The adsorption structure of furan on Pd(111)

Abstract

The structure of molecular furan, C 4 H 4 O, on Pd(111) has been investigated by O K-edge near-edge X-ray absorption fine structure (NEXAFS) and C 1s scanned-energy mode photoelectron diffraction (PhD). NEXAFS shows the molecule to be adsorbed with the molecular plane close to parallel to the surface, a conclusion confirmed by the PhD analysis. Chemical-state specific C 1s PhD data were obtained for the two inequivalent C atoms in the furan, the α-C atoms adjacent to the O atom, and the β-C atoms bonded only to C atoms, but only the PhD modulations for the α-C emitters were of sufficiently large amplitude for detailed evaluation using multiple scattering calculations. This analysis shows the α-C atoms to be located approximately 0.6 Å off-atop surface Pd atoms with an associated C-Pd bondlength of 2.13±0.03 Å. Two alternative local geometries consistent with the data place the O atom in off-atop or near-hollow locations, and for each of these local structures there are two equally-possible registries relative to the fcc and hcp hollow sites. The results are in good agreement with earlier density functional theory calculations which indicate that the fcc and hcp registries are equally probable, but the PhD results fail to distinguish the two distinct local bonding geometries.

The structure and bonding of furan on Pd(111)

“…2, essentially equivalent to the structures explored in the experimental PhD investigation [9]. Note that these models all assume the molecular plane is approximately parallel to the Pd(111) surface, consistent with the experimental NEXAFS and PhD results, but the DFT optimisation procedure clearly allows the molecules to tilt if this proves to be energetically advantageous.…”

“…The bracketed labels of the structural models (1a, 2b etc.) are the nomenclature used in the earlier PhD experimental study [9]. to one β-C atom and one α-C atom.…”

“…Scanning tunnelling microscopy (STM) studies of this adsorption system have been shown to yield images consistent with an essentially flat-lying geometry [7,8], at least at low coverages. Most recently, a combined near-edge X-ray absorption spectroscopy (NEXAFS) and scanned-energy mode photoelectron diffraction (PhD) investigation [9] has concluded that the molecule does lie flat on the surface to relatively high coverages, and has also identified some preferred adsorption sites. In order to distinguish these alternative bonding structures and remove their associated ambiguity, and to understand the nature of the molecule-substrate bonding, we report here the results of a density functional theory (DFT) study of this adsorption system.…”

A structural study of a C3H3 species coadsorbed with CO on Pd(111)

“…In our coadsorption phase the CO coverage is certainly much lower. Our analysis of PhD and NEXAFS data from the intact furan adsorption phase shows the molecular plane to be essentially parallel to the surface [27], and in this case simple close-packing considerations using the atomic van der Waals radii [28] indicates that the maximum coverage is ~0.11 ML. The dissociation on heating actually leads to little change in the total C 1s photoemission intensity, so we may surmise that the coverage of both CO and C 3 H 3 is ~0.1 ML.…”

Effects of van der Waals density functional corrections on trends in furfural adsorption and hydrogenation on close-packed transition metal surfaces

“…The C=O bond in the aldehyde group binds on the off-bridge site. The aromatic ring is centered at the three-fold fcc site [45] so that conjugated C=C bonds can bind to either the bridge site or to the Pd top site. On Pd(111), similar furfural adsorption geometries have been recently reported by Vorontnikov et al using the PBE-D3 functional [27].…”