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with the real chemical reaction it can be neglected. In these cases
the reaction velocity behaves similarly to a homogeneous system.[1]
2. The chemical reaction occurs at a rate which in comparison with
the time necessary for the accumulation can be neglected. In this
case the time necessary can be generally compared with a diffusion
process.[2]
The catalytic processes in heterogeneous systems have excited
interest since BREDIG[3]
showed that the colloidal metals prepared by
him showed catalytic properties. The best-studied process is the decomposition
of H2O2 by colloidal platinum, gold, and other metals or oxides
(MnO2, PbO2). Attention must be called to the small quantity of
catalyst sufficient to decompose H2O2. The action of 1 gram atom
platinum in 70 million liters of reaction mixture has been detected. The
decomposition of H2O2 by platinum catalyst in nearly neutral or faintly
acid solution has been shown to be a monomolecular reaction.
Still certain differences occur from the conditions formed in the
homogeneous catalysis. At one time in certain experiments the value
for k rises considerably during the catalysis, and secondly, k is not
proportional to the ferment concentration, but rises more quickly than
this.
In connection with these experiments BREDIG has expressed the
view that an analogy exists between the catalytic processes of the inorganic
world and the enzyme action of the organic.
The following important facts give support to
BREDIG’S view:
1. In both cases we are dealing with catalytic processes; the metallic sol and
the enzyme are active in very small quantities and during the reaction they do
not undergo any appreciable change.
2. In the decomposition of H2O2 by platinum sols or by the enzyme hæmase,
the reaction is monomolecular.
3. The action of metallic sols as well as enzymes is paralyzed by certain
poisons (HCN, H2S).
4. Both classes of bodies are colloid substances and possess an enormous
surface upon which their catalytic action depends.
According to NEILSON,[4] ethyl butyrate, salicin and amygdalin are decomposed by platinum black as well as by enzymes.
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