New Way To 'Fix' CO₂

In a study with implications for addressing global warming, researchers have devised a new way to remove the greenhouse gas CO₂ from air and form a useful organic feedstock in the process (Science 2010, 327, 313). The technique is still at the demonstration stage but has promising advantages over other CO₂ sequestration strategies.

Previously devised processes for “fixing” CO₂ include stoichiometric reactions with hydroxide to form carbonate or bicarbonate and catalytic transformations to form organic compounds such as formaldehyde and methanol. Catalytic conversion is more efficient and practical for large-scale use, but current catalysts can’t be used on CO₂ in air because they also reduce oxygen, which is present in air at vastly higher levels than CO₂. In addition, they are unselective, creating mixtures of organic products.

Inorganic chemist Elisabeth Bouwman of Leiden University, in the Netherlands, and coworkers have now developed a catalyst that reacts with CO₂ from ambient air to form a single product: oxalate, a useful feedstock for production of methyl glycolate and other organic compounds. After the reaction, the catalyst is regenerated electrochemically at a very low reduction potential, meaning it is unusually favorable energetically.

The process won’t ameliorate the global warming problem right away—and maybe never will. “Our study is purely fundamental, and the findings will need a lot of additional work before they could possibly be applied in an industrial setting,” Bouwman notes.

Nevertheless, “it’s amazing” that this catalyst reduces CO₂ preferentially over oxygen and that the electrochemical step requires so little energy—suggesting that “the catalyst’s structure is almost perfectly matched to the reaction it’s driving,” comments Clifford P. Kubiak of the University of California, San Diego, a specialist in CO₂ conversion. Compared with other ways to remove CO₂ from air, converting the greenhouse gas to oxalate catalytically, efficiently, and selectively “is near the top of the desirability rankings,” he says.]