A3.3 Homogeneous Catalysts
Homogeneous (the opposite of heterogeneous) means “in the same state.” Homogeneous catalysts are more difficult to separate from the products of a reaction.
Homogeneous catalysts work in a different way than heterogeneous catalysts. The reactants react with the catalyst to form a temporary activated complex or reaction intermediate. For example suppose we have a reaction:
$\textsf{R1}+\textsf{R2}\ \rightarrow \textsf{P}$
Activation energy
$\textsf{E}$
where
$\textsf{R1}$
and
$\textsf{R2}$
are Reactants,
$\textsf{P}$
is the Product. The catalysed reaction occurs in two steps involving the catalyst,
$\textsf{C}$
$\textsf{1.}\ \textsf{R1}+\textsf{C} \rightarrow \textsf{X} \\ {\textsf{Activation energy E1}}$
$\textsf{2. } \textsf X+\textsf{R2} \rightarrow \textsf{P}+\textsf{C}\\ \textsf {Activation energy E2 - note the catalyst is recovered}$
Figure 3.1 Homogenous catalysts
Both
$\textsf{E1}$
and
$\textsf{E2}$
are smaller than
$\textsf E$
, so the reaction will be faster.