In the quest for increased control and tuneability of organic patterns at metal surfaces, more and more systems emerge that rely upon coordination of metal adatoms by organic ligands using endgroups such as carbonitriles, amines, and carboxylic acids.[1] Such systems promise great flexibility in the size and geometry of the surface pattern through choice of the ligand shape, the number and arrangement of ligating endgroups, and the nature of the metal centers. Planar (trigonal or square) arrangements of ligands around metal centers occur most commonly as a result of attractive interactions of the ligands with the substrate. In contrast, in the solution phase planar, and in particular trigonal planar, arrangements are quite rare and generally require ligands whose nature (for example bidentate, pincer shape) forces planarity.Given the relatively short history of the field of surface coordination chemistry, compared to its solution-phase counterpart, it is of great interest to know which information can be gleaned from the latter to predict that for the former.

This study presents a systematic detailed experimental and theoretical investigation of the electronic properties of size-controlled free and γ-Al(2)O(3)-supported Pt nanoparticles (NPs) and their evolution with decreasing NP size and adsorbate (H(2)) coverage. A combination of in situ X-ray absorption near-edge structure (XANES) and density functional theory (DFT) calculations revealed changes in the electronic characteristics of the NPs due to size, shape, NP-adsorbate (H(2)) and NP-support interactions. A correlation between the NP size, number of surface atoms and coordination of such atoms, and the maximum hydrogen coverage stabilized at a given temperature is established, with H/Pt ratios exceeding the 1 : 1 ratio previously reported for bulk Pt surfaces.

We have carried out scalar relativistic density functional theory calculations within the projector augmented wave scheme and the pseudopotential approach, to examine the effect of ligands on the geometric and electronic structure of four Au 13 isomers: planar, flake, cuboctahedral, and icosahedral clusters. We find, in agreement with previous theoretical calculations, that for the clean cluster the planar geometry has the lowest total energy while the icosahedral and cuboctahedral structures undergo Jahn-Teller distortion. On the other hand, when ligated by phosphines, the icosahedron is found to assume the lowest total energy. The rationale for the stabilization of the icosahedron in the ligated Au 13 cluster is traced to the ligand-induced charge transfer from the surface Au-Au to Au-ligand bonds leading to the formation of a strong Au-ligand covalent bond and introduction of a compressive strain which further weakens the Au-Au bonds.

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Interfacial and perimeter sites have been known for their high activity in various reactions on supported gold nanoparticles. We find that the higher activity of interfacial sites in Au13/TiO2(110) toward methanol decomposition originates from charge-transfer-induced Coulomb interaction among the gold, reactant, and reducible TiO2 support, brought about through the formation of an ionic O-Au bond between gold and methoxy in such sites, which turns the participating perimeter gold atom cationic. A direct result of such charge-transfer-induced repulsive interaction between cationic gold and positively charged C moiety of methoxy is activation of the positively charged C moiety of methoxy, as manifested by the pronounced elongation of O-C bond length and the tilting of the methoxy axis, which facilitate reaction of methoxy through C-H scission with the bridge oxygen atoms that are readily available from the reducible support. More generally, our proposed mechanism for the reactivity of the gold/TiO2 interface should hold for oxidation of organic molecules with the structure of R-O-R', where R and R' are (saturated) hydrocarbons.

Gaining experimental insight into the intrinsic properties of nanoparticles (NPs) represents a scientific challenge due to the difficulty of deconvoluting these properties from various environmental effects such as the presence of adsorbates or a support. A synergistic combination of experimental and theoretical tools, including X-ray absorption fine-structure spectroscopy, scanning transmission electron microscopy, atomic force microscopy, and density functional theory was used in this study to investigate the structure and electronic properties of small (∼1-4 nm) Au NPs synthesized by an inverse micelle encapsulation method. Metallic Au NPs encapsulated by polystyrene 2-vinylpiridine (PS-P2VP) were studied in the solution phase (dispersed in toluene) as well as after deposition on γ-Al2O3. Our experimental data revealed a size-dependent contraction of the interatomic distances of the ligand-protected NPs with decreasing NP size. These findings are in good agreement with the results from DFT calculations of unsupported Au NPs surrounded by P2VP, as well as those obtained for pure (ligand-free) Au clusters of analogous sizes. A comparison of the experimental and theoretical results supports the conclusion that the P2VP ligands employed to stabilize the gold NPs do not lead to strong distortions in the average interatomic spacing. The changes in the electronic structure of the Au-P2VP NPs were found to originate mainly from finite size effects and not from charge transfer between the NPs and their environment (e.g., Au-ligand interactions). In addition, the isolated ligand-protected experimental NPs only display a weak interaction with the support, making them an ideal model system for the investigation of size-dependent physical and chemical properties of structurally well-defined nanomaterials.

Constructing single atom catalysts with fine-tuned coordination environments can be a promising strategy to achieve satisfactory catalytic performance. Herein, via a simple calcination temperature-control strategy, CeO2 supported Pt single atom catalysts with precisely controlled coordination environments are successfully fabricated. The joint experimental and theoretical analysis reveals that the Pt single atoms on Pt1/CeO2 prepared at 550 °C (Pt/CeO2-550) are mainly located at the edge sites of CeO2 with a Pt–O coordination number of ca. 5, while those prepared at 800 °C (Pt/CeO2-800) are predominantly located at distorted Ce substitution sites on CeO2 terrace with a Pt–O coordination number of ca. 4. Pt/CeO2-550 and Pt/CeO2-800 with different Pt1-CeO2 coordination environments exhibit a reversal of activity trend in CO oxidation and NH3 oxidation due to their different privileges in reactants activation and H2O desorption, suggesting that the catalytic performance of Pt single atom catalysts in different target reactions can be maximized by optimizing their local coordination structures.

We have carried out first-principles calculations of H adsorption on Pd͑211͒ using density-functional theory with the generalized gradient approximation in the plane-wave basis to find out that the most preferred is the threefold hollow site on the terrace of Pd͑211͒ with an adsorption energy of 0.52 eV: the hcp and fcc sites being almost energetically equally favorable. For subsurface H adsorption on Pd͑211͒, the octahedral site with an adsorption energy of 0.19 eV is slightly more favorable than the tetrahedral site ͑0.18 eV͒. Our calculated activation energy barrier for H to diffuse from the preferred surface site to the subsurface one on Pd͑211͒ is 0.33 eV, as compared with 0.41 eV on Pd͑111͒. Thus, there is an enhancement of the probability of finding subsurface hydrogen in Pd͑211͒. Additionally, we find the diffusion barriers for H on the terraces of Pd͑211͒ to be 0.11 eV, while that along the step edge to be only 0.05 eV and that within the second layer ͑subsurface͒ to be 0.15 eV.