PASS Scripta Varia 21 - Pontifical Academy of Sciences

SELF-PRESENTATION OF THE NEW ACADEMICIANS
Gerhard Ertl
I was born in 1936 in Stuttgart, Germany, the son of a miller. I became
interested in the natural sciences already as a boy. It was mainly chemistry, but
also physics. It was not clear to me which would be my preferred subject
until we got teachers in these subjects. We had a good teacher in physics and
a poor teacher in chemistry, so I became a physicist. I got my first degree at
the Technical University of Stuttgart but was still interested in chemistry, so I
moved for my Ph.D. thesis into the field of physical chemistry, which means
the investigation of problems of chemistry with the techniques of physics.
Together with my mentor, Heinz Gerischer, I moved to the Technical University
of Munich where I got my Ph.D. in 1965 on a topic that became my
lifelong interest, namely reactions at solid surfaces. Twenty-five years ago I
moved to Berlin to become one of the directors of the Fritz Haber Institute
of the Max Planck Society, succeeding my teacher Heinz Gerischer.
Chemical reactions – that means transformations of molecules into new
ones – usually involve the collision of molecules to form new ones. But
not every collision is successful, only a small probability exists and this probability
that determines the rate of a chemical reaction is determined by an
activation energy at its start. This has to do with the fact that chemical transformations
always involve breaking of bonds and forming of new bonds,
and the energy barrier we have to overcome in this context is the activation
barrier. The higher the barrier, the lower the probability. If we offer the
chemical reaction an alternative path, we can have a higher rate, a higher
probability, and this is done by a catalyst. A catalyst forms intermediate compounds
with the molecules involved in the reaction. This catalyst can be in
the same phase, these are homogeneous catalysts, in biological systems these
are macromolecules or enzymes and in industry practical applications these
are mainly solid surfaces, and this is heterogeneous catalysis.
The principle of heterogeneous catalysis comprises the interaction of
molecules from the gas phase with a surface of a solid which exposes its
topmost atoms with unsaturated bonds, so new bonds can be formed, socalled
chemisorption bonds, which can also modify existing bonds, i.e. a
molecule may dissociate. These chemisorbed species may diffuse across a
surface and form new molecules which are released into the gas phase. The
overall sequence of all these steps offers a reaction mechanism with a higher
reaction probability. This is the principle of catalysis.
Heterogeneous catalysis is the basis of the chemical industry. About 85%
of all products in the chemical industry are made through catalysis. But also
solution of problems concerning the environment, energy, or climate
change will require the application of catalysis.
The Scientific Legacy of the 20 th Century
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