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Transition metal dichalcogenides (TMDCs) can be used as optical energy conversion materials to catalyze the water splitting reaction. A good catalytical performance requires: (i) well-matched semiconductor bandgaps and water redox potential for fluent energy transfer; and (ii) optimal orientation of the water molecules at the interface for kinetically fast chemical reactions. Interactions at the solid–liquid interface can have an important impact on these two factors; most theoretical studies have employed semiconductor-in-vacuum models. In this work, we explored the interface formed by liquid water and different types of TMDCs monolayers (MoS2, WSe2, and their lateral heterojunctions), using a combined molecular dynamics (MD) and density functional theory (DFT) approach. The strong interactions between water and these semiconductors confined the adsorbed water layer presenting structural patterns, with the water molecules well connected to the bulk water through the hydrogen bonding network. Structural fluctuations in the metal chalcogenide bonds during the MD simulations resulted in a 0.2 eV reduction of the band gap of the TMDCs. The results suggest that when designing new TMDC semiconductors, both the surface hydrophobicity and the variation of the bandgaps originating from the water-semiconductor interface, need to be considered.

The emerging promise of few-atom metal catalysts has driven the need for developing metal nanoclusters (NCs) with ultrasmall core size. However, the preparation of metal NCs with single-digit metallic atoms and atomic precision is a major challenge for materials chemists, particularly for Ag, where the structure of such NCs remains unknown. In this study, we developed a shape-controlled synthesis strategy based on an isomeric dithiol ligand to yield the smallest crystallized Ag NC to date: [Ag9(1,2-BDT)6]3– (1,2-BDT = 1,2-benzenedithiolate). The NC’s crystal structure reveals the self-assembly of two Ag square pyramids through preferential pyramidal vertex sharing of a single metallic Ag atom, while all other Ag atoms are incorporated in a motif with thiolate ligands, resulting in an elongated body-centered Ag9 skeleton. Steric hindrance and arrangement of the dithiolated ligands on the surface favor the formation of an anisotropic shape. Time-dependent density functional theory based calculations reproduce the experimental optical absorption features and identify the molecular orbitals responsible for the electronic transitions. Our findings will open new avenues for the design of novel single-digit metal NCs with directional self-assembled building blocks., An isomeric dithiol-based synthesis strategy is used to synthesize the smallest crystallized Ag nanocluster, [Ag9(1,2-BDT)6]3−. The single-digit cluster reveals novel bonding modes and building blocks, which include the self-assembly of two Ag square pyramids sharing a common vertex and six bidentate thiolate motifs.

The research reported in this study was supported by the King Abdullah University of Science and Technology. The authors acknowledge the support of SABIC in funding this research. Computational resources were provided primarily by the KAUST Supercomputing Laboratory and the Shaheen II supercomputer. Computational work was also partially performed using resources of the National Supercomputing Centre, Singapore (https://www.nscc.sg).

This work was supported by MOST (grant no. 2016YFA0203302), NSFC (grant nos. 21875042, 21634003 and 51573027), STCSM (grant nos. 16JC1400702 and 18QA1400800), SHMEC (grant no. 2017-01-07-00-07-E00062) and Yanchang Petroleum Group. This work was also supported by The Programme for Professor of Eastern Scholar at Shanghai Institutions of Higher Learning. This work was supported by the Ontario Research Fund—Research Excellence Program, NSERC and the CIFAR Bio-Inspired Solar Energy program. This work has also benefited from the use of the SGM beamlines at Canadian Light Source; the 1W1B and 4B9B beamlines at the Beijing Synchrotron Radiation Facility; the BL14W1, BL08U1-A beamline at Shanghai Synchrotron Radiation Facility; and the 44A beamline at Taiwan Photon Source (TPS). Mossbauer spectroscopy measurements were conducted at the Advanced Photon Source, a Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract DE-AC02-06CH11357. We acknowledge the Paul Scherrer Institut, Villigen, Switzerland, for provision of synchrotron radiation beamtime at the beamline SuperXAS of the SLS and would like to thank M. Nachtegaal for assistance. We thank M. Garcia-Melchor and Y. Zhang for discussions on DFT calculations. We thank J. Wu for the assistance with the TEM measurements. We thank R. Wolowiec and D. Kopilovic for their assistance. For computer time, this research used the resources of the Supercomputing Laboratory at KAUST.

