Area of support

Fig. 3. Metal surface areas of supported Pt catalysts as a function of metal loading.

Table 1 shows that the physicochemical properties of the support material were modified by the pre-treatment process. The particle sizes. Dp, which are summarized in the Table 1 were calculated from the X-ray diffraction patterns of prepared catalysts and a commercial catalyst(30 wt% Pt-Ru/C E-TEK) by using Scherrer s equation. To avoid the interference from other peaks, (220) peak was used. All the prepared catalysts show the particle sizes of the range from 2.0 to 2.8nm. It can be thought that these values are in the acceptable range for the proper electrode performance[7]. For the prepared catalysts, notable differences are inter-metal distances(X[nm]) compared to commercial one. Due to their larger surface areas of support materials, active metals are apart from each other more than 2 3 times distance than commercial catalyst. Pt-Ru/SRaw has the longest inter-metal distances. 

For a supported metal catalyst, the BET method yields the total surface area of support and metal. If we perform our measurements in the chemisorption domain, for example with H2 or CO at room temperature, adsorption is limited to the metallic phase, providing a way to determine the dispersion of the supported phase. 

These disadvantages are overcome by the so-called dance-floor principle which is supposed to become the major beamline construction principle of the future. Figure 4.11 shows a dance floor during the construction of the beamline hall at the ANSTO neutron-scattering facility at Lucas Heights near Sydney, Australia. The dance floor is featuring an extremely plane and hard floor surface from granite. Optical components, detectors and sample chambers are mounted on supports with a flat lower surface. While compressed air is blown into the gap between the dance floor and the area of support, components are easily moved and adjusted in the optical beam path. 

In all films there is a distribution of crystallite diameters. An example is shown in Fig. 2 for the film with a specific weight of 0.12 fig cm-2. The smallest particles whose diameters can be measured in a micrograph (and then only very approximately) have diameters of about 10 A, and this is the lower size limit used in Fig. 2. However, particles smaller than this can readily be observed in the micrograph, and there is no doubt that this type of film contains some crystallites down to the limit of microscopic resolution (about 8 A in our case), and presumably beyond. However, their number appears to be relatively small. It is interesting to compare the specific film weight of these ultrathin platinum films with the amount of platinum per unit actual surface area of support for typical supported platinum catalysts. A typical supported catalyst would have 1% (w/w) of platinum on a... 

We summarize here only the laboratory results obtained in this area of supported or unsupported nanoparticles modified by organometallic compounds. We... 

To date the majority of polymer-supported chemistry is conducted only on a few solid support materials. Recently, it has been documented that specific solid-phase effects have significant impact on the success or failure of polymer-supported reactions.15 Considering the limitations of polystyrene, which is the standard material for most applications today, it becomes even more evident that innovations in the area of support materials will open the door to novel opportunities for polymer-supported chemistries. 

Figure 12.3 Even a nonlinear change of the illuminant can be considered to be linear provided the area of support is sufficiently small (a). However, in practice, we use quite large areas of support. Otherwise the gray world assumption would not be correct. In this case, the area of support will probably contain nonlinearities and the estimated local space average color will be incorrect (b).

Fagherazzi, G., Cocco, G., SchifBni, L., Enzo, S., Benedetti, A., Passerini, R. and Tauszik, G.R. (1978) Particle size distribution and surface area of supported metal catalysts. Chim. e J Industria, 60, 892. 

A with macropore diameters of 1000 to 5000 A. The pore volume and the pore size distribution within a porous support determine its surface area. The surface area of supports can range from 0.06 m2/mL (18,300 ftVft3) to 600 m2/mL (1.83 x 108 ffVft3) and above. Higher pore volume catalysts have higher diffusion rate at the expense of reduced crush strength and increased particle attrition. 

On the other hand, rate constants for 0.6 and 5% Pt/alumina catalysts sintered in H2 at 973 K (see Table 1) of 0.53 and 0.84 h 1 are not substantially different. This result is not altogether unreasonable, as the number of crystallites per unit area of support surface and the metal surface area would be about the same in both 0.6 and 5% catalysts because of the much lower dispersion of the 5% catalyst. Nevertheless, it is fascinating that these two catalysts sinter at much different relative rates in air (see discussion above), a fact suggesting that different mechanisms (i.e., atomic migration vs. crystallite migration) may be involved in air versus H2 atmospheres as proposed by Wynblatt and Ahn [5J. 

