Low-coordinated Atoms Research Articles

Highly selective semi-hydrogenation of acetylene over porous gold with twin boundary defects

Porous gold prepared by dealloying Al2Au (PG(Al2Au)) exhibits much higher catalytic performance in the semi-hydrogenation of acetylene than gold powder or porous gold prepared from Ag3Au (PG(Ag3Au)). The selectivity of PG(Al2Au) for ethylene production is above 95% in the temperature range 350–523 K. The high catalytic performance correlates with the presence of a high density of twinning defects in the fcc lattice of PG(Al2Au). In contrast, such defects are barely detectable in PG(Ag3Au) or gold powder using powder X-ray diffraction measurements. On the stepped {211} surfaces of PG (Al2Au) twinning defects create long closed-packed rows of highly reactive low-coordinated atoms denoted as W-chains, which are responsible for the observed high activity and selectivity during acetylene semi-hydrogenation. Ab initio density functional theory (DFT) calculations confirm that these low-coordinated Au sites (CN = 6 or 5) systematically created by twinning defects facilitate hydrogen adsorption, dissociation and subsequent hydrogenation reactions. On the basis of these experimental and DFT results, we propose a reaction scenario for semi-hydrogenation of acetylene over PG(Al2Au).

Roughening of Copper (100) at Elevated CO Pressure: Cu Adatom and Cluster Formation Enable CO Dissociation.

Carbon monoxide participates in many copper-catalyzed reactions, which makes CO-induced structural changes of Cu catalysts key for important industrial processes. We have studied the interaction of carbon monoxide with the Cu(100) single crystal termination at 120, 200, and 300 K by means of low-energy electron diffraction (LEED), temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), polarization-modulation infrared reflection absorption spectroscopy (PM-IRAS), and density functional theory (DFT) calculations. The absorption band of CO (2082–2112 cm–1) at elevated gas pressure (up to 5 mbar) and at 200/300 K was found at a higher wavenumber than the characteristic band of the c(2 × 2)CO structure and was consistent with CO adsorbed on low-coordinated Cu atoms. The combined PM-IRAS/DFT analysis revealed that exposure to CO induced surface roughening through the formation of Cu adatoms and clusters on the (100) terraces. The roughened surface seemed surprisingly active for CO dissociation, which indicates its unique catalytic properties.

Synthesis of a Cyclic Co2Sn2 Cluster Using a Co- Synthon.

[Ar′SnCo]2 (1, Ar′ = C6H3-2,6{C6H3-2,6-iPr2}2), a rare metal–metal bonded cobalt–tin cluster with low-coordinate tin atoms, was prepared by the reaction of [K(thf)0.2][Co(1,5-cod)2] (cod = 1,5-cyclooctadiene) with [Ar′Sn(μ-Cl)]2. This reaction illustrates a promising synthetic strategy to access uncommon metal clusters. The structure of 1 features a rhomboidal Co2Sn2 core with strong metal–metal bonds between tin and cobalt and a weaker tin–tin interaction. Reaction of 1 with white phosphorus afforded [Ar′2Sn2Co2P4] (2), the first molecular cluster compound containing phosphorus, cobalt and tin.

Evaluation of A-Site Ba2+-Deficient Ba1−xCo0.4Fe0.4Zr0.1Y0.1O3−δ Oxides as Electrocatalysts for Efficient Hydrogen Evolution Reaction

