Dispersed Palladium Nanoparticles Research Articles

Carbonized cellulose microspheres loaded with Pd NPs as catalyst in p-nitrophenol reduction and Suzuki-Miyaura coupling reaction

Catalytic reduction of p-nitrophenol is usually carried out using transition metal nanoparticles such as gold, palladium, silver, and copper, especially palladium nanoparticles (Pd NPs), which are characterized by fast reaction rate, high turnover frequency, good selectivity, and high yield. However, the aggregation and precipitation of the metals lead to the decomposition of the catalyst, which results in a significant reduction of the catalytic activity. Therefore, the preparation of homogeneous stabilized palladium nanoparticles catalysts has been widely studied. Stabilized palladium nanoparticles mainly use synthetic polymers. Cellulose microspheres, as a natural polymer material with low-cost and porous fiber network structure, are excellent carriers for stabilizing metal nanoparticles. Cellulose microspheres impregnated with palladium metal nanoparticles were carbonized to have a larger specific surface area and highly dispersed palladium nanoparticles, which exhibited excellent catalytic activity in the catalytic reduction of p-nitrophenol. In this work, the cellulose carbon-based microspheres palladium (Pd@CCM) catalysts were designed and characterized by SEM, TEM, EDS, XRD, FTIR, XPS, TGA, BET, and so on. Furthermore, the catalytic performance of Pd@CCM catalysts was investigated via p-nitrophenol reduction, which showed high catalytic activity. This catalyst also exhibited excellent catalytic performance in the Suzuki-Miyaura coupling reaction. Linking aromatic monomer and benzene through Suzuki-Miyaura coupling was presented as an effective route to obtaining biaryls, and the synthesis method is low-cost and simple. In addition, Pd@CCM showed desirable recyclability while maintaining its catalytic activity even after five recycles. This work is highly suggestive of the design and application of the heterogeneous catalyst.

Precise molecular sieving using metal‐doped ultramicroporous carbon membranes for H2 separation

AbstractBlue hydrogen produced from fossil fuels is recognized as a promising large‐scale technology for realizing the hydrogen economy. Membrane‐based separation is emerging as a viable alternative to traditional hydrogen purification technologies. Here, we present a facile strategy for fabricating carbon molecular sieve (CMS) hollow fiber membranes containing uniformly dispersed palladium (Pd) nanoparticles. The Pd nanoparticles, anchored in the carbon strands of CMS membranes, induced the carbon matrix toward a more ordered structure arrangement through a synergistic effect of entropy‐driven size exclusion and acceleration of graphitization. As a result, the doped Pd nanoparticles facilitated the formation of ultramicropores <3.3 Å in the CMS membranes, which enabled a precise molecular sieving ability between H2 and CO2 with H2/CO2 selectivity up to 247. Furthermore, the membrane presented good mixed gas separation performances and was stable for over 250 h under simulated harsh industrial conditions.

Highly dispersed palladium nanoparticles decorated on nitrogen doped graphene for enhanced photoelectrochemical water splitting

Among various clear energy generation processes, electrocatalytic water splitting or hydrogen evolution reaction (HER) has been considered as an efficient method for the sustainable production of hydrogen (H2) fuel. But, significant efforts are still required to develop cheap, effective and stable electrocatalysts for water splitting to achieve the economical production of H2. In the quest of finding cheap electrocatalysts, herein, we demonstrate the preparation of palladium (Pd) nanoparticles decorated nitrogen (N) doped highly reduced graphene oxide (NDG-Pd) based electrocatalysts. The nitrogen (N) doped highly reduced graphene oxide (NDG) was produced by using graphene oxide as precursor, which was reduced and doped with nitrogen, simultaneously in one-step hydrothermal method. Subsequently, Pd nanoparticles were decorated on the surface of NDG using a facile ultrasonic method to produce NDG-Pd. In order to restrict the amount of precious metal to reduce the cost of catalysts, very small percentage of Pd, such as, 1 and 3 % was utilized during the preparation of electrocatalysts. The as-prepared electrocatalysts were successfully characterized by using different methods such as, XRD, XPS, EDX, BET, SEM and TEM. Results confirmed the formation of slightly agglomerated, smaller size of Pd NPs on the surface of NDG with an average particle size of ∼ 6 nm. The as prepared nanocomposites NDG, NDG-Pd1% and NDG-Pd3% were used to prepare electrodes and their electrocatalytic activity was evaluated towards the production of H2 through water splitting. The results of electrochemical performance of as-prepared electrodes within the voltage range have revealed that among different samples prepared, the NDG did not show any current, whereas NDG-Pd3% showed a good potential for HER with current density ≈24 mA/cm2 at very low potential i.e. −0.2 V vs RHE.