The combination of well-defined molecular cavities and chemical functionality makes crystalline porous solids attractive for a great number of technological applications, from catalysis to gas separation. However, in contrast to other widely applied synthetic solids such as polymers, the lack of processability of crystalline extended solids hampers their application. In this work, we demonstrate that metal–organic frameworks, a type of highly crystalline porous solid, can be made solution processable via outer surface functionalization using N-heterocyclic carbene ligands. Selective outer surface functionalization of relatively large nanoparticles (250 nm) of the well-known zeolitic imidazolate framework ZIF-67 allows for the stabilization of processable dispersions exhibiting permanent porosity. The resulting type III porous liquids can either be directly deployed as liquid adsorbents or be co-processed with state-of-the-art polymers to yield highly loaded mixed matrix membranes with excellent mechanical properties and an outstanding performance in the challenging separation of propylene from propane. We anticipate that this approach can be extended to other metal–organic frameworks and other applications. Solution processability is required for many industrial processes, but metal–organic frameworks are in general not dispersible, hindering their application. Here, a surface modification is reported that allows porous liquid formation and so synthesis of highly loaded and mechanically robust mixed matrix membranes.

Hollow functional metal silicate materials have received the most interest due to their large inner space, permeable and functional shell, lighter density, and better use of material compared to their solid counterparts. While tremendous success has been made in the synthesis of individual metal silicates with uniform morphology, the synthesis of multiphase hollow silicates has not been explored yet, although their direct applications could be promising. In this study, mesoporous aluminosilicate spheres (MASS) are transformed to submicrometer copper aluminosilicate hollow spheres (CASHS) via a one-pot hydrothermal process. CASHS has a hollow interior with Cu-Al-Si thorn-like moieties in a lamellar structure on its outer shell. The structure and morphology of CASHS are unique and different from the previously reported tubular copper silicates that are emanated from Stöber silica spheres. Herein, we also demonstrate that the extent of hollowing in CASHS can be attained by controlling the aluminum content of pristine MASS, highlighting the existence of parameters for in situ controlling the shell thickness of hollow materials. The application of CASHS as a potential heterogeneous catalyst has been directed to important oxidation processes such as olefin oxidation and the advanced oxidation process (AOP). In cyclohexene oxidation, for instance, high selectivity to cyclohex-2-en-1-one is achieved under moderate conditions using

Summary Defect sites are often proposed as key active sites in the design of catalysts. A promising strategy for improving activity is to achieve a high density of homogeneously dispersed atomic defects; however, this is seldom accomplished in metals. We hypothesize that vacancy-rich catalysts could be obtained through the synthesis of quantum dots (QDs) and their electrochemical reduction during the CO2 reduction reaction (CO2RR). Here, we report that QD-derived catalysts (QDDCs) with up to 20 vol % vacancies achieve record current densities of 16, 19, and 25 mAcm−2 with high faradic efficiencies in the electrosynthesis of formate, carbon monoxide, and ethylene at low potentials of –0.2, –0.3, and –0.9 V versus reversible hydrogen electrode (RHE), respectively. The materials are stable after 80 hr of CO2RR. These CO2RR performances in aqueous solution surpass those of previously reported catalysts by 2×. Together, X-ray absorption spectroscopy and computational studies reveal that the vacancies produce a local atomic and electronic structure that enhances CO2RR.

The direct hydrogenation of CO2 to methanol using hydrogen is regarded as a potential technology to reduce greenhouse gas emissions and the dependence on fossil fuels. For this technology to become...

Funding for this work was provided by King Abdullah University of Science and Technology (KAUST). This research used resources of the Supercomputing Laboratory at KAUST. The FAME-UHD project is financially supported by the French "Grand Emprunt" EquipEx (EcoX, ANR-10-EQPX-27-01), the CEA-CNRS CRG consortium and the INSU CNRS institute.

Isomerization is an essential chemical process that often evokes dramatic change of chemical, physical, or biological properties. For a long time, isomerization has been known as a transformation that is induced by certain external energy such as light, heat, or mechanical force. Herein, a new isomerization phenomenon is described, which does not require external energy but simply occurs during molecular packing. The proposed isomerization is demonstrated by a series of symmetric donor-acceptor-donor (D-A-D) molecules, the donor of which may adopt two different stereoisomeric forms. Based on the evidence of the asymmetric isomers in crystals, the occurrence of isomerization during molecular packing is proved. Moreover, the unique asymmetric geometry in the solid state favors the restriction of intramolecular motion, resulting in highly efficient organic solids with quantum yields approaching unity.

