Molecular designed dispersion

The use of dimethyldichlorosilane as a coupling agent for the grafting of VOx structures on the MCM-48 surface, produces a material that is simultaneously hydrophobic (inmiscible with water) and very active (all V-centers are accessible, even for water molecules and the catalytic activity for methanol oxidation has increased). The VOx surface species are grafted by the Molecular Designed Dispersion of VO(acac)2 on the silylated surface, followed by a calcination in air at 450°C. These hydrophobic MCM-48 supported VOx catalysts are stable up to 500°C and show a dramatic reduction in the leaching of the V-centers in aqueous media. Also the structural stability has improved enormously. The crystallinity of the materials does not decrease significantly, even not when the samples are subjected to a hydrothermal treatment at 160°C and 6.1 atm. pressure. 

The reaction of pure silica MCM-48 with dimethyldichlorosilane and subsequent hydrolysis results in hydrophobic materials with still a high number of anchoring sites for subsequent deposition of vanadium oxide structures. The Molecular Designed Dispersion of VO(acac)2 on these silylated samples results in a V-loading of 1.2 mmol/g. Spectroscopic studies evidence that all V is present as tetrahedral Vv oxide structures, and that the larger fraction of these species is present as isolated species. These final catalysts are extremely stable in hydrothermal conditions. They can withstand easily hydrothermal treatments at 160°C and 6.1 atm pressure without significant loss in crystallinity or porosity. Also, the leaching of the V in aqueous conditions is reduced with at least a factor 4. 

Figure 3. Visualization of the Process of Molecular Designed Dispersion with Al(acac)3.

Various mesoporous silicas (MCM-48, SBA-15, MCF, MSU) modified with iron oxides introduced by Fe(acac)3 were prepared using the molecular designed dispersion method (Section The mechanism of interaction between the iron acetylace-... 

FIGURE 21 Visualization of the creation of a heterogeneous AlO catalyst by the molecular designed dispersion process. 

The authors acknowledge China s National Natural Science Foundation for generous support of this work, which is a part of the major project Structural Chemistry and Molecular Design. We are grateful to all our colleagues who have contributed toward a better understanding of the phenomenon of spontaneous monolayer dispersion. Thankful acknowledg-... 

Formation of a bilayer structure is therefore driven by the self-assembhng behavior of amphiphilic molecules or molecular complexes. This research topic started from the dispersion of naturally-occurring phosphohpids in aqueous media, but the development of molecular design and systematic research has lead to the study of bilayer chemistry in various media. 

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