654 kb PDF, Nobel prize lecture for Chemistry on December 2008: physical chemistry of surfaces
Abstract:
This 2007 Nobel lecture in Chemistry is an exciting presentation of the physics and chemistry of catalytic reactions at surfaces, and much more, dwelling on interesting aspects of the physics of complex systems, self-organization, and pattern formation leading to life. Very clearly presented and really exciting Nobel lecture with artistic visuals, such as Van Gogh's "Starry Night" color image of the painting (in the context of pattern formation). The author is a German physicist who has worked both on physical and physical chemistry problems associated with 'clean' surfaces and interfaces. He presents in this lecture most remarkable, very high quality images and illustrations of such clean surfaces along with most interesting computer simulations of the surface reaction patterns. From the Nobel Laureate's own Introduction is the following paragraph:
"The secretary of the Royal Swedish Academy of Sciences, the famous chemist
Jo\"ns Jacob Berzelius, published since 1820 annual review articles on the most significant new developments in his field. Since the early 19th century there were observations from several laboratories whereafter certain substances influenced the progress of a chemical reaction without being consumed and hence apparently not being affected by this reaction. For example, Johann
Wolfgang Doebereiner, professor of chemistry at the university of Jena, reported in July 1823 to his minister, J. W. Goethe, "that finely divided platinum powder causes hydrogen gas to reaction with oxygen gas by mere contact to water whereby the platinum itself is not altered" [1]. In his report published 1835 Berzelius defined this phenomenon as "catalysis", rather in order to introduce a classification than to offer a possible explanation [2]. Throughout the rest of this century the term catalysis remained heavily debated [3], until around 1900 W. Ostwald proposed its valid definition in terms of the concepts of chemical kinetics: "A catalyst is a substance which affects the rate of a chemical reaction without being part of its end products" [4]. In 1909, Ostwald was awarded the Nobel Prize in Chemistry for his contributions to catalysis. A chemical reaction involves breaking of bonds between atoms and the
formation of new ones. This process is associated with transformation of energy
and the energy diagram illustrating the progress of a reaction A+B--><---C is
depicted schematically in fig. 1. The activation energy E* to be surmounted
is usually provided by thermal energy kT, with k being Boltzmann’s constant
and T the temperature, and accordingly not all molecular encounters will be
successful, but only a fraction exp(-E*/kT). An increase of the reaction probability (=rate) can be achieved by either increasing the temperature or by lowering the activation energy E*. The latter is provided by the catalyst which through the formation of intermediate compounds with the molecules involved in the reaction provides an alternate reaction path..."=====
"Under isothermal conditions at low pressures local differences of the
surface concentrations cause surface diffusion of the adsorbates, and
mathematical description can now be obtained in terms of reaction-diffusion
equations, i.e. a set of coupled nonlinear partial differential equations combining the kinetics with the diffusion of the adsorbed species (fig. 20).
Figure 20. Spatio-temporal self-organisation in open systems far from equilibrium." The length scale of the resulting spatio-temporal concentration patterns is no longer governed by atomic dimensions but by the so-called diffusion length, which in our case is of the order of tens of microns [45]. These patterns were imaged by the technique of photoemission electron microscopy (PEEM) [46]: Adsorbed O and CO species are accompanied by different electric dipole moments and hence different work function changes which in turn
give rise to varying intensities of photoemitted electrons. Under other external parameters typical spiral waves as shown in fig. 22 develop and propagate with front speeds of a few micro-meter/s. The core of a spiral
is often formed by a region on the surface with enhanced defect density, and
this effect is also responsible for the fact that the wavelengths of the spiral
vary to some extent [48].Figure 22. PEEM image from the formation of spiral-waves in catalytic CO oxidation on a Pt(110) surface [48].Since the mechanism of this reaction and all its parameters are well established
experimentally, these data may also be used to simulate the resulting
patterns by numerical solution of the underlying differential equations. This
is shown in fig. 23 for the case of spiral wave development [49]. If the parameters are slightly changed, the solution exhibits no longer regular spirals, but they break-up to the situation of spiral-turbulence or spatio-temporal chaos (fig. 24). Experimental verification of such a situation is demonstrated by fig. 25. Figure 23. Computer simulation of the evolution of spiral waves in catalytic CO oxidation [49];... Figure 24. Computer simulation of the break-up of spiral waves to chemical turbulence;...Figure 25. PEEM image from a Pt(110) surface in the state of chemical turbulence."