Tremendous research efforts have been made to electrochemically convert CO2 into useful chemicals, with the main products being limited to hydrocarbons and oxygenates. One-step processes that integ...

Better catalysts are needed to address numerous challenges faced by humanity. In this Perspective, we review concepts and tools in theoretical and computational chemistry that can help to accelerate the rational design of homogeneous and heterogeneous catalysts. In particular, we focus on the following three topics: (1) identification of key intermediates and transition states in a reaction using the energetic span model, (2) disentanglement of factors influencing the relative stability of the key species using energy decomposition analysis and the activation strain model, and (3) discovery of new catalysts using volcano relationships. To facilitate wider use of these techniques across different areas, we illustrate their potentials and pitfalls when applied to the study of homogeneous and heterogeneous catalysts.

The lack of structurally distinct nanoclusters (NCs) of identical size and composition prevented the mechanistic understanding of their structural effects on ion pairing and concomitant optical properties. To produce such highly sought NCs, we designed a new monothiolate-for-dithiolate exchange strategy that enabled the selective transformation of the structure of a NC without affecting its metal atomicity or composition. Through this method, a bimetallic [PtAg28(BDT)12(PPh3)4]4– NC (1) was successfully synthesized from [PtAg28(S-Adm)18(PPh3)4]2+ NC (2) (S-Adm, 1-adamantanethiolate; BDT, 1,3-benzenedithiolate; PPh3, triphenylphosphine). The determined X-ray crystal structure of 1 showed a PtAg12 icosahedron core and a partially exposed surface, which are distinct from a face-centered cubic PtAg12 core and a fully covered surface of 2. We reveal through mass spectrometry (MS) that 1 forms ion pairs with counterions attracted by the core charge of the cluster, which is in line with density functional simula...

A simple and efficient catalyst, benzimidazole (BIMH)-modified copper foil, is developed to enhance the selective conversion of CO2 to C2/C3 products. The overall faradaic efficiency (FE) for CO2 reduction reaches 92.1% and the undesired hydrogen evolution reaction (HER) is lowered to a FE of 7% at −1.07 VRHE.

Atomically precise self-assembled architectures of noble metals with unique surface structures are necessary for prospective applications. However, the synthesis of such structures based on silver is challenging because of their instability. In this work, by developing a selective and controlled doping strategy, we synthesized and characterized a rod-shaped, charge-neutral, diplatinum-doped Ag nanocluster (NC) of [Pt2Ag23Cl7(PPh3)10]. Its crystal structure revealed the self-assembly of two Pt-centered Ag icosahedra through vertex sharing. Five bridging and two terminal chlorides and 10 PPh3 ligands were found to stabilize the cluster. Electronic structure simulations corroborated structural and optical characterization of the cluster and provided insights into the effect of the Pt dopants on the optical properties and stability of the cluster. Our study will open new avenues for designing novel self-assembled NCs using different elemental dopants.

Pd is widely used to catalyse hydrogenation and dehydrogenation reactions. One of them is the hydrogenation of ethylene, which includes the transformation of ethyl species to ethane. Herein, by means of density-functional calculations we address several still insufficiently understood factors affecting the latter process. In particular, we shed light on the following aspects of hydrogenation of alkyls on Pd: (i) the mechanistic details of how subsurface H accelerates the reaction on a (111) surface; (ii) the role of nanoparticle edges; and (iii) the influence of a common spectator ethylidyne, C–CH3. These factors are identified as significant for the height of the ethyl hydrogenation barrier on Pd. Moreover, we show that butyl hydrogenation on Pd is also governed by very similar interactions, which suggests a broader applicability of our conclusions. This study highlights the complexity of alkyl hydrogenation and analyses the factors that need to be taken into account for a more realistic description of the hydrogenation processes on metal surfaces.

