Stabilized Pd Nanoparticles Research Articles

Enhancing Hydrogen Evolution Reaction Activity of Palladium Catalyst by Immobilization on MXene Nanosheets.

Efficient catalysts with minimal content of catalytically active noble metals are essential for the transition to the clean hydrogen economy. Catalyst supports that can immobilize and stabilize catalytic nanoparticles and facilitate the supply of electrons and reactants to the catalysts are needed. Being hydrophilic and more conductive compared with carbons, MXenes have shown promise as catalyst supports. However, the controlled assembly of their 2D sheets creates a challenge. This study established a lattice engineering approach to regulate the assembly of exfoliated Ti3C2Tx MXene nanosheets with guest cations of various sizes. The enlargement of guest cations led to a decreased interlayer interaction of MXene lamellae and increased surface accessibility, allowing intercalation of Pd nanoparticles. Stabilization of Pd nanoparticles between interlayer-expanded MXene nanosheets improved their electrocatalytic activity. The Pd-immobilized K+-intercalated MXene nanosheets (PdKMX) demonstrated exceptional electrocatalytic performance for the hydrogen evolution reaction with the lowest overpotential of 72 mV (@10 mA cm-2) and the highest turnover frequency of 1.122 s-1 (@ an overpotential of 100 mV), which were superior to those of the state-of-the-art Pd nanoparticle-based electrocatalysts. Weakening of the interlayer interaction during self-assembly with K+ ions led to fewer layers in lamellae and expansion of the MXene in the c direction during Pd anchoring, providing numerous surface-active sites and promoting mass transport. In situ spectroscopic analysis suggests that the effective interfacial electron injection from the Pd nanoparticles strongly immobilized on interlayer-expanded PdKMX may be responsible for the improved electrocatalytic performance.

Electron-deficient Pd nanoparticles on nitrogen-doped carbon nanofibers for high selectivity alkyne transfer semi-hydrogenation

The catalytic activity and stability of Pd nanoparticles on nitrogen-doped carbon nanofibers for the semi-hydrogenation of phenylacetylene.

Pd on composite chitosan bead containing a star-like hybrid metal-organic framework: A promising catalyst for hydrogenation of lubricants

A star-like hybrid composite of metal-organic framework with amino-functionalized Fe-based metal-organic framework and zeolitic imidazolate framework components was synthesized, characterized and then embedded in chitosan beads. The beads were cross-linked with glutaraldehyde to furnish robust beads, which were then utilized as supporting materials for stabilizing Pd nanoparticles. The obtained catalytic composite was characterized via XRD, FTIR, TGA, ICP, SEM, EDS, elemental mapping and utilized for the hydrogenation of polyalphaolefin oil. The effects of temperature, catalyst loading and hydrogen pressure were investigated to find the best reaction conditions. According to the results, the present catalyst promoted hydrogenation reaction under relatively mild conditions (P = 8 bar, T = 130 °C and 5 wt% catalyst loading) to give the product in 98% yield and bromine index of 50 mg-Br/100 g. Besides, the catalyst exhibited acceptable recyclability and insignificant Pd leaching, which is very promising for large-scale applications. Hot filtration test also affirmed heterogeneous catalysis.

Role of ammonium ionic liquid and Pd nanoparticles in cavitation-based graphite decontamination and recycling process

Sonochemical recovery of radioactive contaminants from nuclear graphite has been demonstrated to be quite invaluable in recent studies. However, graphite is a soft material and is prone to erosion and wear. This restricts the recycle of graphite cleaned using ultrasound beyond a few decontamination cycles. Hence, it is an imperative to prevent the surface erosion of graphite in the sonic field. The current work studies the efficacy of ultrasound in decontaminating ceria contaminated graphite coupons using a cocktail of acids (0.25 M HNO3 − 1 M HCOOH − 0.2 M [N2H5][NO3]). Based on the superlative effects of ionic liquids in lubrication and erosion prevention, the effect of adding ionic liquid stabilized Pd nanoparticles to the leachate was also studied. It was observed that the Trioctylmethyl ammonium chloride (TOMAC) ionic liquid prevented the generation of the carbon residue due to a protective viscous layer formation reducing the mechanical effects of cavitation on graphite surface. It also helped in maintaining the porosity change in graphite microstructure around 5% after 15 cycles of decontamination. TOMAC also proved to offer better surface protection on graphite compared to imidazolium-based ILs, based on the change in compressive strength and porosity in different ionic liquids. The palladium nanoparticles, on the other hand, helped in reductive dissolution of ceria layer by acting as a reducing agent due to its lower reduction potential compared to cerium. With the surge in demand of graphite worldwide, a non-destructive decontamination process for graphite with no secondary waste generation is the need of the hour. This study is an attempt in that direction.

