Synthesis and Characterization of Mo−SBA-1 Cubic Mesoporous Molecular Sieves

Abstract

A series of Mo−SBA-1 ( Pm 3̄ n ) cubic mesoporous molecular sieves with various H 2 O/HCl and Si/Mo molar ratios have been synthesized at 0 °C using cetyltriethylammonium bromide, tetraethyl orthosilicate, ammonium heptamolybdate and hydrochloric acid. It was found that the Mo−SBA-1 particles synthesized at 0 °C for 4 days were of a characteristic shape having fifty-four, seventy-four, or more crystal faces. Synthesis conditions have been optimized to introduce high percentage of Mo into the well-ordered cubic mosoporous structure. The microstructure of Mo centers has been investigated by diffuse reflectance UV−visible and laser Raman spectroscopies. Both techniques reveal that, in the absence of water, Mo species consist of tetrahedrally and octahedrally coordinated monomers and polymers. The tetrahedral Mo centers were converted to octahedral Mo centers in the presence of moisture partially in directly synthesized Mo−SBA-1 samples and completely in impregnated Mo/SBA-1 samples. It is concluded that the impregnated samples were better dispersed than the directly synthesized samples.