Investigation of the dispersion of MoO 3 onto the support of mesoporous silica MCM-41

Abstract

The dispersion of MoO 3 onto the surface of mesoporous silica MCM-41 by means of thermal spreading was studied using different characterization techniques. The XRD results showed that MoO 3 dispersed on the surface of MCM-41 and transformed into dispersed Mo oxide species after thermal treatment of the mixtures of MCM-41 and MoO 3 at 773 K for 24 h. The critical dispersion capacity of MoO 3 on the surface of MCM-41 was MoO 3/MCM-41 of 0.26 g/g, i.e. 1.6 μmol/m 2 of Mo/MCM-41. The ordered porous structure of MCM-41 was destroyed when the loading of MoO 3 exceeded the critical dispersion value. The surface area and pore volume of the treating mixtures decreased and there was a small reduction in pore size when the loading of MoO 3 was below the critical dispersion capacity, which suggested that the dispersed Mo oxide species was in the pores of MCM-41. A broad band near 957 cm −1 emerged in the laser Raman spectra of the thermally treated mixtures, which was the evidence of dispersed Mo oxide species and was assigned to polymolybdates. The broadening full width at half-maximum (FWHM) and the loss of resolution for the Mo 3d doublet in the X-ray photoelectron spectra for the treated mixtures gave better evidence of the presence of Mo oxide species on the surface of MCM-41 than was found for the physical mixture.