ABSTRACT
The activation of carbon dioxide can be accomplished either by the direct supply of energy — photochemical, electrical, or thermal — or by its reaction with a reactant of high free-energy content. The latter category includes hydrogenation with molecular hydrogen and the reaction with hydrogen-rich molecules, such as ammonia and amines. Probably the earliest example of the scientifically initiated artificial synthesis of an organic compound was Woehler’s preparation of urea from ammonium cyanate. Urea, now produced on a large scale from ammonia and carbon dioxide via ammonium carbamate.
