Photocatalytic Reduction of Greenhouse Gas CO2 to Fuel

Abstract

Sun is the Earth’s ultimate and inexhaustible energy source. One of the best routes to remedy the CO2 problem is to convert it to valuable hydrocarbons using solar energy. In this study, CO2 was photocatalytically reduced to produce methanol, methane and ethylene in a steady-state optical-fiber reactor under artificial light and real sunlight irradiation. The photocatalyst was dip-coated on the optical fibers that enable the light to transmit and spread uniformly inside the reactor. The optical-fiber photoreactor, comprised of nearly 120 photocatalyst-coated fibers, was designed and assembled. The XRD spectra indicated the anatase phase for all photocatalysts. It is found that the methanol yield increased with UV light intensity. A maximum methanol yield of 4.12 μmole/g-cat h is obtained when 1.0 wt% Ag/TiO2 photocatalyst was used under a light intensity of 10 W/cm2. When mixed oxide, TiO2–SiO2, is doped with Cu and Fe metals, the resulting photocatalysts show substantial difference in hydrocarbon production as well as product selectivity. Methane and ethylene were produced on Cu–Fe loaded TiO2–SiO2 photocatalyst. Since dye-sensitized Cu–Fe/P25 photocatalyst can fully harvest the light energy of 400–800 nm from sunlight, its photoactivity was significantly enhanced. Finally, CO2 photoreduction was studied by in situ IR spectroscopy and possible mechanism for the photoreaction was proposed.