Catalysis from first princples: Electrocatalysis meets heterogeneous catalysis
Location: Castle Reisensburg near Ulm/Germany
Organisers
Catalytic processes are of tremendous technological importance. It has been estimated that in the production of 90% of all chemicals synthesized today catalysts are involved in one way or the other and that approximately 20% of the World's GNP is directly related to industrial catalytic processes. In addition, catalysts are also used in order to convert hazardous chemicals into less harmful ones { the car-exhaust catalyst being the most prominent example. In the context of sustainable energy conversion, electrocatalytic processes as they occur in fuel cells are also gaining signicant attention.
In spite of considerable research efforts world-wide there are severe unsolved problems, in particular as far as catalyst materials are concerned. Most catalysts are based on expensive and rare platinum-group metals, but progress in the identification of more abundant, but equally active catalysts materials has been rather slow. Furthermore, there are certain technological tremendously important reactions such as the catalytic conversion of methane [1] in heterogeneous catalysis or the oxygen reduction reaction (ORR) [2] in electrocatalysis whose effciency is not sufficient enough but has not been significantly improved in the last years in spite of considerable research efforts. Here theoretical and computational studies from first principles can be rather helpful in deriving concepts that can contribute to the rational design of better catalysts.
Traditionally, there has been little contact between the scientific communities doing research in heterogeneous catalysis and electrocatalysis. In fact, there are quite some distinct differences between the two fields. In heterogeneous catalysis, reactions occur at solid/gas interfaces, whereas in electrocatalysis they occur at electrode/electrolyte interfaces. In heterogeneous catalysis, temperature and partial pressures of the reactands are external variables that can be tuned,
whereas in electrocatalysis the electrode potential and to a lesser extent the temperature can be modifiied. Still, at the microscopic level the basic bond-making and bond-breaking processes that occur in heterogeneous and in electrocatalysis obey the same fundamental principles. Even the same materials are often used in both fiellds, with platinum being probably the most popular metal in heterogeneous and in electrocatalysis. Furthermore, there are many elementary processes which are of interest in both fields. Prominently, the interaction of oxygen with late transition metals is a crucial process that takes place in the car-exhaust catalyst, but it also plays an eminent role in electrocatalysis in the oxygen reduction reaction occuring in fuel cells.
Methanol synthesis and oxidation are also catalyzed both at metal/gas and electrode/electrolyte interfaces.
The primary objective of this workshop is therefore to bring together experts from the fields of first-principles modeling of heterogeneous catalysis and electrocatalysis, in order to identify the common underlying fundamental principles in order to foster progress in both fields. Following the successful tradition of previous Cat1P conferences this interaction is to be spurred by participation of experimental colleagues and industry. They will provide crucial guidance by formulating experimental challenges to theory and emphasizing unsolved technological aspects of research in catalysis.
In the field of surface science, in which processes at the gas-solid interface are studied, there has been tremendous progress in the last decades [3]. In spite of the fact that a materials and pressure gap exists between surface science and heterogeneous catalysis, insights from surface science studies have provided a better understanding of the principles underlying catalytic activity [4].
The success of surface science has also been based on the fact that the availability of experimental probes with atomistic resolution together with the ever improving computer power and the development of ecient algorithms [5] has resulted in numerous very fruitful collaborations between theoretical and experimental groups addressing surface science problems [6, 7, 8, 9, 10].
The results of such studies are not only interesting from a fundamental point of view, but they are also relevant for the improvement of existing catalysts, as they have for example directly led to the improved design of a surface alloy catalyst for steam reforming [11].
Electronic structure methods based on density functional theory combine computational efficiency with an acceptable accuracy. In fact, theoretical studies are no longer limited to explanatory purposes but have gained predictive power. Furthermore, data from DFT calculations can be used based on reliable reactivity concepts such as the d-band model [12] to derive trends in catalytic activities [4, 13]. Still, there is little progress as far as the important issue of selectivity im complex reaction networks is concerned. Recently, it has been proposed that here concerted reaction mechanisms might be more frequent that assumed so far [14].
As far as electrochemistry and electrocatalysis are concerned, it is fair to say that first-principles approaches have not matured yet. The presence of an electrolyte and varying electrode potentials makes the theoretical description much more complex and challenging. Thus, it is not trivial to model electrochemical systems, in particular charged systems, using periodic DFT calculations. There have been some promising attempts for the more realistic modeling of the electrochemical solid-liquid interface from first principles [15, 16, 17, 18, 19], but there is as yet no generally accepted method for this purpose. Taking the environment and the electrode potential only implicitly into account in a thermodynamic approach now coined computational hydrogen electrode" allows to identify trends in electrocatalytic reactions such as in the oxygen reduction reaction [20, 21], but it remains unclear how severe the neglect of a realistic description of the environment and the explicit influence of the electrode potential are. Hence, there are still severe challenges present, as far as a proper first-principles description of electrocatalysis is concerned.
References
Axel Gross (Ulm University) - Organiser
Karsten Reuter (Fritz-Haber-Institut der MPG) - Organiser