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
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.