Size Of Pd Nanoparticles Research Articles

A novel Ti³⁺-mediated approach for supporting palladium on anodic TiO2 nanotubes: Toward efficient and recyclable catalysis in the heck reaction

A simple electrochemical reduction technique was employed to generate Ti3+ with strong reducing property on the anodic TiO2 nanotubes (ATNTs). Utilizing Ti3+ as the reducing agent, Pd2+ was successfully reduced in situ to Pd0 on the anodic TiO2 nanotubes (Pd@ATNTs). Various characterization methods were employed to confirm that the proportion of Ti3+ and the size of Pd nanoparticles could be controlled by adjusting the electrochemical reduction voltage. The obtained Pd@ATNTs-2.5 exhibited satisfactory catalytic efficiency (TOF: 1302 h−1) in the Heck reaction between various aryl halides and olefins. Furthermore, Pd@ATNTs-2.5 demonstrated high stability, with no significant loss of catalytic activity observed even after six cycles.

Insight into the degradation mechanism of mixed VOCs oxidation over Pd/UiO-66(Ce) catalysts: Combination of operando spectroscopy and theoretical calculation

Herein, Pd/UiO-66(Ce) catalysts were successfully synthesized by N2H4, H2, and NaBH4 reduction methods with UiO-66(Ce) as support. The best catalyst was selected via utilizing o-xylene as the probe molecule, and its degradation performance of mixed VOCs was further investigated. It was found that the reduction methods greatly influenced the size of Pd nanoparticles, the state of surface Pd, and the support structure in the catalysts, which in turn affected their catalytic performance. Among them, Pd/UiO-66(Ce)-Na exhibited the best o-xylene degradation activity (T90 = 192 °C) due to its smaller average Pd particle size (Pd Average = 2.93 nm) and higher surface Pd0 content (Pd0/Pdtotal = 0.79). The performance and interaction of Pd/UiO-66(Ce)-Na catalyst for degradation of mixed VOCs (o-xylene and toluene/benzene) were investigated by DFT adsorption energy calculation, in situ DRIFTS and GC–MS. Results suggested that the single adsorption energy of o-xylene was −1.20 eV, while in the system with toluene/benzene, the adsorption energy decreased to −0.78 and −0.6 eV, respectively. This showed the competitive adsorption effect between benzene and o-xylene was stronger than that between benzene and o-xylene. Finally, combined with in situ DRIFTS and GC–MS, the degradation path of mixed components was analyzed and studied systematically, and the mechanism of intermolecular interaction of benzene in the degradation process of mixed components was further revealed.

A novel tetra(4-pyridyl)porphyrin-palladium(0) functionalized polyacrylonitrile fiber as highly efficient and recyclable heterogeneous catalyst for the Heck reaction

A novel tetra(4-pyridyl)porphyrin-chelated palladium(0) nanoparticles functionalized polyacrylonitrile fiber (PANTPPF-Pd(0)) was prepared for the first time. Some necessary methods including Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), etc. were used to verify the micro structure and properties of PANTPPF-Pd(0). Furthermore, with the Heck reaction chosen as a model reaction to determine the catalytic activity of PANTPPF-Pd(0), the experiment results shows that PANTPPF-Pd(0) can efficiently catalyze the Heck reaction with high yields (47–99%) in extensive substrate scope (46 examples) under non-solvent condition. Noteworthily, the average size of Pd(0) nanoparticles observed by transmission electron microscopy (TEM) slightly increased from 2.32 nm to 2.59 nm after recycled 8 times achieving an 99% isolated yield of Heck reaction catalyzed by PANTPPF-Pd(0), which proves that the PANTPPF-Pd(0) can maintain satisfactory recyclability. Finally, based on the π-π stacking interactions and dipolar-dipolar interaction between tetra(4-pyridyl)porphyrin moieties in PANTPPF-Pd(0) and substrates, a novel heterogeneous “capture-catalyze” mechanisms was proposed.

Pd Nanoparticle Size-Dependent H* Coverage for Cu-Catalyzed Nitrate Electro-Reduction to Ammonia in Neutral Electrolyte.

