[Show abstract][Hide abstract] ABSTRACT: We investigate the heterogeneously catalysed oxidation of HX (X=Cl, Br and I) on the RuO2 (1 1 0) surface with DFT. We also solve a micro‐kinetic model of HX oxidation and compare oxidation activity at different coverages. We further establish linear energy relations for the reaction intermediates over a range of different rutile oxide surfaces. Based on the scaling relations, two descriptors are identified that describe the reactions uniquely. By combining scaling with the micro‐kinetic model, activity volcanoes for the three different oxidation reactions are derived. It is found that the commonly used RuO2 catalyst for HCl oxidation is closest to optimal for all three oxidation processes.
[Show abstract][Hide abstract] ABSTRACT: We analyse the transition state energies for 249 hydrogenation/dehydrogenation reactions of atoms and simple molecules over close-packed and stepped surfaces and nanoparticles of transition metals using Density Functional Theory. Linear energy scaling relations are observed for the transition state structures leading to transition state scaling relations for all the investigated reactions. With a suitable choice of reference systems the transition state scaling relations form a universality class that can be approximated with one single linear relation describing the entire range of reactions over all types of surfaces and nanoclusters.
[Show abstract][Hide abstract] ABSTRACT: Versatile Brønsted-Evans-Polanyi (BEP) relations are found from density functional theory for a wide range of transition metal oxides including rutiles and perovskites. For oxides, the relation depends on the type of oxide, the active site, and the dissociating molecule. The slope of the BEP relation is strongly coupled to the adsorbate geometry in the transition state. If it is final state-like the dissociative chemisorption energy can be considered as a descriptor for the dissociation. If it is initial state-like, on the other hand, the dissociative chemisorption energy is not suitable as descriptor for the dissociation. Dissociation of molecules with strong intramolecular bonds belong to the former and molecules with weak intramolecular bonds to the latter group. We show, for the prototype system La-perovskites, that there is a "cyclic" behavior in the transition state characteristics upon change of the active transition metal of the oxide.
The Journal of Chemical Physics 06/2011; 134(24):244509. DOI:10.1063/1.3602323 · 3.12 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present a computational screening study of ternary metal borohydrides for reversible hydrogen storage based on density functional theory. We investigate the stability and decomposition of alloys containing 1 alkali metal atom, Li, Na, or K (M(1)); and 1 alkali, alkaline earth or 3d/4d transition metal atom (M(2)) plus two to five (BH(4))(-) groups, i.e., M(1)M(2)(BH(4))(2-5), using a number of model structures with trigonal, tetrahedral, octahedral, and free coordination of the metal borohydride complexes. Of the over 700 investigated structures, about 20 were predicted to form potentially stable alloys with promising decomposition energies. The M(1)(Al/Mn/Fe)(BH(4))(4), (Li/Na)Zn(BH(4))(3), and (Na/K)(Ni/Co)(BH(4))(3) alloys are found to be the most promising, followed by selected M(1)(Nb/Rh)(BH(4))(4) alloys.
The Journal of Chemical Physics 08/2009; 131(1):014101. DOI:10.1063/1.3148892 · 3.12 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Introduction The formation of a bond between a molecule and a metal surface is an important phenomenon in a number of processes including heterogeneous catalysis , contact formation in molecular electronics , and anchoring of biomolecules to solids for sensors and other biomedical applications . The adsorption energy is a key quantity describing the strength of the interaction of molecules with the surface. The adsorption energy can be measured by advanced surface science techniques [4-6]. Alternatively, density functional theory (DFT) offers the possibility of calculating adsorption energies with reasonable accuracy [7-11]. While both experiments and DFT calculations are feasible for a limited number of systems, they can hardly be performed in detail for all potentially interesting adsorption systems, thus complicating the search after for example new heterogeneous catalysts. There is therefore a need for simple models with the ability to estimate bond energies in a first screening of interesting systems . Such a model for hydrogen-containing molecules adsorbed on transition metal surfaces has recently been presented , and was shown to be useful in the design of transition metal-containing surface alloys for selective hydrogenation catalysis . While linear energy relations thus are omnipresent and extremely useful in the field of transition metal catalysis, they have not historically played a significant role in the interpretation or oxide or zeolite catalysis. Recently, it is shown that a number of linear energy relations rather surprisingly could be straight-forwardly generalized to the surfaces of more complex compounds such as oxides, sulphides, and nitrides . We here address that observation in more detail, with a focus on the adsorption properties of zeolites. Methods Throughout we apply density functional theory calculations in a plane wave pseudopotential approach, as implemented in the DACAPO package. The full zeolite framework is represented in the calculation, and the exchange-correlation description is RPBE.