Carbon-supported Pd Nanoparticles Research Articles

N, O Co‐Doping Enhanced Adsorption of Chloramphenicol for Highly Efficient and Robust Electrocatalytic Hydrodechlorination

Comprehensive SummaryElectrocatalysis technology can effectively promote the hydrodechlorination of chloramphenicol (CAP) to reduce the bio‐toxicity. However, there are still some challenges such as low degradation rate and poor stability. Here, we prepared porous N, O co‐doped carbon supported Pd nanoparticles composites (Pd NPs/NO‐C) for electrocatalytic degradation of CAP. The doping of N and O not only effectively enhanced the interaction between substrate and CAP, promoting the mass transfer process, but also enhanced the anchoring effect on Pd nanoparticles, avoiding the occurrence of aggregation. The prepared composites achieved removal efficiency of CAP over 99% within 1 h, and the rate constant was as high as 6.72 h–1, outperforming previous reported electrocatalysts. Additionally, Pd NPs/NO‐C composites showed a wide range of pH tolerance, excellent ion interference resistance and long‐term stability. Our work unravels the importance of mass transfer processes in solution to electrocatalytic hydrodechlorination and provides new research ideas for catalysts design.

Construction of MOF-5 derived ZnO composites porous carbon supported Pd nanoparticles as highly stable catalyst for methanol and ethanol oxidation

The preparation of highly active and stable Pd-based catalysts for direct alcohol fuel cells (DAFC) is hampered by inefficient utilization of the active sites, susceptibility to CO poisoning, poor stability, and relatively slow reaction kinetics. Herein, the stability and anti-toxicity of the catalysts (Pd/ZnO/MDC) are tuned by loading Pd nanoparticles on the carbon-coated ZnO support, achieving efficient electrocatalysis for methanol and ethanol oxidation reaction (MOR and EOR). TEM result shows the ZnO is covered by the carbon layer formed outside of MOF-5 derived porous carbon, which can prevent it from dissolving under harsh conditions. The mass activities of the well-tuned catalyst Pd/ZnO/MDC(800) for MOR and EOR are 931.83 mA/mg and 1838.30 mA/mg, respectively. It is due to the improved electron transport efficiency between the Pd and ZnO, and the enhanced stability by carbon layer outside the ZnO. It is also found that the onset potential and the peak potential of Pd/ZnO/MDC(800) (−0.813 V, −0.228 V) in CO stripping experiment in MOR are more negative than Pd/MDC(800) (−0.261 V, −0.215 V). This result indicates that the existence of ZnO helps to provide surface hydroxyl group, which promotes the oxidation of the intermediates. This work indicates provides a feasible idea for DAFC catalyst design and construction.

Spectroscopy vs. Electrochemistry: Catalyst Layer Thickness Effects on Operando/In Situ Measurements.

In recent years, operando/in situ X-ray absorption spectroscopy (XAS) has become an important tool in the electrocatalysis community. However, the high catalyst loadings often required to acquire XA-spectra with a satisfactory signal-to-noise ratio frequently imply the use of thick catalyst layers (CLs) with large ion- and mass-transport limitations. To shed light on the impact of this variable on the spectro-electrochemical results, in this study we investigate Pd-hydride formation in carbon-supported Pd-nanoparticles (Pd/C) and an unsupported Pd-aerogel with similar Pd surface areas but drastically different morphologies and electrode packing densities. Our in situ XAS and rotating disk electrode (RDE) measurements with different loadings unveil that the CL-thickness largely determines the hydride formation trends inferred from spectro-electrochemical experiments, therewith calling for the minimization of the CL-thickness in such experiments and the use of complementary thin-film control measurements.

