Pd Nanoparticles Research Articles

Redox dynamics and surface structures of an active palladium catalyst during methane oxidation

Catalysts based on palladium are among the most effective in the complete oxidation of methane. Despite extensive studies and notable advances, the nature of their catalytically active species and conceivable structural dynamics remains only partially understood. Here, we combine operando transmission electron microscopy (TEM) with near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and density functional theory (DFT) calculations to investigate the active state and catalytic function of Pd nanoparticles (NPs) under methane oxidation conditions. We show that the particle size, phase composition and dynamics respond appreciably to changes in the gas-phase chemical potential. In combination with mass spectrometry (MS) conducted simultaneously with in situ observations, we uncover that the catalytically active state exhibits phase coexistence and oscillatory phase transitions between Pd and PdO. Aided by DFT calculations, we provide a rationale for the observed redox dynamics and demonstrate that the emergence of catalytic activity is related to the dynamic interplay between coexisting phases, with the resulting strained PdO having more favorable energetics for methane oxidation.

Soft-templating synthesis of mesoporous MnSiOx composites as catalytic supports for Pd nanoparticles towards solvent-free oxidation of benzyl alcohol under atmospheric pressure O2

Solvent-free and liquid-phase selective oxidation of aromatic alcohols using O2 as an oxidant is a green strategy for the synthesis of aromatic aldehydes and other carbonyl compounds. Wherein, the design and preparation of heterogeneous catalysts with high activity and selectivity is a hot topic in this process. Herein, a series of manganese oxide-silica (MnSiOx) composites were synthesized using cetyltrimethylammonium bromide as a soft template. During the preparation process, the amounts of tetraethyl orthosilicate and ammonia and the calcination temperature significantly affected the textural properties and Mn cation distributions of MnSiOx. The MnSiOx composites were then employed as catalysts for Pd nanoparticles. In the solvent-free and atmospheric conditions, Pd/MnSiOx materials showed high catalytic conversions of benzyl alcohol (BZA), and the catalytic activity thereof is related to the fractions of Pd0 and Mn3+. As the reaction time and temperature are 4 h and 90 °C, the conversion of BZA (feeding dosage: 4 mL) and the selectivity of benzaldehyde are 64.8 % and 94.9 %, respectively. The catalyst can be reused at least five times without any significant loss of activity. Furthermore, the correlation between physiochemical properties and catalytic activity of Pd/MnSiOx was analyzed.

Metal hydroxide hybridized Pd catalysts via in-situ etching for high current density and pH-universal hydrogen evolution reaction

The development of highly efficient and innovative electrocatalysts is crucial for the commercialization of the hydrogen evolution reaction (HER) at high current densities. An electrocatalyst consisting of Pd nanoparticles electrodeposited on nickel foam (NF) treated with ferric chloride etching, yielding a Pd content of 0.53 wt%, was synthesized. This PdFe/NF-24 h catalyst demonstrated outstanding HER performance across a wide pH range, requiring overpotentials of only 302 mV, 96.4 mV and 637.9 mV to achieve a current density of 1000 mA/cm2 in 1 M KOH, 0.5 M H2SO4 and 1 M Phosphate Buffer Saline (PBS) electrolytes, respectively. The ferric chloride etching increased the active surface area, while iron doping optimized the hydrogen adsorption free energy on Pd. Furthermore, the presence of metal hydroxides facilitated the dissociation of water into adsorbed hydrogen, which then bound to active sites on the Pd surface to produce hydrogen, thereby enhancing the efficiency of hydrogen production. The catalyst operated at 1000 mA/cm2 in 1 M KOH solution for 222 h without degradation; it maintained stability for 124 h in 30 % KOH solution; in 0.5 M H2SO4 solution, it retained 99.6 % performance for 77 h and it remained stable for 230 h in 1 M PBS solution.

Thermal Stability of High-Entropy Alloy Nanoparticles Evaluated by In Situ TEM Observations.

