Supported Metal Nanoparticles Research Articles

Monolithic cellulose supported metal nanoparticles as green flow reactor with high catalytic efficiency

A highly effective, stable and reusable flow microreactor was developed by utilizing the environmentally sustainable porous monolithic cellulose based on a facile temperature induced phase separation (TIPS) method. The obtained microreator could be applied to efficiently and continuously catalysing the reduction reaction of 4-nitrophenol (an important reaction in water treatment) without any post-treatment or regeneration of catalysts. Moreover, the monolith overcame the brittleness of the crystalline cellulose and showed a good mechanical resilience, suggesting a great potential for the practical application in severe environment. Compared with previous reported Pd supported catalytic systems, this microreactor exhibited extremely high catalytic efficiency (turnover frequency, TOF = 4660 h−1, almost 4 times higher than that of cellulose nanocrystals supported catalyst) and long-term stability. This work provided a new strategy to construct highly effective and reusable metal NPs involved catalytic system by utilizing biodegradable cellulose materials.

An overview on metal-related catalysts: metal oxides, nanoporous metals and supported metal nanoparticles on metal organic frameworks and zeolites

Metal nanoparticles (NPs) supported on porous materials have shown great advantages in many catalytic application fields. Supported metal NPs are receiving extensive attention due to their significant contribution in a wide range of current and future applications, and this is arguably one of the fastest growing research fields. In this review, we highlight various types of metal catalysts that possess great potential in several catalytic reactions. The major focus has been on metal oxides, nanoporous metals and metal NPs supported on metal–organic frameworks (MOFs) and zeolites. Special attention has been given to the synthesis strategies and application of the NPs supported on MOFs and zeolites, which are considered highly interesting and rapidly expanding areas in heterogeneous catalysis. Finally, the prospects of these catalysts have been included in the concluding remarks.

Effect of MgO coverage on the synthesis and thermal treatment of Pt-Sn/C catalysts

To prevent sintering of carbon supported metal nanoparticles during high temperature annealing in reductive conditions, Pt-Sn nanoparticles were coated with MgO. The agglomeration of Pt-Sn particles upon thermal annealing was significantly inhibited with a MgO shell. The presence of the oxide shell gave rise to a more homogeneous microstructure and a better electrochemical stability.

Elucidating Interaction between Palladium and N-Doped Carbon Nanotubes: Effect of Electronic Property on Activity for Nitrobenzene Hydrogenation

Nitrogen dopants of carbon materials remarkably improve the stability and tune the catalytic performance of supported metal nanoparticles. However, it is still controversial how the Pd–N metal–support-interaction (MSI) influences the catalysis. Herein, the density function theory (DFT) calculations and X-ray photoelectron spectroscopy (XPS) were combined to rationalize the Pd–N MSI. DFT calculations suggested that Pd adsorbs on N-doped carbon nanotubes (N@CNTs) and donates electrons to pyridinic nitrogen. It was further experimentally proved using XPS through a titration method by gradually increasing Pd content or changing the N content of support by a postheat-treatment. The Pd catalysts display electron-deficiency depending on the intensity of MSI between Pd and pyridinic nitrogen, measured by Pd 3d binding energy. It paves the way to the rational synthesis of Pd catalysts with a tunable electronic state for the targeted catalytic reaction. Using the hydrogenation of nitrobenzene as the probe reaction,...

Wet-Chemistry Strong Metal–Support Interactions in Titania-Supported Au Catalysts

Classical strong metal-support interactions (SMSI), which play a crucial role in the preparation of supported metal nanoparticle catalysts, is one of the most important concepts in heterogeneous catalysis. The conventional wisdom for construction of classical SMSI involves in redox treatments at high-temperatures by molecular oxygen or hydrogen, sometimes causing sintered metal nanoparticles before SMSI formation. Herein, we report that the aforementioned issue can be effectively avoided by a wet-chemistry methodology. As a typical example, we demonstrate a new concept of wet-chemistry SMSI (wcSMSI) that can be constructed on titania-supported Au nanoparticles (Au/TiO2-wcSMSI), where the key is to employ a redox interaction between Auδ+ and Ti3+ precursors in aqueous solution. The wcSMSI is evidenced by covering Au nanoparticles with the TiO x overlayer, electronic interaction between Au and TiO2, and suppression of CO adsorption on Au nanoparticles. Owing to the wcSMSI, the Au-TiO x interface with an improved redox property is favorable for oxygen activation, accelerating CO oxidation. In addition, the oxide overlayer efficiently stabilizes the Au nanoparticles, achieving sinter-resistant Au/TiO2-wcSMSI catalyst in CO oxidation.

