Ultrafine Palladium Nanoparticles Research Articles

Coordination-induced amidated modified polyacrylonitrile loaded ultrafine palladium nanoparticles for thermocatalytic hydrogen evolution

A promising approach for powering hydrogen fuel cells (HFCs) involves the in-situ production of hydrogen from formic acid decomposition, with Pd-based catalysts recognized as effective for formic acid dehydrogenation. However, the immobilization of ultrafine palladium nanoparticles (Pd NPs) on catalytic supports presents a challenge and necessitates further investigation into their formation mechanism. We propose a coordination-induced strategy to understand the behavior of ultrafine Pd NPs formation based on multi-functional groups. To establish the structure–activity relationship for tunable Pd microenvironment and catalytic performance, we synthesized various polyacrylonitrile (PAN) carriers through hydrolysis and amidation modification. Molecular dynamics simulations confirmed that a stronger coordination-induced microenvironment facilitates the dispersion of Pd2+, suppressing aggregation and enhancing Pd loading. Our experimental results and density functional theory (DFT) calculations demonstrated that the catalytic activity of Pd@APAN(15_1%) with ultrafine Pd NPs (1.5 nm) exhibits over 10 times higher than that of Pd@PAN NPs with the turnover of frequency climbing from 112.6 h−1 to 1309.4 h−1 at 323 K. And Pd-imine and Pd-secondary amine moieties were verified to contribute to the creation of a favorable catalysis microenvironment. This study provides new insights into the design of modified supports with various groups to load well-dispersed and ultrafine Pd for highly efficient catalysts based on a coordination-induced strategy.

3D-Continuous Nanoporous Covalent Framework Membrane Nanoreactors with Quantitatively Loaded Ultrafine Pd Nanocatalysts.

The confinement effect of catalytic nanoreactors containing metal catalysts within nanometer-sized volumes has attracted significant attention for their potential to enhance reaction rate and selectivity. Nevertheless, unregulated catalyst loading, aggregation, leaching, and limited reusability remain obstacles to achieving an efficient nanoreactor. A robust and durable catalytic membrane nanoreactor prepared by incorporating palladium nanocatalysts within a 3D-continuous nanoporous covalent framework membrane is presented. The reduction of palladium precursor occurs on the pore surface within 3D nanochannels, producing ultrafine palladium nanoparticles (Pd NPs) with their number density adjustable by varying metal precursor concentrations. The precise catalyst loading enables controlling the catalytic activity of the reactor while preventing excess metal usage. The facile preparation of Pd NP-loaded free-standing membrane materials allows hydrodechlorination in both batch and continuous flow modes. In batch mode, the catalytic activity is proportional to the loaded Pd amount and membrane area, while the membrane retains its activity upon repeated use. In continuous mode, the conversion remains above 95% for over 100h, with the reactant solution passing through a single 50µm-thick Pd-loaded membrane. The efficient nanoporous film-type catalytic nanoreactor may find applications in catalytic reactions for small chemical devices as well as in conventional chemistry and processes.

Boosting the catalytic activity of Pd-nanocatalysts by anchoring transition metal atoms on carbon supports for formic acid dehydrogenation

Liquid formic acid (FA) dehydrogenation, which needs high-performance catalysts to generate green hydrogen at room temperature, is a promising chemical hydrogen storage technology that can replace fossil fuels in energy-related devices. In this work, a novel nanocatalyst with ultrafine palladium nanoparticles (Pd NPs) immobilized on a transition metal atom-decorated carbon support was synthesized for the dehydrogenation of liquid FA. Via a hydrothermal of glucose and carbonitride with a following Co doping through a heat treatment process, porous carbons with evenly dispersed Co-sites on it were strategically achieved, which could be used as a support for immobilizing Pd NPs. The obtained Pd/NC-Co1% catalyst exhibited much superior catalytic activities to those samples without Co doping on the support (Pd/NC and PdCo1%/NC), showing an impressive turnover frequency of 3045 h−1 at 50 °C for FA dehydrogenation. Other transition metal species such as Fe- and Ni-decorated carbon nanocatalysts also showed an improved catalytic activity for FA dehydrogenation. This work not only provides an efficient method to synthesize nanocatalysts with ultrafine metal NPs but also demonstrates that highly dispersed metal atoms on the support can effectively affect the immobilized NPs, resulting in an enhancement of catalytic performance.