The stability and atomic ordering in Pt–Sn nanoalloys supported on CeO2 thin films have been studied by means of synchrotron radiation photoelectron spectroscopy and density functional calculations. Using CO molecules as a probe, we explored the development of the surface structure of supported Pt–Sn nanoalloys with respect to a reference Pt/CeO2 model system. We found a significant decrease in the density of CO adsorption sites on supported Pt–Sn nanoalloys caused by Sn segregation to the surface upon annealing. Additionally, we found that atomic ordering in Pt–Sn nanoalloys is driven by the balance between the surface segregation energy of Sn atoms and the energy of heteroatomic bond formation. Our calculations demonstrate a clear tendency for Sn segregation to the nanoalloy surface. For Pt105Sn35 and Pt1097Sn386 nanoparticles, we calculated a surface stoichiometry of Pt2Sn which is only slightly dependent on temperature in thermodynamic equilibrium. The analysis of Bader charges in Pt–Sn nanoalloys revealed a strong correlation between the charge and the coordination number of Sn atoms with respect to Pt neighbors. In particular, the magnitude of the charge transfer from Sn to Pt increases as a function of the Sn coordination number.

Pt-doped CeOx thin film electrocatalysts have recently been shown to exhibit high activity and stability at the anode of proton exchange membrane fuel cells (PEM-FC). To identify the role of the Pt dopant and the origin of the high stability of Pt–CeOx films, we applied electrochemical in situ IR spectroscopy on Pt–CeOx model thin film catalysts during methanol (1 M methanol) oxidation. The model catalysts were prepared by magnetron cosputtering of Pt (9–21 atom %) and CeO2 onto clean and carbon-coated Au supports. All samples were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) before and after reaction. At pH 1 (0.1 M HClO4) the Pt–CeOx dissolves partially during potential cycling, whereas the films are largely stable at pH 6 (0.1 M phosphate buffer). Electrochemical IR spectroscopy of the adsorbed CO shows that metallic Pt is formed on all Pt–CeOx samples during methanol oxidation. In comparison to Pt(111), Pt a...

Despite progress in the understanding of how nanostructuring affects activity of heterogeneous catalysts, there are still fundamental questions to be answered. Do nanoparticle edges have the same catalytic properties as steps on single-crystal surfaces? How much does the increased structural flexibility of nanoparticles contribute to their activity? How do reaction barriers depend on the nanoparticle size? Herein we address these questions regarding an exemplary reaction sequence of complete methane dehydrogenation. Using density functional theory methods we calculate energy profiles of this reaction on edges of 1.2 nm large Pd79 and 1.6 nm large Pd140 particles as well as on Pd(1 1 1) and steps on Pd(2 1 1) single-crystal surfaces. The barriers of the two slowest reaction steps, CH4 → CH3 + H and CH → C + H, notably decrease in the following series of substrates: Pd(1 1 1) ≳ Pd(2 1 1) > Pd 140 > Pd 79 . Importantly, these barriers differ by ⩾20 kJ/mol on Pd140 and Pd(2 1 1), whereas the differences between the barriers on Pd(1 1 1) and Pd(2 1 1) are only ⩽11 kJ/mol. Also, the structural flexibility contributes to higher reactivity several times stronger for Pd79 than for Pd(1 1 1). All calculated elementary steps follow Bronsted–Evans–Polanyi relationships. This study advances the understanding of heterogeneous catalysis by shedding light on several fundamental questions concerning structure–property relationships in nanostructured catalysts.

Recently we have tested a magnetron sputtered Pt-Co catalyst in a hydrogen-fed proton exchange membrane fuel cell and showed its high catalytic activity for the oxygen reduction reaction. Here we present further investigation of the magnetron sputtered Pt-Co thin film catalyst by both experimental and theoretical methods. Scanning electron microscopy and transmission electron microscopy experiments confirmed the nanostructured character of the catalyst. The surface composition of as-deposited and annealed at 773 K Pt-Co films was investigated by surface analysis techniques, such as synchrotron radiation photoelectron spectroscopy and X-ray photoelectron spectroscopy. Modeling based on density functional theory showed that the surface of 6 nm large 1:1 Pt-Co nanoparticles is almost exclusively composed of Pt atoms (>90%) at typical operation conditions and the Co content does not exceed 20% at 773 K, in agreement with the experimental characterization of such films annealed in vacuum. According to experiment, the density of valence states of surface atoms in Pt-Co nanostructures is shifted by 0.3 eV to higher energies, which can be associated with their higher activity in the oxygen reduction reaction. The changes in electronic structure caused by alloying are also reflected in the measured Pt 4f, Co 3p and Co 2p photoelectron peak binding energies.

