Synthesis and Characterization of Atomically Dispersed, Vanadosilicate Catalysts in Si8O20-Based Building Block Solids

Silica supported vanadium complexes have attracted interest as catalysts for a variety of catalytic reactions in the past two decades. Although many strategies have been developed for incorporating vanadyl species on silica surfaces, controlling dispersion and loading while simultaneously producing single site catalysts remains a challenging goal in this context and in catalysis as well.

A simple strategy for producing single-site and site-isolated vanadyl species has been explored which allows for control of both the connectivity to the support as well as the local surface structure around a V=O group. The main elements of this strategy involve construction of the support from silicate building blocks linked by groups that both hold the matrix together and act as catalytically active sites. Controlled sequential dosing lead to catalysts in which control of the identity of the sites, their connectivity to the support and dispersion is maintained. The specific system that will be described involves the controlled reaction of vanadyl chloride (VOCl3) and vanadium tetrachloride (VCl4) with the tin functionallized spherosilicate cube, (SnMe3)8Si8O20. Labeled 17O (SnMe3*O)8Si8O12 and (Cl3Si)8Si8O20 molecule have also been synthesized successfully by using totally new synthetic methodologies. The physico-chemical properties of these vanadium catalysts were characterized by solid state 51V and 17O NMR, gravimetric analysis, EXAFS, and atomic absorption spectroscopy.

A quick survey of isopropanol dehydration and dehydrogenation with these vanadium (IV and V) catalysts has been studies. The acid-base property of these single-site and site-isolated catalysts has been assessed by the conversion of isopropanol. Preliminary results of highly selectivity (>97%) of isopropanol conversion to propene will be described.