Topochemical polymerization of hydrogen-bonded organic framework for supporting ultrafine palladium nanoparticles

Topochemical polymerization of hydrogen-bonded organic framework for supporting ultrafine palladium nanoparticles

Low-temperature control over deposition of ultrafine Pd nanoparticles on porous carbon nanosheets for highly efficient dehydrogenation of ammonia borane

The search for simply synthetic strategies of small-size metal nanoparticles is of significant relevance but still faces challenges. In this paper, a method of lowtemperature regulation (LTR) of ultrafine palladium nanoparticles deposited on porous carbon nanosheets is proposed for efficient dehydrogenation of ammonia borane. The LTR method might relieve the sintering of metal particles, thereby resulting in ultrafine Pd nanoparticles of 1.7 nm and their high dispersion on porous carbon. As suggested by the catalytic experiments hereby, Pd/NPC-LTR contributes to higher turnover frequencies of ammonia borane hydrolysis relative to most Pd-based catalysts reported previously. Furthermore, the catalytic performance could be further enhanced by the addition of NaOH under the same reaction conditions, with the hydrolysis completion time shortened by 2.5 times. Moreover, the recycle tests reveal that Pd/NPC-LTR catalyst has good stability and reusability in the hydrolysis of ammonia borane, preserving 70% of its initial catalytic activity even after 10 recycles. The insights reported here can be easily extended to slick preparation and rational design of Pd-catalysts for practical applications. • Low-temperature control over deposition of Pd NPs without any complicated treatments. • Highly dispersed and ultrafine Pd NPs are well deposited on porous carbon nanosheets. • Good performance for catalytic dehydrogenation of ammonia borane. • Highly stability and reusability even after 10 recycles.

Ultrafine Palladium Embedded in N‐doped Porous Carbon Material from Carbazole‐covalent Triazine Polymer for Green Suzuki‐Miyaura Coupling Reaction

AbstractHere, we develop a facile synthesis route to fabricate ultrafine palladium nanoparticles embedded in N‐doped porous carbon material (Pd@N‐PCM), in which carbazole‐covalent triazine polymers obtained by Friedel‐Crafts alkylation at room temperature are used as precursor of N‐doped carbon. The obtained Pd@N‐PCM as a green catalyst shows the high catalytic efficiency (TOF=982 h−1) for Suzuki‐Miyaura coupling reaction of chlorobenzene under the mild reaction condition (room temperature, a non‐toxic solvent and air atmosphere). The brilliant catalytic activity of Pd@N‐PCM gives the credit to the concerted effect from the ultrafine Pd and N‐doped porous carbon.

Efficiently catalytic transfer hydrogenation of aryl and heteroaryl halides by ultrafine palladium nanoparticles confined into UiO-66

The hydrodehalogenation of aryl and heteroaryl halides (AHHs) is very crucial for academic and industrial applications. Herein, ultrafine palladium nanoparticles (Pd NPs) with the size distribution about 1.77 ± 0.35 nm, were in-situ synthesized and confined into the metal-organic framework of UiO-66 (named as Pd@UiO-66) by impregnation reduction method without tedious post-reducing step. Pd@UiO-66 shows excellent activity with a high conversion (>90%) efficiency in the catalytic transfer hydrogenation (CTH) of AHHs under mild water systems utilizing ammonium formate as hydrogen donor. Furthermore, Pd@UiO-66 maintains highly excellent stability (conversion >95%) after 5 times reused cycles without losing catalytic activity and leaching Pd nanoparticles. This study supplies a new method for hybrid catalysts by immobilizing ultrafine Pd nanoparticles into crystalline MOFs, displaying efficient transform performance for halogen compounds by catalytic hydrogenation.

Ultrafine palladium nanoparticles confined in polydopamine functionalized chlorinated poly(vinyl chloride) nanofibers for Heck reaction

AbstractPolydopamine has been considered as the adhesive of mussels to solid surfaces in biological systems. The development of dopamine and polydopamine functionalized nanofibrous materials is highly desirable for catalysis, drug delivery and tissue engineering. Polydopamine induced surface functionalized solid matrices have been proved to be efficient supporting materials for palladium nanoparticles. In this study, the dopamine monomers were first incorporated into the Pd2+/chlorated poly(vinyl chloride) (CPVC) composite nanofibers by electrospinning and then polymerized in basic and reductive solution at elevated temperature to prepare stable polydopamine functionalized CPVC supported palladium composite nanofibers. Scanning electron microscopy images show that uniform and smooth nanofibers with diameter of ~325 nm have been prepared and high temperature can promote their solvent resistance. Fourier transformed infrared and UV–visible (UV–Vis) spectra confirmed the synthesis of polydopamine inside the composite nanofibers. The ultrafine palladium nanoparticles inside the composite nanofibers were characterized by X‐ray spectroscopy and transmission electron microscopy. Although these palladium nanoparticles were confined inside the nanofibers, they exhibited excellent catalytic efficiency for the Heck reactions of aryl iodides with alkenes. Moreover, this novel fibrous catalyst could be easily recovered by simple filtration and reused at least five times without obviously loss of initial catalytic activity. In all, we have developed a distinctive way for the synthesis of polydopamine functionalized polymeric materials for catalysis and other applications.

