Dehydration and reduction reactions favored under medium pressure and temperature assisted by photocatalysis

Abstract

The impact of UV irradiation on the catalytic transformation of dihydroxyacetone molecule (DHA) has been investigated under inert atmosphere, medium pressure (5 Bars) and temperature (<=120°C) in presence of commercial anatase TiO2 samples (UV100 and A100), rutile TiO2 (R100) and mixture of anatase and rutile phase (P90). In absence of light, the main products formed are pyruvaldehyde and lactic acid whatever the temperature playing only a role on kinetic. Under UV irradiation, we highlighted their decomposition and the formation of new compounds, hydroxyacetone (HydA) in high concentration and acrylic acid (AcrAc) together with H2, CO2 and acetaldehyde in gas phase and new condensation products. The higher the number of photons emitted, the greater the HydA and AcrAc formation highlighting the importance of light and especially of the (e-, h+) pairs generated by photocatalysis. Actually, whereas the formation of HydA and AcrAc is similar in presence of all TiO2 samples containing anatase phase, these compounds are formed in low concentration in presence of TiO2 rutile. Mechanisms of the formation of hydA and AcrAc under photocatalysis assisted by pressure and temperature were discussed considering the formation of H+ and reducing agent made possible thanks to simultaneous oxidation reaction occurring via h+ and or OH°