Fabrication and Characterization of an Electrochemical Platform for Formaldehyde Oxidation, Based on Glassy Carbon Modified with Multi-Walled Carbon Nanotubes and Electrochemically Generated Palladium Nanoparticles.

This study outlines the fabrication process of an electrochemical platform utilizing glassy carbon electrode (GCE) modified with multi-walled carbon nanotubes (MWCNTs) and palladium nanoparticles (PdNPs). The MWCNTs were applied on the GCE surface using the drop-casting method and PdNPs were produced electrochemically by a potentiostatic method employing various programmed charges from an ammonium tetrachloropalladate(II) solution. The resulting GCEs modified with MWCNTs and PdNPs underwent comprehensive characterization for topographical and morphological attributes, utilizing atomic force microscopy and scanning electron microscopy along with energy-dispersive X-ray spectrometry. Electrochemical assessment of the GCE/MWCNTs/PdNPs involved cyclic voltammetry (CV) and electrochemical impedance spectroscopy conducted in perchloric acid solution. The findings revealed even dispersion of PdNPs, and depending on the electrodeposition parameters, PdNPs were produced within four size ranges, i.e., 10-30 nm, 20-40 nm, 50-60 nm, and 70-90 nm. Additionally, the electrocatalytic activity toward formaldehyde oxidation was assessed through CV. It was observed that an increase in the size of the PdNPs corresponded to enhanced catalytic activity in the formaldehyde oxidation reaction on the GCE/MWCNTs/PdNPs. Furthermore, satisfactory long-term stability over a period of 42 days was noticed for the GCE/MWCNTs/PDNPs(100) material which demonstrated the best electrocatalytic properties in the electrooxidation reaction of formaldehyde.

Mesoporous Silica (MCM-41) Containing Dispersed Palladium Nanoparticles as Catalyst for Dehydrogenation, Methanolysis, and ReductionReactions.

: Generating highly dispersed metal NPs of the desired size on surfaces such as porous silica is challenging due to wettability issues. Here, we report highly active and well-dispersed Pd incorporated mesoporous MCM-41 (Pd@MCM) using a facile impregnation via a molecular approach based on hydrogen bonding interaction of a palladium β-diketone complex with surface silanol groups of mesoporous silica. Controlled thermal treatment of so obtained materials in air, argon, and hydrogen provided the catalysts characterized by electron microscopy, nitrogen physisorption, X-ray diffraction and spectroscopy. Gratifyingly, our catalyst provided the lowest ever activation energy (14.3 kJ/mol) reported in literature for dehydrogenation of NaBH4. Moreover, the rate constant (7 × 10-3 s-1) for the reduction of 4-nitrophenol outperformed the activity of commercial Pd/C (4 × 10-3 s-1) and Pd/Al2O3 (5 × 10-3 s-1) catalysts.