Ultrafine palladium nanoparticles supported on mesoporous silica: An outstanding catalytic activity for hydrogen production from dodecahydro-N-ethylcarbazole

SBA-15 was treated to form a negatively charged silica surface (-Si-O-) with alkali. The ultrafine Pd nanoparticles (Pd NPs) supported on SBA-15 (Pd/SBA15) were prepared via the NaBH4 reduction of (-Si-O-)2Pd2+ formed by ionic adsorption between -Si-O- and Pd cations. The as-prepared Pd/SBA15 has showed an outstanding catalytic performance for dehydrogenation of dodecahydro-N-ethylcarbazole (H12-NEC). The dehydrogenation efficiency reached 98.27% for 1 h at 180 °C and 96.15% for 3 h at 165 °C, which was much higher than that reported in literature. Pd/SBA15 catalysts were characterized by XRD, TEM, FT-IR, XPS, N2 physical adsorption–desorption and H2 chemisorption. The results showed that Pd NPs were uniformly dispersed on pore surface of SBA-15 with high Pd dispersion of 57%. The Pd NPs was too fine to be detected by TEM. The ionic adsorption of -Si-O- and Pd cations prevented agglomeration of nanoparticles. The coordination of Pd NPs with hydroxyl on the surface of SBA-15 improved catalytic stability. The apparent activation energy of Pd/SBA15 catalyst was 74.23 KJ/mol.

Promotion of sulfonic acid groups on biomass carbons loading ultrafine palladium nanoparticles for the efficient hydrodeoxygenation of vanillin in water

Carbonaceous catalysts with sulfonic acid (-SO3H) groups are showing promising performances in the conversion of mono- and poly-saccharides, however, their applications in the hydrodeoxygenation (HDO) of oxygen-rich lignin derivatives are rarely reported. Herein, we report a facile synthetic approach for one-step preparation of porous carbonaceous solid acids with –SO3H groups (OHCA) where monosaccharide, polysaccharide, and raw biomass can be used as carbon precursors. These porous carbonaceous solid acids supported ultrafine palladium nanoparticles (Pd/OHCA) exhibited excellent performances in the HDO of vanillin (VAN) in water. We found that Pd nanoparticles (Pd NPs) were responsible for the hydrogenation of VAN to vanillyl alcohol (VAL) and acidic groups were crucial for the hydrogenolysis of generated VAL to 2-methoxy-4-methylphenol (MMP). Importantly, VAL once generated can be immediately converted to MMP via synergistic catalysis between acidic groups and Pd NPs, avoiding the formation of by-products. Pd/OHCA catalyst also exhibited excellent stability in the HDO of VAN and retained its activities in the six consecutive runs. The findings of this work provide a new thought for the HDO of biomass derivatives over biomass-based carbon catalysts.

Ultrafine palladium nanoparticles supported on poly(4-vinylpyridine)-grafted carbon nanotubes as heterogeneous catalysts for cross-coupling reaction between organoindium halide and alkyl iodide

The rational design of a stable and recyclable nanocatalyst based on robust support for the application in palladium (Pd)-catalyzed coupling reactions always fuels great interest. Pd nanoparticles (NPs) deposited onto carbon nanotubes (CNTs) to form CNT–PdNPs hybrid nanocomposites has been thoroughly studied. And they can serve as heterogeneous catalysts to implement the Pd-catalyzed cross-coupling reactions. However, the utilization of CNT–PdNPs nanohybrids for cross-coupling reaction between organoindium halide and alkyl iodide is a blank area, and no example has been reported. In this work, we provide an effective approach for the fabrication of a Pd-based heterogeneous nanocatalyst, where Pd NPs with small average size (~2.5 nm) are uniformly immobilized on the surface of poly(4-vinylpyridine) (P4VP)-grafted carbon nanotube (CNT). Owing to the uniform distribution of Pd NPs on the CNT surface, high stability and good dispersibility of CNT-g-P4VP/PdNPs composites, the as-fabricated heterogeneous nanocatalyst exhibits excellent catalytic activity for cross-coupling of organoindium halide with alkyl iodide. It is the first report that the CNT–PdNP nanohybrid catalyst is applied to the cross-coupling reaction between organoindium halide and alkyl iodide. This work may pave the way for the construction of CNT-supported metallic NPs for a variety of efficient catalytic applications.

