Ammonia, grafted silica

Preparation of new basic mesoporous silica catalysts by ammonia grafting... 

Preparation of new basic mesoporous silica catalysts by ammonia grafting H. Yoshida, Y. Inaki, Y. Kajita, K. Ito and T. Hattori 837... 

Finally, we will cite the new basic mesoporous silica cataly.st obtained by ammonia grafting [269] which has SiNH2 and SiOH pair sites formed at lower NHj-treatment temperatures and exhibits higher turnover frecuencies in comparison with SiNHj simple sites for Knocvenagcl condensation between benzaldehyde and ethyl cyanoacetate. 

Inaki. Y Kajita, Y Yoshida. H Ito. K Haitori, T. New basic mesoporous silica catalyst obtained by ammonia grafting. Chemical Communications, 2001 2358-2359. 

Highly dispersed grafted species can be obtained after grafting of Mods [8] or SbCls [34] on silica, the elimination of the released metal species during washing with ammonia solution and water, respectively, leads to the formation of highly dispersed isolated species. 

Fig. 5. Schematic representation of the structure of a grafted PDMS layer at the surface of silicas 2A-D (1) samples as a whole (2) samples swollen in C2CI4 (3) those swollen in C2Clt in an ammonia atmosphere. A solid ellipse indicates adsorption bonds at the silica surface. The chain portions responsible for the T2 relaxation components are indicated by dashed lines.

The grafting of Zr(Np)4 was not only restricted to silica surface but also to other well-defined oxide surfaces. Recently, amino-modified SBA-15 surfaces were prepared by the reaction of partially dehydroxylated SBA-15 at 1100°C with ammonia at 200 and 500°C to generate [(=Si-NH2)(=Si-OH)] (5) and [(=Si-NH2)2] (6). The advantage of this method is the preparation of adjacent groups in close vicinity. The surface organometallic complexes were prepared by the reaction of [Zr(Np)4] with [(=Si-NH2)(=SiOH)] and [(=Si-NH2)2l in pentane for 8 h at room temperature (Scheme 4) [20]. 

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