H₂ Production from the Photocatalytic Reforming of Ethylene Glycol: Effect of Tio₂ Crystalline Phase on Photo-Oxidation Mechanism

In this work, the mechanism of H₂ production from ethylene glycol as a model compound for photoreforming over platinized TiO₂ is presented with particular focus on the effect of the TiO₂ polymorph. It was found that Pt/anatase and Pt/anatase:rutile (P25) had similar H₂ 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 TiO₂ crystalline phases. In particular, ethylene glycol complexation on Ti5c sites on the dominant (110) facet of rutile leads to a direct hole transfer and an oxidative C-C cleavage mechanism prevailing.