Iron-based catalyst reduces CO₂ to CH₄ photochemically

Researchers have been trying to develop efficient techniques that use electrical or sun energy to convert carbon dioxide to methane to supplement fossil-fuel sources and reduce climate-changing CO₂ in the atmosphere. But few CO₂-reduction catalysts have long-lasting stability and high selectivity for specific products, instead of product mixtures. And the reductions generally produce carbon monoxide, formic acid, or hydrocarbon-oxygenate mixtures. Marc Robert, Julien Bonin, and coworkers at Paris Diderot University now report that an inexpensive iron-based tetraphenylporphyrin catalyst (shown), in the presence of an iridium-phenylpyridine photosensitizer, photochemically reduces CO₂ to CO and then to CH₄ at ambient temperature and pressure (Nature 2017, DOI: 10.1038/nature23016). The catalyst is stable when used over several days, and its selectivity for CH₄ is up to 82%, compared with 35% or less for previous catalysts. CO₂ reduction expert Paul J. A. Kenis of the University of Illinois, Urbana-Champaign, comments that CH₄ derived from natural gas is currently cheap, making it hard for chemical synthesis to compete, but achieving high selectivity for CH₄ with an Earth-abundant catalyst is “a significant achievement.”