H2 hitting on graphene supported palladium cluster: molecular dynamics simulations

Abstract

Dissociative adsorption of impinging gas-phase molecular hydrogen (H2) on a palladium cluster (Pd4) supported on defective graphene (C47) was studied by periodic density functional theory molecular dynamics simulations. The H2 on Pd4/C47 collision dynamics were investigated without any particular constraint, except for the Born–Oppenheimer approximation. The study, which had mostly method-testing aims, provided, anyway, valuable information about the collision kinetics of gas-phase molecular hydrogen. This was treated as an impacting projectile having different kinetic energy values. At lower kinetic energies, sticking was ruled by steering effects imputable to the Pd cluster that easily reoriented the incoming hydrogen molecule to the metallic surface sites, favoring fragmentation hence adsorption. Sticking decreased at higher kinetic energies for which the very fast corresponding projectile acquired a kind of elusiveness toward the metallic surface that for this was not able to steer and adsorb the gas-phase hydrogen molecule. Interestingly, altered steering effects, in this case, ruled by already adsorbed surface hydrogen, seemed to play a decisive role in refocusing both H2 hitting and sticking on the supported palladium surface, irrespective of the energy characterizing the impinging gas-phase molecules

Hydrogen Arrangements on Defective Quasi-Molecular BN Fragments

“…With respect to this, it has here to be recalled that the use of BN catalytic materials, both as the metal support − and as the metal-free species, is not new in the literature. In particular, the BN materials were employed for catalytic reactions that involved either the H 2 use and its production or oxidative dehydrogenation ,, and oxidation processes. However, the systematic exploitation of defective sites in BN materials for practical aims would represent a rather new approach, whose study could suggest a great deal of potential future applications.…”

H2 Transformations on Graphene Supported Palladium Cluster: DFT-MD Simulations and NEB Calculations

“…One of the key phenomena concerning the hydrogen involvement is clearly its interaction with the supported metal systems [1]. Therefore, the understanding at atomistic level of the mechanisms involving the interaction of hydrogen with such systems represents a substantial target in catalysis [14][15][16][17][18][19][20][21][22][23][24]. Typical elementary events considered as critical in investigating the surface dynamic phenomena are both the physical and chemical molecular H 2 sorption as well as the subsequent fragmentation/recombination, migration and desorption of any surface hydrogen species [1,[14][15][16][17][18][19][20][21].…”

“…A lot of information has been acquired both by experimental and theoretical studies [14][15][16][17][18][19][20][21][22][23][24][25][26], but the analysis of the causes, which dynamically originate the local surface coverage, is still poor [24,27]. In this context, as an example, hydrogen spillover is simply defined as the migration of H atoms to the support from the metal particles, following the dissociative adsorption of H 2 molecule on the metallic sites [28].…”

“…Recently, Prestianni et al [24], in an article from now on referred as paper I, introduced a new, quite simple, approach in which the H 2 molecules were addressed "as projectiles" on a supported metal crystallite, namely on a Pd 4 cluster supported on graphene. At lower values of the H 2 kinetic energies, it was observed that the molecular sticking, hence the cluster site hitting was ruled by steering effects imputable to the Pd cluster, which easily reoriented the incoming H 2 molecule to the metallic surface sites, and in this way prompting the fragmentation thus atomic adsorption.…”