Core Shell Nanocatalysts Research Articles

Enhancement of Cu+ stability under a reducing atmosphere by the long-range electromagnetic effect of Au.

In conventional thermocatalytic reactions under a reducing atmosphere, stabilization of the active Cu+ component and inhibition of over-reduction into metallic Cu0 are extremely challenging. In this study, Au@Cu2O core-shell nano-catalysts with different Cu2O shell thicknesses were synthesized, and the effect of the Au nano-core on Cu+ stability under a reducing atmosphere and the catalytic performance of Cu+ in the ethynylation of formaldehyde were investigated. The Au nano-core facilitates Cu2O dispersion and leads to an increase of 0.2-0.5 eV in electron binding energies of Cu2O and Cu2C2 in the range of 27-55 nm, attributed to the long-range electromagnetic effect of Au NPs. Specifically, active Cu+ centers exhibit high stability under a reducing atmosphere due to the long-range electromagnetic effect of the Au nano-core. In the ethynylation of formaldehyde as a probe reaction, Cu+/(Cu0 + Cu+) on Au@Cu2O catalysts remained at 88-91%. The catalytic performance in the ethynylation of formaldehyde revealed that the introduction of an Au nano-core into Cu-based catalysts increased the TOF from 0.37 to 0.7 h-1, and decreased the activation energy from 42.6 to 38.1 kJ mol-1. Additionally, the Cu+/(Cu0 + Cu+) ratios and the catalytic performance in the ethynylation of formaldehyde (BD yield = 65%, BD selectivity = 95%) on Au@Cu2O catalysts remained constant after nine cycles, while pure Cu2O readily deactivated due to the dramatically reduced Cu+/(Cu0 + Cu+) ratios and carbyne deposition. In summary, Cu+ in Cu-based catalysts showed high catalytic activity and stability during the ethynylation of formaldehyde due to the long-range electromagnetic effect of the Au nano-core.

Introducing a green nanocatalytic process toward the synthesis of benzo[a]pyrano-[2,3-c]phenazines utilizing copper oxide quantum dot-modified core-shell magnetic mesoporous silica nanoparticles as high throughput and reusable nanocatalysts.

In this contribution, a green, simple, efficient, and straightforward nanocatalytic process was developed for the synthesis of benzo[a]pyrano[2,3-c]phenazine derivatives under mild thermal conditions. In this regard, the copper oxide quantum dot-modified magnetic silica mesoporous nanoparticles (M-MSNs/CuO(QDs)) were synthesized by surface modification of M-MSNs with CuO QDs to prepare a highly powerful magnetic core–shell nanocatalyst. The prepared nanocatalyst was then characterized for its functionality, size, morphology, elemental composition, surface area, crystallinity, and magnetic properties. Afterwards, it was applied for the synthesis of benzo[a]pyrano[2,3-c]phenazine derivatives under green reaction conditions. The factors affecting the reaction yield were optimized by the one-factor-at-a-time optimization method. Under obtained optimal conditions, the developed method showed a reaction yield range as high as 86–95% for different derivatives. The reusability studies were performed for indexing the cycling stability of the prepared magnetic nanocatalyst. The results exhibited that the catalytic efficiency of the nanocatalyst was saved for at least 5 operational times, showing high cycling stability of M-MSNs/CuO(QDs). Finally, the catalytic performances of the nanocatalyst was compared with the reported ones, revealing that the M-MSNs/CuO(QDs) presents very better performances toward the synthesis of benzo[a]pyrano[2,3-c]phenazine derivatives than the reported ones.

Wox Nanowire Supported Ultra-Fine Ir-Irox Core-Shell Nanocatalyst with Compelling Oer Activity and Durability

Wox Nanowire Supported Ultra-Fine Ir-Irox Core-Shell Nanocatalyst with Compelling Oer Activity and Durability

Reductant free green synthesis of magnetically recyclable MnFe2O4@SiO2-Ag coreshell nanocatalyst for the direct reduction of organic dye pollutants.