Amino-functionalized CuFe2O4 supported Pd nanoparticles as magnetically catalyst for H2 production from methanolysis of ammonia borane and hydrogenation of nitro aromatics

Small and equally distributed Pd nanoparticles (NPs) are tightly anchored on the surface of magnetic and amino (–NH2) functionalized CuFe2O4 to obtain magnetically separable CuFe2O4–NH2@Pd catalyst with core-shell structure. Compared to the inherent catalytic activity of CuFe2O4, the catalytic performance of CuFe2O4–NH2@Pd for dehydrogenation of ammonia-borane (AB) and concurrent hydrogenation of different nitro aromatics by H2 generated from AB methanolysis can be boosted more effectively than that of CuFe2O4@Pd, which is the control catalyst and is prepared by loading Pd NPs on pristine CuFe2O4. As electron donating groups, the –NH2 groups covalently bonded to the surface of CuFe2O4 play vital roles in stabilizing Pd NPs, providing strong metal-support interaction and rendering enhanced catalytic activity. However, we find that the catalytic performance of CuFe2O4, CuFe2O4@Pd and CuFe2O4–NH2@Pd for the hydrogenation reduction of mercapto-substituted nitro aromatics (p-nitrothiophenol, p-NTP) is far inferior to that for the reduction of nitroarenes that do not contain a sulfur substituent. Therefore, it is quite essential to research and develop the new-type catalysts with more excellent catalytic performance.

ZnCo2O4 supported low-loading Pd as an enhanced catalyst for low temperature oxidation of carbon monoxide

We have successfully synthesized a series of Pd/ZnCo2O4 supported catalytic materials with low noble metal loading and high activity by the impregnation method. The Pd/ZnCo2O4 catalysts containing 0.2% Pd have superior performance for oxidizing CO at 80 °C, achieving 100% conversion. There is also no loss of activity after four cycles of tests, with the conversion remaining approximately 100%. Aside from that, various advanced physicochemical characterizations indicate that this excellent catalytic performance stems from the interaction between metal Pd and carrier ZnCo2O4. Pd provides a higher degree of accessibility to the active site, while ZnCo2O4 as a carrier can better stabilize Pd nanoparticles. The 0.2% Pd/ZnCo2O4 exhibits higher levels of Pd2+ species as the electronic interaction between Pd and ZnCo2O4 improves, thus improving CO oxidation catalytic efficiency. Furthermore, the low loading of Pd is crucial for reducing the cost of noble metal catalysts and ameliorating their practicality in industrial applications.

Synthesis of ultrafine Pd nanoparticles encapsulated in imidazolium-based porous polymers for semi-hydrogenation of alkynes

Interaction between metal and support can dramatically affect the activity and selectivity of supported metallic nanoparticles. Therefore, the development of novel support is a critical path to achieve advanced catalysis. Here, we report that imidazolium-based porous polymers were prepared through a free-radical cross-linking reaction. These imidazolium-based porous polymers with high specific surface area and abundant imidazonium units were utilized as supports to synthesize ultra-small and narrow dispersed Pd nanoparticles . The optimized catalyst displayed 99% selectivity for styrene at 98% conversion in alkyne semi-hydrogenation under ambient conditions with a general application. Comprehensive characterizations demonstrated that the interaction between cationic imidazolium-based porous polymers and Pd enhanced the alkene selectivity by weakening the adsorption on Pd, as well as stabilized Pd nanoparticles by the anchoring and spatial confining effects. The pivotal roles of the Pd-imidazonium interaction and the mesoporous structure provide valuable guidance for the manufacture of high-performance metallic nanoparticles catalyst for selective hydrogenation.

