Impregnated Catalysts the Role of Metal, Support and Promoters

Impregnated Catalysts the Role of Metal, Support and Promoters 

The severe working conditions often encountered in an H2 production process, such as high temperature and high space velocity, combined with the necessity for a long catalyst lifetime, impose the development of an appropriate synthetic procedure to stabilize the catalyst. The reforming activity and product distribution over supported metal catalysts depend on the choice of metal and its content, the presence of promoters, the type of support and method of catalyst preparation. 

Transition metals are used extensively as reforming catalysts and the variation in the catalytic activity can be determined by the differences in the strength of the adsorbate-surface interaction with various metals. One of the fundamental properties of a metal surface is in fact its ability to bond or to interact vflth surrounding atoms and molecules. The bonding ability determines the state of the metal surface when exposed to a gas or liquid and it determines the ability of the surface to act as a catalyst. During catalysis, the surface forms chemical bonds to the reactants and it helps in this way the breaking of intramolecular bonds and the formation of new bonds. 

Alumina is one the best known catalyst support materials and is frequently used in both research and industrial applications not only for its relatively high surface area on which active metal atoms/crystallites can spread out as reaction sites, but also for its enhancement of productivity and/or selectivity through metal-support interaction and spillover phenomena. 

The use of promoters in formulating a catalyst is often critical to the performance. Promoters can provide an extra edge to the performance of a catalyst by improving its operation. Promoters can be many and varied. They can be additives to stabilize a particular oxidation state of the catalyst, to optimize a particular phase or stmcture of the active ingredient(s), to provide additional pathways for facilitating reactions, to alter the concentration of a particular oxidation state in the active phase of the catalyst, to increase the activity or selectivity (chemical), to preserve mechanical strength and limit sintering (stmctural), to increase the surface area of the catalyst or to alter the 

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