The present paper describes in situ green immobilization of silver nanoparticles on MnFe2O4@SiO2 nanospheres using Epilobium parviflorum (EP) without using any other toxic chemicals and reducing or stabilizing agents. The morphology, composition, and magnetic properties of the resulting MnFe2O4@SiO2-Ag core-shell nanocatalyst were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). The catalytic performance of the synthesized MnFe2O4@SiO2-Ag was employed on the organic pollutants dyes such as rhodamine B (RhB) and methylene blue (MB). The results revealed significant reduction performances for the MB (116.28 s-1 g-1) and RhB (27.12 s-1 g-1) over the existing literature. Furthermore, the MnFe2O4@SiO2-Ag exhibited high stability for the completion of the reduction of RhB between the reaction times of 13.1 (first) and 19.8 min (final) with the 100% decolorization efficiency even after several cycles with an excellent magnetic separation. Overall, this work demonstrates a simple and practical green synthetic route for the preparation of magnetic recyclable core-shell nanocatalyst that can be a good candidate for the treatment of organic contaminants in wastewater adhering to green chemistry principles for the environmental pollution concerns.

Penta-Twinned Rh@Pt Core-Shell nanobranches with engineered shell thickness for reversible and active hydrogen redox electrocatalysis

Surface defects on electrocatalysts can effectively reduce reaction barriers and facilitate the kinetics of hydrogen evolution and oxidation reactions (HER/HOR). However, precisely engineering such surface structures remains a significant challenge. Herein, penta-twinned (PTw) Rh@Ptx core–shell nanobranches (NBs) with intense surface strains were facilely synthesized using PTw Rh NBs as the seeds for overgrowth of active Pt-shells. Through precisely regulating the supply of Pt precursor solution via a micro-syringe pump, the ultrathin Pt-shells conform to and replicate the twin defects of the PTw Rh seeds. Significantly, the shell thickness can be precisely controlled from 1.0, 2.0, and 3.8 to 5.0 atomic layers. Due to the integration of surface twinned defects, compressive strain and the core–shell ligand effect, these Rh@Ptx NBs exhibit superior hydrogen redox electrocatalytic performance compared to state-of-the-art Pt/C. Among the prepared materials, the Rh@Pt0.83 NBs with a 3.8 atomic layer Pt-shell showed the highest mass activity (2.36 A mgPt−1) and specific activity (6.55 mA cm−2) for HER at –0.07 V and presented the lowest overpotential (44 mV) at 10 mA cm−2, less than half the overpotential of the commercial Pt/C (98 mV). In terms of HOR, the Rh@Pt0.83 NBs showed a superior exchange current density (1.97 mA cm−2), approximately 7 times higher than that of Pt/C. Our work provides a facile method to synchronously engineer the Pt-shell thickness and surface defects of Rh@Pt core–shell nanocatalysts for the creation of robust and bifunctional hydrogen redox electrocatalysts.

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.

Ru/Nb co-doped perovskite anode: Achieving good coking resistance in hydrocarbon fuels via core-shell nanocatalysts exsolution

Ru/Nb co-doped (Pr0.5Sr0.5)0.9Fe0.8Ru0.1Nb0.1O3-δ (PSFRN) cubic perovskite oxide was fabricated and used as the solid oxide fuel cell (SOFC) anode material. After treated in wet H2 at 900 °C for 2 h, the PSFRN was partially transformed into Ruddlesden-Popper (RP) layered perovskite PrSrFe0.8Ru0.1Nb0.1O4+δ (RP-PSFRN), and Fe0.7Ru0.3 alloy-FeOx oxide (FRA@FO) core-shell nanoparticles were in-situ exsolved on the reduced-PSFRN (R-PSFRN) substrate surface. The phase transition and the exsolution of the nanoparticles were investigated using X-ray diffraction, transmission electron microscope and X-ray photoelectron spectroscopy. Modified by the in-situ exsolved FRA@FO core-shell nanoparticles, the R-PSFRN anode material showed high catalytic activity for hydrogen and hydrocarbon fuels. The power density of SOFC reached 0.683 and 0.537 W cm−2 with wet H2 and C3H8 as fuel at 800 °C, respectively. Moreover, the SOFC showed a stable output under a constant current load of 0.15 A cm−2 in C3H8, demonstrating a high resistance to carbon deposition and coking.