Mesoporous hybrid organosilica for stabilizing Pd nanoparticles and aerobic alcohol oxidation through Pd hydride (Pd–H2) species

The hybrid periodic mesoporous organosilica (PMO) with APTES/DAR Schiff-based precursor 3-aminopropyltriethoxysilane (APTES) and 4,6-diacetylresorcinol (DAR) was synthesized in the presence of a structure-directing agent cetyltrimethylammonium bromide and tetraethoxysilane. Then, Pd (II) ions, as well as Pd nanoparticles, were incorporated inside the pore walls of the synthesized APTES/DAR-PMO. The PMO structure was characterized by HRTEM, FT-IR, TEM, FE-SEM, BET, SEM-EDX, low angle XRD, HADAF-mapping, TGA, and atomic absorption spectroscopy (AAS). Subsequently, the as-fabricated green heterogeneous nanocatalysts (Pd-NPs@APTES/DAR-PMO) was used as effective and sustainable catalysts for the aerobic oxidation of benzylic alcohols into their corresponding aldehydes in pure water A high Pd-NPs@APTES/DAR-PMO-catalyzed conversion level of the primary and secondary alcohols was demonstrated. Furthermore, the environmentally friendly catalyst showed outstanding stability, so that readily separated by centrifugation and reused for seven consecutive cyclic terms with good retention of high catalytic activities.

Efficiently catalytic transfer hydrogenation and fast separation of unsaturated alkene compounds over Pd/UiO-66 under green conditions

Stable Pd nanoparticles (Pd NPs) have been uniformly dispersed and immobilized into the metal-organic framework of UiO-66, Pd/UiO-66, by a facile impregnation reduction method. Pd/UiO-66 retains the integrity of the UiO-66 crystal structure and incorporated with ultrasmall Pd NPs(1.70 ± 0.32 nm). Using ammonium formate(AF) as a H-donor and water as solvent under green condition, the optimized 1.16 wt% Pd/UiO-66 catalyst exhibits remarkable activity in the catalytic transfer hydrogenation(CTH) of α-methylstyrene(AMS) into cumin(achieving 99.6% conversion of AMS and almost full selectivity to cumin with an extremely high turnover frequency value 456.7 h−1 at 323.15 K). Pd/UiO-66 also show superior catalytic activity in CTH of unsaturated alkene compounds to saturated compounds with excellent stability and recyclability. Furthermore, the as-formed saturated alkanes can be fast and automatic separated easily from the aqueous catalytic media. This study supplies a general method for immobilizing ultrafine Pd nanoparticles into crystalline MOFs and a “green” path for hydrogenation of unsaturated alkene compounds.

Hollow mesoporous aluminosilicate spheres imbedded with Pd nanoparticles for high performance toluene combustion

In the past few decades, persistent efforts have been directed toward the stabilization of Pd nanoparticles during catalytic reaction processes carried out at relatively higher temperatures. In this study, small-sized Pd nanoparticles imbedded into hollow mesoporous aluminosilicate sphere catalysts (Pd/HMAS-1) have been synthesized. The physical and chemical properties of Pd/HMAS-1 were studied by the means of XRD, TEM, and XPS analysis. The prepared Pd/HMAS-1 catalyst was evaluated for its catalytic performance in the combustion of toluene. Pd/HMAS-1 showed excellent activity for toluene oxidation with T90 at 150 °C, which was much higher than that of Pd/HMAS-2 (T90 at 220 °C) with Pd nanoparticle supported on the external surface of HMAS and Pd/HMAS-CTAB (T90 at 200 °C) with perpendicular pore channel occupied by CTAB. Furthermore, Pd/HMAS-1 exhibited an outstanding long-term stability and maintained the conversion efficiency of 100 % at 200 °C for 20 h. The superior catalytic performance of Pd/HMAS-1 has been attributed to the confinement effect of ordered mesopore in stabilizing Pd nanoparticles and improvement in mass transfer efficiency and active Pd metal accessibility. Furthermore, the oxidation pathway of toluene over Pd/HMAS-1 was proposed based on the analysis of key intermediates generated during the catalytic combustion process by in situ-DRIFTS analysis. This study provides a promising strategy to design novel high-performance ordered mesoporous zeolite-confined metal/metal oxide catalysts for industrial VOCs combustion.

