Single-atoms supported (Fe, Co, Ni, Cu) on graphitic carbon nitride for CO2 adsorption and hydrogenation to formic acid: First-principles insights

The non-noble metal single-atom catalysts (SACs) of Fe, Co, Ni and Cu supported on graphitic carbon nitride (g-C3N4) for CO2 adsorption and hydrogenation to formic acid have been investigated with periodic density functional theory calculations. From our calculations, we found the adsorption energies of CO2 in the range of −0.16 to −0.40 eV with the highest stability over Fe-g-C3N4. The van der Waals interaction was included in the calculation due to its significant role in CO2 adsorption. The 2-step proposed reaction mechanism involves the CO2 hydrogenation to form a formate intermediate and hydrogen abstraction to formic acid as the end product. Based on the rate-determining step activation barrier, the catalytic activity order was found as Fe-g-C3N4 > Co-g-C3N4 > Cu-g-C3N4 > Ni-g-C3N4. From our findings, the better understanding of the effect of the non-noble metal coordination on CO2 adsorption and hydrogenation provides hints to the rational catalyst design.