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Autori: Enache, Dan I.; Bordes-Richard, Elisabeth; Ensuque, Alain; Bozon-Verduraz, Francois.
Editorial: Applied Catalysis, A: General, 278(1), p.93-102, 2004.
A high surface area amorphous zirconia and a medium surface area tetragonal zirconia were used as supports for vanadium oxide catalysts and compared with titania (anatase). The vanadia phase is deposited according to various methods: impregnation of the supports by colloidal vanadia solutions (an original procedure), conventional impregnation by ammonium metavanadate, grafting of vanadylacetylacetonate. The characterization is performed at the different preparation stages by various spectroscopic methods (FT-IR, Raman, UV–vis–NIR diffuse reflectance, ESR and XPS) and XRD.
The structure of the vanadia species is shown to depend on the nature of the precursor, on the nature of the support and on the preparation method: (i) the samples prepared by grafting and calcination contain only surface polyvanadates whatever the support whereas impregnation with NH4VO3 and calcination lead to crystallized V2O5 on both tetragonal and amorphous zirconia; (ii) the deposition of colloidal vanadia on tetragonal zirconia generates crystallized V2O5 whereas it forms polyvanadates on amorphous zirconia and on anatase; the propensity of amorphous zirconia to insert vanadium ions induces its crystallization into tetragonal and monoclinic zirconia between 500 and 600 °C; (iii) in all cases, the amount of surface V4+, estimated by ESR and XPS, is significant after outgassing at moderate temperatures without action of reducing agents.
Cuvinte cheie: Vanadium oxide catalysts; Zirconia; Anatase; Colloidal vanadium oxide; UV–vis–NIR diffuse reflectance spectroscopy; Raman spectroscopy; ESR