Highly efficient catalytic reduction of 4-nitrophenol and organic dyes by ultrafine palladium nanoparticles anchored on CeO2 nanorods.

Uniformly dispersed Pd nanoparticles on certain supports exhibit exceptional catalytic performance toward various environmental applications. In this work, ultrafine Pd nanoparticles anchored on CeO2 nanorods were synthesized via an absorption-in situ reduction method. The activity of the CeO2/Pd nanocomposites was systematically investigated toward reduction of 4-nitrophenol (4-NP) and organic dyes including methyl blue, rhodamine B, methyl orange, and Congo red. The results indicated that the CeO2/Pd nanocomposites with different weight ratios of Pd nanoparticles (10.23 wt%, 11.01 wt%, and 14.27 wt%) can almost completely reduce 4-NP with a rate constant of 3.31×10-1, 3.22×10-1, and 2.23×10-1 min-1. Besides, the 10.23 wt% CeO2/Pd nanocomposites exhibit remarkable enhanced catalytic activity toward reduction of organic dyes. The catalysts display ideal stability after being used for three times for the reduction of 4-NP. We believe that our strategy demonstrated here offers insights into the design and fabrication of novel Pd-based nanocomposites for various heterogeneous catalysis applications.

Ensemble-Exciting Effect in Pd/alk-Ti3C2 on the Activity for Efficient Hydrogen Production

Creating active sites to improve the mass activity and durability of metal catalysts by elucidating the relationship between the metal and the support is a major challenge. In this study, ultrafine palladium nanoparticles (Pd NPs) were supported on alkalized Ti3C2 (alk-Ti3C2) to obtain a catalytically active interfacial ensemble. The catalyst Pd/alk-Ti3C2 with a Pd loading of 1.0 wt % exhibited the highest activity in ammonia borane (AB) hydrolysis reaction, with an initial turnover frequency of 230.6 min–1. A comprehensive analysis revealed that an ensemble-exciting effect originated from the Pd and the alk-Ti3C2. The hydroxylation of alk-Ti3C2 regulated the local coordination environment of Pd. Water and AB were effortlessly activated by the −OH group and Pd atom aggregates composed of electron-deficient support alk-Ti3C2 and electron-rich Pd, respectively. The efficient generation of hydrogen at the interface of Pd/alk-Ti3C2 was further guaranteed by the interfacial activation. This work on precision active sites opens new avenues for developing high-activity noble-metal catalysts for AB hydrolysis.

Controlled Synthesis of Palladium Nanoparticles with Size-Dependent Catalytic Activities Enabled by Organic Molecular Cages.

Particle size plays a key role in the performance of metal nanoparticles (MNPs). However, the size-controlled synthesis of MNPs still represents a challenging task. In this work, we revealed a strong solvent effect on the growth of palladium nanoparticles (PdNPs), which was directed by a porous [2 + 3] organic molecular cage (OMC, Phos-cage) containing triphenylphosphine moieties. PdNPs with different average diameters of 0.8, 1.2, and 3.3 nm supported by Phos-cage were obtained by simply varying the reaction media. The catalytic performance of such ultrafine PdNPs in the reduction of p-nitrophenol and a Suzuki-Miyaura coupling reaction has been studied, which clearly shows size-dependent catalytic activity and stability. The knowledge gained in this study, controlling the size of PdNPs supported by the OMC template in different solvents, will open new possibilities for size-controlled synthesis of ultrafine MNPs with high catalytic activity and stability.

N‐Monomethylation of Amines with Methanol by Syndiotactic Poly(aminostyrene)‐supported Palladium Nanoparticle Catalyst

AbstractPalladium nanocatalyst supported on dimethylamino‐functionalized syndiotactic polystyrene (Pd@sPS‐NMe2) showed high activity and selectivity for the N‐monomethylation of various primary amines using methanol as methylation reagent under air. The excellent catalytic performance could be associated with the ultrafine palladium nanoparticles and high amine‐adsorbing capacity of the catalyst. The Pd@sPS‐NMe2 catalyst was highly robust, and could be easily recovered by filtration and reused more than ten times without decrease in activity and selectivity.