Heterogeneous catalyst of porous anodic aluminum oxide with Al substrate supported metal nanoparticles

Porous anodic aluminum oxide with Al substrate ([email protected]) supported metal nanoparticles (Pd, Cu, Ag) was synthesized by a facile pyrolysis method. The synthesized metal nanoparticles displayed homogeneous dispersion into the AAO. Pd/[email protected] was characterized in detail using scanning electron microscopy, transmission electron microscopy and x-ray photoelectron spectroscopy. Metal nanoparticles immobilized on ordered porous solid materials are not prone to leak and can provide more active sites for catalytic activity. Pd/[email protected] as heterogeneous catalyst showed excellent catalytic activity for Suzuki cross-coupling reactions and the reduction reaction of 4-nitrophenol. The metal nanoparticles supported on solid sheets could be separated and recovered from reaction solutions easily just by taking out of the sheets. The construction of solid sheets supported metal catalysts is expected to be a promising catalysts systems for heterogeneous catalysis application.

Biofabrication of supported metal nanoparticles: exploring the bioinspiration strategy to mitigate the environmental challenges

Biosynthesis of metal nanoparticles (MNPs) has recently emerged as a novel ecofriendly process for the preparation of supported MNPs to alleviate the environmental challenges.

In situ synthesis of supported metal nanocatalysts through heterogeneous doping

Supported metal nanoparticles hold great promise for many fields, including catalysis and renewable energy. Here we report a novel methodology for the in situ growth of architecturally tailored, regenerative metal nanocatalysts that is applicable to a wide range of materials. The main idea underlying this strategy is to selectively diffuse catalytically active metals along the grain boundaries of host oxides and then to reduce the diffused metallic species to form nanoclusters. As a case study, we choose ceria and zirconia, the most recognized oxide supports, and spontaneously form various metal particles on their surface with controlled size and distribution. Metal atoms move back and forth between the interior (as cations) and the exterior (as clusters) of the host oxide lattice as the reductive and oxidative atmospheres repeat, even at temperatures below 700 °C. Furthermore, they exhibit excellent sintering/coking resistance and reactivity toward chemical/electrochemical reactions, demonstrating potential to be used in various applications.

Selective Benzyl Alcohol Oxidation over Pd Catalysts

In the last decades, the selective liquid phase oxidation of alcohols to the corresponding carbonyl compounds has been a subject of growing interest. Research has focused on green methods that use “clean” oxidants such as O2 in combination with supported metal nanoparticles as the catalyst. Among the alcohols, benzyl alcohol is one of the most studied substrates. Indeed, benzyl alcohol can be converted to benzaldehyde, largely for use in the pharmaceutical and agricultural industries. This conversion serves as model reaction in testing new potential catalysts, that can then be applied to other systems. Pd based catalysts have been extensively studied as active catalytic metals for alcohol oxidation for their high activity and selectivity to the corresponding aldehyde. Several catalytic materials obtained by careful control of the morphology of Pd nanoparticles, (including bimetallic systems) and by tuning the support properties have been developed. Moreover, reaction conditions, including solvent, temperature, pressure and alcohol concentration have been investigated to tune the selectivity to the desired products. Different reaction mechanisms and microkinetic models have been proposed. The aim of this review is to provide a critical description of the recent advances on Pd catalyzed benzyl alcohol oxidation.

The Catalytic Reduction of Carboxylic Acid Derivatives and CO2 by Metal Nanoparticles on Lewis-Acidic Supports.

