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Catalyst Preparation And Characterization Essay

6105 words - 25 pages

Catalysis is of importance to today's chemical industry. There are only a small number of chemical processes that are still conducted without the use of a catalyst. Catalysts are use in an array of applications from the production of consumer goods to the protection of the environment. The approach involves a wide number of specific competencies of solid state chemistry, analytical chemistry, physical chemistry, kinetics and rheology. The fundamental aspects in the preparation of heterogeneous catalysts starting from catalyst design up to the catalyst in its final form are briefly reviewed. The literature will also be treating mechanisms of catalyst deactivation. Mechanisms of catalyst ...view middle of the document...

Typical forms of industrial catalysts include powder, pellets, rings, spheres, extrudates or granules, as shown in Figure 1. More recent innovations include the monolithic supports in their various forms (see Figure (2)).2.1 Catalyst ComponentAlthough some catalytic materials are composed of single substances, most catalysts have three types of distinguishable components, as shown in Figure 3 and stated below:1.active components,2.a support or carrier, and3.promoters2.1.1 Active ComponentsActive components are responsible for the principal chemical reaction. Selection of the active component of the active component is the first step in catalyst design. The main type of active component is metals, where approx. 70 per cent of known catalytic reaction involves metallic component . Industrially, metals are used in catalytic reforming, hydro-cracking, ammonia and methanol synthesis. An example of an active component will be copper in the Cu-ZnO-Al2O3 catalyst used in methanol synthesis.2.1.2 PromotersPromoters are an agent, when added, results in desirable activity, selectivity or stability effects and are designed to assist either the support or the active component. One important example of support promotion is control stability. Support oxides may occur in several different phases, some undesirable. With Al2O3, for example, the preferred phase is γ- Al2O3 . This phase has high surface area, a certain degree of acidity, and forms solid solutions with transition oxides such as CoO. When heated, γ- Al2O3 transforms into α- Al2O3, which has a hexagonal structure and low surface area. The transition begins at about 900oC, a temperature not usually encountered during process conditions but possible during catalyst regeneration. Most often, promoters are added to support in order to inhibit undesirable activity, such as coke formation.Promotion of the active component may be either structural or electronic. For metals an example can be ammonia synthesis. Ammonia synthesis catalysts consist of iron doubly promoted with alumina and potassium . The indications that alumina promotes the iron by stabilizing surface planes which are 500 times more active than other times .2.1.3 SupportSupport perform many functions, but most important in maintenance of high surface area for the active component. This is shown with platinum, an important catalytic metal used for catalytic reforming and automotive exhaust clean-up. For high activity, platinum crystallites must have the highest surface area possible.Support function as stable surfaces over which the active component is dispersed in such a way that sintering is reduces . The support itself must be secure from thermal growth, which means high melting point, at least higher than that of the active component.There are many types of supports used for the catalyst, of which a brief discussion will centre around three types:1.Alumina Support2.Silica Support3.Carbon Support2.1.3.1 Alumina...

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