کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
42181 45913 2010 11 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Phase transitions of V-Mo-W mixed oxides during reduction/re-oxidation cycles
موضوعات مرتبط
مهندسی و علوم پایه مهندسی شیمی کاتالیزور
پیش نمایش صفحه اول مقاله
Phase transitions of V-Mo-W mixed oxides during reduction/re-oxidation cycles
چکیده انگلیسی

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.

Tungsten-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 high-quality image (112 K)Download as PowerPoint slide

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Applied Catalysis A: General - Volume 379, Issues 1–2, 15 May 2010, Pages 155–165
نویسندگان
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