Last night, I was lulled to sleep by the sound of 2007 chemistry laureate Gerhard Ertl’s gentle voice. Ertl wasn’t in my hotel room, I hasten to add. I had switched on my television and there he was on local network giving an interview… in German, naturally.
I managed to identify a few words, such as “electron”, “atom”, “positive” and “negative” and so assumed he was discussing his prizewinning work in surface chemistry, which explained how fundamental molecular processes at the gas-solid interface take place. I thought to myself that it would be highly unlikely to come across such a good, old-fashioned technical interview on a UK television channel. Then I fell asleep.
This morning, from the window of a bus, I spotted Ertl in the middle of a roundabout — this time in the form of a giant black and white portrait in a gallery erected to publicize the 59th Lindau meeting.
Finally, there he was in the flesh – kicking off the meeting with a half hour talk about, you guessed it, surface chemistry.
When Ertl emerged as the sole recipient of the 2007 prize, some chemists expressed surprise that others were not recognized alongside him – a familiar story to the Nobel committee. But all agreed it was high time surface chemistry was recognized publicly. Before coming to Lindau this year, I certainly hadn’t appreciated just how far reaching this branch of chemistry is in our daily lives — not least in helping feed a sizeable fraction of the world’s population.
It’s simple when you think about it: the important stuff that takes place during a chemical reaction does so at surfaces, where the atoms have fewer neighbours and so are able to form new bonds or have their bonds broken. Surfaces are where catalysts – substances that alter the rate of a reaction without being part of the its end products – do their work, and this is where Ertl made his mark.
In the 1970s and 80s, using techniques such as scanning tunnelling microscopy, Ertl and his team at Ludwig Maximilian University in Munich determined the molecular mechanism that underpins the production of ammonia – the essential ingredient of fertilizer. More technically known as the Haber-Bosch process, which had been discovered 70 years earlier, this reaction sees a metal catalyst such as iron split atmospheric nitrogen molecules into atomic nitrogen, which then can combine with hydrogen to form ammonia.
During his talk, Erlt put up a sobering graph showing the growth in world population over the last century and the steep rise in the rate of ammonia production made possible in part by his unearthing of the solid–gas catalytic mechanism.
Gerhard Ertl starting his talk in Lindau (Credit: Fleming / www.lindau-nobel.de):
One life-enhancing chemical mystery solved, Ertl turned his attention to the mechanism by which carbon monoxide (CO) oxidizes on platinum surfaces – a reaction that take place in the catalytic converters now fitted to every car to make exhaust fumes less toxic. The rate of this reaction was thought to oscillate, and Ertl found that this was due to a cyclic process whereby the CO collects on two different crystalline phases of the platinum.
As CO accumulates on one phase, a hexagonal arrangement, it pushes the crystal into a more square-like phase which speeds up the oxidization until the surface saturates and slows down again, causing the crystal to return to its hexagonal phase. Ertl illustrated this behaviour, which can be described by a set of nonlinear differential equations, by analogy with the population dynamics of hares and lynxes: the lynx population grows as they find enough hares to eat, which causes the hare population to decline until the lynxes start to starve and die out themselves, allowing the hare population time to recover…
Ertl’s work opened up a whole world of such oscillatory reactions, some of which he showed us via films made using femtosecond laser spectroscopy. To him, the complex molecular dances, spirals and rhythms on the surfaces of solids resemble van Gogh’s “Star night” or the 4000 year old carvings on a stone in Malta.
And thanks to the following speaker at this morning’s session, the 1991 chemistry laureate Richard Ernst — who spoke about the importance of having passions and activities outside science and advised students not to be “one-sided nerds” — we now know the secret of Ertl’s surface success: he is an accomplished pianist with a passion for music.
|» Matthew Chalmers completed a PhD in physics and works as a freelance writer.|