The alarming atmospheric concentration and continuous emissions of carbon dioxide (CO2) require immediate action. As a result of advances in CO2 capture and sequestration technologies (generally involving point sources such as energy generation plants), large amounts of pure CO2 will soon be available. In addition to geological storage and other applications of the captured CO2, the development of technologies able to convert this carbon feedstock into commodity chemicals may pave the way towards a more sustainable economy. Here, we present a novel multifunctional catalyst consisting of Fe2O3 encapsulated in K2CO3 that can capture and simultaneously transform CO2 into olefins. In contrast to traditional systems in Fischer-Tropsch reactions, we demonstrate that when dealing with CO2 activation (in contrast to CO), very high K loadings are key to capturing the CO2 via the well-known ‘potassium carbonate mechanism’. The proposed catalytic process is demonstrated to be as productive as existing commercial processes based on synthesis gas while relying on economically and environmentally advantageous CO2 feedstock.

A simple and efficient catalyst, benzimidazole (BIMH)-modified copper foil, is developed to enhance the selective conversion of CO2 to C2/C3 products. The overall faradaic efficiency (FE) for CO2 reduction reaches 92.1% and the undesired hydrogen evolution reaction (HER) is lowered to a FE of 7% at -1.07 VRHE.

The high catalytic activity of Pt-Co nanoalloys in oxygen reduction and other reactions is usually attributed to their Pt-rich surfaces. However, identification of the precise near-surface structure is by no means easily achievable experimentally. In this work we systematically analyzed the chemical ordering and surface composition of PtXCo(79-X) and PtXCo(140-X) bimetallic nanoparticles by means of a recently developed method based on topological energy expressions and electronic structure calculations. Pt is found to segregate on the surface, especially on corner and edge sites, forming a one atomic layer thick skin independent of the size and composition of the nanoparticle. In turn, the subsurface shell of the particle is composed mostly of Co, whereas the core area has a mixed composition, which depends on the overall stoichiometry. The formation of an outer Pt shell is corroborated by thoroughly analyzed data of X-ray photoelectron spectroscopy experiments performed with various photon energies on annealed Pt-Co particles prepared in vacuum by magnetron sputtering. The core-shell structure of Pt-Co particles is calculated to be more stable than the respective L10 structure. The obtained topological energy expressions are shown to depend only very moderately on the nanoparticle size, which allowed us to apply them to determine the ordering in ∼4 nm big PtXCo(1463-X) species. The presented results deepen our understanding of the intrinsic structure of Pt-Co nanoparticles depending on their size and composition.

Dry reforming of methane (DRM) proceeds via CH4 decomposition to leave surface carbon species, followed by their removal with CO2-derived species. Reactivity tuning for stoichiometric CH4/CO2 reactants was attempted by alloying the non-noble metals Co and Ni, which have high affinity with CO2 and high activity for CH4 decomposition, respectively. This study was focused on providing evidence of the capturing surface coverage of the reactive intermediates and the associated structural changes of the metals during DRM at high temperature using in-operando X-ray absorption spectroscopy (XAS). On the Co catalysts, the first-order effects with respect to CH4 pressure and negative-order effects with respect to CO2 pressure on the DRM rate are consistent with the competitive adsorption of the surface oxygen species on the same sites as the CH4 decomposition reaction. The Ni surface provides comparatively higher rates of CH4 decomposition and the resultant DRM than the Co catalyst but leaves some deposited carbon on the catalyst surface. In contrast, the bimetallic CoNi catalyst exhibits reactivity towards the DRM but with kinetic orders resembling Co catalyst, producing negligible carbon deposition by balancing CH4 and CO2 activation. The in-operando X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements confirmed that the Co catalyst was progressively oxidized from the surface to the bulk with reaction time, whereas CoNi and Ni remained relatively reduced during DRM. Density functional theory (DFT) calculation considering the high reaction temperature for DRM confirmed the unselective site arrangement between Co and Ni atoms in both the surface and bulk of the alloy nanoparticle (NP). The calculated heat of oxygen chemisorption became more exothermic in the order of Ni, CoNi, Co, consistent with the catalytic behavior. The comprehensive experimental and theoretical evidence provided herein clearly suggests improvement to the catalyst design protocol by selecting the appropriate composition of Co-Ni alloy.

