title: Niobium-silica catalysts for the selective epoxidation of cyclic alkenes: the generation of the active site by grafting niobocene dichloride.
abstract: Niobium-containing silica materials obtained by deposition via liquid-phase grafting or dry impregnation of niobocene(iv) dichloride are active and selective catalysts in the epoxidation of alkenes in the presence of aqueous hydrogen peroxide. The generation of the catalytically-active Nb species was followed step-by-step, and investigated using a combined DR-UV-Vis, NIR, Raman, XRD, XANES and EXAFS analyses. At the end of the grafting procedure, the nature of the surface active species can be described as an oxo-Nb(v) site, tripodally grafted onto the silica surface in close proximity to other Nb(v) centres. The liquid-phase methodology provides a better dispersion of the metal sites onto the siliceous support than the dry-impregnation approach. The niobium-silica catalysts were then tested in the epoxidation of cyclohexene and 1-methylcyclohexene, as model substrates.
authors.affiliation: CNR-Institute of Molecular Sciences and Technologies, Via C. Golgi 19, Milan, Italy.
authors.forename: Cristina
authors.initials: C
authors.lastname: Tiozzo
authors.forename: Chiara
authors.initials: C
authors.lastname: Bisio
authors.forename: Fabio
authors.initials: F
authors.lastname: Carniato
authors.forename: Alessandro
authors.initials: A
authors.lastname: Gallo
authors.forename: Susannah L
authors.initials: SL
authors.lastname: Scott
authors.forename: Rinaldo
authors.initials: R
authors.lastname: Psaro
authors.forename: Matteo
authors.initials: M
authors.lastname: Guidotti
mesh_terms: D002384:Catalysis; D020134:Catalytic Domain; D003516:Cycloparaffins / Q000737:chemistry*; D003517:Cyclopentanes / Q000737:chemistry*; D004852:Epoxy Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D009556:Niobium / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*
chemical_list: D003516:Cycloparaffins; D003517:Cyclopentanes; D004852:Epoxy Compounds; D009942:Organometallic Compounds; D009556:Niobium; C103086:niobocene dichloride; D012822:Silicon Dioxide