Uniform distribution of metal

An example is the thermal decomposition of a metal onto a support involving an ammine complex having the formula [Me(NH3)6] C03 where Me is the metal. In this complex, six ammonia molecules coordinate symmetrically from the central metal ion and form an octahedral structure. It is therefore possible to form small metal crystallite-sized catalyst by using ammine complex as a precursor. The unique features of a catalyst made from ammine decomposition include uniform distribution of metal throughout the catalyst particles, smooth and homogenous surface morphology, and high thermal stability. ... 

Electrodeposition has the ability to produce a relatively uniform distribution of metal upon a cathode of irregular shape. Though the uniformity depends on the distribution of electric fields inside the electrolyte toward the surface of the electrode, other important factors have to be considered. The addition of agents (additives) to the electrolyte, for example, can affect the microscopic mechanism of electrodeposition, reducing the roughness of the deposit and producing a visual effect known as brightening. 

Uniform charging taking care during charging to get a uniform distribution of metal and coke... 

The concentration of metal atoms in mercury electrodes depends on the potential (/face) and the duration (/acc) of accumulation, the bulk concentration of ions (CMe(b)) and the hydrodynamic conditions in the solution [26]. The simplest model considers the reversible electrode reaction on a thin mercury film rotating disk electrode with a fully developed diffusion layer in the solution and uniform distribution of metal atoms in the mercury film ... 

Toshima [162, 164, 165] has studied a series of PVP protected colloidal bimetallic PtPd catalysts in olefin hydrogenation catalysis. The highest activity for the hydrogenation of 1,3-cyclooctadiene to cyclooctene was observed at a Pd Pt radio of 4 1. On the basis of EXAFS analysis [165] it was concluded that the distribution of the two metals in the particles is nonuniform, and that at the most active composition the colloid particles had a platinum core coated with palladium. A less active 1 1 Pd/Pt catalyst, with the same particle size, apparently had a more uniform distribution of metals, with both platinum and p ladium atoms at the surface. 

Certain researchers have preferred soluble salts such as iron(III) nitrate [236] to represent deliberate contamination, whilst others have used insoluble forms. However, even iron (III) oxide in the form of rust is found to vary in catalytic activity depending on physical form. Although uniform distribution of the contamination, at least below a relatively low concentration, has been claimed to be less troublesome than localised concentrations, there is not even agreement on this. A further complication is that different studies have been carried out in either the absence or the presence of a cellulosic substrate. With these provisos in mind, the catalytic behaviour of trace metals and the effects of some preventive agents will be outlined. 

SEM studies of the obtained TEG-Si powders have shown almost uniform distribution of silicon particles on TEG surface. These metal coated particles were found to be of the spherical shape, mostly similar in size... 

Fig. 10. X-ray elemental map in the electron microscope of metal-substituted aluminophosphate (MAPO-36 (with M = Zn)) catalyst. The map shows a uniform distribution of the elements in the sample.

TOF-SIMS images (Figs. 13.5 and 13.6) illustrate the ability to detect changes in the dispersion (uniform or presence of metal clusters) of the active phase in supported-oxide catalysts. Figure 13.5 shows nearly uniform distribution of molybdenum. The surface contamination with NH4+ ions coming from a precursor, which were not removed during the catalyst preparation process, is also observed. Cobalt clusters in the range of several micrometers are clearly visible in Fig. 13.6. 

The mechanism of coprecipitation reUes upon the condensation of hexa-aquo complexes in solution in order to build brucite-like layers having a uniform distribution of both metallic cations and solvated interlamellar anions [7]. Two methods of coprecipitation have been commonly used precipitation at low supersaturation and precipitation at high supersaturation. 

To be even more specific, one notes that the distribution of metal deposited is also influenced markedly by the variation of cathodic CE with current density. This can, however, sometimes be of help in building deposits of even (uniform) thickness. Thus, in some cyanide metal baths (e.g., Cu, Zn see Chapter 11), especially those with a high cyanide/metal ratio, the CE value drops as current density increases consequently, thicknesses in regions of high current density do not much exceed the... 

For model evaporated binary alloy or bimetallic systems, normally a double crucible containing ingots of the two components of the alloy are used in an evaporator and the electron beam is switched between the two metallic sources. The dwell time is varied so as to obtain a uniform distribution of each metal in the required amounts on the support. 

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