Hydrogen-Mediated Thin Pt Layer Formation on Ni3N Nanoparticles for the Oxygen Reduction Reaction.

A simple wet-chemical route for the preparation of core-shell-structured catalysts was developed to achieve high oxygen reduction reaction (ORR) activity with a low Pt loading amount. Nickel nitride (Ni3N) nanoparticles were used as earth-abundant metal-based cores to support thin Pt layers. To realize the site-selective formation of Pt layers on the Ni3N core, hydrogen molecules (H2) were used as a mild reducing agent. As H2 oxidation is catalyzed by the surface of Ni3N, the redox reaction between H2 and Pt(IV) in solution was facilitated on the Ni3N surface, which resulted in the selective deposition of Pt on Ni3N. The controlled Pt formation led to a subnanometer (0.5-1 nm)-thick Pt shell on the Ni3N core. By adopting the core-shell structure, higher ORR activity than the commercial Pt/C was achieved. Electrochemical measurements showed that the thin Pt layer on Ni3N nanoparticle exhibits 5 times higher mass activity and specific activity than that of commercial Pt/C. Furthermore, it is expected that the proposed simple wet-chemical method can be utilized to prepare various transition-metal-based core-shell nanocatalysts for a wide range of energy conversion reactions.

Poly(ionic liquid)s based nano core-shell catalyst SiO2@V-PIL for efficient oxidative desulfurization of diesel

For efficient oxidative desulfurization (ODS) of fuel oils with cumene hydroperoxide (CHP), a poly(ionic liquid)s based nano core-shell catalyst SiO2@V-PIL was prepared by reacting poly vinylimidazole (PVIM) with peroxovanadic acid on nano-particles of SiO2. The structure and composition of SiO2@V-PIL, V-PIL/SiO2 and V-PIL were studied through TEM, SEM, XRD and other methods. Compared to micron-sized V-PIL and V-PIL/SiO2, the core-shell Nano catalyst can significantly enhance the oxidation rate of the sulfides. The catalytic difference may arise from their specific surface exposure and active center distribution. Dibenzothiophene (DBT) can be oxidized completely within 60 min under appropriate conditions, and 99 % of catalytic performance can be retained after 5 recycled uses. The Nano core-shell structuring might be used as a viable and universal way to significantly upgrade the catalytic activity of the composite catalysts.

Performance of Pd@FeCo Catalyst in Anion Exchange Membrane Alcohol Fuel Cells

The performances of the core-shell nano-electrocatalysts (FeCo@Fe@Pd/CNT-OH and their monometallic Pd counterparts (Pd/CNT-OH) on carbon nanotubes in passive and active direct methanol fuel cells (DMFCs) and direct ethanol fuel cells (DEFCs) have been studied. The direct alcohol alkaline fuel cell (DAAFCs) performances of the two nanocatalysts studied revealed the outstanding performances of the core shell, FeCo@Fe@Pd catalysts over the single Pd metal on the same substrates. A fourfold increase in power density value was observed in the DEFC while a threefold increase was seen in the DMFC while operating both passive DAAFCs at moderate temperatures using the core shell nanocatalysts. The core-shell-modified electrode also gave an exceptional activity of over 50% columbic efficiency in comparison with its Pd counterpart in the passive DEFC. Density functional theory calculations carried out to further comprehend the electrocatalytic oxidation of the nanocatalysts towards both methanol and ethanol fuels corroborated the experimental findings. An increase in the readily available electrons of the partially filled d-orbitals was found to be involved in the catalytic reactions on the surface of the FeCo@Fe@Pd/CNT-OH core shell catalysts as opposed to those of the p-orbitals of Pd/CNT-OH, thus enhancing its catalytic activities in both DAAFCs.

Supporting effects of a N-doped carbon film electrode on an electrodeposited Ni@Ni(OH)2 core-shell nanocatalyst in accelerating electrocatalytic oxidation of oligosaccharides.

The supporting effect of a N-doped carbon film induced superior crystallinity in electrodeposited Ni@Ni(OH)2 core–shell nanoparticles. This improvement resulted in a much higher regeneration rate of catalytic sites (NiOOH), leading to higher oxidation currents of sugars. Also, the overpotential of the maltopentaose (G5) oxidation reaction decreased significantly, probably due to the effect of the electrostatic interaction between NPs and G5.

