Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Scattering of hydrogen makes calculation easier

22.02.2006


Leiden chemists in Science: Chemical reaction between hydrogen molecule and metal surface straightforward to calculate



The chemical reaction of hydrogen molecules (H2) with a platinum surface can be calculated much more straightforwardly than many researchers to date had thought. This is encouraging for research into hydrogen as a clean fuel and heterogeneous catalysis, which is where the reactions of molecules to metal surfaces plays a significant role. Chemists can now test theories on a broad scale which describe the interaction of molecules with metal surfaces.

Born-Oppenheimer


The Leiden theoretical chemists Ernst Pijper, Roar Olsen and Geert-Jan Kroes, together with colleagues from Amsterdam and from Spain, demonstrated that the Born-Oppenheimer approach can be used in predicting the reaction of hydrogen molecules with a metal surface. This is an approach which considerably simplifies chemical calculations by splitting them in two. A heated debate is currently raging on the applicability of the Born-Oppenheimer approach to reactions of molecules with a metal surface - a class of reactions which is very important in this application.

’Hot results’

The researchers published their findings last Thursday on the site of Science Express. This site publishes on the web a number of what they call hot results, sometimes weeks before they appear in the journal Science. The Born-Oppenheimer approach can be used, according to the researchers in their article, because a hydrogen molecule which is fired at a platinum surface, first splits into two atoms or is scattered at the surface before any strong interaction with the platinum takes place.

Complicated

Chemical reactions are generally so complicated that it is difficult to make predictions using quantum mechanical calculations, the specialism of theoretical chemistry. The Born-Oppenheimer approach is a useful tool for making these chemical calculations.

Born and Oppenheimer in 1927 postulated the idea that you can split a chemical calculation in two. First you solve the movement of the electrons and then the movement of the atomic nuclei which are so much heavier and slower than electrons that you can imagine they are standing still in comparison.

This makes the calculation much easier, and the Born-Oppenheimer approach is then also a welcome tool for predicting the progress of chemical reactions of complex systems. It works particularly well in calculating the behaviour of many gas phase reactions.

Out of step

The Born-Oppenheimer approach can only be applied if the reaction processes are adiabatic, which means that the electrons follow the movements of the nuclei and do not get out of step. And a lot of reactions of molecules with a metal surface are not adiabatic.

It has been shown for a number of molecules investigated to date which have been fired at a metal surface, that they already form a strong bond with the surface before they dissociate or are scattered. The consequence is that the molecules affect the metal surface, by forming so-called electron-hole pairs. This process is non-adiabatic; the electrons no longer follow the movement of the nuclei, and the Born-Oppernheimer approach cannot therefore be used.

Firing

Other molecules, like nitrogen, which when stretched like to take up electrons, can, if they are fired in a highly excited state at a metal surface that weakly binds electrons, shoot electrons out of a metal surface. This case also constitutes a breakdown of the Born-Oppenheimer approach.

But, based on calculations and experiments, the three Leiden researchers and their colleagues have been able to show that hydrogen molecules behave very differently if they are fired at a metal surface.

Back-scattering

At first, hydrogen molecules split into two atoms, or are back-scattered to the platinum surface before they form the strong bond with the metal whereby electron-hole pairs can be formed.

Secondly, a hydrogen molecule has a low electron affinity, which means that it does not readily take up an electron. Therefore, it does not tend to ’take’ an electron of the metal far from the surface. So, here too there is no risk of forming electron-hole pairs.

The reaction of molecular hydrogen with a platinum surface, and the scattering of the molecule on the surface is then an adiabatic process, and the Born-Oppenheimer approach can readily be applied to this class of reactions.

Hydrogen economy

‘It is not the case that hydrogen economy will be a fact next year as a result of this discovery,’ says Prof. dr. Geert-Jan Kroes, who is conducting fundamental research into hydrogen as a source of clean energy, and who transformed his faculty into a hydrogen plaza on the Science Day in 2005. ’But it is encouraging, because some hydrogen storage systems are based on the disassociation of hydrogen, that is the breaking of the hydrogen-hydrogen bond. Sometimes a metal is added, such as palladium. And disassociation can be described with the Born-Oppenheimer approach. Platinum is not a candidate for promoting the storage of hydrogen. We do know now that a whole class of reactions, particularly dissociation of hydrogen on metal surfaces, can be solved simply, so that we can conduct large scale testing of theories which describe the interaction of molecules with metal surfaces.‘

Hilje Papma | alfa
Further information:
http://research.leidenuniv.nl/

More articles from Life Sciences:

nachricht When Air is in Short Supply - Shedding light on plant stress reactions when oxygen runs short
23.03.2017 | Institut für Pflanzenbiochemie

nachricht WPI team grows heart tissue on spinach leaves
23.03.2017 | Worcester Polytechnic Institute

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

When Air is in Short Supply - Shedding light on plant stress reactions when oxygen runs short

23.03.2017 | Life Sciences

Researchers use light to remotely control curvature of plastics

23.03.2017 | Power and Electrical Engineering

Sea ice extent sinks to record lows at both poles

23.03.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>