Norskov and Coworkers

By combining the results of the Newns-Andersons model and the considerations from the tight binding model it is now possible to explain a number of trends in surface reactivity. This has been done extensively by Norskov and coworkers and for a thorough review of this work we refer to B. Hammer and J.K. Norskov, Adv. Catal. 45 (2000) 71. We will discuss the adsorption of atoms and molecules in separate sections. 

Norskov and coworkers have determined the stability of reaction intermediates (mostly oxygen) on many single crystals and alloys of noble metals. Energy corrections due to solvent, zero-point energy, and entropy effects afforded experimentally relevant free energies for each mechanistic step. Their calculations treated the electrode potential with the same approach as Anderson, whereby each proton transfer was coupled with an energy shift of -et/ U being the potential difference between... 

Predicting the Total Reaction Rate for an Ru Catalyst. Based on the information above, Honkala, Norskov and coworkers took on the extremely challenging task of seeking to predict the overall reaction rate for ammonia synthesis on a real catalyst with essentially no experimental input.35 To do so, they had to tackle two principal hurdles to connect their previous DFT results with a real material the fact that a real material is typically covered by a complex arrangement of adsorbates and the need to describe the number of step sites on a realistic catalyst quantitatively. An important note for an in depth reading of the paper by Honkala et al. is that much of the technical detail is included in the supplementary information associated with the online version of the paper. 

Norskov and coworkers have used the effective-medium theory to study the dissociation of molecular hydrogen on Mg(OOOl), finding an activation barrier for molecular adsorption, a precursor molecular state and an activation barrier (which depends strongly on adsorption site geometry) for dissociation. 

Useful information on the mechanism of poisoning and promotion for a simple model catalyst has come from the effective medium theory of Norskov and coworkers . Their method involves... 

The theory indicates that the strength of the adsorption and bonding of reactants on catalyst snrfaces is closely related to the symmetry and spin state of reactants molecnlar or atomic orbitals, and depends on matching the energy levels of the reactants to those of the catalyst surface as well. Norskov and coworkers invoked a so-called d-band center theory based on a large body of experimental and theoretical results, which emphasizes that the density of d-band valence electrons near the Fermi level is an important factor affecting catalytic reactions [27], It is thus particularly attractive to be able to modulate metallic NP reactivity by controlling (1) their location (inside vs. outside CNTs), (2) CNT diameter, and (3) CNT helicity (metallic vs. saniconductor). 

In the work of Lee and coworkers, the explanation for this phenomenon was proposed with the use of the concept of d-band center ej (i.e., weighted mean energy of a systems d-band) [129]. The concept was introduced by Norskov and coworkers [132] and states that a linear correlation exists between the catalytic activity of spatially confined transition metal catalyst and it s d-band center. The binding energy ofthe Pt atom decreases linearly with (see Figure 11.5) when... 

Fig. 3.10 Di iron site proposal illustrating essential features of the lowest energy path forwarded by Norskov and coworkers.

Micro-kinetic modeling represents the state of the art in describing the kinetics of catalytic reactions. It was pioneered by Stoltze and Norskov in the mid-1980s and was further explored by Dumesic and coworkers in the early 1990s [J.A. Dumesic,... 

The theory of catalysis has been notably advanced through the work in density functional theory (DFT) of Jens Norskov. He and coworkers have formulated scaling models of catalytic rates dependent upon an element s position in the periodic table and surface structural factors linked to low coordinate and highly active catalytic sites on the surface of that element. This work provides a quantitative foundation... 

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