Core Shell Nanocatalysts Research Articles

Synthesis of Highly Active Sub-Nanometer Pt@Rh Core-Shell Nanocatalyst via a Photochemical Route: Porous Titania Nanoplates as a Superior Photoactive Support.

Sub-nanometer Pt@Rh nanoparticles highly dispersed on MIL-125-derived porous TiO2 nanoplates are successfully prepared for the first time by a photochemical route, where the porous TiO2 nanoplates with a relatively high specific surface area play a dual role as both effective photoreductant and catalyst support. The resulting Pt@Rh/p-TiO2 can be utilized as a highly active catalyst.

Self-healing Pd3Au@Pt/C core-shell electrocatalysts with substantially enhanced activity and durability towards oxygen reduction

Pt shells were synthesized on Pd-based alloy-cores via the chemical reduction method. Pt shells containing 1, 2, or 3 layers were prepared by controlling the amounts of Pt precursor used during synthesis. The thicknesses of Pt shell layers were calculated using the difference in the particle size between core and core-shell nanocatalysts, as determined from Cs-corrected scanning transmission electron microscopy (Cs-STEM) data. The shape and elemental distribution in the core-shell structured nanoparticles were analyzed using line profiles and elemental mapping from Cs-STEM. High-resolution X-ray diffraction and X-ray photoelectron spectroscopy analyses suggested that the structural and electronic properties of core-shell nanocatalysts were dependent on the number of shell layers. The activity and durability of the core-shell nanocatalysts were analyzed by the electrochemical method. Accelerated durability tests (ADT) were conducted in the potential range of 0.6–1V for 10000 cycles, and the mass and specific activities of ADT were shown to be stable for the carbon-supported core-shell nanocatalyst with two Pt shell layers (core@Pt[2](*)/C). In addition, excellent electrochemical performance was observed for the core@Pt[2]/C sample before and after the ADT compared to the commercial samples as well as other samples prepared in this study. Importantly, the optimized Pt usage demonstrated in this study would significantly contribute to the commercialization of proton exchange membrane fuel cells.

Synthesis of Durable Small-sized Bilayer Au@Pt Nanoparticles for High Performance PEMFC Catalysts

Design of small-sized Au@Pt core-shell nanocatalysts with high activity and stability is crucial area for a wide range of electronic and chemical devices. Here, we report a novel reduction method using UV treatment at room temperature by a weak reducing agent of H2O2 enabling to produce carbon-supported small Au nanoparticles as the core of Pt shells. Different thicknesses of Pt layers are deposited on the Au to configure small-sized core@shell nanocatalysts. We acquire superior catalytic activity of Au@Pt catalysts toward cyclic voltammetry analysis and oxygen reduction reaction (ORR) via atomic level control of the particle size and the electronic structure. Underlying mechanism of the ORR activity is described from the aspect of compressive strain caused by shorter Au-Au distance than the bulk counterpart. The thickness of the Pt shell is shown to play an important role in stabilizing the nanocatalyst. Using density functional theory (DFT) calculations we validate the experimental outcomes. Top-quality power density above 2Wcm−2 at low Pt loading (0.1mgcm−2) is achieved by a bilayer small-size Au@Pt core-shell catalyst with an excellent durability over 10,000 cycles by ADT, which is, indeed, beyond the recent DOE targets for a proton exchange membrane fuel cell system.

In Situ Generation of Pd-Pt Core-Shell Nanoparticles on Reduced Graphene Oxide (Pd@Pt/rGO) Using Microwaves: Applications in Dehalogenation Reactions and Reduction of Olefins.

