The surface chemistry of norbornadiene and norbornene on Pd(111) and Pd(100): a comparative DFT study.

CONTEXT: The interaction of norbornadiene (NBD) and norbornene (NBE) with the palladium (111) and (100) surfaces have been investigated using density functional theory (DFT). Five configurations of adsorbed NBD may be formed on Pd(111): endo-tetra-σ, endo-di-σ,π, endo-di-π, exo-di-σ, and exo-π. The NBE molecule adsorbed on Pd(111) may exist in 4 configurations: endo-di-σ, endo-π, exo-di-σ, and exo-π. On Pd(100), a smaller number adsorption configurations of NBD and NBE are formed, since the double bonds of these molecules in the endo-orientation are bound only in a di-σ mode. The adsorption energy of NBD and NBE molecules on Pd(100) is noticeably higher compared to Pd(111), which is due to the surface geometry of Pd(100). The most stable configurations on both Pd facets are endo-tetra-σ for NBD and exo-di-σ for NBE. However, due to smaller adsorption area of the exo-di-σ configuration on Pd(111), a larger number of NBD molecules may adsorbed on the same surface area. Energetically favorable endo-tetra-σ (NBD) and exo-di-σ (NBE) configurations are very mobile on Pd(111). On Pd(100), only NBE molecules can migrate, while NBD migration is hindered due to the high activation barrier. METHODS: All DFT calculations were performed using the Perdew-Burke-Ernzerhof density functional (PBE) with the relativistic SBK effective core potential and TZ2P basis set in the PRIRODA program.

Estimation of conjugated C = C bonds effective number and conjugation energy of carotenoids.

Effective numbers of conjugated double C = C bonds, Neff, were estimated for the first time for three groups of carotenoids containing ß-rings-ß-apo-hydrocarbons, ß-apo-carotenols, and ß-carotene homologues. The estimations were performed by comparing the 0-0 energies of the S0 → S2 transitions in the electronic spectra of the selected molecules with the energies of the respective electronic transitions of the corresponding linear carotenoids with the same number of conjugated C = C double bonds, N. To verify these results, the conjugation energies of the carotenoids were calculated for the first time and it was shown that the conjugation energy relations of the containing ß-rings and linear compounds are in good agreement with the Neff/N ratios. It is also shown that the conjugation energy of the ß-ring double bond with the linear conjugated chain practically does not depend on N, only slightly increasing with its length (less than 5%). According to the DFT calculations, the contribution of the ß-ring C = C bond to the conjugation energy of ß-apo-carotenoids and ß-carotene homologues is on average about 0.3 of the contribution of the linear chain C = C bond. Thus, for ß-apo-carotenoids (one ß-ring), the dependence of Neff on N may be expressed by the equation Neff = (N - 0.7) and for ß-carotene homologues (2 ß-rings) by the equation Neff = (N - 1.4).

Adsorption of phenylacetylene and styrene on palladium surface: a DFT study.

In this paper, a DFT study of phenylacetylene and styrene interactions with different surfaces ({111}, {100}, edge and corner) of Pd86 cluster was performed. The results obtained show that the interaction of phenylacetylene with Pd{111} or Pd{100} surfaces is stronger than that of styrene, but on the edges of Pd86 the adsorption of styrene is more preferable. The results agree with experimental observations, namely, with the nanoparticle size effect in the PhA semihydrogenation on Pd catalysts.