Exploring earth-abundant and cost-effective catalysts with high activity and stability for a hydrogen evolution reaction (HER) is of great importance to practical applications of alkaline water electrolysis. Here, we report on A-site Ba2+-deficiency doping as an effective strategy to enhance the electrochemical activity of BaCo0.4Fe0.4Zr0.1Y0.1O3−δ for HER, which is related to the formation of oxygen vacancies around active Co/Fe ions. By comparison with the benchmarking Ba0.5Sr0.5Co0.8Fe0.2O3−δ, one of the most spotlighted perovskite oxides, the Ba0.95Co0.4Fe0.4Zr0.1Y0.1O3−δ oxide has lower overpotential and smaller Tafel slope. Furthermore, the Ba0.95Co0.4Fe0.4Zr0.1Y0.1O3−δ catalyst is ultrastable in an alkaline solution. The enhanced HER performance originated from the increased active atoms adjacent to oxygen vacancies on the surface of the Ba0.95Co0.4Fe0.4Zr0.1Y0.1O3−δ catalyst induced by Ba2+-deficiency doping. The low-coordinated active atoms and adjacent oxygen ions may play the role of heterojunctions that synergistically facilitate the Volmer process and thus render stimulated HER catalytic activity. The preliminary results suggest that Ba2+-deficiency doping is a feasible method to tailor the physical and electrochemical properties of perovskite, and that Ba0.95Co0.4Fe0.4Zr0.1Y0.1O3−δ is a potential catalyst for HER.

Empirical interatomic potential approach to the stability of graphitic structure in BAlN and BGaN alloys

Empirical bond-order potential (BOP) with the aid of ab initio calculations is applied to investigate structures and miscibility of BxAl1−xN and BxGa1−xN alloys with 3-fold coordinated hexagonal (Hex) and 4-fold coordinated wurtzite (WZ) structures. We find that the Hex structure is stabilized for free-standing BxAl1−xN and BxGa1−xN alloys with boron composition x ≥ 0.9 while the WZ structure is favorable for BxAl1−xN (BxGa1−xN) alloy with lattice constraint of AlN (GaN) over the entire boron composition range. Furthermore, we reveal that the miscibility of BxAl1−xN and BxGa1−xN alloys with Hex structure is lower than that with WZ structure due to the relaxation of atoms within in-plane directions in Hex structure. These results suggest that our approach using BOP is feasible to clarify stability and miscibility of BxAl1−xN and BxGa1−xN alloys including the systems consisting of low-coordinated atoms.

Assembly of TiO2 ultrathin nanosheets with surface lattice distortion for solar-light-driven photocatalytic hydrogen evolution

Atomically two-dimensional semiconductor nanomaterials have drawn tremendous attention in photocatalytic applications due to their unique and remarkable properties. Herein, the assembly of TiO2 ultrathin nanosheets was fabricated from the titanate sheets using a gas-assisted liquid exfoliation method combined with hydrogenation treatment strategy. The hydrogenation treatment can introduce more surface point defects such as oxygen vacancies without damaging the ultrathin two-dimensional structure. The ultrathin two-dimensional assembly has high percentages of low-coordinated surface atoms and large specific surface areas (340 m2/g), which could increase the absorption of photon and accelerate the photocatalytic reaction process. Meanwhile, homogeneous oxygen vacancies and large fraction of low-coordinated surface atoms in TiO2 nanosheets can cause surface lattice distortion, which leads to a reduction in band gap and an upshift of conduction band minimum. The assembly possesses strong solar-light absorption, efficient charge transfer, and more surface-reactive sites for photocatalytic reactions. As a result, the assembly exhibits fast photocatalytic hydrogen evolution rate of 540.7 μmol h−1 (30 mg catalyst) and good cycling stability under simulated solar irradiation. This work may provide perspectives for designing two-dimensional semiconductor materials besides TiO2 ultrathin nanosheets as photocatalysts.

One pot synthesized CeO2-WO3-TiO2 catalysts with enriched TiO2 (0 0 1) facets for selective catalytic reduction of NO with NH3 by evaporation-induced self-assembly method

