Structural Transformation of Tungsten-Zirconium Hydroxide Crystals Upon Calcination Characterized by XRD, XAFS and Acid Catalyzed Reaction

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  • YAMAMOTO Takashi
    Department of Natural Science, Division of Science and Technology, Tokushima University Department of Mathematical and Material Sciences, Faculty of Integrated Arts and Sciences, Tokushima University
  • KONDO Maki
    Department of Mathematical and Material Sciences, Faculty of Integrated Arts and Sciences, Tokushima University
  • IRIE Tomoaki
    Department of Mathematical and Material Sciences, Faculty of Integrated Arts and Sciences, Tokushima University
  • TANIMA Naoto
    Department of Mathematical and Material Sciences, Faculty of Integrated Arts and Sciences, Tokushima University

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Other Title
  • タングステンジルコニウム水酸化物結晶脱水過程のXRD/XAFS観察およびその酸触媒特性
  • タングステンジルコニウム スイサンカブツ ケッショウ ダッスイ カテイ ノ XRD/XAFS カンサツ オヨビ ソノ サン ショクバイ トクセイ

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Abstract

<p>Tungsten zirconium hydroxides (ZWOH) with the molar ratio of W/Zr=2 were synthesized by a hydrothermal process at 453 K for 6-72 h. Structure of the hydroxides with different crystallinity and the transformation upon calcination were characterized by XRD, XAFS, UV-vis spectroscopic techniques. The ill-crystallized ZWOH with large surface area (>100m2·g-1; phase-I) was formed via hydrothermal treatment till 12 h, and well crystallized ZrW2O7(OH)2(H2O)2 (<2 m2·g-1; c-ZWOH) was formed after 24 h. W L-edge XAFS, optical bandgap and thermal gravity analyses gave direct evidence to support the previous suggestion about dehydration process of c-ZWOH to ZrW2O8, where ZrW2O8 polymorphism with low crystallinity (phase-II) and cubic ZrW2O8 crystal formed after calcination in the range of 573-773 and 823-873 K, respectively. The ZWOH phase-I was found to promote alkylation of benzylalcohol with anisole, and the activity exhibited the maximum after calcination at 873 K. The c-ZWOH and ZrW2O8 polymorphisms were catalytically inert for the reaction. Existence of active phase-I as a minor species in ZrW2O8 little influence on XRD pattern, but surface area measurements and the catalytic performance might help to evaluate fraction of phase-I in the Zr-W-O system. The ZWOH phase-I was candidate for a model catalyst of tungstated zirconia strong solid acid to investigate the acidity generation mechanism.</p>

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