Selective Photocatalytic Oxidation of Alcohols to Aldehydes in Water by TiO₂ Partially Coated with WO₃

Abstract

Semiconductor TiO(2) particles loaded with WO(3) (WO(3)/TiO(2)), synthesized by impregnation of tungstic acid followed by calcination, were used for photocatalytic oxidation of alcohols in water with molecular oxygen under irradiation at λ>350 nm. The WO(3)/TiO(2) catalysts promote selective oxidation of alcohols to aldehydes and show higher catalytic activity than pure TiO(2). In particular, a catalyst loading 7.6 wt % WO(3) led to higher aldehyde selectivity than previously reported photocatalytic systems. The high aldehyde selectivity arises because subsequent photocatalytic decomposition of the formed aldehyde is suppressed on the catalyst. The TiO(2) surface of the catalyst, which is active for oxidation, is partially coated by the WO(3) layer, which leads to a decrease in the amount of formed aldehyde adsorbed on the TiO(2) surface. This suppresses subsequent decomposition of the aldehyde on the TiO(2) surface and results in high aldehyde selectivity. The WO(3)/TiO(2) catalyst can selectively oxidize various aromatic alcohols and is reusable without loss of catalytic activity or selectivity.

Enhanced visible-light-driven photocatalytic performance of mesoporous W-Ti-SBA-15 prepared through a facile hydrothermal route

“…Under visible-light irradiation (420 nm < < 780 nm), WO 3 is easily excited to produce photogenerated electron-hole pairs due to its suitable bandgap energy and TiO 2 keeps in ground state. Excited electrons in WO 3 move to conduction band with a band edge potential (E CB ) of +0.4 eV and holes remain on valence band with a band edge potential (E VB ) of +3.2 eV [50]. E VB of WO 3 is much more positive than the E VB (+2.95 eV) of TiO 2 and hereby the holes on valence band of WO 3 tends to transfer across interfaces to that of TiO 2 [50].…”

“…Excited electrons in WO 3 move to conduction band with a band edge potential (E CB ) of +0.4 eV and holes remain on valence band with a band edge potential (E VB ) of +3.2 eV [50]. E VB of WO 3 is much more positive than the E VB (+2.95 eV) of TiO 2 and hereby the holes on valence band of WO 3 tends to transfer across interfaces to that of TiO 2 [50]. Electrons stay on conduction band of WO 3 since the E CB of WO 3 is less negative than that of TiO 2 .…”

Photo-Induced Electron Transfer Between a Reactant Molecule and Semiconductor Photocatalyst: In Situ Doping

“…Although mpg-C 3 N 4 exhibits excellent catalytic performance under visible light irradiation, high pressure of oxygen ([0.5 MPa) and benzotrifluoride as a solvent are required to give a good yield. Shiraishi and co-workers reported that TiO 2 partially covered with WO 3 showed activity for the photooxidation of alcohols in water with molecular oxygen under irradiation at k [ 350 nm [74]. In the case of photooxidation of benzylalcohol, the selectivity to benzaldehyde reached at 56% at 50% of alcohol conversion under diluted condition (5 mg of catalysts, 0.1 mmol of benzylalcohol, 5 mL of water as a solvent).…”

Promotion of multi-electron transfer for enhanced photocatalysis: A review focused on oxygen reduction reaction

“…Alternatively, when the particle size of WO 3 was not small enough to shift the CB energy level to a more negative potential, how does the ORR proceed over WO 3 surface in WO 3 /TiO 2 heterojunction? In 2011, Tsukamoto et al [78] have prepared WO 3 /TiO 2 heterojunction by impregnation of tungstic acid onto the TiO 2 particles followed by calcinations. They investigated the oxygen reduction reaction over In fact, multi-electron ORR is also observed in other type II heterojunction.…”