Synthesis via microemulsion of photo-catalysts for glycerol conversion

The current environmental crisis and increasing demand for fuels represent a problem in energy production and H2 plays a fundamental role. Photocatalytic reactions represent one of the alternatives to produce sustainable H2. To perform these reactions, a semiconductor is needed such as TiO2. A way to synthesise titania nanoparticles consists in the exploitation of microemulsions (ME), that permits a fine tuning of the final properties of the titania nanoparticles. In this work, the standard (STD) ME synthesis, developed in previous studies, is revised modyfing the hydrolysis and heating time, the type of acid used and adding a ME containing a base (NH4OH or NaOH). By implementing these modifications, it was possible to synthesise TiO2 samples with better properties than the STD sample, namely a lower bulk density and a higher surface area. In addition to that, TiO2 particles were obtained in nanoscale dimension and the utilization of NH4OH with a base/acid ratio (molar) higher than 0.7 allowed to synthesise just the anatase polymorph. If a longer stirring time was used or if HCl was employed rather than HNO3, also rutile formed as the only polymorph. On the other hand, the presence of NaOH resulted in the synthesis of an anatase and rutile mixture. Then, the TiO2 samples with the best characteristics were tested in the glycerol photo reforming reaction, since this substrate is obtained in huge amounts as a by-product from biodiesel production. The photoactivity of the bare TiO2 supports is expressed as H2 productivity (µmol H2/gcatalyst/h). The sample synthesised with NH4OH and a base/acid ratio of 0.7 showed the highest value for H2 productivity, even greater than the STD and commercial P-25 samples. Moreover, in this case, glyceraldehyde and glycolaldehyde were produced as liquid products, meaning that the decomposition of glycerol started. Conversely, using the STD sample no liquid products have been observed, thus mainly the water splitting reaction occurred.