Support supported catalysts, types

There is an enormous volume of Hterature available on the appHcations for supported catalysts. Examples are compiled here based on important synthesis methods and industrial uses. The organization is according to specific reactions and appHcations rather than according to catalyst type. 

Catalysts vary both in terms of compositional material and physical stmcture (18). The catalyst basically consists of the catalyst itself, which is a finely divided metal (14,17,19) a high surface area carrier and a support stmcture (see Catalysts, supported). Three types of conventional metal catalysts are used for oxidation reactions single- or mixed-metal oxides, noble (precious) metals, or a combination of the two (19). 

Catalyst type Coal minerals Coal minerals Coal minerals Supported aKZO-aO-60 aKZO-aO-60... 

In general, encapsulated metal particles were observed on all graphite-supported catalysts. According to Ref. [4] it can be the result of a rather weak metal-graphite interaction. We mention the existence of two types of encapsulated metal particles those enclosed in filaments (Fig. 1) and those encapsulated by graphite. It is interesting to note that graphite layers were parallel to the surface of the encapsulated particles. 

A kinetic model which accounts for a multiplicity of active centres on supported catalysts has recently been developed. Computer simulations have been used to mechanistically validate the model and examine the effects on Its parameters by varying the nature of the distrlbultons, the order of deactivation, and the number of site types. The model adequately represents both first and second order deactivating polymerizations. Simulation results have been used to assist the interpretation of experimental results for the MgCl /EB/TlCl /TEA catalyst suggesting that... 

Finally, a simple method for a rapid evaluation of the activity of high surface area electrocatalysts is to observe the electrocatalytic response of a dispersion of carbon-supported catalyst in a thin layer of a recast proton exchange membrane.This type of electrode can be easily obtained from a solution of Nafion. As an example. Fig. 11 gives the comparative... 

Table 1 shows that catalysts prepared on the same type of support have about the same particle size distribution (PSD). Table 1 also shows that the newly developed CPS4 supported catalysts have the smallest span of particle size distribution, therefore, it has the fastest filtration rate. Filtration rate is measured by measuring the filtration time of 350 ml of 4-benzyloxyphenol debenzylation products. 

The above example outlines a general problem in immobilized molecular catalysts - multiple types of sites are often produced. To this end, we are developing techniques to prepare well-defined immobilized organometallic catalysts on silica supports with isolated catalytic sites (7). Our new strategy is demonstrated by creation of isolated titanium complexes on a mesoporous silica support. These new materials are characterized in detail and their catalytic properties in test reactions (polymerization of ethylene) indicate improved catalytic performance over supported catalysts prepared via conventional means (8). The generality of this catalyst design approach is discussed and additional immobilized metal complex catalysts are considered. 

No suppression in hydrogenolysis of the C-O bond was observed over either bimetallic catalysts or Ti02-supported catalysts, indicating involvement of different types of sites than C-C bond hydrogenolysis.58... 

In many cases there is an interaction between the carrier and the active component of the catalyst so that the character of the active surface will change. For example, the electronic character of the supported catalyst may be influenced by the transfer of electrons across the catalyst-carrier interface. In some cases the carrier itself has a catalytic activity for the primary reaction, an intermediate reaction, or a subsequent reaction, and a dual-function catalyst is thereby obtained. Materials of this type are widely employed in reforming processes. There are other cases where the interaction of the catalyst and support are much more subtle and difficult to label. For example, the crystal size and structure of supported metal catalysts as well as the manner in which the metal is dispersed can be influenced by the nature of the support material. 

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... 

Recently, ultrathin evaporated films have been used as models for dispersed supported metal catalysts, the main object being the preparation of a catalyst where surface cleanliness and crystallite size and structure could be better controlled than in conventional supported catalysts. In ultrathin films of this type, an average metal density on the substrate equivalent to >0.02 monolayers has been used. The apparatus for this technique is shown schematically in Fig. 8 (27). It was designed to permit use under UHV conditions, and to avoid depositing the working film on top of an outgassing film. ... 

Interesting results have been obtained using metallophthalocyanines supported on porous carbon gas diffusion electrodes.132-136 In the case of CoPc and NiPc, CO is formed with a current efficiency of almost 100%.135 With Sn, Pb, and In phthalocyanines, mainly HC02H is formed, while Cu and Ti phthalocyanines promote the formation of CH4. The reason why some metal Pc complexes give CO or CH4, while others yield HC02H, has been interpreted in terms of the electron configuration in the metal.137 A rather different type of reaction is the very recent demonstration of the simultaneous reduction of C02 and N02 to give urea (NH2)2CO, which can be achieved with an efficiency up to 40% at similar gas-diffusion electrode devices with a NiPc supported catalyst.138... 

Catalyst Type of support Metal content by weight (%) d , from x-ray line broadening (A) d from H2 chemisorption at room temp. (A)... 

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