Photocatalytic TiO2-based nafion membranes to be used for CO2 conversion

The reduction of CO2 with water by using photocatalysts is one of the most promising new methods to be investigated for the conversion of CO2 to valuable hydrocarbons, as it represents an attractive route from an economic and environmental point of view. The main interest is addressed to the production of methanol, as it can be easily transported, stored and used as gasoline-additives, as well as a starting material for other chemicals. The use of catalytic membranes is a promising strategy to perform efficient and eco-friendly catalytic chemical processes, taking advantages from the better exposition of catalyst to UV light to carry out the reaction, the tailoring of reactants and catalyst contact, the reduction of catalyst aggregates formation and an easier recovery of the catalyst. In this work, home prepared TiO2 was embedded into membranes made of Nafion. A solvent evaporation preparation method was developed and membranes with different catalyst weight percentage were prepared. They were characterized by SEM, IR and UV-Vis spectroscopy and then tested in order to verify their suitability for photocatalytic CO2 reduction with water. The experiments were carried out in a continuous mode, feeding pure CO2 into a membrane reactor module, equipped with a quartz window, by means of a mass flow controller. To the feed line a water stream was also sent by using a pump, the CO2:H2O molar ratio being 1:5. Chromatographic analysis showed that methanol was obtained as a product. By using the membrane with the best TiO2 distribution, a MeOH production rate of 45 µmol gcat-1 h-1 was obtained. Such a value results to be higher than most of the data reported in literature up to date. Nevertheless many efforts have to be made to improve the already interesting results, focusing on the amelioration of the catalyst distribution into the polymeric matrix at higher catalyst content and on the tuning of the reactor operating conditions.