Interplay of theoretical calculations and experiments for a study of catalysis by gold

A Review of State of the Art in Phosphine Ligated Gold Clusters and Application in Catalysis

Atomically precise gold clusters are highly desirable due to their well-defined structure which allows the study of structure-property relationships. In addition, they have potential in technological applications such as nanoscale catalysis. The structural, chemical, electronic, and optical properties of ligated gold clusters are strongly defined by the metal-ligand interaction and type of ligands. This critical feature renders gold-phosphine clusters unique and distinct from other ligand-protected gold clusters. The use of multidentate phosphines enables preparation of varying core sizes and exotic structures beyond regular polyhedrons. Weak gold-phosphorous (Au-P) bonding is advantageous for ligand exchange and removal for specific applications, such as catalysis, without agglomeration. The aim of this review is to provide a unified view of gold-phosphine clusters and to present an in-depth discussion on recent advances and key developments for these clusters. This review features the unique chemistry, structural, electronic, and optical properties of gold-phosphine clusters. Advanced characterization techniques, including synchrotron-based spectroscopy, have unraveled substantial effects of Au-P interaction on the composition-, structure-, and size-dependent properties. State-of-the-art theoretical calculations that reveal insights into experimental findings are also discussed. Finally, a discussion of the application of gold-phosphine clusters in catalysis is presented.

Non-covalent Interactions and Charge Transfer between Propene and Neutral Yttrium-Doped and Pure Gold Clusters

The dopant and size-dependent propene adsorption on neutral gold (Aun ) and yttrium-doped gold (Aun-1 Y) clusters in the n=5-15 size range are investigated, combining mass spectrometry and gas phase reactions in a low-pressure collision cell and density functional theory calculations. The adsorption energies, extracted from the experimental data using an RRKM analysis, show a similar size dependence as the quantum chemical results and are in the range of ≈0.6-1.2 eV. Yttrium doping significantly alters the propene adsorption energies for n=5, 12 and 13. Chemical bonding and energy decomposition analysis showed that there is no covalent bond between the cluster and propene, and that charge transfer and other non-covalent interactions are dominant. The natural charges, Wiberg bond indices, and the importance of charge transfer all support an electron donation/back-donation mechanism for the adsorption. Yttrium plays a significant role not only in the propene binding energy, but also in the chemical bonding in the cluster-propene adduct. Propene preferentially binds to yttrium in small clusters (n<10), and to a gold atom at larger sizes. Besides charge transfer, relaxation also plays an important role, illustrating the non-local effect of the yttrium dopant. It is shown that the frontier molecular orbitals of the clusters determine the chemical bonding, in line with the molecular-like electronic structure of metal clusters.

Theoretical investigation of oxidation of NO (NO + ½ O2 → NO2) on surfaces of nickel-doped nanocages (Ni-C60 and Ni-B30N30)

In present study, the NO oxidation on Ni-carbon nanocage and Ni-boron nitride nanocage surfaces was investigated. The Ni-C₆₀ and Ni-B₃₀N₃₀ catalysts can oxidize the NO molecule by Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms. In this study, the NO molecule was joined to Ni atom of the Ni-surface-O₂* and Ni-surface-O* to generate the intermediates with low barrier energies. It can be concluded that the cis-Ni-surface-ONOO* complex in the ER pathway is more stable than four-elements-ring complex in LH pathway ca 0.06 and 0.08 eV, respectively. In the LH pathway, the studied catalysts were deactivated by irreversible absorption of NO₂ molecules in Ni atoms of Ni-C₆₀ and Ni-B₃₀N₃₀. In contrast, in the ER pathway two NO₂ molecules were released in the normal temperature. In this study, the abilities of the Ni-C₆₀ and Ni-B₃₀N₃₀ to oxidation of NO molecule was demonstrated. Finally, the systematic scheme to design of metal-doped nano-catalysts to oxidation of toxic gases was proposed.

Transition of surface phase of cobalt oxide during CO oxidation

Transition of surface phase of cobalt oxide nanoparticle catalyst during CO oxidation in 60–200 °C tracked through AP-XPS.

Colorimetric Biosensor for Detection of Cancer Biomarker by Au Nanoparticle-Decorated Bi2Se3 Nanosheets

The colorimetric biosensors have attracted intensive interest; however, their relatively low sensitivity limits their applications in clinic detection. Herein, we develop an effective colorimetric biosensor based on highly catalytic active Au nanoparticle-decorated Bi₂Se₃ (Au/Bi₂Se₃) nanosheets. Au/Bi₂Se₃ nanosheets are facilely synthesized by simply sonicating Au precursor with the as-synthesized Bi₂Se₃ nanosheets in aqueous solution. Because of the low redox potential and typical topological insulating properties, Bi₂Se₃ nanosheets is capable of providing and accumulating electrons on its surface. Such unique properties of Bi₂Se₃ nanosheets contribute to strong synergistic catalytic effects with Au nanoparticles, particularly when Au/Bi₂Se₃ nanosheets are utilized for catalyzing the reduction of 4-nitrophenol (4-NP) by NaBH₄ (K = 386.67 s^-1g^-1). The excellent catalytic activity of Au/Bi₂Se₃ nanosheets can be "switched off" upon treatment of antibody of cancer biomarker such as anticarcinoembryonic antibody (anti-CEA). Addition of the corresponding antigen such as cancer biomarker carcinoembryonic antibody (CEA) can successively help "switch on" the catalytic activity of Au/Bi₂Se₃ nanosheets, where the resuming degree however depends on the antigen concentration. This cancer biomarker depended catalytic behavior therefore allows Au/Bi₂Se₃ nanosheets to be employed as a colorimetric sensor for detection of a particular cancer biomarker, for the reduction of 4-nitrophenol (4-NP) by NaBH₄ itself involves apparent color change. The sensor shows high sensitivity and selectivity for the cancer biomarker, even for a concentration as low as 160 pg/mL for CEA, which fully satisfies the requirement for real clinical applications. The developed colorimetric sensor shows good generality for detection of different types of cancer biomarkers, such as α-fetoprotein (AFP) and prostate-specific antigen (PSA). Furthermore, real clinic sample analyzing result shows that the prepared biosensor is efficient for detection of CEA, providing an alternative method in cancer diagnosis.

The electric dipole moments in the ground states of gold oxide, AuO, and gold sulfide, AuS

The B²Σ^- - X²Π_3/2(0,0) bands of a cold molecular beam sample of gold monoxide, AuO, and gold monosulfide, AuS, have been recorded at high resolution both field free and in the presence of a static electric field. The observed electric field induced splittings and shifts were analyzed to produce permanent electric dipole moments, μ→_el, of 2.94±0.06 D and 2.22±0.05 D for the X²Π_3/2(v = 0) states of AuO and AuS, respectively. A molecular orbital correlation diagram is used to rationalize the trend in ground state μ→_el values for AuX (X = F, Cl, O, and S) molecules. The experimentally determined μ→_el are compared to those computed at the coupled-cluster singles and doubles (CCSD) level augmented with a perturbative inclusion of triple excitations (CCSD(T)) level of theory.