bleach and other aqueous oxidants to prevent stench. Sulfur is dirt cheap, but it was used stoichiometrically.

As you say though, the biggest step forward was already done by this group - switching feedstock to biomass. I hope to see more and more of this type of research to deliver on the promise of ‘green chemistry’, which in my past experience has been used as a label somewhat dubiously just to make a journal submission stand out.