A comparative study of hydrogen photocatalytic production from glycerol and propan-2-ol on M/TiO2 systems (M=Au, Pt, Pd)

Two different C-3 alcohols (glycerol and propan-2-ol) were tested as sacrificial agents for H-2 photocatalytic production on M/TiO2 (M = Pt, Pd and Au) solids. In all cases, synthetic methods led to average metal particle sizes in the 2-5 nm range (for nominal metal loadings of 0.5-3% by weight). Glycerol underwent photo-reforming whereas propan-2-ol was selectively oxidized to acetone. Under the present experimental conditions, both processes were structure-sensitive with higher TOF values being obtained for bigger metal particle sizes. As for the influence of metal loading, the highest TOF values corresponded to the lowest Pt and Au contents (0.5% by weight). In the case of propan-2-ol, dehydrogenation activity followed the order expected considering the work function of the metals (Pt > Pd > Au). On the contrary, for more complex glycerol photoreforming TOF values decreased in the order Pt approximate to Au>Pd. For both substrates, a dissociative adsorption Langmuir-Hinshelwood mechanism was found. Results were interpreted in terms of the different adsorption strength of glycerol and propan-2-ol as evidenced by a competitive adsorption experiment. All in all, the highest hydrogen production rate values corresponded to the use of propan-2-ol as the sacrificial agent, its TOF value being ca. 5.5 s(-1) on Pt-0.5% synthesized by photo-deposition method. (C) 2016 Elsevier B.V. All rights reserved.