USC team develops highly efficient catalyst system for converting CO2 to methanol; 79% yield from CO2 captured from air
Researchers at Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California, have developed a highly efficient homogeneous Ru-based catalyst system for the production of methanol (CH3OH) from CO2 and H2 in an ethereal solvent (initial turnover frequency = 70 h−1 at 145 °C).
In a paper published in the Journal of the American Chemical Society, they reported demonstrating for the first time that CO2 captured from air can be directly converted to CH3OH in 79% yield using the new homogeneous catalytic system.
They demonstrated ease of separation of CH3OH by simple distillation from the reaction mixture. They recycled the catalyst over five runs without significant loss of activity (turnover number > 2000). Various sources of CO2 can be used for this reaction including air, despite its low CO2 concentration (400 ppm). Implementing the method in a flow system could deliver continuous production of CH3OH, the researchers said.
The work, led by G.K. Surya Prakash and George Olah of the USC Dornsife College of Letters, Arts and Sciences, is part of a broader effort to stabilize the amount of carbon dioxide in the atmosphere by using renewable energy to transform the greenhouse gas into its combustible cousin. Methanol is a clean-burning fuel for internal combustion engines, a fuel for fuel cells and a raw material used to produce many petrochemical products.
The researchers bubbled air through an aqueous solution of pentaethylenehexamine (or PEHA), adding a catalyst to encourage hydrogen to latch onto the CO2 under pressure. They then heated the solution, converting 79% of the CO2 into methanol. Though mixed with water, the resulting methanol can be easily distilled, Prakash said.
|Credit: ACS, Kothandaraman et al. Click to enlarge.|
Prakash and Olah hope to refine the process to the point that it could be scaled up for industrial use, though that may be 5 to 10 years away.
Of course it won’t compete with oil today, at around $30 per barrel. But right now we burn fossilized sunshine. We will run out of oil and gas, but the sun will be there for another five billion years. So we need to be better at taking advantage of it as a resource.—G.K. Surya Prakash
Despite its outsized impact on the environment, the actual concentration of CO2 in the atmosphere is relatively small—400 parts per million is 0.04% of the total volume. (For a comparison, there’s more than 23 times as much the noble gas Argon in the atmosphere—which still makes up less than 1% of the total volume.)
Previous efforts have required a slower multistage process with the use of high temperatures and high concentrations of CO2, meaning that renewable energy sources would not be able to efficiently power the process, as Olah and Prakash hope.
|CO2 capture from air and conversion to CH3OH. Credit: ACS, Kothandaraman et al. Click to enlarge.|
The new system operates at around 125 to 165 degrees Celsius (257 to 359 degrees Fahrenheit), minimizing the decomposition of the catalyst—which occurs at 155 degrees Celsius (311 degrees Fahrenheit). It also uses a homogeneous catalyst, making it a quicker “one-pot” process.
Olah and Prakash collaborated with graduate student Jotheeswari Kothandaraman and senior research associates Alain Goeppert and Miklos Czaun of USC Dornsife. The research was supported by the USC Loker Hydrocarbon Research Institute.
Jotheeswari Kothandaraman, Alain Goeppert, Miklos Czaun, George A. Olah, and G. K. Surya Prakash (2016) “Conversion of CO2 from Air into Methanol Using a Polyamine and a Homogeneous Ruthenium Catalyst” Journal of the American Chemical Society 138 (3), 778-781 doi: 10.1021/jacs.5b12354