Shell Nanocatalysts Research Articles

Effect of Interfacial Interaction on Electrocatalytic Activity and Durability of Pt-Based Core–Shell Nanocatalysts

Effect of Interfacial Interaction on Electrocatalytic Activity and Durability of Pt-Based Core–Shell Nanocatalysts

Magnetic yolk-shell structured periodic mesoporous organosilica supported palladium as a powerful and highly recoverable nanocatalyst for the reduction of nitrobenzenes

A novel palladium-loaded yolk-shell structured nanomaterial with magnetite core and phenylene-based periodic mesoporous organosilica (PMO) shell (Fe3O4@YS-Ph-PMO/Pd) nanocatalyst was synthesized for the reduction of nitrobenzenes. The Fe3O4@YS-Ph-PMO/Pd was prepared through cetyltrimethylammonium bromide (CTAB) directed condensation of 1,4-bis(triethoxysilyl)benzene (BTEB) around Fe3O4@silica nanoparticles followed by treatment with palladium acetate. This nanocatalyst was characterized by using Fourier transform infrared (FT-IR) spectroscopy, thermal gravimetric analysis (TGA), low-angle and wide-angle powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) analyses. These analyses showed a magnetic nanomaterial with high chemical and thermal stability for the designed composite. The Fe3O4@YS-Ph-PMO/Pd nanocomposite was employed as a powerful and highly recoverable catalyst in the green reduction of nitroarenes in H2O at room temperature. A variety of nitroarene derivatives were applied as substrate in the presence of 0.9 mol% of Fe3O4@YS-Ph-PMO/Pd catalyst. All nitroarenes were selectively converted to their corresponding amines with high to excellent yields (92–96%) within short reaction times (10–18 min). This catalyst was recovered and reused at least 11 times without significant decrease in efficiency and stability.

Design of Pt@Sn core–shell nanocatalysts for highly selective hydrogenation of cinnamaldehyde to prepare cinnamyl alcohol

The selective hydrogenation of cinnamaldehyde (CAL) to prepare cinnamyl alcohol (COL) is challenging as the unwanted hydrogenation of CC bond in CAL is thermodynamically more favorable than the hydrogenation of CO bond. We herein designed core–shell structured nanoparticles (NPs) that consisted of Pt cores and Sn shells to catalyze the CAL to COL conversion. By simply changing the amount of Sn precursor, we generated Pt@Sn NPs with different Sn shell thickness and catalytic performance. Among the samples, Pt@Sn/SiO2 with Pt/Sn of 1/1 achieved the highest CAL conversion (87.2 %) as well as the COL selectivity (95.4 %), which were 5-fold and 6-fold, respectively, higher than those of Pt/SiO2. This catalyst was also applicable to the hydrogenation of other α, β-unsaturated aldehyde and unsaturated carbonyl compounds. Both experiments and theoretical calculations indicated that the strong Pt-Sn interaction and the partial coverage of Pt by Sn facilitated their adsorption of CO bonds, thus enhancing the conversion of CAL and the selectivity towards COL.

Fe-N-C core–shell catalysts with single low-spin Fe(II)-N4 species for oxygen reduction reaction and high-performance proton exchange membrane fuel cells

Fe-N-doped carbon materials (Fe-N-C) are promising candidates for oxygen reduction reaction (ORR) relative to Pt-based catalysts in proton exchange membrane fuel cells (PEMFCs). However, the intrinsic contributions of Fe-N4 moiety with different chemical/spin states (e.g. D1, D2, D3) to ORR are unclear since various states coexist inevitably. In the present work, Fe-N-C core–shell nanocatalyst with single low-spin Fe(II)-N4 species (D1) is synthesized and identified with ex-situ ultralow temperature Mössbauer spectroscopy (T = 1.6 K) that could essentially differentiate various Fe-N4 states and invisible Fe-O species. By quantifying with CO-pulse chemisorption, site density and turnover frequency of Fe-N-C catalysts reach 2.4 × 1019 site g−1 and 23 e site−1 s−1 during the ORR, respectively. Half-wave potential (0.915 VRHE) of the Fe-N-C catalyst is more positive (approximately 54 mV) than that of Pt/C. Moreover, we observe that the performance of PEMFCs on Fe-N-C almost achieves the 2025 target of the US Department of Energy by demonstrating a current density of 1.037 A cm−2 combined with the peak power density of 0.685 W cm−2, suggesting the critical role of Fe(II)-N4 site (D1). After 500 h of running, PEMFCs still deliver a power density of 1.26 W cm−2 at 1.0 bar H2-O2. An unexpected rate-determining step is figured out by isotopic labelling experiment and theoretical calculation. This work not only offers valuable insights regarding the intrinsic contribution of Fe-N4 with a single spin state to alkaline/acidic ORR, but also provides great opportunities for developing high-performance stable PEMFCs.

