Organocatalysts Convert Carbon Dioxide to Methanol

N-heterocyclic carbene (NHC) organocatalysts promise to transform carbon dioxide, a greenhouse gas that poses environmental concerns, into a desirable feedstock, say scientists at the Institute of Bioengineering and Nanotechnology (IBN), Singapore. “We have now shown that NHCs can… be applied successfully to the conversion of carbon dioxide into methanol, helping to unleash the potential of this highly abundant gas,” notes Yugen Zhang, IBN team leader and principal research scientist.

“We do not anticipate problems for the large-scale production of NHCs.”

- Yugen Zhang, IBN team leader

Low levels of NHCs spur the reaction of CO₂ with hydrosilane. “Hydrosilane provides hydrogen, which bonds with CO₂ in a reduction reaction. This CO₂ reduction is efficiently catalyzed by NHCs even at room temperature. Methanol can be easily obtained from the product of the CO₂ reaction,” adds Zhang.

The team has achieved more than 90% yields of methanol (based on silane) at room temperature and atmospheric pressure. Activity reportedly far exceeded that of organometallic catalysts. The NHC catalysts provided a turnover number of up to 1,840 and a turnover frequency as high as 25.5/hr. for the CO₂ hydrosilylation. In contrast to conventional transition-metal catalysts for CO₂ reduction with silanes, which usually are very sensitive to oxygen, the NHC catalysts tolerate oxygen, allowing dry air to be used as feedstock. Details are given in a paper in Angewandte Chemie.

The catalyst is stable and nontoxic. “We do not anticipate problems for the large-scale production of NHCs,” notes Zhang.

Hydrosilane is an expensive source of hydrogen, though. “We need to find a way to produce hydrosilane at low cost or replace it with a cheaper hydrogen source. We also need to find other uses for the siloxane byproduct, which has potential applications in the silicone resin industry,” explains Zhang. “We have already started work on finding alternative hydrogen sources that can be generated via green methods,” he adds. IBN hopes to work with industry on the development.