Pd nanoparticles anchored and stabilized on N-doped boehmite@C with enhanced catalytic performance in 2-ethyl-9,10 anthraquinone hydrogenation

Pd nanoparticles (NP) immobilized on nitrogen (N)-doped boehmite@C composites (CCB) with enhanced catalytic performance for 2-ethyl-9,10 anthraquinone hydrogenation were successfully prepared by a mild vapor-phase hydrothermal method. The characterization results showed that the phase structures, morphologies and texture properties of CCB are analogous to the corresponding boehmite. The dosages of sucrose and urea determined the contents of C and N in CCB, which controlled the loading capacities of 0.64–1.50%, particle sizes of 3.75–5.48 nm and dispersity of 18.6–33.8% of the Pd NP. The C, N atoms and -OH groups on the surface of CCB are beneficial to anchor and stabilize Pd NP in situ reduction. Compared with the hydrogenation efficiency of Pd/boehmite (8.68 g/L), the corresponding value of Pd/CCB (11.18 g/L) increased by 28.8%. Furthermore, compared with the traditional preparation methods of catalyst in the field of anthraquinone hydrogenation, this effective and mild vapor-phase hydrothermal method does not use any excess reductant and capping reagent, and thus provides an alternative approach for preparing high-performance catalyst.

Pd nanoparticles anchored on porous boron nitride nanofibers as highly active and stable electrocatalysts for formic acid oxidation

Direct formic acid fuel cells (DFAFCs) are promising power generation technologies for various electronic devices. The design of efficient and stable electrocatalysts for the formic acid oxidation reaction (FAOR) plays an important role for the commercial applications of the DFAFCs. Herein, porous boron nitride (BN) supported Pd nanoparticles (NPs) have been developed as unique and effective composite catalysts for FAOR. Porous BN nanofibers (BNNFs) has been utilized as a functional support to anchor of Pd NPs. The high specific surface area and rich porosity of BNNFs play a key role for the well-dispersion and stabilization of Pd NPs with uniform ultra-small size (~2.32 nm) on their surface. The developed Pd/BNNFs composite catalyst exhibits excellent catalytic activity for FAOR with the mass activity of 725 mA mg−1Pd and a very low onset potential (about −0.12 V). Comparative experiments confirm that the microstructure of porous BN carrier greatly affects the electrocatalytic behaviors of the composite catalyst in FAOR. As compared with the composite catalyst using BN microfibers (BNMFs) as a support, the developed Pd/BNNFs catalyst shows superior catalytic activity and long-term stability owing to the larger specific surface area of BNNFs and stronger interaction between Pd NPs and support. This study not only illustrates that porous BN is a desirable catalyst carrier for catalytic FAOR but also provides new ideas for the design of novel BN-based catalysts.

Enhancing Hydrogen Storage Capacity of Pd Nanoparticles by Sandwiching between Inorganic Nanosheets

AbstractH2 is regarded to play a crucial role in the transition from a fossil fuel‐based energy economy towards an environmentally friendly one. However, storage of H2 is still challenging, but palladium (Pd) based materials show exciting properties. Therefore, nanoparticulate Pd has been intensely studied for hydrogen storage in the past years. Here, we stabilize Pd nanoparticles by intercalation between inorganic nanosheets of hectorite (NaHec). Compared to nanoparticles stabilized by the polymer polyvinylpyrrolidone (PVP), the H2 storage capacity was found to be 86 % higher for identical Pd nanoparticles being intercalated between nanosheets. We attribute this remarkably enhanced H2 storage capacity to the partial oxidation of Pd, as evidenced by X‐ray photoelectron spectroscopy (XPS). The higher amount of holes in the 4d band leads to a higher amount of H2 that can be absorbed when Pd is stabilized between the nanosheets of hectorite compared to the PVP stabilized nanoparticles.

Pd Doped on TCH@SBA-15 Nanocomposites: Fabrication and Application as a New Organometallic Catalyst in the Three-Component Synthesis of N-Benzo-imidazo- or -thiazole-1,3-thiazolidinones.