One-pot synthesis of Pt@Sn core-shell nanocatalysts for the hydrogenation of halonitrobenzene to produce haloaniline with ultra-high selectivity

Pt nanocatalysts exhibits superior activity towards the hydrogenation reaction of halonitrobenzenes (HNBs), but the selectivity to the valuable product haloanilines (HANs) is always poor due to the unavoidable dehalogenation process. In this study, we find that coating a thin Sn layer on Pt nanoparticles (NPs) could improve not only the hydrogenation activity but also the selectivity to HANs. These core–shell structured Pt@Sn NPs with different Sn shell thickness were synthesized by one-pot reduction, and their catalytic performance in the hydrogenation reaction of p-chloronitrobenzene to p-chloroaniline could be effectively regulated by the Pt/Sn ratio. The catalyst with a Pt/Sn ratio of 5/1 achieved the highest p-chloronitrobenzene conversion (96.5 %) and excellent selectivity to p-chloroaniline (97.9 %). The kinetic study and H2-TPD analysis indicated that the Sn species on Pt could facilitate the adsorption of p-chloronitrobenzene and the dissociation of H2. The designed Pt@Sn core–shell nanocatalysts are applicable to a wide range of hydrogenation reactions.

Fabrication of recyclable magnetic Fe3O4–SiO2–Cu2O/Cu core–shell nano-catalyst for high-efficient reduction of aromatic nitro compound

Fabrication of recyclable magnetic Fe3O4–SiO2–Cu2O/Cu core–shell nano-catalyst for high-efficient reduction of aromatic nitro compound

Dynamic Monitoring of the Structural Evolution of Au@Pd under Electrochemistry

Core–shell nanocatalysts have shown superior catalytic activity than monometallic catalysts. However, these metastable materials are susceptible to structural changes during catalysis. Comprehending the evolution of surface sites and their stability under different reaction conditions is crucial for designing durable and highly active core–shell nanocatalysts. Herein, structural transformation of the atomic layer thickness of Pd shells on Au nanocubes in different electrolytes at various electrochemical windows was investigated by a combination of cyclic voltammetry (CV), surface-enhanced Raman spectroscopy (SERS) of adsorbed probe molecules, and elemental analysis. Pd sites are stable under basic and neutral conditions but experience severe structure evolution under acidic conditions. Pd atoms that are directly coordinated by Au atoms, upon oxidation at evaluated potential, transform into Pd ions via the reaction with H+ which would also be adsorbed on the Au sites. These Pd ions are easily coreduced with the formed Au ions into surface alloys in the backward CV scan. In contrast, Pd atoms in the thick Pd overlayer (>1 monolayer) are likely to dissolute into the electrolyte solution and leach. SERS revealed that the change of Pd sites primarily occurred at contiguous Pd sites and isolated Pd sites were relatively stable. This evolution mechanism provides new insight into the rational design of efficient and stable catalysts and is expected to promote further application of core–shell nanocatalysts.

Synthesis of NaKCO3@(Mn-Na2 WO4/SiO2) core-shell catalyst for oxidative coupling of methane

Oxidative Coupling of Methane (OCM) is a process to produce ethylene as one of the most widely used petrochemicals from methane natural gas. The core–shell nano-catalyst of NaKCO3@(Mn-Na2WO4/SiO2) was prepared with different ratios of Na/K, and its activity in the OCM process was investigated and its performance was compared with the conventional Mn-Na2WO4/SiO2 nano-catalyst. The effect of temperature and methane-to-oxygen ratio on nano-catalyst performance was investigated. The performance criteria included methane conversion, ethylene selectivity, and C2+ yield. The formation of the core–shell structure has been deliberated using XRD and FE-SEM characterization tests. The results of characterization and reactor experiments indicated that the best performance was related to the nano-catalyst prepared with a ratio ofNa/K = 2/2.4, operating conditions: 850 °C, atmospheric pressure, and CH4/O2 ratio = 2 in the reaction feed. The formation of the core–shell structure does not reduce the nano-catalyst activity, but rather increases the selectivity of the main product, ethylene, by improving the nano-catalyst performance even at 850 °C. Stability tests were performed to examine the catalytic activity under high temperatures.

