SupraFixCO2 · Supramolecular Catalysis for Chemofixation and Electroreduction of CO2

Supramolecular Catalysis for Chemofixation and Electroreduction of CO2

Global warming has become one of the global concerns which is threatening all life on our planet. There is no doubt that human influence, especially the emission of greenhouse gases (e.g. CO2), is one of the major causes of global warming. The proposed project for the Marie Curie Fellowship aims to construct new systems of supramolecular catalysis for CO2 utilization by making full use of latest advances in host-guest chemistry. Cucurbit[n]urils (CB[n]s) are a family of water-soluble macrocyclic hosts, capable of binding different kinds of small molecules, macromolecules and even gases. Among them, CB[5] and CB[6] with their relatively small-sized cavities in the CB[n] family are able to encapsulate gases, e.g. N2, O2, Ar, CO, CO2, etc. Recently, CB[8] has been shown capable of binding a range of gas molecules with the aid of first guest incorporation into its nanocavity; additionally, CB[6]-modified Au surfaces have been found to efficiently promote and modulate CO2 electroreduction. It can be envisioned that CB[n], acting as a gas nanoreactor, could be employed to develop new supramolecular catalysts to promote gas-involved covalent reactions. In general, there are at least two different ways of encapsulating CO2 into CB[n]’s cavity: one is to use an organic reactant as the first guest molecule, and the other is to directly insert an appropriate catalyst. Following the above strategies, two kinds of CO2-involved catalytic reactions, chemofixation of CO2 into epoxides to cyclic carbonates and electroreduction of CO2 to form CO, have been explored using CB-based host-guest interactions. After a two-year investigation, it is shown that indeed host-guest complexations between CB macrocycles and organic reactants/catalyst did work as expected; unfortunately, no significant improvement on the catalytic conversion of CO2 could be observed. The main reason behind this is that the energy barrier to break the covalent bonds within CO2 remains at extremely high levels even within a nanoscale reaction cavity. More in-depth considerations and rational designs need to be taken into account for such aqueous supramolecular catalysis. It is hoped that this work may provide some initial information on the limitation of CO2 bond activation in aqueous media and attract more research interest from chemists into the areas of supramolecular chemistry and CO2 utilisation.

Data: CORDIS, © European Union