At a port across from Gibraltar, two European monarchs made a rare joint appearance in June to bestow their imprimatur on a bold and risky endeavor.

Standing alongside freight ships in Algeciras, King Felipe VI of Spain and King Willem-Alexander of the Netherlands inaugurated a new maritime corridor. The critical cargo that attracted the attention of modern royalty was: green ammonia — a way to transport hydrogen and a key part of Spain’s plans to become the continent’s hub for clean energy.

The rest of Europe might not be ready.