High-entropy alloy (HEA) nanoparticles (NPs) have attracted attention in several fields because of their fascinating properties. The high mechanical strength, good thermal stability, and superior corrosion resistance of HEAs, which are derived from their high configurational entropy, are attractive features. Herein, we investigated the thermal stability of FeCoNiCuPd HEA NPs on reduced graphene oxide via in situ transmission electron microscopy observations at elevated temperatures. The HEA NPs maintained their structure, size, and composition at 700 °C, and their size gradually decreased accompanied by the preferential sublimation of Cu. On the contrary, the deterioration of the monometallic Pd NPs begins at temperatures greater than 700 °C according to Ostwald ripening, which involves the migration of adatoms or mobile molecular species. Theoretical calculations revealed that the detachment of adatoms from clusters (i.e., the first step of Ostwald ripening) was suppressed in the case of HEA NPs because of the high-configuration-entropy effect.

Enhanced photocatalytic hydrogen evolution performance of Pd/g-C3N4 with carbon vacancies

Exploration of highly active, stable and environmentally friendly photocatalytic materials is key to address the problem for hydrogen production by photocatalytic water splitting. Among all the photocatalysts, graphitic carbon nitride (g-C3N4) has gained attention for its stable graphite-like electronic structure, appropriate band gap (∼2.7 eV), and high stability. However, the limited visible light absorption capacity and fast recombination of electron-hole pairs severely limit the photocatalytic performance of g-C3N4. In this study, Pd/g-C3N4 Schottky heterojunctions with carbon vacancies were prepared by an impregnation method. The surface plasmon resonance (SPR) effect of Pd0 nanoparticles and the incorporation of carbon vacancies synergistically reduce the band gap of g-C3N4, expanding its light response absorption capacity and increasing surface active sites, as a result of these modifications, the separation of electron-hole pairs is effectively improved, and photocatalytic water splitting for hydrogen production is greatly enhanced. Photocatalytic performance of Pd/g-C3N4 photocatalysts demonstrate outstanding hydrogen evolution efficiency under solar light irradiation. A convincing mechanism for the enhanced photocatalytic performance of the Pd/g-C3N4 Schottky heterojunctions was suggested. This investigation emphasizes a straightforward and efficient approach for fabricating of based g-C3N4 composite materials with exceptional photocatalytic efficiency.

Completely recyclable and reusable automatic phase-separable catalytic system for the reductive debromination of polybrominated diphenyl ethers

An automatic phase-separable catalytic system was developed for the reductive debromination of polybrominated diphenyl ethers (PBDEs) using thiol-modified Pd nanoparticles (thiol-Pd NPs) as the catalyst, H2 as the reducing agent, and n-butanol (oil phase) and water (water phase) as solvents. This system achieved efficient and complete debromination of various PBDEs with 1–10 bromine atoms and other bromo-organic pollutants at concentrations ranging from 15 to 1500 mg L−1. Typically, this system achieved a debromination efficiency of 100 % within 15 min for all the tested bromo-organic pollutants. Importantly, the debromination reaction was conducted in a microemulsion state under stirring; upon stopping the stirring, the microemulsion automatically separated into an upper oil phase, a down water phase, and a thiol-Pd NP self-assembled membrane phase at the oil/water interface. These three phases could be easily separated from each other, allowing for their reuse across multiple debromination cycles with good reusability. The thiol modifier enhanced the stability and reusability of Pd NPs and improved the adsorption of PBDEs, facilitating their reaction with atomic hydrogen (the dominant reactive species). This method successfully eliminated PBDEs in soils by integrating with a pre-extraction process.

Maillard Reaction Inspired Microexplosion toward Fast Synthesis of Two-Dimensional Mesoporous Tin Oxides for Efficient Chemiresistive Gas Sensing.

