Modern Surface Science and Surface Technologies: An Introduction

Data-Driven Structure Recognition of Scanning Tunneling Microscopy Images in a Case of Iron Carbide

Scanning tunneling microscopy (STM) serves as a critical tool for high-resolution surface imaging, yet deciphering the atomic structures from STM images on multielement surfaces, such as oxides and carbides, remains a challenging task that heavily relies on the expertise and intuition of researchers. In this study, we introduce a data-driven method for rapid structural recognition from STM images. This method involves extracting structural features, filtering through a structural database, and matching with simulated STM images and surface energy analyses, thereby providing researchers with several of the most probable structures. We demonstrate the capabilities of this technique using our previously reported iron carbide grown on an Fe(110) crystal. By proposing a candidate structure set and establishing a comprehensive database linking STM images to corresponding structures and surface energies, we selected 6 out of more than 10 000 possible surfaces. On the basis of these 6 recommendations, researchers can conveniently determine the real surface structures. Our work provides an efficient tool for the structure recognition of STM images to construct surface structures, potentially serving as a universal auxiliary tool for STM structural analysis.

One-Shot Dual-Detection-Based Single-Molecule Super-Resolution Imaging Method for Real-Time Observation of Spatiotemporal Catalytic Activity Variations on the Plasmonic Gold Nanoparticle Surface

Understanding the relationship between the surface properties of a single plasmonic nanoparticle and its catalytic performance is critical for developing highly efficient nanocatalysts. In this study, a one-shot dual-detection-based single-molecule super-resolution imaging method in the evanescent field was developed to observe real-time spatiotemporal catalytic activity on a single plasmonic gold nanoparticle (AuNP) surface. The scattering intensity of AuNPs and the fluorescence of resorufin molecules produced on the AuNP surface were obtained simultaneously to investigate the relationship between nanoparticles and catalytic reactions at a single-molecule level. Chemisorbed adsorbates (i.e., catalytic product and resorufin) changed the electron density of individual AuNPs throughout the catalytic cycle, resulting in the fluctuation of the scattering intensity of individual AuNPs, which was attributed to the electron transfer between reactant resazurin molecules and AuNPs. The increase in the electron density of individual AuNPs affected the catalytic reaction rate. Furthermore, sequential mapping of individual catalytic events at the subdiffraction limit resolution was completed for real-time surface dynamics and spatiotemporal activity variations on the single AuNP surface. The developed method can aid in understanding surface-property-dependent catalytic kinetics and facilitate the development of nanoparticle-based heterogeneous catalysts at subdiffraction limit resolution.

Recent advances in in-situ transmission electron microscopy techniques for heterogeneous catalysis

The process of heterogeneous catalytic reaction under working conditions has long been considered a "black box", which is mainly because of the difficulties in directly characterizing the structural changes of catalysts at the atomic level during catalytic reactions. The development of in situ transmission electron microscopy (TEM) techniques offers opportunities for introducing a realistic chemical reaction environment in TEM, making it possible to uncover the mystery of catalytic reactions. In this article, we present a comprehensive overview of the application of in situ TEM techniques in heterogeneous catalysis, highlighting its utility for observing gas-solid and liquid-solid reactions during thermal catalysis, electrocatalysis, and photocatalysis. in situ TEM has a unique advantage in revealing the complex structural changes of catalysts during chemical reactions. Revealing the real-time dynamic structure during reaction processes is crucial for understanding the intricate relationship between catalyst structure and its catalytic performance. Finally, we present a perspective on the future challenges and opportunities of in situ TEM in heterogeneous catalysis.

