Dynamic photocatalytic reduction of CO2 to CO in a honeycomb monolith reactor loaded with Cu and N doped TiO2 nanocatalysts

Abstract

Cordierite honeycomb monoliths loaded with N/TiO2 and Cu/TiO2 nanocatalysts for dynamic photocatalytic CO2 reduction with H2 to CO in a continuous photoreactor illuminated with UV-light irradiations have been investigated. The nanocatalysts, loaded over the monoliths channels using sol-gel dip-coating method, were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), N2 adsorption-desorption, X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance and photoluminescence (PL) analysis. Crystalline and anatase TiO2 structure with nanoparticles evenly supported over the cordierite monolith channels were observed. Cu and N presented over TiO2, shifted band gap energy towards visible region and hindered charges recombination rate. Loading Cu and N greatly improved TiO2 photoactivity for dynamic CO2 reduction to CO. Due to high photoactivity and selectivity, Cu/TiO2 assisted system yielded 14 times higher CO than the N/TiO2 and 64 times the amount of copper observed over pure TiO2 in a continuous operation of photoreactor. This significant improvement in Cu/TiO2 activity was noticeable due to efficient trapping and transport of electrons by Cu-metal. With unique properties, N/TiO2 showed good activity for continuous CO2 reduction to CH4. In addition, a photocatalytic reaction mechanism is proposed to understand the experimental results over Cu and N modified TiO2 catalysts in a continuous operation of photoreactor.