Noble Metal Nanoparticle Catalysts Research Articles

One-dimensional array of nanoparticles using segmented polyurethane nanofibers as a template for enhanced catalytic efficiency

Metal nanoparticles are used to catalyze chemical reactions. Among them, noble metal nanoparticle catalysts need to be used in small quantities. Some reports reveal catalytic activity is further improved by controlling nanoparticle arrangement and distribution. Much research has been directed toward the formation of one-dimensional arrays by compositing metal nanoparticles with template materials. However, previously reported methods form arrays that lack linearity or suitable interparticle distances, which is ascribable to array crossover and particle aggregation, in addition their fabrication procedures are expensive and not suitable for large-scale practical use. Here we show that one-dimensional arrays of platinum nanoparticles (PtNPs) were formed by using electrospun polyurethane nanofibers as a template. PtNPs adsorbed on each polyurethane nanofiber form a one-dimensional array over longer distances. The catalytic H2O2 decomposition performance of the prepared one-dimensional PtNP arrays was 45.6% decomposition in 15 min, which revealed a decomposition rate more than twice that obtained using the same number of PtNPs randomly distributed on the template or dispersed in a liquid. Although this method is a very simple method for one-dimensional arrangement of metal nanoparticles, thereby improving catalytic efficiency per metal nanoparticle, which help to reduce the amount of metal nanoparticles used during catalysis and contributes the cost of catalysis products cost.

Finned Zn-MFI zeolite encapsulated noble metal nanoparticle catalysts for the oxidative dehydrogenation of propane with carbon dioxide

Oxidative dehydrogenation of propane with carbon dioxide (CO2-ODP) characterizes the tandem dehydrogenation of propane to propylene with the reduction of the greenhouse gas of CO2 to valuable CO. However, the existing catalyst is limited due to the poor activity and stability, which hinders its industrialization. Herein, we design the finned Zn-MFI zeolite encapsulated noble metal nanoparticles (NPs) as bifunctional catalysts (NPs@Zn-MFI) for CO2-ODP. Characterization results reveal that the Zn2+ species are coordinated with the MFI zeolite matrix as isolated cations and the NPs of Pt, Rh, or RhPt are highly dispersed in the zeolite crystals. The isolated Zn2+ cations are very effective for activating the propane and the small NPs are favorable for activating the CO2, which synergistically promote the selective transformation of propane and CO2 to propylene and CO. As a result, the optimal 0.25%Rh0.50%Pt@Zn-MFI catalyst shows the best propylene yield, satisfactory CO2 conversion, and long-term stability. Moreover, considering the tunable synergetic effects between the isolated cations and NPs, the developed approach offers a general guideline to design more efficient CO2-ODP catalysts, which is validated by the improved performance of the bifunctional catalysts via simply substituting Sn4+ cations for Zn2+ cations in the MFI zeolite matrix.

Hierarchically porous polyHIPEs fabricated via ex-situ swelling strategy towards supports for noble-metal Ag nanoparticles

This work demonstrates an ex-situ swelling strategy for fabrication of the robust hierarchically porous polyHIPE. Specially, a cationic polyHIPE was prepared by copolymerization of 2-(methacryloyloxy) ethyltrimethylammonium chloride, styrene and divinylbenzene within a water-in-oil (w/o) high internal phase emulsion (HIPE). The hierarchically porous polyHIPE was achieved via simply swelling the polyHIPE in decane at 70 °C, and subsequent removal of the solvent at room temperature. There were large amounts of small pores found on the void wall surface. Compared with the hierarchically porous polyHIPE fabricated with decane as porogen (in-situ swelling, conventional route), the ex-situ swelling strategy endowed the materials semblable complex pore morphology but much less damage to its compression performance. The young's modulus of the hierarchically porous polyHIPE herein was 37% higher than that obtained by a conventional way. Afterwards, the hierarchically porous polyHIPE was utilized as a carrier for AgNPs (AgNPs@polyHIPE). The AgNPs@polyHIPEs exhibited eminent catalytic activity and recyclability for the reduction of the rhodamine B. Thereby, a facile approach for preparation of high strength and hierarchically porous polyHIPE was presented, and the resulted polyHIPE can be an ideal support for noble metal nanoparticle catalysts.