Facile and green fabrication of copper‐based magnetically recoverable yolk–shell nanocatalysts with high catalytic performance for nitroaromatic reduction

A simple method was reported to achieve a green yolk–shell Fe3O4@SiO2@CuO nanocatalysts (YS‐Fe3O4@SiO2@CuO). Glucose (G) and lactose (L), as a grafting agent, were applied for decorating CuO on the magnetic nanoparticles surface and then using calcination method, yolk–shell structure was obtained. Characterization of nanocatalysts was carried out using inductively coupled plasma–optical emission spectrometry (ICP‐OES), field emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), energy‐dispersive X‐ray (EDX)‐Mapping, thermogravimetric analysis (TGA), X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FT‐IR), X‐ray photoelectron spectroscopy (XPS), Brunauer, Emmett, and Teller (BET), and vibrating sample magnetometer (VSM) analyses and the results confirmed the successful synthesis of these catalysis. The activity of the nanocatalysts were studied to reduce nitroaromatic compounds monitoring by UV–Vis spectra. In the model reaction, 4‐nitrophenol was reduced using YS‐Fe3O4@SiO2@CuO(G) and YS‐Fe3O4@SiO2@CuO(L), with the activity factors (k′) of 3218 and 2023 s−1 g−1, and rate constants (Kapp) of 0.56 and 1.19 min−1, respectively. The advantages of prepared nanocatalysts were good stability and high conversion. The magnetic property of nanocatalysts makes them easy to recover in multiple cycles.

A recyclable photocatalyst Cu2O/Fe3O4@C/Cu nanocomposite for efficient photocatalytic reduction of 4-nitrophenol

Photocatalytic process using core–shell nano-catalyst is an efficient, eco-friendly, and cost-effective process for removal or minimize hazard of pollutants in waste water. Herein, a recyclable and robust Cu2O/Fe3O4@C/Cu core–shell nanocomposite with photocatalyst activities is designed based on the synergistic photocatalytic activities of Cu2O and Cu and the magnetic property and stability of Fe3O4@C. The Cu2O/Fe3O4@C/Cu is shown to act as nano-catalyst to almost completely convert 4-Nitrophenol (4-NP) to 4-aminophenol (4-AP) within 3 min by sufficient electrons in the electron-rich region formed under ultraviolet light irradiation. The Cu2O/Fe3O4@C/Cu nanocomposite shows a good stability, reusability and magnetic separation ability after five recycles. In addition, a photocatalytic mechanism of 4-NP reduction over this nanocomposite is proposed, and the roles of each nanocomponent of this nanostructure played in the synergistic enhancing photocatalytic performance via cascade reaction is demonstrated. This work suggests that Cu2O/Fe3O4@C/Cu nanocomposite with high activity, good stability and magnetically recyclability could be applied for the elimination of pollutants in wastewater.

Pd–Ag Bimetallic Catalysts with Core–Shell Engineering for Efficient Hydrogen Production from Formic Acid Decomposition

Fine control of the ligand and strain effects of secondary elements on the catalytic function of primary elements is critical for developing high-performance bimetallic catalysts. In this paper, we describe a method for making Pd–Ag bimetallic core–shell nanocatalysts with synergistic ligand and Ag strain effects. (PdAg alloy core)@(ultrathin Pd shell) nanocrystals with regulated core compositions and shell thicknesses, as well as a well-defined octahedral shape, could be achieved through precision core–shell engineering. The produced octahedral PdAg@Pd core–shell nanocrystals showed excellent catalytic activity in the creation of hydrogen from the breakdown of formic acid. The highest catalytic activity was attained using PdAg@Pd nanocrystals made up of PdAg alloy cores with an average Pd/Ag atomic ratio of 3.5:1 and a 1.1 atomic layer of Pd shells, which set a new record for catalytic activity.

Well-Arranged Hollow Au@Zn/Ni-MOF-2-NH2 Core–Shell Nanocatalyst with Enhanced Catalytic Activity for Biomass-Derived d-Xylose Oxidation

Well-Arranged Hollow Au@Zn/Ni-MOF-2-NH₂ Core–Shell Nanocatalyst with Enhanced Catalytic Activity for Biomass-Derived <scp>d</scp>-Xylose Oxidation

Effect of PdO-PdO2 core–shell nanocatalysts on hydrogen sensing performances of flame-made spinel Zn2SnO4 nanoparticles