In this study, Pd(II)/TCH@SBA-15 nanocomposites were synthesized by the grafting of 3-chloropropyltriethoxysilane and thiocarbohydrazide on SBA-15 and subsequent deposition of palladium acetates through the ligand–metal coordination method. The structure and morphology of this nanoporous nanocomposite was thoroughly identified by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, thermogravimetric analysis, atomic absorption spectroscopy, and Brunauer–Emmett–Teller instrumental analyses. Furthermore, the catalytic activity of this nanocomposite was investigated in the three-component synthesis of 3-benzimidazolyl or benzothiazoleyl-1,3-thiazolidin-4-ones via a reaction of 2-aminobenzimidazole or 2-aminobenzothiazole, aromatic aldehydes, and thioglycolic acid in an acetone–H2O mixture under green conditions. The Pd/TCH@SBA-15 nanocatalyst is demonstrated to exhibit a high catalyzing activity in the three-component reaction of the synthesis of N-heterocyclic thiazolidinones with good to excellent yields. One of the advantages of the suggested method is the direct application of the thiocarbohydrazide ligand to stabilize Pd nanoparticles through formation of a stable ring complex without creating an additional Schiff base step. Moreover, this organometallic nanocatalyst can be recycled several times with no notable leaching or loss of performance.

Photo-promoted in situ reduction and stabilization of Pd nanoparticles by H2 at photo-insensitive Sm2O3 nanorods

Controlled synthesis of noble metal nanoparticles with well-defined size and good dispersion on supports has been a long-standing challenge in heterogeneous catalysis. Here we report a facile photo-assisted H2in situ reduction process to synthesize monodispersed Pd nanoparticles with 2–4 nm size on photo-insensitive Sm2O3 rare-earth metal oxide with nanorod morphology. Thanks to the contribution of UV irradiation, the photoelectrons generation in the Sm2O3 support accelerates the H2 reduction of Pd2+ ions into Pd0 and stabilize the growth of very small Pd nanoparticles homogeneously dispersed on the support. The homogeneous distribution of the Pd NPs on the surface of Sm2O3 is most likely attributed to the profuse nucleation sites created by the UV irradiation and the abundance of hydroxyl groups on the support. The hydrogenation of styrene to ethylbenzene was studied as a model reaction. As a result, the UV radiated sample shows an excellent TOF value of 7419 h−1, which is quadruple of the sample without UV irradiation, under the condition of 0.1 MPa H2 at a content of 1.0 wt% Pd. Besides, UV radiated sample shows a negligible performance degradation during the repeated cycling process. This photo-promoted H2 reduction process provides a convenient and straightforward route for assembling materials with novel structures and functions for nanotechnology applications.

Hydrogen separation using polybenzimidazole membrane with palladium nanoparticles stabilized by polyvinylpyrrolidone

An innovation in hydrogen (H2) selective membrane holds the substantial key of H2 economy. Polymers are the most practical and economical material for membrane fabrication, but their application in H2 separation is always constrained within the selectivity-permeability “trade-off” boundary. The expensive palladium (Pd) thin films offer higher selectivity by facilitating the dissociation, diffusion and re-association of H2 gas. This work reports on the incorporation of Pd nanoparticles into polybenzimidazole (PBI) membranes to surpass the mentioned limitations. Pd nanoparticles were synthesized and stabilized in the inversed microemulsion of polyvinylpyrrolidone (PVP) prior to blending. The X-ray diffraction and energy dispersive X-ray results proved the presence of Pd nanoparticles blended into PBI membrane with dense structure. The agglomerated and the stabilized Pd nanoparticles PBI matrix behaved very differently in H2 adsorption at the rising temperature as shown in temperature-programmed reduction results. The ideal H2/CO2 selectivity of PBI membrane with 1 wt% of Pd nanoparticles was improved by 49% compared to the PBI membrane at 150°C. This membrane surpassed the upper bound Robeson plot at 300°C (ideal H2/CO2 selectivity of 83.57; H2 permeability of 151.73 Barrer) and the H2 permeation could be correlated with Van't Hoff-Arrhenius equation.

