Catalytic Properties Of Metal Nanoparticles Research Articles

Surface‐Functionalized Nanoparticles as Catalysts for Artificial Photosynthesis

AbstractAnalogously to enzymatic catalysis, where the active metal sites and their environment are controlled by protein residues, the catalytic properties of metal nanoparticles (NPs) can be tuned by carefully selecting their surface‐coordinated species. In artificial photosynthesis, surface‐functionalization emerged in the last decade, grounded on the development of reliable methods for tailored synthesis, advanced characterization and theoretical modeling of metal NPs, altogether with the aim of transferring to the nanoscale the mechanistic knowledge acquired from molecular complexes. Metal NPs surface‐functionalization modulates the energetics of key catalytic intermediates, introduces second coordination sphere effects, influences the catalyst‐electrolyte interface, and determines the metal NPs surface coverage and, accordingly, the number of accessible active sites. In photoactivated systems, metal NPs surface‐functionalization may play a key role in modulating the charge transfers and recombination processes between the light absorber and the active sites and in the light absorber itself. Thus, after a presentation of the most relevant synthetic methods to produce well‐defined surface‐functionalized metal NPs, a critical analysis of why the above effects are the cornerstone in enhancing their catalytic performance in the key processes of artificial photosynthesis, namely the oxygen evolution reaction, the hydrogen evolution reaction, and the CO2 reduction reaction, is given.

Efficient CO2 electroreduction on Pd-based core-shell nanostructure with tensile strain

• Core-shell nanocatalysts are fabricated to study the strain effect on CO 2 reduction. • The catalytic performance follows the trend of Au@Pd > Pd > AuCu@Pd. • The catalytic activity is positively related to the tensile strain effect. • The increased tensile strain with thinner shell thickness enhances catalytic activity. Strain effect has been utilized to tune the catalytic properties of metal nanoparticles. However, in-depth understanding of the strain effect on CO 2 electroreduction over the core-shell structure catalyst is still unclear. In this work, we report a prominent strain-dependent activity/selectivity in the electroreduction of CO 2 over Pd-based core-shell nanoparticles. Tensile and compressive strain are generated in Au@Pd and AuCu@Pd nanoparticles, respectively, due to the different lattice spacing of Au > Pd > AuCu. In CO 2 electroreduction, Au@Pd exhibits a maximum Faradaic efficiency for CO production of 89.6% at −0.9 V versus reversible hydrogen electrode, which is 1.2 and 1.7 times of Pd and AuCu@Pd, respectively. Moreover, when using Au@Pd with different thicknesses of Pd shell as electrocatalysts, we also find that the decreased tensile strain with the increasing thickness of Pd shell results in inferior catalytic activity. This may be because tensile strain on Pd-based electrocatalysts enhanced the CO 2 adsorption, thus promoting the catalytic performance. This work offers a pathway with the regulation of lattice strain to rationally design effective electrocatalysts towards CO 2 electroreduction.

Low-Temperature Conversion of Hydrogen Modifications on Nanoparticles of 1B-Group Metals

The catalytic properties of metal nanoparticles of the 1B group (Cu, Ag, Au) in the reaction of low-temperature ortho-vapor conversion of hydrogen are investigated. It is shown that, upon transition to nanoscale particles, inert bulk metals adsorb hydrogen at low temperatures and become active in the reaction of the conversion of hydrogen modifications. Among the metals studied, gold nanoparticles have the highest specific catalytic activity. Conversion occurs on all ortho-vapor nanoparticles by the physical magnetic mechanism, which indicates the presence of magnetic properties of copper, silver, and gold nanoparticles.

Single Particle Approaches to Plasmon-Driven Catalysis.

Plasmonic nanoparticles have recently emerged as a promising platform for photocatalysis thanks to their ability to efficiently harvest and convert light into highly energetic charge carriers and heat. The catalytic properties of metallic nanoparticles, however, are typically measured in ensemble experiments. These measurements, while providing statistically significant information, often mask the intrinsic heterogeneity of the catalyst particles and their individual dynamic behavior. For this reason, single particle approaches are now emerging as a powerful tool to unveil the structure-function relationship of plasmonic nanocatalysts. In this Perspective, we highlight two such techniques based on far-field optical microscopy: surface-enhanced Raman spectroscopy and super-resolution fluorescence microscopy. We first discuss their working principles and then show how they are applied to the in-situ study of catalysis and photocatalysis on single plasmonic nanoparticles. To conclude, we provide our vision on how these techniques can be further applied to tackle current open questions in the field of plasmonic chemistry.

