Through a process called chemical looping, researchers believe they have found a way to use coal without generating significant amounts of carbon dioxide (CO 2).

The process, detailed recently in the American Chemical Society journal ACS Sustainable Chemical Engineering, turns hydrogen sulfide -- more commonly called "sewer gas" -- into hydrogen fuel.

Transition-metal-free dinitrogen fixation mediated by barium hydride. Image Credit: Yeqin Guan. Prof. Tejs Vegge of the Technical University of Denmark and Prof. Ping Chen of the Dalian Institute of ...