Noble metal nanodendrites: growth mechanisms, synthesis strategies and applications

Inorganic nanodendrites (NDs) have become a kind of advanced nanomaterials with broad application prospects because of their unique branched architecture. The structural characteristics of nanodendrites include highly branched morphology, abundant tips/edges and high-index crystal planes, and a high atomic utilization rate, which give them great potential for usage in the fields of electrocatalysis, sensing, and therapeutics. Therefore, the rational design and controlled synthesis of inorganic (especially noble metals) nanodendrites have attracted widespread attention nowadays. The development of synthesis strategies and characterization methodology provides unprecedented opportunities for the preparation of abundant nanodendrites with interesting crystallographic structures, morphologies, and application performances. In this review, we systematically summarize the formation mechanisms of noble metal nanodendrites reported in recent years, with a special focus on surfactant-mediated mechanisms. Some typical examples obtained by innovative synthetic methods are then highlighted and recent advances in the application of noble metal nanodendrites are carefully discussed. Finally, we conclude and present the prospects for the future development of nanodendrites. This review helps to deeply understand the synthesis and application of noble metal nanodendrites and may provide some inspiration to develop novel functional nanomaterials (especially electrocatalysts) with enhanced performance.

Facet effect of hematite on the hydrolysis of phthalate esters under ambient humidity conditions

Phthalate esters (PAEs) have been extensively used as additives in plastics and wallcovering, causing severe environmental contamination and increasing public health concerns. Here, we find that hematite nanoparticles with specific facet-control can efficiently catalyze PAEs hydrolysis under ambient humidity conditions, with the hydrolysis rates 2 orders of magnitude higher than that in water saturated condition. The catalytic performance of hematite shows a significant facet-dependence with the reactivity in the order {012} > {104} ≫ {001}, related to the atomic array of surface undercoordinated Fe. The {012} and {104} facets with the proper neighboring Fe-Fe distance of 0.34-0.39 nm can bidentately coordinate with PAEs, and thus induce much stronger Lewis-acid catalysis. Our study may inspire the development of nanomaterials with appropriate surface atomic arrays, improves our understanding for the natural transformation of PAEs under low humidity environment, and provides a promising approach to remediate/purify the ambient air contaminated by PAEs.

Neumann's principle based eigenvector approach for deriving non-vanishing tensor elements for nonlinear optics

Physical properties are commonly represented by tensors, such as optical susceptibilities. The conventional approach of deriving non-vanishing tensor elements of symmetric systems relies on the intuitive consideration of positive/negative sign flipping after symmetry operations, which could be tedious and prone to miscalculation. Here, we present a matrix-based approach that gives a physical picture centered on Neumann's principle. The principle states that symmetries in geometric systems are adopted by their physical properties. We mathematically apply the principle to the tensor expressions and show a procedure with clear physical intuition to derive non-vanishing tensor elements based on eigensystems. The validity of the approach is demonstrated by examples of commonly known second and third-order nonlinear susceptibilities of chiral/achiral surfaces, together with complicated scenarios involving symmetries such as D6 and Oh symmetries. We then further applied this method to higher-rank tensors that are useful for 2D and high-order spectroscopy. We also extended our approach to derive nonlinear tensor elements with magnetization, which is critical for measuring spin polarization on surfaces for quantum information technologies. A Mathematica code based on this generalized approach is included that can be applied to any symmetry and higher order nonlinear processes.

Carbon Deposition on Heterogeneous Pt Catalysts Promotes the Selective Hydrogenation of Halogenated Nitroaromatics

Pt-based heterogeneous metal catalysts are commonly used in the hydrogenation of nitro groups. However, the continuous large metal domain size and the complex interaction between the substrates and metal surface usually inevitably result in side reactions, such as dehalogenation of halogenated nitroaromatics. In this work, by simply treating the Pt-based catalysts with CO at elevated temperature, the Boudouard reaction taking place on Pt surface results in the deposition of carbon species thereon. The carbon deposition not only inhibits the dehalogenation by restricting the planar interaction of the aromatic group with the Pt surface that is segmented by C, the hydrogenation activity of the nitro group is also enhanced on the partially positively charged surface Pt sites created by the electron-withdrawing interstitial C. Such a simple treatment strategy is effective for fabricating Pt-based catalysts on different supports toward the selective hydrogenation of a wide range of halogenated nitroaromatics.

