Photocatalytic Reduction of CO2 with H2O By Engineered TiO2 Nanocomposites

Photocatalytic conversion of CO₂ with H₂O to solar fuels is a promising technology to recycle CO₂, a major greenhouse gas. However, the CO₂-to-fuel conversion efficiency is typically low, mainly due to the fast recombination of photo-excited electron-hole pairs and limited absorption of sunlight by wide band-gap photocatalysts like TiO₂. In addition, some scientific challenges have been overlooked including the photocatalyst’s ability to adsorb CO₂ and the adsorption/desorption kinetics on the catalyst surface. To promote charge transfer, visible light response, and CO₂ adsorption and activation, we have engineered a series of TiO₂ nanocomposites including Cu/TiO₂, oxygen deficient TiO₂, TiO₂ nanocrystals with mixed exposed facets, porous microsphere MgO/TiO₂, and nano-TiO₂ dispersed on MgAl-layered oxide materials. Photocatalytic CO₂ reduction experiments have been conducted under UV and visible light irradiation, respectively, with CO and CH₄ being the major products. Furthermore, we have compared the CO₂ adsorption and reduction intermediates and reaction kinetics at near room temperature and near flue gas temperature (~150 ^oC), using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The higher reaction temperature enhanced intermediate/product desorption, and the addition of basic materials (MgO and MgAl-LDO) improves CO₂ adsorption particularly in the presence of water vapor, thus enhancing the catalytic activity and stability of the photocatalyst.