In this research, flame-spray-made Pd-loaded Zn2SnO4 nanoparticles with 0.1–2 wt% Pd contents were synthesized and thoroughly investigated for hydrogen (H2) sensing. The flame-made nanoparticles were formed into sensing films via spin coating and tested towards H2 over the concentration ranging from 300 − 10000 ppm at varying working temperatures of 200–350 °C in dry air. X-ray analysis, nitrogen adsorption, and electron microscopic results revealed that Pd-loaded Zn2SnO4 nanostructures consisted mainly of 5–15 nm round and polygonal Zn2SnO4 nanoparticles uniformly decorated with 1–2 nm PdO-PdO2 core–shell nanoparticles. According to gas-sensing test data, the 1 wt% Pd-loaded Zn2SnO4 sensing film exhibited the greatest sensor response of ∼ 5612 to 10000 ppm H2 at 300 °C, which was more than three orders of magnitude higher than that of unloaded one. In addition, Pd-loaded Zn2SnO4 nanoparticles display moderately low humidity sensitivity and high H2 selectivity against C8H10, C7H8, C6H6, CH4, HCHO, CH3OH, C2H5OH, C3H6O, CH2O2, C2H4O2, C3H6O2, C4H8O2, C5H10O2 and C3H6O3. Therefore, the 1 wt% Pd-loaded Zn2SnO4 sensor is highly promising for selective and sensitive H2 detections in practical applications.

Methanol-assisted energy-efficient water splitting over rambutan-like Au@PdRu core–shell nanocatalysts

We report a simple strategy for the synthesis of trimetallic Au@PdRu rambutan-like nanocatalysts for efficient hydrogen production with the assistance of methanol oxidation.

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.

Cu0.33@Co0.22Ni0.45 core–shell nanoparticles as hydrogen generation catalysts via hydrolysis of ammonia borane

A Cu0.33@Co0.22Ni0.45 core–shell nanocatalyst was produced for hydrolysis of ammonia borane and hydrogen generation. The catalyst has high hydrogen release rate, low activation energies, high cycle performance and excellent structural stability.

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.

A magnetic-void-porous MnFe2O4/carbon microspheres nano-catalyst for catalytic ozonation: Preparation, performance and mechanism

Wastewater treatment is essential to guarantee human health and ecological security. Catalytic ozonation with nanocatalysts is a widely studied and efficient treatment technology. However, this method has always been limited by nanocatalysts disadvantages such as easily loss, difficult to separate and reuse, and catalytic ability decay caused by aggregation, which could cause severe resources waste and potential risk to human health and ecosystem. To remedy these challenges, a magnetic-void-porous MnFe2O4/carbon microsphere shell nanocatalyst (CMS-MnFe2O4) was successfully synthesized using renewable natural microalgae. The separation test showed CMS-MnFe2O4 was rapidly separated within 2 min under an external magnetic field. In catalytic ozonation of oxalic acid (OA), CMS-MnFe2O4 showed efficient and stable catalytic efficiency, reaching a maximum total organic carbon removal efficiency of 96.59 % and maintained a 93.88 % efficiency after 4 cycles. The stable catalytic efficiency was due to the supporting effects of the carbon microsphere shell, which significantly enhanced CMS-MnFe2O4 chemical stability and reduced the metal ions leaching to 10–20 % of MnFe2O4 through electron transfer. To explore the catalytic mechanism, radical experiments were conducted and a new degradation pathway of OA involving superoxide anions rather than hydroxyl radicals was proposed. Consequently, this study suggests that an efficient, recyclable, stable, and durable catalyst for catalytic ozonation could be prepared.

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.

Synthesis of magnetic core@dual shell Fe3O4@SiO2@WO3 nanocatalysts for olefin double bond oxidative cleavage

AbstractHerein, we report a new and efficient method for preparing Fe3O4@SiO2@WO3 core@dual shell nanocatalysts featuring enhanced catalytic activity for the oxidative cleavage of the oleic acid double bond and fast magnetic separation. Various characterization techniques including EDS, XPS, SEM, and advanced elemental HRTEM mapping were used to characterize this type of magnetic core@dual shell nanocatalysts. The obtained core@shell structure is composed of a central magnetite core with a strong response to external fields, an interlayer of SiO2, and an outer layer of WO3 nanocrystals. This core@shell nanocatalyst exhibited higher catalytic activity than reported tungsten based heterogenous catalysts for the oxidative cleavage of the oleic acid double bond. The presence of the SiO2 interlayer prevents any deterioration of the catalytic efficiency of the WO3 nanocrystal shell as well as the chemical and thermal stability of the Fe3O4 core. This nanocatalyst can be easily recycled by applying an external magnetic field while maintaining its catalytic activity during at least three cycles of use.