Core-shell nanocatalysts are a distinctive class of nanomaterials with varied potential applications in view of their unique structure, composition-dependent physicochemical properties, and promising synergism among the individual components. A one-pot microwave (MW)-assisted approach is described to prepare the reduced graphene oxide (rGO)-supported Pd-Pt core-shell nanoparticles, (Pd@Pt/rGO); spherical core-shell nanomaterials (∼95 nm) with Pd core (∼80 nm) and 15 nm Pt shell were nicely distributed on the rGO matrix in view of the choice of reductant and reaction conditions. The well-characterized composite nanomaterials, endowed with synergism among its components and rGO support, served as catalysts in aromatic dehalogenation reactions and for the reduction of olefins with high yield (>98%), excellent selectivity (>98%) and recyclability (up to 5 times); both Pt/rGO and Pd/rGO and even their physical mixtures showed considerably lower conversions (20 and 57%) in dehalogenation of 3-bromoaniline. Similarly, in the reduction of styrene to ethylbenzene, Pd@Pt core-shell nanoparticles (without rGO support) possess considerably lower conversion (60%) compared to Pd@Pt/rGO. The mechanism of dehalogenation reactions with Pd@Pt/rGO catalyst is discussed with the explicit premise that rGO matrix facilitates the adsorption of the reducing agent, thus enhancing its local concentration and expediting the hydrazine decomposition rate. The versatility of the catalyst has been validated via diverse substrate scope for both reduction and dehalogenation reactions.

Enhanced photocatalytic water splitting by gold carbon dot core shell nanocatalyst under visible/sunlight

Hydrogen production from water using photocatalysts under sunlight still remains a huge challenge.

Porous silica-encapsulated and magnetically recoverable Rh NPs: a highly efficient, stable and green catalyst for catalytic transfer hydrogenation with “slow-release” of stoichiometric hydrazine in water

A porous core–shell nanocatalyst hydrazine hydrate water system has been developed for the catalytic transfer hydrogenation of nitroarenes.

One-step synthesis of magnetically recyclable Co@BN core–shell nanocatalysts for catalytic reduction of nitroarenes

The possible mechanism for Co@BN catalyzed 4-nitrophenol reduction in the presence of NaBH4. Moreover, the 13.6 wt% Co@BN core–shell nanoparticles exhibited the excellent catalytic activity in hydrogenation of nitroaromatic compounds.

ZIF-derived porous carbon supported Pd nanoparticles within mesoporous silica shells: sintering- and leaching-resistant core-shell nanocatalysts.

A facile strategy to prepare sintering- and leaching-resistant core-shell nanocatalysts is reported. ZIF-derived porous carbon supported Pd nanoparticles are coated with a mesoporous silica shell, preventing Pd nanoparticles from sintering at high temperature and leaching in a catalytic process. This nanocatalyst exhibits excellent catalytic activity and recyclability for the oxidation of benzyl alcohol.

Fine Tuning the Composition and Nanostructure of Fe‐Based Core–Shell Nanocatalyst for Efficient CO2 Hydrogenation

AbstractHydrogenation of CO2 to hydrocarbons is one of the crucial technologies to address the energy deficit and increasing environmental pollution. In this work, we have synthesized and systematically studied the influence of composition and nanostructure of a Fe‐based, carbon‐coated core–shell nanocatalyst. The synthesis method offered good control over the thickness of the carbon coating in the core–shell catalyst, which in turn controlled the chemical composition of the core. The results emphasized an optimal amount of Fe3O4, Fe5C2 in the core and partially graphitized carbon in the shell for a high catalytic activity in the conversion of CO2 at atmospheric pressure with higher selectivity to C2‐C4 olefins.

Enhanced Nickel-Catalyzed Methanation Confined under Hexagonal Boron Nitride Shells

Encapsulation of metal nanoparticles with porous oxide shells is a successful strategy to design catalysts with high catalytic performance. We suggest an alternative route to cover metal nanoparticles with two-dimensional (2D) material shells such as hexagonal boron nitride (h-BN), in which active metal components are stabilized by the outer shells and meanwhile catalytic reactions occur at interfaces between cores and shells through feasible intercalation of the 2D material covers. As an illustration, Ni nanoparticles encapsulated with few-layer h-BN shells were constructed and applied in syngas methanation. Ni@h-BN core–shell nanocatalysts exhibit enhanced methanation activity, higher resistance to particle sintering, and suppressed carbon deposition and Ni loss in reactions. Surface science studies in h-BN/Ni(111) model systems and chemisorption data confirm the occurrence of methanation reactions on Ni surfaces under h-BN cover. The confinement effect of h-BN shells improves Ni-catalyzed reaction acti...