Utility of Core–Shell Nanomaterials in the Catalytic Transformations of Renewable Substrates

In recent years, core-shell nano-catalysts have received increasing attention due to their tunable properties and broad applications in catalysis. Control of the two components of these materials allows their catalytic properties to be tuned to various sustainable processes in synthetic and energy-related applications. This Concept article describes recent state-of-the-art core-shell materials and their application as heterogeneous catalysts for a range of sustainable catalytic transformations, focusing on two important classes of renewable substrates, CO2 and biomass. In the discussion, emphasis is directed to the role of the constituent parts of the core-shell structure and how they can be manipulated to enhance activity.

Preparation of a trihydrazinotriazine-functionalized core-shell nanocatalyst as an extremely efficient catalyst for the synthesis of benzoxanthenes

In recent years, there is a high demand on utilizing heterogeneous nanocatalysts in organic synthetic routes because of their green approach, facile purification of the products, and reusability of the catalyst. Herein, we introduced trihydrazinotriazine (THDT)-coated Fe3O4@SiO2 as a novel amino-functionalized magnetic nanocompostie. We fully characterized the nanocatalyst and proved the morphology and magnetic property of the nanoparticles by using essential analyses. The basic attribute of the amino-rich porous surface of the nanocomposite provides a desirable environment for enhancing various reaction conditions. To examine the applicability of the nanocatalyst in organic reactions, we synthesized several benzoxanthenes using Fe3O4@SiO2-THDT nanocatalysts. The nanocomposite successfully improved the reaction conditions and provided the benzoxanthenes in an environmentally friendly procedure, which afforded product in excellent yields (80–96%) and reduced time. The nanomagnetic catalyst was easily recovered after each trial by using an external magnet. After six successive runs, the loss of catalytic activity of the nanocomposite was negligible. Finally, we propounded a plausible mechanism for the preparation of the benzoxanthenes derivatives using the THDT-functionalized core-shell magnetic nanocatalyst.

Highly selective hydrogen production from propane by Ru–Ni core–shell nanocatalyst deposited on reduced graphene oxide by sequential chemical vapor deposition

Highly selective hydrogen production from propane by <scp>Ru–Ni</scp> core–shell nanocatalyst deposited on reduced graphene oxide by sequential chemical vapor deposition

Selective Acceptorless Dehydrogenation of Primary Amines to Imines by Core-Shell Cobalt Nanoparticles.

Core–shell nanocatalysts are attractive due to their versatility and stability. Here, we describe cobalt nanoparticles encapsulated within graphitic shells prepared via the pyrolysis of a cationic poly‐ionic liquid (PIL) with a cobalt(II) chloride anion. The resulting material has a core–shell structure that displays excellent activity and selectivity in the self‐dehydrogenation and hetero‐dehydrogenation of primary amines to their corresponding imines. Furthermore, the catalyst exhibits excellent activity in the synthesis of secondary imines from substrates with various reducible functional groups (C=C, C≡C and C≡N) and amino acid derivatives.

Oxygen Reduction Activities of Strained Platinum Core-Shell Electrocatalysts Predicted by Machine Learning.

Core-shell nanocatalyst activities are chiefly controlled by bimetallic material composition, shell thickness, and nanoparticle size. We present a machine learning framework predicting strain with site-specific precision to rationalize how strain on Pt core-shell nanocatalysts can enhance oxygen reduction activities. Large compressive strain on Pt@Cu and Pt@Ni induces optimal mass activities at 1.9 nm nanoparticle size. It is predicted that bimetallic Pt@Au and Pt@Ag have the best mass activities at 2.8 nm, where active sites are exposed to weak compressive strain. We demonstrate that optimal strain depends on the nanoparticle size; for instance, strengthening compressive strain on 1.92 nm sized Pt@Cu and Pt@Ni, or weakening compressive strain on 2.83 nm sized Pt@Ag and Pt@Au, can lead to further enhanced mass activities.