Chemical Identity of Poly(N-vinylpyrrolidone) End Groups Impact Shape Evolution During the Synthesis of Ag Nanostructures

Ag nanocubes (AgNCs) are predominantly synthesized by the polyol method, where the solvent (ethylene glycol) is considered the reducing agent and poly(N-vinylpyrrolidone) (PVP) the shape-directing agent. An experimental phase diagram for the formation of Ag nanocubes as a function of PVP monomer concentration (C_m) and molecular weight (M_w) demonstrated end groups of PVP impact the final Ag product. Measured rates of the initial Ag⁺ reduction at different PVP C_m and M_w confirmed the reducing effect originates from end-groups. PVP with well-defined aldehyde and hydroxyl end groups lead to the formation of Ag nanocubes and nanowires respectively, indicating the faster reducing agent formed kinetically preferred nanowires. We demonstrate PVP end-groups induce initial reduction of Ag⁺ to form seeds followed by autocatalytic reduction of Ag⁺ by ethylene glycol (and not solvent oxidation products) to form Ag nanostructures. The current study enabled a quantitative description of the role of PVP in nanoparticle shape-control and demonstrates a unique opportunity to design nanostructures by combining nanoparticle synthesis with polymer design to introduce specific physicochemical properties.

Sum frequency generation spectroscopy in heterogeneous model catalysis: a minireview of CO-related processes

Sum frequency generation (SFG) vibrational spectroscopy is applied to ambient pressure surface science studies of adsorption and catalytic reactions at solid/gas interfaces.

An ultrahigh vacuum-compatible reaction cell for model catalysis under atmospheric pressure flow conditions

Atmospheric pressure reactions on model catalysts are typically performed in so-called high-pressure cells, with product analysis performed by gas chromatography (GC) or mass spectrometry (MS). However, in most cases, these cells have a large volume (liters) so that the reactions on catalysts with only cm2 surface area can be carried out only in the (recirculated) batch mode to accumulate sufficient product amounts. Herein, we describe a novel small-volume (milliliters) catalytic reactor that enables kinetic studies under atmospheric pressure flow conditions. The cell is located inside an ultrahigh vacuum chamber that is deliberately limited to basic functions. Model catalyst samples are mounted inside the reactor cell, which is locked to an oven for external heating and closed by using an extendable/retractable gas dosing tube. Reactant and product analyses are performed by both micro-GC and MS. The functionality of the new design is demonstrated by catalytic ethylene (C2H4) hydrogenation on polycrystalline Pt and Pd foils.

Chiral Surface and Geometry of Metal Nanocrystals

Chirality is a basic property of nature and has great importance in photonics, biochemistry, medicine, and catalysis. This importance has led to the emergence of the chiral inorganic nanostructure field in the last two decades, providing opportunities to control the chirality of light and biochemical reactions. While the facile production of 3D nanostructures has remained a major challenge, recent advances in nanocrystal synthesis have provided a new pathway for efficient control of chirality at the nanoscale by transferring molecular chirality to the geometry of nanocrystals. Interestingly, this discovery stems from a purely crystallographic outcome: chirality can be generated on high-Miller-index surfaces, even for highly symmetric metal crystals. This is the starting point herein, with an overview of the scientific history and a summary of the crystallographic definition. With the advance of nanomaterial synthesis technology, high-Miller-index planes can be selectively exposed on metallic nanoparticles. The enantioselective interaction of chiral molecules and high-Miller-index facets can break the mirror symmetry of the metal nanocrystals. Herein, the fundamental principle of chirality evolution is emphasized and it is shown how chiral surfaces can be directly correlated with chiral morphologies, thus serving as a guide for researchers in chiral catalysts, chiral plasmonics, chiral metamaterials, and photonic devices.