Promotion of Sulfonic Acid Groups on Biomass Carbons Loading Ultrafine Palladium Nanoparticles for the Efficient Hydrodeoxygenation of Vanillin in Water

Promotion of Sulfonic Acid Groups on Biomass Carbons Loading Ultrafine Palladium Nanoparticles for the Efficient Hydrodeoxygenation of Vanillin in Water

Three‐Dimensional Covalent‐Organic Frameworks Loaded with Highly Dispersed Ultrafine Palladium Nanoparticles as Efficient Heterogeneous Catalyst

AbstractIn this work, we exploited the notable advantages of using three‐dimensional covalent organic frameworks (3D COFs) as supports for efficiently and controllably loading Pd. Tetraphenylmethane based 3D COF (TPM‐3D‐COF‐BPY) bearing bipyridine as coordination sites was constructed. A 7‐fold interpenetrated dia structure was revealed by the aid of powder X‐ray diffraction (PXRD) and structural simulation. The unique side‐by‐side 1D channels of TPM‐3D‐COF‐BPY provide enormous easily accessible active surface areas for heterogeneous catalysis throughout the topological structure. The delicate 7‐fold interpenetration of the bipyridine linked frameworks yields discrete and widespread coordination sites and enables super‐efficient heterogeneous catalysis after metalation of nitrogen coordination sites in TPM‐3D‐COF‐BPY. As a demonstration, Pd(II) was selectively anchored to the bipyridine coordination sites in the TPM‐3D‐COF‐BPY matrix. Further reduction of Pd(II) loaded in the topological structure leads to highly dispersed ultrafine Pd nanoparticles (NPs) with an average size of 1.12 nm confined within channels of TPM‐3D‐COF‐BPY. The as‐prepared Pd@TPM‐3D‐COF‐BPY as heterogeneous catalyst exhibits excellent efficiency, stability, and recyclability in catalyzing the Suziki‐Miyaura coupling reactions reaching a 98% yield within 2 h under facile conditions.

Anchoring Pd-nanoparticles on dithiocarbamate- functionalized SBA-15 for hydrogen generation from formic acid

Hydrogen (H2) generation from natural biological metabolic products has remained a huge challenge for the energy arena. However, designing a catalytic system with complementary properties including high surface area, high loading, and easy separation offers a promising route for efficient utilization of nanoreactors for prospective H2 suppliers to a fuel cell. Herein, selective dehydrogenation of formic acid (FA) as a natural biological metabolic product to H2 and CO2 gas mixtures has been studied by supporting ultrafine palladium nanoparticles on organosulfur-functionalized SBA-15 nanoreactor under ultrasonic irradiation. The effects of the porous structure as a nanoreactor, and organosulfur groups, which presented around the Pd due to their prominent roles in anchoring and stabilizing of Pd NPs, studied as a superior catalyst for selective dehydrogenation of FA. Whole catalytic systems were utilized in ultrasonic irradiation in the absence of additives to provide excellent TOF/TON values. It was found that propose catalyst is a greener, recyclable, and more suitable option for the large-scale application and provide some new insights into stabilization of ultra-fine metal nanoparticle for a variety of applications.

Ultrafine palladium nanoparticles anchored on NH2-functionalized reduced graphene oxide as efficient catalyst towards formic acid dehydrogenation

The development of active and stable catalyst is of significance for hydrogen generation from formic acid. Herein, a novel palladium catalyst with ultrafine metallic nanoparticles anchored on NH2-functionalized reduced graphene oxide (NH2-rGO) was synthesized by a facile wet chemical reduction process using sodium borohydride as the reducing agent. The TEM and XPS characterization results confirmed the successful functionalization of rGO with 3-aminopropyltriethoxysilane (APTES), which plays a very important role in evenly dispersing ultrafine Pd nanoparticles with a small average size of about 2.3 nm. As a result, the as-prepared Pd/NH2-rGO catalyst exhibited excellent activity with a high initial turnover frequency of 767 h−1 and 100% hydrogen selectivity, which was predominant among the currently available pure Pd catalysts towards formic acid dehydrogenation under room temperature.

Surfactant‐directed Pd‐nanoparticle assemblies as efficient nanoreactors for water remediation

AbstractDevising new catalytic systems for the efficient removal of organic chlorides from contaminated sites has important benefits for the human health. Efficiency requires the use of performing catalysts and the extraction of the contaminant from the environment. Here we describe a novel strategy that combines both aspects. A one‐pot surfactant‐directed approach allows the preparation of ultrafine palladium nanoparticles (PdNPs) finely dispersed inside well‐ordered geometric structures, ranging from loose vesicles to nanocubes, from cylindrical to spherical assemblies. These assemblies work as nanoreactors where hydrophobic organic chlorides can be concentrated in the surfactant‐tail environment and efficiently reduced by the PdNP catalysts. As a proof‐of‐concept, we studied the dechlorination of the notorious pollutant 4‐chlorophenol. The nanoreactors display rapid dechlorination ability, excellent catalytic activity, and good stability and recyclability. This study provides a new methodology for effective water remediation that combines the advantages of both extraction and supported heterogeneous catalysis.image