Photocatalytic CC bond cleavage in ethylene glycol on TiO2: A molecular level picture and the effect of metal nanoparticles

- A molecular picture of photocatalytic ethylene glycol (EG) dissociation on TiO2.
- The CC bond cleavage of EG is the only pathway, forming formaldehyde and H2.
- The rate determining step is the desorption of surface adsorbed H (Hads).
- The metal nanoparticles promote the desorption of Hads into H2.
- In-situ surface science studies are coupled with in-situ IR-mass spectrometry.

Polyol conversion to value-added products is of great interest for the bio-diesel industry. Photocatalytic oxidation processes may offer a green approach for polyol conversion; however the lack of comprehensive mechanistic understanding from an interdisciplinary perspective limits or even misleads the design of highly selective and efficient photocatalysts for such process. Here we have studied the photocatalytic polyol conversion on pristine TiO2 and metal (Au, Pd, and Pt) nanoparticles (NPs) decorated TiO2 using ethylene glycol (EG) as the model compound. We have developed a mechanistic picture at molecular level by coupling in-situ surface science study on rutile (110) surface with in-situ vibrational-mass spectrometry study on TiO2 nanopowders. The CC bond cleavage was found to be the only pathway in EG photo-conversion under deaerated conditions, leading to the formation of formaldehyde and hydrogen. We rationalized that the desorption of the surface adsorbed H (Hads) to be the rate determining step (RDS), making pristine TiO2 a poor photocatalyst that only catalyze the EG conversion at very low surface coverages. The addition of metal NPs on TiO2 surface promotes the desorption of Hads significantly, thus leading to an enhanced CC bond cleavage performance at higher surface coverages that is more applicable.

The CC bond cleavage is the only pathway in photo-conversion of ethylene glycol on TiO2 under deaerated conditions. The desorption of surface adsorbed H is the rate determining step and can be promoted by the addition of metal promoters (i.e., Au, Pd, Pt).115