Synthesis of modified TiO2-based catalysts for the photocatalytic production of solar fuels from synthesis gas

Abstract

New alternative routes to traditional Fischer-Tropsch Synthesis (FTS) must be established to get a more efficient process from the point of view of energy and sustainability. Solar photocatalytic-assisted FTS is a promising new path to obtain fuels from renewable resources. However, proper photocatalysts must be designed to enhance the photocatalytic activity under solar/visible radiation. In this work, Fe and Co-doped TiO2 catalysts were synthesized by a traditional impregnated method and by a hydrothermal route. The oxygen vacancies generation on TiO2 photocatalysts was studied by Raman, XPS and Diffuse Reflectance Spectroscopy (DRS) and correlated with the decrease of the band gap and the photoactivity in the syngas conversion into solar fuels under solar radiation. Metal doping and H2 reduction treatment favour the oxygen vacancies generation that decreases the band gap from 3.3 eV for P25 to values as low as 2.2 and 2.5 eV for Fe- and Co-doped TiO2. This lower band gap increases the methanation activity under solar radiation. Moreover, this metal doping does not only affect the band gap and CO methanation activity under solar radiation but also the CC coupling, favouring the production of ethanol. Thus, in presence of P25, only CO2 and CH4 are obtained whereas the addition of Fe and Co enhances the CH4 generation and favours ethanol production. Therefore, the present work opens new opportunities for the photocatalytic Fischer-Tropsch conversion (PFTS) of crude syngas, which can be obtained from biomass or MSW gasification, into fuels under solar light.