Porous support material

A rather new concept for biphasic reactions with ionic liquids is the supported ionic liquid phase (SILP) concept [115]. The SILP catalyst consists of a dissolved homogeneous catalyst in ionic liquid, which covers a highly porous support material (Fig. 41.13). Based on the surface area of the solid support and the amount of the ionic liquid medium, an average ionic liquid layer thickness of between 2 and 10 A can be estimated. This means that the mass transfer limitations in the fluid/ionic liquid system are greatly reduced. Furthermore, the amount of ionic liquid required in these systems is very small, and the reaction can be carried in classical fixed-bed reactors. 

This method involves the repeated dipping of porous support materials into a solution containing the desired catalytic agent. It is then dried and calcined to transform the metal into insoluble form. The agent must be applied uniformly in a predetermined quantity to a preset depth of penetration. The metal loading in the finished catalyst is typically 1-5%, Fig. 6.5. 

Nitrogen sorptiometry, also referred to as BET method (named after their inventors Brunauer [202], Brunauer and Emmet [203], and Teller and coworkers [204]), is an approach for the determination of the specific surface area of a (porous) support material based on the multilayer adsorption of nitrogen at the temperature of liquid nitrogen (77 K) according to following procedure ... 

A few studies have reported the embedding of an MIP film between two membranes as a strategy for the construction of composite membranes. For example, a metal ion-selective membrane composed of a Zn(II)-imprinted film between two layers of a porous support material was reported [253]. The imprinted membrane was prepared by surface water-in-oil emulsion polymerisation of divinylbenzene as polymer matrix with 1,12-dodecanediol-0,0 -diphenylphosphonic acid as functional host molecule for Zn(II) binding in the presence of acrylonitrile-butadiene rubber as reinforcing material and L-glutamic acid dioleylester ribitol as emulsion stabiliser. By using the acrylonitrile-butadiene rubber in the polymer matrix and the porous support PTFE, an improvement of the flexibility and the mechanical strength has been obtained for this membrane. 

Each bead represents one catalyst as a member of a library of solid catalysts. It may consist of an unporous material like a-Al2C>3 or Steatit or of typical porous support materials - such as A1203, Si02, Ti02, or the like. These beads can be subjected to different synthesis procedures and sequences like impregnation, coating etc. In addition, full mixed metal oxide catalysts can also be formed as spherical particles. 

The strong interaction of dextran sulfates with cationic functions in porous support materials is exploited to create new highly charged surfaces for adsorption of proteins. It was revealed that new and strong ionic exchange resins are accessible by simple and rapid deposition of dextran sulfates on commercial DEAE- or MANAE-agarose. The material is characterised by an increased charge density on the porous surface of the support, which can perfectly bind protein material, as demonstrated in Fig. 15 [153]. 

In this example, the composition of the catalyst surface is responsible for its activity. Therefore, catalysts are placed on porous supporting material (pellets) which have specific surface areas of some hundred m2/g pellet. Because the pellet core has the largest surface area, the reaction predominantely takes place here. 

Other reagents and solvents were obtained from commercial sources. The samples were prepared by mixing various chiral bases with racemic acids in 0.5 1 molar ratio. A porous supporting material (Perfilt), impregnated with these mixtures, was put into the extractor vessel and extracted with supercritical carbon dioxide. 

The dynamic membranes originally developed by Union Carbide are protected by three core patents U.S, 3977967, 4078112, and 4412921 (Trulson and Litz, 1976 Bibeau, 1978 and Leung and Cacciola, 1983) and their foreign equivalents. Those patents cover a broad range of metal oxides such as zirconia, gamma alumina, magnesia>alumina spinel, tantalum oxide and silica as the membrane materials and carbon, alumina, aluminosilicates, sintered metals, fiberglass or paper as the potential porous support materials. However, their marketed product, trade named Ucarscp membranes, focused on dynamic membranes of hydrous zirconium oxide on porous carbon support. 

Electroplating. Basically in electroplating, a substrate is coated with a metal or its alloy in a plating bath where the substrate is the cathode and the temperature is maintained constant Membranes from a few microns to a few millimeters thick can be deposited by carefully controlling the plating time, temperature, current density and the bath composition. Dense membranes made of palladium and its various alloys such as Pd-Cu have been prepared. Porous palladium-based membranes have also been made by deposition on porous support materials such as glass, ceramics, etc. 

The best prospects seem to be present for deposition of Pd(Ag) plugs into the pores of a porous support material as e.g. reported by Morooka et al. [21]. Further research to confirm the reproducible s)mthesis of this system and of its long-term stability for hydrogen separation is worthwhile. 