CeO2-WO3-TiO2 catalysts were directly synthesized by evaporation-induced self-assembly (EISA) method and used for selective catalytic reduction of NO with NH3. The percentage of enriched TiO2 (001) facets on CeO2-WO3-TiO2 catalysts were modified by the P123:Ti ratio. While the P123:Ti ratio was 0.02, the percentage of enriched TiO2 (001) facets were the maximum on CeO2-WO3-TiO2 catalysts. At this condition, the catalytic activity and the percentage of TiO2 (001) facets presented linear relationship. With the increase of the percentage of TiO2 (001) facets, catalytic activity of catalysts presented a rising trend. Thus CeO2-WO3-TiO2-0.02 catalyst showed the best catalytic activity for selective catalytic reduction of NO with NH3. Besides, the modulation of P123:Ti ratio could also influence the reducing capacity and acid sites for catalysts, which would promote catalytic activity of catalysts. Based on those influence factors, CeO2-WO3-TiO2-0.02 catalyst showed the best catalytic activity. Simultaneously, CeO2-WO3-TiO2-0.02 catalyst showed excellent resistance of H2O and SO2. Various characterization results indicated that the surface atomic ratio of Oβ/(Oα + Oβ) had a certain decrease for poisoned catalyst, which would result in the decrease of low-coordinated atoms on TiO2 (001) facets. At the same time, when pumped of H2O and SO2, the ammonium sulfate salt deposition and competitive adsorption of SO2 and NO would occur so that result in the decrease of catalytic activity.

Geometrical Structure of the Gold-Iron(III) Oxide Interfacial Perimeter for CO Oxidation.

The geometrical structure of the Au-Fe2 O3 interfacial perimeter, which is generally considered as the active sites for low-temperature oxidation of CO, was examined. It was found that the activity of the Au/Fe2 O3 catalysts not only depends on the number of the gold atoms at the interfacial perimeter but also strongly depends on the geometrical structure of these gold atoms, which is determined by the size of the gold particle. Aberration-corrected scanning transmission electron microscopy images unambiguously suggested that the gold particles, transformed from a two-dimensional flat shape to a well-faceted truncated octahedron when the size slightly enlarged from 2.2 to 3.5 nm. Such a size-induced shape evolution altered the chemical bonding environments of the gold atoms at the interfacial perimeters and consequently their catalytic activity. For Au particles with a mean size of 2.2 nm, the interfacial perimeter gold atoms possessed a higher degree of unsaturated coordination environment while for Au particles with a mean size of 3.5 nm the perimeter gold atoms mainly followed the atomic arrangements of Au {111} and {100} facets. Kinetic study, with respect to the reaction rate and the turnover frequency on the interfacial perimeter gold atom, found that the low-coordinated perimeter gold atoms were intrinsically more active for CO oxidation. 18 O isotopic titration and Infrared spectroscopy experiments verified that CO oxidation at room temperature occurred at the Au-Fe2 O3 interfacial perimeter, involving the participation of the lattice oxygen of Fe2 O3 for activating O2 and the gold atoms for CO adsorption and activation.

Size-dependent dynamic structures of supported gold nanoparticles in CO oxidation reaction condition

Gold (Au) catalysts exhibit a significant size effect, but its origin has been puzzling for a long time. It is generally believed that supported Au clusters are more or less rigid in working condition, which inevitably leads to the general speculation that the active sites are immobile. Here, by using atomic resolution in situ environmental transmission electron microscopy, we report size-dependent structure dynamics of single Au nanoparticles on ceria (CeO2) in CO oxidation reaction condition at room temperature. While large Au nanoparticles remain rigid in the catalytic working condition, ultrasmall Au clusters lose their intrinsic structures and become disordered, featuring vigorous structural rearrangements and formation of dynamic low-coordinated atoms on surface. Ab initio molecular-dynamics simulations reveal that the interaction between ultrasmall Au cluster and CO molecules leads to the dynamic structural responses, demonstrating that the shape of the catalytic particle under the working condition may totally differ from the shape under the static condition. The present observation provides insight on the origin of superior catalytic properties of ultrasmall gold clusters.

