Abstract
The d-band center model of Hammer and Nørskov is widely used in understanding and predicting catalytic activity on transition metal (TM) surfaces. Here, we demonstrate that this model is inadequate for capturing the complete catalytic activity of the magnetically polarized TM surfaces and propose its generalization. We validate the generalized model through comparison of adsorption energies of the NH3 molecule on the surfaces of 3d TMs (V, Cr, Mn, Fe, Co, Ni, Cu and Zn) determined with spin-polarized density functional theory (DFT)-based methods with the predictions of our model. Compared to the conventional d-band model, where the nature of the metal-adsorbate interaction is entirely determined through the energy and the occupation of the d-band center, we emphasize that for the surfaces with high spin polarization, the metal-adsorbate system can be stabilized through a competition of the spin-dependent metal-adsorbate interactions.
Highlights
There are few studies on the adsorption of molecules on metal surfaces with high spin polarization
From a comparison of the adsorption energies of an NH3 molecule on 3d transition metals (TMs) obtained from spin-polarized and spin-unpolarized calculations, we find a significant effect of spin polarization on adsorption
The characteristic length rd of the d-orbitals of different TM atoms is taken from ref
Summary
We quantify the energy contributions mentioned in Eqns (2, 3 and 4). This better fit arises because the spin-dependent competing metal-adsorbate interaction (which is important for Mn, Fe, Co, and Ni) is absent in the Hammer-Nørskov model. The variation of the chemisorption energy from one metal surface to another as predicted in the conventional d-band center model[33] is as follows: δ∆Ed. The first term in Eqn (8) corresponds to the covalent interaction between the metal and the adsorbate, while the second term corresponds to the Pauli repulsion due to orthogonalization[34] of TM and adsorbate ( ) ( ) states. This coupling can lead a change of site preference, even in a mono-component antiferromagnetic material
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