Microplasma Assembly a High-Efficient and Catalytic Platform Reduction 4-Nitrophenol Based on Reusable Au@Ag Nanoparticle / Cellulose Paper

Grafting metal nanoparticles (NPs) on flexible platforms is being increasingly attempted to advance their usage in the field of catalysis, sensing, energy storage, etc. However, anchoring NPs on substrates is nontrivial as it involves surface modification of the NPs and/or the substrate, which makes the whole process tedious. On the other hand , Bimetallic nanoparticles, which are composed of two metal elements in a particle, exhibit much higher catalytic activity than respective monometallic ones due to new bi-functional or synergistic effects, so-called a ligand and/or an ensemble effect. Here we present the green, facile, less-time, one-step process fabrication of 3-dimension porous Au(core)@Ag(shell) NP /filter paper by Microplasma-assisted system. The aim of our work is to develop a high efficient catalytic substrate on common filter paper loaded on Au@Ag NPs. In our work, we found Au@Ag NP /filter paper can be synthesized and in a minute time scale. We further extend this technology to fabricated Au@Ag NP /paper and characterized them by SEM, Raman, XRD and UV-Vis spectroscopies. Besides, The as-prepared Au@Ag NP / filter paper is stable, uniform, and exhibits high efficiency and reusability in the catalytic reduction of 4-nitrophenol (4-NP) with a high rate constant as well as an average conversion of 96% in 3 minutes during 6 times. While acting as catalysts, the composites display excellent surface enhanced Raman scattering (SERS) efficiency, allowing the real-time monitoring of chemical reactions. The obtained Au@Ag bimetallic catalysts /filter paper show an exceptional superior catalytic activity for the reduction of 4-nitrophenol (4-NP) which can be completely reduced to 4-aminophenol (4-AP) in a single step within seconds., surpassing most reported noble metal nanoparticle catalysts. The results have not only paved the way for the wide application of Au@Ag NPs / filter paper but also provide a new road for the application of other bimetallic NPs Figure 1

Water-Soluble Noble Metal Nanoparticle Catalysts Capped with Small Organic Molecules for Organic Transformations in Water.

This article recaps a variety of interesting catalytic studies based on solubilized and freely movable noble metal nanoparticle catalysts employed for organic reactions in either pure water or water-organic biphasic systems. Small organic ligand-capped metal nanoparticles are fundamentally attractive materials due to their enormous potential as a well-defined system that can provide spatial control near active catalytic sites. The nanoparticle catalysts are first grouped based on the synthetic method (direct reduction, phase transfer, and redispersion) and then again based on the type of reaction such as alkene hydrogenation, arene hydrogenation, nitroaromatic reduction, carbon-carbon coupling reactions, etc. The impacts of various ligands on the catalytic activity and selectivity of semi-heterogeneous nanoparticles in water are discussed in detail. The catalytic systems using polymers, dendrimers, and ionic liquids as supporting or protecting materials are excluded from the subject of this review.

Light-Induced Voltages in Catalysis by Plasmonic Nanostructures.

ConspectusPlasmonic nanostructures have garnered widescale scientific interest because of their strong light-matter interactions and the tunability of their absorption across the solar spectrum. At the heart of their superlative interaction with light is the resonant excitation of a collective oscillation of electrons in the nanostructure by the incident electromagnetic field. These resonant oscillations are known as localized surface plasmon resonances (LSPRs). In recent years, the community has uncovered intriguing photochemical attributes of noble metal nanostructures arising from their LSPRs. Chemical reactions that are otherwise unfavorable or sluggish in the dark are induced on the nanostructure surface upon photoexcitation of LSPRs. This phenomenon has led to the birth of plasmonic catalysis. The rates of a variety of kinetically challenging reactions are enhanced by plasmon-excited nanostructures. While the potential utility for solar energy harvesting and chemical production is clear, there is a natural curiosity about the precise origin(s) of plasmonic catalysis. One explanation is that the reactions are facilitated by the action of the intensely concentrated and confined electric fields generated on the nanostructure upon LSPR excitation. Another mechanism of activation involves hot carriers transiently produced in the metal nanostructure by damping of LSPRs.In this Account, we visit a phenomenon that has received less attention but has a key role to play in plasmonic catalysis and chemistry. Under common chemical scenarios, plasmonic excitation induces a potential or a voltage on a nanoparticle. This photopotential modifies the energetics of a chemical reaction on noble metal nanoparticles. In a range of cases studied by our laboratory and others, light-induced potentials underlie the plasmonic enhancement of reaction kinetics. The photopotential model does not replace other known mechanisms, but it complements them. There are multiple ways in which an electrostatic photopotential is produced by LSPR excitation, such as optical rectification, but one that is most relevant in chemical media is asymmetric charge transfer to solution-phase acceptors. Electrons and holes produced in a nanostructure by damping of LSPRs are not removed at the same rate. As a result, the slower carrier accumulates on the nanostructure, and a steady-state charge is built up on the nanostructure, leading to a photopotential. Potentials of up to a few hundred millivolts have been measured by our laboratory and others. A photocharged nanoparticle is a source of carriers of a higher potential than an uncharged one. As a result, redox chemical reactions on noble metal nanoparticles exhibit lower activation barriers under photoexcitation. In electrochemical reactions on noble metal nanoparticles, the photopotential supplements the applied potential. In a diverse set of reactions, the photopotential model explains the photoenhancement of rates as well as the trends as a function of light intensity and photon energy. With further gains, light-induced potentials may be used as a knob for controlling the activities and selectivities of noble metal nanoparticle catalysts.

