Protein switches are active everywhere in the body and often affect the generation of diseases. Thanks to a special method, researchers from Bochum have gained new insights into their workings. Using a combination of infrared spectroscopy and computer simulation, researchers at Ruhr-Univers ... more
Processes at the Surface of CatalystsUsing Infrared Spectroscopy, Scientists Detect that Oxygen Defects Act as Active Centers
Chemistry of defects: Defect concentration on rutile surfaces of both monocrystals and powder particles can be determined by infrared spectroscopy using carbon monoxide as a probe molecule.
In chemical industry, heterogeneous catalysis is of crucial importance to the manufacture of basic or fine chemicals, in catalytic converters of exhaust gas, or for the chemical storage of solar energy. Scientists of Karlsruhe Institute of Technology (KIT) and Ruhr-Universität Bochum (RUB) have developed a new infrared spectroscopy method in order to study processes at surfaces of oxides used as catalysts. Their results are published in the renowned “Angewandte Chemie” journal.
Highly complex chemical processes
Catalysts support many chemical reactions. In heterogeneous catalysis, the substance used as a catalyst and the reacting substances exist in various phases. Usually, the catalyst is a solid, while the reacting substances are gaseous. At the surface of catalytically active solids, highly complex chemical processes take place. They have to be understood in detail in order to further improve products and reduce costs. The processes are known well for metals. However, conversions at the surface of oxides – compounds of metals or non-metals with oxygen – have hardly been studied so far.
Bridging the gap between fundamental and applied research
The research team of Professor Christof Wöll from KIT and Professor Martin Muhler from RUB first studied processes at surfaces of oxide monocrystals and then transferred the findings to powders, the technically most important form of oxide materials. Doing this, they were the first to bridge the gap between fundamental research into reference systems and applied research into real catalysts. A newly developed combination device for infrared spectroscopy (IR) allows for highly precise measurements of the vibration frequency of carbon monoxide. The exact value of this vibration frequency is highly sensitive to defects.
High catalytic activity
Such defects result from the removal of individual oxygen atoms from oxide materials. “Oxygen defects act as active centers and give the material a high catalytic activity,” explains Professor Christof Wöll, Director of the Institute of Functional Interfaces (IFG) of KIT. With the new combination device for infrared spectroscopy, the researchers from Karlsruhe and Bochum developed a method that was first calibrated for reference systems. For the first time, they then measured defect densities of real catalyst powders using a high-performance FTIR spectrometer made by Bruker Optics (VERTEX series).
Defects have only been detected indirectly so far
To demonstrate their new method, the researchers used rutile, the most important modification of titanium dioxide (TiO2). “This material used as white pigment and in photocatalysis normally is chemically highly inert and rendered catalytically active by the oxygen defects only,” explains Professor Christof Wöll. Professor Martin Muhler from RUB points out that such defects in powder materials have only been detected indirectly so far.
“Surface Science” approach
With their method, the researchers, including Dr. Mingchun Xu, Dr. Heshmat Noei, and Dr. Yuemin Wang from RUB as well as Dr. Karin Fink from the Institute of Nanotechnology (INT) of KIT, followed the “Surface Science” approach developed by the Noble Prize laureate Gerhard Ertl. They demonstrated the potential of their method by studying the carbon-carbon coupling reaction of formaldehyde to ethylene. Doing this, it was confirmed that the density of oxygen defects at the surface of r-TiO2 nanoparticles is of decisive importance to the catalytic activity of the oxide powder and, hence, to the yield.
- infrared spectroscopy
- Ruhr-Universität Bochum
- FT-IR spectrometers
Molecules from the solvent environment that at first glance seem to be uninvolved can be essential for chemical reactions. This has been shown by researchers studying the formation of an ether in pure solvents and in their mixtures. They explained the underlying mechanisms in detail using a ... more
Using molecular dynamics simulations, researchers have analysed the properties of supercritical water. The researchers showed which structure of the hydrogen bond network is formed in different supercritical states and also simulated the relevant terahertz spectra. This approach may help in ... more
Optical microscopy is applied widely in the life sciences sector. Among others, it is used to minimally invasively examine living cells. Resolution of conventional light microscopy, however, is limited to half the wavelength of light, i.e. about 200 nm, such that finest cellular structures ... more
Scientists using computational techniques to look at processes in DNA have employed a surface-hopping approach to predict the degree of charge localisation across nucleobases. The technique should allow more accurate modeling of the effects of charge transfer within the molecule. Different ... more
The world’s smallest tunnels have a width of a few nanometers only. Researchers from Karlsruhe Institute of Technology (KIT) and Rice University, USA, have dug such tunnels into graphite samples. This will allow structuring of the interior of materials through self-organization in the nanom ... more