The second lecture aims to provide an overview of the various current research directions concerning the exploitation ofCO2 for the synthesis of useful carbonaceous molecules. This begins with an understanding of the fundamental reactivity of theCO2 molecule and the mechanisms employed by metal catalysts to lower the activation barrier associated with its use in chemistry. By associating with a metal ion (M) that modifies its electronic properties, theCO2 molecule can be activated to react with substrates that are themselves also activated by interaction with the catalyst. Its insertion in M-H bonds leads to formic acid, in M-C bonds to carboxylic acids and in M-O bonds to carbonates. The reaction ofCO2 with epoxides, for example, is interesting in that it leads to polymers, polycarbonates, which have very interesting applications in the chemical industry.
Another area of active research is that ofCO2 reduction, which is briefly described here as it is the subject of specific lectures. This may involve electroreduction, photoreduction or hydrogenation ofCO2. In all these reactions, the process leads to the storage of electrical or solar energy in the form of chemical energy, through the formation of energy-rich carbon products (CO, formic acid, methanol...) which can then be used as fuels or carbon sources for the chemical industry. This provides an opportunity to introduce the concept of artificial photosynthesis, which will be the subject of a separate lecture.
Finally, this is an opportunity to talk a little about natural photosynthesis, which is also being exploited technologically through the use of photosynthetic microorganisms, such as cyanobacteria or microalgae, for the production of bioethanol and biodiesel, so-called "third-generation" biofuels. The advantages and disadvantages of the different types of biofuels are discussed.
