CATALYST Chemische Eigenschaften,Einsatz,Produktion Methoden
Definition
A substance that alters
the rate of a chemical reaction without
itself being changed chemically in the reaction.
The catalyst can, however, undergo
physical change; for example, large lumps
of catalyst can, without loss in mass, be
converted into a powder. Small amounts of
catalyst are often sufficient to increase the
rate of reaction considerably. A positive
catalyst increases the rate of a reaction and
a negative catalyst reduces it. Homogeneous
catalysts are those that act in the
same phase as the reactants (i.e. in gaseous
and liquid systems). For example, nitrogen(
II) oxide gas will catalyze the reaction
between sulfur(IV) oxide and oxygen in the
gaseous phase. Heterogeneous catalysts act
in a different phase from the reactants. For
example, finely divided nickel (a solid) will
catalyze the hydrogenation of oil (liquid).
The function of a catalyst is to provide
a new pathway for which the rate-determining
step has a lower activation energy
than in the uncatalyzed reaction. A catalyst
does not change the products in an equilibrium
reaction and their concentration is
identical to that in the uncatalyzed reaction;
i.e. the position of the equilibrium remains
unchanged. The catalyst simply
increases the rate at which equilibrium is
attained.
In autocatalysis, one of the products of
the reaction itself acts as a catalyst. In this
type of reaction the reaction rate increases
with time to a maximum and finally slows
down. For example, in the hydrolysis of
ethyl ethanoate, the ethanoic acid produced
catalyzes the reaction.
CATALYST Upstream-Materialien And Downstream Produkte
Upstream-Materialien
Downstream Produkte