Heteroatom doping of atomically precise nanoclusters (NCs) often yields a mixture of doped and undoped products of single-atom difference, whose separation is extremely difficult. To overcome this challenge, novel synthesis methods are required to offer monodisperse doped NCs. For instance, the direct synthesis of PtAg

Electron microscopy and modelling are used to study CO oxidation on oxide-supported Pd. The perimeter of the metal/oxide interface is shown to affect CO tolerance of the entire particle, demonstrating a long-range effect over micrometre length scales.

N.W., Z.C., and X.Z. contributed equally to this work. This work was supported by the Ontario Research Fund – Research Excellence Program, the Natural Sciences and Engineering Research Council of Canada, and the CIFAR Bio-Inspired Solar Energy program. N.W. and X.D.Z. acknowledge support from International Cooperation Projects of the Ministry of Science and Technology (2014DFE60170), National Natural Science Foundation of China (61474065), and (61674084), Tianjin Research Key Program of Science and Technology (18ZXJMTG00220), 111 Project (B16027), and Fundamental Research Funds for the Central Universities. B.Z. and H.S.P. acknowledge funding from Ministry of Science and Technology (2016YFA0203302), the National Natural Science Foundation of China (21875042), and the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning and Science and Technology Commission of Shanghai Municipality (18QA1400800). This work benefited from access to the 1W1B beamline at Beijing Synchrotron Radiation Facility. The TEM studies in this work were supported by Jingshan Luo. The simulations were performed using the KAUST supercomputer (HPC).

Cerium dioxide (CeO2, ceria) nanoparticles possess size-dependent chemical properties, which may be very different from those of the bulk material. Agglomeration of such particles in nanoarchitectures may further significantly affect their properties. We computationally model the self-assembly of CenO2n particles (n = 38, 40, 80)-zero-dimensional (0D) structures-in one- and two-dimensional (1D and 2D) nanoarchitectures by employing density-functional methods. The electronic properties of 1D Ce80O160 and 2D Ce40O80 resemble those of larger 0D crystallites, Ce140O280, rather than those of their building blocks. These 0D, 1D and 2D nanostructures are employed to study the size dependence of the formation energy of an oxygen vacancy, Ef(Ovac), a central property in ceria chemistry. We rationalize within a common electronic structure framework the variations of the Ef(Ovac) values, which are computed for the CenO2n nanostructures with different sizes and dimensionalities. We identify: (i) the bandwidth of the unoccupied density of states projected onto the Ce 4f levels as an important factor, which controls Ef(Ovac); and (ii) the corner Ce atoms as the structural motif essential for a noticeable reduction of Ef(Ovac). These results help to understand the size dependent behaviour of Ef(Ovac) in nanostructured ceria., Financial support has been provided by the European Community (FP7-NMP.2012.1.1-1 project ChipCAT, Ref. Nº310191), the Spanish MINECO (CTQ2012-34969, FIS2012-37549-C05-02, RYC-2011-09582) and the Generalitat de Catalunya (2014SGR97, 2014SGR301, XRQTC). SMK thanks the Spanish Ministerio de Educación for a pre-doctoral FPU grant AP2009-3379.

The article deals with an issue of density-functional description of heterogeneous catalysts by nanoparticle models instead of still commonly employed slab models. Typically, active (metal) components are present in catalysts as nano-aggregates formed of many thousands atoms, remaining due to their size inaccessible even for modern first-principles computations. However, such species could be rather realistically represented by notably smaller computationally tractable model nanoparticles, whose surface sites only marginally change the reactivity with increasing particle size. Herein presented results are mainly related to methane dehydrogenation on Pt catalysts, methanol decomposition on Pd catalysts and the composition of active sites on Pt/ceria catalysts. They document the feasibility of taking nanostructuring effects into account in density-functional modeling (at least for transition metals) and, more importantly, demonstrate that ignoring the nanoeffects in these systems leads to misrepresentation of their catalytic properties.

The performance of various commonly used density functionals is established by comparing calculated values of atomic structure data, cohesive energies, and bulk moduli of all transition metals to available experimental data. The functionals explored are the Ceperley-Alder (CA), Vosko-Wilk-Nussair (VWN) implementation of the Local Density Approximation (LDA); the Perdew-Wang (PW91) and Perdew-Burke-Ernzerhof (PBE) forms of the Generalized Gradient Approximation (GGA), and the RPBE and PBEsol modifications of PBE, aimed at better describing adsorption energies and bulk solid lattice properties, respectively. The present systematic study shows that PW91 and PBE consistently provide the smallest differences between the calculated and experimental values. Additional calculations of the (111) surface energy of several face centered cubic (fcc) transition metals reveal that LDA produces the most accurate results, while all other functionals significantly underestimate the experimental values. RPBE severely underestimates surface energy, which may be the origin for the reduced surface chemical activity and the better performance of RPBE describing adsorption energies.

