Over the past century, the development of efficient processes for converting fossil resources into a broad range of chemicals, materials, and fuels could undoubtedly be considered one of the most important scientific developments. The vast majority of chemicals are produced based on catalysis technologies, and essentially all transportation fuels are refined through a number of catalytic processes. It has been estimated that approximately 20% of the World’s GNP is directly related to industrial catalytic processes. One such important catalytic process is the Haber–Bosch ammonia synthesis, which through its use in the production of artificial fertilizer helps providing food for approximately half of the World’s population. This process was suggested in a “millennium essay” in Nature to be the single most important discovery of the past century – even ahead of tremendous breakthroughs such as those of penicillin, the transistor, and the integrated circuit [V. Smil, Nature 400, 415 (1999)]. Like many other processes, the ammonia synthesis relies heavily on fossil resources, since the hydrogen consumed in the synthesis reaction is primarily obtained from natural gas (through the also-catalytic steam-reforming and water–gas shift processes). It is clear today that as a consequence of our reliance on fossil resources, the pressure on the environment has drastically increased. Even the best available processes do not completely avoid undesirable byproducts, and a range of catalytic technologies have therefore been developed to diminish the associated problems, for example three-way catalysts for gasoline-powered vehicles and the selective catalytic reduction of nitric oxide in fossil-fuel-based power plants. The continuously increasing use of fossil resources also directly contributes to the increasing carbon dioxide levels in the atmosphere. It is becoming more and more evident that our consumption, during the course of a few centuries, of the fossilized carbon resources deposited during the course of tens of millions of years may have a dramatic impact on the global climate. Therefore there is currently a significant push towards reducing the dependence on fossil carbon resources. This calls for the development of a range of new and improved sustainable catalytic technologies. A key issue in the development of these new technologies is the search for new catalysts with improved stability, activity, and selectivity. The availability of highly optimized catalysts made of cheap Earth-abundant elements is the key limiting factor for a wide range of sustainable energy technologies. Our ability to meet this challenge may well determine whether we can sustain high living standards in the industrialized part of the world and whether living standards can be significantly improved in the developing countries. The search for new catalysts and the construction of efficient tools to carry out this search may therefore well be the greatest scientific and technological challenge that mankind is facing in our time.
The catalytic properties of an active site on a catalyst are completely determined by the local electronic structure, and it is therefore a goal in itself to become able to understand and “design” the local electronic structure of the active sites by changing the catalytic materials structure and composition. During the course of the past few decades the understanding of why a given material can act as a good catalyst for a given reaction has drastically improved. The improvement has been achieved through the close integration of experimental and theoretical methods in surface science . The number of possible atomic arrangements that one must investigate and understand in order to find a new and highly selective catalyst for a complex chemical reaction is, however, enormous, and the detailed atomic-level understanding of catalytic systems that have been found to work therefore by no means guarantee that an alternative good catalyst can be determined easily. The major part of the design challenge—the inversion of insight—therefore still exists: How can we, instead of deriving the catalytic properties from known materials structure and composition, derive appropriate materials and their structures and compositions only from the knowledge of the desired catalytic properties and perhaps the relevant working conditions? 
The objective of atomic-scale design through engineering of the electronic structure is not limited to catalytic materials. It is a general challenge in materials science, chemistry, physics, and molecular biology, and extensive progress has been achieved in some research areas, for example, new molecules for homogeneous catalysis  and materials for hydrogen storage , batteries , and photo-absorption . The catalytic reactions at surfaces may be particularly well-suited for electronic structure engineering, since the link between the atomic-scale properties and the macroscopic functionality is relatively well understood . This understanding has come about to a large extent through the theoretical description of surface reactions, which has been considerably sharpened by the availability of a broad range of quantitative experimental surface science studies of surface adsorption and reaction properties . First-principles simulations have indeed now reached a state of maturity where they can be used to elucidate a wide range of materials properties , reaction mechanisms on transition metals , transition metal oxides , and in zeolites . In a few cases it has even led to the design of new technical catalysts directly inspired by the calculations [12,2]. Advances in this field are closely tied to the improved inclusion of thermodynamic and kinetic effects at the surface .