The influence of preparation conditions on the surface area and phase formation of MoO3/ZrO2 catalysts

Citation
A. Calafat et al., The influence of preparation conditions on the surface area and phase formation of MoO3/ZrO2 catalysts, APP CATAL A, 201(2), 2000, pp. 215-223
Citations number
20
Categorie Soggetti
Physical Chemistry/Chemical Physics","Chemical Engineering
Journal title
APPLIED CATALYSIS A-GENERAL
ISSN journal
0926860X → ACNP
Volume
201
Issue
2
Year of publication
2000
Pages
215 - 223
Database
ISI
SICI code
0926-860X(20000710)201:2<215:TIOPCO>2.0.ZU;2-V
Abstract
In this study, MoO3/ZrO2 catalysts have been prepared by co-precipitation a t different Mo/Zr ratios and at different digestion times of the catalyst p recursors. MoO3/ZrO2 catalysts have higher surface areas than pure ZrO2. As the MoOs content increases, the surface area of the samples increases and reaches a maximum. The value of this maximum and the correspondent MoO3 con tent depend on the calcination temperature. Addition of Mo also preserves Z rO2 in the metastable tetragonal phase instead of turning into the monoclin ic phase. A minor modification of the preparation procedure has a tremendou s effect on the surface areas of the catalysts. Samples obtained by additio n of (NH4)(6)Mo7O24 after formation of the Zr(OH)(4) gel have larger surfac e areas than those obtained by co-precipitation. The surface areas of MoO3/ ZrO2 decrease when the digestion time of the catalyst precursors is increas ed from 0 to 72 h. For long digestion times, the XRD patterns clearly show the formation of Zr(MoO4)(2) at high MoOs contents. In addition, Mo cannot oppose the tetragonal to monoclinic transition. Mo-Zr interactions seem to be the key factors in the different results obtained here, as suggested by XRD and TPR. (C) 2000 Elsevier Science B.V. All rights reserved.