The development of heterogeneous catalysts for green chemical synthesis is currently a growing area in catalysis and sustainable chemistry. Especially the use of renewable carbon resources such as carbon dioxide (CO2 ) and biomass-derived compounds (e. g. carboxylic acids, esters, and amides) represent highly attractive research targets. As these substances reside in a high oxidation state, efficient reduction processes are required in order to convert these substrates into useful and value-added chemicals. Moreover, in the interest of mass production, these substrates should be reduced by molecular H2 and a heterogeneous catalyst. In this context, our group has developed advanced catalysts and established design guidelines for catalysts that promote the reductive transformations of carboxylic acid derivatives and CO2 . Our studies show that cooperative catalysis between Lewis-acidic sites on the catalyst support and supported metal nanoparticles are crucial for the success of these challenging hydrogenations. In this review, we summarize the results of our recent studies on the direct synthesis of value-added chemicals from CO2 and carboxylic acid derivatives using supported transition-metal catalysts, and we propose a design concept for heterogeneous catalysts that promote these processes.

Ni modified Pd nanoparticles immobilized on hollow nitrogen doped carbon spheres for the simehydrogenation of phenylacetylene

In this work, Ni modified Pd nanoparticles immobilized on hollow nitrogen doped carbon spheres were successfully prepared, denoted as Pd/Ni-N/C. The Pd/Ni-N/C showed a moderate catalytic activity for the catalytic reduction of 4-nitrophenol as a model reaction. When applied for the simehydrogenation of phenylacetylene, the Pd/Ni-N/C exhibited a much better catalytic performance than some other Pd-based catalysts. What’s more, the selectivity of styrene could be kept at high levels even when the reaction time was prolonged. The superior catalytic performance may be ascribed to the incorporation of Ni and N species, which were detailedly characterized and contrastively demonstrated. The contained N groups could disperse and stabilize the supported metal nanoparticles. The Pd/Ni-N/C displayed no obvious decrease of catalytic activity and selectivity in the recycling tests, indicating the potential for various industrial applications.

Sinter-resistant metal nanoparticle catalysts achieved by immobilization within zeolite crystals via seed-directed growth

Supported metal nanoparticle catalysts are widely used in industry but suffer from deactivation resulting from metal sintering and coke deposition at high reaction temperatures. Here, we show an efficient and general strategy for the preparation of supported metal nanoparticle catalysts with very high resistance to sintering by fixing the metal nanoparticles (platinum, palladium, rhodium and silver) with diameters in the range of industrial catalysts (0.8–3.6 nm) within zeolite crystals (metal@zeolite) by means of a controllable seed-directed growth technique. The resulting materials are sinter resistant at 600–700 °C, and the uniform zeolite micropores allow for the diffusion of reactants enabling contact with the metal nanoparticles. The metal@zeolite catalysts exhibit long reaction lifetimes, outperforming conventional supported metal catalysts and commercial catalysts consisting of metal nanoparticles on the surfaces of solid supports during the catalytic conversion of C1 molecules, including the water-gas shift reaction, CO oxidation, oxidative reforming of methane and CO2 hydrogenation. Supported metal nanoparticles are indispensable catalysts in industry, yet they are often subjected to severe sintering. Now, a general method based on metal immobilization within zeolite is reported for the preparation of highly sinter-resistant catalysts for a broad range of industrially relevant processes.

Significance of surface oxygen-containing groups and heteroatom P species in switching the selectivity of Pt/C catalyst in hydrogenation of 3-nitrostyrene

The selectivity of 3-nitrostyrene (NS) hydrogenation over 0.5 wt-% Pt catalysts supported on carbon materials can be switched simply by changing reduction temperature. When the reduction temperature was 150 °C, 1-ethyl-3-nitrobenzene (ENB) was mainly produced in a selectivity of 93% at a conversion of 95% (at 100 °C). When the reduction was conducted at a higher temperature of 450 °C, in contrast, the main product was switched to 3-aminostyrene (AS) in a selectivity of 96% at a conversion of 91%. That is, the Pt/C catalysts reduced at low and high temperatures could preferentially catalyze the hydrogenation of vinyl and nitro groups of NS, respectively. This switching of the product selectivity may be ascribed to actions of surface oxygen-containing functional groups and surface hetero P species. The quantity and nature of these surface species were examined in detail by a few different methods. For the low-temperature reduced catalyst, surface acidic groups present close to Pt nanoparticles (∼2 nm) would interact with the nitro group of a NS molecule and make its vinyl group more likely to interact with the surface active metal species of Pt nanoparticles; this facilitates the hydrogenation of the latter and produces ENB selectively. For the high-temperature reduced catalyst, however, P species would interact with Pt and form Pt-POx complex, on which a NS molecule is likely to be adsorbed with its nitro group, facilitating the selective production of AS via its hydrogenation. It is demonstrated that surface functional groups and surface hetero atoms (like P), in addition to main active metal species (like Pt), should have direct actions in the catalysis for such a catalyst that exposes a larger quantity of surface functional groups and/or hetero atoms compared to the number of supported metal nanoparticles.

