Low-temperature CO removal: Carbon monoxide deactivates fuel cell catalysts, so it must be removed from H ₂ generated from hydrocarbons on site. Yao et al. developed a catalyst composed of layered gold clusters on molybdenum carbide (MoC) nanoparticles to convert CO through its reaction with water into H ₂ and CO ₂ at temperatures as low as 150°C. Water was activated on MoC to form surface hydroxyl groups, which then reacted with CO adsorbed on the gold clusters. Science , this issue p. 389