Electrochemical conversion of nitrate (NO3 -) to ammonia (NH3) is an effective approach to reduce nitrate pollutants in the environment and also a promising low-temperature, low-pressure method for ammonia synthesis. However, adequate H* intermediates are highly expected for NO3 - hydrogenation, while suppressing competitive hydrogen evolution. Herein, the effect of H* coverage on the NO3RR for ammonia synthesis by Cu electrocatalysts is investigated. The H* coverage can be adjusted by changing Pd nanoparticle sizes. The optimized Pd@Cu with an average Pd size of 2.88nm shows the best activity for NO3RR, achieving a maximum Faradaic efficiency of 97% (at -0.8V vs RHE) and an NH3 yield of 21mg h-1 cm- 2, from an industrial wastewater level of 500ppm NO3 -. In situ electrochemical experiments indicate that Pd particles with 2.88nm can promote NO3 - hydrogenation to NH3 via well-modulated coverage of adsorbed H* species. Coupling the anodic glycerol oxidation reaction, ammonium and formate are successfully obtained as value-added products in a membrane electrode assembly electrolyzer. This work provides a feasible strategy for obtaining size-dependent H* intermediates for hydrogenation.

Pd nanoparticles on functionalized carbon nanotubes for enhanced formic acid hydrogen production under ambient conditions

Herein, carbon nanotubes (CNTs) are acidified and M (M = B or N) doped to support Pd nanoparticles (PdNPs) for upgrading to Pd/MCNT catalysts used in H2 production from formic acid (FA). The characterization analysis demonstrates the support composition affects the electronic properties and size of PdNPs, thus impacting the performance of Pd/MCNTs. Among the assessed materials, Pd/BCNTs exhibit the largest specific surface area (128.1273 m2g−1) and smallest PdNPs particle size (6.28 nm). These properties result in significant improvements in FA conversion (41.67 %), and turnover frequency value (3451 h−1) compared to conventional Pd/CNTs (17.36 % and 564 h−1, respectively). The study evaluates the service life and repeatability of Pd/BCNTs and analyzes the catalyst mechanism. This study filled the vacancy of acidification-modified and doped CNTs in Pd regulation, enhanced Pd's catalytic performance, and further supported FA as an H2 storage material.

Maximized nanojunctions in Pd/SnO2 nanoparticles for ultrasensitive and rapid H2 detection

H2 energy has gained massive attraction as a promising candidate for future energy sources. However, the explosive properties of H2 arouse significant safety concerns, emphasizing the need for the development of real-time H2 detection systems. This study presents the fabrication of an ultrasensitive and selective H2 gas sensor using Pd/SnO2 nanoparticles (NPs) synthesized through the utilization of Pluronic F-127. Pluronic F-127 improves the dispersion and regulates the particle size of Pd NPs. Pd/SnO2 NPs, which are comprised of numerous nanojunctions, exhibit H2 response of 27,190 and a response time of 3 s when exposed to 50 ppm of H2 at 100 °C. The practical applicability of Pd/SnO2 NPs was demonstrated by detecting H2 generated from water-splitting cells, exhibiting promising features for H2 energy industries. Overall, the synthetic method of this study proposes advanced strategies for development of sensing materials with maximized gas sensing performance.

Facile Abatement of Oxygenated Volatile Organic Compounds via Hydrogen Co-Combustion over Pd/Al2O3 Catalyst as Onsite Heating Source

Catalytic combustion of volatile organic compounds (VOCs) usually requires external energy input to hold the desired reaction temperature via electric heating. This work presents an example of internal onsite heating of the catalytic active sites via hydrogen catalytic combustion with air over a conventional Pd/Al2O3 catalyst. Hydrogen combustion was ignited by the catalyst at room temperature without electric heating, and thus the temperatures were readily varied with the concentrations of H2. Representative oxygenated VOCs such as methanol, formaldehyde and formic acid can be completely oxidized into CO2 and water by co-feeding with H2 below its low explosion limit of 4% using Pd/Al2O3 as shared catalyst. The catalytic performance apparently is not sensitive to the sizes of Pd nanoparticles in fresh and spent states, as revealed by XRD and STEM. This provides an option for using renewable green hydrogen to eliminate VOC pollutants in an energy-efficient way.