Molecular dynamics simulations of ternary PtxPdyAuz fuel cell nanocatalyst growth

Molecular dynamics simulation of PEMFC cathodes based on ternary Pt70Pd15Au15 and Pt50Pd25Au25 nanocatalysts dispersed on carbon indicate systematic Au segregation from the particle bulk to the surface, leading to an Au layer coating the cluster surface and to the spontaneous formation of a Pt@Pd@Au core–shell structure. For Au content below 25 at%, surface PtxPdy active sites are available for efficient oxygen reduction reaction, in agreement with DFT calculations and experimental data. Simulations of direct core@shell system prepared in conditions mimicking those of plasma sputtering deposition pointed out an increase of the number of accessible PtxPdy surface active sites. Core-shell nanocatalyst morphology changes occur due to impinging Pt kinetic energy confinement and dissipation.

Magnetically nano core–shell Fe3O4@Cu(OH)x: a highly efficient and reusable catalyst for rapid and green reduction of nitro compounds

Magnetically separable nano core–shell Fe3O4@Cu(OH)x with 22 % Cu content was prepared by the addition of sodium hydroxide to a mixture of CuCl2·2H2O and nano Fe3O4 in water. Characterization of the impregnated copper hydroxide was carried out by X-ray fluorescence (XRF), X-ray diffraction (XRD) atomic absorption spectroscopy (AAS), scanning electron microscopy (SEM), value stream mapping (VSM) and Brunauer–Emmett–Teller (BET) analysis. The core–shell nanocatalyst exhibited the excellent catalytic activity toward reduction of various nitro compounds to the corresponding amines with NaBH4. All reactions were carried out in H2O (55–60 °C) within 3–15 min to afford amines in high to excellent yields. Reusability of core–shell Cu(OH)x catalyst was examined 9 times without significant loss of its catalytic activity.

Facet‐Dependent and Light‐Assisted Efficient Hydrogen Evolution from Ammonia Borane Using Gold–Palladium Core–Shell Nanocatalysts

AbstractAu–Pd core–shell nanocrystals with tetrahexahedral (THH), cubic, and octahedral shapes and comparable sizes were synthesized. Similar‐sized Au and Pd cubes and octahedra were also prepared. These nanocrystals were used for the hydrogen‐evolution reaction (HER) from ammonia borane. Light irradiation can enhance the reaction rate for all the catalysts. In particular, Au–Pd THH exposing {730} facets showed the highest turnover frequency for hydrogen evolution under light with 3‐fold rate enhancement benefiting from lattice strain, modified surface electronic state, and a broader range of light absorption. Finite‐difference time‐domain (FDTD) simulations show a stronger electric field enhancement on Au–Pd core–shell THH than those on other Pd‐containing nanocrystals. Light‐assisted nitro reduction by ammonia borane on Au–Pd THH was also demonstrated. Au–Pd tetrahexahedra supported on activated carbon can act as a superior recyclable plasmonic photocatalyst for hydrogen evolution.

Facet-Dependent and Light-Assisted Efficient Hydrogen Evolution from Ammonia Borane Using Gold-Palladium Core-Shell Nanocatalysts.

Au-Pd core-shell nanocrystals with tetrahexahedral (THH), cubic, and octahedral shapes and comparable sizes were synthesized. Similar-sized Au and Pd cubes and octahedra were also prepared. These nanocrystals were used for the hydrogen-evolution reaction (HER) from ammonia borane. Light irradiation can enhance the reaction rate for all the catalysts. In particular, Au-Pd THH exposing {730} facets showed the highest turnover frequency for hydrogen evolution under light with 3-fold rate enhancement benefiting from lattice strain, modified surface electronic state, and a broader range of light absorption. Finite-difference time-domain (FDTD) simulations show a stronger electric field enhancement on Au-Pd core-shell THH than those on other Pd-containing nanocrystals. Light-assisted nitro reduction by ammonia borane on Au-Pd THH was also demonstrated. Au-Pd tetrahexahedra supported on activated carbon can act as a superior recyclable plasmonic photocatalyst for hydrogen evolution.

