Synthesis and Characterization of Porous Vanadium Silicates in Organic Medium
| Autor: | Keith Morgan, Dugald J. MacLachlan, Vittorio Luca |
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| Rok vydání: | 1997 |
| Předmět: | |
| Zdroj: | Chemistry of Materials. 9:2720-2730 |
| ISSN: | 1520-5002 0897-4756 |
| DOI: | 10.1021/cm960621k |
| Popis: | Porous vanadium silicates have been synthesized in ethanolic medium by base hydrolysis of a mixture of tetraethoxysilicon(IV) and cetyltrimethylammonium vanadate precursors. The materials are similar to mesoporous silicates such as MCM-41 but have smaller pores and specific surface areas ranging from 270 to 1100 m2/g for samples with vanadium concentrations from 32 to 8 at. %. Using a variety of techniques, it is shown that the synthesis method results in isolated tetrahedral vanadate units homogeneously incorporated into and on the silicate matrix. On calcination, a similar vanadium coordination is found, but adsorption of water causes cleavage of Si−O−V bonds to give a mixture of isolated tetrahedral vanadium species in addition to polymeric vanadates and vanadium oxides. Nevertheless, the vanadium in these samples appears to be in a highly dispersed state. Silicon-29 MAS NMR of uncalcined samples shows that the degree of SiO4 condensation decreases with increasing vanadium content. The thermal stabilit... |
| Databáze: | OpenAIRE |
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