Catalyst carriers dispersion

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 this study it was demonstrated that with the aid of solventless ball-milling of catalyst components, dispersions of active components on carrier materials could be achieved, as measured by TPR, XPS and XANES, that are comparable to the dispersions achieved through conventional impregnation techniques of catalyst preparation. Comparable catalytic results are obtained by both preparation methods. Specifically, catalysts supported... 

Phthalocyanine (Pc) complexes of transition metals have received much attention in the scientific literature of the last two decades, not only as mild catalysts for selective oxidation reactions but also as functional models for enzymes. Unfortunately, their use is hampered by their reduced solubility in solvents and their tendency to form adducts even when used in solution. Provided such complexes can be immobilized individually on a catalyst carrier, it is expected that an enhanced dispersion of the complex will be achieved. The use of heterogenized Pc complexes will also no longer be restricted by the nature of the reaction medium or solvent. The issue has been reviewed as early as 1986 [3]. 

OTHER COMMENTS used as a local anesthetic used in the manufacture of silicones, methyl cellulose, quaternary amines, and agricultural chemicals also used as a food additive, dispersing agent, thickening agent, sizing agent, and an adhesive use as a catalyst carrier at lower temperatures. 

A second and somewhat simpler approach that can be applied to obtain supported ionic liquid catalyst systems involves the treatment of a solid, porous carrier material by a substantial amount of a catalytically active ionic liquid, allowing the reaction to take place in the dispersed phase. In these systems the ionic liquid phase can itself act as the catalytically active component or it may contain other dissolved compounds or reagents, for example, transition metal complexes, which function as the catalytically active species (i.e. generating SILP catalysts). Importantly, the ionic liquid catalyst phase in these SILP catalyst systems are confined to the carrier surface only by weak van der Waals interactions and capillary forces interacting in the pores of the support. In special cases electrostatic attachment of the ionic liquid phase may also be applied. Usually, the catalysts are prepared by traditional impregnation techniques, where a volatile solvent is used initially to reduce viscosity for the impregnation process and is finally removed by evaporation leaving the ionic catalyst solution dispersed on the support. 

One of the simplest, most commonly used techniques for preparing a catalyst involves dispersing an active component (or components) on a support material. Normally, one impregnates the carrier material with a solution of a soluble precursor of the catalyst and then converts this precursor to the product desired by oxidation, reduction, thermal decomposition, or some other suitable step. Where appropriate, it is preferable to use a granular support instead of a powder, because it eliminates the necessity for pelleting or extrusion to obtain the final product. 

Polypropylene (PP) is one of the most widely used plastics in large volume. To overcome the disadvantages of PP, such as low toughness and low service temperature, researchers have tried to improve the properties with the addition of nanoparticles that contains p>olar functional groups. An alkylammonium surfactant has been adequate to modify the clay surfaces and promote the formation of nanocomposite structure. Until now, two major methods, i.e., in-situ polymerization( Ma et al., 2001 Pirmavaia, 2000) and melt intercalation ( Manias et al.,2001) have been the techniques to prepare clay/PP nanocomposites. In the former method, the clay is used as a catalyst carrier, propylene monomer intercalates into the interlayer space of the clay and then polymerizes there. The macromolecule chains exfoliate the silicate layers and make them disperse in the polymer matrix evenly. In melt intercalation, PP and organoclay are compounded in the molten state to form nanocomposites. 

In order to coat metallic surfaces with catalyst, a pretreatment to improve the adherence is required [11]. Besides mechanical roughening, chemical and thermal pretreatment are applied frequently. Once the surface is pretreated, the coating slurry needs to be prepared. The most prominent method is to prepare a dispersion of finished catalyst including gelation steps if necessary. The catalyst carrier or the catalyst itself is mixed with binder... 

The most effective way to cover GDL with MPL and the catalyst carrier is to disperse the chosen ingredients in solvents and form the so-called ink or slurry. The ink can then be brought up on the... 

After dispersing catalyst loaded particles or catalyst carrier in solvents, sedimentation of particles is normal. This lead to short lifetime of inks or complex equipment to keep the particles dispersed. Alternative stabilization agents can be added to the dispersion to avoid phase separation. According to the added stabilizer, foam blocker, thickener or additional solvent may be necessary to adjust the slurry to the machinery requirements. 

