Supported catalyst systems

Interestingly, 36 (Fig. 22) combined with MgCl2/z-BunAl(OR)3 n (MAO-free, MgCl2-supported catalyst system) forms higher tacticity PP with higher Tm (rr 97%, Tm 155 °C) than that of the MAO-activated homogeneous system described above... 

In the preparation and stablization of small, supported-catalyst particles, the consideration of surface mobility is essential. If the active component is in a high state of dispersion, conditions under which high mobility is attained must be avoided, since these conditions lead to particle size growth. On the other hand, a poorly dispersed component may be partially redispersed by treatment in a more highly mobile state. In supported catalyst systems, the interaction between the dispersed species (the active component) and the support is always of important concern, and a measure of the mobility of the active component is an indirect measure of this important interaction. 

As in the case of normal supported catalysts, we tried with this inverse supported catalyst system to switch over from the thin-layer catalyst structure to the more conventional powder mixture with a grain size smaller than the boundary layer thickness. The reactant in these studies (27) was methanol and the reaction its decomposition or oxidation the catalyst was zinc oxide and the support silver. The particle size of the catalyst was 3 x 10-3 cm hence, not the entire particle in contact with silver can be considered as part of the boundary layer. However, a part of the catalyst particle surface will be close to the zone of contact with the metal. Table VI gives the activation energies and the start temperatures for both methanol reactions, irrespective of the exact composition of the products. 

In conclusion, EXAFS has provided important structural information on several supported catalyst systems. Two more applications - on the structure of the metal support interface and on the structure of metal sulfide catalysts - are discussed in Chapter 9. An important requirement for meaningful EXAFS data on catalysts is that the particles are monodisperse, such that the average environment, which determines the EXAFS signal, is the same throughout the entire cat-... 

While many studies have been performed for the oxidation of methanol and carbon monoxide on supported catalyst systems [66,99-103] and Pt-Ru bulk alloys [61,104— 107], relatively few studies have been initiated on single-crystal platinum surfaces modihed with ruthenium. Of those performed these have largely involved the investigation of platinum single crystals modihed by ruthenium dosed electro-chemically [92,93] or spontaneously [80-82,90,91] from aqueous chloride solutions. This approach is discussed in Section 5.4. 

General Methods of Preparation for Supported Catalyst Systems... 

Catalyst deactivation in hydrodemetallisation (HDM) is caused by the interaction of the metal deposits with the original active phase ( active site poisoning ) and the loss of pore volume due to the obstruction of catalyst pores i pore plugging) (1). However, metal deposits also have an auto-catalytic effect on the hydrodemetallisation reaction, thus active site generation may occur in low active phase loaded or bare support catalyst systems. 

Type (c) or type (d) behavior in which the rate may either start at a maximum value or rise very rapidly to a maximum value and then decrease rapidly with time is exhibited by many high-activity supported catalyst systems, e.g., MgCl2/ethylbenzoate/TiCl4—AJEts system when used for either ethylene or propylene polymerization. 

Name a few solid-support catalyst systems and the monomers for which they can be used. How is the stereoregularity achieved in these polymerizations ... 

However, only XPS has been widely applied to supported catalyst systems. Since the excitation process in XPS concerns core electrons, the technique is element-specific and elements can be identified on the basis... 

While this new support/catalyst system works about as well as the commercial catalyst (C-11 NK), further optimization of support and catalyst composition may yield even more active and selective catalysts. 

Finally, it can be ejq)ected that the number of methods will steadily increase in the future. And it wiU certainly remain a chaUenge to develop supported catalyst systems which at least equal their homogeneous coimterparts with regard to activity and selectivity and which are sufficiently economic. 

A wide variety of other techniques are available for the characterization of supported catalyst systems including X-ray absorption fine structure (EXAFS), Mossbauer, Auger electron. X-ray, and u.v. spectroscopies, magnetic susceptibilities, electron spin resonance spectroscopy, and transmission electron microscopy. However these techniques have not been employed to any significant effect. 

Silica-supported catalyst systems comprised of tetra-n-butylammonium chloride and PdCl2 with C0CI2/CUCI2 promotors (melting points ca. 60 °C) have also been used for hydrodechlorination of chloroform with hydrogen at 90-150 °C [60]. As one reason for the observed catalyst deactivation the authors propose the thermal ionic liquid decomposition ([Bu4N]Cl, Td = 170 °C), which seems very likely since tetraalkyl ammonium salts are known to undergo dealkylation under the applied conditions [61,62]. 

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