Hydrogenation of levulinic acid to γ-valerolactone over Fe-Re/TiO2 catalysts

Hydrogenation of levulinic acid to γ-valerolactone is a key reaction in the valorization of carbohydrates to renewable fuels and chemicals. State-of-the-art catalysts are based on supported noble metal nanoparticle catalysts. We report the utility of a bimetallic Fe-Re supported on TiO2 for this reaction. A strong synergy was observed between Fe and Re for the hydrogenation of levulinic acid in water under mild conditions. Fe-Re/TiO2 shows superior catalytic performance compared to monometallic Fe and Re catalysts at similar metal content. The hydrogenation activity of the bimetallic catalysts increased with Re content. H2-TPR, XPS, XANES, EXAFS, Mössbauer spectroscopy, TEM, and low-temperature CO IR spectroscopy show that the bimetallic catalysts contain metallic Re nanoparticles covered by FeOx species and small amounts of a Fe-Re alloy. Under reaction conditions, the partially reduced surface FeOx species adsorb water and form Brønsted acidic OH groups, which are involved in dehydration of reaction intermediates. Under optimized conditions, nearly full conversion of levulinic acid with a 95 % yield of γ-valerolactone could be achieved at a temperature as low as 180 °C in water at a H2 pressure of 40 bar.

Catalytic electrooxidation of formic acid by noble metal nanoparticle catalysts on reduced graphene oxide

The noble metals (Pt and Pd) loaded on polydopamine (PDA) modified graphene oxide (GO) as catalysts were prepared by a reduction. The catalysts were characterized by Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The reduced graphene oxide (rGO) was prepared for use as a matrix to integrate alloyed metal catalysts. The results show that the dispersed small-catalyst nanoparticles are loaded on both GO and rGO supports and the PtxPdy catalysts on rGO are smaller than the PtxPdy catalysts on GO. Both cyclic voltammetry (CV) and chronoamperometry (CA) results reveal that bimetallic PtxPdy/PDA-GO catalysts have superior activity, CO tolerance, electron transfer and stability towards formic acid oxidation, compared to PtxPdy/GO and the commercial PtRu/C catalyst. The bimetallic PtxPdy and PDA loaded on GO could be capable of enhanced oxidation and hopefully used in direct formic acid fuel cells.

Cage-like hierarchically mesoporous hollow silica microspheres templated by mesomorphous polyelectrolyte-surfactant complexes for noble metal nanoparticles immobilization

In this paper, well-defined CHMSs were synthesized through co-hydrolysis of tetraethylsiloxane (TEOS) and 3-aminopropyltriethoxysilane (APTS) template by mesomorphous complexes of hexadecylpyridinium chloride (CPC) and poly(acrylic acid) (PAA). It was demonstrated that the adding amount of APTS in the reaction system played a key role in the formation of the hollow cage-like structure and a possible formation mechanism of CHMSs was proposed. The synthesized CHMSs presented as uniform microsphers with average diameter of 600 nm and possessed tri-model pore structure that were the ordered mesopores (˜3 nm) originated from CPC micelle, the secondary nanopores (˜55 nm) templated by phase separated PAA chain in the silica shell as well as the hollow cavity (several hundred nanometer). At the same time, the co-hydrolysis of APTS resulted in amino groups functionalized silica framework of the CHMSs. Ascribed to the unique structure and the inherent amino groups, the CHMSs were utilized as scaffold for preparation of heterogeneous noble metal nanoparticle catalysts. By choosing the palladium (Pd) as a typical example, 1-Pd@CHSMs catalysts containing 1.0 wt% Pd and uniform distributed small size Pd nanoparticles (˜2.9 nm) were obtained. The catalytic reduction of 4-nitrophenol demonstrated that the heterogeneous 1-Pd@CHSMs catalyst was efficient and reusable.

Development of N-Doped Carbon-Supported Cobalt/Copper Bimetallic Nanoparticle Catalysts for Aerobic Oxidative Esterifications Based on Polymer Incarceration Methods.