In Figure 1.12(c), the catalyst is dispersed in the porous substrate of the membrane to form a membrane catalyst. One of the reactants or products traverses through the membrane into or out of the reaction zone. In classical reactors, the reaction conversion is often limited by the diffusion of reactants into the pores of the catalyst or catalyst carrier pellets. If the catalyst is inside the pores of the membrane, the combination of the open pore path and transmembrane pressure provides easier access of the reactants to the catalyst as shown in Figure 1.13. As a result, the access of reactants to the catalyst is improved and the catalytic efficiency can be increased greatly. If the membrane thickness and porous texture, as well as the quantity and location of the catalyst in the membrane, are adapted to the kinetics of the reaction, the membrane catalyst can be 10 times more active than that in the form of pellets [10,11]. 

Catalyst Carrier Pd vol. content (g.lOOcm ) Pd mass content (%) Apparent bulk density (g.crn Metallic dispersion (%)... 

A few industrial catalysts have simple compositions, but the typical catalyst is a complex composite made up of several components, illustrated schematically in Figure 9 by a catalyst for ethylene oxidation. Often it consists largely of a porous support or carrier, with the catalyticaHy active components dispersed on the support surface. For example, petroleum refining catalysts used for reforming of naphtha have about 1 wt% Pt and Re on the surface of a transition alumina such as y-Al203 that has a surface area of several hundred square meters per gram. The expensive metal is dispersed as minute particles or clusters so that a large fraction of the atoms are exposed at the surface and accessible to reactants (see Catalysts, supported). 

Pesticides. Many pesticides are highly concentrated and are in a physical form requiring further treatment to permit effective appHcation. Typically carriers or diluents are used (see Insectcontroltechnology). Although these materials are usually considered inert, they have a vital bearing on the potency and efficiency of the dust or spray because the carrier may consist of up to 99% of the final formulation. The physical properties of the carrier or diluent are of great importance in the uniform dispersion, the retention of pesticide by the plant, and in the preservation of the toxicity of the pesticide. The carrier must not, for example, serve as a catalyst for any reaction of the pesticide that would alter its potency. 

With the increasing emphasis on energy conservation and environmental considerations, additives for fuels that can correct combustion-related problems have aroused considerable interest. Many commercial fuel additives are combinations of organometaHics, dispersants, emulsifiers, and carrier solvents. The organometaHic, often a metal soap, acts as a combustion catalyst, increasing efficiency with reduction of smoke, deposits, and corrosion. 

The precious metal or metal oxide imparts high intrinsic activity, the carrier provides a stable, high surface area for catalyst dispersion, and the mechanical support gives a high geometric surface area for physical support and engineering design features (20). Only the correct combination of these... 

Carrier. The metal catalyst is generally dispersed on a high surface area carrier, ie, the carrier is given a washcoat of catalyst, such that very small (2—3 nm dia) precious metal crystaUites ate widely dispersed over the surface area, serving two basic functions. It maximizes the use of the cosdy precious metal, and provides a large surface area thereby increasing gas contact and associated catalytic reactions (18). 

Consequently the absolute potential is a material property which can be used to characterize solid electrolyte materials, several of which, as discussed in Chapter 11, are used increasingly in recent years as high surface area catalyst supports. This in turn implies that the Fermi level of dispersed metal catalysts supported on such carriers will be pinned to the Fermi level (or absolute potential) of the carrier (support). As discussed in Chapter 11 this is intimately related to the effect of metal-support interactions, which is of central importance in heterogeneous catalysis. 

Since the catalytically active phase is frequently quite expensive (e.g. noble metals) it is clear that it is in principle advantageous to prepare catalysts with high, approaching 100%, catalyst dispersion Dc. This can be usually accomplished without much difficulty by impregnating the porous carrier with an aqueous solution of a soluble compound (acid or salt) of the active metal followed by drying, calcination and reduction.1... 

Successful and reproducible preparation of highly dispersed catalysts crucially depends on the state of the carrier surface and on the concentration and pH of the impregnating solution. It is an art and a science for which several goodbooks and reviews exist.1 5... 

---