A catalyst is a substance you add in tiny amounts to “spark” a huge chemical process — while barely wearing out itself. About 90% of all the world's chemicals depend on one, and the catalytic converter in your car's exhaust is the single biggest user of precious metals like platinum, palladium, and rhodium on Earth. But the clean-energy era is flipping the script: fewer ICE cars means less demand for exhaust catalysts, while a new breed of catalyst for green hydrogen is rising.