Highly efficient hydrogen evolution from formic acid using B, N co-doped carbon-supported Pd nanoparticles

A facile novel B, N co-doped carbon was fabricated by high-temperature pyrolysis of a mixture of ethylenediamine tetraacetic acid disodium salt and boric acid, on which Pd nanoparticles were loaded to synthesize highly efficient Pd/BNC catalyst for dehydrogenation of formic acid. The type and content of N are regulated by the doping of B elements in carbon materials. The high content of N and B doping provides more anchor sites for Pd and strengthens the interaction between the support and Pd nanoparticles, thus forming highly dispersed Pd nanoparticles and regulating the electronic property of Pd. Therefore, the obtained Pd/BNC catalyst displayed enhanced performance (TOF = 2760 h−1) and a lower activation barrier (31.84 kJ/mol). Furthermore, the catalyst also exhibited wonderful cycling stability for hydrogen evolution from formic acid.

Efficient Ullmann and Suzuki-Miyaura cross-coupling reactions catalyzed by heterogeneous Pd-porous carbon beads catalysts in aqueous media

Carbon-carbon coupling reactions are of great interest for a wide range of applications including pharmaceutical compounds and biologically active molecules. Usually, coupling reactions were performed using a homogeneous catalyst and organic solvent. Thus, the use of greener solvents as well as the heterogenization of the classical metal-based catalyst are desirable and still under development. This contribution describes the synthesis of biaryl compounds in water by Ullmann and Suzuki reactions with carbon-supported Pd nanoparticles. As expected, the microwave activation method drastically decrease the reaction time. The utilization of trioctylphosphine (TOP) or triphenylphosphine (TPP) ligands slow down the Pd leaching without cancelling it compared to the unliganded Pd catalyst. Moreover, a treatment with H2O2 appears beneficial with respect to a thermal-oxidative treatment at 1500 °C due to higher hydrophilicity of the resultant carbon support. These results and methodology contribute to a greener future for C–C coupling reactions.

Fast charge separation and transfer strategy in polymeric carbon nitride for efficient photocatalytic H2 evolution: Coupling surface Schottky junctions and interlayer charge transfer channels

Reinforcing the charge separation and transfer in layered polymeric carbon nitride (PCN) is the key issue to enhance its photocatalytic activity but still remains very challenging. Herein, for the first time, the synergetic Pd single atoms (PdSAs) and carbon-supported Pd nanoparticles (NPs) are introduced into the interlayer and surface of layered PCN respectively to address this challenge. The PdSAs are in intimate contact with the adjacent PCN layers and serve as interlayer charge transfer channels, while the carbon-supported Pd NPs contribute to multistep PCN-carbon-Pd NPs Schottky junctions on PCN surface. Experiments and theoretical calculations demonstrate that such unique architectures provide intrinsic driving force to extract the electrons from PCN to outermost Pd NPs with high migration rate via vertical PdSAs channels. This directional charge transfer in PCN greatly expedite the separation of charge carriers in both inner and surface of PCN and simultaneously yield electron-rich Pd NPs active sites with optimized H2 adsorption energy, thus leading to improved intrinsic H2 evolution reaction kinetics. Consequently, the Pd/PCN2 performs ultrahigh photocatalytic H2 evolution rate of 83.34 mmol g−1 h−1 in the dispersed particulate system and 100.4 mmol h−1 m−2 in the film form under simulated sunlight. This work provides a new promising approach to engineer the spatial charge transfer behaviors for high-performance PCN-based photocatalysts.

Bio-inspired N self-doped 3D macroporous carbon supported Pd nanoparticles as an efficient catalyst for selective hydrogenation of 1, 3-butadiene

BackgroundThe selective hydrogenation of 1, 3-butadiene values in industrial application and scientific research, and Pd catalysts are widely used in this reaction. However, it is still a challenge to achieve high butenes selectivity at a high conversion rate. MethodsHere we report the N self-doped 3D macroporous pollen-like carbon (pollen-C) derived from the biomass of rape pollen to achieve higher butenes selectivity at high conversion rates after Pd loading. Significant findingsExperimental results reveal that the properties of pollen-C, especially the content and type of N doping, will influence the particle size and the valence of the supported Pd, thereby affecting the catalytic performance. As a result of more N dopant and unique macroporous structure, the Pd/pollen-C-500 showed better butenes selectivity of 95% at 80 °C than Pd/commercial activated carbon (Pd/AC).

