Dehydration and dehydrogenation of ethylene glycol on rutile TiO2(110)

The interactions of ethylene glycol with a partially reduced rutile TiO2(110) surface have been studied using temperature programmed desorption (TPD). The saturation coverage on surface Ti rows is determined to be 0.43 monolayer (ML), slightly less than one ethylene glycol per two Ti sites. Most of the adsorbed ethylene glycol (similar to 80%) undergoes further reactions to yield other products. Two major channels are observed, dehydration yielding ethylene and water and dehydrogenation yielding acetaldehyde and hydrogen. Hydrogen formation is rather surprising as it has not been observed previously on TiO2(110) from simple organic molecules. The coverage dependent yields of ethylene and acetaldehyde correlate well with those of water and hydrogen, respectively. Dehydration dominates at lower ethylene glycol coverages (<0.2 ML) and plateaus as the coverage is increased to saturation. Dehydrogenation is observed primarily at higher ethylene glycol coverages (>0.2 ML). Our results suggest that the observed dehydration and dehydrogenation reactions proceed via different surface intermediates.