Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

'Hot' oxygen atoms on titanium dioxide motivated by more than just temperature

12.02.2008
PNNL scientists find unexpected chemical behavior on catalyst surface

Like two ballroom dancers waltzing together, the two atoms of an oxygen molecule severed by a metal catalyst usually behave identically. But new research reveals that on a particular catalyst, split oxygen atoms act like a couple dancing the tango: one oxygen atom plants itself while the other shimmies away, probably with energy partially stolen from the stationary one.

Scientists from the Department of Energy's Pacific Northwest National Laboratory found the unanticipated behavior while studying how oxygen interacts with reduced titanium oxide surfaces. The chemists are trying to understand how molecular oxygen -- the stuff we breathe -- interacts with metals and metal oxides, which are used as catalysts in a variety of environmental and energy applications. Researchers worldwide are exploring the use of titanium dioxide, especially in hydrogen production for solar fuel cells.

The team was a bit surprised by the unequal sharing of resources among the oxygen atoms.

"It is unique that one atom stays in place and the other one is mobile and probably gets most of the energy," says lead scientist Igor Lyubinetsky, who performed the work at the The Environmental Molecular Sciences Laboratory, a DOE national scientific user facility located at PNNL, with funding by DOE's Office of Basic Energy Sciences. Their work will be published as the cover article in the Journal of Physical Chemistry C on February 21, 2008, and previously appeared online January 5, 2008.

Researchers have yet to determine if this short-lived extra mobility plays a role in chemical reactions, but understanding the basic chemistry might be important in processes that break down pollutants or split water to generate hydrogen.

Previous research has revealed much about how oxygen molecules interact with metals. For example, when molecular oxygen (O2) hits a platinum surface, the platinum helps split the molecule apart and each oxygen atom zips over the surface in opposite directions, eventually sticking to the metal. Chemists call the pumped up atoms "hot" because the extra energy released by the breaking and reforming bonds gives the atoms their boost.

Titanium dioxide is not only a popular catalyst, but it also serves as a great model oxide to study basic chemistry. PNNL scientists, led by Lyubinetsky, wanted to know if molecular oxygen behaved on titanium dioxide the way it behaves on metals such as platinum. Oxides have different properties than metals: Rust, for example, is iron oxide, which flakes off from iron metal.

To find out, the team started with a slice of titanium oxide crystal, oriented so that titanium and oxygen atoms line up on the surface in alternating strips, forming grooves of titanium troughs between oxygen rows. By heating the sample, the team created imperfections on the surface, or spots where an oxygen atom vacated its row. Using scanning tunneling microscopy, the researchers found that molecular oxygen only broke apart when it encountered a vacancy, indicating that oxygen molecules bounce along flawless titanium oxide surfaces and don't react, as expected from previous results.

The team also expected one of the atoms to make the vacancy its home, and the second to situate itself right next to its former partner. Instead, the chemists found that the second oxygen behaved like a "hot" atom and was free to move one or two crystal lattice spaces away. Out of 110 molecules the team counted, more than three quarters of the hot atoms hopped one or two spaces away before becoming mired on the surface.

"This is one of the first time chemists have looked at oxygen on metal oxides at the atomic level, and this finding was unexpected," says Lyubinetsky.

But a skittering atom requires some sort of energy to propel it, so the researchers explored how a splitting oxygen molecule divvied up its energetic resources. The team found that a free oxygen atom at room temperature (about 20 C or 68 F) is virtually immobile on a titanium oxide surface. However, previous calculations have suggested that the energy is released from the rearrangement of the bonds -- from within the oxygen molecule and between the oxygen atom and titanium surface -- and the team has concluded this might be the source of the hot atom's burst after its partner anchored itself in the vacancy: the calculated energy was about two to three times that required to get an immobilized oxygen unstuck. Lyubinetsky postulates that the hot oxygen atom uses this energy to move around on the titanium oxide surface.

The scientists are trying to better understand the mechanism because it might be significant in basic catalytic chemistry.

"This finding may be important in surface reactivity. We don't know yet," Lyubinetsky says. The chemical event could, for example, be affected by the extra energy the oxygen atom possesses. The effect might also play into whether surface oxygen atoms interfere with the chemistry between the catalyst and other reagents.

