Reaction mechanism, oxidation encapsulants

Figure 4.4.7 (A) CO2 production over Pt(lll), iron oxide films on Pt(lll), and Pt/ Fe3C>4(lll) annealed to 600 and 850 K. (B) STM images of the encapsulated Pt particle on Fe3C>4(lll) and, for comparison, of the FeO(lll)/Pt(lll) film, both exposed to 20 mbar O2 at 450 K. The scheme illustrates the reaction mechanism. (See the text.)...

To study the promotion mechanism of Pt wire/FSM-16 in the PROX reaction, the Pt nanowires were extracted by HF/EtOH treatment from FSM-16, and the wires were again deposited on the external surface of FSM-16 from the ethanol solution. We found that the resulting external Pt wire/FSM-16 catalyst gave low TOFs (>35) and lower CO selectivity (>30%) in the PROX reaction [32]. This implies that the encapsulation of Pt wires in the silica channels of FSM-16 is a key to promote the selective CO oxidation in the PROX reaction. Furthermore, from the structural characterization by XANES, XPS and IR in CO chemisorption... 

The synthesis of the Y zeolite-encapsulated manganese complex of the salen ligand has been reported recently [51]. It was found to have catalytic activity in the oxidation of cyclohexene, styrene, and stilbene with PhlO. Typically, 1 Mn(salen) is present per 15 supercages, resulting in catalytic turn-overs in the order of 60. The reactions investigated with the respective product yields are given in Scheme 5. Typical oxidation products are epoxides, alcohols and aldehydes. In comparison to the homogeneous case encapsulation seems to lower the reaction rate. From cyclohexene the expected oxidation product cyclohexene oxide is present in excess and is formed on the Mn(salen) site. 2-cyclohexene-l-ol is probably formed on residual Mn cations via a radical mechanism. 

Kitamoto and Abe applied power ultrasonic waves (19.5 kHz, 600 W) to 300 ml of FeCh aqueous solution (pH 7.0) at 70 °C, and succeeded in encapsulating polyacrylate spheres of 250 nm diameter with magnetite ferrite coatings [49]. From TEM observations of the cross sections it was seen that the polymer spheres were covered with uniform columnar crystallites of 30-40 nm in diameter at the bottom and 60-70 nm at the top. The ultrasound waves produce OH groups on the polymer surfaces which work as ferrite nucleation sites this improves the quality of the ferrite coatings. The ferrite-encapsulated particles will greatly improve the performance of the enzyme immunoassay as a cancer test reagent. The above possible mechanism for the formation of the blue oxide is consistent with explanations in the literature for a sonochemical reaction. 

Fortifying foods with minerals and vitamins is becoming more and more common. Mineral deficiency is one of the most important nutritional problems in the world. The best method to overcome this problem is to make use of an external supply, which may be nutritional or supplementary, like the fortification of foods with highly bioavailable mineral sources. Major interests of mineral encapsulation are linked to the fact that this technique enables to reduce mineral reactions with other ingredients, when they are added to dry mixes to fortify a variety of foods, and it can also incorporate time-release mechanisms of the minerals into the formulations. For example, iron is the most difficult mineral to add to foods and ensure adequate absorption, and iron bioavailability is severely affected by interactions with food ingredients (e.g., tannins, phytates, and polyphenols). Additionally, iron catalyses the oxidative degradation of fatty acids and vitamins (Schrooyen et al., 2001). 

The results of radiolysis ( "Co y-rays and neutrons) experiments on CF -CgF mixtures encapsulated in aluminium [the predominant products were CjFg, i-CiFu, i-CsFu, and (CF3)2CF-CF(CFs)2 oxygenated products, e.g. (CjFslaO, presumably arose through attack on aluminium oxide) have been quoted in support of the contribution of fluorine-abstraction reactions to the mechanisms of radiation-induced fluorocarbon transformations [for example CF CFj + F 2 CFj- C,F -b F- CFj -I- C2F ... 

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