Silica-supported magnetite, particle

When a series of silica supported-magnetite catalysts of varying iron oxide particle size were investigated, it was determined that Si substitutes into the magnetite lattice according to the following reaction(49) ... 

Recently, a silica-modified magnetite particle-supported bifunctional hybrid material (IL/SMNP) combining TEMPO (2,2,6,6-tetramethylpiperidine-l-oxyl) based IL and polyoxometalate moieties was developed for aerobic oxidation of alcohol [82]. The involvement of the TEMPO moiety improves the catalytic activity dramatically. Greater than 70% yields compared to the corresponding aldehydes were obtained even using primary ahphatic alcohols such as 1-octanol as starting material. 

Comparison of Magnetite Particle Size Determinations for Silica-Supported Samples ... 

The effect of Si substitution on the turnover frequency for WGS is shown in Figure 11. The turnover frequencies plotted in this figure were based on the magnetite surface area as determined by the NO chemisorption technique. The turnover frequencies shown for unsupported Fe O indicate that the factor of 10 decline in activity for the silica-supported catalysts is not a particle size effect, but instead is a consequence of the substitution of Si into the lattice. However, when the adsorption of CO/COo at 663 K was used to titrate the surface sites instead of NO, the resulting turnover frequencies were essentially constant as shown in Figure 12. Accordingly, the CO/CO2 mixture apparently titrates the sites active for WGS. Clearly, the number of active sites is decreased markedly as the particle size decreases in the silica-substituted magnetite catalysts. 

In a number of cases, PAMAM dendrons were also prepared on other polymer particle cores, such as alumina, chitosan, cellulose, zirconia-urea-formaldehyde resin, silica-coated magnetite, and carbon nanotubes. Like the silica support (see above), at least in the case of the chitosan, the theoretically predicted propagation of the dendrons was not achieved, presumably due to the steric hindrance in the support pores. 

Galactosidase has been attached to glass in this way.56 The immobilized enzyme is useful in removing lactose from milk, for the benefit of those persons who are intolerant of lactose. A similar technique was used to attach glucose oxidase to magnetite (I i O-i) particles, starting with a trimethoxysilane.57 This permits easy separation with a magnet. The immobilized enzyme was 50% less active than the native enzyme, but kept 95% of its activity after 9 months at 4°C. Another way to attach an enzyme to a support is to treat the metal oxide support first with 2,4,6-trichloro 1,3,5 triazine (cyanuric chloride) (5.18), then with the enzyme.58 This was done on both alumina and on silica. 

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