AVS 47th International Symposium
    Material Characterization Tuesday Sessions
       Session MC-TuP

Paper MC-TuP19
Structural Characterization of V@sub 2@O@sub 5@/TiO@sub 2@ Catalysts

Tuesday, October 3, 2000, 5:30 pm, Room Exhibit Hall C & D

Session: Poster Session
Presenter: P.A.P. Nascente, Universidade Federal de Sao Carlos, Brazil
Authors: C.B. Rodella, Universidade de Sao Paulo, Brazil
P.A.P. Nascente, Universidade Federal de Sao Carlos, Brazil
V.R. Mastelaro, Universidade de Sao Paulo, Brazil
M.R. Zucchi, Universidade de Sao Paulo, Brazil
R.W. Franco, Universidade de Sao Paulo, Brazil
C.J. Magon, Universidade de Sao Paulo, Brazil
J.P. Donoso, Universidade de Sao Paulo, Brazil
A.O. Florentino, Universidade Estadual Paulista, Brazil
Correspondent: Click to Email
Vanadia supported on titania constitutes a well-know catalytic system for selective oxidation of o-xylene, ammoxidation of hydrocarbons and selective reduction of NO@subx@ with NH@sub3@. A series of V@sub2@O@sub5@/TiO@sub2@ samples was synthesized by sol-gel and impregnation method with different contents of vanadia and treated in different calcination temperature. The samples were characterized by X-ray diffraction (XDR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and electronic paramagnetic resonance (EPR). XDR detected rutile as the predominant phase for pure TiO@sub2@ prepared by the sol-gel method when calcined at 450@super0@C. The structure changed to anatase when the vanadia loading was increased. Also anatase was the predominant phase for samples obtained by the impregnation method. XPS results indicated that the Ti ions were surrounded tetrahedrally by oxygen ions. The V/Ti atomic ratios showed that V ions were highly dispersed on the vanadia/titania surface obtained by sol-gel method. Raman measurements identified three species of surface vanadium: monomeric vanadyl (V@super4+@), polymeric vanadates (V@super5+@) and V@sub2@O@sub5@ crystalline. EPR analysis detected three V@super4+@ ion types: two of them were located in axial symmetry sites substituting the Ti@super4+@ in the rutile structure, and the third one was constituted by a magnetically interacting V@super4+@ ions in the form of pairs or clusters. For the materials with higher concentrations of vanadium, a partial oxidation of V@super4+@ to V@super5+@ was evident from EPR analysis.