Kinetic and mechanistic study of the photocatalytic reforming of methanol over Pt/TiO2 catalyst

The kinetics and mechanism of photo-reforming reaction of methanol have been studied over Pt/TiO2 suspensions irradiated with near-UV light (lambda(max) = 365 nm). The effects of initial methanol concentration in solution (C-MeOH), photocatalyst content in suspension (C-cat) and incident light intensity (I-0) on the reaction rate have been investigated in detail. It has been found that the reaction rate depends strongly on methanol concentration and increases by more than two orders of magnitude with increase of C-MeOH from zero to 1.0 M. The dependence of the reaction rate on C-MeOH can be described by saturation-type kinetics according to the Langmuir-Hinselwood model. Increase of photocatalyst content in suspension results in an increase of the reaction rate, which tends to stabilize for C-cat > 3 g L-1. The rate of hydrogen evolution varies with incident light intensity in a manner which depends on the initial methanol concentration in solution. In particular, the order of the reaction with respect to I-0 is unity for C-MeOH = 100 mM and 0.5 for C-MeOH = 3.0 mM. Analysis of reaction intermediates in solution and on the photocatalyst surface indicates that, under the present experimental conditions, the reaction proceeds via progressive oxidation of adsorbed methoxy species to formaldehyde, dioxymethylene and formate. These species do not desorb from the photocatalyst surface but remain in the adsorbed mode until they are completely reformed to H-2 and CO2. (C) 2013 Elsevier B.V. All rights reserved.