Considering global warming and increasing emission of greenhouse gases, a method to convert CO2 to base chemicals such as CO, methanol, or methane, is required. Photocatalysis is a very promising approach for an ecological conversion of CO2, since it can use sunlight as energy source. The homogeneous photocatalytic reduction of CO2 to CO with rhenium(I) bipyridine complexes has been studied for several decades. Nevertheless, the performance of current catalytic systems is still considerably low for industrial applications. Understanding the mechanistic background and deactivation processes of a catalytic system is crucial for the improvement of its activity and stability. Recently, two deactivation processes starting from the one electron reduced (OER) species of the rhenium catalyst were reported. Herein, we present methods to avoid these deactivation processes. First, application of pulsed light in the nano- and picosecond scale suppresses light induced deactivation processes. Time-dependent structuring of the photon flux is shown to increase the turnover numbers (TONs) and turnover frequencies (TOFs) in the photocatalytic reduction of CO2. By using pulsed light, the irradiation of the OER species can be reduced, and therefore, light-induced deactivation processes are suppressed. Second, adding small amounts of DBU to a photocatalytically active CO2 reduction system containing rhenium-based catalysts, the amount of the sacrificial electron donor triethanolamine (TEOA) can be significantly reduced. As a consequence, TON and TOF values are not just retained with respect to the original system, but they even increase. Presumably, DBU helps to decrease the likelihood of deactivation processes involving TEOA radicals.

Suppression of deactivation processes in homogeneous photocatalytic reduction of CO2

256th National Meeting (2018)

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