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

Abstract

A series of supported 1-60% TiO(2)/SiO(2) catalysts were synthesized and subsequently used to anchor surface VO(x) redox and surface WO(x) acid sites. The supported TiO(x), VO(x), and WO(x) phases were physically characterized with TEM, in situ Raman and UV-vis spectroscopy, and chemically probed with in situ CH(3)OH-IR, CH(3)OH-TPSR and steady-state CH(3)OH dehydration. The CH(3)OH chemical probe studies revealed that the surface VO(x) sites are redox in nature and the surface WO(x) sites contain acidic character. The specific catalytic activity of surface redox (VO(4)) and acidic (WO(5)) 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.

New insight into the structure of dispersed titania by combining normal-mode analysis with experiment

“…Least-squares analysis using Lorentzian functions identified five peaks at 945, 1045, 1085, 1120 and 1180 cm −1 . As reported in the literature, the Raman features at 1085 and 945 cm −1 may be attributed to Ti-perturbed silica vibrations[23,30] …”

Tin-grafted TiO2 with enhanced activity for photocatalytic hydrogen generation from aqueous methanol solutions

“…Thus, grafting is a powerful method to investigate the influence of surface properties and surface modifications on catalytic behavior. Depending on the surface concentration, two different oxide species exist: isolated species at a low content and agglomerated species with excess loading [27]. Alkoxide precursors are usually preferred over acetylacetonates when the aim is the synthesis of isolated sites by means of grafting, because previous work has indicated that acetylacetonates might lead to the formation of agglomerates already at lower loadings [28,29].…”

Synthesis of Different CeO2 Structures on Mesoporous Silica and Characterization of Their Reduction Properties

“…88,91,94 However, in the cases of noncrystalline TiO x and VO x species on SiO 2 , a higher UV-vis edge energy has been attributed to a smaller domain size of the supported transition metal oxide due to quantum size effects. 95 The electronic states are more localized in smaller clusters, leading to higher absorption edge energy. 96 Applying this concept to the CeO 2 /SiO 2 samples, we conclude that for any loading, the samples prepared with Ce(O t Bu) 4 have the smallest CeO 2 domains.…”