Atomically precise self-assembled architectures of noble metals with unique surface structures are necessary for prospective applications. However, the synthesis of such structures based on silver is challenging because of their instability. In this work, by developing a selective and controlled doping strategy, we synthesized and characterized a rod-shaped, charge-neutral, diplatinum-doped Ag nanocluster (NC) of [Pt

Heteroatom doping of atomically precise nanoclusters (NCs) often yields a mixture of doped and undoped products of single-atom difference, whose separation is extremely difficult. To overcome this challenge, novel synthesis methods are required to offer monodisperse doped NCs. For instance, the direct synthesis of PtAg28 NCs produces a mixture of [Ag29(BDT)12(TPP)4]3- and [PtAg28(BDT)12(TPP)4]4- NCs (TPP: triphenylphosphine; BDT: 1,3-benzenedithiolate). Here, we designed a ligand-exchange (LE) strategy to synthesize single-sized, Pt-doped, superatomic Ag NCs [PtAg28(BDT)12(TPP)4]4- by LE of [Pt2Ag23Cl7(TPP)10] NCs with BDTH2 (1,3-benzenedithiol). The doped NCs were thoroughly characterized by optical and photoelectron spectroscopy, mass spectrometry, total electron count, and time-dependent density functional theory (TDDFT). We show that the Pt dopant occupies the center of the PtAg28 cluster, modulates its electronic structure and enhances its photoluminescence intensity and excited-state lifetime, and also enables solvent interactions with the NC surface. Furthermore, doped NCs showed unique reactivity with metal ions - the central Pt atom of PtAg28 could not be replaced by Au, unlike the central Ag of Ag29 NCs. The achieved synthesis of single-sized PtAg28 clusters will facilitate further applications of the LE strategy for the exploration of novel multimetallic NCs.

Chemical ordering in bimetallic nanocrystallites can now be efficiently determined by density-functional calculations with the help of topological energy expressions. Herein, we deal with extending the usage of that computational scheme. We show that it enables one to structurally characterize bimetallic nanoparticles of less regular shapes than previously studied magic-type particles. In fcc Pd-Au particles of different shapes (cuboctahedral Pd58Au58, C3v Pd61Au61, cubic Pd68Au67, and truncated octahedral Pd70Au70), we identify the surface segregation of gold as the driving force to the lowest-energy chemical ordering. We applied the calculated descriptor values quantifying the segregation propensity of Au and energies of Pd-Au bonds in these ∼1.5 nm large particles to optimize and analyze the chemical ordering in 3.7-6 nm large Pd-Au particles. We also discuss how to predict the chemical ordering in nanoalloys at elevated temperatures. The present study paves the way to advanced structural investigations of nanoalloys to substantially accelerate their knowledge-driven engineering and manufacturing.

Combining density functional theory (DFT) calculations with experimental data from temperature-programmed desorption (TPD) and polarization-modulated infrared reflection absorption spectroscopy (PM-IRAS), we have provided evidence for the rearrangement of Pd and Zn atoms in PdZn surface alloys on Pd(111) in the presence of CO. Such systems represent valuable models for novel methanol steam reforming catalysts, with CO being an undesired byproduct of this reaction. The reconstructed surface was calculated to be more stable in the presence of CO and capable of adsorbing CO on top of Pd atoms up to a saturation coverage of 1/2 monolayer (ML). To the contrary, on a surface with conventional, bulklike geometric arrangement of Pd and Zn atoms in rows, CO adsorption on bridge sites with a saturation coverage of ∼1/3 ML was predicted. Adsorption of CO on top sites was confirmed with PM-IRAS and the saturation coverage of 1/2 ML was derived from TPD experiments, supporting the suggested reconstruction of PdZn/Pd(1...

Steps are ubiquitous structural features present on surfaces. They often exhibit unique physical and chemical properties, which in many cases are of even greater practical importance than the respe...