The purpose of the present Section is twofold first to draw attention to the problems and ambiguities which have arisen in connection with the reporting of gas adsorption (physisorption) data and second to formulate proposals for the standardization of procedures and terminology which will lead to a generally accepted code of practice. It does not aim to provide detailed operational instructions or to give a comprehensive account of the theoretical aspects of physisorption. The determination of the surface area of supported metals is not dealt with here - despite the importance of this topic in the context of heterogeneous catalysis - since this necessarily involves chemisorption processes. 

Surface area of supported PcFe. The surface area of PcFe deposits has been determined by measuring the amount of water molecules irreversibly adsorbed on their surface. We have shown that each surface molecule of the PcFe crystal retains on the average one molecule of water according to the following reaction (16, 19). 

The influence of support preparation parameters and parameters of hydrothermal processing on specific surface area of supports ... 

Phase 0/Phase 1 process responsibility, support owner, extent and areas of support location, etc. 

Spedl ic surface area of support before preparation. 

The Analytical Chemistry Branch (ACB) of the Environmental Mon-itoring and Support Laboratory of the U.S. Environmental Protection Agency has a number of responsibilities for analytical support. Analyses of fuels, sources, and ambient samples are performed along with the analyses of divers other types of specimens including tissue, both plant and animal. One of the major areas of support rendered by the ACB is in support of the National Air Siurveillance Networks (NASN) a portion of this support consists of the analysis of collected material for airborne metallic elemental content. This chapter will, in the main, be a summary of the work done by the ACB with respect to the collection and analysis of airborne metallic elements. 

Specific Surfaci 3 Areas of Supported Nickel Catalysts ... 

The use of selective chemisorption to determine the surface area of a metal component of a composite catalyst was first demonstrated by Emmett and Brunauer in their classic studies of promoted iron catalysts for the synthesis of ammonia (17). Other applications of selective chemisorption to determine the surface area of supported metals have been collected by Gregg and Sing (18). 

For chemisorption study, the adsorption isotherm (first isotherm) was obtained in each case by plotting the amount of O2 adsorbed at 300 °C against the O2 equilibrium pressure, Peq, up to 250 mm Hg. The resorption isotherm (second isotherm) was measured after outgassing for one hour at the same temperature. The total chemisorption values were taken as the difference between the first and the second isotherms. To minimize adsorption on the support and maximize adsorption on the supported complex, the total chemisorption values on pure support were subtracted from the total chemisorption producing the so called net adsorption values (a ) on the supported complex as expressed in m mol O2 g" CoPc. These values were used to calculate the degrees of dispersion (D), the chemisorption stoichiometries and specific surface areas of supported CoPc phase [18,19],... 

Knowing the stoichiometry of adsorption, the specific surface area of supported CoPc could be calculated as ... 

The specific surface area of supported CoPc shows unrealistic values in the case of supported samples on alumina and alumina-rich supports. Consequently, the calculated degrees of CoPc dispersion are relatively high. On the other hand, the specific surface area of CoPc supported on silica and silica-rich support show much lower values with much lower degrees of dispersion. These parameters decrease markedly as the complex loading increases up to 10.4% w/w. It is of interest to notice that, the stoichiometry of adsorption of oxygen on samples of supported CoPc on alumina and alumina-rich supports is almost close to 1. However, in samples of CoPc supported on silica and silica-rich supports, the stoichiometry becomes >2. These findings indicate clearly that supported CoPc molecules interact with the different support surfaces under study along widely different ways. 

Amounts adsorbed per unit surface area of support. 

BET surface areas of supports (0.2-0.5 mm) were 9-78 m /g, and those of catalysts - 62-110 m /g. XPS measurements were performed on a VG Scientific ESCA-3 spectrometer using AlKa. g radiation (1486.6 eV) from an X-ray source operating at 13 kV and 10 mA [4]. Binding energies were referenced to the Cls peak at 284.8 eV. Chemical analysis was carried out on a RF-510 Hitachi atomic absorption spectrometer. GLC analysis was performed using a column (2.5 m x 3... 

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