Greening our world

1 Sep 2016. NUS chemists have developed a type of copper-based catalyst, which could efficiently reduce carbon dioxide, a greenhouse gas, into n-propanol.

Currently, most of the world’s energy needs are met by combusting fossil fuels such as oil, coal and natural gas. The supply of these fuels is limited and will eventually run out. Burning fossil fuels also generates carbon dioxide (CO₂), which is a suspected accelerant of global warming. A viable way to reduce these CO₂ emissions is to recycle them into useful carbon-based chemicals and fuels. This process is however very tough, as CO₂ is very stable and is difficult to chemically activate. It is also challenging to selectively convert it into desirable target molecules.

Among the CO₂ reduction products that could be formed, n-propanol has a very high octane number and energy density. Being an oxygenate, it can also be blended with gasoline to deliver a cleaner burning fuel with lower CO₂ and hydrocarbon emissions. The high market value of n-propanol (compared to other common CO₂ reduction products such as methane) also adds value to its production from CO₂, and makes the process more commercially-attractive.

A team led by Prof Boon Siang Jason, YEO from the Department of Chemistry in NUS and lead author, Mr REN Dan recently reported that agglomerates of ~15 nanometer (nm)-sized copper nanocrystals exhibited unprecedented catalytic activity for the electrochemical reduction of CO₂ to n-propanol in a single step under room temperature and pressure conditions. These copper nanocrystals were facilely prepared from cheap commercially-available copper salts and do not involve the use of environmentally harmful organic solvents. n-Propanol was formed on the Cu nanocrystals with a yield that is ~25 times larger than that found on normal Cu⁰ nanoparticles. Remarkably, the Cu nanocrystals were catalytically-stable for at least six hours, and only 14% deactivation was observed after 12 hours of CO₂ reduction. This work, which demonstrates the successful reduction of CO₂ to a commercially valuable liquid fuel, has potential applications in the energy industry.

Figure shows the reduction of CO₂ to n-propanol (PrOH) in a single step using our copper nanocrystals and electricity which can be generated from sustainable sources. [Image credit: Boon Siang Jason Yeo]

Reference

Ren D, Wong NT, Handoko AD, Huang Y, Yeo BS. The Journal of Physical Chemistry Letters 7 (2016) 20.