On the role of oxidation states in the electronic structure via the formation of oxygen vacancies of a doped MoVTeNbOx in propylene oxidation

• Published in: Applied surface science Vol. 573; p. 151428
• Main Authors: Ramírez-Salgado, Joel, Quintana-Solórzano, Roberto, Mejía-Centeno, Isidro, Armendáriz-Herrera, Héctor, Rodríguez-Hernández, Andrea, Guzmán-Castillo, María de Lourdes, Valente, Jaime S.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 30.01.2022
• Subjects: Metal oxides; Oxidation states; Oxygen vacancies; Partial oxidation; Propylene; XPS; Metal oxides; Propylene; Oxygen vacancies; XPS; Partial oxidation; Oxidation states
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2021.151428

[Display omitted] •K or Bi doping impacts Mo 6+/5+ and V4+/5+ RedOx pairs and production/mobility of O vacancies.•HR-XPS was used to obtain band gap form the energy-loss peak of the O 1s spectra of materials.•Varying O vacancies concentration affects both valence band and band gap structure energy.•Catalyst’s performance in propylene oxidation to acrylic acid vary after doping with K or Bi. The Mars-van Krevelen mechanism alludes to a RedOx process in which, metal oxide catalysts are able to provide lattice oxygen atoms to gas phase organic compounds. After reduction, lattice oxygen induces oxygen vacancies in the framework of metal oxides upon their removal. Hence, a key condition for the appropriate operation of oxidation catalysts pertains to their ability to exchange electrons. In this work, XPS is applied to investigate the influence of oxygen vacancies on the electronic properties of a (K or Bi) doped MoVTeNb oxide. The XPS results indicate that oxygen vacancies produce changes in the electronic structure of Mo and V ions modifying the 4d and 3d orbitals, respectively, attributed to a process of electrons transfer caused by lattice oxygen removal and band gap decrease in the (K or Bi) doped material. The deconvoluted O 1s binding structure spectra are analysed as well. In propylene oxidation to acrylic acid used as test reaction, a correlation between the catalytic performance (propylene and oxygen conversion as well as acrylic acid selectivity) and the number of oxygen vacancies in the (K or Bi) doped MoVTeNb oxide is found. Though K-doping produces a slower replacement of lattice oxygen thus reducing its capacity to convert propylene, it leads to a notably larger acrylic acid selectivity compared to undoped and Bi-doped materials. Aside, the (K or Bi) doped catalyst’s performance appears to be linked not only to the density of the V5+ species but also to their reducibility to V4+.