Unveiling the formic acid dehydrogenation dynamics steered by Strength-Controllable internal electric field from barium titanate

Formic acid is a desirable liquid hydrogen storage compound for solving transport and storage problems of hydrogen for onboard fuel cells. Optimizing adsorption/desorption energy of intermediates can directly modulate the performance of Pd catalysts in formic acid dehydrogenation (FAD). Herein, we introduce internal electric field with controllable strength to regulate the adsorption/desorption of intermediates on Pd. Non-ferroelectric cubic-phase barium titanate (CBT) is heat-treated at high temperature to obtain ferroelectric tetragonal-phase barium titanate (TBT(C)), which exhibits internal electric field. The strength of the internal electric field is successfully adjusted by heat treatment at different temperatures. The size of Pd nanoparticles is restricted between 2.2 and 2.7 nm, and the electronic effect of Pd is effectively eliminated by coating TBT(C) with mesoporous carbon shell (TBT(C)@SC). Experimental results prove that the internal electric field promotes the desorption of hydrogen on Pd. Pd/TBT(C)@SC-800 obtained by heat treatment at 800 °C, with the optimal internal electric field strength, exhibits high activity and hydrogen selectivity for FAD. This work provides a new strategy for designing FAD catalysts.

Improving the Performance of Pd for Formic Acid Dehydrogenation by Introducing Barium Titanate.

Formic acid, a safe and widely available organic compound, produces hydrogen under mild conditions, with the existence of Pd-based catalysts. Efficiently generating hydrogen via formic acid decomposition (FAD) is restricted by the cleavage of the C-H bond in adsorbed HCOO* and strong adsorption of hydrogen on the Pd surface. Herein, tetragonal-phase barium titanate (TBT) was in situ grown on reduced graphene oxide (rGO) to support Pd (Pd/TBT/rGO) for FAD. The internal electric field exists around TBT owing to its spontaneous polarization capacity. The physical characterizations illustrate that the introduction of barium titanate affects the catalytic performance of the catalyst by decreasing the particle size of Pd nanoparticles (NPs) and forming electron-rich Pd. The as-synthesized Pd/TBT/rGO exhibited excellent catalytic activity and hydrogen selectivity for FAD with a high initial turnover frequency up to 3019.72 h-1 at 333 K. The reason for this enhancement is not only the small-size Pd NPs but also the internal electric field from TBT, which promotes the desorption of adsorbed hydrogen on the Pd surface. Additionally, the electron-rich Pd is favorable to the cleavage of the C-H bond in HCOO*. This work will improve the understanding of the characterization of barium titanate and provide a new design strategy for the FAD catalyst.

Biocompatible Palladium Nanoparticles Prepared Using Vancomycin for Colorimetric Detection of Hydroquinone.

Hydroquinone poses a major threat to human health and is refractory to degradation, so it is important to establish a convenient detection method. In this paper, we present a novel colorimetric method for the detection of hydroquinone based on a peroxidase-like Pd nanozyme. The vancomycin-stabilized palladium nanoparticles (Van-Pdn NPs, n = 0.5, 1, 2) were prepared using vancomycin as a biological template. The successful synthesis of Van-Pdn NPs (n = 0.5, 1, 2) was demonstrated by UV-vis spectrophotometry, transmission electron microscopy, and X-ray diffraction. The sizes of Pd nanoparticles inside Van-Pd0.5 NPs, Van-Pd1 NPs, and Van-Pd2 NPs were 2.6 ± 0.5 nm, 2.9 ± 0.6 nm, and 4.3 ± 0.5 nm, respectively. Furthermore, Van-Pd2 NPs exhibited excellent biocompatibility based on the MTT assay. More importantly, Van-Pd2 NPs had good peroxidase-like activity. A reliable hydroquinone detection method was established based on the peroxidase-like activity of Van-Pd2 NPs, and the detection limit was as low as 0.323 μM. Therefore, vancomycin improved the peroxidase-like activity and biocompatibility of Van-Pd2 NPs. Van-Pd2 NPs have good application prospects in the colorimetric detection of hydroquinone.