Fewer Defects in the Surface Slows the Hydrolysis Rate, Decreases the ROS Generation Potential, and Improves the Non‐ROS Antimicrobial Activity of MgO

Magnesium oxide (MgO) is recognised as exhibiting a contact-based antibacterial activity. However, a comprehensive study of the impact of atomic-scale surface features on MgO's antibacterial activity is lacking. In this study, the nature and abundance of the native surface defects on different MgO powders are thoroughly investigated. Their impacts on the hydrolysis kinetics, antibacterial activity against Escherichia coli (ATCC 47076), Staphylococcus epidermidis and Pseudomonas aeruginosa and the reactive oxygen species (ROS) generation potential are determined and explained. It is shown that a reduction in the abundance of low-coordinated oxygen atoms on the surface of the MgO improves its resistance to both hydrolysis and antibacterial activity. The ROS generation potential, determined in-situ using a fluorescence microplate assay and electron paramagnetic resonance spectroscopy, is not an inherent property of the studied MgO, rather it is a side product of hydrolysis (only for the most highly defected MgO particles) and/or a consequence of the MgO/bacteria interaction. The evaluation of the mutual correlations of the hydrolysis, the antibacterial activity and the ROS generation, with their origin in the surface defects' peculiarities, led to the conclusion that the acid/base reaction between the MgO surface and the bacterial wall contributes considerably to the MgO's antibacterial activity.

N-Modified NiO Surface for Superior Alkaline Hydrogen Evolution.

Boosting the sluggish kinetics of the hydrogen evolution reaction in alkaline environments is key for the large-scale application of water-alkali and chlor-alkali electrolysis. In this study, nitrogen atoms are used to precisely modulate electrochemical active sites on the surface of nickel oxide with low-coordinated oxygen atoms, to achieve enhanced kinetics in alkaline hydrogen evolution. Theoretical and experimental results demonstrate that surface charge redistribution after modulation facilitates both the initial water dissociation step and the subsequent recombination of Had from low-coordinated oxygen sites and desorption of OHad- from nickel sites, thus accelerating the overall hydrogen evolution process. The N-modulated nickel oxide enriched in low-coordinated oxygen atoms exhibits significantly enhanced activity with a small overpotential of -100 mV at the current density of -10 mA cm-2 and a robust stability over 90 h for hydrogen evolution in 1.0 m KOH.

Degradation of organic pollutants by Co3O4-mediated peroxymonosulfate oxidation: Roles of high-energy {0 0 1}-exposed TiO2 support

Co3O4-mediated heterogeneous activation of peroxymonosulfate (PMS) is an efficient strategy to generate sulfate radicals for environmental pollutants degradation. The rate-limiting step is CoOH− complex formation, and it highly depends on the thermodynamic capacity of water dissociation to generate surface hydroxyl groups. Herein, for efficient PMS activation and pollutants degradation, the water dissociation capacity of TiO2, a promising Co3O4 support, was facilely refined by its shape-tailored synthesis with dominant high-energy {0 0 1} facet. The polar {0 0 1} facet is characterized by a high density of atomic steps, edges and kinks of the low-coordinate surface atoms with a large number of dangling bonds, all of which can serve as reactive sites for water adsorption and dissociation and thus improve CoOH− complex formation dynamics in sulfate radical formation. Co3O4 deposited on TiO2-{0 0 1} exhibited a much higher PMS activation capacity and pollutants degradation efficiency, i.e. p-nitrophenol and rhodamine B, and a much lower Co2+ leaching. This superiority could be mainly attributed to the strong Ti5c-centered water adsorption and dissociation, the high density of surface hydroxyl groups, the robust CoOH− complex generation and the intimate catalyst-support interactions. Our findings might provide a new chance to refine Co-mediated sulfate radical generation and other Fenton-like systems for advanced water treatment with reduced secondary pollution.

Electrochemical Synthesis of Cu2O Concave Octahedrons with High-Index Facets and Enhanced Photoelectrochemical Activity.

