Catalysis: Blueprint for a break-up
Computer simulations reveal how rhodium catalysts with ‘stepped’ surface structures break ethanol molecules into hydrogen atoms and why they are so efficient
Hydrogen gas (H2) is an ideal energy carrier for fuel cells, but finding sustainable ways to produce large quantities of hydrogen continues to be a technological challenge. Jia Zhang at the A*STAR Institute of High Performance Computing and co-workers have now used sophisticated calculations to uncover a critical chemical mechanism that may make catalytic transformation of safe, renewable liquid ethanol into hydrogen fuel easier than ever before.
Currently, steam reforming is the popular method for producing hydrogen gas from ethanol. In this technique, ethanol is injected into a hot, steam-filled chamber containing a catalyst such as rhodium. The catalyst promotes the dissociation of ethanol molecules into smaller molecules, such as carbon monoxide and H2. Although chemists have had good success in using steam reforming to ‘crack’ ethanol, they have had difficulties in improving the efficiency of the catalyst because of the many diverse and complex chemical reactions at play in the system.
According to Zhang, catalysts need to selectively crack the carbon–carbon bonds of surface-adsorbed ethanol to be viable for steam reforming. Recent experimental efforts have shown that ‘stepped’ catalyst surfaces — tiny staircase-like defects present in a normally flat rhodium surface — are unusually active at both carbon-hydrogen and carbon–carbon bond cleaving. One problem, however, is that the actual mechanism of ethanol decomposition on stepped surfaces is still unclear.
The research team overcame this challenge by using high-powered computer simulations to work out which ethanol decomposition pathways are most probable on a particular stepped rhodium surface known as rhodium (211). Exhaustive calculations using density functional theory (DFT) methods revealed that there were two ways of breaking ethanol down into H2, and both shared a common intermediate species with the chemical formula CH3COH.
Crucially, the team found that this CH3COH intermediate exists only on stepped rhodium surfaces. While flat catalyst surfaces fracture ethanol through an oxametallacycle intermediate, the step-type defects preferentially absorb the alcohol and then activate the decomposition cycle by sequentially removing hydrogen atoms from the intermediate. The researchers note that the surface-sensitivity of ethanol steam reforming is an important finding because step-defects are extremely common on state-of-the-art nanoscale rhodium catalysts.
“Steam reforming is a very complicated chemical process, and our current DFT study on ethanol decomposition mechanism is just the tip of the iceberg — many factors such as temperature, concentration, substrate influence, and water effects can influence the results,” says Zhang. “However, this work is an important first step for establishing theoretical rules to guide development of new, high-performance catalyst materials.”
The A*STAR-affiliated researchers contributing to this research are from the Institute of High Performance Computing
Zhang, J. et al. Density functional theory studies of ethanol decomposition on Rh(211). Journal of Physical Chemistry C 115, 22429–22437 (2011)
A*STAR Research | Research asia research news
The most recent press releases about innovation >>>
Die letzten 5 Focus-News des innovations-reports im Überblick:
Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.
For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...
What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.
To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...
A bacterial enzyme enables reactions that open up alternatives to key industrial chemical processes
The research team of Prof. Dr. Oliver Einsle at the University of Freiburg's Institute of Biochemistry has long been exploring the functioning of nitrogenase....
Larsen C Ice Shelf rift finally breaks through
A one trillion tonne iceberg - one of the biggest ever recorded -- has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice,...
Physics supports biology: Researchers from PTB have developed a model system to investigate friction phenomena with atomic precision
Friction: what you want from car brakes, otherwise rather a nuisance. In any case, it is useful to know as precisely as possible how friction phenomena arise –...