The adsorption and diffusion of benzene, hexafluorinated benzene, perylene, perylene-3,4,9,10-tetracarboxylic-3,4,9,10-diimide (PTCDI) and perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) on graphene has been studied by density functional means on a generalized gradient approximation level, including a semi-empirical correction to account for dispersive forces. It is shown that for all considered molecules the adsorption strength is mainly due to the latter, with the electronic interaction being relatively small and repulsive. As a rule-of-thumb, the strength of the adsorption interaction is 11–13 kJ mol −1 per C atom. The adsorption energies are large enough to avoid desorption at room temperature. The estimated diffusion and rotation barriers are remarkably small, thus allowing a rapid diffusion and self-arrangement even at cryogenic temperatures. Finally, the adsorption of benzene or perylene derivatives may act, depending on the molecule and nature of the substituents, as a source for n - or p -doping, achieving up to 0.2 electrons(holes)/molecule. The lowest unoccupied molecular orbitals of PTCDI and PTCDA are close in energy to the Dirac point of graphene and induce a conduction gap of ∼210–240 meV in the graphene band structure. Thus, they can be used for graphene band gap engineering and doping by the non-aggressive method of molecular adsorption.

We have studied the interaction of water with stoichiometric CeO2(111)/Cu(111), partially reduced CeO2–x/Cu(111), and Pt/CeO2/Cu(111) model catalysts by means of synchrotron–radiation photoelectron spectroscopy (SRPES), resonant photoemission spectroscopy (RPES) at the Ce 4d edge, infrared reflection absorption spectroscopy (IRAS), and density functional (DF) calculations. The principal species formed during adsorption of water at 160 K on CeO2(111) films is chemisorbed molecular water. On the surface of CeO2–x water partially dissociates yielding hydroxyl groups. By use of core-level PES, differentiation between chemisorbed water and hydroxyl groups is complicated by the overlap of the corresponding spectral features. Nevertheless, we determined three characteristic indicators for OH groups on ceria: (i) the presence of 1π and 3σ states in valence band (VB) PES; (ii) an increase of the binding energy (BE) separation between the O 1s spectral components of lattice oxygen and OH/H2O; (iii) an increase of t...

The basic bonding mechanisms of graphene on transition-metal surfaces leading to chemisorption and physisorption are identified and studied in the example of graphene adsorption on Ni(111) by means of density functional theory at the general gradient approximation level with semiempirical corrections for dispersive interactions. In the more stable chemisorbed graphene, relatively strong Pauli repulsion between graphene and the substrate is compensated by donation/back-donation bonding of the same magnitude. In this case, the electronic interactions with the substrate significantly perturb the electronic structure of graphene, but the adsorption energy is still dominated by van der Waals (vdW) interactions. In physisorbed graphene, weak Pauli repulsion equilibrates the vdW attraction without affecting the electronic structure of graphene. The relative stability of physisorbed and chemisorbed graphene is shown to be changed by carbidic C impurities in the subsurface region.

Scanning tunneling microscopy (STM) combined with density functional theory (DFT) are used to analyze the structural and electronic properties of step edges on the surface of CeO2(111) films grown ...

This computational study deals with the adsorption of CH3, CH2, CH, CH2OH, CH3O, CH2O and CHO species on a nanoparticle Pd79 that mimics experimentally investigated model Pd catalysts. We quantify structural, energetic and vibrational parameters of these adsorption complexes and analyse their dependence on the adsorption site. Most of the considered low coordinated adsorption sites are found to be favoured by 20–50 kJ/mol over the sites on (1 1 1) facets. Some of the studied species have distinguishable vibrational parameters at different adsorption sites of the model nanoparticle, making possible spectroscopic characterization of respective adsorption complexes. Fil: Kozlov, Sergey M.. Universidad de Barcelona; España Fil: Cabeza, Gabriela Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Física; Argentina Fil: Neyman, Konstantin M.. Institució Catalana de Recerca i Estudis Avançats; España

A combined high-resolution X-ray photoelectron spectroscopy (HR-XPS) and ab initio density functional theory study on graphene on Ni(111) shows the coexistence of two structures, a bridge-top and a top-fcc structure, that have almost identical energies according to DFT calculations. Consequently, both geometries are detected simultaneously on the Ni(111) surface by HR-XPS, while their relative fractions depend on minor surface defect concentrations (pinning sites). The two structures are identified due to their different core level shifts that are in line with DFT calculations.