Heterogeneous nitrogen-doped carbon-incarcerated cobalt/copper bimetallic nanoparticle (NP) catalysts, prepared from nitrogen-containing polymers, were developed, and an efficient catalytic process for aerobic oxidative esterification was achieved in the presence of a low loading (1 mol %) of catalyst that could be reused and easily reactivated. This protocol enabled diverse conditions for the bimetallic NP formation step to be screened, and significant rate acceleration by inclusion of a copper dopant was discovered. The catalytic activity of the bimetallic Co/Cu catalysts is much higher than that for cobalt catalysts reported to date and is even comparable with noble-metal NP catalysts.

Supercritical fluid-assisted immobilization of Pd nanoparticles in the mesopores of hierarchical porous SiO2 for catalytic applications

Pd nanoparticles were successfully immobilized in the mesopores of hierarchical porous SiO2 and TiO2 using supercritical carbon dioxide (scCO2)-acetone solution. The hierarchical porous SiO2 with macropores and mesopores demonstrated remarkable properties as a support for noble metal nanoparticle catalysts. The nanoparticle precursor, palladium(II) acetate (Pd(OAc)2), was impregnated into the mesopores of hierarchical porous SiO2 and TiO2 microparticles using scCO2. These samples were subsequently reduced by treatment in a stream of H2 at 473K. During reduction, the formed Pd nanoparticles were dispersed within the hierarchical porous SiO2, with a uniform three-dimensional distribution of nanoparticles in the mesopores revealed by TEM images. The resulting Pd@hierarchical porous SiO2 exhibited high activity for the heterogeneous catalytic hydrogenation reaction of styrene in methanol solution. The catalytic activity of the Pd@hierarchical porous SiO2 was higher than that of Pd@conventional porous SiO2 without hierarchical porosity or the Pd@hierarchical porous TiO2.

Identifying low-coverage surface species on supported noble metal nanoparticle catalysts by DNP-NMR.

DNP-NMR spectroscopy has been applied to enhance the signal for organic molecules adsorbed on γ-Al2O3-supported Pd nanoparticle catalysts. By offering >2500-fold time savings, the technique enabled the observation of (13)C-(13)C cross-peaks for low coverage species, which were assigned to products from oxidative degradation of methionine adsorbed on the nanoparticle surface.

Moving from convergence to divergence: the future of nanotechnology

Nanotechnology has been considered as a main hub for the convergence and multidisciplinarity of research fields. Since it emerged, a number of researchers with a variety of backgrounds, including, but not limited to, chemistry, biology, and physics, have converged in this academic melting pot, where synergetic designs of merging multiple principles have been conducted to generate substantial and unprecedented outputs. Based on this interdisciplinary nature, nanotechnology plays a central role nowadays as a bridge to interconnect multiple scientific boundaries. During the convergence in nanotechnology, however, there were unexpected challenges and debates that suppressed the progress of the research development. For example, the integration of different scientific disciplines that were already established in their own fields sometimes had to face troubles owing to the lack of gold standards and clarified definitions. In some cases, reproducibility of the research results was doubted. One suitable example is the case of nanoparticle syntheses. The shape and size of certain types of nanoparticles were often unable to be systematically controlled as reported in literature. The era of uncertainty of nanotechnology, however, is almost over. The gold standards in a variety of fields of nanotechnology are being set up, and the necessary definitions have been prepared, or at least they are ongoing. For example, there are ongoing activities on the creation of the systematic nomenclature of nanomaterials. The systematic and worldwide evaluation of the toxicity of nanomaterials is also in progress. The development of molecular spectroscopy has clearly elucidated the role of trace impurities in synthesis of nanoparticles, which had not been carefully discussed in conventional chemical reactions. Based on such accomplishments today, nanotechnology has not only consolidated its territory as an independent research area but also expanded to divergent areas as a starting point. That is, nanotechnology does not simply merge things together just to see something new anymore, but has begun to provide divergent views and scopes to researchers to better understand and investigate their own sciences. The reviews in this special issue distinctly demonstrate both the convergent and divergent aspects of nanotechnology, by reporting the recent studies and results in their own fields in view of nanotechnology. The investigation of perovskite-type superconducting copper oxides by electron microscopy and diffraction is explained by Oku, where nanotechnology certainly provides a stateof-the-art tool for materials science and physics. The conventional photonics in combination of nanotechnology for the investigation of DNA is outlined by Bregadze et al., where nanotechnology is taken advantage of for biological investigation. The modeling of mass transfer at nanoscale is demonstrated by Kalinitchev, which is an exemplary review of using nanotechnology for investigating theoretical physics. Lee’s review on the silver nanomaterials for the detection of chemical and biological targets deals with how new nanomaterials can be utilized for practical purposes in our lives, with respect to both chemistry and biology. Finally, in a research highlight, the advantages of noble metal nanoparticle catalysts over the conventional ones are reviewed in association with their synthetic methods by Sergeev et al., which obviously show that chemistry can also be an ultimate destination from nanotechnology based on its divergence. All these articles provide excellent demonstrations of advances in diverging nanotechnology heading to the distinctive, major sciences, such as materials science, biology, physics, and chemistry. This collection indicates that such divergence of nanotechnology is definitely noticeable, as a part of the scientific research orientation. As the beginning of convergence of nanotechnology showed troubles, however, the effort to understand the conventional sciences through the window of nanotechnology may also have potential difficulties. Plenty of discussions and communications would be needed to guide researchers in an appropriate way in the future, and I believe that this special issue could be a good point to begin with.

