Porous catalyst carrier

Salejova, G., Kosek, J., Nevoral, V., Solcova, O., and Schneider, P. Effective Transport Properties of Reconstructed Porous Catalyst Carriers. Proceedings of CHISA 2004 , 22-25 August 2004, Prague, Czech Republic (2004). 

Stepanek, F., Kubicek, M., Marek, M., and Adler, P. M., Computer-Aided Screening of Adsorbents and Porous Catalyst Carriers, in European Symposium on Computer Aided Process Engineering - 10 (S. Pierucci Ed.), pp. 667-672. Elsevier Science, Amsterdam (2000). Stepanek, F., Marek, M., and Adler, P. M. AIChE J. 45, 1901-1912 (1999). 

In the case of porous catalyst carriers, impregnated throughout with active catalytic material, the catalyst within the pores of the individual granules is at least partly effective. The increased catalyst exposure thus obtained comprises one of the advantages of porous carriers. The relative effectiveness of the catalyst in the interior pores is, of course, dependent upon the rate at which the reactants can reach it, the rate at which the products can leave, and the velocity at which the reactants pass over the catalyst mass. With slow gas rates the interior" catalyst can be more effective, whereas with high gas rates the proportion of reaction which occurs within the pores is diminished. However, the longer exposure of reactants to catalyst possible in the pores may have a detrimental effect in... 

Oxidative Dehydrogenation of Ethane to Ethylene over Sr-Promoted La203 Catalyst Supported on Low Surface Area Porous Catalyst Carrier... 

The adsorption process is usually fast on evaporated films. However, on bulk solids, e.g. porous catalyst carriers, adsorption rates are usually slow and activated with activation energies typically in the range 10-40 kcal/g mole (Hayward and Trapnell, 1964). Some activation energies for typical activated chemisorption process are given in Table 5.9. In their investigation of the catalytic dehydration of methylcyclohexane, Sinfelt et al. (1960) found that to obtain a suitable kinetic expression finite rates of the adsorption-desorption process must be taken into consideration. In this section allowance is made for finite rates of adsorption and both activated and non-activated adsorption are considered ... 

Presting et al. from Daimler Chrysler reported the anodic etching of sflicon as a method of introducing porous catalyst carriers into microreactors on the smallest scale [126]. A pore depth of 250 pm was achieved by these means, the pore diameter was as low as 1.1pm and the pore wall thickness much less than 100 nm (see Figure 4.1). 

Choudhary, V.R., Uphade, B.S., and MuUa, S.A.R. Oxidative coupling of methane over a Sr-promoted La203 catalyst supported on a low surface area porous catalyst carrier. Ind Eng. Ghent. Res. 1997, 36, 3594-3601. 

Usually they are employed as porous pellets in a packed bed. Some exceptions are platinum for the oxidation of ammonia, which is in the form of several layers of fine-mesh wire gauze, and catalysts deposited on membranes. Pore surfaces can be several hundred mVg and pore diameters of the order of 100 A. The entire structure may be or catalytic material (silica or alumina, for instance, sometimes exert catalytic properties) or an active ingredient may be deposited on a porous refractory carrier as a thin film. In such cases the mass of expensive catalytic material, such as Pt or Pd, may be only a fraction of 1 percent. 

Triflic acid has also been supported on a porous silica carrier (220). The authors emphasized the importance of a strong interaction between the acid and the support to prevent leaching of the acid. In pulsed liquid-phase isobutane/ 1-butene alkylation experiments at 298 K, the catalysts produced a very high-quality alkylate, made up almost exclusively of isooctanes. With silanol groups on the silica surface or with added water, triflic acid was found to form a monohydrate that was firmly grafted to the silica surface. 

A colloidal suspension prepared according to the method described in Section 13.2.3 was contacted with a porous alumina carrier to obtain a bimetallic palladium-tin catalyst. Evaluation of the catalytic properties of this system is detailed... 

The ability of the STM to achieve atom-resolved real-space images of localized regions of a surface and to directly resolve the local atomic-scale structure has provided essential insight into the active sites on catalysts and emphasized the importance of edges, kinks, atom vacancies, and other defects, which often are difficult to detect with other techniques (46-49). It is evident, however, that STM cannot be used to image real catalysts supported on high-surface-area, porous oxide carriers. 

Internal diffusion in porous catalysts, if dominant, also reduces the observed activity of the biocatalyst. The decisive coefficient for mass transfer is the effective diffusion coefficient De((, which is defined in Eq. (5.56), where D0is the diffusion coefficient in solution, e the porosity of the carrier, and t the tortuosity factor. 

The structure of the porous media can also be shaped by mechanical and electrostatic forces, e.g., sheeting of granules at conveyor walls (Yao et al., 2004), deposition of solid grains in the porous media, and fragmentation of catalyst carriers. Simple examples of mechanical diagenesis of porous media were already illustrated in Section II.D.4. In this section, we first describe the morphological operation of skeletonization and the methods used for the... 

