The reduction of CO₂ into useful fuels and chemicals (e.g. CO, CH₃OH etc.) is an increasingly important field of research, particularly due to the twin problems of global warming and the world's rapidly depleting fossil fuel reserves. Our goal is to harness the Sun's unlimited supply of solar energy by using efficient photocatalysts to perform these reactions. We are developing homogeneous catalysts based on the general formula, [Re(CO)₃(4,4'-X₂-2,2'-bipyridine)L]ⁿ⁺ (X = polyfluorinated substituents; L = Cl^- (n=0), and various neutral ligands (n=1)) for the photoreduction of CO₂ to CO in supercritical CO₂. These compounds have been designed to exhibit a high solubility in supercritical CO₂, and thus they allow us to carry out the photoinduced reduction of CO₂ in the absence of conventional solvents, which have been shown to significantly hinder the catalytic cycle.

In this talk we will present the results of photophysical and photochemical studies on some of these catalysts, in both conventional solvents and supercritical CO₂. This includes nanosecond UV-vis transient absorption and time-resolved infrared spectroscopy to characterize the metal-to-ligand charge transfer excited state and the one-electron reduced species, which is formed by quenching of the MLCT state by an electron donor. The photocatalytic activities of the catalysts will also be compared to previously studied catalysts in this family.

This research was supported under contract DE-AC02-98CH10886 with the US Department of Energy.