Density Functional Theory in Surface Science and Heterogeneous Catalysis
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Density Functional Theory in Surface Science and Heterogeneous Catalysis J.K. Nørskov, M. Scheffler, and H. Toulhoat Abstract Solid surfaces are used extensively as catalysts throughout the chemical industry, in the energy sector, and in environmental protection. Recently, density functional theory has started providing new insight into the atomic-scale mechanisms of heterogeneous catalysis, helping to interpret the large amount of experimental data gathered during the last decades. This article shows how density functional theory can be used to describe the state of the surface during reactions and the rate of catalytic reactions. It will also show how we are beginning to understand the variation in catalytic activity from one transition metal to the next. Finally, the prospects of using calculations to guide the development of new catalysts in industry will be discussed. Keywords: catalytic, simulation, surface reaction.
Introduction A catalyst is a substance that can facilitate a chemical reaction; catalytic technology provides a range of products, from fuels and fertilizers to plastics and pharmaceuticals. Catalysis is also used to clean emissions from cars, power plants, and industrial production. The importance of catalysis to society is reflected by estimates suggesting that more than 20% of manufacturing in the industrialized world is dependent on catalysis.1 Most catalysts used in industry are solids, and the catalysis typically takes place on the surface of nanoparticles of the active material. We are rapidly approaching the 100th anniversary of the first large-scale industrial catalytic process, ammonia synthesis, introduced by Haber and Bosch.2 Since then, the understanding of the way solid surfaces can interact with gas-phase molecules, break them down, and form new products has increased enormously, and recently, catalyst development has been refined substantially by the introduction
MRS BULLETIN • VOLUME 31 • SEPTEMBER 2006
of parallel synthesis and screening methods.3 There are new developments which show that progress is being made toward a new, molecular-scale picture of the way solids work as catalysts. One very important development is that electronicstructure calculations based primarily on density functional theory (DFT) are beginning to provide information that is hard to obtain by experimental methods. The calculations can illuminate the nature of the transition states of molecules undergoing chemical transformation at the surface of a solid. In doing so, trends in reactivity and conceptual models of the way solids act as catalysts can be developed. In this article, we will briefly review some of the developments that have made it possible to understand how surfacecatalyzed reactions proceed. First, we will discuss how DFT calculations can be used to describe the working state of a catalyst under realistic high-pressure and
high-temperature operation. Next, we will discuss how an understanding of the variations in catalytic activity from one material to the next is beginning to emerge, a
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