H2 production from the photocatalytic reforming of ethylene glycol: Effect of TiO2 crystalline phase on photo-oxidation mechanism

• Photocatalytic oxidation mechanism is dependent on TiO 2 crystalline phase. • Oxidative C–C cleavage of ethylene glycol was dominant pathway over rutile TiO 2 . • Over rutile TiO 2 conversion was efficient however H 2 evolution was low. • Anatase can convert aldehyde intermediates effectively but rutile cannot. In this work, the mechanism of H 2 production from ethylene glycol as a model compound for photoreforming over platinized TiO 2 is presented with particular focus on the effect of the TiO 2 polymorph. It was found that Pt/anatase and Pt/anatase:rutile (P25) had similar H 2 production activities and both catalysts followed an indirect oxidation pathway where ethylene glycol was oxidised via hydroxyl radicals to glycolaldehyde. In contrast, Pt/rutile primarily oxidised ethylene glycol directly into formaldehyde. The formaldehyde was unable to react further, which significantly reduced the formation of hydrogen despite similar conversion of ethylene glycol compared with the other supports used. We propose that these differences are due to different adsorption behaviour and hole transfer mechanism on the different TiO 2 crystalline phases. In particular, ethylene glycol complexation on Ti 5c sites on the dominant (110) facet of rutile leads to a direct hole transfer and an oxidative C–C cleavage mechanism prevailing.