Highly active SiO2-supported palladium nanoparticles prepared by a modified ammonia evaporation method for lean methane oxidation

By optimizing the ammonia evaporation (AE) method, highly active palladium nanoparticles were successfully deposited on fumed silica (f-SiO2) and exhibited excellent catalytic activity for the catalytic combustion of methane (CCM). It was manifested that the timing of ammonia introduction was of great importance in determining the particle sizes and electronic states of palladium nanoparticles, the desilication degree of SiO2 support material, and the redox properties and methane affinity of the Pd/f-SiO2-AE catalysts. The optimal Pd/f-SiO2-AE-2 catalyst, which converted 90% of lean methane at 333 °C at GHSV of 30,000 h − 1, performed better than its AE-1- and IM-prepared counterparts. In combination with complementary characterizations, DFT calculations and designed experiments, it was revealed that the uniformly dispersed palladium nanoparticles endowed the Pd/f-SiO2-AE-2 catalyst with more accessible sites. Moreover, the presence of Pd4+ species effectively promoted the methane adsorption capacity of the main active PdO phase, which was another critical reason for the outstanding performance. In addition, the necessity of the ammonia evaporation step was also elucidated by designed experiments. More importantly, taking the universality of this optimized AE method into consideration, our work thus put forward an effective and simple procedure to fabricate highly-active palladium nanoparticles for catalyst designers.

Highly dispersed palladium nanoparticles anchored on polyethylenimine-modified carbon nanotubes for dehydrogenation of formic acid

Formic acid has been recognized as an excellent liquid hydrogen storage material. The development of catalysts with high performance for the dehydrogenation of formic acid is significant. Herein, we employed polyethylenimine-modified carbon nanotubes as a carrier for Pd nanoparticles to synthesize a novel catalyst by a wet chemical reduction method. It was found that the amino polymers on polyethylenimine-modified carbon nanotubes have great effects on reducing the size of Pd nanoparticles, changing the electronic state of Pd, and enhancing the hydrophilicity of catalyst. Therefore, the as-synthesized Pd/CNTs-A-PEI1800 catalyst showed superior activity for FA dehydrogenation in the absence of additives with an initial TOF value of 1506 h−1 and a 100% selectivity of hydrogen.

Highly dispersed palladium nanoparticles supported on an imidazolium-based ionic liquid polymer: an efficient catalyst for oxidation of alcohols

Highly dispersed palladium nanoparticles supported on an imidazolium-based ionic liquid polymer: an efficient catalyst for oxidation of alcohols

Highly dispersed palladium nanoparticles supported on graphitic carbon nitride for selective hydrogenation of nitro compounds and Ullmann coupling reaction

High catalytic activity and superior stability are important criterion for the utilization of a noble metal‐based nano‐composite catalyst. Herein, we report a facile synthesis of highly dispersed palladium nanoparticles embedded on graphitic carbon nitride (Pd@CNx) by ultrasound assisted method without aid of any external reducing agent. The Pd@CNx composite was well characterized by different techniques. This Pd@CNx shows effective catalytic activity towards easy dehydrogenation of sodium borohydride (NaBH4) and ammonia borane in aqueous medium and also can easily hydrogenate 4‐nitrophenol to 4‐aminophenol with fast kinetics. The catalyst is highly selective towards nitro groups in presence of other reducible groups with good stability. Furthermore, the catalyst exhibits superior catalytic activity towards Ullmann coupling reaction of different aryl halides with broad range of substrates scope with easy recovery of the catalyst and notable recycling property.

Solvent‐Induced Flower‐ and Cudgel‐Shaped Porous Organic Polymers: Effective Supports of Palladium Nanoparticles for Dehalogenation in Net Water