High-index-faceted nano-/microcrystals exhibit enhanced catalytic activity and can thus serve as new-generation catalysts owing to their high density of low-coordinated atoms, leading to significantly enhanced catalytic activity. In this study, an effective electrochemical approach termed cyclic scanning electrodeposition (CSE) was developed to convert a thin Cu film into Cu2O concave octahedrons enclosed by 24 {344} high-index facets at room temperature with high yield and high throughput. The formation mechanism and the role of each ion in the electrolyte were systematically studied, which facilitated the design of a high-index-faceted metal/metal oxide through CSE. We also presented a general formula to identify the structure of an individual crystal enclosed by {khh} high-index facets based on the crystals oriented along three low-index zone axes and imaged by transmission electron microscopy. Experimental results demonstrated the Cu2O concave octahedrons to be highly efficient, cost-effective catalysts for photoelectrochemical hydrogen production. This new technology is a promising route for the synthesis of metal or metal oxide crystals with high activity and has a great potential for several advanced applications, such as clean energy conversion.

Towards Controlling the Electrocatalytic Hydrogenation of Oxygenated Hydrocarbons through Particle Size Effects

Metal-catalyzed hydrogenations are regarded as non-sensitive reactions in the gas phase. However, varying proportions of high- and low-coordination surface atoms may lead to differences in the selectivity when hydrogenation is performed in aqueous phase especially under electrochemical condition where H2 evolution reaction (HER) appeared to be a major competitive route. The aim of this work was to test this hypothesis by performing the electrocatalytic hydrogenation (ECH) of aromatic hydrocarbons on Pt/C and Pd/C catalysts with varying metal particle sizes. Phenol and benzaldehyde, representative model compounds for bio-oils derived from lignocellulosic biomass, were chosen as target compounds. ECH Experiments were performed at ambient conditions using H-cells wherein cathodic potential was varied systematically. The results of these experiments were compared with catalytic thermal hydrogenation, where the reduction equivalents are provided by H2 dissociation. In the studied range (from -0.6 V to -0.8 V vs Ag/AgCl), the rates of both ECH and HER increase with increasing cathodic potentials. These increases, however, depended on the metal loading of the cathode. As an exemplary result, the figure shows that the rates of phenol ECH reached a maximum at the Pt dispersion of 26%, which corresponded to a Pt loading of 5 wt.% on carbon. However, the rates normalized per active site showed a different picture. TOF values increased as the dispersion of the metal decreased. In stark contrast, the rates of the H2 evolution reaction (HER) were proportional to the dispersion. Hence, the main conclusion of this work is that the intrinsic rates of ECH of polar molecules are higher on extended metal surfaces than in the corners and edges exhibited by small metal particles. The intrinsic rates of HER, on the other hand, are favored by small particles under the applied reaction conditions. The combination of these two opposite trends rendered the catalyst with Pt particles with the average size of 4.5 nm (5 wt.% Pt on C in this work) as the most active catalyst per gram. However, the catalyst with average Pt particle size of 10 nm shows the highest intrinsic activity as well as faradaic efficiency (30%) Thermal catalytic hydrogenation (TCH) also followed the negative particle size effect to the activity trend, thus, coincide with ECH experiments. This strongly suggests the particle size effect noted in the electrochemical experiments is primarily related to the aqueous environment of the reaction instead of presence of electric potential or competing HER. It is worth highlighting that ECH rates were higher than TCH rates at cathodic potentials higher than -0.7 V vs Ag/AgCl for all tested substrates, which is ascribed to higher coverages of reactive H. This work contributes to the understanding of metal catalysis at low temperatures in condensed phases. It also shows directions for the development of highly active electrocatalysts for the conversion of polar molecules. In specific, we show that as the dispersion of the metal phase increases, the compromise between increasing concentrations of available active sites and their decreasing reactivity leads to optimum particle sizes. Figure caption. Left: Rates of phenol hydrogenation on Pt/C along with dispersion at varying cathodic potentials (vs Ag/AgCl). Right: Turnover frequency (TOF) for phenol hydrogenation on Pt/C along with dispersion at varying cathodic potentials (vs Ag/AgCl). The points labeled as "thermal" correspond to hydrogenation performed with H2 gas. Figure 1

