Comparative study on the photocatalytic decomposition of methanol on TiO2 modified by N and promoted by metals

The photo-induced vapor-phase reaction of methanol was investigated on Pt metals deposited on pure and N-doped TiO2. Infrared spectroscopic measurements revealed that illumination of the CH3OH–TiO2 and CH3OH-M/TiO2 systems led to the conversion of adsorbed methoxy species into adsorbed formate. In the case of metal-promoted TiO2 catalysts CO bonded to the metals was also detected. Pure titania exhibited very little photoactivity, its efficiency, however, increased with the narrowing of its bandgap by N-doping, a feature attributed to the prevention of electron–hole recombination. Deposition of Pt metals on pure and N-doped TiO2 dramatically enhanced the extent of photoreaction of methanol even in visible light: hydrogen and methyl formate with selectivities of 83–90% were the major products. The most active metal was Pt followed by Pd, Ir, Rh, and Ru. The effect of metal was explained by a better separation of charge carriers induced by illumination and by enhanced electronic interaction between metal nanoparticles and TiO2.