ID 111228
Title Alternative
Structural Transformation of Tungsten-Zirconium Hydroxide Crystals Upon Calcination Characterized by XRD, XAFS and Acid Catalyzed Reaction
Author
Kondo, Maki Tokushima University
Irie, Tomoaki Tokushima University
Tanima, Naoto Tokushima University
Keywords
タングステンジルコニウム水酸化物
ZrW2O8
脱水過程
XAFS
固体酸性
Tungsten zirconium hydroxide
Dehydration process
Solid acid
Content Type
Journal Article
Description
W:Zr 比が2:1 の二元系水酸化物を水熱合成法にて調製し,水熱処理の保持時間および焼成温度の異なる物質の構造をX 線回折,X 線吸収分光法で検討し,酸触媒特性を評価した.453 K での水熱処理では12 時間までは高表面積かつ結晶性の低い化学種(I 相)が生じ,24 時間以降で結晶性の高い水和物(ZWOH 結晶)が得られた.ZWOH 結晶は573−773K で結晶性の低いZrW2O8 多形(II 相),823−873K で立方晶ZrW2O8 へ変化することをX 線分析,UV-Vis 分光法および熱重量分析で確認した.I 相はアニソールのベンジルアルコールによるアルキル化を促進する固体強酸触媒として機能し,873K 焼成体が最高活性を示した.ZWOH 結晶およびZrW2O8 はアルキル化活性を示さなかった.立方晶系ZrW2O8 の結晶性の低いI 相が混在しても通常のXRD 解析では検出困難であるが,表面積測定および活性試験を併用すると混在の推定が可能であった.
Description Alternative
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.
Journal Title
Advances in X-Ray Chemical Analysis, Japan
ISSN
09117806
NCID
AN0000592X
Publisher
日本分析化学会
Volume
48
Start Page
137
End Page
148
Published Date
2017-03-31
Rights
©公益社団法人日本分析化学会X線分析研究懇談会
EDB ID
FullText File
language
jpn
TextVersion
Publisher
departments
Science and Technology