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 degrees C, and thermally driven above 250 degrees C. An increase in the overall reaction rates is observed when both photons and heat (photo-thermal effect) are present in the 125-225 degrees C temperature window for acetaldehyde and hydrogen production (via ethanol dehydrogenation; C2H5OH -> CH3CHO + H-2). 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 1.5x for acetaldehyde and 10x 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 degrees 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 degrees C and 225 degrees C, respectively.

Automated summary

The study found that the Ag/TiO2 catalyst can effectively promote the reaction of ethanol to produce hydrogen and acetaldehyde under photo-thermal conditions, leading to an increase in the reaction rates of the products. The activation energy for ethanol dehydrogenation reaction is lower under photo-thermal conditions, which enhances the production rates of the products.