Studies of processes occurring during alkoxide derived V–O–W unsupported catalyst formation

Autor: J. Banaś, Anna Białas, Elżbieta Bielańska, Dang Sheng Su, Fujio Mizukami, M. Najbar, Pawel Kornelak, Aleksandra Wesełucha-Birczyńska, B. Borzęcka-Prokop
Rok vydání: 2004
Předmět:
Zdroj: Catalysis Today. 90:93-102
ISSN: 0920-5861
DOI: 10.1016/j.cattod.2004.04.013
Popis: The aim of this paper is to investigate the processes occurring during V-O-W unsupported catalyst formation in order to gain the knowledge necessary to design supported catalysts. Sol-gel synthesis of V-W hydroxo-oxide hydrate (W:V = 9:1) from tungsten and vanadyl isopropoxides is described. The hydrate structure is shown to be related to WO 3 .0.33H 2 O. The role of vanadium in the formation of this structure is discussed. Hydrate dehydration is shown to result in the formation of V-W hydroxo-oxide isostructural with hexagonal WO 3 . Further heating of hydroxy-oxide causes a loss of hydroxy groups accompanied by the formation of V-W oxide bronze isostructural with tetragonal WO 3 . Annealing the bronze in an air atmosphere results in the removal of vanadium from the bronze crystallites as a results of its surface segregation. The formation of the surface vanadia-like species on WO 3 -related crystallites is found to be a result of vanadium segregation. Increasing the annealing temperature causes recrystallisation of the surface species. The synthesis of a V-W/TiO 2 oxide catalyst via a mixed oxide formation in the presence of titania sols followed, by surface vanadium segregation in an air containing atmosphere, is proposed. The application of the knowledge gained during our investigation of the formation of the unsupported V-O-W catalyst to the discussion of the morphology of the V-O-W/Ti(Sn)O 2 (rutile) catalyst is also demonstrated.
Databáze: OpenAIRE
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