Polyaniline-decorated cellulose aerogel nanocomposite with strong interfacial adhesion and enhanced photocatalytic activity

Cellulose aerogel has attracted considerable attention due to its high surface area and the added advantages of being cost-effective and environmentally benign. It has been applied as supporting material for noble metal nanoparticle catalysts to prevent their agglomeration. In this paper, we have demonstrated a facile method to prepare polyaniline (PANI)-decorated cellulose aerogel via a dissolve/regeneration route using ionic liquid as solvent. Cellulose aerogel acted as a supporting material for PANI nanoparticles to prevent their agglomeration as confirmed by scanning electron microscopy. The strong interfacial interaction between PANI and cellulose aerogel was verified by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermal gravimetric analysis and X-ray diffraction. PANI-cellulose aerogel exhibited excellent photocatalytic activity towards the degradation of methylene blue. The degradation efficiency reached 95% after 2 h. The approach promotes the use of renewable natural resources to prepare a variety of nanofibrillated cellulose-supported nanocomposites for catalysis, sensors, and other potential applications.

Biphasic catalysis using amphiphilic polyphenols-chelated noble metals as highly active and selective catalysts

In the field of catalysis, it is highly desired to develop novel catalysts that combine the advantages of both homogeneous and heterogeneous catalysts. Here we disclose that the use of plant pholyphenol as amphiphilic large molecule ligand/stabilizer allows for the preparation of noble metal complex and noble metal nanoparticle catalysts. These catalysts are found to be highly selective and active in aqueous-organic biphasic catalysis of cinnamaldehyde and quinoline, and can be reused at least 3 times without significant loss of activity. Moreover, the catalytic activity and reusability of the catalysts can be rationally controlled by simply adjusting the content of polyphenols in the catalysts. Our strategy may be extended to design a wide range of aqueous-organic biphasic catalysis system.

Solvent-Free Aerobic Oxidation of Benzyl Alcohol by Resin Supported Noble Metal Catalysts

Noble metal nanoparticle catalysts supported by resin were prepared by a simple adsorption method. Resin D261 is an organic polymer containing quaternary ammonium group. The specific interaction between quaternary ammonium groups and different kinds of noble metal precursors can be generally applied for the preparation of supported noble metal catalysts. Due to the specific interaction, an easy control of the loading of noble metal can be achieved. Furthermore, without using volatile organic solvents and calcinations in the preparation procedure, the method reported here is environmentally benign and economically feasible. The catalysts were tested in aerobic oxidation of benzyl alcohol to benzaldehyde under solvent- and base-free conditions and exhibited high activity and excellent selectivity.

Facile preparation of supported noble metal nanoparticle catalysts with the aid of templating surfactants in mesostructured materials

Quaternary ammonium surfactants were generally used as templates in the synthesis of mesoporous materials, and the surfactants were removed by extraction or calcination to give the space of mesopores. Here with the cetyltrimethylammonium bromide templated mesostructured materials, we directly utilized the surfactants as capturing and stabilizing agents to prepare supported noble metal nanoparticle catalysts. The Pd-supported catalysts exhibited high and stable activity in hydrogenation of allyl alcohol (with a remarkably high turnover frequency of 5676 h −1) and aerobic oxidation of benzyl alcohol. During the recycle use of the catalyst, though surfactants were gradually leached into the reaction medium, the amount of Pd in the catalyst remained constant within experimental error. It is facile and energy-saving to use directly the as-synthesized mesostructured materials as support for noble metal nanoparticles without further calcination or further modification treatment. This method is versatile to prepare other noble metal (such as Au and Pt) supported catalysts by altering the metal precursors.