The Role Catalysts In Chemical Reactions, Their Importance In Industry

The Role Catalysts In Chemical Reactions, Their Importance In Industry, Problems and New Developments

OXFORD AND CAMBRIDGE SCHOOLS EXAMINATION BOARD. General Certificate Examination

- Advanced Level Chemistry (Salters') - Paper 3 mock.

ROBERT TAYLOR U6JW.

A Catalyst is a substance that alters the rate of a reaction. The catalyst remains unchanged at the end of the reaction. The process is called catalysis.

In this report I aim going to explain the role of catalysts in chemical reactions and their importance in industry. I will also outline the problems associated with the use of some catalysts and discuss, using appropriate examples, new developments in this area which will help reduce damage to the environment. The process of catalysis is essential to the modern day manufacturing industry.

Ninety per cent, over a trillion dollars' worth, of manufactured items are produced with the help of catalysts every year. It is therefore logical that scientists are constantly searching for new improved catalysts which will improve efficiency or produce a greater yield.

An acidic catalyst works due its acid nature. Catalysts are strong acids and readily give up hydrogen ions, or protons: H+. Protons can be released from hydrated ions, for example H3O+, but more commonly they are released from ionisable hydroxyl groups (R-OH) where the O-H bond is broken to produce R-O- and H+. When the reactant receives protons from an acid it undergoes a conformational change, (change in shape and configuration), and becomes a reactive intermediate. The intermediate can then either become an isomer by returning a proton to the catalyst, or it may undergo a further reaction and form a completely new molecule.

Up until the mid - 1960's silica-alumina gels were used to catalyse the cracking of hydrocarbons. This form of cracking is where the large molecules in oil are converted into small, highly volatile molecules. However because the size of the pores of silica-alumina gels was so variable, (ranging from 0.1nm to 50nm), and the fact that their shape was so variable, they were hardly ideal catalysts. Due to the large size of their cavities, large carbonaceous products were able to form in the cavities thus lowering the reactivity if the catalyst. Catalysis with alumina silica-gels was also difficult to control precisely because of their indefinite structure, and therefore uneven d...

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...ce on the surface of the solid therefore the solvent only acts as a form of heat transfer and a working fluid.

In summary I see Supported reagents as the best possible solution to the problems associated with catalysis due to their easy use and their ability to be recovered and re-used. They have a high level of activity and improved selectivity in reactions. This is accompanied by their highly catalytic activity which leads to the best possible level of performance in commercial uses. This has already been proven by the use of active reagents in Friedel - Crafts reactions. These reactions originally had the drawbacks of firstly the hydrolysed aluminium chloride containing aqueous effluent which is produced, and secondly the by-products such as polymeric tars and di- and polysubstituted by- products which are produced which unless they can be successfully removed make the product impure. By using a supported reagent catalyst, in most cases the desired level of activity can be achieved but the catalyst can be removed easily from the reaction mixture and re-used. I personally therefore feel that the future of environmentally friendly catalysis lies with supported reagent

catalysts.