Catalysis Informatics Group
The geometric and electronic structure of surfaces determine their chemical reactivity. Many material properties can therefore be understood directly based on the atomic-scale studies of surface structure. This includes materials heterogeneous catalysis.
The main theory tools we employ are currently density functional theory (DFT), statistical mechanics, and micro kinetic modelling (MKM). At CAMD we are developing and maintaining DFT programs based plane waves/pseudopotentials and a real-space grid implementation of the projector augmented wave (PAW) formalism.
The research on Catalysis Informatics at The Lundbeck Foundation's Center for Atomic-scale Materials Design is funded in part through the STVF Research Framework Program entitled "Heterogeneous catalysis for chemical production and environmental protection". The Catalysis Informatics group is also a central contributer to the recently commenced Catalysis for Sustainable Energy - CASE - program at DTU.
Our research focusses on the understanding of atomic-scale processes at surfaces, with a strong emphasis on processes which are of large importance for the society, either today or in the near future. A special focus area in our research is the systematic analysis of trends in heterogeneous catalysis. These are some of the reactions, processes and materials we are currently studying:
- Synthetic Natural Gas and Methanation
- Fischer-Tropsch synthesis
- Steam reforming
- Selective hydrogenation of hydrocarbons
- Environmental catalysis (NO decomposition, CO oxidation)
- Haber-Bosch and electrochemical synthesis of ammonia
- Reactivity trends for reactions over transition metals, oxides, sulfides, nitrides, and carbides
- Zeolite catalysis
The methodological developments that we carry out are based on the needs created through our study of specific processes or reactions. Some of the methodological improvements and implementations we are currently working on in order to describe specific materials and reactions at a more satisfactory level are:
- Van der Waals interactions in correlation functionals
- Error Estimation on exchange functionals
- Sampling methods of entropic free energy contributions
J.K. Nørskov, T. Bligaard, and J. Kleis: Rate control and reaction engineering, Science 324, 1655 (2009)
J.K. Nørskov, T. Bligaard, J. Rossmeisl, and C.H. Christensen: Towards computational design of solid catalysts, Nature Chemistry 1, 37-46 (2009)
T. Jiang, D.J. Mowbray, S. Dobrin, H. Falsig, B. Hvolbæk, T. Bligaard, and J.K. Nørskov: Trends in CO oxidation rates for metal nanoparticles and close-packed, stepped, and kinked surfaces, Journal of Physical Chemistry C 113, 10548 (2009)
P.G. Moses, J.J. Mortensen, B.I. Lundqvist, and J.K. Nørskov: Density functional study of the adsorption and van der Waals binding o aromatic and conjugated compounds on the basal plane of MoS2, J. Chem. Phys., 130, 104709 (2009)
S. Saadi, B. Hinnemann, S. Helveg, C.C. Appel, F. Abild-Pedersen, and J.K. Nørskov: First-principles investigations of the Ni3Sn alloy at steam reforming conditions, Surf. Sci., 603, 762 (2009)
A.K. Kelkkanen, B.I. Lundqvist, J.K. Nørskov: Density functional for van der Waals forces accounts for hydrogen bond in benchmark set of water hexamers, J. Chem. Phys., 131, 046102 (2009)
A. Hellman, K. Honkala, I.N. Remediakis, A. Logadottir, A. Carlsson, S. Dahl, C.H. Christensen, and J.K. Nørskov: Ammonia synthesis and decomposition on a Ru-based catalyst modeled by first-principles, Surf. Sci., 603, 1731 (2009)
P. Ferrin D. Simonetti, S. Kandoi, E. Kunkes, J.A. Dumesic, J.K. Nørskov, and M. Mavrikakis: Modeling Ethanol Decomposition on Transition Metals: A Combined Application of Scaling and Bronsted-Evans-Polanyi Relations, J. Am. Chem. Soc., 131, 5809 (2009)
A. Vojvodic, B. Hinnemann, and J.K. Nørskov: Magnetic edge states in MoS2 characterized using density-functional theory, Phys. Rev. B., 80, 125416 (2009)
A. Vojvodic, A. Hellman, C. Ruberto, and B.I. Lundqvist: From Electronic Structure to Catalytic Activity: A Single Descriptor for Adsorption and Reactivity on Transition-Metal Carbides, Phys. Rev. Lett., 103, 146103 (2009)
