Carbon dioxide (CO₂) is a harmful greenhouse gas. Chemists could help to find ways to reduce CO₂ levels in the atmosphere. However, it costs a lot of energy to break the molecule’s C=O bonds and convert CO₂ back to one of its original energy-rich reduced forms.

Nature has developed several enzymes to convert CO₂ efficiently on a huge scale. In the enzyme carbon monoxide dehydrogenase (CODH), for example, a nickel-iron-based catalytic active site (pictured left) reversibly reduces CO₂ to carbon monoxide (CO). The enzyme features two amino acids that hold the CO₂ molecule in place through hydrogen bonds while electrons and protons are being added.

Ally Aukauloo, CEA Saclay, Gif-sur-Yvette, France, and Université Paris Sud, Orsay, France, Zakaria Halime, Université Paris Sud, and colleagues have modified an iron porphyrin catalyst (pictured right) with urea groups to lock a metal-bound CO₂ in place by multiple hydrogen bonds. The resulting structure resembles the hydrogen‐bond stabilization scheme of the CO₂ adduct in CODH.

Using this approach, the capture of CO₂ is enhanced and less energy is needed to convert it to CO. The catalyst selectively generates CO with high Faradaic efficiency. These results might be beneficial for the development of cost-effective molecular catalysts for CO₂ reduction.

• Second-Sphere Biomimetic Multipoint Hydrogen-Bonding Patterns to Boost CO₂ Reduction of Iron Porphyrins,
  Philipp Gotico, Bernard Boitrel, Régis Guillot, Marie Sircoglou, Annamaria Quaranta, Zakaria Halime, Winfried Leibl, Ally Aukauloo,
  Angew. Chem. Int. Ed. 2019.
  https://doi.org/10.1002/anie.201814339