Effect of temperature on the photoreactions of ethanol over Ag/TiO2 in steady state catalytic conditions

The photo-thermal reaction of ethanol to hydrogen and acetaldehyde over Ag/TiO2 is studied in flow conditions. Hydrogen production is mostly photo driven below 170 °C, and thermally driven above 250 °C. An increase in the overall reaction rates is observed when both photons and heat (photo-thermal effect) are present in the 125−225 °C temperature window for acetaldehyde and hydrogen production (via ethanol dehydrogenation; C2H5OH → CH3CHO + H2). The activation energies for photo-thermal and thermal reactions, measured in steady state conditions, are 31 and 40 kJmol−1, respectively. The maximum enhancement in reaction rates is 1.5× for acetaldehyde and 10× for hydrogen production. The enhancement for these two product should be the same. Reasons for these discrepancies are discussed. Other minor reaction products including ethylene and acetone appeared above 225 °C. Possible reasons for the enhanced rate of ethanol reaction under photo-thermal conditions, linked to plasmon resonance of Ag particles of Ag/TiO2, are discussed. Light to Chemical Energy Conversion (LCEC) was found equal to 0.12 % and 0.25 % at 170 °C and 225 °C, respectively.