Surface reconstruction of fluorites in vacuum and aqueous environment

Surfaces and interfaces of bulk materials with liquids are of importance for a wide range of chemical processes. In this work, we systematically explore reconstructions on the (100) surface of calcium fluoride $({\mathrm{CaF}}_{2})$ and other fluorites $(M{\mathrm{F}}_{2})$, $M={\text{Sr},\text{Cd},\text{Ba}}$ by sampling the configurational space with the minima hopping structure prediction method in conjunction with density functional theory calculations. We find a large variety of structures that are energetically very close to each other and are connected by very low barriers, resulting in a high mobility of the topmost surface anions. This high density of configurational states makes the ${\mathrm{CaF}}_{2}$ (100) surface a very dynamic system. The majority of the surface reconstructions found in ${\mathrm{CaF}}_{2}$ are also present in ${\mathrm{SrF}}_{2},{\mathrm{CdF}}_{2}$, and ${\mathrm{BaF}}_{2}$. Furthermore, we investigate in detail the influence of these reconstructions on the crystal growth of ${\mathrm{CaF}}_{2}$ in solvents by modeling the fluorite-water interface and its wetting properties. We perform a global structural search both by explicitly including water molecules and by employing a recently developed soft-sphere solvation model to simulate an implicit aqueous environment. The implicit approach correctly reproduces both our findings with the explicit-water model and the experimentally reported contact angles for the partial-hydrophobic (111) and hydrophilic (100) surfaces. Our simulations show that the high anion mobility and the low coordination of the (100) surface atoms strongly favors the adsorption of water molecules over the (111) surface. The aqueous environment makes terminations with low-coordination surface atoms more stable, promoting (100) growth instead of the (111).

TGMin: A global-minimum structure search program based on a constrained basin-hopping algorithm

In this article, we introduce Tsinghua Global Minimum (TGMin) as a new program for the global minimum searching of geometric structures of gas-phase or surface-supported atomic clusters, and the constrained basin-hopping (BH) algorithm implemented in this program. To improve the efficiency of the BH algorithm, several types of constraints are introduced to reduce the vast search space, including constraints on the random displacement step size, displacement of low-coordination atoms, and geometrical structure adjustment after displacement. The ultrafast shape-recognition (USR) algorithm and its variants are implemented to identify duplicate structures during the global minimum search. In addition to the Metropolis acceptance criterion, we also implemented a morphology-based constraint that confines the global minimum search to a specific type of morphology, such as planar or non-planar structures, which offers a strict divide-and-conquer strategy for the BH algorithm. These improvements are implemented in the TGMin program, which was developed over the past decade and has been used in a number of publications. We tested our TGMin program on global minimum structural searches for a number of metal and main-group clusters including C60, Au20 and B20 clusters. Over the past five years, the TGMin program has been used to determine the global minimum structures of a series of boron atomic clusters (such as [B26]–, [B28]–, [B30]–, [B35]–, [B36]–, [B39]–, [B40]–, [MnB16]–, [CoB18]–, [RhB18]–, and [TaB20]–), metal-containing clusters Li n (n = 3–20), Au9(CO)8 + and [Cr6O19]2–, and the oxide-supported metal catalyst Au7/γ-Al2O3, as well as other isolated and surface-supported atomic clusters. In this article we present the major features of TGMin program and show that it is highly efficient at searching for global-minimum structures of atomic clusters in the gas phase and on various surface supports.

Oxidative Etching of Pd Decahedral Nanocrystals with a Penta-twinned Structure and Its Impact on Their Growth Behavior

We report a systematic study of the oxidative etching of penta-twinned Pd decahedral nanocrystals by O2/I– under different conditions and its impact on their subsequent growth behavior. Analysis by transmission electron microscopy shows significant rounding of the decahedral structure. More specifically, the etching is found to begin at the equatorial vertices, due to their high surface free energy, and proceed along the adjacent, equatorial edges through the dissolution of low-coordination atoms. Comparison of the etching behaviors under different conditions reveals the critical role of a reductive environment for the initiation of oxidative etching, possibly due to the presence of a protective oxide layer on the surface of Pd decahedra. Overgrowth on the seeds with a rounded profile generates penta-twinned Pd nanorods with an asymmetric, tapered structure as a result of simultaneous axial and radial growth. In comparison, the original decahedral seeds only show axial growth, leading to the formation of ...

