Dynamics of hydrogen dissociation at the sulfur-covered Pd(100) surface

Abstract

We report calculations of the dissociative adsorption and associative desorption of H 2 at Pd͑100͒ covered with 1/4 monolayer of sulfur using quantum dynamics as well as molecular dynamics and taking all six degrees of freedom of the two H atoms fully into account. The potential energy surface ͑PES͒ has been derived from density-functional theory calculations. The absolute value of the calculated sticking coefficient turns out to be at variance with a molecular beam experiment. However, the relative change of the sticking coefficient as a function of the angle of incidence as well as the mean kinetic energy and the rotational alignment of desorbing hydrogen molecules agree quite well with the experiment. This indicates that the calculated PES reproduces the most favorable reaction path, but that in the experiment the sulfur adlayer was probably not very well ordered.

Ab Initio Molecular Dynamics Simulations of the Adsorption of H2 on Palladium Surfaces

“…[40,44,45] Still, it should be noted that there are large significant quantitative and qualitative differences as far as the sticking probability is concerned. The measured probabilities are much smaller than the calculated ones.…”

“…After about 1.5 ps it Figure 6. The measured sticking probability of H 2 on S-covered Pd(100) [8] is compared to the results of classical MD simulation [45] based on a parameterization of DFT results [87,43] and to the results of AIMD simulations. For E kin = 0.4 eV, additional AIMD runs with the substrate kept fixed were performed.…”

“…In order to study the dynamical consequences of the sulfurpoisoning on the hydrogen adsorption dynamics, six-dimensional quantum and classical dynamical studies were performed [40,44,45] on a parameterization of previous DFT calculations. [43,86] Figure 6 shows the calculated classical sticking probabilities as a function of the initial kinetic energies for initially non-rotating and non-vibrating molecules which are denoted by MD in the legends.…”

“…However, not only the coverage of the considered adsorbents itself can influence the adsorption probability, but also the coadsorption of other species can poison or promote reactions on surfaces. On Pd, in particular the influence of sulfur on the hydrogen-Pd interaction dynamics was studied both experimentally [8,9,39,40] as well as theoretically, [40][41][42][43][44][45] but CO coadsorption was also considered. [46] The H 2 -Pd dynamics on low-index metal surfaces has usually been treated quantum mechanically because of the light mass of hydrogen, [2,11,12,16,[47][48][49] but classical dynamical studies have also been performed.…”

Vibrational and rotational population distribution ofD2associatively desorbing from Pd(100)

“…6,11 In all cases the PES is both energetically and geometrically corrugated which means that the height as well as the location of the dissociation barrier varies within the surface unit cell. On six-dimensional potential-energy surfaces quantum dynamical calculations of the sticking probability of hydrogen have been performed for H 2 /Pd(100), [12][13][14][15] H 2 /(2ϫ2)S/Pd(100), 16,17 H 2 /Cu(100), 18,19 and H 2 /Cu(111). 20,21 In these simulations all six hydrogen degrees of freedom were explicitly taken into account while the substrate was kept fixed.…”