The Chemical Nature of Atomic Oxygen Adsorbed on Rh(111) and Pt(111):  A Density Functional Study

Abstract

The bonding of atomic oxygen on Pt(111) and Rh(111) was examined using density functional theory in order to understand their different chemical properties. The oxygen-surface interactions were modeled by bonding atomic oxygen to 10-atom clusters of Pt and Rh designed to model the (111) surface. Density functional theory was applied using the local density and generalized gradient approximations; results were obtained for both double-and triple-basis sets. Optimized geometries and binding energies were computed and favorably compared to available experimental values. Interestingly, the ionic bonding in the two cases is nearly the same, based on the similarities in the charge on oxygen. The Hirshfeld charges on oxygen were -0.225 and -0.207 for Rh 10 -O and Pt 10 -O , respectively, using the double-basis set. A more detailed analysis of the covalent bonding using crystal orbital overlap populations indicated that the 2p orbitals of oxygen interact in a greater bonding fashion with both the sp and d orbitals of Rh than with those of Pt. Additional calculations with adsorbed hydroxyl on these metal clusters show differences in covalent bonding similar to that of oxygen. In this case, however, differences in ionic bonding play a role; oxygen in hydroxyl has a greater charge on Pt than Rh. This leads to smaller differences in the interaction energies of hydroxyl on Rh and Pt compared with oxygen, resulting in differences in chemical reactivity between the two metals, especially with respect to reactions involving hydrogen transfer.

Nature of the Metal–Support Interaction in Supported Pt Catalysts: Shift in Pt Valence Orbital Energy and Charge Rearrangement

“…The MO results for an isolated metal cluster indicate that the Pt 6sp orbitals overlap strongly forming bonding and antibonding MOs or bands which are positioned on both sides of the 5d band (35,38,40,41). Consistent with this, Kua and Goddard (35,38) suggest that the 6s orbitals form "interstitial bond orbitals" (IBO and IBO*), in contrast to the 5d orbitals that are almost nonbonding, giving a narrower overall d band.…”

“…These calculations use different levels of approximation (e.g., density functional theory, DFT (40,41,43), or generalized valence bond, GVB (35,38), theory). However, they all use some approximate linear combination of atomic orbitals to construct the molecular orbitals (LCAO-MO).…”

“…The orbital mixing proposed and illustrated here is based on the results of Chen et al (40) for O and OH adsorbates on an isolated Pt 10 cluster, along with the restrictions required by symmetry arguments in the highly symmetric Pt 4 O 3 cluster. Their results indicate that both the bonding and antibonding (Pt 5d)-(O 2 p) MOs are nearly filled so that little net bonding occurs between O 2 p z and the Pt 5d orbitals.…”

Monte Carlo simulations of a simple model for the electrocatalytic CO oxidation on platinum

“…This would agree with recent ab initio quantum-chemical calculations which indicate that OH binds more strongly to Rh than to Pt, and is hence more reactive on Pt. 35 If CO diffusion on Pt is fast, as one would conclude from a comparison of the experimental and simulated voltammetry, our model would predict deviations from the classical BFT current transients in potential step experiments, a typical example of which is shown in Fig. 5͑c͒.…”

Effect of Coadsorbed Water on Deep Oxidation Mechanisms: Temperature-Programmed Reactions of Benzene and Hydroxyl on the Pt(111) Surface

“…The structure and bonding of OH formed through this reaction on the Pt(111) surface has been characterized by several surface science techniques [10,[12][13][14][15]. Based on these results, hydroxyl produced by the above reaction is suggested to form a ( ffiffi ffi 3 p  ffiffi ffi 3 p )R30°structure composed of two O-containing groups in on-top positions [12,13].…”