Graphitic carbon nitride based hydrogen treated disordered titanium dioxide core-shell nanocatalyst for enhanced photocatalytic and photoelectrochemical performance

Effect of g-C3N4 loading on hydrogen treated TiO2 photocatalyst was studied towards the efficient photocatalytic and photoelectrochemical application. The tailored optical properties and enhanced photoinduced electron-hole separation in crystalline TiO2 (c-TiO2) was achieved by creating an amorphous shell (a-TiO2) around c-TiO2. The a-TiO2/c-TiO2 core-shell particles were further modified by g-C3N4 coating, where amorphous a-TiO2 act as an interlayer between g-C3N4 and c-TiO2 nanocrystals. It was observed that photocatalytic degradation of Methylene Blue (MB) and water splitting to produce hydrogen was remarkably increased under visible-light upon coupling of a-TiO2/c-TiO2 core-shell particles with g-C3N4 and results in the best MB degradation performance of ∼82% in 1 h and water splitting photocurrent density of 450 μA/cm2. The results from UV–vis absorption study, Fourier transform infrared spectroscopy and electron microscopy, photoluminescence, photoelectrochemical measurements and electrochemical impedance spectroscopy suggest that the improved photoactivity is due to the increased light absorption in visible region and efficient charge separation as a result of effective interfacial electron transfer between g-C3N4, a-TiO2 and c-TiO2 in g-C3N4/a-TiO2/c-TiO2 composite.

Ruthenium–platinum core–shell nanocatalysts with substantially enhanced activity and durability towards methanol oxidation

Platinum-based alloy nanocatalysts are highly attractive for both heterogeneous catalysis and electrocatalysis. However, their stability remains a major concern for their application under realistic operating conditions. We herein report a microwave-assisted synthesis of atomically ordered Ru-core Pt-shell (Ru@Pt) nanoparticles that show superior catalytic properties for methanol electrooxidation. The Ru@Pt catalysts are found to display higher methanol oxidation activity and CO-deactivation resistance than the commercial Pt–Ru catalysts. Shell-thickness variation induced properties is of great importance for core–shell catalysis. Above all, well-ordered Ru@Pt with sub-nm Pt shell exhibit superior durability in long-term and extreme operation condition in direct methanol fuel cell (DMFC). This type of core–shell catalysts thus hold great potential to be applied as high performance anode catalysts in DMFCs.

Corrigenda: Synthesis of Pyranopyrazoles Using Magnetically Recyclable Heterogeneous Iron Oxide‐silica Core‐shell Nanocatalyst

Corrigenda: Synthesis of Pyranopyrazoles Using Magnetically Recyclable Heterogeneous Iron Oxide‐silica Core‐shell Nanocatalyst

Cu–EDTA-modified APTMS-Fe3O4@SiO2 core–shell nanocatalyst: a novel magnetic recoverable catalyst for the Biginelli reaction

A novel copper–ethylenediamine tetracarboxylate modified core–shell magnetic catalyst is introduced.

AuCu@Pt Nanoalloys for Catalytic Application in Reduction of 4-Nitrophenol

To enhance and optimize nanocatalyst ability for nitrophenol (4-NP) reduction reaction we look beyond Au-metal nanoparticles and describe a new class of Au nanoalloys with controlled composition for core of AuCu-metals and Pt-metal shell. The reduction of 4-NP was investigated in aqueous media spectroscopically on 7.8 nm Au nanospheres (AuNSs), 8.3 nm AuCuNSs, and 9.1 nm AuCu@Pt core-shell NSs in diameter. The rate constants of the catalyzed reaction at room temperature, activation energies, and entropies of activation of reactions catalyzed by the AuCu@Pt core-shell NSs are found to have different values to those of the pure metal NSs. The results strongly support the proposal that catalysis by nanoparticles is taking place efficiently on the surface of NSs. These core-shell nanocatalysts exhibited stability throughout the reduction reaction and proved that heterogonous type mechanisms are most likely to be dominant in nanoalloy based catalysis if the surface of the NSs is not defected upon shell incorporation.

Fluorescence-marked mesoporous silica core–shell nanocatalyst for asymmetric transfer hydrogenation

Fluorescence-marked core–shell structured nanocatalyst was prepared through co-condensation method. The catalyst exhibits good catalytic efficiency for asymmetric transfer hydrogenation of aromatic ketones and can be recovered and reused several times. The strong fluorescent emission easily tracks the recovery process of the nanocatalyst.