AbstractDehalogenation of aromatic halides is one of the most important reactions for detoxification of water ecosystems; at the same time the ability is inevitably tied to the dispersibility of catalyst in aqueous medium. Herein, we present aporous organic polymers containing hydrophilic urea groups (UPOPs) for effective immobilization of palladium nanoparticles (NPs) through a facile urea‐forming condensation reaction. The urea groups not only serve as an intriguing linkage of organic framework, but also endows Pd@UPOPs outstanding dispersibility in H2O. The morphology of UPOPs have exerted important influence upon the size and dispersion of palladium NPs as well as their catalytic performances. The palladium NPs are well dispersed on the surface of UPOP‐1 with an average size of 2.1±0.3 nm. In contrast, palladium NPs on UPOP‐2 exhibit a dual size distribution with an average diameter of 2.0±0.4 and 4.2±0.4 nm. The dehalogenation reactions of chlorobenzene have demonstrated that Pd@UPOP‐1 with flower‐shaped morphology show higher catalytic activity, recyclability and stability than that of Pd@UPOP‐2 with cudgel‐shaped morphology. This work offers/supplies a new insight for the development of efficient catalytic systems based on porous organic polymers supported metal NPs in aqueous medium.

Interfacing with Fe-N-C Sites Boosts the Formic Acid Dehydrogenation of Palladium Nanoparticles.

Hierarchical micro-/mesoporous carbons with abundant Fe-N-C sites were prepared through one-step carbonization of a metal-organic framework (MOF) with sodium iron ethylenediaminetetraacetic acid [NaFe(III)EDTA], which can facilitate the nucleation and growth of ultrafine (∼1.4 nm) and highly dispersed palladium nanoparticles (Pd NPs). Interfacing Pd NPs with Fe-N-C sites has been demonstrated for the first time to boost the heterogeneous catalysis of hydrogen production from formic acid, affording an ultrahigh turnover frequency (TOF) value of 7361 h-1 at 323 K. The robust synergistic interactions between Pd NPs and Fe-N-C sites together with the small size effects of Pd NPs are responsible for the enhanced catalytic activity.

Palladium nanoparticles encapsulated in polyimide nanofibers: An efficient and recyclable catalyst for coupling reaction

In this study, palladium‐encapsulated poly(amic acid) (Pd@PAA) nanofibers were prepared by electrospinning, followed by thermal imidization to synthesize palladium‐encapsulated polyimide (Pd@PI) nanofibers. Scanning electron microscopy (SEM) images confirmed the preparation of uniform and smooth Pd@PAA and Pd@PI nanofibers. Thermogravimetric analysis (TGA) results reveal that the Pd@PI nanofibers possessed excellent thermal stability. The dispersion of palladium nanoparticles in the polyimide nanofibers was characterized by transmission electron microscopy (TEM) and X‐ray diffraction (XRD). The catalysis results show that this Pd@PI fibrous catalyst was very efficient to catalyze the cross‐coupling reactions of aromatic iodides with n‐butyl acrylate (Heck reaction) or phenylboronic acid derivatives (Suzuki reaction) to afford the desired products in good to excellent yields. Moreover, the Pd@PI catalyst could be easily separated and recovered from the reaction mixture by simple filtration due to the regular fibrous structure and reused for 10 times for both Heck and Suzuki reactions without obvious loss of its initial catalytic activity. Thus, the Pd@PI nanofiber catalyst holds great potential in chemical industry in terms of its excellent catalytic activity and stability.

A comparative study of catalytic activity on iron‐based carbon nanostructured catalysts with Pd loading: Using the Box–Behnken design (BBD) method in the Suzuki–Miyaura coupling

AbstractHighly dispersed palladium nanoparticles immobilized on surface‐modified Fe3O4 NPs and magnetic carbon nanostructures (CNSs; carbon nanotubes/graphene oxide) were synthesized and applied as a recyclable and reusable nanocatalyst to achieve palladium (II)‐catalyzed Suzuki–Miyaura reaction of arylboronic acid with aryl bromides. Carbon nanostructures with immobilized hydantoin (PH)‐Pd complex display excellent stability, including a high performance at low catalyst loading. Magnetic separation prevents catalyst centrifuge or filtration and also contributes to practical techniques for recovery. Next, a response surface method based on a three‐level Box–Behnken design was used, which involved three factors: catalyst loading, reaction time, and solvent. The Box–Behnken method was advantageous to parameters optimization for obtaining a yield, with high efficiency and accuracy. As a result of catalytic tests, the TONs and TOFs were calculated from all coupling reactions. The prepared nano‐magnetic catalysts, after the catalysis reaction, can be easily recovered through the magnetic field. Evaluated catalytic performance indicates that these types of catalysts can function as effective recyclable catalysts at least five times without losing the initial level of catalytic activity.

