Featured Research

from universities, journals, and other organizations

When water speaks: Solvents make catalysts more efficient

Date:
February 21, 2013
Source:
Ruhr-Universitaet-Bochum
Summary:
Why certain catalyst materials work more efficiently when they are surrounded by water instead of a gas phase is unclear. Chemists have now gleaned some initial answers from computer simulations. They showed that water stabilizes 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.
Credit: M. Farnesi Camellone, D. Marx

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

"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.


Story Source:

The above story is based on materials provided by Ruhr-Universitaet-Bochum. Note: Materials may be edited for content and length.


Journal References:

  1. Matteo Farnesi Camellone, Dominik Marx. On the Impact of Solvation on a Au/TiO2Nanocatalyst in Contact with Water. The Journal of Physical Chemistry Letters, 2013; 4 (3): 514 DOI: 10.1021/jz301891v
  2. Luis Martνnez-Suαrez, Johannes Frenzel, Dominik Marx, Bernd Meyer. Tuning the Reactivity of a Cu/ZnO Nanocatalyst via Gas Phase Pressure. Physical Review Letters, 2013; 110 (8) DOI: 10.1103/PhysRevLett.110.086108

Cite This Page:

Ruhr-Universitaet-Bochum. "When water speaks: Solvents make catalysts more efficient." ScienceDaily. ScienceDaily, 21 February 2013. <www.sciencedaily.com/releases/2013/02/130221084705.htm>.
Ruhr-Universitaet-Bochum. (2013, February 21). When water speaks: Solvents make catalysts more efficient. ScienceDaily. Retrieved July 25, 2014 from www.sciencedaily.com/releases/2013/02/130221084705.htm
Ruhr-Universitaet-Bochum. "When water speaks: Solvents make catalysts more efficient." ScienceDaily. www.sciencedaily.com/releases/2013/02/130221084705.htm (accessed July 25, 2014).

Share This




More Matter & Energy News

Friday, July 25, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

TSA Administrator on Politics and Flight Bans

TSA Administrator on Politics and Flight Bans

AP (July 24, 2014) — TSA administrator, John Pistole's took part in the Aspen Security Forum 2014, where he answered questions on lifting of the ban on flights into Israel's Tel Aviv airport and whether politics played a role in lifting the ban. (July 24) Video provided by AP
Powered by NewsLook.com
Creative Makeovers for Ugly Cellphone Towers

Creative Makeovers for Ugly Cellphone Towers

AP (July 24, 2014) — Mobile phone companies and communities across the country are going to new lengths to disguise those unsightly cellphone towers. From a church bell tower to a flagpole, even a pencil, some towers are trying to make a point. (July 24) Video provided by AP
Powered by NewsLook.com
Algonquin Power Goes Activist on Its Target Gas Natural

Algonquin Power Goes Activist on Its Target Gas Natural

TheStreet (July 23, 2014) — When The Deal's Amanda Levin exclusively reported that Gas Natural had been talking to potential suitors, the Ohio company responded with a flat denial, claiming its board had not talked to anyone about a possible sale. Lo and behold, Canadian utility Algonquin Power and Utilities not only had approached the company, but it did it three times. Its last offer was for $13 per share as Gas Natural's was trading at a 60-day moving average of about $12.50 per share. Now Algonquin, which has a 4.9% stake in Gas Natural, has taken its case to shareholders, calling on them to back its proposals or, possibly, a change in the target's board. Video provided by TheStreet
Powered by NewsLook.com
Robot Parking Valet Creates Stress-Free Travel

Robot Parking Valet Creates Stress-Free Travel

AP (July 23, 2014) — 'Ray' the robotic parking valet at Dusseldorf Airport in Germany lets travelers to avoid the hassle of finding a parking spot before heading to the check-in desk. (July 23) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

    Health News

      Environment News

        Technology News



          Save/Print:
          Share:  

          Free Subscriptions


          Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

          Get Social & Mobile


          Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

          Have Feedback?


          Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
          Mobile iPhone Android Web
          Follow Facebook Twitter Google+
          Subscribe RSS Feeds Email Newsletters
          Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins