CO₂ reduction: Boron in its element

Angew. Chem. Int. Ed. http://doi.org/f9v5zk (2017)

Converting CO₂ into other molecules using artificial photosynthetic processes powered by solar energy is a route to produce fuels and fuel precursors. Photocatalytic approaches to CO₂ conversion typically rely on the use of semiconductors to absorb photons, generating electron–hole pairs to drive the reduction of CO₂. Now, Jinhua Ye and colleagues in Japan and China report a system in which the photothermal heating properties and catalytic activity of elemental boron are exploited to produce CH₄ and CO from CO₂ using only water and light irradiation in a photothermocatalytic process.

The researchers use largely amorphous boron particles, which, when irradiated with solar energy, are heated due to the photothermal effect, reaching temperatures of almost 380 °C. This causes localized heating that helps to activate CO₂ molecules and leads to hydrolysis of surface boron to produce H2 and boron oxides. The H₂ reacts with CO₂ catalytically over the boron particles to form the reduced products CH₄ and CO. A control experiment using Al₂O₃ as a substrate, rather than boron, heated to comparable temperatures in a CO₂/H2 gas stream yielded no CH₄, demonstrating the ability of boron to not only provide the necessary temperatures for reduction of CO₂ but also to catalyse the conversion of CO₂. Under visible light irradiation the system produces CO at a rate of 0.8 μmol h,1 and CH₄ at a rate of 1.9 μmol h,1, which is competitive with other systems for photocatalytic CO₂ reduction.