Selection of Support Material

Table 10.1 A selection of support materials and their key properties.

Way, Noble and Bateman (49) review the historical development of immobilized liquid membranes and propose a number of structural and chemical guidelines for the selection of support materials. Structural factors to be considered include membrane geometry (to maximize surface area per unit volume), membrane thickness (<100 pm), porosity (>50 volume Z), mean pore size (<0.1)jm), pore size distribution (narrow) and tortuosity. The amount of liquid membrane phase available for transport In a membrane module Is proportional to membrane porosity, thickness and geometry. The length of the diffusion path, and therefore membrane productivity, is directly related to membrane thickness and tortuosity. The maximum operating pressure Is directly related to the minimum pore size and the ability of the liquid phase to wet the polymeric support material. Chemically the support must be Inert to all of the liquids which It encounters. Of course, final support selection also depends on the physical state of the mixture to be separated (liquid or gas), the chemical nature of the components to be separated (inert, ionic, polar, dispersive, etc.) as well as the operating conditions of the separation process (temperature and pressure). The discussions in this chapter by Way, Noble and Bateman should be applicable the development of immobilized or supported gas membranes (50). 

Because the LbL method has great flexibility in selection of support materials, various advanced uses have been considered. Recently, LbL methods have been used for various advanced purposes including integration with device structures, advanced biomedical applications, hybridization of nanomaterials, and construction of hierarchic structures. In this section, these aspects are introduced with recent enzyme-related examples. 

Apart from the method itself, the selection of support materials is another crucial decision to be made in the course of preparing cell immobilization. Ideally, the support materials should meet the following criteria ... 

In this case the designer has freedom of choice of both form and dimension as well as in the selection of the materials. Given this freedom, it would be desirable to examine several of the alternatives to see which would provide the best seating at the lowest cost. Obviously, there is no point in doing all of the possibilities so a selection should be made on the basis of anticipated use as well as style requirements. Three types will be analyzed. They are the single curve sheet cantilever mounted from the back, the molded pan supported on four legs, and the structural foam molding which is front supported. 

Highly active gold catalysts can be prepared by an appropriate selection of preparation methods such as CP, DP, DR, and SG with dimethyl Au(III) acetylacetonate, depending on the kind of support materials and reactions... 

One of the most important, yet latent, applications of controlled-potential electrolysis is electrochemical synthesis. Although electrolysis has been used for more than a century to synthesize various metals from their salts, application to other types of chemical synthesis has been extremely limited. Before the advent of controlled-potential methods, the selectivity possible by classical electrolysis precluded fine control of the products. The only control was provided by appropriate selection of electrode material, solution acidity, and supporting electrolyte. By these means the effective electrode potential could be limited to minimize the electrolysis of the supporting electrolyte or the solvent. Today potentiostats and related controlled-potential-electrolysis instrumentation are commercially available that provide effective control of the potential of the working electrode to 1 mV, and a driving force of up to 100 V for currents of up to several amperes. Through such instrumentation electrochemical syn-... 

Sucholeiki reviews the selection of supports for solid-phase organic synthesis. To address many of the problems presented above, we are seeing the use of a wide range of solid supports from the traditional Merrifield resin to newer composites, cellulose, silica, and others. This chapter presents the pros and cons of many of these potential supports, reviews modifications to enhance the solution-like behavior of the bound materials, and methods to increase the loading capacities. 

The design considerations of the supporting structure are covered in earlier sections of the book consideration of the selection of specific materials is discussed later in this section. 

Because of the long-term instability of GPO, this enzyme was stabilized by immobilization on Eupergit C 250 L. Under proper selection of the immobilization conditions, an activity yield of 84% was obtained with 51 units of activity per gram of supporting material [138,139]. 

In the catalysis community, it is generally accepted that there are two types of support materials for heterogeneous oxidation catalysts [84]. One variety is the reducible supports such as iron, titanium, and nickel oxide. These materials have the capacity to adsorb and store large quantities of molecules. The adsorbed molecules diffuse across the surface of the support to the catalyst particle where they are activated to a superoxide or atomically bound state. The catalytic reaction then takes place between the reactant molecules and the activated on the catalyst particle. Irreducible supports, in contrast, have a very low ability to adsorb O. Therefore, can only become available for reaction through direct adsorption onto the catalyst particle. For this reason, catalysts deposited on irreducible supports generally exhibit turnover frequencies that are much lower than those deposited on reducible supports [84]. More recent efforts in our laboratory are focused on characterizing catalyst support materials that are commonly used in industry. These studies are aimed at deciphering how specific catalyst and support material combinations result in superior catalytic activity and selectivity. 

Methanol synthesis over noble metal catalysts has been pursued in a number of laboratories. However, the research is very much of academic interest since the catalysts have poor selectivity for methanol synthesis (ref. 22). The activity and selectivity of the noble metal catalysts is influenced by both the metal and the support (ref. 22). Metals that have been investigated include Rh (refs. 22,23), Pd (refs. 22,25), Ir (ref. 22) and Pt (refs. 22-26). A wide range of support materials have also been investigated including MgO, CeC, ... 

However, this high activity is accompanied by low N2 selectivity, i.e., large quantities of nitrous oxide (N2O) are formed [2]. By appropriate choice of support material, e.g., introducing acidic groups on the surface, the selectivity towards N2 can be enhanced [4]. 

Tables 22-2.1 provide some lists on the types of standard tests available. None of the lists are anywhere near inclusive of all the tests which are available. Tests are particularly useful for the comparison of materials, usually to assist the selection of a material or materials for further evaluation. The ultimate selection phase usually stems from the investigational tests in contact with the product, and is finally supported by formal stability programmes. In all these data must be adequately detailed, properly recorded and, where necessary, relevant conclusions must be drawn.

In the present work, we investigated the influence of the metal precursor and of the nature of the support on the performences of ruthenium catalysts for the wet air oxidation of p-hydroxybenzoic (p-HBZ) acid chosen as a model of phenolic pollutants. Titanium and zirconium oxides were selected as supporting materials. The preparation method adopted for supports was sol-gel combined with the use of supercritical drying. The motivation of such combination is to prepare aerogel supports with high BET surface area and unique morphological and chemical properties [9,10]. 

The results indicate that the choice of support material influences the activity and the product distribution in catalytic oxidation of ethanol. Both platinum and palladium are active materials for ethanol oxidation, but the selectivity for acetaldehyde production is high at low temperatures. The selectivity for acetic acid formation is low for the palladium catalysts. The yield of acetic acid in the platinum catalyst experiments is of the same magnitude as the odour threshold. Acetic acid is not formed via oxidation of acetaldehyde. 

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