2. Upgrading with chemical transformation

There are various chemical pathways for CO ₂ valorization. They involve either inserting a CO ₂ molecule into a carbon chain (carboxylation) or mineral chain (mineralization), or on the contrary reducing this CO ₂ by adding hydrogen, for example. The reduction pathways take various forms, depending on the reactant used and technical specificities: the use of very high temperatures (thermochemistry), electricity (electrolysis), methane (reforming), or hydrogen (hydrogenation)... (see figure  1 ).