Visible-Light Photochemical Reduction of CO2 to CO Coupled to Hydrocarbon Dehydrogenation

Research on the photochemical reduction of CO2, initiated already 40 years ago, has with few exceptions been performed by using amines as sacrificial reductants. Hydrocarbons are high-volume chemicals whose dehydrogenation is of interest, so the coupling of a CO2 photoreduction to a hydrocarbon-photodehydrogenation reaction seems a worthwhile concept to explore. A three-component construct was prepared including graphitic carbon nitride (g-CN) as a visible-light photoactive semiconductor, a polyoxometalate (POM) that functions as an electron acceptor to improve hole-electron charge separation, and an electron donor to a rhenium-based CO2 reduction catalyst. Upon photoactivation of g-CN, a cascade is initiated by dehydrogenation of hydrocarbons coupled to the reduction of the polyoxometalate. Visible-light photoexcitation of the reduced polyoxometalate enables electron transfer to the rhenium-based catalyst active for the selective reduction of CO2 to CO. The construct was characterized by zeta potential, IR spectroscopy, thermogravimetry, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). An experimental Z-scheme diagram is presented based on electrochemical measurements and UV/Vis spectroscopy. The conceptual advance should promote study into more active systems.