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Catalysts can be divided into two types: homogeneous and
heterogeneous.
Homogeneous catalysts occupy the samephase as the reaction
mixture, while heterogeneous catalysts
occupy a differentphase.
Homogeneous catalysts allow for greater mixing and interaction
with the reaction mixture than
heterogeneous catalysts.
catalyst
a substance that increases the rate of a chemical reaction
without being consumed in the process
Catalysts are compounds that, when added to chemical reactions,
increase the reaction rate and reduce
the activation energy, as shown in Figure 0.
The amount of a catalyst does not change during a reaction, as
it is not consumed as part of the
reaction process. Catalysts lower the energy required to reach
the transition state of the reaction,
allowing more molecular interactions to achieve that state.
However, catalysts do not affect the degreeto which a reaction
progresses. In other words, though catalysts affect reaction
kinetics, the
equilibrium state remains unaffected.
Catalysts can be classified into two types: homogeneous and
heterogeneous. Homogeneous catalysts
are those which exist in the samephase (gas orliquid) as the
reactants, while heterogeneous catalysts
are not in the samephase as the reactants. Typically,
heterogeneous catalysis involves the use ofsolid
catalysts placed in a liquid reaction mixture.
There are advantages and disadvantages to both types of
catalysis. For instance, while homogeneous
catalysis allows for more effective mixing of the catalyst with
the reaction mixture, heterogeneous
catalysis provides the opportunity for the recovery of expensive
catalysts, which is a useful property
for the manufacturing processes.
Examples of homogeneous catalysis include acid, organometallic,
and enzymatic catalysis, with
proton acids being one of the most commonly used catalysts (for
example, in the esterification of
acids). Like many other catalysts, the addition of acid can
speed reactions by affecting bond
polarization.
Homogeneous catalysts are used in variety of industrial
applications, as they allow for an increase in
reaction rate without an increase in temperature.
https://www.boundless.com/chemistry/chemical-kinetics/catalysis/homogeneous-
catalysis/
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Catalysts do one very simple but vitally important thing, they
speed up chemical reactions
without being used up in the process. The way catalysts achieve
this is by providing an
alternative route for the reaction to follow that has a lower
activation energy.
You can think of this as being on one side of a mountain pass.
Even though your destination
on the other side is closer to sea level you just dont have
enough stamina to climb the pass inorder to go back down the other
side. The catalyst provides a tunnel that takes you through
the mountains so that you never have to climb that high. An
important thing to remember is
that the route takes two-way traffic and so it cannot affect the
final concentrations of
reactants and products, just how soon the final concentrations
are reached. The normal way of
saying this is that a catalyst cannot affect the equilibrium
position of a reaction, just the rate.
The two types of catalyst you will meet are called homogeneous
and
heterogeneous catalysts. Whilst they achieve the same result
they work in
fundamentally different ways.
With homogeneous catalysts the catalyst and all the reactants
are in a singlephase usually either liquid or an aqueous solution.
Invariably the catalyst is
taken up into the chemical reaction before being spat out at the
end.
Most industrial catalysed reactions are of the heterogeneous
type. Here the
reactants and the catalyst are in different phases. Usually the
catalyst is in the
solid phase whilst the reactants are either liquid or gaseous.
In industrial
applications the catalyst is often supported on a substrate that
allows the
effective surface area to be increased and the catalyst to be
fixed in place.
http://spaceflight.esa.int/impress/text/education/Catalysis/index.html
http://spaceflight.esa.int/impress/text/education/Catalysis/index.htmlhttp://spaceflight.esa.int/impress/text/education/Catalysis/index.html