In-situ one-step deposition of highly dispersed palladium nanoparticles into zirconium metal–organic framework for selective hydrogenation of furfural

• Pd nanoparticles are deposited on SBUs of UiO-66 by an in-situ method. • UiO-66-Pd catalyst is active in the furfural hydrogenation in liquid phase. • The UiO-66-Pd shows 71% furfural conversion and 94% furfuryl alcohol selectivity. • In comparison to two-step method, UiO-66-Pd demonstrates higher activity (17%). Palladium nanoparticles highly dispersed into UiO-66 as an efficient and selective hydrogenation catalyst is synthesized by a one-step in-situ method of incorporation of the Pd centers on the secondary building units (SBUs) of UiO-66 as the support and compared to a two-step method. Using DMF as both a solvent and a reducing agent, HCl as an enhancer of the terminal OH groups on Zr-clusters by linker elimination, and a temperature profile result in the incorporation of Pd precursor at lower temperatures and generation of Pd nanoparticles at higher temperatures. The catalysts were characterized by BET surface area measurement, SEM, XRD, HR-TEM, XPS, H 2 -TPR, and CO pulse chemisorption methods. The regulation of the temperature and time in the one-step method results in the formation of Pd nanoparticles embedded in the MOF with a higher dispersion and accessibility in comparison to the two-step method. An automated high-pressure semicontinuous setup was used for the furfural hydrogenation. The 1 wt% Pd on UiO-66 exhibits a high conversion of 71% and selectivity of 94% for hydrogenation of furfural to furfuryl alcohol in the liquid phase at 20 bar H 2 , 110 ˚C and 4 h reaction. The catalyst was used repeatedly without significant deactivation.

Highly Dispersed Palladium Nanoparticles on Silica Spheres for Photocatalytic Hydrodeoxygenation of Vanillin

Highly Dispersed Palladium Nanoparticles on Silica Spheres for Photocatalytic Hydrodeoxygenation of Vanillin

"PALLADIUM ON COAL" CATALYST OBTAINED BY PYROLYSIS OF POWDER CELLULOSE GRANULES IM-PREGNATED WITH PALLADIUM NITRATE

By pyrolysis of powdered cellulose granules impregnated with palladium nitrate, catalysts of 1–8% Pd / C were obtained. Pyrolysis was carried out in a reactor with a water seal at 600 ° C. Metal reduction was carried out with pyrolysis gases and matrix carbon. It was found that the ash content of powdered cellulose granules is ~ 40 times less than the ash content of sulfate cellulose, from which they were made. It was shown by X-ray phase analysis and electron microscopy that palladium in the catalysts is present in the form of Pd (0) nanoparticles uniformly covering carbon fibers and shapeless massive metal precipitates up to 20 μm in diameter. In catalysts 1–3% Pd / С, nanoparticles 10–40 nm dominate (> 95%), in 8% Pd / С, 20–70 nm. The share of massive metal formations in Pd (1%) / C, Pd (3%) / C and Pd (8%) / C is: ~ 2%, ~ 5% and ~ 60%, respectively. They consist of aggregated spherical particles 0.05–0.15 µm in diameter. XRD palladium oxide was not detected in the catalysts. The presence of palladium nitrate in powdered cellulose during its carbonization has a significant effect on the formation of the carbon matrix. With an increase in the content of palladium nitrate in powdered cellulose, the yield of carbon material decreases and its total porosity increases. Infrared spectroscopy revealed the presence of oxygen-containing ether groups in the carbon matrix of palladium catalysts. The activity of catalysts in the model process of decomposition of hydrogen peroxide increases with increasing dispersion of palladium nanoparticles.

