Catalytic converters for cleaning exhaust emissions are more efficient when they use nanoparticles with many edges. This is one of the findings of a study carried out at DESY's X-ray source PETRA III. A team of scientists from the DESY NanoLab watched live as noxious carbon monoxide was converted into common carbon dioxide on the surface of noble metal nanoparticles like those used in catalytic converters of cars. The scientists are presenting their findings in the journal Physical Review Letters. Their results suggest that having a large number of edges increases the efficiency of catalytic reactions, as the different facets of the nanoparticles are often covered by growing islands of a nano oxide, finally rendering these facets inactive. At the edges, the oxide islands cannot connect, leaving active sites for the catalytic reaction.
Catalytic converters usually use nanoparticles because these have a far greater surface area for a given amount of the material, on which the catalytic reaction can take place. For the study presented here, the scientists at DESY's NanoLab grew platinum-rhodium nanoparticles on a substrate in such a way that virtually all the particles were aligned in the same direction and had the same shape of truncated octahedrons (octahedrons resemble double pyramids). The scientists then studied the catalytic properties of this sample under the typical working conditions of an automotive catalytic converter, with different gaseous compositions in a reaction chamber that was exposed to intense X-rays from PETRA III on the P09 beamline.
[...] The investigation showed that the reactivity of the nanoparticles increases sharply at a certain oxygen concentration. "This happens when just enough oxygen is available to oxidise each carbon monoxide molecule and turn it into carbon dioxide," says Stierle. Beyond that concentration, the reactivity gradually drops again because a thick oxide layer grows on the surface of the particles, impeding the reaction. The X-ray analysis reveals the atomic structure of the surface of the nanoparticles at the best resolution yet under the conditions at which the reaction occurs. This shows that once a certain oxygen concentration is exceeded, the different crystal faces of the nanoparticles become coated with an oxygen-rhodium-oxygen sandwich, until eventually the surface of the metal is completely covered by this nano oxide layer.
"The surface oxide eventually forms a closed layer over the nanoparticles," reports Hejral. "This is unfavourable for the desired reaction at first, because it makes it difficult for carbon monoxide molecules to attach themselves to the surface. However, the oxygen is unable to form a closed film along the edges between the faces of the nanoparticles, which means that the reactivity along the edges is higher." This finding suggests a direct pathway to making catalytic converters more efficient: "We would expect catalytic converters to be increasingly efficient the more edges the nanoparticles have for a given surface area," says Stierle. This finding can probably also be applied to many other catalytic reactions. Additional studies will have to show by how much the efficiency can be increased as a result.
(Score: 5, Funny) by DannyB on Thursday March 29 2018, @02:03PM (8 children)
So how quick will car manufacturers incorporate an innovation like this?
I hope Tesla is all over this.
Why is it that when I hold a stick, everyone begins to look like a pinata?
(Score: 2) by bart9h on Thursday March 29 2018, @02:39PM (7 children)
Do electric cars have exhaust emissions?
(Score: 2) by broggyr on Thursday March 29 2018, @03:47PM (3 children)
What's that whooshing sound? :D
Taking things out of context since 1972.
(Score: 0) by Anonymous Coward on Thursday March 29 2018, @04:17PM
exhaust emissions
(Score: 3, Funny) by DannyB on Thursday March 29 2018, @05:24PM (1 child)
That whooshing sound means you need to replace the belts on your catalytic converter, and soon!
The server will be down this weekend for replacement of vacuum tubes, belts, worn parts and lubrication of gears and bearings.
We appreciate your patience.
Why is it that when I hold a stick, everyone begins to look like a pinata?
(Score: 0) by Anonymous Coward on Thursday March 29 2018, @11:42PM
https://en.wikipedia.org/wiki/Smog_pump [wikipedia.org]
The catalytic converter is like a muffler welded into your exhaust system! (Depending on the car they are actually welded or bolted in. In California they require a stamped serial number if replaced, or look close enough to OEM that a smog tech won't flag it. Smog Pumps were a big deal on cars between 75 and ~85, mostly american, along with a few foreign cars, both japanese and european.)
(Score: 2) by DannyB on Thursday March 29 2018, @05:20PM (2 children)
If the electricity is generated by clean coal, then they do have exhaust emissions.
Oh, wait. I said clean coal. We're going to take all the coal and clean it all up.
Why is it that when I hold a stick, everyone begins to look like a pinata?
(Score: 2) by bob_super on Thursday March 29 2018, @05:32PM (1 child)
Is it more efficient to clean coal when it has edges and corners ?
Like, very flat, with 4 edges and 4 corners. Flat and a few inches long, a few inches wide. It will clean easier if it's green too, and for an easier check of cleanliness, put a dead inventor's picture on it.
Yep, that's the right form factor for optimum clean coal, right there!
(Score: 2) by DannyB on Thursday March 29 2018, @05:42PM
I don't know about more efficient. But is a lot neater if the clean coal comes in perfect cubes of the same size.
It is much easier for the children to stack. The children can come home in the same bright white clothes they were wearing when they left for work in the mines 16 hours earlier.
Why is it that when I hold a stick, everyone begins to look like a pinata?
(Score: 4, Funny) by requerdanos on Thursday March 29 2018, @02:05PM (2 children)
"In applications where having more surface area helps more gas get exposed to a surface, it helps if you have more surface area so more gas gets exposed to the surface (because there is more surface area)."
Thanks, guys. Good work.
(Score: 2) by RS3 on Thursday March 29 2018, @04:07PM
The article was ghost-written by Captain Obvious https://www.soundandvision.com/images/styles/600_wide/public/090914_Signals_promo.png [soundandvision.com]
(Score: 4, Interesting) by FatPhil on Thursday March 29 2018, @10:13PM
The nanoparticle crystals have faces with different surface 'textures', and the deposits seem to grow better on one texture (face centred cubic - a square grid arrangement of the atoms) than the neighbouring texture (body cenred cubic, IIRC). And therefore the growths come to a stop at the boundaries. Yay, goog science.
Buuuuuuuuuut, why couldn't the just make the surface the body-centred cubic one, everywhere? Science is hard...
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 2) by bart9h on Thursday March 29 2018, @02:36PM (2 children)
The surface area thing seems pretty intuitive to me.
What was less expected is that giving more oxygen than needed will decrease efficiency.
(Score: 0) by Anonymous Coward on Thursday March 29 2018, @03:01PM (1 child)
Combustion is already controlled carefully to be near stoichiometric (just enough oxygen to react with the fuel). At least part of this is so the "3-way catalyst" can treat the three major pollutants properly (someone else might understand the chemistry).
The one time I worked in an emissions lab was in the 1980s. I learned that, even back then, something called a wash coat was used on the inside of the ceramic catalyst to increase surface area. The area was remarkably huge, something like an acre (~1/6 hectare)...if my old memory can be trusted.
If this new invention increases the area even more, perhaps the package size of the catalyst can be decreased--car designers would be all in favor of this.
(Score: 3, Interesting) by RS3 on Thursday March 29 2018, @04:28PM
They're working on many new engine designs trying to improve combustion, but IC engines don't completely combust everything, hence the need for catalytic converters.
Actually they need excess oxygen in the exhaust. The catalytic converter unites that oxygen with the NO (nitrous oxide), CO (carbon monoxide), and generally unburned HC (hydrocarbons). The oxygen sensors in the exhaust keep the computer informed of how much oxygen is left over after combustion. Some cars need an air pump system that injects air (oxygen) into the exhaust stream. I've even seen some catalytic converters that have a small tube for air injection directly into the converter.