Mapping Electrochemical Heterogeneity at Gold Surfaces: A Second Harmonic Imaging Study

Designing efficient catalysts requires correlating surface structure and local chemical composition with reactivity on length scales from nanometers to tens of microns. While much work has been done on this structure/function correlation on single crystals, comparatively little has been done for catalysts of relevance in applications. Such materials are typically highly heterogeneous and thus require methods that allow mapping of the structure/function relationship during electrochemical conversion. Here, we use optical second harmonic imaging combined with cyclic voltammetry to map the surface of gold nanocrystalline and polycrystalline electrodes during electrooxidation and to quantify the spatial extent of surface reconstruction during potential cycling. The wide-field configuration of our microscope allows for real-time imaging of an area ∼100 μm in diameter with submicron resolution. By analyzing the voltage dependence of each pixel, we uncover the heterogeneity of the second harmonic signal and quantify the fraction of domains where it follows a positive quadratic dependence with increasing bias. There, the second harmonic intensity is mainly ascribed to electronic polarization contributions at the metal/electrolyte interface. Additionally, we locate areas where the second harmonic signal follows a negative quadratic dependence with increasing bias, which also show the largest changes during successive cyclic voltammetry sweeps as determined by an additional correlation coefficient analysis. We assign these areas to domains of higher roughness that are prone to potential-induced surface restructuring and where anion adsorption occurs at lower potentials than expected based on the cyclic voltammetry.

Imaging the Heterogeneity of the Oxygen Evolution Reaction on Gold Electrodes Operando: Activity is Highly Local

Understanding the mechanism of the oxygen evolution reaction (OER), the oxidative half of electrolytic water splitting, has proven challenging. Perhaps the largest hurdle has been gaining experimental insight into the active site of the electrocatalyst used to facilitate this chemistry. Decades of study have clarified that a range of transition-metal oxides have particularly high catalytic activity for the OER. Unfortunately, for virtually all of these materials, metal oxidation and the OER occur at similar potentials. As a result, catalyst surface topography and electronic structure are expected to continuously evolve under reactive conditions. Gaining experimental insight into the OER mechanism on such materials thus requires a tool that allows spatially resolved characterization of the OER activity. In this study, we overcome this formidable experimental challenge using second harmonic microscopy and electrochemical methods to characterize the spatial heterogeneity of OER activity on polycrystalline Au working electrodes. At moderately anodic potentials, we find that the OER activity of the electrode is dominated by <1% of the surface area and that there are two types of active sites. The first is observed at potentials positive of the OER onset and is stable under potential cycling (and thus presumably extends multiple layers into the bulk gold electrode). The second occurs at potentials negative of the OER onset and is removed by potential cycling (suggesting that it involves a structural motif only 1–2 Au layers deep). This type of active site is most easily understood as the catalytically active species (hydrous oxide) in the so-called incipient hydrous oxide/adatom mediator model of electrocatalysis. Combining the ability we demonstrate here to characterize the spatial heterogeneity of OER activity with a systematic program of electrode surface structural modification offers the possibility of creating a generation of OER electrocatalysts with unusually high activity.

Nature-inspired electrocatalysts and devices for energy conversion

A NICE approach for the design of nature-inspired electrocatalysts and electrochemical devices for energy conversion.

Recent advances in two-dimensional materials and their nanocomposites in sustainable energy conversion applications

Two-dimensional (2D) materials have a wide platform in research and expanding nano- and atomic-level applications. This study is motivated by the well-established 2D catalysts, which demonstrate high efficiency, selectivity and sustainability exceeding that of classical noble metal catalysts for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and/or hydrogen evolution reaction (HER). Nowadays, the hydrogen evolution reaction (HER) in water electrolysis is crucial for the cost-efficient production of a pure hydrogen fuel. We will also discuss another important point related to electrochemical carbon dioxide and nitrogen reduction (ECR and N2RR) in detail. In this review, we mainly focused on the recent progress in the fuel cell technology based on 2D materials, including graphene, transition metal dichalcogenides, black phosphorus, MXenes, metal-organic frameworks, and metal oxide nanosheets. First, the basic attributes of the 2D materials were described, and their fuel cell mechanisms were also summarized. Finally, some effective methods for enhancing the performance of the fuel cells based on 2D materials were also discussed, and the opportunities and challenges of 2D material-based fuel cells at the commercial level were also provided. This review can provide new avenues for 2D materials with properties suitable for fuel cell technology development and related fields.