Exploring the Fundamental Roles of Functionalized Ligands in Platinum@Metal-Organic Framework Catalysts.

The metal nodes, functionalized ligands, and uniform channels of metal-organic frameworks (MOFs) are typically utilized to regulate the catalytic properties of metal nanoparticles (MNPs). However, though the ligand functionalization could impact the properties of the metal nodes and channels, which might further regulate the catalytic activity and selectivity of MNPs, related research in the design of MNP/MOF catalysts was usually neglected. Herein, we synthesized a series of Pt@UiO-66 composites (Pt@UiO-66-NH2, Pt@UiO-66-SO3H, and Pt@UiO-66) with slightly different organic ligands, which enhanced steric hindrance and contributed to multipathway electron transfer in selective hydrogenation of linear citronellal. The selectivity toward citronellol was gradually improved along with the increased size of functional groups (hydrogen, amino groups, and sulfo groups) on organic ligands, which enhanced steric hindrance provided by channels. In addition, the X-ray photoelectron spectroscopy measurements also revealed that the electronic state of Pt NPs was regulated through multipathway electron transfer from Pt NPs to metal nodes, between organic ligands and Pt NPs/metal nodes. Our research proved that the ligand functionalization altered physiochemical properties of the channels and metal nodes, further together managing the catalytic performance of Pt NPs through enhanced steric hindrance and multi-pathway electron transfer.

NanoUV-VIS: An Interactive Visualization Tool for Monitoring the Evolution of Optical Properties of Nanoparticles Throughout Synthesis Reactions.

Engineered nanoparticles (NPs) are being used for a broad array of high technology applications including sensing, imaging, targeted drug delivery, bio-diagnostics, catalysis, optoelectronics and film growth seeding. The enhanced optical, electrical and catalytic properties of metal NPs are strongly correlated with their size, shape, and structure. As such, physicochemical characterization of NPs is critically important to ensure their effective use and applicability. In this context, Ultraviolet/Visible Spectroscopy (UV/VIS) is one of the most widely used methods for measuring the optical properties and electronic structures of NPs. UV/VIS absorption bands are related to important properties such as the diameter, shape, and polydispersity of metallic and semi- conducting NPs. Thus, this analytical technique is used during NP synthesis to monitor NP formation, assess suspension stability under different conditions and media, and to establish the optical properties of the newly formed nanomaterials. In view of the extensive use of UV/VIS for NP characterization and monitoring of NP formation during synthesis reactions, we have developed NanoUV-VIS, an interactive web application designed for the analysis of multiple UV-VIS absorbance spectra measured as a function of time. Graphical visualizations of the data in 2 dimensions (spectrum plot, contour plot) and 3 dimensions (surface plot) are created by this tool. In addition, the NanoUV-VIS tool evaluates and estimates important parameters related to the absorption bands of NPs, including, maximum optical absorbance, Surface Plasmon Resonance (SPR) peak and the Full Width at Half Maximum (FWHM) of the UV/VIS spectra. This information is available to download as a table in the software, as well as in the form of interactive plots, where the scientist can compare the behavior of these parameters in order to better interpret the outcomes of the experiment.

Room-temperature ammonia gas sensor based on reduced graphene oxide nanocomposites decorated by Ag, Au and Pt nanoparticles

We report a novel and highly sensitive two-dimensional (2D) gas sensing material based on metal nanoparticles-reduced graphene oxide (rGO) nanocomposite for the detection of ammonia gas. The rGO samples decorated by Ag, Au and Pt nanoparticles (NPs) were successfully synthesized using a single-step chemical reduction process, and the effect of different metal NPs on the gas sensing performance for ammonia gas were systematically investigated. The samples were characterized by TEM and XRD methods. The gas-sensing properties of the fabricated sensors were investigated for NH3 and other target gases at room temperature. The sensor decorated by AgNPs has higher sensitivity, selectivity, better response/recovery times and great stability to ammonia gas than sensors decorated by Au and Pt NPs. AgNPs-rGO presented the highest performance, confirming a strong dependence on the metal type. The enhanced sensing properties of the samples may be attributed to the combined effect of the superior conductivity of rGO and metal nanoparticles, chemical sensitization caused from proposed production method, catalytic properties of metal nanoparticles and active oxygen species on the rGO surface.

ChemInform Abstract: Tailoring the Catalytic Properties of Metal Nanoparticles via Support Interactions

AbstractReview: 170 refs.