Synthesis of Highly Dispersed Palladium Nanoparticles Supported on Silica for Catalytic Combustion of Methane

Palladium nanoparticles supported on silica catalysts (Pd/SiO2) were prepared by wet impregnation (WI), dry impregnation (DI), strong electrostatic adsorption (SEA), and charge-enhanced dry impregn...

Pd Catalysts Supported on Bamboo-Like Nitrogen-Doped Carbon Nanotubes for Hydrogen Production

Bamboo-like nitrogen-doped carbon nanotubes (N-CNTs) were used to synthesize supported palladium catalysts (0.2–2 wt.%) for hydrogen production via gas phase formic acid decomposition. The beneficial role of nitrogen centers of N-CNTs in the formation of active isolated palladium ions and dispersed palladium nanoparticles was demonstrated. It was shown that although the surface layers of N-CNTs are enriched with graphitic nitrogen, palladium first interacts with accessible pyridinic centers of N-CNTs to form stable isolated palladium ions. The activity of Pd/N-CNTs catalysts is determined by the ionic capacity of N-CNTs and dispersion of metallic nanoparticles stabilized on the nitrogen centers. The maximum activity was observed for the 0.2% Pd/N-CNTs catalyst consisting of isolated palladium ions. A ten-fold increase in the concentration of supported palladium increased the contribution of metallic nanoparticles with a mean size of 1.3 nm and decreased the reaction rate by only a factor of 1.4.

Fast improved polyol method for synthesis of Pd/C catalyst with high performance toward ethanol electrooxidation

Highly dispersed palladium nanoparticles that are successfully decorated on the charcoal activated carbon by a rapid and simple improved polyol method in Ethylene Glycol (EG) media in the presence of ethanolic sodium hydroxide, without any protection by capping agent, is proposed for the first time in this paper. Along this process, H2PdCl4 in ethylene glycol media can be reduced to metallic palladium at 40°C in the presence of alcoholic sodium hydroxide. Therefore, it can be claimed that ethanolic sodium hydroxide is behaving like a mild reducing agent in the EG media. Pd/C catalysts are also synthesized using improved and traditional methods for comparison. Catalysts synthesized in two different ways were characterized by Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The results illustrated that Pd/C synthesized using the improved polyol method had better dispersity and its diameter was equal to 8–10 nm which was lower compared to the conventional polyol method. The electrocatalytic performance of both Pd/C catalysts synthesized by two methods was investigated by cyclic voltammetry and chronoamperometry in the solution of 1.0 M EtOH +1.0 M NaOH at room temperature. The results showed that the Pd/C catalyst synthesized by the improved method had a significantly enhanced the activity and durability for Ethanol Oxidation Reaction (EOR) that can be related to the good dispersity of Palladium nanoparticles over support due to the improved polyol method.

One-step fabrication of a highly dispersed palladium nanoparticle-decorated reduced graphene oxide electrocatalyst for methanol electro-oxidation in acidic media

Reduced graphene oxide (RGO) was successfully decorated with homogeneous highly dispersed palladium nanoparticles (PdNPs) by a novel single-step hydrothermal-assisted formic acid reduction reaction without the use of any surfactants. The structure, surface morphology, and elemental composition of the as-prepared PdNP-RGO electrocatalyst were extensively characterized. The PdNP-RGO electrocatalyst demonstrated outstanding electrocatalytic activity (8.65 mA/cm2) toward the methanol oxidation reaction (MOR) in an acidic medium that is 1.4 times higher than PdNP-decorated Vulcan XC72 (6.2 mA/cm2) and also comparable with that of Pd-based electrocatalysts in alkaline media from the previous reports. Furthermore, the as-prepared PdNP-RGO electrocatalyst also shows remarkable stability performance for the MOR in an acidic medium and thus offer new insights into the processing method of an outstanding electrocatalyst at the anode electrode in the direct methanol fuel cell with reasonable cost, clean and facile synthesis approach.