JNCASR-Bengaluru scientists devise way to convert carbon dioxide to methane without toxicity

BENGALURU: Bengaluru scientists have devised a toxic-free method that converts the most common greenhouse gas (GHG) carbon dioxide (CO2) to methane (CH4) - known to be the cleanest fossil fuel - a process that can effectively help in reducing levels of atmospheric carbon dioxide levels which is a major climate change concern.

The converted CH4 can directly be used in fuel cells as a hydrogen carrier. It is also the main component of natural gas and has the potential to replace coal for electricity generation and provide energy supply to renewable generators.

The scientists from Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Bengaluru, achieved this using non-metal catalysts, unlike procedures that are in use, which are found to release toxic gases in the process.

In doing so, the scientists, led by Professor Tapas Kumar Maji from the Chemistry and Physics of Materials Unit of JNCASR, have designed a cost-effective metal-free catalyst to achieve the conversion by absorption of visible light.

There are several ways in which CO2 can be reduced using photochemical, electrochemical, photoelectrochemical, photothermal methods. The photochemical uses solar light as a renewable energy source.

JNCASR scientists explained that some key requirements to convert CO2 by absorption of visible light into value-added products, like CH4, are light-harvesting property, the separation proficiency, and presence of proper electronically aligned conduction band.

But these pose a challenge to reduce CO2 to CH4 selectively and efficiently. Only a handful of catalysts are able to reduce CH4 selectively and efficiently, but most of these catalysts contain metal which are toxic and expensive.

To overcome this challenge, the JNCASR scientists designed a metal-free porous organic polymer in such a way that it absorbs the visible light and catalyzes the CO2 reduction reaction as well.

They did this by developing a donor-acceptor assembly to form a robust, thermally stable conjugated microporous organic polymer which they used as a catalyst. In this, a Ketone group containing a carbon-oxygen double bond acted as a catalytic site in stead of other conventional metal-based catalysts where the metal component carry out the CO2 conversion to value-added products, like CH4.

During the catalysis process, first, the chemical called conjugated microporous polymer (CMP) could uptake CO2 onto its surface due to its high CO2 intake capability at room temperature, converting it into methane as a value-added product, without any toxic by-products.

Prof Maji and his team said utilization of this cost-effective, metal-free system with a high production rate of CH4 can lead to new strategic ways for carbon capture and reduction of atmospheric CO2. Their work has been accepted for publication in the Journal of the American Chemical Society.