The structure gap concept derives from the difficulty of knowing to what extent idealized catalysts are representative of the results obtained with real-life catalysts. The most idealized catalysts expose only one well-defined single crystal plane with surface areas of the order of 1 cm and are most often studied under UHV conditions. In contrast to such simple single crystal model systems, real-life catalysts normally consist of small-supported nanoparticles buried in a porous support material. For example, in emission cleaning... 

Within the currently ubiquous nanoscience and nanotechnology efforts, the use of nanoparticles and nanostructured materials in catalysis appears as one of the most successful approaches [1]. It has been said that the most important drawback in nanoparticle appUcations is their tendency to aggregate and their dispersion in porous media has been shown to be a good way to prevent this. In this chapter a particularly interesting porous supporting material for nanoparticles, the aerogels, will be reviewed and their use in catalytical processes analyzed. 

A preferred embodiment of an oxygen transport membrane would thus have a thin porous support on the feed side to improve oxygen exchange, a thin dense separation membrane, a fine pore structure interfacial layer to facilitate oxygen transfer out of the membrane and a coarse porous support to maximize product flow and provide the structural support. An example is shown in Fig. 6.4. The coarse porous support material could be made out of inert material because it is not chemically active in the transport of oxygen. This allows the use of less expensive materials which may also have better strength characteristics. 

One of the best known methods for producing catalysts is the impregnation of porous support materials with solutions of active components [9,10]. Especially catalysts with expensive active components such as noble metals are employed as supported catalysts. A widely used support is AI2O3. After impregnation the catalyst particles are dried, and the metal salts are decomposed to the corresponding oxides by heating. The process is shown schematically in Scheme 6-2. 

In the spiral-wound type, a planar membrane is used and a flat, porous support material is sandwiched between the membranes. Then the membranes, support, and a mesh feed-side spacer are wrapped in a spiral around a tube. In the hollow-fiber type, fibers of 100 to 200 iJ,m diameter with walls about 25 /rm thick are arranged in a bundle similar to a heat exchanger (LI, Rl). 

The catalyst layer consists of the platinum catalyst, carbon as porous support material and an ionomer coating that is usually a polysulfonic acid, forming a three-phase boundary between the electrically conductive material, the ionic conductive material, and the gas phase. The hydrogen oxidation reaction (HOR)... 

SOFCs have largely converged on standard configurations, such as tubular or planar, with the structural support provided by the electrolyte, the anode, the metallic intercormector, or an inert porous support material. Each of these concepts has its own combination of advantages and disadvantages. In this section, some unconventional SOFC configurations and devices are discussed, and their performance and potential applications are considered in comparison with the more conventional approaches. This will include microtubular fuel cells, mixed reactant fuel cells, micro-planar fuel cells, and dual proton-oxygen ion fuel cells. 

In tubular membrane modules membranes are cast on a relatively thick and mechanically strong porous support material. Tube diameters are typically in the range of 10-25 mm. The feed solution is fed through the tubular bundle while the permeate is collected on the shell side of the module (Fig. 2.3c). These systems allow an efficient control of the concentration polarization and membrane fouling phenomena and are easy to clean. However, as the tube diameter increases, they occupy a larger space and require high pumping costs. 

There are variations in a given technique identified in Table 7.1.5. For example, in liquid-liquid chromatography (LLC), normaiiy the stationary-phase liquid is polar and the mobile phase is nonplolar, both being immiscible with each other, in reversed-phase LLC, the stationary-phase liquid is nonpoiar, whereas the mobile phase is polar the polar phase can even be water. In many cases, the stationary liquid phase may be a monomoiecular iayer chemically bonded to the surface groups of the porous support material. This is often achieved with a nonpolar hydrocarbon liquid phase. 

In the spiral-wound configuration an envelope is formed with two membrane sheets separated by a porous support material. Typically the module consists of several such envelopes. The material between the membranes (permeate channel spacer) supports them against the operating pressure and defines the permeate flow channel. The envelope is sealed on three sides. The fourth side is sealed to a perforated permeate collection tube, and the envelope is wrapped around the collection tube with a net-like spacer sheet that has two functions ... 

Assume that for an enzyme immobifized on the surface of a non-porous support material, the external mass transfer resistance is not negligible as compared to the reaction rate. The enzyme is subject to substrate inhibition. Could the effectiveness factor be greater than 1 Explain your answer. (From [14]). 

---