Confinement Impact for the Dynamics of Supported Metal Nanocatalyst.

Supported metal nanoparticles play key roles in nanoelectronics, sensors, energy storage/conversion, and catalysts for the sustainable production of fuels and chemicals. Direct observation of the dynamic processes of nanocatalysts at high temperatures and the confinement of supports is of great significance to investigate nanoparticle structure and functions for practical utilization. Here, in situ high-resolution transmission electron microscopy photos and videos are combined with dynamics simulations to reveal the real-time dynamic behavior of Pt nanocatalysts at operation temperatures. Amorphous Pt surface on moving and deforming particles is the working structure during the high operation temperature rather than a static crystal surface and immobilization on supports as proposed before. The free rearrangement of the shape of Pt nanoparticles allows them to pass through narrow windows, which is generally considered to immobilize the particles. The Pt particles, no matter what their sizes, prefer to stay inside nanopores even when they are fast moving near an opening at temperatures up to 900 °C. The porous confinement also blocks the sintering of the particles under the confinement size of pores. These contribute to the continuous high activity and stability of Pt nanocatalysts inside nanoporous supports during a long-term evaluation of catalytic reforming reaction.

Neural-network-enhanced evolutionary algorithm applied to supported metal nanoparticles

We show that approximate structural relaxation with a neural network enables orders of magnitude faster global optimization with an evolutionary algorithm in a density functional theory framework. The increased speed facilitates reliable identification of global minimum energy structures, as exemplified by our finding of a hollow ${\mathrm{Pt}}_{13}$ nanoparticle on an MgO support. We highlight the importance of knowing the correct structure when studying the catalytic reactivity of the different particle shapes. The computational speedup further enables screening of hundreds of different pathways in the search for optimum kinetic transitions between low-energy conformers and hence pushes the limits of the insight into thermal ensembles that can be obtained from theory.

Layered Pt.ZSM-5-C by Greener Chemical Reduction for Catalysing Fuel Cell Reactions

Metal ion exchanged catalysts are known now and are successfully used for many catalytic processes. But supported metal nanoparticles on the zeolite bed, and their use as catalysts is still under experimental probe. ZSM-5 supported platinum nanoparticles are synthesized from in-situ chemical reduction of platinum chloride solution in the presence of zeolite, by zinc dust chemical reduction method which is comparatively ‘greener’. This platinum nanoparticle loaded ZSM-5 is studied in the role of catalyst in electrooxidation of methanol and ethanol using Nafion-117 to bind the catalyst on carbon felt. The platinum nanoparticle loaded ZSM-5 is found to be a better catalyst compared to pure ZSM-5 and pure platinum. This greener chemical reduction method can be used as the results show that zeolite modified catalysts are as good as those prepared by other less environment friendly methods, if not better.

Reconstruction of Supported Metal Nanoparticles in Reaction Conditions.

Metal nanoparticles (NPs) dispersed on a high-surface-area support are normally used as heterogeneous catalysts. Recent in situ experiments have shown that structure reconstruction of the NP occurs in real catalysis. However, the role played by supports in these processes is still unclear. Supports can be very important in real catalysis because of the new active sites at the perimeter interface between nanoparticles and supports. Herein, using a developed multiscale model coupled with in situ spherical aberration-corrected (Cs-corrected) TEM experiments, we show that the interaction between the support and the gas environment greatly changes the contact surface area between the metal and support, which further leads to the critical change in the perimeter interface. The dynamic changes of the interface in reactive environments can thus be predicted and be included in the rational design of supported metal nanocatalysts. In particular, our multiscale model shows quantitative consistency with experimental observations. This work offers possibilities for obtaining atomic-scale structures and insights beyond the experimental limits.

