Understanding the Enhanced Catalytic CO2 Reduction upon Adhering Cobalt Porphyrin to Carbon Nanotubes and the Inverse Loading Effect

Adhering a cobalt porphyrin (Co­(TPP)) catalyst on a carbon nanotube (CNT) supporting material greatly enhances its reactivity and enables catalysis in water, which is otherwise impossible. However, the effect of solvent as well as supporting materials on catalysis is still elusive. On the basis of computational results we found that water as a reaction medium lowers the reductive potential required due to the stabilization of intermediates and transition states, and provides higher availability of protons. To understand the effect of the support materials, we combine computations and experiments and illustrate that the curvature of the nanotubes plays an essential role in aggregation through the competition between the π–π interactions between the porphyrin rings as well as between the Co­(TPP) and the nanotube, providing an insight into lessening the degree of aggregation.