Tailoring the Catalytic Properties of Metal Nanoparticles via Support Interactions

The development of new catalysts for energy technology and environmental remediation requires a thorough knowledge of how the physical and chemical properties of a catalyst affect its reactivity. For supported metal nanoparticles (NPs), such properties can include the particle size, shape, composition, and chemical state, but a critical parameter which must not be overlooked is the role of the NP support. Here, we highlight the key mechanisms behind support-induced enhancement in the catalytic properties of metal NPs. These include support-induced changes in the NP morphology, stability, electronic structure, and chemical state, as well as changes in the support due to the NPs. Utilizing the support-dependent phenomena described in this Perspective may allow significant breakthroughs in the design and tailoring of the catalytic activity and selectivity of metal nanoparticles.

Chemoelectronic circuits based on metal nanoparticles.

To develop electronic devices with novel functionalities and applications, various non-silicon-based materials are currently being explored. Nanoparticles have unique characteristics due to their small size, which can impart functions that are distinct from those of their bulk counterparts. The use of semiconductor nanoparticles has already led to improvements in the efficiency of solar cells, the processability of transistors and the sensitivity of photodetectors, and the optical and catalytic properties of metal nanoparticles have led to similar advances in plasmonics and energy conversion. However, metals screen electric fields and this has, so far, prevented their use in the design of all-metal nanoparticle circuitry. Here, we show that simple electronic circuits can be made exclusively from metal nanoparticles functionalized with charged organic ligands. In these materials, electronic currents are controlled by the ionic gradients of mobile counterions surrounding the 'jammed' nanoparticles. The nanoparticle-based electronic elements of the circuitry can be interfaced with metal nanoparticles capable of sensing various environmental changes (humidity, gas, the presence of various cations), creating electronic devices in which metal nanoparticles sense, process and ultimately report chemical signals. Because the constituent nanoparticles combine electronic and chemical sensing functions, we term these systems 'chemoelectronic'. The circuits have switching times comparable to those of polymer electronics, selectively transduce parts-per-trillion chemical changes into electrical signals, perform logic operations, consume little power (on the scale of microwatts), and are mechanically flexible. They are also 'green', in the sense that they comprise non-toxic nanoparticles cast at room temperature from alcohol solutions.

Green Synthesis of Metal Nanoparticles via Natural Extracts: The Biogenic Nanoparticle Corona and Its Effects on Reactivity

The optical and catalytic properties of metal nanoparticles have attracted significant attention for applications in a wide variety of fields, thus prompting interest in developing sustainable synthetic strategies that leverage the redox properties of natural compounds or extracts. Here, we investigate the surface chemistry of nanoparticles synthesized using coffee as a biogenic reductant. Building on our previously developed synthetic protocols for the preparation of silver and palladium nanoparticle/carbon composite microspheres, a combination of thermogravimetric and spectroscopic methods was used to characterize the carbon microsphere and nanoparticle surfaces. Infrared reflectance spectroscopy and single particle surface enhanced Raman spectroscopy were used to characterize Pd and Ag metal surfaces, respectively, following synthesis. Strongly adsorbed organic layers were found to be present at metal nanoparticle surfaces after synthesis. The catalytic activity of Pd nanoparticles in hydrogenation reactions was leveraged to study the availability of surface sites, and coffee-synthesized nanomaterials were compared to commercial Pd-based hydrogenation catalysts. Our results demonstrate that biogenic adsorbates block catalytic surface sites and affect nanoparticle functionality. These findings highlight the need for careful analysis of surface chemistry as it relates to the specific applications of nanomaterials produced using greener or more sustainable methods.

Preparation of tailor-made supported catalysts using asymmetric flow field flow fractionation and their application in hydrogenation

AbstractThe optical, chemical, and catalytic properties of metallic nanoparticles (NPs) depend strongly on their particle size and shape. Therefore, the preparation of monodisperse metallic NPs is very important for fundamental studies and practical applications. However, the isolation of the different structures by separation from a polydisperse sample, especially in the size range below 10 nm, is not well applied so far. Here, the asymmetric flow field flow fractionation (AF4) is adapted for the preparative separation of the Pd NPs regarding their size and shape in the sub-10-nm size range. To prove the efficiency of the applied method, small-angle X-ray scattering (SAXS) and high-resolution transmission electron microscopy (TEM) were utilized to determine the particle size distribution at different stages of the separation process. A major benefit of this method compared to most of the other separation techniques, the removal of impurities during the separation process, was proven by proton nuclear magnetic resonance (NMR). The obtained results demonstrate that the AF4 is well suited for the rapid preparation of the purified uniform precious metal NPs at the applied size range. Single fractions of the different-sized and -shaped Pd NPs were deposited on titania (TiO2) and tested in the catalytic hydrogenation of 2,5 hydroxymethylfurfural (HMF) in aqueous solution under mild conditions. While the spherical-shaped particles show a high activity, the separated agglomerated particles show a higher selectivity to the desired products.

