Characterization of Mo—V—W Mixed Oxide Catalysts by ex situ and in situ X-Ray Absorption Spectroscopy

Autor: Jan Kunert, Guido Schimanke, Herbert Vogel, Manfred Martin
Rok vydání: 2005
Předmět:
Zdroj: ChemInform. 36
ISSN: 1522-2667
0931-7597
DOI: 10.1002/chin.200527020
Popis: Mixed oxides in the system Mo-V-W-O are important catalysts for partial oxidation reactions, e.g. the partial oxidation of acrolein to acrylic acid. Multiphase catalysts of the overall composition Mo8V2WyOx were prepared by spray drying and crystallization. The charge states of the potential catalytic centers Mo, V and W were investigated by ex situ X-ray absorption spectroscopy (XAS). In the as prepared samples the cations exist essentially as Mo6+, V5+ and W6+. Exposure of the as prepared samples to acrolein results in a reduction of both Mo6+ and V5+ whereas W6+ is inert. Re-oxidation with oxygen causes a reversible oxidation of Mo and V. The kinetics of the reduction and re-oxidation processes of the catalyst samples was studied at a temperature of 500 °C by in situ X-ray absorption spectroscopy at the Mo K-edge with carbon monoxide and oxygen as reducing and oxidizing gases. The in situ experiments show that the reduction of Mo6+ in CO is about one order of magnitude slower than the subsequent re-oxidation in oxygen.
Databáze: OpenAIRE
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