Types of catalysis

In my last post, I have discussed about the general catalysis phenomena, and its most basic types. But the homogeneous and heterogeneous catalysis are not the only types of the catalysis. The chemical engineer also classifies catalysis on the basis of the nature of species responsible for the catalytic activity. These types are mostly inter-related with other types of the same nature. E.g. molecular catalysts can be used as homogeneous, as well as heterogeneous catalysts, Surface catalysts are heterogeneous catalysts etc. Some of the types are:

1) Molecular Catalysis:

This term is used for the systems, where identical molecular species are the catalytic entity. Many of these catalysts are used as homogeneous catalysts, but these can also be used in heterogeneous (multi-phase) catalysis.

2) Surface Catalysis:

Surface catalysis takes place on the surface atoms of the extended solid. It depends on the different properties of the surface atoms, and different types of the molecular sites. Surface catalysts are solid, so these are heterogeneous catalysts by nature.

3) Enzyme Catalysis:

Enzymes are proteins, polymers of amino acids, so this type of catalysis is used to catalyze reactions in living organism, biological and biochemical reactions. The enzyme catalysis is usually molecular catalysis.

4) Auto Catalysis:

In autocatalysis, there is no need to use a separate catalysis, but in a reaction one of the products acts as a catalyst it self. Some biochemical reactions are experimentally observed as the auto catalysis reactions.

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Catalysis

Catalysis is the key to optimized and efficient process engineering. Catalysis is the major problem for the chemical engineer while understanding the basic chemical reaction engineering. Catalysis is used in most of the industrial and biological processes, and the products of these processes include food, drugs, clothing, plastics, fuels or detergents.

To understand the phenomena of the catalysis, a chemical engineer must understand that what is catalyst? Catalyst is the substance, which changes the rate of the chemical reaction, with out being consumed in the reaction it self. But practically after the completion of the process, the catalyst transforms (not consumed), so mostly, the catalysts needed to be regenerated and can be used again.

These catalysts may be in any state of matter, i.e. liquid, gas or solids. There can be two types of a catalyst:

• positive catalysts : increases the rate of the reaction.

• negative catalysts : decreases the rate of the reaction. These are also called as inhibitors.

Catalysis is the phenomena of change in the rate of a chemical reaction in presence of a catalyst. There can be two types of the catalysis.

1) Homogeneous catalysis:

The catalysts are in the same phase as the reactants are. I.e. the homogeneous catalysts are co-dissolved substances in the solvent, with the reagents. The acid catalysis can be taken as an example of the homogeneous catalysis. In which the water, after self ionization forms protons (most penetrating homogeneous catalyst).

2) Heterogeneous catalysis:

The catalysts are in different phase, as that of the reactants. Most heterogeneous catalysts are solids (in a liquid or gaseous reaction mixture). But as the surface area of the catalyst (especially in solid catalyst case) has important effect on the rate of reaction. So the catalysts are generally crushed into the smaller particle size, as the smaller the particle size, the more will be the surface area of the catalyst.

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