Atomic hydrogen-mediated enhanced electrocatalytic hydrodehalogenation on Pd@MXene electrodes

In this study, a Pd@MXene catalyst was synthesized to enhance the electrocatalytic hydrodehalogenation (ECH) of emerging halogenated organic pollutants (HOPs) by improving the dispersibility, catalytic activity, and stability of palladium (Pd). The average size of Pd nanoparticles (NPs) was reduced to 3.62 ± 0.34 nm with a more intensive peak of Pd (111), which facilitated atomic hydrogen (H*) production. The Pd@MX/CC electrode demonstrated superior ECH activity for diclofenac (DCF) degradation, with a reaction rate constant (kobs) 2.48 times higher than that of Pd/CC (without MXene). The satisfactory ECH performance of Pd@MX/CC remained consistent within a wide range of initial DCF concentrations (5–100 mg/L), and no significant ECH attenuation was observed even after up to 10 batches. Furthermore, the high activity of Pd@MX/CC was also observed in the ECH of other halogenated organic pollutants (levofloxacin, tetrabromobisphenol A, and diatrizoate). Density functional theory (DFT) calculations revealed that electronic configuration modulation of the Pd@MXene catalyst optimized binging energies to H* , DCF, and dechlorinated products, thereby enhancing the ECH efficiency of DCF.

Wafer-Level Manufacturing of MEMS H2 Sensing Chips Based on Pd Nanoparticles Modified SnO2 Film Patterns.

In this manuscript, a simple method combining atomic layer deposition and magnetron sputtering is developed to fabricate high-performance Pd/SnO2 film patterns applied for micro-electro-mechanical systems (MEMS) H2 sensing chips. SnO2 film is first accurately deposited in the central areas of MEMS micro hotplate arrays by a mask-assistant method, leading the patterns with wafer-level high consistency in thickness. The grain size and density of Pd nanoparticles modified on the surface of the SnO2 film are further regulated to obtain an optimized sensing performance. The resulting MEMS H2 sensing chips show a wide detection range from 0.5 to 500ppm, high resolution, and good repeatability. Based on the experiments and density functional theory calculations, a sensing enhancement mechanism is also proposed: a certain amount of Pd nanoparticles modified on the SnO2 surface could bring stronger H2 adsorption followed by dissociation, diffusion, and reaction with surface adsorbed oxygen species. Obviously, the method provided here is quite simple and effective for the manufacturing of MEMS H2 sensing chips with high consistency and optimized performance, which may also find broad applications in other MEMS chip technologies.

Structure sensitivity reaction of chloroform hydrodechlorination to light olefins using Pd catalysts supported on carbon nanotubes and carbon nanofibers

The upgrading of wasted chloroform in hydrodechlorination for the production of olefins such as ethylene and propylene is studied by employing four catalysts (PdCl/CNT, PdCl/CNF, PdN/CNT, and PdN/CNF) prepared by different precursors (PdCl2 and Pd(NO3)2) supported on carbon nanotubes (CNT) or carbon nanofibers (CNF). TEM and EXAFS-XANES results confirm that Pd nanoparticle size increases in the order: PdCl/CNT < PdCl/CNF ∼ PdN/CNT < PdN/CNF, descending the electron density of Pd nanoparticles in the same order. It illustrates that PdCl-based catalysts show donation of electrons from support to Pd nanoparticles, which is not observed in PdN-based catalysts. Moreover, this effect is more evident in CNT.The smallest and well-dispersed Pd nanoparticles (NPs) on PdCl/CNT with high electron density favor an excellent and stable activity and a remarkable selectivity to olefins. In contrast, the other three catalysts show lower selectivity to olefins and lower activities which suffer strong deactivation due to the formation of Pd carbides on their larger Pd nanoparticles with lower electron density, compared to PdCl/CNT.

