Tuning the Electronic and Molecular Structures of Catalytic Active Sites with Titania Nanoligands

A series of supported 1-60% TiO2/SiO2 catalysts were synthesized and subsequently used to anchor surface VOx redox and surface WOx acid sites. The supported TiOx, VOx, and WOx, phases were physically characterized with TEM, in situ Raman and UV-vis spectroscopy, and chemically probed with in situ CH3OH-IR, CH3OH-TPSR and steady-state CH3OH dehydration. The CH3OH chemical probe studies revealed that the surface VOx sites are redox in nature and the surface WOx sites contain acidic character. The specific catalytic activity of surface redox (VO4) and acidic (WO5) sites coordinated to the titania nanoligands are extremely sensitive to the degree of electron delocalization of the titania nanoligands. With decreasing titania. domain size, < 10 nm, acidic activity increases and redox activity decreases due to their inverse electronic requirements. This is the first systematic study to demonstrate the ability of oxide nanoligands to tune the electronic structure and reactivity of surface metal oxide catalytic active sites.