Three-dimensional morphology of anatase nanocrystals obtained from supercritical flow synthesis with industrial grade TiOSO4 precursor

Anatase TiO2 (a-TiO2) nanocrystals are vital in catalytic applications both as catalysts (e.g. photodegradation) and as a carrier material (e.g. NOx removal from exhaust). The synthesis of a-TiO2 nanocrystals and their properties have been heavily scrutinized, but there exists a clear gap between the scientific literature, and the scale and price expectation of industrial application. Here it is demonstrated that the industrially most attractive Ti precursor, titanyl sulfate (TiOSO4), can be combined with the green, scalable and fast supercritical flow method to produce phase pure and highly crystalline a-TiO2 nanoparticles with high specific surface area. Control of the nanocrystal morphology is important since it is known that certain facets substantially promote catalytic activity. It is, however, in itself challenging to determine nanocrystal morphology to provide a rational basis for the synthesis control. Here we advocate the use of advanced Rietveld refinement of powder X-ray diffraction data including anisotropic size broadening models in aiding to establish the sample three-dimensional morphology. This relatively quick and robust method assists in overcoming the often encountered ambiguity inherent in two-dimensional to three-dimensional reconstruction of selected particle morphologies with transmission electron microscopy and tomography techniques.

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.

Revisiting the Polyol Synthesis of Silver Nanostructures: Role of Chloride in Nanocube Formation

Chloride (Cl^-) is often used together with polyvinylpyrrolidone (PVP) in the polyol synthesis of Ag nanocubes. In the literature, shape control is attributed predominantly to the preferential binding of PVP to Ag(100) facets compared to Ag(111) facets, whereas the role of Cl^- has not been well studied. Several hypotheses have been proposed regarding the role of Cl^-; however, there is still no consensus regarding the exact influence of Cl^- in the shape-controlled synthesis of Ag nanocubes. To examine the influence of Cl^-, we undertook a joint theoretical-experimental study. Experimentally, we examined the influence of Cl^- concentration on the shape of Ag nanoparticles (NPs) at constant H⁺ concentration. In the presence of H⁺, in situ formed HNO₃ etches the initially formed Ag seeds and slows down the overall reduction of Ag⁺, which promotes the formation of monodisperse Ag NPs. Ex situ experiments probed the evolution of Cl^- during the growth of Ag nanocubes, which involves the initial formation of AgCl nanocubes, and their subsequent dissolution to release Cl^-, which adsorbs onto the surfaces of single crystal seeds to impact shape evolution through apparent thermodynamic control. The formation of cubes is independent of the source of AgCl, indicating temporal control of the Cl^- chemical potential in solution leads to high-yield synthesis of Ag nanocubes. Increasing the concentration of Cl^- alone leads to a progression in shape from truncated octahedra, to cuboctahedra, truncated cubes, and ultimately cubes, directly demonstrating the importance of Cl^- in Ag NP shape control. We used ab initio thermodynamics calculations based on density functional theory to probe the role of Cl^- in directing shape control. With increasing Cl chemical potential (surface coverage), calculated surface energies γ of Ag facets transition from γ₁₁₁ < γ₁₀₀ to γ₁₀₀ < γ₁₁₁ and predict Wulff shapes terminated with an increasing (100) contribution, consistent with experimental observations. The combination of theory and experiment is beneficial for advancing the understanding of nanocrystal formation.

An efficient thin-walled Pd/polypyrrole hybrid nanotube biocatalyst for sensitive detection of ascorbic acid

Controllable fabrication of novel and uniform noble metal nanoparticles on a specific support with a superior catalytic or electrocatalytic performance is of significantly importance for practical applications. In this report, we demonstrated an effective way to fabricate uniform thin-walled Pd/polypyrrole (PPy) hollow nanotubes. The prepared Pd/PPy hybrid nanotubes exhibited an excellent peroxidase-like activity to oxidize a typical peroxidase substrate such as 3,3',5,5'-tetramethylbenzidine in comparison with traditional Pd/C and Pd black catalysts. The outstanding catalytic activity of the Pd/PPy hybrid nanotubes for peroxidase mimicking could be resulting from their unique hollow characteristic and an interfacial effect between PPy and Pd components. Based on the favorable catalytic property of the Pd/PPy hybrid nanotubes, a convenient and rapid colorimetric way to sensitively determine ascorbic acid has been presented. The detection limit was around 0.062 μM and an excellent selectivity was also achieved. The developed detection system in this study could be extended to the fields of bioscience and biotechnology with promising prospects.

