HETEROGENEOUS PHOTOCATALYTIC DEHYDROGENATION FROM ETHANOL AND HEAVY-WATER
- 化学化工－已发表论文 
An isotopic method was used, with ethanol as hydrogen source and heavy water as deuterium source, to investigate the effect of ethanol concentration and pH value of the solution on the gaseous products (D2, HD and H-2) and H/D ratio during the photocatalytic dehydrogenation on Pd-CdS powdered photocatalyst. In a neutral medium of equimolar concentration, H/D = 2.08 is observed. In media with a wide range of pH values, H/D > 1 and a maximum H/D ratio of 2.5 is obtained at pH 12. This demonstrates that a larger number of effectively dissociated adsorptive ions are obtained from ethanol than from D2O, and that water acts as a reactant not a mere mediator. The occurrence of a maximum H/D value indicates the competition between dissociative adsorption of ethanol and D2O on the CdS surface. A detailed reaction mechanism is proposed. At a reaction temperature above room temperature using M-CdS, the rate-determining step is considered to be the transfer of photoproduced holes; this occurs when they are captured by adsorbed alcoholate ion RO-, followed by alpha-H separation, in acidic, neutral or weak basic media, or when they are captured by adsorbed hydroxyl ion OH-, followed by free radical OH . formation, in strongly basic (pH greater-than-or-equal-to 12) medium.