Formation and stabilization of nanosized Pd particles in catalytic systems: Ionic nitrogen compounds as catalytic promoters and stabilizers of nanoparticles

• Pd catalytic systems usually contain nanoparticles regardless of the type of pre-catalyst and require special stabilizers. • Ionic nitrogen compounds stabilize Pd nanoparticles and open up new fields of application in organic synthesis. • The structure of the ionic compound affects the stabilization mechanism and the efficiency of the catalysts. • The catalytic action of the ionic nitrogen compound can outweigh the action of the ligands. • The overall effect of stabilization can be highly dependent on the nature of catalysis and reaction conditions. Actual palladium catalysts in synthetic transformations in reaction mixtures are usually represented by dynamic catalytic systems that contain various interconvertible forms of metal particles, including molecular complexes, metal clusters, and nanoparticles. The low thermodynamic stability of Pd nanoparticles can lead to their aggregation and, as a consequence, to the deactivation of the catalytic systems. Therefore, stabilization of nanosized Pd particles is of key importance to ensure efficient catalysis. This review discusses the main pathways for the formation of Pd nanoparticles and clusters from various precatalysts in catalytic systems, as well as current views on the mechanisms of stabilization of these nanosized Pd particles using various types of ionic nitrogen compounds, such as ammonium, amidinium, azolium, and pyridinium salts. The use of ionic nitrogen compounds as specially added or in situ formed stabilizers, ligands, catalytic promoters, heterogenized catalysts (supported ionic liquid phase, SILP) and reaction media (ionic liquids) is exemplified by several important catalytic reactions. The main effects of ionic nitrogen compounds on catalytic processes are also discussed, including possible involvement in catalytic cycles and unwanted side reactions.

Celluloses as Green Support of Palladium Nanoparticles for Application in Heterogeneous Catalysis: A Brief Review

Palladium (Pd) is considered as powerful catalyst in many organic syntheses of industrial importance, employed in areas like medicine, pharmacology, cosmetics, pesticides and degradation of organic pollutants. In heterogeneous catalysis, stabilization of Pd nanoparticles (NPs) is foremost to prevent aggregation for getting high catalytic efficiency. Celluloses, being green support, have been widely used in different forms such as bulk, modified or nanocelluloses for stabilizing Pd NPs. The unique properties like high mechanical strength, thermal stability, high functionality, insolubility in water and in most organic solvents and good anchoring ability with metal NPs had made them good support for Pd NPs. However, special attention is needed on further improving the binding efficiency of Pd NPs with cellulose without affecting the catalytic property for achieving long term recycle stability. This review will focus on the merits and demerits of the existing cellulose supported Pd catalysts and propose solutions to overcome the limitations.

Synthesis and characterization of supported stabilized palladium nanoparticles for selective hydrogenation in water at low temperature.

Zirconia supported vacant phosphotungstate stabilized Pd nanoparticles (Pd–PW11/ZrO2) were prepared using a simple impregnation and post reduction method, characterized and their efficiency for selective C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C hydrogenation of unsaturated compounds explored. The establishment of a hydrogenation strategy at low temperature using water as solvent under mild conditions makes the present system environmentally benign and green. The catalyst shows outstanding activity (96% conversion) with just a small amount of Pd(0) (0.0034 mol%) with high substrate/catalyst ratio (29 177/1), TON (28 010) and TOF (14 005 h−1) for cyclohexene (as a model substrate) hydrogenation. The catalyst was recovered by simple centrifugation and reused for up to five catalytic cycles without alteration in its activity. The present catalyst was found to be viable towards different substrates with excellent activity and TON (18 000 to 28 800). A study on the effect of addenda atom shows that the efficiency of the catalyst can be enhanced greatly by increasing the number of counter protons. This challenging strategy would greatly benefit sustainable development in chemistry as it diminishes the use of organic solvents and offers economic and environmental benefits as water is cheap and non-toxic.

Thermoresponsive Starch Hydrogel Stabilized Pd Nanoparticles: Soft Catalyst for the Preparation of (±)-α-Methylbiphenylalanine in Water Aiming at Bioorthogonal Chemistries

The corn-starch was able to reduce Pd(II) species under relatively low concentration (5.0 wt/vol) leading to the formation of a thermoresponsive palladium nanoparticles-containing hydrogel with D = 16.1 nm ± 6.4 nm. It was successfully applied to the Suzuki–Miyaura reaction step in neat water involved in the synthesis of (±)-N-acetyl-α-methyl-4-biphenylalanine ethyl ester, a direct precursor of an unnatural quaternary biarylalanine.