Communication
Photocatalytic-controlled olefin isomerization over WO3–x using low-energy photons up to 625 nm

https://doi.org/10.1016/S1872-2067(21)63815-9Get rights and content

Abstract

WO3–x (W-1) was used to achieve controllable photoisomerization of linear olefins without substituents under 625 nm light irradiation. Thermodynamic and kinetic isomers were obtained by regulating the carbon chain length of the olefins. Terminal olefins were converted into isomerized products, and the internal olefin mixtures present in petroleum derivatives were transformed into valuable pure olefin products. Oxygen vacancies (OVs) in W-1 altered the electronic structure of W-1 to improve its light-harvesting ability, which accounted for the high activity of olefin isomerization under light irradiation up to 625 nm. Additionally, OVs on the W-1 surface generated unsaturated W5+ sites that coordinated with olefins for the efficient adsorption and activation of olefins. Mechanistic studies reveal that the in situ formation of surface π-complexes and π-allylic W intermediates originating from the coordination of coordinated unsaturated W5+ sites and olefins ensure high photocatalytic activity and selectivity of W-1 for the photocatalytic isomerization of olefins via a radical mechanism.

Graphical Abstract

Oxygen vacancies in WO3–x improve the light-harvesting ability and surface reaction kinetics of WO3–x, which ensure high activity and selectivity of WO3–x for the photocatalytic isomerization of terminal olefins and internal olefin mixtures.

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      Noteworthily, an additional broad peak at 531.7 eV derived from the oxygen species adsorbed at oxygen vacancies, appeared in the XPS spectrum of WO3−x-N2.0, which has been recognized as a typical feature of defect-rich metal oxides [46,50]. Moreover, the oxygen vacancy was also confirmed by high resolution W 4f XPS spectra depicted in Fig. 5d. Two peaks located at binding energy of 37.6 and 35.5 eV were ascribed to W6+ 4f5/2 and W6+ 4f7/2 respectively [51,52], implying only W6+ ions were present in WO3-A2.0. For the synthesized WO3−x-N2.0 sample, two new peaks at binding energy at 36.6 and 34.6 eV could be observed and were assigned to 4f5/2 and 4f7/2 of W5+ ions [51,52], further indicating the existence of oxygen vacancies in WO3−x-N2.0.

    Available online 20 June 2021

    This work was supported by the National Natural Science Foundation of China (21773284, 22072176) and the Hundred Talents Program of the Chinese Academy of Sciences and Shanxi Province.

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