Two-dimensional (2D) mesoporous transition metal oxides are highly desired in various applications, but their fast and low-cost synthesis remains a great challenge. Herein, a Maillard reaction inspired microexplosion approach is applied to rapidly synthesize ultrathin 2D mesoporous tin oxide (mSnO2). During the microexplosion between granular ammonia nitrate with melanoidin at high temperature, the organic species can be carbonized and expanded rapidly due to the instantaneous release of gases, thus producing ultrathin carbonaceous templates with rich functional groups to effectively anchor SnO2 nanoparticles on the surface. The subsequent removal of carbonaceous templates via calcination in air results in the formation of 2D mSnO2 due to the confinement effect of the templates. Pd nanoparticles are controllably deposited on the surface of 2D mSnO2 via in situ reduction, forming ultrathin 2D Pd/mSnO2 nanocomposites with thicknesses of 6-8 nm. Owing to the unique 2D mesoporous structure with rich oxygen defects and highly exposed metal-metal oxide interfaces, 2D Pd/mSnO2 exhibits excellent sensing performance toward acetone with high sensitivity, a short response time, and good selectivity under low working temperature (100 °C). This fast and convenient microexplosion synthesis strategy opens up the possibility of constructing 2D porous functional materials for various applications including high-performance gas sensors.

Palladium doped PDA-coated hercynite as a highly efficient catalyst for mild hydrogenation of nitroareness

Hercynite magnetic nanoparticles were produced through the co-precipitation of ferrous and aluminum cations. The surface of hercynite was respectively coated with silica, 2,4,6-trichloro-1,3,5-triazine, and 1H-pyrazole-3,5-dicarboxylic acid to provide a suitable substrate for Pd(II) loading, furnishing Pd@Her-TCT-PDA. Subsequently, the introduced Pd(II) was reduced to Pd(0) using NaBH4. FT-IR, EDS, XRD, TGA, TEM and SEM images were the characteristic methods to prove the success of catalyst synthesis. The SEM image illustrated the particles with a nanosize of 25–50 nm and TEM image confirmed the presence of Pd nanoparticles with sizes lower than 2 nm. EDS elemental analysis of the catalyst proved the existence of Pd, Fe, and Al atoms along with the C, O, N, and Si atoms belong to the heterocyclic moieties. VSM analysis clarified a considerable drop in the magnetic properties of the hercynite core of the final catalyst due to its modified surface. TGA curve demonstrated that Pd@Her-TCT-PDA contains 20% organic content, attributed to the anchored heterocyclic ligands. Finally, Pd@Her-TCT-PDA was employed along with NaBH4 as a catalytic system to reduce completely the nitro group of aromatic compounds to their corresponding amines. The recyclability tests showed low drop in the catalytic activity of Pd@Her-TCT-PDA after third run with negligible leaching of Pd NPs.

Electrostatic Self-Assembly Synthesis of Pd/In2O3 Nanocatalysts with Improved Performance Toward CO2 Hydrogenation to Methanol.

CO2 hydrogenation to methanol has emerged as a promising strategy for achieving carbon neutrality and mitigating global warming, in which the supported Pd/In2O3 catalysts are attracting great attention due to their high selectivity. Nonetheless, conventional impregnation methods induce strong metal-support interaction (SMSI) between Pd and In2O3, which leads to the excessive reduction of In2O3 and the formation of undesirable PdIn alloy in hydrogen-rich atmospheres. Herein, we innovatively synthesized Pd/In2O3 nanocatalysts by the electrostatic self-assembly process between surface-modified composite precursors with opposite charges. And the organic ligands concurrently serve as Pd nanoparticle protective agents. The resultant Pd/In2O3 nanocatalyst demonstrates the homogeneous distribution of Pd nanoparticles with controllable sizes on In2O3 supports and the limited formation of PdIn alloy. As a result, it exhibits superior selectivity and stability compared to the counterparts synthesized by the conventional impregnation procedure. Typically, it attains a maximum methanol space-time yield of 0.54 gMeOH h-1gcat -1 (300 °C, 3.5 MPa, 21,000 mL gcat -1 h-1). Notably, the correlation characterization results reveal the significant effect of small-size, highly dispersed Pd nanoparticles in mitigating MSI. These results provide an alternative strategy for synthesizing highly efficient Pd/In2O3 catalysts and offer a new insight into the strong metal-support interaction.

