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Characterization of Mo‐V‐W Mixed Oxide Catalysts by ex situ and in situ X‐Ray Absorption Spectroscopy
Author(s) -
Schimanke Guido,
Martin Manfred,
Kunert Jan,
Vogel Herbert
Publication year - 2005
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.200500064
Subject(s) - catalysis , x ray absorption spectroscopy , oxidizing agent , acrolein , chemistry , absorption spectroscopy , carbon monoxide , absorption (acoustics) , mixed oxide , oxide , oxygen , spectroscopy , partial oxidation , inorganic chemistry , crystallization , in situ , xanes , redox , analytical chemistry (journal) , materials science , organic chemistry , physics , quantum mechanics , composite material
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 Mo 8 V 2 W y O x 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 Mo 6+ , V 5+ and W 6+ . Exposure of the as prepared samples to acrolein results in a reduction of both Mo 6+ and V 5+ whereas W 6+ 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 Mo 6+ in CO is about one order of magnitude slower than the subsequent re‐oxidation in oxygen.