A novel application of a symmetric porous membrane as a catalyst carrier but not as a permselective barrier is to use the membrane itself as the reaction zone for precise control of the stoichiometric ratio [Sloot et al., 1990]. In this case, the reactants are fed to the different sides of the membrane which is impregnated with a catalyst for a heterogeneous reaction. The products diffuse out of the membrane to its both sides. If the reaction rate is faster than the diffusion rate of the reactant in the membrane, a small reaction zone or theoretically a reaction plane will exist in the membrane. An interesting and important consequence of this type of membrane reactor is that within the reaction zone the molar fluxes of the reactants arc always in stoichiometric ratio and the presence of one reactant in the opposing side of the membrane is avoided. The reaction zone can be maintained inside the membrane as long as the membrane is symmeuic and not ultrathin. Therefore, membrane reactors of this fashion are particularly suited for those processes which require strict stoichiometric feed rates of premixed reactants. A symmetric porous a-alumina membrane of 4.5 mm thick was successfully tested to demonstrate the concept [Sloot et al., 1990]. 

When the catalyst is immobilized within the pores of an inert membrane (Figure 25.13b), the catalytic and separation functions are engineered in a very compact fashion. 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 for the reactants to the catalyst. Two contactor configurations—forced-flow mode or opposing reactant mode—can be used with these catalytic membranes, which do not necessarily need to be permselective. It is estimated that a membrane catalyst could be 10 times more active than in the form of pellets, provided that 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. For biphasic applications (gas/catalyst), the porous texture of the membrane must favor gas-wall (catalyst) interactions to ensure a maximum contact of the reactant with the catalyst surface. In the case of catalytic consecutive-parallel reaction systems, such as the selective oxidation of hydrocarbons, the gas-gas molecular interactions must be limited because they are nonselective and lead to a total oxidation of reactants and products. For these reasons, small-pore mesoporous or microporous... 

The key problem here is the preparation of these plates. The plates contained one inert hydrophobic part close to the hydrogen gas side, and another part consisting of a catalytically active metal on various types of carrier powder. The hydrophobic layer was made of 30-50-fjLm nonporous PTFE particles. The catalyst carrier particles were porous (mean pore diameter of 10 nm) with a particle size of about 5 p.m. The catalytic material was of three different types 10% Pd on alumina, 10% Pd on carbon, and 1.9% Pd on Ni0/Si02. In addition to these powder materials, the plates contained nets of nickel wire (0.16 mm) or glass fibers (0.2 mm) as reinforcement. The catalytic plates were prepared... 

Aside from this effect, porous carriers have an advantage in their ability to hold the catalyst firmly in place. Solid catalyst carriers, such as granular metal, should simulate the porous carriers in having a rough surface to which the active catalyst material may be firmly bonded. This is especially important in the case of reactions which are conducted at high space velocities where the tendency is to blow the catalyst from the support and out of the reaction chamber. 

The Supported Sr-promoted La203 catalysts with different Sr/La ( 0.0, 0.03, 0.3, 2.0, 10.0) ratios and with Sr-La203 loading of 16 1.5 wt% were prepared by impregnating 22-30 mesh size particles of commercial low surface area porous, inert catalyst carrier ( SA-5205 obtained from Norton Co., USA) by the active catalyst mass. The impregnation of mixed nitrates of Sr and La from their aqueous solution on the support particles was done by the incipient wetness technique. The resulting supported catalyst mass was dried at 90°C for 16 h and then calcined in static air at 950°C for 4 h. 

In our efforts to verify deductively our modified capillary condensation theory we found two commercial porous bodies in which spherical elementary particles are arranged in a definite pattern. Therefore, if the radius of the elementary particles and their packing are given, a whole model of pore structure is clearly available for these specimens. By using these specimens as a catalyst or a catalyst carrier a series of investigations was carried out on catalytic activity in relation to the pore structure. 

The comparison of a number of Pd-supported catalysts on non-po-rous and porous materials confirmed that non-porous ultrafine carriers like titania, seem to be most suitable for hydrogenation of ( )-2-phenylcinnamic acid. Thus, for porous and non-porous supports results of hydlrogenation were as follows on Si02 49.1% and 30.7%, on Ti02 62.0% and 29.4%, respectively (Nitta et al. ). 

Dromard impregnated porous inorganic carrier materials (4 pm-S mm) with solutions of monomers and polymers [16]. After evaporation of the solvent, films on the carrier surface were obtained. These catalysts can be activated with sulfonic or phosphonic add groups. The catalysts were used for the production of silicones. The preparation procedure seems to be problematic, because during polymeriza-... 

New Catalyst Concept Porous Polymer/Carrier Composite... 

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