Pd‐Pt Bimetallic Catalysts for Enhanced Low‐Temperature Hydrodeoxygenation of Vanillin

AbstractTo make pyrolytic bio‐oil useful as a transportation fuel, the oxygen content must be reduced, and this can be carried out by using catalytic hydrodeoxygenation (HDO) reaction. The greatest challenge is associated with the removal of strongly bound oxygenated groups without saturating the aromatic ring while preserving the number of carbons. However, the development of a stable catalyst that can selectively remove such oxygenated groups with low hydrogen consumption is still challenging. In this context, a systematic study on HDO of vanillin on bimetallic Pd−Pt catalysts was carried out. It aims to study the effect of bimetallic synergy in terms of activity and selectivity to creosol. Metallic nanoparticles of Pd and Pt were synthesized by sol immobilization technique and deposited on TiO2. The conversion of vanillin was correlated to the Pd−Pt atomic ratio, while the production of the creosol was correlated to the Pd(0)/(Pd+Pt) ratio at the surface. Full conversion of vanillin was obtained at low reaction temperature (20 °C) achieving nearly 100 % selectivity to creosol. These results represent a step forward in advancing the development of more efficient and sustainable processes for bio‐oil upgrading.

Hollow UiO-66-NH2 Encapsulated Pd Catalysts for Highly Selective Hydrogenation of Furfural to Furfuryl Alcohol.

The selective hydrogenation of furfural (FFA) to furfuryl alcohol (FA) is regarded as attractive transformation to achieve the sustainable synthesis of value-added chemicals from biomass resources. However, the conventional supported catalysts are significantly restricted by their narrow pore size, ununiform dispersion and easy leaching or aggregation of catalytic sites. Herein, we designed hollow UiO-66-NH2 as the support to encapsulate Pd nanoparticles (Pd@H-UiO-66-NH2) to achieve the highly active and selective conversion of FFA to FA. Benefiting from the void-confinement effect and substrate enrichment of hollow structure, as well as the surface wrinkles, the as-prepared catalyst Pd@H-UiO-66-NH2 exhibited 96.8 % conversion of FFA with satisfactory selectivity reaching up to 92.4 % at 80 °C, 0.5 MPa H2 in isopropanol solvent within 6 h. More importantly, as-prepared Pd@H-UiO-66-NH2 catalyst exhibited excellent long-term stability, as well as good universality toward a series of hydrogenation of unsaturated hydrocarbons.

Palladium effect on electrochemical hydrogen storage properties of nanoporous silicon

Coating porous silicon with metal catalysts such as palladium is considered a reliable method to improve the hydrogen storage performance of electrodes. Here, in order to evaluate the most effective use of Pd nanoparticle or Pd thin film, Pd nanoparticles with a size of 36 nm obtained by electroless method, and a Pd thin film with a thickness of 30 nm deposited by thermal evaporation were coated onto nanoporous silicon sample” and studied. The Pd deposits were confirmed by Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The obtained electrode materials: PS and Pd/PS were characterized by different electrochemical characterization techniques: cyclic voltammetry (CV) and galvanostatic charge/discharge. The results showed that Pd NPs/PS achieved the highest hydrogen storage capacity with a value of 425.9 mA h g-1. These results confirm that using Pd nanoparticles as catalyst metal is more suitable to improving the hydrogen storage capacity of electrode materials.

Highly dispersed Pt nanoparticles onto dendritic silica as colorimetric probe for CO sensing in mainstream cigarette smokes

