Key points are not available for this paper at this time.
Doubly useful: The use of a mesoporous graphitic carbon nitride (mpg-C3N4) as a heterogeneous, metal-free catalyst enabled the direct activation of CO2 and the oxidation of benzene to phenol (see picture). The formed CO can be used in situ for subsequent reactions, as is shown for a Pauson–Khand reaction.
Goettmann et al. (2007) studied this question.