D.C. Langreth, B.I. Lundqvist, S.D. Chakarova-Kack, V.R. Cooper, M. Dion, P. Hyldgaard, A. Kelkkanen, J. Kleis, L.Z. Kong, S. Li, P.G. Moses, E. Murray, A. Puzder, H. Rydberg, E. Schroder, and T. Thonhauser: A density functional for sparse matter, J. Phys. Cond. Mat., 21, 084203 (2009)
S. Li, V.R. Cooper, T. Thonhauser, B.I. Lundqvist, and D.C. Langreth: Stacking Interactions and DNA Intercalation, J. Phys.Chem., 113, 11166 (2009)
J.K. Nørskov and F. Abild-Pedersen: Bond control in surface reactions, Nature 461, 1223 (2009)
F. Studt, F. Abild-Pedersen, T. Bligaard, R.Z. Sørensen, C.H. Christensen, and J.K. Nørskov: On the Role of Surface Modifications of Pd Catalysts in the Selective Hydrogenation of Acetylene, Angew. Chem. Int. Ed. 47, 9299-9302 (2008)
J.K. Nørskov, T. Bligaard, B. Hvolbæk, F. Abild-Pedersen, I. Chorkendorff, and C.H. Christensen: The nature of the active site in heterogeneous metal catalysis, Chem. Soc. Rev. 37, 2163-2171 (2008)
G. Jones, J.G. Jakobsen, S.S. Shim, J. Kleis, M.P. Andersson, J. Rossmeisl, F. Abild-Pedersen, T. Bligaard, S. Helveg, B. Hinnemann, J.R. Rostrup-Nielsen, I. Chorkendorff, J. Sehested, and J.K. Nørskov: First Principles Calculations and Experimental Insight into Methane Steam Reforming over Transition Metal Catalysts, J. Catal. 259, 147-160 (2008)
T.R. Munter, T. Bligaard, C.H. Christensen, and J.K. Nørskov: BEP-relations for N2 dissociation over stepped transition metal and alloy surfaces, Phys. Chem. Chem. Phys. 10, 5202-5206 (2008)
H. Falsig, B. Hvolbæk, I.S. Kristensen, T. Jiang, T. Bligaard, C.H. Christensen, and J.K. Nørskov: Trends in the catalytic CO oxidation activity of nanoparticles, Angewandte Chemie International Edition 47, 4835-4839 (2008)
F. Studt, F. Abild-Pedersen, T. Bligaard, R.Z. Sørensen, C.H. Christensen, and J.K. Nørskov: Rational catalyst design applied to the selective hydrogenation of acetylene, Science 320, 1320-1322 (2008)
E.M. Fernández, P.G. Moses, A. Toftelund, H.A. Hansen, J.I. Martínez, F. Abild-Pedersen, J. Kleis, B. Hinnemann, J. Rossmeisl, T. Bligaard, and J.K. Nørskov: Scaling relations for adsorption energies on transition metal oxide, sulfide and nitride surfaces, Angew. Chem. Int. Ed. 47, 4683-4686 (2008)
M.P. Andersson, F. Abild-Pedersen, I. Remediakis, T. Bligaard, G. Jones, J. Engbæk, O. Lytken, S. Horch, J.H. Nielsen, J. Sehested, J.R. Rostrup-Nielsen, J.K. Nørskov, and I. Chorkendorff: Structure Sensitivity of the Methanation Reaction: H2 induced CO dissociation on nickel surfaces, J. Catal. 255, 6 (2008)
G. Jones, T. Bligaard, F. Abild-Pedersen, and J.K. Nørskov: Using scaling relations to understand trends in the catalytic activity of transition metals, J. Phys.: Cond. Mat. 20, 064239 (2008)
C.H. Christensen and J.K. Nørskov: A molecular view of heterogeneous catalysis, J. Chem. Phys. 128, 182503 (2008)
B. Hinnemann, P.G. Moses, and J.K. Nørskov: Recent density functional of hydrodesulfurization catalysts: insight into structure and mechanism, J. Phys.: Cond. Mat. 20, 064236 (2008)
M.P. Andersson, F. Abild-Pedersen, I.N. Remediakis, T. Bligaard, G. Jones, J. Engbæk, O. Lytken, S. Horch, J.H. Nielsen, J. Sehested, J.R. Rostrup-Nielsen, J.K. Nørskov, I. Chorkendorff: Structure sensitivity of the methanation reaction: H2-induced CO dissociation on nickel surfaces, Journal of Catalysis 255, 6-19 (2008) (pdf)
Figure. Measurements of the relative rate of CO methanation activity per Ni catalyst mass plotted as a function of the inverse particle size, d, for a series of nickel catalysts. The methanation reaction is measured in 1% CO in H2 at 523 K and a total pressure of 1 bar. Note that both axes are logarithmic. It is seen that the measurements (black circles) are best described by an exponent of 2.6, which is in between exponents expected for steps and kinks, suggesting that the reaction is structure sensitive, and that the highly under-coordinated sites are the active sites for the methanation reaction.
