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modification of MoO3 nanoparticles supported on mesoporous SBA-15: characterization using X-ray scattering, N2 physisorption, transmission electron microscopy, high-angle annular darkfield technique, Raman and XAFS spectroscopy
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modification of MoO3 nanoparticles supported on mesoporous SBA-15: characterization using X-ray scattering, N2 physisorption, transmission electron microscopy, high-angle annular darkfield technique, Raman and XAFS spectroscopy
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modification of MoO3 nanoparticles supported on mesoporous SBA-15: characterization using X-ray scattering, N2 physisorption, transmission electron microscopy, high-angle annular darkfield technique, Raman and XAFS spectroscopy
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Journal Article
modification of MoO3 nanoparticles supported on mesoporous SBA-15: characterization using X-ray scattering, N2 physisorption, transmission electron microscopy, high-angle annular darkfield technique, Raman and XAFS spectroscopy
2008
Overview
MoO₃ was dispersed onto mesoporous SBA-15 by using ammonium heptamolybdate as MoO₃ source. The formation of MoO₃ was carried out by heating the loaded material to 500 °C for 3 h in air. Below 13 wt% Mo loading, no reflections of MoO₃ occur in the X-ray powder patterns and even for high MoO₃ contents, the intensities of the reflections are much lower than expected for fully crystalline material. A detailed XAFS analysis reveals that at low Mo contents, the metastable hexagonal modification of MoO₃ is formed despite the high calcination temperature of 500 °C. It is highly likely that the nanosize of the particles and the interaction between MoO₃ and SBA-15 stabilize the metastable modification of the material. Nitrogen physisorption experiments show the typical type-IV isotherms indicating that the mesoporosity of the materials is preserved despite the large amount of MoO₃. Transmission electron micrographs demonstrate the presence of MoO₃ inside the SBA-15 support. The Raman spectra display a remarkable size-dependent intensity loss and several features give evidences for a bond formation between nano-sized MoO₃ particles and the silica support. Moreover, the spectroscopic details suggest the formation of (MoO₃)ₙ oligomers. MoO₃ nanoparticles are successfully introduced into the pores of mesoporous SBA-15. Up to about 13 wt% Mo the material is amorphous and even for higher loadings a large amount of MoO₃ is still not crystalline. Nitrogen physisorption and transmission electron microscopy evidences that the mesoporosity of the material is retained. At low Mo loading, the metastable hexagonal modification of MoO₃ appears to be stabilized by the interaction with the SBA-15 support material (XAFS).
Publisher
Springer US,Springer,Springer Nature B.V
Subject
/ Characterization and Evaluation of Materials
/ Chemistry and Materials Science
/ Colloidal state and disperse state
/ Condensed matter: electronic structure, electrical, magnetic, and optical properties
/ Cross-disciplinary physics: materials science; rheology
/ Crystallography and Scattering Methods
/ Exact sciences and technology
/ General and physical chemistry
/ heat
/ Nanoscale materials and structures: fabrication and characterization
/ nitrogen
/ Physical and chemical studies. Granulometry. Electrokinetic phenomena
/ Physics
/ silica