Reconstruction of Supported Metal Nanoparticles in Reaction Conditions

AbstractMetal nanoparticles (NPs) dispersed on a high‐surface‐area support are normally used as heterogeneous catalysts. Recent in situ experiments have shown that structure reconstruction of the NP occurs in real catalysis. However, the role played by supports in these processes is still unclear. Supports can be very important in real catalysis because of the new active sites at the perimeter interface between nanoparticles and supports. Herein, using a developed multiscale model coupled with in situ spherical aberration‐corrected (Cs‐corrected) TEM experiments, we show that the interaction between the support and the gas environment greatly changes the contact surface area between the metal and support, which further leads to the critical change in the perimeter interface. The dynamic changes of the interface in reactive environments can thus be predicted and be included in the rational design of supported metal nanocatalysts. In particular, our multiscale model shows quantitative consistency with experimental observations. This work offers possibilities for obtaining atomic‐scale structures and insights beyond the experimental limits.

Metal‐Organic Frameworks as Catalyst Supports: Influence of Lattice Disorder on Metal Nanoparticle Formation

Because of their high tunability and surface area, metal‐organic frameworks (MOFs) show great promise as supports for metal nanoparticles. Depending on the synthesis route, MOFs may contain defects. Here, we show that highly crystalline MIL‐100(Fe) and disordered Basolite® F300, with identical iron 1,3,5‐benzenetricarboxylate composition, exhibit very divergent properties when used as a support for Pd nanoparticle deposition. While MIL‐100(Fe) shows a regular MTN‐zeotype crystal structure with two types of cages, Basolite® F300 lacks long‐range order beyond 8 Å and has a single‐pore system. The medium‐range configurational linker‐node disorder in Basolite® F300 results in a reduced number of Lewis acid sites, yielding more hydrophobic surface properties compared to hydrophilic MIL‐100(Fe). The hydrophilic/hydrophobic nature of MIL‐100(Fe) and Basolite® F300 impacts the amount of Pd and particle size distribution of Pd nanoparticles deposited during colloidal synthesis and dry impregnation methods, respectively. It is suggested that polar (apolar) solvents/precursors attractively interact with hydrophilic (hydrophobic) MOF surfaces, allowing tools at hand to increase the level of control over, for example, the nanoparticle size distribution.

Degradation of IrOx Nanoparticles Supported Onto Sb-Doped SnO2 Aerogel Monitored By Dynamic Electrochemical Impedance Spectroscopy and Identical-Location TEM

Supporting metal nanoparticles is a common approach in heterogeneous gas-phase catalysis to decrease the metal loading, prevent agglomeration and thus minimize the cost of a catalytic conversion. This approach proved particularly successful in proton-exchange membrane fuel cells (PEMFC) where the replacement of Pt-blacks (used in early PEMFCs) by carbon-supported Pt nanoparticles has significantly improved the Pt specific power density. Using the same material’s concepts in proton-exchange membrane water electrolysers (PEMWE) could minimize the noble metal loading especially at the anode where the oxygen evolution reaction (OER) takes place. However, high-surface area carbon supports are rapidly degraded in the operating conditions of a PEMWE anode (E > 1.6 V vs. the reversible hydrogen electrode, T = 80 °C) calling for alternative support materials. In this contribution, IrOx nanoparticles were synthesized using the polyol method and deposited onto antimony doped tin dioxide aerogel (ATO) or Vulcan XC-72 (as a reference), and tested as OER electrocatalysts. By combining classical electrochemical techniques, dynamic Electrochemical Impedance Spectroscopy (dEIS) and Identical-Location Transmission Electron Microscopy (IL-TEM), we gained some insights into the mechanisms leading to loss of OER activity. IL-TEM images (Figure 1) provide strong evidence that the activation step was detrimental to the ATO support while no major degradation was observed at higher voltages (OER region). Approximately 73 % of the initial activity was lost for IrOx/ Vulcan XC-72 after 4,000 potential cycles between 1.2 and 1.6 V vs. the reversible hydrogen electrode (RHE) compared to 16 % for IrOx/ATO. The polarization resistance measured in the OER region by dEIS remains roughly the same for IrOx/ATO while a large increase was observed for IrOx/Vulcan XC-72. Figure 1