The photocatalytic reduction of carbon dioxide (CO2) on jet spray formed titanium dioxide (TiO2) was studied using light-emitting diode (LED) illumination centred at a wavelength of 388 nm. In addition, the photocatalytic reduction of CO2 under soft X-ray irradiation was also studied. Specifically, the experiments examined the reduction of CO2 in a gaseous and liquid-gas system using residual gas analysis mass spectrometry. A photochemical reduction of CO2 was observed over a course of 250 min, with transformation to a major product, C2H3O- (ethenolate), until equilibrium was reached. The product was observed to be surface stabilised, with it reverting back to CO2 over the course of 100 min without illumination. A proposed free radical mechanism is presented for the formation of this product. A similar effect to that of UV illumination is also observed to occur under the influence of soft X-rays, which presents a potentially significant alternative method for the activation of TiO2. (c) 2011 Elsevier B.V. All rights reserved.