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[Henk Elegeert]

REPLY TO: D66 at nic.surfnet.nl

Op 10 februari 2010 12:44 heeft Henk Elegeert <hmje at home.nl> het
volgende geschreven:

> Over welke *feiten* (die voor zich zouden spreken) heeft ie het dan?

http://www.esrf.eu/news/general/platinum/
"
A new perspective for understanding the mechanisms of catalytic conversion
last modified 09-02-2010 11:52

PRESS RELEASE - The oxidation of toxic carbon monoxide (CO) to carbon
dioxide occurs every day in millions of cars. Despite being one of the
most studied catalytic processes, the exact mechanism of interaction
between the carbon monoxide molecule and the catalyst, often platinum,
is not fully understood. An important step in the reaction is the
adsorption of CO on the surface of the catalyst. A team of scientists
from the ESRF and the ETH in Zurich (Switzerland) has managed to see
how the electrons in the platinum reorganize as the adsorption is
taking place and why catalysts are “poisoned”, i.e. why their activity
is reduced. It is the first time that this type of experiment is
carried out at the same high temperatures and pressures as in a real
car exhaust catalyst.

When the CO or other toxic gases get in contact with the catalyst, a
noble metal such as platinum, they oxidize to become less dangerous
gases. In this case, CO turns to CO2, which the car expels via the
exhaust pipe. However, the efficiency of the catalytic conversion
decreases considerably when the catalyst is at low temperature. The
scientists from the ESRF and ETH in Zurich determined how the CO
poisons the surface of the catalyst. The strong bond between CO and
the platinum blocks active sites and makes the metal less susceptible
to reaction with oxygen, lowering its reactivity.

Scientists around the world have studied thoroughly the electron
structure of adsorbed CO using techniques like vibration and soft
X-ray spectroscopy, but few have studied the electrons in the
platinum, and it has proven extremely difficult to do it on
nanoparticles under ambient pressure. In fact, very few experimental
techniques are compatible with the required temperature, gas
environment, and the low metal concentration of supported
nanoparticles.

The team has developed a technique where they can investigate the
platinum electrons that take part in the bond with CO. “We have, for
the first time, combined a novel experimental and theoretical approach
with an important application in catalysis research. This enables us
to look at the adsorption of CO on Pt nanoparticles from a new
perspective that was previously not accessible” explains Pieter
Glatzel, scientist at the ESRF.

A bare platinum nanoparticle is shown on the left, a CO-covered
particle on the right. Credits: ETH Zürich.

 The next step is to look at the changes in catalyst structure under
actual catalytic conditions, such as those occurring during the
preferential oxidation of CO and the water gas shift reaction. “We are
very hopeful of this new technique and are sure that it will enable us
to improve our knowledge about catalytic systems and, with it, make
them better”, says Jeroen van Bokhoven, scientist at the ETH.


Reference:
Glatzel, P. et al, J. Am. Chem. Soc., Articles ASAP (As Soon As
Publishable), February 3, 2010 (Communication),DOI: 10.1021/ja907760p
"

'Spreekt' voor zich ...

Henk Elegeert

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