US EPA

7737874 

Journal Article 

Pseudotetrahedral O3/2V=0 centers immobilized on the walls of a mesoporous, cubic MCM-48 support: Preparation, characterization, and reactivity toward water as investigated by V-51 NMR and UV-vis spectroscopies 

Morey, M; Davidson, A; Eckert, H; Stucky, G 

1996 

Yes 

Chemistry of Materials
ISSN: 0897-4756
EISSN: 1520-5002 

American Chemical Society 

8 

2 

486-492 

English 

10.1021/cm950397j 

WOS:A1996TW40500032 

The high hydroxyl content of mesoporous silicates makes it possible to use them as anchors for the attachment of transition-metal species. In the present study, three different samples corresponding to atomic V/Si ratio of 0.01, 0.05, and 0.10 have been prepared by reacting a silica-based mesoporous matrix of the cubic MCM-48 structure, with dry hexane solutions of O=V(OiPr)3. Bulk structural characterization (X-ray diffraction and BET) shows that the cubic structure is maintained during the impregnation process. In the presence of V centers, a noticeable decrease of the main-pore diameter and of the a unit-cell parameter is observed. Thus, a strong interaction between the mesoporous walls and the V centers is suggested. The microstructural configuration of V centers has been investigated further by 51V NMR and UV-vis spectroscopies. Both techniques reveal that, in the absence of water, pseudotetrahedral O3/2V=O centers, probably coordinated by three (Si-O-V) bridges, are grafted to the mesoporous walls. The presence of these functional groups and their particular reactivity toward entering ligands such as water impart a number of unique properties to the bulk V/MCM-48, including color changes from white to orange in the presence of moisture.