Synergy between single atoms and nanoclusters of Pd/g-C3N4 catalysts for efficient base-free CO2 hydrogenation to formic acid

In base-free CO2 hydrogenation to HCOOH over C3N4-supported Pd catalysts, a synergy between Pd single atoms and nanoclusters has been discovered by observing the highest catalytic activity when an optimum ratio of the two Pd states is present in the catalyst. It is demonstrated that Pd clusters are mainly involved in H2 activation by dissociative adsorption, while single atoms are more effec-tive for CO2 activation. Thus, at an optimum single atom ratio (number of single atoms/number of single atoms + nanoclusters) of 41％, the catalyst shows the highest activity, which is superior to all Pd catalysts reported previously in the literature under the similar reaction conditions.