Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

How the newest diesel engines emit very little greenhouse gas nitrous oxide

11.09.2013
The latest catalytic converters reduce pollution by unusual mechanism

The newest catalytic converters in diesel engines blast away a pollutant from combustion with the help of ammonia. Common in European cars, the engines exhaust harmless nitrogen and water. How they do this hasn't been entirely clear. Now, new research shows that the catalyst attacks its target pollutant in an unusual way, providing insight into how to make the best catalytic converters.


This computer model of a zeolite catalyst shows nitric oxide (ball-and-stick) interacting with a positively charged copper ion (copper ball) at an unexpected angle (red dotted lines).
Photo courtesy of Kwak et al.

Reporting in the journal Angewandte Chemie International Edition, a team of researchers in the Institute for Integrated Catalysis at the Department of Energy's Pacific Northwest National Laboratory led by chemist Janos Szanyi showed that the artificial catalyst works much the same way that similar bacterial enzymes do: by coming at the target from the side rather than head on.

"What I find exciting is the correlation between this artificial catalysis and enzyme catalysis," said Szanyi. "Nature is telling us what to do. Nature's been at it for many millions of years, and it does this beautifully."

Surprise Chemistry

Zeolites are crystalline alumino-silicate minerals that can accommodate metal ions — metal atoms with a slight charge — for catalytic applications. In some catalytic zeolites, the metal ions can break down the pollutant nitric oxide in vehicle emissions. However, the zeolites crumble and clog easily, leading to early failure. In addition, they produce as a byproduct the greenhouse gas nitrous oxide (known to dental patients everywhere as laughing gas).

Recently, researchers have produced a new zeolite that is surprisingly stable and makes very little nitrous oxide from nitric oxide, a chemical that depletes ozone. The zeolite produces mainly water and atmospheric nitrogen — the main component of air — but it needs to be fed ammonia, such as from urea.

Some of the diesel vehicles in Europe are now using this catalyst, and drivers must top off their urea tank as well as their diesel. Called Cu-SSZ-13, the zeolite uses copper as its added metal and has smaller spaces in its alumino-silicate scaffolding compared to other zeolites.

Researchers have assumed that this zeolite would break down nitric oxide in the same way that other zeolites do, following the same series of chemical reaction steps. However, something else must be going on because researchers can make the older zeolites work faster by adding nitrogen dioxide — but Cu-SSZ-13 doesn't respond in the same way. This indicates Cu-SSZ-13 must be taking a different chemical route.

To explore how Cu-SSZ-13 breaks down nitric oxide, the team of researchers investigated the structure of the zeolite in the process of performing the reaction. Using tools designed to find such answers at EMSL, DOE's Environmental Molecular Sciences Laboratory on PNNL's campus, team members first looked at what molecules stuck to the surface of the zeolite.

There they unexpectedly found a charged nitric oxide molecule bound to the copper ions. This molecular combination could only happen one of two ways, the more common of which requires the presence of nitrogen dioxide. Because the researchers saw no nitrogen dioxide, they ruled out that common reaction pathway.

That left the copper metal itself directly hooking up with nitric oxide. In the process, copper borrows one of nitric oxide's electrons, giving nitric oxide a charge. This early theft sets the stage for ammonia to react with the charged nitric oxide in the first of several chemical steps, ultimately pumping out atmospheric nitrogen and water.

Catalysis Imitating Life

Zooming in on the zeolite's structure and reconstructing it with NWChem, software that models molecular chemistry, the team found something unusual. In most zeolite catalysts, nitric oxide is essentially a barbell combining a nitrogen atom and an oxygen atom. The barbell is bound to the metal atom on its head, most often at the nitrogen end of the molecule. However, in Cu-SSZ-13, the copper metal bonded with both the nitrogen and the oxygen halves of the nitric oxide barbell, as if the copper and nitric oxide formed a three-membered ring. Chemists refer to this orientation as "side-on".

"The side-on complex is uncommon in this type of synthetic catalysis," said Szanyi. "But bacteria have an enzyme called nitrite reductase that works this way. This enzyme breaks down nitrites into atmospheric nitrogen."

The chemists also determined that the side-on angle causes the barbell to bend slightly. With no bend, the angle is 180 degrees, but positioned within the zeolite, the angle between the nitrogen and oxygen is about 146 degrees.

The computer reconstruction of Cu-SSZ-13 in action showed the spaces within the aluminum and silicon lattice can only hold one nitric oxide molecule. Other zeolites have almost twice as much space for the nitric oxide to move around.

"The small pore size just fits the reactants and provides precise control," said Szanyi. "This reaction mechanism explains the prior studies — things like why we don't get nitrous oxide."

The researchers are continuing to explore whether this side-on intermediate is common in other catalyst materials and in other reactions.

This work was supported by the Department of Energy Office of Energy Efficiency and Renewable Energy.

Reference: Ja Hun Kwak, Jong H. Lee, Sarah D. Burton, Andrew S. Lipton, Charles H. F. Peden, and Janos Szanyi. A Common Intermediate for N2 Formation in Enzymes and Zeolites: Side-On Cu-Nitrosyl Complexes, Angewandte Chemie International Edition, Aug. 12, 2013, doi: 10.1002/anie.201303498.

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

More articles from Ecology, The Environment and Conservation:

nachricht A new indicator for marine ecosystem changes: the diatom/dinoflagellate index
21.08.2017 | Leibniz-Institut für Ostseeforschung Warnemünde

nachricht Value from wastewater
16.08.2017 | Hochschule Landshut

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

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

Im Focus: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

Nagoya physicists resolve long-standing mystery of structure-less transition

21.08.2017 | Materials Sciences

Chronic stress induces fatal organ dysfunctions via a new neural circuit

21.08.2017 | Health and Medicine

Scientists from the MSU studied new liquid-crystalline photochrom

21.08.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>