Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

When water speaks: solvents make catalysts more efficient

21.02.2013
RUB researchers analyse interfaces between water and catalyst with computer simulations

Why certain catalyst materials work more efficiently when they are surrounded by water instead of a gas phase is unclear. RUB chemists have now gleamed some initial answers from computer simulations. They showed that water stabilises specific charge states on the catalyst surface.


Snapshot of the charge transfer: Water-induced charge transfer at the interface between water and catalyst. The red and blue areas in the left and right image quantify the decrease or increase of the electron density due to the charge transfer at a given time. The blue and red mesh in the lower image section represents the oxide, the grey and yellow balls at the oxide surface the metal. The small blue and red molecules in the upper image section are water molecules.
Image: M. Farnesi Camellone, D. Marx

“The catalyst and the water sort of speak with each other” says Professor Dominik Marx, depicting the underlying complex charge transfer processes. His research group from the Centre for Theoretical Chemistry also calculated how to increase the efficiency of catalytic systems without water by varying pressure and temperature. The researchers describe the results in the journals “Physical Review Letters” and “Journal of Physical Chemistry Letters.”

Heterogeneous catalysis: water or gas as the second phase

In heterogeneous catalysis, researchers combine substances with two different phases - usually solid and gas. Chemical reactions work faster at the resulting interfaces than without a catalyst. Industry uses heterogeneous catalysis for many processes, for example to transform alcohols into certain aldehydes. Titanium dioxide with gold particles bonded to the surface, for example, is suitable as the solid phase. Water - instead of a gas - as the second phase has several advantages: environmentally harmful substances which are required in traditional procedures for the oxidation of alcohols can easily be replaced by atmospheric oxygen. Also, the whole reaction in water is very efficient, even at moderate temperatures.

Charge transfer between water and catalyst

The theoretical chemists have studied what happens in the catalysis at the molecular level by means of so-called ab initio molecular dynamics simulations. The result: a charge transfer takes place between the water and the catalyst. Electrons, or more specifically portions of electron densities, are moved between the solid and the liquid phase. The researchers speculate that in this way the liquid phase stabilises charge states on the gold surface. The sites where this occurs could be the active centres of the catalyst, where the chemical reactions work efficiently. Unlike water, a gas phase is not able to “talk” to the catalyst in this way, because no charge transfer is possible with the gas phase.

Increasing the efficiency through thermodynamics

In a further study, the team led by Dominik Marx examined a related metal/oxide catalyst of copper and zinc oxide, which is used for the large-scale industrial synthesis of methanol. As the computer simulations showed, especially the interplay between the solid phase and the gas phase is important here for the efficiency. Depending on the pressure and temperature conditions, hydrogen binds to the catalyst surface and thus indirectly stabilises catalytically active centres that occur in this case due to an electron transfer between the metal and the oxide. “Without the hydrogen, put bluntly the centres would not exist”, says Marx. In this way, the thermodynamic conditions in the gas phase put the surface into a certain state which is particularly favourable for the work of the catalyst.

Added value through combination

The two studies thus show that the catalytic efficiency can be controlled both by a solvent and by thermodynamics – namely through the pressure and temperature of the gas phase. However, completely different mechanisms are responsible for this, which the researchers were nevertheless able to elucidate using the same simulation methods. This makes the results directly comparable. In this way, the theorists aim to study in future whether they can improve the copper/zinc oxide system even further by replacing the gas phase with a suitable solvent.

Funding

The chemists at the RUB explore the active role of the solvent in catalytic reactions in the Excellence Cluster “Ruhr Explores Solvation” RESOLV (EXC 1069), which was approved by the German Research Foundation in June 2012.

Bibliographic records

M. Farnesi Camellone, D.Marx (2013). On the Impact of Solvation on a Au/TiO2 Nanocatalyst in Contact with Water, The Journal of Physical Chemistry Letters, doi: 10.1021/jz301891v

L. Martínez-Suárez, J. Frenzel, D. Marx, B. Meyer (2013): Tuning the Reactivity of a Cu/ZnO Nanocatalyst via Gas Phase Pressure, Physical Review Letters, doi: 10.1103/PhysRevLett.110.086108

Further information

Prof. Dr. Dominik Marx, Centre for Theoretical Chemistry, Department of Chemistry and Biochemistry at the Ruhr-Universität, 44780 Bochum, Germany, Tel.+49/234/32-28083, E-mail: dominik.marx@rub.de

Click for more

Theoretical Chemistry at the RUB
http://www.theochem.rub.de/home.en.html
Solvation Science@RUB (RESOLV)
http://www.rub.de/solvation/
Editor: Dr. Julia Weiler

Dr. Josef König | idw
Further information:
http://www.ruhr-uni-bochum.de

More articles from Life Sciences:

nachricht Toward a 'smart' patch that automatically delivers insulin when needed
18.01.2017 | American Chemical Society

nachricht 127 at one blow...
18.01.2017 | Stiftung Zoologisches Forschungsmuseum Alexander Koenig, Leibniz-Institut für Biodiversität der Tiere

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

A big nano boost for solar cells

18.01.2017 | Power and Electrical Engineering

Glass's off-kilter harmonies

18.01.2017 | Materials Sciences

Toward a 'smart' patch that automatically delivers insulin when needed

18.01.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>