Buffer layers, catalytic

Nanocrystalline cubic SiC (P-SiC) films were grown on silicon (100) substrate by catalytic chemical vapor deposition (Cat-CVD) at a temperature as low as 300°C with a pre-carbonization process. To enhance nucleation density of P-SiC, a buffer layer was made by carbonizing the substrate surface. From the comparison between both carbonized sample and non-carbonized sample, the precarbonization process has beneficial effects on the growth of nanociystalline p-SiC films. Mechanistic interpretations are given to explain the carbonization process and catalyzing deposition process. 

Cerium (Ce) is a second element of lanthanides in periodic table. Cerium oxide (Ce02) has a cubic fluorite-type structure with a lattice constant (a) of 0.5411 nm. Ce02 thin films are highly attractive for electronic and electrochemical device applications as insulating buffer layers, ion-conducting layers, or ion-storage layers. Recently, a lot of interest has been generated in nano-structured cerium oxide for various electro-catalytic applications due to its... 

Optimization of Catalytic Cap Layers/BufFer Layers The hydrogenation process of a metal hydride MH capped by a catalyst layer is a complicated process [214]. Hydrogen molecules absorb at the catalyst surface (physisorption), split into chemisorbed hydrogen atoms, diffuse into the catalyst subsurface layers, diffuse towards the MHx boundary and cross the catalyst/MHx boundary. 

A breakthrough in sensor development was the introduction of triple layers a catalytic cap layer, a buffer layer and the optically active Mg2Ni layer [241]. The... 

Molecular. sieves are the most expen.sive, but provide the lowest dew point. They are normally used to dehydrate natural gas feed streams for cryogenic hydrocarbon recovery units. Type 4A is the type most commonly employed, but 3A is gaining favor because it is less active catalytically and can be regenerated at a lower temperature than 4A. A disadvantage of molecular sieves for gas dehydration is that they can be fouled by impurities in the gas, such as amine, caustic, chlorides, glycol, and liquid hydrocarbons. However, fouling problems can be minimized by the installation of a buffer layer of one foot or more of activated alumina (for amine, caustic, and chlorides) or activated carbon (for glycol or hydrocarbon liquids) on top of the molecular sieve bed (Veldman, 1991). 

Adiponitrile is readily hydrogenated catalytically to hexamethylenediamine, which is an important starting material for the prodnction of nylons and other plastics. The electrochemical production of adiponitrile was started in the United States in 1965 at present its volume is about 200 kilotons per year. The reaction occurs at lead or cadmium cathodes with current densities of np to 200 mA/cm in phosphate buffer solutions of pH 8.5 to 9. Salts of tetrabntylammonium [N(C4H9)4] are added to the solution this cation is specihcally adsorbed on the cathode and displaces water molecules from the first solution layer at the snrface. Therefore, the concentration of proton donors is drastically rednced in the reaction zone, and the reaction follows the scheme of (15.36) rather than that of (15.35), which wonld yield propi-onitrile. 

The concept of a biocatalytic membrane electrode has been extended to the use of a tissue slice as the catalytic layer. An example of this approach is an electrode for AMP which consists of a slice of rabbit muscle adjacent to an ammonia gas electrode. NHj is produced by enzymatic action of rabbit muscle constituents on AMP The electrode exhibits a linear range of 1.4 x 10 to 1.0 x 10 M with a response time varying from 2.5 to 8.5 min, depending on the concentration. Electrode lifetime is about 28 days when stored between use in buffer with sodium azide to prevent bacterial growth. Excellent selectivity enables AMP to be determined in serum. 

Figure 12.5 (a) Layer-by-layer deposition of glucose oxidase and the polyallylamine Os3 +n + -polypyridine polyelectrolyte on the electrode, (b) Typical catalytic current responses for different glucose concentrations obtained by self-assembled nanostructured thin films based on different architectures (i) PAH/Os/GOx, (ii) cysteamine/GOx/PAH-Os, (iii) PAH/GOx/ -Os, and (iv) (PAH-Os)2/(GOx)i. All measurements were performed in 0.1 M tris buffer at pH 7.5. Part (b) Reproduced with permission from Ref. 34a. Copyright Wiley-VCH Verlag GmbH Co. KGaA. 

The catalytic procedure described here allows a fast, cheap and highly selective conversion of primary alcohols into aldehydes, using sodium hypochlorite as the oxidant in a two-phase (dichloromethane-water) system. Aqueous sodium hypochlorite is buffered at pH 8.6-9.5 to ensure the presence of hypochlorous acid in the organic layer.13... 

Fig. 6 Examples of data obtained with catalytic RuCl-PVP layer in films (a) SWV of PSS/RuCl-PVP/DNA/PDDA/DNA films after incubations at 37°C and pH 5.5 with saturated styrene oxide (SO) for 5, 10, 20, and 30 min, respectively. Incubations in toluene gave no changes in peak current, (b) Influence of reaction time (37°C, pH 6.5) of PSS/RuCl-PVP/DNA/PDDA/DNA films incubated in 2 mM dimethyl sulfate ( ), 2 mM methyl methanesulfonate (O), and buffer control (A) on ratio of final SWV peak current to initial peak current of PSS/RuCl-PVP. (From Ref. [49] with permission. Copyright American Chemical Society.) (View this art in color at www. dekker. com.)...

Fig. 6 Cyclic voltammetric analysis of the kinetics of an electrode coated with antigen-antibody immobilized monomolecular layer of redox enzyme with a one-electron reversible cosubstrate in the solution, (a) Cyclic voltammetry at saturation coverage (2.6 x 10 mol cm ) of glucose oxidase with 0.1 M glucose and 0.1 mM ferrocenemethanol in a pH 8 phosphate buffer (0.1 M ionic strength). The dotted and dashed lines represent the cyclic voltammogram (0.04 V sec ) in the absence and presence of glucose (0.1 M), respectively. The full line represents the catalytic contribution to the current,/ cat (see text), (b) Primary plots obtained under the same conditions with, from top to bottom, 0.01, 0.02, 0.05, and 0.1 M glucose, (c) Secondary plot derived from the intercepts of the primary plots in (b).

Fig. 15 Variations of the catalytic plateau current in the cyclic voltammetry of ferrocene methanol in the presence of 0.5 M glucose in a phosphate buffer (pH = 8, ionic strength = 0.1 M), at 25 °C and a scan rate of 0.04 V sec at three different electrodes, (a) Electrode coated with 10 inactivated (Fg = 2.0 X 10 mol cm ) and 1 active (F° = 1.5 x 10 mol cm ) glucose oxidase monomolecular layers, (b) Electrode coated with 1-10 active glucose oxidase monomolecular layers (F = 1.5 x 10 mol cm ).

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