Carbon monoxide (CO) is a typical substance harmful to human body produced during cigarette smoking. Its content in cigarette smoke is one of the important indicators for evaluating its toxicity and the filtration effect of cigarette filter tips, which provides important guidance for its rational design. In this work, Pt nanoparticles with superior peroxidase catalytic ability were synthesized and loaded onto fibrous SiO2 nanoparticles as nanozymes to detect CO in cigarette smoke by taking advantage of the reduced catalytic performance of CO adsorption on the active sites of the nanozymes. The fibrous SiO2 not only provide abundant sites for the deposition and dispersion of Pt NPs, but also prevent their aggregation and thus maintain their high catalytic activity. Density functional theory calculations reveal that Pt nanoparticles exhibits superior peroxidase ability over Au and Pd nanoparticles, which can be significantly inhibited by CO. Accordingly, a nanozyme-inhibition based colorimetric method was developed for the detection of CO in cigarette smoke with the limit of detection of 0.15 mg/L. The applicability of this method was validated by analyzing the CO contents in 8 kinds of cigarette smoke with different types of filter tips. The concentrations of CO are in the range of 5.40–6.73 mg/branch, which are in good agreement with those of GC results, indicating the accuracy and reliability of our method. This assay is fast, convenient and sensitive for quantitatively assessing the CO content in cigarette smoke, and it lays the foundation for prompting the widespread use of nanozyme-inhibition in chemical sensing.

The role of Au and Pd in photocatalytic activation of molecular oxygen: A mechanistic study

Activation of molecular oxygen plays an important role in photocatalytic selective oxidation reactions and complete degradation of organic pollutants. Noble metal cocatalysts are often employed to modulate the activation of oxygen to reach an optimum photocatalytic performance. However, the role of the metal nanoparticles (NPs) still remains unclear and deserves investigation for the design of efficient photocatalysts. Here, Au and Pd NPs are deposited on the TiO2 photocatalyst to study the promotional mechanism of O2 dissociation with the presence of glycerol under irradiation by near-ambient-pressure photoelectron spectroscopy and in-situ spectrometry approaches. While both Au and Pd NPs can dissociate O2 into activated oxygen species, a relatively strong bonds of dissociated oxygen atom is observed on Au NPs than on the Pd NPs. This results in a moderate reduction rate of O2 and eventually favors a mild oxidation reaction process for Au, and a rapid reduction rate of O2 and eventually a deep oxidation reaction process for Pd, respectively.

Preparation of palladium-based catalyst by plasma-assisted atomic layer deposition and its applications in CO2 hydrogenation reduction

Supported Pd catalyst is an important noble metal material in recent years due to its high catalytic performance in CO2 hydrogenation. A fluidized-bed plasma assisted atomic layer deposition (FP-ALD) process is reported to fabricate Pd nanoparticle catalyst over γ-Al2O3 or Fe2O3/γ-Al2O3 support, using palladium hexafluoroacetylacetonate as the Pd precursor and H2 plasma as counter-reactant. Scanning transmission electron microscopy exhibits that high-density Pd nanoparticles are uniformly dispersed over Fe2O3/γ-Al2O3 support with an average diameter of 4.4 nm. The deposited Pd-Fe2O3/γ-Al2O3 shows excellent catalytic performance for CO2 hydrogenation in a dielectric barrier discharge reactor. Under a typical condition of H2 to CO2 ratio of 4 in the feed gas, the discharge power of 19.6 W, and gas hourly space velocity of 10000 h−1, the conversion of CO2 is as high as 16.3% with CH3OH and CH4 selectivities of 26.5% and 3.9%, respectively.

Pd Nanoparticles Supported on N-Doped Porous Carbon Cathodes for the Catalytic Semideuteration of Alkynes

Pd Nanoparticles Supported on N-Doped Porous Carbon Cathodes for the Catalytic Semideuteration of Alkynes

Utilizing in situ construction of N-doped hierarchical porous carbon to achieve electronic control of highly dispersed Pd nanoparticles for efficient catalytic hydrogenation of CO2 to formic acid

Hydrogenation of CO2 to produce formic acid/formate is a significant pathway for future energy storage and utilization. The development of heterogeneous catalysts with high activity and stability for this process is still a challenge. In this work, the in-situ N-doped hierarchical porous carbon derived from distiller's grains was used as a support for Pd-based catalysts (Pd/NC) to convert CO2 into valuable chemicals while making high-value use of waste biomass. The optimum catalyst, Pd/NC-800, shown exceptional catalytic performance, achieving a turnover frequency (TOF) of 2060 h−1 at 100℃, 4 MPa in the catalytic CO2 hydrogenation to formate reaction. Comprehensive experimental results and density functional theory calculations indicate that the electronic effect between the pyridine N in the support and the Pd nanoparticles (NPs) can make the Pd surface reach the state of electron enrichment and enhance the metal-support interaction. Moreover, the synthesized material has hierarchical pore structure, which provides abundant Pd anchor location sites and improves mass transfer efficiency. The results not only provide a feasible strategy for the preparation of efficient CO2 hydrogenation catalysts, but also break a new and effective avenue for the resource utilization of distiller's grains.

