Applications of Catalysis
90% of all chemical processes make use of catalysts in one way or another.
Some of the uses of catalysis are:
inorganic chemicals (NH3, H2SO4, etc)
organic chemical (hydrogenation, polymerization, oxidation, reduction,
etc)
petroleum technology (cracking, reforming, isomerization, etc.)
production of synthetic fuels (coal liquefaction, coal gasification, etc)
pollution control (automotive, industrial)
energy conversion (fuel cells)
The field of catalysis is multidimensional and multidisciplinary
requires an integrated approach based on different established practices of
engineering and science.
“Catalysis” first used by Berzelius in 1800’s. He observed that several
reactions were aided by the presence of certain foreign substances
“Catalytic Force” involved.
Several discoveries and patents were made involving catalysis in the 1800s &
early 1900s.
The progress was limited in scientific understanding and the discoveries were
made by chance “Black box” technology.
• A slide on Homogeneous Catalysis
• A slide on Heterogeneous Catalysis
Early 1900’s -theories and postulates were put forward
• Catalysts increase the rate of those processes that are
thermodynamically favorable
kf



kb
• For A
B
any increase the catalyst brings about in rate constant of forward reaction
is accompanied by a corresponding increase in the rate constant of the
backward reaction
equilibrium reached faster
• For given reactants the appropriate choice of catalyst aids in selecting
the desired path
• Theories of catalytic reactions are pointless since the method of
operation are varied
Despite this
Sabatier
 chemical intermediates
Langmuir  how reactions occur on surfaces
Development of relationship between various rates &pressures
Langmuir–Hinshelhood
Eley–Rideal
Taylor active sites/centers
Theories:
Balandin-
interpretation of catalytic activity in terms of geometric arrangement
of atoms
Beck-
relationship between lattice spacing and activity
Schwab-
electronic concentration in metal alloys was related to catalytic
activity
Ammonia synthesis a very
important process
• Ammonia is used to make fertilizers and other
chemicals
• Produced from N2 and H2
N2 + 3H2  2NH3 (-DH = 109 kJ/mol @ 773 K)
– High temperature and high pressure
– Catalyst required
• Catalyst must be cheap and stable since
ammonia is a low priced chemical
• Catalyst is primarily based on iron
Variation of Surface Area with
Particle Size
Solid catalysts play a key role in
the chemical industry
• Desired properties of catalysts
– High and stable activity
– Consistently high selectivity
– Controlled surface area and porosity
– Good resistance to poisons
– Good resistance to high temperatures
and temperature fluctuations
– High mechanical strength
• A slide showing different catalyst shapes
Other important factors to
consider
• Whether the catalyst should be supported
• What should be the shape of the catalyst
• What should be the void fraction
• Whether diffusional control is necessary
• How to achieve appropriate mechanical
strength