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
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 distribution of protons.
By the mid-1960's it was obvious that silica-alumina gels were inefficient as
catalysts and they were replaced by zeolites. Zeolites are highly porous
crystals with minute channels ranging from 0.3nm to 0.8nm in diameter. Due to
their definite crystalline structure and the fact that their pores are too small
to contain carbonaceous build-up, zeolites do not share the problems of silica-
Zeolites are able to exhibit shape-selective crystals i.e.. their active sites
are specific to only a few product molecules (the ones that will fit into the