Abstract
V 2O 5-TiO 2(anatase) catalysts have been studied under oxidizing and reducing conditions using in situ laser Raman spectroscopy (LRS) and temperature-programmed reduction (TPR) and oxidation (TPO). Quantitative Raman and TPO analysis of the oxidized samples show that these materials are comprised of a distribution of monomeric vanadyls, polymeric vanadates, and crystallites of V 2O 5. At low loadings, the predominant species are monomeric vanadyls, with the remaining vanadia being present in the form of polymeric vanadates. As the surface concentration of V 2O 5 increases, a maximum in the concentration of the polymeric vanadates is detected. Crystallites of V 2O 5 form at the expense of the polymeric vanadates as the loading is raised above the dispersive capacity of the TiO 2(anatase) support. An equilibrium polymerization model is proposed to account for the observed concentration of vanadia species, which leads to an initial polymer size of ∼2 at low loadings, consistent with the formation of dimeric species. Raman and TPR/TPO studies of the reduction process indicate that the terminal V = 0 groups of the monomeric and polymeric vanadia species are removed preferentially to the bridging oxygen atoms of the polymeric species. The maximum loss of oxygen upon reduction is one oxygen atom per vanadium atom.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.