Supported gold nanoparticles are promising catalysts for production of H2O2 from O2 and H2. Size, structure, and palladium doping effects play the key role in activity and selectivity of a gold catalyst. We performed a study of the influence of Au20 and Au19Pd structure features on the main steps of H2O2 formation on the atomic level, using the DFT/PBE approach with relativistic all electron basis set. The top, edge, and facet atoms of the tetrahedral Au20 cluster as well as a palladium atom of Au19Pd located on the top, edge, and facet of a tetrahedron have been considered as active sites of steps involved in H2O2 synthesis. The thermodynamic and kinetic data including Gibbs free energies and the activation Gibbs free energies were calculated for the steps determining the formation of H2O2 (H(s) + OOH(s) = H2O(2(s)), H2O(2(s)) = H2O(2(g))) and for one step decreasing the selectivity (H2O(2(s)) = OH(s) + OH(s)). Gold tends to have low activity and high selectivity in H2O2 synthesis regardless of the structure of active site. Low coordinated palladium atoms promote H2O2 formation as well as its dissociation. Pd on a facet of a cluster facilitates H2O2 production with high activity and selectivity.

Organic thiols are known to react with gold surface to form self-assembled monolayers (SAMs), which can be used to produce materials with highly attractive properties. Although the structure of various SAMs is widely investigated, some aspects of their formation still represent a matter of debate. One of these aspects is the mechanism of S-H bond dissociation in thiols upon interaction with gold. This work presents a new suggestion for this mechanism on the basis of DFT study of methanethiol interaction with a single gold atom and a Au(20) cluster. The reaction path of dissociation is found to be qualitatively independent of the model employed. However, the highest activation barrier of S-H bond dissociation on the single gold atom (12.9 kcal/mol) is considerably lower than that on the Au(20) cluster (28.9 kcal/mol), which can be attributed to the higher extent of gold unsaturation. The energy barrier of S-H cleavage decreases by 4.6 kcal/mol in the presence of the second methanethiol molecule at the same adsorption site on the model gold atom. In the case of the Au(20) cluster we have observed the phenomenon of hydrogen transfer from one methanethiol molecule to another, which allows reducing the energy barrier of dissociation by 9.1 kcal/mol. This indicates the possibility of the "relay" hydrogen transfer to be the key step of the thiol adsorption observed for the SAMs systems.

The morphology and charged state of gold clusters play a crucial role in heterogeneous catalysis. The selection and optimization of theoretical approaches are necessary for the investigation of active sites on isolated and supported gold clusters. In the present paper, a study of the potential isomers of the Au12 cluster is performed within the DFT/PBE framework using a scalar-relativistic approach. We have found Au12 to be a dynamic cluster with at least 24 isomers due to the Jahn–Teller distortion. The majority of these isomers exhibit low symmetry, resulting in the formation of low-coordinated atoms, which are discussed in terms of frontier molecular orbitals and a Hirschfeld analysis of their atomic charges. The energy difference between the most energetically stable 2D (D 3h ) and 3D (C 2v ) isomers of Au12 is small (equal to 25 kJ/mol), which is evidence of their coexistence. The influence of the support on properties of the cluster is investigated using Au12/MgO(100). The 2D isomer of Au12 can interact with the surface either in an upright position, with two (E ads/atom = 24 kJ/mol) or three atoms (E ads/atom = 25 kJ/mol); the preferred position is planar (E ads/atom = 30 kJ/mol). The small deformation energy is required to distort a dynamic structure of Au12 compared to rigid gold clusters. The 3D isomer interacts with MgO(100) with two of its atoms (E ads/atom = 24 kJ/mol). The Au–Au distances across the surface increase, whereas the Au–Au distances at an angle to the surface are compressed with respect to the distances in the free clusters. The weak adsorption energies of Au12 on MgO and the low activation barriers for gold atom migration (15 kJ/mol) between oxygen sites facilitate the diffusion of nanoparticles on the MgO surface.

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The interaction of gold clusters Au 10 of different structural and charge states with various hydrocarbons was studied by the PBE density functional method. Saturated hydrocarbons interact weakly with the neutral cluster Au 10 , for charged Au 10 + the alkane-cluster bond energies increase threefold. Unsaturated hydrocarbons interact with cluster surface more strongly than saturated hydrocarbons, while coordination to the benzene ring is possible for aromatic compounds PhC 2 H, PhC 2 H 3 , and PhC 2 H 5 . The low coordinative gold atoms located on the peaks and edges of the cluster are the active adsorption site of the cluster. The appearance of a positive charge on the cluster leads to a greater increase in the hydrocarbon-gold cluster bond energy than the transition from the planar 2D structure to the three dimensional (3D) structure of the neutral cluster.