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Phase transitions of V-Mo-W mixed oxides during reduction/re-oxidation cycles

Paper ID Volume ID Publish Year Pages File Format Full-Text
42181 45913 2010 11 PDF Available
Title
Phase transitions of V-Mo-W mixed oxides during reduction/re-oxidation cycles
Abstract

V-Mo-W mixed oxides are prepared by a hydrochemical preparation route with a stoichiometry of V2Mo8WxOy with 0 ≤ x ≤ 5 via evaporation/crystallization and by spray-drying of ammonium polyoxometallate solutions combined with a subsequent calcination procedure. The phase composition has been examined by electron and X-ray powder diffraction. Significant changes are observed after reduction/re-oxidation and after/during reactions in an air–acrolein atmosphere for all crystalline samples. Samples prepared from spray-dried precursors with tungsten contents x > 1 are amorphous/nanocrystalline. Independent of the preparation and reaction procedure, the formation of the thermodynamically metastable, tetragonal Mo5O14 phase is detected. Deactivation starts at the latest at 723 K in air with the formation of thermodynamically stable phases like orthorhombic MoO3. Smaller particles exhibit higher stability against deactivation or reduction. Reaction networks are established to illustrate the effect of various chemical reactions on crystalline and amorphous/nanocrystalline structures. The temperatures of the industrial processes are interpreted on the basis of the presented results.

Graphical abstractTungsten-doped vanadium molybdenum oxide catalysts for the selective oxidation of acrolein to acrylic acid prepared from evaporated or spray-dried precursors form different phases. Treatments under reducing and oxidizing mostly acrolein-containing atmospheres between 653 and 773 K uncover steps of active phase formation and catalyst deactivation depending on tungsten content and preparation. The results are related to industrial acrylic acid production.Figure optionsDownload full-size imageDownload high-quality image (112 K)Download as PowerPoint slide

Keywords
Vanadium molybdenum oxides; Oxidation catalysis; Acrolein; Acrylic acid; Phase transition; Deactivation; X-ray powder diffraction; Electron diffraction
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Phase transitions of V-Mo-W mixed oxides during reduction/re-oxidation cycles
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 379, Issues 1–2, 15 May 2010, Pages 155–165
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
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