Atomic and molecular hydrogen interacting with Pt(111)

Abstract

This computational study is motivated by the apparent conflict between an experiment on dissociation of H 2 and D 2 on Pt͑111͒, which suggests a rather corrugated potential energy surface ͑PES͒ for the H 2 /Pt͑111͒ system, and an experiment showing only weak nonzero-order diffraction of HD scattering from Pt͑111͒. In the calculations we have used density functional theory ͑DFT͒ within the generalized gradient approximation ͑GGA͒, including scalar relativistic effects and modelling the Pt͑111͒ surface as a slab. We have found that the H 2 /Pt͑111͒ PES is both energetically and geometrically corrugated. We have also found that there are reaction paths without or with very low barriers leading to dissociation of H 2 on the Pt͑111͒ surface, but that there are other reaction paths with substantial barriers. By performing extensive calculations on H interacting with a Pt͑111͒ surface we have shown that a DFT/GGA approach that includes scalar relativistic effects is capable of describing the interaction between a hydrogen atom and a Pt͑111͒ surface in a way that is, for the most part, consistent with experiments.

First-principles calculations of the phonon dispersion curves of H on Pt(111)

“…Our calculated adsorption energies for 1 ML H coverage are 0.41 eV (fcc), 0.37 eV (hcp), and 0.31 eV (on-top) showing a slight preference for fcc site adsorption, and in close agreement with experimental results (0.23 ~ 0.47 eV ) for a range of coverage. 2, 19 -23 In a detailed theoretical study 9 in which density functional theory calculations were carried out for the H/Pt(111) system with both LDA and the generalized gradient approximation (GGA), as well as, scalar relativistic and spin-orbit corrections, the preferred adsorption site for H on Pt(111) was also predicted to be the fcc hollow. Interestingly, Olsen et al 9 find GGA to provide better agreement with experimental values of the adsorption energies while LDA is found to overestimate them: 0.75 eV ~ 0.81 eV (fcc) and 0.71 eV ~ 0.8 eV (top) depending on whether full relativistic or scalar relativistic corrections were used.…”

“…12 -16 The extent of anharmonicity of the H modes has also been discussed with the conclusion that while the mode polarized normal to the surface is reasonably harmonic, the one in the direction parallel to the surface is significantly anharmonic. 9,12,16 The issue of the adsorption site is all the more intriguing because in the thermal desorption data taken by Jacobi and coworkers 12 there is the onset of an additional peak for H coverage exceeding an estimated 0.75 ML. The diffusion barrier for H on Pt(111) has also been found to be small (~70 meV), 17 giving further testimony to the equivalence of the three adsorption sites: fcc-hollow, hcp-hollow, and on-top.…”

Step effects and coverage dependence of hydrogen atom diffusion onPt(111)surfaces

“…The interaction of hydrogen with transition metal surfaces, in particular, platinum, has received extensive experimental [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] and theoretical [18][19][20][21][22][23][24][25][26][27][28] attention, primarily because platinum is an important heterogeneous catalyst in the hydrogenation reactions, and the hydrogen atom is the simplest chemisorption species which provides the ideal model system for testing the theoretical models and dynamical concepts. Hydrogen is also interesting due to its small mass that opens the possibility of observation of crossover from classical dynamics to quantum dynamics.…”

Energetics and Vibrational States for Hydrogen on Pt(111)

“…More recent FP calculations [10][11][12][13] at lower coverages indicate that unlike for H͞Ni͑111͒ and H͞Pd͑111͒ [20][21][22][23], the top site for H͞Pt͑111͒ is also a local minimum only slightly higher in energy than the fcc site. In addition, the energy barrier for the fcc-hcp-fcc path is only about 70 meV.…”

“…Our results convincingly demonstrate the need to go beyond the local harmonic oscillator picture to understand the dynamics of this system. Hydrogen on metal surfaces, and in particular on Pt(111), has received considerable experimental [1][2][3][4][5][6][7] and theoretical [8][9][10][11][12][13][14][15] attention. Together with Pd, Pt is the most important material for heterogeneous catalysis of hydrogenation reactions.…”