Size-modulated photo-thermal catalytic CO2 hydrogenation performances over Pd nanoparticles

Size of metal nanoparticles significantly influences their catalytic behaviors. However, it is still challenging to obtain monodispersed metal nanoparticles with successively tuned sizes to unveil their size-dependent catalytic performances, especially for photo-thermal catalytic reverse water–gas shift (RWGS) reaction. Herein, a library of Pd nanoparticles of 2.8, 3.4, 4.7, 5.3, 6.3 and 8.1 nm were synthesized and supported on TiO2 for photo-thermal catalytic RWGS reaction. The catalytic activity presented volcano-like dependence on sizes of Pd nanoparticles with 6.3 Pd/TiO2 exhibiting the highest catalytic efficiency. Based on the results of X-ray photoelectron spectroscopic analysis, photo-to-thermal conversion efficiency evaluation and density functional theory (DFT) calculations following the formate (*HCOO) pathway revealed by in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) measurements, the volcano-type tendency in catalytic activity could be attributed to the superposition of size-governed surface electronic properties over Pd nanoparticles.

High-Dispersive Pd Nanoparticles on Hierarchical N-Doped Carbon Nanocages to Boost Electrochemical Co2 Reduction to Formate at Low Potential.

Electrochemical CO2 reduction reaction (CO2 RR) to value-added chemicals/fuels is an effective strategy to achieve the carbon neutral. Palladium is the only metal to selectively produce formate via CO2 RR at near-zero potentials. To reduce cost and improve activity, the high-dispersive Pd nanoparticles on hierarchical N-doped carbon nanocages (Pd/hNCNCs) are constructed by regulating pH in microwave-assisted ethylene glycol reduction. The optimal catalyst exhibits high formate Faradaic efficiency of >95% within -0.05-0.30V and delivers an ultrahigh formate partial current density of 10.3mAcm-2 at the low potential of -0.25V. The high performance of Pd/hNCNCs is attributed to the small size of uniform Pd nanoparticles, the optimized intermediates adsorption/desorption on modified Pd by N-doped support, and the promoted mass/charge transfer kinetics arising from the hierarchical structure of hNCNCs. This study sheds light on the rational design of high-efficient electrocatalysts for advanced energy conversion.

Emerging co-synthesis of dimethyl oxalate and dimethyl carbonate using Pd/silicalite-1 catalyst with synergistic interactions of Pd and silanols

An emerging synthetic route for the co-synthesis of dimethyl oxalate (DMO) and dimethyl carbonate (DMC) via the indirect oxidative carbonylation of CH3OH is presented. The promising co-synthesis process combines the advantages of two separate routes of DMO and DMC syntheses. Herein, palladium containing silicalite-1 zeolite (Pd/S-1) catalyst was first found to be highly active and stable for the co-synthesis of DMO and DMC. The catalytic performance strongly depended on the catalyst activation, as the heat treatment could tune the silanols around the Pd species on the silicalite-1 zeolite. The Pd/S-1 catalyst with abundant silanols exhibited a higher turnover frequency (TOF) of 0.18 s−1 and a lower apparent activation energy of 51 kJ mol−1 in comparison to the catalyst with low silanol sites (0.06 s−1 and 101 kJ mol−1). The best performing catalyst had an average Pd nanoparticle size of 3.2 nm and Pd loading of 0.48 wt%. This catalyst showed a high CO conversion of 78% and DMO + DMC selectivity of 96%, maintaining high stability for at least 200 h. Furthermore, the synergistic interactions of silanols of silicalite-1 zeolite and Pd were confirmed by a series of in situ infrared experiments, and were found to be responsible for the enhanced activity. The silanols of S-1 zeolite played an essential role in forming the Pd active sites and had a very pronounced effect on the adsorption of CO reactant on the Pd species. Understanding the interactions between metal species and silanols of zeolite is critical for the development of high-performance zeolite catalysts.

