The influence of preparation conditions on the surface area and phase formation of MoO 3/ZrO 2 catalysts

Abstract

In this study, MoO 3/ZrO 2 catalysts have been prepared by co-precipitation at different Mo/Zr ratios and at different digestion times of the catalyst precursors. MoO 3/ZrO 2 catalysts have higher surface areas than pure ZrO 2. As the MoO 3 content increases, the surface area of the samples increases and reaches a maximum. The value of this maximum and the correspondent MoO 3 content depend on the calcination temperature. Addition of Mo also preserves ZrO 2 in the metastable tetragonal phase instead of turning into the monoclinic phase. A minor modification of the preparation procedure has a tremendous effect on the surface areas of the catalysts. Samples obtained by addition of (NH 4) 6Mo 7O 24 after formation of the Zr(OH) 4 gel have larger surface areas than those obtained by co-precipitation. The surface areas of MoO 3/ZrO 2 decrease when the digestion time of the catalyst precursors is increased from 0 to 72 h. For long digestion times, the XRD patterns clearly show the formation of Zr(MoO 4) 2 at high MoO 3 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.