Structural and electronic properties of the Pt_n–PAH complex (n = 1, 2) from density functional calculations

Abstract

A detailed density functional study of the Pt atom and Pt dimer adsorption on a polyaromatic hydrocarbon (PAH) is presented. The preferred adsorption site for a Pt atom is confirmed to be the bridge site. Upon adsorption of a single Pt atom, however, it is found here that the electronic ground state changes from the triplet state (5d 9 6s 1 configuration) to the closed-shell singlet state (5d 10 6s 0 configuration), which consequently will affect the catalytic activity of Pt when single Pt atoms bind to a carbon surface. The preferred adsorption site for the Pt dimer in the upright configuration is the hollow site. In contrast to the adsorption of a single Pt atom, the formation of a Pt-C bond in the adsorption of a Pt dimer is not accompanied by a change in the spin state, so the most stable electronic state is still the triplet state. While the atomic charge on the Pt atoms and dimers (in parallel configuration) in the Pt n /PAH complex is positive, a negative charge is found on the upper Pt atom for the upright configuration, indicating that single layers of Pt atoms will have a different catalytic activity as compared to Pt clusters on a carbon surface. Comparing the Pt-C bond length and the charge transfer on different sites, the magnitude of the charge transfer decreases with bond elongation, indicating that the catalytic activity of the Pt atom and dimer can be changed by modifying its chemical surroundings. The adsorption energy for the Pt dimer on a PAH surface is larger than for two individual Pt atoms on the surface indicating that aggregation of Pt atoms on the PAH surface is favorable.

Influence of Carbon Support on Electronic Structure and Catalytic Activity of Pt Catalysts: Binding to the CO Molecule

“…13,14 Interfaces between transition metals (TM) and graphene have been investigated extensively by several theoretical and experimental techniques. [16][17][18][19][20][21][22] Müller et al investigated a single Pt atom, Pt dimers and trimers on highly oriented pyrolytic graphite using a scanning tunneling microscope (STM) in air. 21 The Pt particles were produced by evaporation of platinum onto the surface and the position of the Pt atoms were stable, without changes for many scans.…”

Chemical Bonding and Electronic Properties of the Co Adatom and Dimer Interacting with Polyaromatic Hydrocarbons

“…78 In a previous work, 42 we found that when a single Pt atom approaches the PAH surface, its ground-state changes from triplet (5d 9 6s 1 ) to the closed-shell (5d 10 6s 0 ) singlet state. According to the results in Table 4, for adsorption of the Co adatom on the PAH surface, the doublet state is the electronic ground state, which means that upon adsorption of a Co atom, its most stable electronic structure undergoes a transition from quartet state (3d 7 4s 2 configuration) to the doublet state (3d 9 4s 0 configuration).…”

“…[72][73][74][75][76][77] Graphene is an ideal system whereas real systems include defects, and therefore a realistic description of the adsorption of the Co atom and dimer on the graphene needs a proper model to represent the graphene surface. Polyaromatic hydro-carbons (PAHs) have been successfully utilized as model systems for graphene 42,59,[78][79][80] and are considered as model structures for the adsorption of the Co atom and dimer on graphene in this study since bonding to PAHs represents a model for binding to the π system relatively near defects in a real graphene material. Therefore, in this study the stability, electronic and magnetic properties of Co adatom and dimer adsorbed on PAH surface at several different adsorption sites and for different spin states are investigated.…”

“…[61][62][63][64][65][66] Grimme's dispersion correction 67,68 has been demonstrated to successfully stabilize the adhesion of a graphene layer on a Ni(111) substrate 69 and adsorption of Pt atom and dimer on graphene surface. 42 Furthermore, for a correct description of heavier elements with Z ≥ 20, relativistic effects become important. 70,71 Hence, the scalar and full ZORA approches are used to treat relativistic effect.…”

“…[42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58] For example, we have recently studied the interactions between the Pt adatom and dimer and PAH surface, where it turns out that the electron transfer between the metal and the surface is substantial. 42,59 We have shown that the magnitude of charge transfer and the adsorption energy of the Pt atoms and dimers bound to PAH depend upon the adsorption site and adsorption configuration. Sevinçli et al 14 investigated the electronic and magnetic properties of graphene and graphene nanoribbons functionalized by 3d TM atoms.…”