Probing the roles of S atom and nanoparticle size over different sizes of S-modified Cu and Pd nanoparticles in regulating catalytic performance of acetylene Semi-hydrogenation

Probing the roles of S atom and nanoparticle size over different sizes of S-modified Cu and Pd nanoparticles in regulating catalytic performance of acetylene Semi-hydrogenation

Size-Controlled Palladium Nanoparticles Encapsulated in Silicalite-1 for Methane Catalytic Combustion

A series of Pd catalysts with different nanoparticle sizes encapsulated in Silicalite-1 (S-1) zeolite were synthesized using the one-step hydrothermal method to investigate the size dependence on methane catalytic oxidation. The obtained Pd nanoparticle (NP) sizes ranging from 1.8 to 3.2 nm were modulated by changing the addition of the ethylenediamine (EN) ligand during the synthesis process, and Pd/S-1-in-6EN (2.1 nm, the molar composition of 1 Pd:6 EN) displayed the remarkable catalytic performance. Meanwhile, long-term stability tests indicate the outstanding water resistance of Pd/S-1-in-6EN with a smaller particle size. According to the results of in situ CO-DRIFTS, a volcano-shaped curve between the fraction of the step site by size control of Pd nanoparticles and the catalytic performance was presented, and Pd/S-1-in-6EN possessed the optimum one. These allow the further study of the particle size effect on zeolite-confined noble metal catalysts for methane combustion.

Mechanistic insight into the photocatalytic N-alkylation of piperazine with alcohols over TiO2 supported Pd catalysts

N-alkylated piperazines can be synthesized by the thermal catalytic alkylation of piperazine with alkyl halides or alcohols in the presence of supported metal catalysts. However, these processes either discharge large amounts of waste or require harsh conditions. Here, we report the results of N-alkylation of piperazine with lower alcohols (methanol, ethanol, and propanol) without external hydrogen addition at room temperature in the presence of a TiO2-supported Pd catalyst (Pd/TiO2-P) prepared by photodeposition method. Compared with the catalysts prepared by the conventional chemical reduction or hydrogen reduction, the Pd/TiO2-P catalyst showed the highest conversion of piperazine and the best selectivity to N-alkypiperazines. The mechanistic studies indicated that this phenomenon occurs via tandem photocatalytic reactions involving alcohol dehydrgenation to aldehyde, aldehyde condensation with piperazine to enamine, and enamine hydrogenation to N-alkylated piperazines. Considering the experimental results of methanol isotope kinetics, the α-C–H cleavage of methanol to form hydroxymethyl radical (·CH2OH) was proven to be the rate-determining step in the N-alkylation reaction of piperazine with low carbon alcohols. The characterization and control experiments revealed that the size of Pd nanoparticles and the valence of Pd species were vital to the reaction. The Pd/TiO2-P catalyst with an average of 2.5 ± 0.5 nm Pd particles and approximately 68% Pd0 species on surfaces presented the highest activity for the photocatalytic tandem reactions of methanol dehydrogenation and enamine hydrogenation.

The effect of SnO2 on enhancing electrocatalytic property of palladium toward formic acid oxidation

Although palladium (Pd) based materials are considered the best catalyst for formic acid oxidation reaction (FAOR), they are still confronted with a lot of barriers, such as the growth/sintering of Pd nanoparticles (NPs) and the accumulation of adsorbed poisoning intermediates. Herein, tin dioxide (SnO2) decorated carbon black was utilized as the catalyst carrier to synthesize Pd/SnO2/C for FAOR. The introduction of SnO2 significantly reduced the particle size of Pd NPs and forming the Pd–O–Sn structure. Compared with Pd/C, Pd/SnO2/C owned higher concentration of Oads and less adsorption amount of poisoning intermediates. The oxygen atoms adsorbed on Pd surface were rapidly transferred to SnO2 due to the spillover effect. The FAOR reaction kinetic results showed that the introduction of SnO2 accelerated the diffusion rate of formic acid on the electrode surface. Pd/SnO2/C exhibited high specific activity (5.97 mA cm−2), excellent durability, and high anti-CO poisoning ability toward FAOR due to the introduction of SnO2.