Catalyst high-area-supported

Metals Dispersion from LEISS. Since He scattering Is very selective to Che outermost surface layer, one should anticipate that LEISS would be a valuable Cool for studies of metals dispersion for supported catalysts. For low oietal concentrations on high area supports, the (oietal/support) LEISS Intensity ratio should be directly proportional to metals dispersion. Recent stiidles In our laboratory have confirmed that expectation. 

Typical substances that find wide use as high-area supports include silica gel and y-alumina, which can be obtained with surface areas in the range 100-800 m2/g. Materials used as low-area supports ( 1 m2/g) include a-alumina and mullite (alumina-silica). It is not easy to make general statements about the preparation of industrial catalysts because of the great variety of forms they take, but in many cases one can distinguish between the chemical operations in which the various components are assembled in the desired form, and the fabrication step in which they are made into the desired shape. The first step will be illustrated by a description of the method of preparing of silica gel and y-alumina support material [1]. 

High area supports commonly used in catalyst manufacturing are listed in Table 2.3. 

Very important in current and prospective electrochemical technology are dispersed electrocatalysts on high-area supports. Opportunities exist for developing new catalysts, such as alloy clusters, improved dispersion techniques, superior supports (especially among the oxides, carbides, and nitrides), and new binding polymers for composite electrodes. 

There could be some compatibility problems with the NO catalyst, if the NO catalyst did not retain S but did retard the heating of the oxidation catalyst. Large pellet beds (260 in.3) could be advantageous because a much larger base metal surface area would be available since most of the bed is high area support. As stated previously, the cobalt surface area for a 3-6 lb bed would be 10 times that for the honeycomb, and the time for heat-up would be only about twice as long. 

In this account of work in progress, we report that the kinetics of CH4 production over initially clean Ni(lOO) are in excellent agreement with previous data for polycrystalline nickel foil and high-area-supported nickel catalysts. Traces of surface impurities such as iron act as poisons, causing a marked lowering of the reaction rate. 

The values of Nch4 determined in the present work are plotted in Arrhenius form in Figure 3 the activation energy determined from the slope of this line is 24.6 kcal/mol. For comparison, the values of Nch4 measured for both polycrystalline nickel foil and high-area-supported nickel catalysts are also shown. The rates are all normalized to a 4 1 H2 C0 mixture at a total pressure of 120 Torr. Generally speaking, a... 

In Section 5.3 it was demonstrated with many examples that ionic hquids are indeed a very attractive class of solvents for catalysis in liquid-liquid biphasic operation (for some selected reviews see Refs. [16-20]). In this section, we wfll focus on a different way to apply ionic liquids in catalysis, namely the use of an ionic liquid catalyst phase supported on a solid carrier, a technology that has become known as supported ionic liquid phase (SILP) catalysis. In comparison to the conventional liquid-liquid biphasic catalysis in ionic liquid-organic liquid mixtures, the concept of SILP-catalysis combines well-defined catalyst complexes, nonvolatile ionic liquids, and porous solid supports in a manner that offers a very efficient use of the ionic liquid catalyst phase, since it is dispersed as a thin film on the surface of the high-area support. Recently, the initial applications using such supported ionic liquid catalysts have been briefly summarized [21]. In contrast to this report, where the applications were distinguished by the choice of support material, the compilation here will divide the applications using the supported ionic liquid catalysts into sections according to the nature of the interaction between the ionic liquid catalyst phase and the support. 

High area supports such as y-alumina, chromia, etc. can be used for catalysts for low-temperature adiabatic reforming, but these supports suffer from substantial sintering and weakening at temperatures above 500°C. The deterioration is strongly accelerated by the high steam partial pressure and stability tests at atmospheric pressure can therefore be misleading. Stabilisation methods applied in, for instance, auto-exhaust catalysts may become ineffective. 

Taking into account dispersion and coverage, for the important class of high-area supported catalysts, appropriate quantitative models have been derived which are based on the idea that such samples can be modeled as stacks of support material sheets each covered by promoter particles (cf Fig. 11 or Ref 63). The surface area of the support and the density of the support material define the corre.sponding sheet thickness d. For example, a typical porous silica is characterized by d = 2.6 nm. When considering this stratified layer model it turns out that the simple expression... 

The saturation coverage during chemisorption on a clean transition-metal surface is controlled by the fonnation of a chemical bond at a specific site [5] and not necessarily by the area of the molecule. In addition, in this case, the heat of chemisorption of the first monolayer is substantially higher than for the second and subsequent layers where adsorption is via weaker van der Waals interactions. Chemisorption is often usefLil for measuring the area of a specific component of a multi-component surface, for example, the area of small metal particles adsorbed onto a high-surface-area support [6], but not for measuring the total area of the sample. Surface areas measured using this method are specific to the molecule that chemisorbs on the surface. Carbon monoxide titration is therefore often used to define the number of sites available on a supported metal catalyst. In order to measure the total surface area, adsorbates must be selected that interact relatively weakly with the substrate so that the area occupied by each adsorbent is dominated by intennolecular interactions and the area occupied by each molecule is approximately defined by van der Waals radii. This... 

The primary determinant of catalyst surface area is the support surface area, except in the case of certain catalysts where extremely fine dispersions of active material are obtained. As a rule, catalysts intended for catalytic conversions utilizing hydrogen, eg, hydrogenation, hydrodesulfurization, and hydrodenitrogenation, can utilize high surface area supports, whereas those intended for selective oxidation, eg, olefin epoxidation, require low surface area supports to avoid troublesome side reactions. 

Some catalyst supports rely on a relatively low surface area stmctural member coated with a layer of a higher surface area support material. The automotive catalytic converter monolith support is an example of this technology. In this appHcation, a central core of multichanneled, low surface area, extmded ceramic about 10 cm in diameter is coated with high surface area partially hydrated alumina onto which are deposited small amounts of precious metals as the active catalytic species. 

Solid catalysts for the metathesis reaction are mainly transition metal oxides, carbonyls, or sulfides deposited on high surface area supports (oxides and phosphates). After activation, a wide variety of solid catalysts is effective, for the metathesis of alkenes. Table I (1, 34 38) gives a survey of the more efficient catalysts which have been reported to convert propene into ethene and linear butenes. The most active ones contain rhenium, molybdenum, or tungsten. An outstanding catalyst is rhenium oxide on alumina, which is active under very mild conditions, viz. room temperature and atmospheric pressure, yielding exclusively the primary metathesis products. 

Describe the morphology of a typical heterogeneous catalyst on a high-sur-face area support. 

The typical solid catalyst used in technology consists of small catalytically active species, such as particles of metal, metal oxide, or metal sulfide, dispersed on a low-cost, high-area, nearly inert porous support such as a metal oxide or zeolite. The catalytic species are typically difficult to characterize in-... 

In order to obtain high mass activity of Pt, it is essential to disperse Pt or alloy nanoparticles on high surface area supports. Some questions then arise. What kind of alloys and composition should we choose Is there any good parameter for screening the catalysts What size of catalyst particles should we prepare to obtain the maximum performance Unfortunately, there has been much controversy about such issues in the literature. 

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