The researchers made the metal-organic photocatalyst, Ni (TPA/TEG), through a light-catalysed reaction. Solutions of TEG, TPA and nickel ions were irradiated with an unfocussed infrared laser for around three hours. This creates a catalyst with a crystalline architecture but with a significant number of defects. The catalyst is similar in structure to a metal organic framework, with the metal ions connected with rigid organic linkers, however in this case, the linkers are flexible.
The team tested the catalyst in a sealed reactor. After one hour at room temperature, 1 g of the catalyst produced 400 ml of CO. The reaction reduces CO2 using electrons from water to make CO. The reaction would normally also produce H2 gas, but this was undetectable with the use of the new catalyst. The researchers believe that the architecture of the catalyst suppresses the alternate reaction by favouring the binding of CO2 anions, leaving no space for hydrogen.
The researchers also tested the catalyst after enriching it with silver and rhodium nanocrystals. The silver-enriched catalyst produced acetic acid, with the rhodium-enriched catalyst produced formic acid. Both of these chemicals are widely used in industry, but more importantly, the researchers point out that it shows the catalysts can generate carbon-carbon links, which is important in the generation of liquid fuels.
Zheng and the team now plan to look at a tandem catalyst system which could use visible light, and developing more advanced metal-organic heterogeneous photocatalysts, which can use a broader spectrum of light and better fix CO2.
Science Advances doi.org/b95d