The catalytic methanation reaction, CO + 3H2 → CH4 + H2O, has attracted considerable interest since it was reported by Sabatier . This reaction is used in various industrial processes, including the removal of oxo-compounds (COx) in the feed gas for the ammonia synthesis , in connection with gasification of coal, where it can be used to produce methane from synthesis gas , and in relation to Fischer–Tropsch synthesis . Another motivation for understanding this process in detail is purely scientific: It is one of the simplest catalytic reactions and serves as a test bed for our fundamental understanding of heterogeneous catalysis. Pioneering work by Goodman et al. [5–7] made the first comparison between surface science single-crystal experiments  and supported Ni catalysts . One of the conclusions from this work was that the methanation process proceeds with comparable rates per Ni atom on Ni(111) and Ni(100), as well as on supported Ni catalysts. It thus appears from these experiments that the reaction is structure-insensitive, whereas the reverse reaction, the steam reforming process, is structure-sensitive [9–13]. In this work, we address the influence of the surface structure on the CO activation on Ni. In general, the geometry of transition metal surface sites can have a profound impact on the dissociation probability of diatomic molecules. For example, NO has been found to dissociate preferentially on steps on Ru(0001) surfaces . The same is true for N2 dissociation, for which both theory and experiments have demonstrated a very large difference in reactivity between close packed surfaces and steps, corresponding to a difference in activation energy for dissociation of >1 eV [15,16]. Density functional theory (DFT) calculations have shown this to be true in numerous cases [17–21], indicating that the step site should play an important role both in model systems and for supported nanoparticles .
We have combined extensive density functional theory calculations, ultra-high vacuum experiments on well-defined single crystals, and catalytic activity measurements on supported catalysts in a study of the dissociation mechanism of CO on Ni surfaces. We have found that this process is highly structure sensitive and also is sensitive to the presence of hydrogen: Under ultra-high vacuum, with no hydrogen present, the dissociation proceeds through a direct route in which only under-coordinated sites (e.g. steps) are active. Under methanation conditions, the dissociation also proceeds most favorably over under-coordinated sites, but through a COH surface intermediate. The difference in the reaction mechanism under UHV and methanation conditions clearly demonstrates the importance of combining surface science techniques with ab initio calculations when bridging the pressure gap.
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Figure. Free energy diagrams for the methanation and ammonia synthesis reactions for a number of metals. In both cases realistic industrial conditions and a stoichiometric reactant mixture has been used: Methanation: 30 bar, 475 K, 90% conversion. Ammonia synthesis: 100 bar, 675 K, 20% conversion.
Computational methods based on density functional theory (DFT) have attained a sufficient level of accuracy and efficiency that they can be used to describe surface chemical processes of interest in heterogeneous catalysis. There are a number of cases where complete catalytic reactions on surfaces have been outlined in terms of activation energies and reaction energies [1–8] and considerable insight has been obtained about mechanisms and kinetics in this way. Such calculations are, however, quite demanding. While there are examples where a family of catalysts has been investigated in this way , extensive calculations of whole reaction pathways are typically done for a single metal and a single surface. In the present study we have introduced a method for evaluating reaction energies for all steps in a catalytic reaction on a range of transition metal surfaces on the basis of a database of adsorption energies of a few atoms and molecules—C, O, H, N, and CO. The key to the new method is the recent discovery of scaling relations between the adsorption energies of different partially hydrogenated intermediates . We will show that it is possible to quite easily generate data for a number of metals and in this way obtain reactivity trends. We also show that the reaction energies can be used to generate families of free energy diagrams for complete reactions. The approach is illustrated by applying it to two simple catalytic reactions, the methanation reaction and the ammonia synthesis reaction. We use it to show how an overview of reactivity trends can be generated.
We have shown that it is possible to get qualitative agreement between DFT and what is found experimentally for the methanation and ammonia synthesis reaction. With this knowledge we can then use a limited number of DFT calculations combined with the models developed based on these calculations to screen for new catalysts with a better catalytic performance.
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