Urea gelators

Metallic gold has also been dissolved from pure ceria,51 from gadolinium-doped ceria,51 and from catalysts made by a urea gelation/coprecipitation method ,52 without significant effect on their activities for water-gas shift. The only problem that has been identified is the formation of a cerium hydroxycarbonate, which occurs during shut-down when water is present. The very extensive work performed on this system48-52 ensures that its conclusions are given full consideration. 

Fig. 4.9 a Polymerizable bis-urea gelator G22 capable of producing highly porous dried gel b TEM micrographs of butyl acetate gel of G22 before polymerization (5 mg/mL, bar 1,000 nm) c SEM of a benzene gel of G22 after irradiation (5 mg/mL, bar 400 nm). Reprinted with permission from Ref. [59]. Copyright 1997 Ameriean Chemieal Society... 

Fig. 1 Typical viscoelastic behavior of a strong gel. in this case, of his-urea gelator 13 in 1-hexanol (left). The TEM micrograph of this gel is shown at the right and reveals that the minimum width of the fibers amounts to 15-20 nm. which is still an order of magnitude larger than the molecular dimensions of 13. (Scale bar is 500 nm. reproduced from Ref. [37].)...

Keywords Hydrogen bonding Self-assembly Supramolecular chemistry Amide gelators Urea gelators... 

A novel approach to polymerized gel systems has been followed by our group. Based on the design principles described in the previous section, we successfully prepared a new polymerizable bis-urea gelator 35, which is capable of gelating a many different organic solvents [68]. On the other hand, the bis-amide derivative does not gel... 

Tabakova et aV " studied the influence of the amount of iron oxide in ceria on WGS catalytic activity. Mixed oxide supports were prepared by urea gelation co-precipitation. The following order of activity was observed ... 

Scheme 5.5 Bis (urea) gelators used to form gels for crystal growth of pharmaceuticals.

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