Support bodies

In another example, Ti02 can be deposited on a siHca support body in order to obtain a stable high surface titania. This is necessary because Ti02 sinters badly on heating in the bulk oxide and loses surface area. The Ti02 Si02 combination is useful as a catalyst for the oxidation of o-xylene to phthaHc anhydride. 

Porosity and Pore Size. The support porosity is the volume of the support occupied by void space and usually is described in units of cm /g. This value represents the maximum amount of Hquid that may be absorbed into the pore stmcture, which is an especially important consideration for deposition of metal salts or other active materials on the support surface by Hquid impregnation techniques. The concentration of active material to be used in the impregnating solution is deterrnined by the support porosity and the desired level of active material loading on the catalyst. If the porosity is too low, inefficient use of the support material and reactor volume may result. If the porosity is too high, the support body may not contain sufficient soHd material to provide the strength necessary to survive catalyst manufacture and handling. 

Attrition Loss. The tendency of a support body to be reduced to powder is termed susceptibiHty to attrition, and the measurement of such susceptibiHty is termed attrition loss. Attrition can occur when support bodies mb against one another and abrade the surface, such as during calcination in a rotary kiln or sizing on moving screens. 

Catalytic Support Body Monolithic Honeycomb Unit. The terms substrate and brick are also used to describe the high geometric surface area material upon which the active coating material is placed. Monolithic honeycomb catalytic support material comes in both ceramic and metallic form. Both are used in automobile catalysts and each possesses unique properties. A common property is a high geometric surface area which is inert and does not react with the catalytic layer. 

Quadraxially oriented (four directional layer) glass fabric-TS vinyl ester polyester RP sheet panels with a foam core and gel coating are used. Most of the panels are 3 mm thick with molded-in rib structure supports. Body skins are bonded to the chassis with a double-stick acrylic tape developed by 3M Co. as well as mechanical fasteners. Unlike most steel designs, no B-pillar structural component between the front and rear doors is required thus providing more interior space and easy entry since doors open in opposite directions. 

Manjikian, S. 1966. Production of semipermeable membranes directly on the surfaces of permeable support bodies. U.S. Patent 3,544,358. 

Impregnation of Supports and Drying. Most obvious is incipient wetness impregnation of a support with a solution of an active precursor and subsequent drying and calcination of the thus loaded support [6], Incipient wetness or pore-volume impregnation is especially attractive with preshaped support bodies. When the active component has to be in the metallic state, reduction can be carried out after the calcination step. Often, the catalyst is reduced after loading into the reactor to prevent a separate passivation step, in which the surface of the pyrophoric reduced catalyst is carefully oxidized. However, to achieve reproducible catalysts the catalyst manufacturer usually reduces the catalyst and delivers the passivated catalyst, which then only needs a short additional reduction. 

Application of one or more precursors) uniformly over the internal surface of preshaped support bodies is attractive for the development of industrial catalysts within a short period of time. Since impregnation and drying often leads to deposition more or less exclusively at the external edge of the support bodies, an improved procedure is highly desirable. 

Extremely good distributions of the active precursor over the internal surface of the support bodies were obtained. The difficulty, however, is the loading that can be achieved. The limited pore volume of preshaped support bodies and the solubility of the precursor to be deposited and of the agent(s) for deposition-precipitation necessitate multiple impregnations in order to achieve loadings characteristic of base metal (compounds). With urea and simple nitrates, however, highly... 

Palladium nanoparticles vfith a size of a few nanometers supported on carbon are widely used as catalysts, for instance in three-way automotive exhaust catalysts and fuel cells, and can easily be prepared by impregnation of a porous support body with a precursor solution, followed by drying, decomposition of the precursor and, if necessary, reduction. It is well-known that the activity and selectivity of these catalysts for hydrogenation reactions depend on the palladium dispersion for particles sizes in the range 1-10 nm. It is, hence, not surprising that the interaction of Pd with hydrogen, and the infiuence of nanosizing, have been widely studied. 

The use of powders in a metal hydride tank is limited by the fact that the development of mechanical stresses during cycling (due to the different densities of the metal and the corresponding hydride) can affect the stability of the tank system. The mechanical stability of macroscopic support bodies can prevent mechanical stress and significant overall changes in shape and size, as is well known from catalytic reactors. 

Figure 1.1 shows a plot of this calculation. As an example, nickel has been chosen. It is obvious that only at low values of the particle sizes (l-10nm) are reasonable surface areas obtained. It is impossible to apply such small particles in reactors, and therefore support bodies are applied. Catalyst... 

In the case of wet impregnation, a fourth process is operative, viz. transport of solute to the outer particle surface. Depending on the process conditions, different profiles of the active phase over the support body will be obtained. For instance, depending on the pH, the interaction with the support can be strong or weak, and even repulsion can exist. 

Impregnation profiles on pre-shaped catalyst support bodies... 

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