A Quantum-Chemical Study of Dissociation of H₂Molecule on Palladium Clusters

Energetics and dynamics of hydrogen adsorption, desorption and migration on a carbon-supported palladium cluster

“…The process appears to be barrierless, and the chemisorption energy is approximately 50 KJ/mol. The latter value, for H 2 chemisorption on a coronene supported Pd 4 cluster, is in agreement with that for chemisorption on the unsupported cluster calculated by Zhou et al, 8 but it is a bit larger than that reported by Matsura et al 34 These chemisorption energies were calculated from the optimized geometries before and after bringing H 2 and Pd 4 together; the calculated H-H bond distances were 0.82 A 8 and 0.85 A 34 and the H 2 moleculae was referred to as ''stretched'' or ''weakened'' in the chemisorbed state. The present results of our molecular dynamics simulations suggest H 2 dissociation to a greater extent (cf.…”

“…The energy difference between the two configurations for the unsupported Pd 4 cluster, however, is significantly higher. 34 Further migration of the H atoms requires the system to cross an energy barrier of $ 3.5 KJ/mol; the H atoms gradually move towards the carbon support to reach a configuration, characterized by snapshot S 3 , which is 5 KJ/mol lower in energy. It should be noted that the latter configuration (S 3 ) is not the lowest energy one for the unsupported Pd4 cluster.…”

“…39 In studies of the interaction of molecular hydrogen with a palladium cluster, the vertices of the metal cluster were shown to be the initial point of interaction. 34 A low energy barrier has also been reported for the diffusion of hydrogen atoms adsorbed on the surface of an unsupported palladium cluster. 8,40 Finally, hydrogen atoms, while forming hydride, were shown to favour the octahedral site in a palladium cluster.…”

“…[21][22][23][24][25][26][27][28][29] In the absence of transition metal, hydrogen physisorbs on the carbon materials in its molecular form, 10,11,13,14,16,17,19,20,22 and it is believed that the addition of transition metal to carbons alters this mode of interaction, with molecular hydrogen dissociatively chemisorbing on the transition metal clusters, getting absorbed as metal hydride and atomic hydrogen possibly migrating on the cluster and eventually on to the carbon support. 4,5,7,8,18,20,24,[26][27][28][30][31][32][33][34] The latter phenomenon is usually referred to as spillover. The interaction mechanism of hydrogen with metal-doped carbon materials has been mostly inferred from experimental studies of complicated, multistep catalytic processes and the paucity of specific studies of hydrogen interaction with these materials has casted some doubts about the mechanism, energetics and dynamics of spillover, let alone its very existence.…”

Methanol synthesis from CO2 hydrogenation over a Pd4/In2O3 model catalyst: A combined DFT and kinetic study

“…In fact, atomically dispersed supported metal catalysts have become an intensely focused area of research in recent years [33][34][35][36][37]. H 2 adsorption and dissociation on the pure Pd surfaces or particles have been studied both experimentally [31,38] and theoretically [39][40][41]. The interaction of H 2 and Pd is closely related to the H 2 pressure and particle size of Pd.…”