Inactive supports

The support materials for the stationary phase can be relatively inactive supports, e.g. glass beads, or adsorbents similar to those used in LSC. It is important, however, that the support surface should not interact with the solute, as this can result in a mixed mechanism (partition and adsorption) rather than true partition. This complicates the chromatographic process and may give non-reproducible separations. For this reason, high loadings of liquid phase are required to cover the active sites when using high surface area porous adsorbents. 

Most catalysts consist of active components dispersed as small crystallites on a thermally stable, chemically inactive support such as alumina, ceramics, or metallic wires and screens. The supports are shaped into spheroids, cylinders, monolithic honeycombs, and metallic mesh or saddles. 

If M and R are in the same solvent S containing only an inert, surface-inactive supporting electrolyte, AE equals the difference in the potentials of zero charge between the two metals ... 

Composite electrodes used in the electrochemical processes are often partially active since they are composed of the active powder material and the inactive binder and conductor. The partially blocked active electrode can be characterized by the contiguous fractal with dy < 2.0. In the case of the electrodes composed of the active islands on an inactive support, they are characterized by the non-contiguous fractal with dy < 2.0.121... 

For these reasons, it is usual to determine practical potential windows voltam-metrically, using appropriate indicator electrodes. A voltammogram is measured in a solvent under study, in the presence of an electro-inactive supporting electrolyte. The negative end of the potential window is where the reduction current begins to flow, while the positive end is where the oxidation current begins to flow. However, in order that the reduction and oxidation of solvents can occur at the... 

Partial oxidations (e.g., ethylene + 02- acetaldehyde )/catalytic microporous layer deposited on a macropo-rous inactive support... 

This leads us to the concept called nanocatalysis, and specifically to nanofabricated model catalysts, as an approach to bridge the structure gap. In Fig. 4.4, some examples of planar model structures of increasing complexity are depicted, which fulfill these criteria. At the top, there is a simple array of catalyst particles on an inactive support. The inactive support can be replaced by an active support (second picture from the top), meaning a support that significantly affects the properties of the nanoparticles via particle-support interactions (a clear distinction between inactive and active is not easy or not even possible—there is always some influence of the support on the supported particle). In some cases, the size of the support particle has an influence on the overall catalytic activity. This is, for example, the case when there is a spillover or capture zone for reactants or intermediates, which move by diffusion from the catalyst nanoparticle to the support or vice versa. In order to study such effects, one may want to systematically vary the radius of the... 

The most usual supports are transition metal oxides [7,38,53,54,154,155]. The role of these is still a matter of discussion and two different classes of oxides can be identified [90,152]. The first class comprises active supports. These are materials that can be relatively easily reduced such as NiO, Fc203 or Ti02. The second class is formed by inert, so-called inactive supports such as MgO, AI2O3 and Si02. These supports can, in some cases, lead to catalysts as active as those with reducible supports [32], but it is very important to ensure a high dispersion of very small particles of gold on the oxide [47,90]. 

Figure 2c shows the spectra of Pt/SiC when exposed to the reactant gas at different temperatures. No absorption bands can be seen at any temperature. This is expected as SiC is considered to be an inactive support and the Pt content is low. 

To solve the problem of metal recycle, one idea was to fix the rhodium on an inactive support. This rhodium was then extracted from the support by a triphenyl-phosphine-containing solution, thus producing in situ the homogeneous homophase catalyst solution. Friedrich et al. [46] described such a process of rhodium-catalyzed hydroformylation including filtration of the supported catalyst, cooking of the support in a rotary furnace, and thermal stressing distillation of the filtrate, thus separating Rh from the products. 

This current is caused by the acceleration of ions towards (or away from) the electrode by electrostatic attraction. It is not a useful type of current. It does not have a linear relationship with concentration. It is usually supressed by adding at least a fiftyfold excess of an inactive supporting electrolyte which shields the ions of interest from the electrostatic attraction. 

The importance of the carboxylic acid moiety for activity is clearly illustrated by the next group of compounds. Removal of the carbethoxy substituent provided 7,8-dimethoxypyrimido[4,5-b]quinolin-4(3H)-one (LIN) which is inactive at 3 mg/kg i.v. in the PCA procedure. Interestingly, the 2-methyl analog (LIV) exhibits excellent oral activity while displaying only weak intravenous activity. This may be rationalized on the basis of metabolic oxidation of this compound to the carboxylic acid (LX, Figure 10). The fact that the 2-ethyl (LV), 2-trifluoromethyl (LVI), and 2-acetyI (LVIl) analogs are considerably less active, and the 2-phenyl (LVI II) and 2-hydroxy (LIX) analogs are inactive, supports this explanation. 

Selective oxidation of benzene to maleic anhydride vanadium molybdenum oxide on fused corundum (catal5Uically inactive support without pores)... 

Figure 14. Effective transfer coefficient a (true value a = 0.5) in the case of reduction of an ion with valency Z versus potential, with respect to the zero charge potential in surface-inactive supporting electrolytes of different concentrations (according to Ref. 95).

Intermetallic compounds (solid solution of several metals such as CueSns) again obey the principle of dispersion of the active species, as seen with lithium in a matrix comprising metallic elements which play the part of an inactive support. In this type of alloys, MM, the inactive metal versus lithium plays the role of a buffer and limits the consequences of the volumetric expansion of the active metal. 

Various mechanisms have been proposed for the attachment of cells to an inactive support, such as glass or plastic (adhesion) to themselves before or after a degradative process (aggregation) to antibodies, other... 

In the present chapter, we classify the methodologies devoted to heterogeneize HP As in three main groups. In the first one the HPA is immobilized by a photocata-lytically inactive support, in the second one HPA is immobilized onto a photocata-lytically active material (generally a semiconductor oxide) and in the third one HPA is not supported but heterogeneized by immobilization in a host-guest insoluble composite. 

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