A century-old carbonylation reaction now has a cleaner route, thanks to zeolite catalysts, researchers reported in Nature on Oct. 21. Led by Liu Zhongmin at the Dalian Institute of Chemical Physics, the team replaced precious metals with porous crystal sieves, pairing water with propylene or ethylene to make isobutyric acid for cosmetics and propionic acid for food preservation. The pores cage molecules, blocking unwanted byproducts, and can be tuned like a molecular switch. No acidic wastewater, and in principle, any olefin qualifies.