New process for the production of efficient catalyst systems for the synthesis of methanol
Methanol is not only an important starting material for the chemical industry;
it is gaining attention as an energy source for fuel cells. In contrast to
hydrogen, liquid methanol would be easy to transport and could be distributed by
means of the existing network of filling stations. It is no wonder that the
search is on for better catalysts for the synthesis of methanol. Researchers
working for a Special Research Area of the German Research Society (SFB 558)
based at the Ruhr University in Bochum have reported success on this front with
an unusual vaporization technique.
Industrial production of methanol usually involves the conversion of synthesis
gas, a mix of carbon dioxide, carbon monoxide, and hydrogen, using copper/zinc
oxide catalysts. The effectiveness of the catalysts is clearly affected by
interactions between the metallic copper and the zinc oxide, which acts as a
support. The team headed by Roland A. Fischer thus looked for a way to maximize
contact at the interface between the copper and zinc oxide. This led them to the
idea of using porous silicate materials as a support for their catalyst systems.
These materials have the advantage of having both a very highly specific surface
and a precisely controllable nanoscopic pore structure; they have also
previously proven to be excellent support materials in many cases. Instead of
applying the catalytically active substances -- copper and zinc oxide -- by
means of conventional impregnation processes, the Bochum researchers used a
method called organometallic chemical vapor deposition. First they vaporize an
oxygen-containing organocopper compound in a vacuum. The vapor is then firmly
adsorbed onto the silicate support. Diethyl zinc is then deposited in the same
manner and the material is carefully heated. On the molecular level, the
following occurs: the zinc atoms take the place of copper atoms, which are
deposited as metallic copper. Heating causes all of the organic compounds to be
burned off, leaving the zinc behind as zinc oxide. What is special about all of
this is that the copper and zinc oxide are extremely finely divided, so that
they are in particularly close contact with each other. In this way, the
researchers obtained catalytic materials that are at least as effective as the
classic copper/zinc oxide catalysts. "The catalytic activity of one sample
exceeds that of the classic system to a surprising degree," says Fischer. "The
reason for this is the special three-dimensional pore structure of this silicate
support, which allows for an especially efficient diffusion of the penetrating
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