Toward Rationally Designing Surface Structures of Micro- and Nanocrystallites: Role of Supersaturation

Tailoring the surface structures of nanocrystals is an exciting research area on account of appealing surface-dependent properties in various applications. Although significant progress has been made in recent years, current synthetic approaches are mainly dependent upon trial and error because of the ambiguous roles of various influencing factors in complicated environments. Therefore, a general theory for predicting and guiding the rationally controlled synthesis of micro- and nanocrystallites with specific surface structures is highly desired. Of note, previous research attention was mainly focused on the crystal growth in near equilibrium conditions. However, in supersaturated growth environments (nonequilibrium conditions), the corresponding crystal growth theories are still limited. Recently, the supersaturation-controlled surface structure strategy, which is derived from thermodynamics and the Thomson-Gibbs equation, has opened up a new avenue for the control the surface structures of crystals. This strategy involves manipulating the supersaturation of growth units to control the surface structure of micro- and nanocrystallites, as the surface energy of exposed facets is correlated to the supersaturation of growth blocks. Based on the proposed theory, micro- and nanocrystallites with various surface structures, especially high-energy facets, have been successfully synthesized by our group and other researchers in past years. In order to draw lessons from previous studies, it is imperative to give a timely research account related to the supersaturation strategy and corresponding applications in controlling surface structures of different crystallites. In this Account, we explore the supersaturation-controlled surface structure strategy to construct functional nanomaterials with desired architectures. First, we highlight the role of supersaturation of growth units from theoretical analysis after a short introduction of fundamental principles for crystal growth. Then, some detailed cases concerning evolution of surface structures are presented to highlight the key experimental factors involved in manipulating the supersaturation of growth units during synthetic processes. These factors include solvents, reaction rates, and additives in wet chemical routes as well as overpotential in electrochemical routes. In addition, we briefly discuss the role of supersaturation in growth kinetics with focus on explaining the formation of spherical micro- and nanocrystallites at extremely high supersaturation. Finally, a general summary of the supersaturation-dependent surface structure control and future prospects in this field are provided. It is expected that this Account will deepen the current understanding on fundamental principles behind the control of surface structures of micro- and nanocrystallites, which can help us to construct desirable nanomaterials and promote their practical applications.

Rapid estimation of activation energy in heterogeneous catalytic reactions via machine learning

Estimation of activation energies within heterogeneous catalytic reactions is performed using machine learning and catalysts dataset. In particular, descriptors for determining activation energy are revealed within the 788 activation energy dataset. With the implementation of machine learning and chosen descriptors, activation energy can be instantly predicted with over 90% accuracy during cross-validation. Thus, rapid estimation of activation energies within heterogeneous catalytic reactions can be made achievable via machine learning, leading toward the acceleration of catalysts design and characterization. © 2018 Wiley Periodicals, Inc.

Atmospheric pressure reaction cell for operando sum frequency generation spectroscopy of ultrahigh vacuum grown model catalysts