Facile synthesis of Ternary Au@PdNi core-shell nanoparticles with enhanced electrocatalytic performance for ethanol oxidation reaction

We report a facile synthesis of ternary Au@PdNi core-shell nanoparticles (C-SNPs). Au NPs with 15 nm in diameter served as seeds, Pd2+ and Ni2+ were co-reduced on the surface of Au NPs to obtain C-SNPs. These C-SNPs exhibited outstanding catalytic performance (5891 mA mgPd−1) and stability for ethanol oxidation reaction (EOR). The activity was 9.48 times higher than the commercial Pd/C (20% wt). The catalytic mechanism was investigated, and the enhanced catalytic performance of Au@PdNi C-SNPs was mainly attributed to electronic effects between Pd and Au/Ni, and the unique core-shell nanostructure. The present work provides a strategy for rational design of ternary metallic core-shell nanocatalysts, which can achieve high catalytic activity and durability.

Core–Shell Nanocatalysts of Co3O4 and NiO Shells from New (Discarded) Resources: Sustainable Recovery of Cobalt and Nickel from Spent Lithium-Ion Batteries, Ni–Cd Batteries, and LCD Panel

This work focuses on end-of-life Ni-Cd and Li-ion batteries and introduces a novel approach to prepare two types of core-shell nanocatalysts consisting of NiO and CoO as the shells, respectively. Using a hydrometallurgical technique, we are able to successfully recover metals such as Co and Ni, and then use the recovered metals as precursors in preparation of catalysts via a precipitation technique using an alumina-borosilicate substrate which has been fabricated from scrap LCDs. The structures of the obtained nanocatalysts are carefully investigated by electron microscopes. It is revealed that the NiO show nanowire structure, while the CoO has nanobelt structure shells over the core of the substrates. The synthesized nanomaterials are used as photocatalysts to decompose methylene blue as an organic pollution model available in wastewater. Our nanocatalysts exhibit high photocatalytic performance with four times the reusability under a very low power UV (9 W) irradiation.

Deciphering nanoconfinement effects on molecular orientation and reaction intermediate by single molecule imaging

Nanoconfinement could dramatically change molecular transport and reaction kinetics in heterogeneous catalysis. Here we specifically design a core-shell nanocatalyst with aligned linear nanopores for single-molecule studies of the nanoconfinement effects. The quantitative single-molecule measurements reveal unusual lower adsorption strength and higher catalytic activity on the confined metal reaction centres within the nanoporous structure. More surprisingly, the nanoconfinement effects on enhanced catalytic activity are larger for catalysts with longer and narrower nanopores. Experimental evidences, including molecular orientation, activation energy, and intermediate reactive species, have been gathered to provide a molecular level explanation on how the nanoconfinement effects enhance the catalyst activity, which is essential for the rational design of highly-efficient catalysts.

Recent Developments in Nanostructured Palladium and Other Metal Catalysts for Organic Transformation

Nanocatalysis is an emerging field of research and is applicable to nearly all kinds of catalytic organic conversions. Nanotechnology is playing an important role in both industrial applications and academic research. The catalytic activities become pronounced as the size of the catalyst reduces and the surface area-to-volume ratio increases which ultimately enhance the activity and selectivity of nanocatalysts. Similarly, the morphology of the particles also has a great impact on the activity and selectivity of nanocatalysts. Moreover, the electronic properties and geometric structure of nanocatalysts can be affected by polar and nonpolar solvents. Various forms of nanocatalysts have been reported including supported nanocatalysts, Schiff-based nanocatalysts, graphene-based nanocatalysts, thin-film nanocatalysts, mixed metal oxide nanocatalysts, magnetic nanocatalysts, and core-shell nanocatalysts. Among a variety of different rare earth and transition metals, palladium-based nanocatalysts have been extensively studied both in academia and in the industry because of their applications such as in carbon-carbon cross-coupling reactions, carbon-carbon homocoupling reactions, carbon-heteroatom cross-coupling reactions, and C-H activation, hydrogenation, esterification, oxidation, and reduction. The current review highlights the recent developments in the synthesis of palladium and some other metal nanocatalysts and their potential applications in various organic reactions.