Efficient CO Oxidative Coupling to Dimethyl Oxalate over the Pd/Al2O3 Nanocatalyst with the Assistance of Co Doping

AbstractCO oxidative coupling to dimethyl oxalate (DMO) is an important approach for the product of ethylene glycol and CO elimination. In this work, the Co doped Pd/Al2O3 nanocatalyst was highly effective for CO oxidative coupling and enhanced remarkably CO conversion and the formation of DMO. The maximum DMO STY reached 1082 g L−1 h−1 over the Pd/Al2O3@1/20Co catalyst at 130 °C for 2 h under the space velocity of 3000 h−1, which is two times higher than that over the Pd/Al2O3 catalyst. The Co modification and its influence on the structure of the Pd/Al2O3 catalyst were also studied systematically by XRD, TEM, CO‐TPD, N2 physical adsorption and XPS techniques. An appropriate Co doing was confirmed to promote distinctly the generation of smaller Pd particles and the adjustment of the adsorption or activation of CO over the catalyst. A positive interaction between Pd nanoparticles and the modulated support with Co doping was demonstrated and favored the enhanced activity of the catalyst for the reaction.

TiO2 nanotubes modification by photodeposition with noble metals: Characterization, optimization, photocatalytic activity, and by-products analysis

Self-organized TiO2 nanotubes (TNTs) with 4 µm length were obtained by anodization method and calcined to obtain anatase crystallite phase. The photocatalysts were further decorated with Au, Ag, Pt or Pd nanoparticles (NPs), varying the metal loads (0.50, 0.75, 1, 2 and 5 mol%) by photodeposition. The material characterization confirmed the presence of nanoparticles in the TNTs surface, signs of the localized surface plasmon resonance (LSPR) effect for some samples and a bandgap energy of 3.1–3.2 eV. Photoluminescence measurements also confirmed that most of the samples with metallic nanoparticles had the recombination of photogenerated carriers lowered due to the trapping effect of the deposited metal NPs. The photoactivity was evaluated by phenol degradation using UV-Vis or visible radiation. Under UV-Vis, the best samples (2 and 5 mol% of Au-TNTs and 0.75, 1, and 2 mol% of Pd-TNTs) led to 97% phenol removal in 60 min while pristine TNTs reached 92% removal. Under visible radiation, the pristine and the Au-TNTs led to about 3% removal, with the best sample being 2 mol% Pd-TNTs with 14% removal in 60 min. Similar results were obtained for 1 and 5 mol% Pd-TNTs (12% and 13% of phenol removal, respectively). The by-products analysis suggest different degradation mechanisms and it is observed different kinetic rates for different metal types, metal loads or types of radiation.

Metal-enzyme nanogel biochemical composite: An efficient platform for one-pot dynamic kinetic resolution of amines

One-pot dynamic kinetic resolution (DKR) has garnered considerable attention for its potential to generate enantiomerically pure compounds in high yields and simplifying operation. However, the challenge lies in achieving compatibility between enzymes and metals due to their distinct operating conditions. In this study, we present a novel cascade catalytic platform for the DKR of amines to address this issue. Pd nanoparticles were immobilized on lysine-decorated lipase nanogels, forming isolated metal-enzyme catalysts. The microwave-assisted one-pot DKR of amines was carried out under non-pressurized conditions at 50 °C for 5 h. The metal-enzyme nanogel biochemical composite exhibited excellent performances, with a high conversion rate of 98% and enantiomeric excess values exceeding 99%. This innovative approach demonstrates the potential of constructing a multifunctional metalloenzyme catalytic platform with a distinctive three-dimensional structure, which offers promising prospects for DKR applications.