Adsorption of CO on Ni3Al(111): A combined theoretical and experimental study

Adsorption of CO on metal atoms surfaces is one of the most thoroughly studied adsorption systems. It is a prototypical model system for investigating molecular adsorption, and of fundamental importance in many catalytic reactions. However, real catalysts often consists of several components, and offer geometric and electronic properties different from the elemental surfaces. The Ni3Al(111) surface is a very attractive model system for theoretical and experimental studies of adsorption, as it has an ordered and well-defined surface [1]. Density functional theory (DFT) calculations have become a valuable tool in predicting the properties of clean and adsorbate covered surfaces. However, there are some well known cases where DFT fail to predict the correct adsorption site for CO on a metal surface, notably the Pt(111), Rh(111), and Cu(111) surfaces [2]. Additional information can then be very useful, for example it has been shown that the correct adsorption site for CO on Rh(111) can be predicted by comparing theoretically obtained C 1s core level binding energy shifts to experimentally obtained shifts [3]. In the work presented here we use this approach to characterise the CO adsorption on the Ni3Al(111) surface. We have studied the adsorption of CO on the Ni3Al(111) surface using DFT and high-resolution photoemission spectroscopy (HR-PES). Previous studies of CO on Ni3Al(111) have shown that CO adsorbs in Ni-dominated sites [5–8]. In the present study, a new contribution in the Al 2p photoemission spectra was observed. The DFT calculations predict that CO adsorb in Ni hollow sites at low coverage, and that the adsorption induces a large inward relaxation of nearby surface Al atoms. The calculated Al 2p core level binding energy shifts compare well with the experimental values and reveal that CO adsorption in Ni sites induce core level binding energy shifts in nearby Al atoms. The C 1s spectra has one peak at low coverage, assigned