Useful carbon dioxide: NMR plots its redemption

Carbon feedstock

Researchers at the Institut Rayonnement Matière de Saclay in Gif-sur-Yvette, France, have developed a novel method for converting the greenhouse gas, carbon dioxide, into either useable building blocks for chemical syntheses or new fuels. The team used nuclear magnetic resonance spectroscopy to track progress of their reactions.

As we have all come to learn over the last decade. Carbon dioxide is chemical anathema. Its release through the burning of fossil fuels, wood and any other organic matter whether waste or fuel, is raising the atmospheric concentration of the greenhouse gas and initiating what some observers suggest might be catastrophic and irreversible climate change. However, carbon dioxide need not be viewed solely as a useless planetary pollutant a waste product of our energy needs and nothing more. Carbon dioxide, could act as a carbon source, if only there were a simple, efficient and sustainable method to trap it from power station exhaust gases in a form that could be used as a carbon source and so fed back into industry as a feedstock.

This abhorrent gas might be redeemed to some extent if it were converted to a renewable resource. The once evil CO₂ might be transformed into an environmentally friendly chemical reagent. The development of technology that allows us to reduce carbon pollution and perhaps even usefully extract the gas from the atmosphere might even allow us to reverse some of the damage we have wrought on the planet through wanton burning of fossil fuels since the dawn of the Industrial Revolution. If we could find a technically viable way to use it, it would not only allow us to reduce overall emissions into the atmosphere, but also reduce our dependence on dwindling petrochemical supplies.

Closer to the ideal

Writing in Angewandte Chemie, scientists in France have developed a novel approach that might take us closer to such an ideal: a way to convert carbon dioxide into useable building blocks for chemical synthesis and new fuels.

"Carbon dioxide is a non-toxic, abundant C₁ building block," explains Thibault Cantat, "Only a handful of processes using this starting material have been developed, because carbon dioxide is a very stable molecule that cannot easily be made to react." Therein lies the problem. It is its spectroscopic characteristics and stability that make carbon dioxide such a good greenhouse gas, but also in general preclude its use in industrial chemistry as a carbon source.

Researchers have for many years attempted to remedy this situation and have developed two different approaches so far. The first is the "vertical" approach in which the carbon dioxide is reduced, by replacing oxygen with hydrogen. This allows chemists to generate methanol or formic acid, which can then be readily converted into fuel compounds." These products have a higher energy content than carbon dioxide, but only a handful of chemicals can be produced this way," explains Cantat. In the second, "horizontal" approach, the carbon atom is not reduced, it is functionalized, by the creation of new bonds to oxygen, nitrogen, or additional carbon atoms to make urea and other molecules. Given that the oxidation state does not change, the products of this approach have the same energy, these compounds can thus be used as building blocks for the chemical syntheses of more complicated materials as feedstocks for yet other processes.

The French team has now devised a third way, which is a hybrid of the vertical and horizontal. Not surprisingly they refer to it as a "diagonal" approach. In their method, the carbon dioxide is both reduced and functionalized in a single reaction step. This allows them to generate many more different chemicals, directly from the gas. The approach uses three key ingredients: a reducing agent (such as inexpensive and non-toxic organosilanes), an organic molecule that will be attached to the carbon atom of the carbon dioxide (for example, an amine), and finally a catalyst that can accelerate the reduction and the functionalization processes simultaneously. It is the development of an organic base consisting of a nitrogen-containing ring system: 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD).

Variations on a theme

"Variation of the reaction partners should allow us to make a whole series of chemical compounds that are normally obtained from petrochemical feedstocks," explains Cantat, "for example, formamide derivatives, which are important intermediates for both chemical and pharmaceutical industries."

"Further work is underway to extend this diagonal strategy for the recycling of carbon dioxide to other functionalized and reduced chemicals by tuning independently the functionalizing and reducing agents," the team concludes.

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.