PHOTOASSISTED HYDROGEN-PRODUCTION FROM A WATER-ETHANOL SOLUTION - A COMPARISON OF ACTIVITIES OF AU-TIO2 AND PT-TIO2

A comparison of the photocatalytic activity for H-2 generation between Au-TiO2 and Pt-TiO2 has been made. The deposition of Au and Pt was carried out using TiO2 powders in aqueous suspensions containing HAuCl4 . 4H(2)O or H2PtCl6 .. 6H(2)O by deposition-precipitation (DP), impregnation (IMP), photodeposition (FD) and, in the case of Au, by mixing TiO2 with colloidal gold suspensions (MIX). The main reaction products obtained from the irradiation of an aqueous 5 M C2H5OH suspension containing Au-TiO2 or Pt-TiO2 were hydrogen, methane, carbon dioxide and acetaldehyde. Small amounts of acetic acid were also detected. The overall activity of Au samples was generally about 30% lower than that of Pt samples. The activity of Au samples strongly depended on the method of preparation and decreased in the order Au-TiO2-FD>Au-TiO2-DP>Au-TiO2-IMP>Au-TiO2-MIX. The activities of the platinum samples were less sensitive to the preparation method and decreased in the order Pt-TiO2-FD>Pt-TiO2-DP approximate to Pt-TiO2-IMP. Gold and platinum precursors calcined in air at 573 K showed the highest activity towards H-2 generation, followed by a decline in activity with increasing calcination temperature. The H-2 yield was found to be dependent on the metal content on TiO2 and showed a maximum in the ranges 0.3-1 wt.% Pt and 1-2 wt.% Au. The exposed surface area of gold had only a small influence on the rate of hydrogen generation. On the other hand, the rate of H-2 production was strongly dependent on the initial pH of the suspension. pH values in the range 4-7 gave better yields, whereas highly acidic and basic suspensions resulted in a considerable decrease in the H-2 yield.