Highly selective immobilized bimetallic Ni-Au nanoparticle catalyst for the partial hydrogenation of m-dinitrobenzene

Transition metal nanoparticles (NPs) are extensively used as catalysts for a wide and diverse range of organic transformations when immobilized on appropriate solid supports. We describe the development of a highly active and highly selective heterogeneous catalyst based on Ni-Au NPs supported on activated carbon fibers (ACFs) for the partial reduction of m-dinitrobenzene (m-DNB) to m-nitroaniline (m-NAN), an important platform chemical used in the synthesis of dyes and polymers. Initially, Ni NPs with narrow size distribution and ranging from 2 to 14nm were prepared with poly-N-vinyl-2-pyrrolidone (PVP) as a stabilizer. Evaluation of the NPs as catalysts in the liquid-phase hydrogenation of m-dinitrobenzene led to the establishment of an antipathetic structure sensitivity, i.e. the larger NPs displayed a 6-fold higher turnover frequency than the smaller NPs. The selectivity to the target m-NAN product is independent of the size of the Ni NPs, possibly due to preferential PVP absorption of the NP edges and vertices. Consequently, Ni NPs of 2nm were supported on ACFs and residual PVP was removed by a ultra-violet ozone (UVO) treatment, rendering a highly selective structured catalyst that affords m-NAN in almost 96% yield. A two-site (plane vs. edge Ni-atoms) Langmuir–Hinshelwood kinetic model is consistent with the experimental kinetic data confirming that low-coordination atoms (edges and vertices) are responsible for selective reaction. Consequently, we prepared bimetallic Ni-Au NPs (Ni:Au=1:1) aiming to generate Ni surface sites mimicking the properties of edge and vertex atoms. The resulting UVO-treated Ni-Au NPs of 3nm immobilized on ACFs afford m-NAN with a yield exceeding 98%. Such a high yield appears to be unprecedented and shows how careful nanocatalyst design, guided by detailed structural characterization and mechanistic studied, can lead to highly selective catalysts of industrial relevance.

A Photochemical, Room-Temperature, and Aqueous Route to the Synthesis of Pd Nanocubes Enriched with Atomic Steps and Terraces on the Side Faces

Palladium nanocubes enriched with atomic steps and terraces on the side faces were synthesized at room temperature in an aqueous solution containing a salt precursor, ascorbic acid, KBr, and poly(vinylpyrrolidone) under UV–vis irradiation. The key to the success of this synthesis was the use of PdBr42– as a precursor with strong absorption in the region of 300–600 nm. Single-crystal seeds were formed in the reaction system upon exposure to a medium pressure Hg arc lamp, and the seeds then grew into cubic nanocrystals under extended irradiation. Because the adatoms inherently diffuse slowly across the surface at room temperature, the nanocrystals favored an asymmetric growth mode, generating side faces covered by a series of atomic steps and terraces rather than smooth {100} facets. The steps and terraces would disappear to generate smooth side faces if the sample was subjected to postsynthesis annealing at 130 °C. When applied as catalysts toward the electrochemical oxidation of formic acid, the low-coordination surface atoms such as those presented on the atomic steps resulted in significant reduction of activity relative to the smooth {100} facets. This trend could be rationalized through the overbinding of reactive species to the low-coordination sites.

Stability and local reactivity of Pd-Au nanoclusters

ABSTRACTFirst-principles method has been employed to investigate the stability and local reactivity of Au-Pd nanoparticles. AucorePdshell nanoclusters are generally more stable than PdcoreAushell counterparts for studied nanoparticles (55, 85, 147-atom). The stability of Au-Pd nanocluster is attributed to the strong charge transfers from Pd to Au atoms. The d-band centre and Fukui function values indicate that the low-coordination atoms possess the higher reactivity relative to other atoms. The two descriptors are generally in good agreement.