A porphyrin co-catalyst enhancing low-temperature CO2 hydrogenation at the water–CuxAuy/ZnO interface

Abstract

The activation of CO₂ at the liquid/solid interface is highly promising for various catalytic processes and applications, offering the significant advantage of reduced mass and heat transfer effects compared to gas/solid interface. Considering water as a green reaction medium, this process is particularly challenged by the limited solubility of CO₂ and H₂ leading to low hydrogenation rates. Herein, we demonstrated that a water-soluble porphyrin derivative, chlorophyllin complex, can act as a co-catalyst for the conversion of CO₂ to methanol in water on CuAu/ZnO catalysts. While chlorophyllin itself is catalytically inactive, its presence increases the water solubility of reaction gases leading to up to a 3-fold increase in CO₂ conversion at 160 °C, while maintaining high selectivity toward methanol. Zeta potential results suggest electrostatic interactions between CO₂ and chlorophyllin, enhancing solubility. Spin trap-assisted EPR spectroscopy indicated the formation of C-center and OH radicals during the reaction, with their concentration increasing in the presence of chlorophyllin. These results represent a further step towards enabling the capture and hydrogenation of CO₂ at liquid/solid interfaces.