The active phase on Rh/ZrO2 is further clarified for HDO process
of fatty acid esters into biofuel products. Different activity zones
may exist simultaneously: (1) at a low-activity zone far away from
the metal particles, HDO reaction slowly proceeds on the oxygen
vacancies in a similar mechanism as occurred on bare ZrO2; (2)
at a medium-activity zone nearby the metal particles, the dissociated
hydrogen by metal can spillover and accelerate the HDO on
ZrO2; (3) the most-active zone is located at the perimeter of Rh
metal nanoparticle. At this zone, the support is electronically modified
so that the oxygen vacancies have better redox properties and
therefore higher activity for the deoxygenation pathway.