Photonic efficiency and selectivity study of M (M=Pt, Pd, Au and Ag)/TiO2 photocatalysts for methanol reforming in the gas phase

Abstract

A number of different M/TiO2 photocatalysts, where M (the co-catalyst) = Pt, Pd, Au and Ag, are used to drive the steam reforming of methanol (MeOH) in a gas phase continuous flow reactor operated at 100 °C. The rate of H2 production is: Pt > Pd > Au > Ag >> no metal. The photonic efficiency of Pt/TiO2 photocatalyst is ca. 120% which suggests some of the hydrogen derives from a current-doubling reaction mechanism. The Pt/TiO2 photocatalyst drives the steam reforming of MeOH, which generates H2 and CO2, with an apparent selectivity of 100% over a wide UV irradiance range (i.e. 1–9.5 mW cm−2 at 365 nm). In contrast, in the dark, the decomposition of MeOH, which generates H2 and CO, dominates with a selectivity of ca. 67%. In contrast to Pt, the Pd/TiO2 photocatalyst is non-selective to either MeOH reforming or its decomposition, so that CO2 and CO are generated with equal rates. The Au and Ag photocatalysts are less active than either the Pt or Pd co-catalysts and exhibit a variation in selectivity with UV irradiance which is intermediate between that of Pt and Pd. The possible use of photocatalysis as a means to generate H2 from alcohol-based biofuels is briefly discussed.