Enhancing Colloidal Metallic Nanocatalysis: Sharp Edges and Corners for Solid Nanoparticles and Cage Effect for Hollow Ones

There are two main classes of metallic nanoparticles: solid and hollow. Each type can be synthesized in different shapes and structures. Practical use of these nanoparticles depends on the properties they acquire on the nanoscale. Plasmonic nanoparticles of silver and gold are the most studied, with applications in the fields of sensing, medicine, photonics, and catalysis. In this Account, we review our group's work to understand the catalytic properties of metallic nanoparticles of different shapes. Our group was the first to synthesize colloidal metallic nanoparticles of different shapes and compare their catalytic activity in solution. We found that the most active among these were metallic nanoparticles having sharp edges, sharp corners, or rough surfaces. Thus, tetrahedral platinum nanoparticles are more active than spheres. We proposed this happens because sharper, rougher particles have more valency-unsatisfied surface atoms (i.e., atoms that do not have the complete number of bonds that they can chemically accommodate) to act as active sites than smoother nanoparticles. We have not yet resolved whether these catalytically active atoms act as catalytic centers on the surface of the nanoparticle (i.e., heterogeneous catalysis) or are dissolved by the solvent and perform the catalysis in solution (i.e., homogenous catalysis). The answer is probably that it depends on the system studied. In the past few years, the galvanic replacement technique has allowed synthesis of hollow metallic nanoparticles, often called nanocages, including some with nested shells. Nanocage catalysts show strong catalytic activity. We describe several catalytic experiments that suggest the reactions occurred within the cage of the hollow nanocatalysts: (1) We synthesized two types of hollow nanocages with double shells, one with platinum around palladium and the other with palladium around platinum, and two single-shelled nanocages, one made of pure platinum and the other made of pure palladium. The kinetic parameters of each double-shelled catalyst were comparable to those of the single-shelled nanocage of the same metal as the inside shell, which suggests the reactions are taking place inside the cavity. (2) In the second set of experiments, we used double-shelled, hollow nanoparticles with a plasmonic outer gold surface and a non-plasmonic inner catalytic layer of platinum as catalysts. As the reaction proceeded and the dielectric function of the interior gold cavity changed, the plasmonic band of the interior gold shell shifted. This strongly suggested that the reaction had taken place in the nanocage. (3) Finally, we placed a catalyst on the inside walls of hollow nanocages and monitored the corresponding reaction over time. The reaction rate depended on the size and number of holes in the walls of the nanoparticles, strongly suggesting the confinement effect of a nanoreactor.

Nanosized Pt-, Ru-, and Pd-containing catalysts for organic synthesis and solution of environmental issues

Synthesis of Pt-, Ru-, and Pd-containing nanoparticles in the pores of polymeric matrix of hypercrosslinked polystyrene, their structure and catalytic properties are under consideration. Physicochemical studies have shown that metal nanoparticle formation depends on the properties of the polymeric matrix porous structure, the nature of metal precursors and the synthesis conditions. The study of catalytic properties of metal nanoparticles stabilized in mesoporous matrices showed promising applications of these systems in the reactions of selective oxidation and hydrogenation, which are intermediate stages in the synthesis of precursors of vitamins and medicines. In order to solve environmental problems, nanocatalysts were investigated in the processes of oxidative degradation of phenol and reductive denitrification of nitrates for purification of sewage and natural water.

ChemInform Abstract: Synthesis and Catalytic Properties of Metal Nanoparticles: Size, Shape, Support, Composition, and Oxidation State Effects

AbstractReview: 329 refs.

Microplasma synthesis of metal nanoparticles for gas-phase studies of catalyzed carbon nanotube growth

Catalytic properties of metal nanoparticles toward gas-phase carbon nanotube (CNT) growth are presented. Narrow dispersions of iron (Fe) and nickel (Ni) nanoparticles are prepared in a direct current microplasma reactor and subsequently introduced with acetylene (C2H2) and hydrogen (H2) into a heated flow furnace to catalyze CNT growth. Aerosol size classification and high-resolution transmission electron microscopy show that CNT growth occurs on Ni particles at lower temperatures than that for similarly produced Fe nanoparticles. Activation energies of 117 and 73kJ∕mol are found for Fe and Ni catalyst particles, respectively, suggesting that CNT growth occurs by carbon surface diffusion.