In any event, the result will keep chemists tango-ing with new questions for a long time.

The team published their results in the following paper: Y. Du, Z. Dohnalek, and I. Lyubinetsky, Transient Mobility of Oxygen Adatoms upon O2 Dissociation on Reduced TiO2(110), J. Phys. Chem. C, 2008, 10.1021/jp077677u. Published online January 5, 2008; print February 21, 2008

The William R. Wiley Environmental Molecular Sciences Laboratory is a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory.

PNNL is a DOE Office of Science national laboratory that solves complex problems in energy, national security and the environment, and advances scientific frontiers in the chemical, biological, materials, environmental and computational sciences. PNNL employs 4,000 staff, has a $760 million annual budget, and has been managed by Ohio-based Battelle since the lab's inception in 1965.

Mary Beckman | EurekAlert!
Further information:
http://www.pnl.gov

More articles from Physics and Astronomy:

nachricht Immortal quantum particles: the cycle of decay and rebirth
14.06.2019 | Technische Universität München

nachricht Small currents for big gains in spintronics
13.06.2019 | University of Tokyo

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

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

Im Focus: MPSD team discovers light-induced ferroelectricity in strontium titanate

Light can be used not only to measure materials’ properties, but also to change them. Especially interesting are those cases in which the function of a material can be modified, such as its ability to conduct electricity or to store information in its magnetic state. A team led by Andrea Cavalleri from the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg used terahertz frequency light pulses to transform a non-ferroelectric material into a ferroelectric one.

Ferroelectricity is a state in which the constituent lattice “looks” in one specific direction, forming a macroscopic electrical polarisation. The ability to...

Im Focus: Determining the Earth’s gravity field more accurately than ever before

Researchers at TU Graz calculate the most accurate gravity field determination of the Earth using 1.16 billion satellite measurements. This yields valuable knowledge for climate research.

The Earth’s gravity fluctuates from place to place. Geodesists use this phenomenon to observe geodynamic and climatological processes. Using...

Im Focus: Tube anemone has the largest animal mitochondrial genome ever sequenced

Discovery by Brazilian and US researchers could change the classification of two species, which appear more akin to jellyfish than was thought.

The tube anemone Isarachnanthus nocturnus is only 15 cm long but has the largest mitochondrial genome of any animal sequenced to date, with 80,923 base pairs....

Im Focus: Tiny light box opens new doors into the nanoworld

Researchers at Chalmers University of Technology, Sweden, have discovered a completely new way of capturing, amplifying and linking light to matter at the nanolevel. Using a tiny box, built from stacked atomically thin material, they have succeeded in creating a type of feedback loop in which light and matter become one. The discovery, which was recently published in Nature Nanotechnology, opens up new possibilities in the world of nanophotonics.

Photonics is concerned with various means of using light. Fibre-optic communication is an example of photonics, as is the technology behind photodetectors and...

Im Focus: Cost-effective and individualized advanced electronic packaging in small batches now available

Fraunhofer IZM is joining the EUROPRACTICE IC Service platform. Together, the partners are making fan-out wafer level packaging (FOWLP) for electronic devices available and affordable even in small batches – and thus of interest to research institutes, universities, and SMEs. Costs can be significantly reduced by up to ten customers implementing individual fan-out wafer level packaging for their ICs or other components on a multi-project wafer. The target group includes any organization that does not produce in large quantities, but requires prototypes.

Research always means trying things out and daring to do new things. Research institutes, universities, and SMEs do not produce in large batches, but rather...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

SEMANTiCS 2019 brings together industry leaders and data scientists in Karlsruhe

29.04.2019 | Event News

Revered mathematicians and computer scientists converge with 200 young researchers in Heidelberg!

17.04.2019 | Event News

First dust conference in the Central Asian part of the earth’s dust belt

15.04.2019 | Event News

 
Latest News

Concert of magnetic moments

14.06.2019 | Information Technology

Materials informatics reveals new class of super-hard alloys

14.06.2019 | Materials Sciences

New imaging modality targets cholesterol in arterial plaque

14.06.2019 | Medical Engineering

VideoLinks
Science & Research
Overview of more VideoLinks >>>