A new custom-designed ultrahigh vacuum (UHV) chamber coupled to a UHV and atmospheric-pressure-compatible spectroscopic and catalytic reaction cell is described, which allows us to perform IR-vis sum frequency generation (SFG) vibrational spectroscopy during catalytic (kinetic) measurements. SFG spectroscopy is an exceptional tool to study vibrational properties of surface adsorbates under operando conditions, close to those of technical catalysis. This versatile setup allows performing surface science, SFG spectroscopy, catalysis, and electrochemical investigations on model systems, including single crystals, thin films, and deposited metal nanoparticles, under well-controlled conditions of gas composition, pressure, temperature, and potential. The UHV chamber enables us to prepare the model catalysts and to analyze their surface structure and composition by low energy electron diffraction and Auger electron spectroscopy, respectively. Thereafter, a sample transfer mechanism moves samples under UHV to the spectroscopic cell, avoiding air exposure. In the catalytic cell, SFG spectroscopy and catalytic tests (reactant/product analysis by mass spectrometry or gas chromatography) are performed simultaneously. A dedicated sample manipulation stage allows the model catalysts to be examined from LN₂ temperature to 1273 K, with gaseous reactants in a pressure range from UHV to atmospheric. For post-reaction analysis, the SFG cell is rapidly evacuated and samples are transferred back to the UHV chamber. The capabilities of this new setup are demonstrated by benchmark results of CO adsorption on Pt and Pd(111) single crystal surfaces and of CO adsorption and oxidation on a ZrO₂ supported Pt nanoparticle model catalyst grown by atomic layer deposition.

Catalyst design by scanning probe block copolymer lithography

Scanning probe block copolymer lithography (SPBCL), in combination with density-functional theory (DFT), has been used to design and synthesize hydrogen evolution catalysts. DFT was used to calculate the hydrogen adsorption energy on a series of single-element, bimetallic, and trimetallic (Au, Pt, Ni, and Cu) substrates to provide leads that could be synthesized in the form of alloy or phase-separated particles via SPBCL. PtAuCu (18 nm, ∼1:1:1 stoichiometry) has been identified as a homogeneous alloy phase that behaves as an effective hydrogen evolution catalyst in acidic aqueous media, even when it is made in bulk form via solution phase methods. Significantly, the bulk-prepared PtAuCu/C nanocatalyst discovered via this process exhibits an activity seven times higher than that of the state-of-the-art commercial Pt/C catalyst (based upon Pt content). The advantage of using SPBCL in the discovery process is that one can uniformly make particles, each consisting of a uniform phase combination (e.g., all alloy or all phase-segregated species) at a fixed elemental ratio, an important consideration when working with polyelemental species where multiple phases may exist.

Reduction of NO with NH3 over ferric oxide nanocrystals: the crystallographic facet-induced catalytic enhancement

The {001} surface of the Fe₂O₃ hexagon-shaped catalyst is particularly active for NO removal, which is of major environmental interest for air pollution control.

Insights into structure and dynamics of (Mn,Fe)Ox-promoted Rh nanoparticles

The mutual interaction between Rh nanoparticles and manganese/iron oxide promoters in silica-supported Rh catalysts for the hydrogenation of CO to higher alcohols was analyzed by applying a combination of spectroscopy and microscopy.

Recent progress on single-molecule nanocatalysis based on single-molecule fluorescence microscopy

Understanding the heterogeneous catalytic properties of nanoparticles is of great significance for the development of high efficient nanocatalysts, but the intrinsic heterogeneities of nanocatalysts were always covered in traditional ensemble studies. This issue can be overcome if one can follow the catalysis of individual nanoparticles in real time. This paper mainly summarizes recent developments in single-molecule nanocatalysis at single particle level in Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. These developments include the revealing of catalytic kinetics of different types (plane & edge) of surface atoms on individual Pd nanocubes, the observing of in situ deactivation of individual carbon-supported Pt nanoparticles during the electrocatalytic hydrogen-oxidation reaction, and the measurement of catalytic activation energies on single nanocatalysts for both product formation process and dissociation process, etc. These studies further indicate the advantages or unique abilities of single-molecule methods in the studies of nanocatalysis or even chemical reactions.

Operando chemistry of catalyst surfaces during catalysis

The chemistry of a catalyst surface during catalysis is crucial for a fundamental understanding of the mechanisms of a catalytic reaction performed on the catalyst in the gas or liquid phase.

Moderate oxidation levels of Ru nanoparticles enhance molecular oxygen activation for cross-dehydrogenative-coupling reactions via single electron transfer

Ruthenium nanoparticles with altered surface oxidation states showed a volcano shaped relationship in molecular oxygen activation via single electron transfer for cross-dehydrogenative-coupling reactions.

Seed-Mediated Growth of Colloidal Metal Nanocrystals

Seed-mediated growth is a powerful and versatile approach for the synthesis of colloidal metal nanocrystals. The vast allure of this approach mainly stems from the staggering degree of control one can achieve over the size, shape, composition, and structure of nanocrystals. These parameters not only control the properties of nanocrystals but also determine their relevance to, and performance in, various applications. The ingenuity and artistry inherent to seed-mediated growth offer extensive promise, enhancing a number of existing applications and opening the door to new developments. This Review demonstrates how the diversity of metal nanocrystals can be expanded with endless opportunities by using seeds with well-defined and controllable internal structures in conjunction with a proper combination of capping agent and reduction kinetics. New capabilities and future directions are also highlighted.

3D Quantification of Low-Coordinate Surface Atom Density: Bridging Catalytic Activity to Concave Facets of Nanocatalysts in Fuel Cells

A protocol to quantify the distribution of surface atoms of concave nanocatalysts according to their coordination number is proposed. The 3D surface of an Au@Pd concave nanocube is reconstructed and segmented. The crystallographic coordinates and low-coordinate surface atom densities of the concave facets are determined. The result shows that 32% of the surface atoms are low-coordinated, which may contribute to the high activity.

Surface Spectroscopy on UHV-Grown and Technological Ni-ZrO2 Reforming Catalysts: From UHV to Operando Conditions

Ni nanoparticles supported on ZrO₂ are a prototypical system for reforming catalysis converting methane to synthesis gas. Herein, we examine this catalyst on a fundamental level using a 2-fold approach employing industrial-grade catalysts as well as surface science based model catalysts. In both cases we examine the atomic (HRTEM/XRD/LEED) and electronic (XPS) structure, as well as the adsorption properties (FTIR/PM-IRAS), with emphasis on in situ/operando studies under atmospheric pressure conditions. For technological Ni–ZrO₂ the rather large Ni nanoparticles (about 20 nm diameter) were evenly distributed over the monoclinic zirconia support. In situ FTIR spectroscopy and ex situ XRD revealed that even upon H₂ exposure at 673 K no full reduction of the nickel surface was achieved. CO adsorbed reversibly on metallic and oxidic Ni sites but no CO dissociation was observed at room temperature, most likely because the Ni particle edges/steps comprised Ni oxide. CO desorption temperatures were in line with single crystal data, due to the large size of the nanoparticles. During methane dry reforming at 873 K carbon species were deposited on the Ni surface within the first 3 h but the CH₄ and CO₂ conversion hardly changed even during 24 h. Post reaction TEM and TPO suggest the formation of graphitic and whisker-type carbon that do not significantly block the Ni surface but rather physically block the tube reactor. Reverse water gas shift decreased the H₂/CO ratio. Operando studies of methane steam reforming, simultaneously recording FTIR and MS data, detected activated CH₄ (CH₃ and CH₂), activated water (OH), as well as different bidentate (bi)carbonate species, with the latter being involved in the water gas shift side reaction. Surface science Ni–ZrO₂ model catalysts were prepared by first growing an ultrathin “trilayer” (O–Zr–O) ZrO₂ support on an Pd₃Zr alloy substrate, and subsequently depositing Ni, with the process being monitored by XPS and LEED. Apart from the trilayer oxide, there is a small fraction of ZrO₂ clusters with more bulk-like properties. When CO was adsorbed on the (fully metallic) Ni particles at pressures up to 100 mbar, both PM-IRAS and XPS indicated CO dissociation around room temperature and blocking of the Ni surface by carbon (note that on the partially oxidized technological Ni particles, CO dissociation was absent). The Ni nanoparticles were stable up to 550 K but annealing to higher temperatures induced Ni migration through the ultrathin ZrO₂ support into the Pd₃Zr alloy. Both approaches have their benefits and limitations but enable us to address specific questions on a molecular level.