Significant Promotion of Carboxyl Groups in Palladium Nanoparticles-Supported Biomass Carbon Catalysts for Efficient Low-Temperature Hydrodeoxygenation of Lignin Derivatives in Water

Selective and efficient low-temperature hydrodeoxygenation (HDO) of lignin derivatives in water for the production of valuable biofuel and chemicals is still challenging. Herein, we reported biomass carbon-supported ultrafine Pd nanoparticles as highly active and stable catalysts for low-temperature HDO of vanillin (a typical lignin-derived compound) to 2-methoxy-4-methylphenol (MMP). We found that the abundant carboxyl groups on the resultant catalyst greatly accelerated the conversion of the generated intermediate (vanillyl alcohol, VAL), and then, the synergistic catalysis between carboxyl groups and Pd nanoparticles promoted the efficient production MMP through a free-radical pathway. Other lignin derivatives with different functional groups were also efficiently converted to the corresponding products over the prepared catalyst. This work may provide a new idea for designing a biomass-derived catalyst for efficient transformation of various lignin derivatives to produce value-added biofuels and chemicals.

Porous chitosan-derived activated N-doped carbon-supported Pd nanoparticles encaged in Al, Fe pillared montmorillonite as novel heterogeneous catalysts

Novel pillared montmorillonite encaging porous chitosan derived activated N-doped carbon-supported Pd nanoparticles catalyst (Pd@Al, Fe-Mt/N-C) was synthesized by ion-exchange of the chitosan/Pd precursors into the layered-nanospaces of Al, Fe-pillared montmorillonite and subsequent confinement carbonization. N2 adsorption-desorption study indicated that the resulting nanocomposites have rich mesoporous structures. Effective encagement and in-situ reduction of Pd species led to a decrease in surface area and N2 adsorption, respectively. TEM images of the prepared Pd@Al, Fe-Mt/N-C showed that most of the Pd species with a size of 1–3 nm were well dispersed in the interlayer spaces of the pillared montmorillonite. The catalysts showed high catalytic efficiency for the Sonogashira reactions of aryl iodides or bromides with terminal aryl alkynes, and can be recycled 20 runs with no significant loss of activities. The unique encagement of the porous carbon-supported metal catalysts in the layered nanospaces of pillared montmorillonite was further elucidated by the positron annihilation spectroscopy analysis and other structural characterization methods. This layered-nanospace confinement strategy achieves a perfect combination of the advantages of activated carbon and montmorillonite as metal nanoparticle carrier.

Mesoporous Carbon-Supported Pd Nanoparticles in the Metallic State-Catalyzed Acylation of Amides with Aryl Esters via C-O Activation.

Carbon, an abundant, inexpensive, and nonmetallic material, is an inimitable support in heterogeneous catalysis, and variable carbonaceous materials have been utilized to support metal nanoparticle catalysts. We developed an efficient and stable heterogeneous catalyst with highly dispersed metallic palladium nanoparticles embedded in an ordered pore channel of mesoporous carbon and first applied the catalyst to construct imides from amides using aryl esters as an acylation reagent via C–O activation. The catalyst represents excellent catalytic performance and could be reused and recycled five times without any significant decrease in activity. The heterogeneous nature of metallic state palladium was proven to be the active center in the acylation reaction.

N-functionalized mesoporous carbon supported Pd nanoparticles as highly active nanocatalyst for Suzuki-Miyaura reaction, reduction of 4-nitrophenol and hydrodechlorination of chlorobenzene

A series of nanocatalysts derived from immobilization of palladium nanoparticles (Pd NPs) into three dimensional (3D) tube-type architecture of nitrogen (N) functionalized and without functionalized mesoporous carbon CMK-9 is developed by dual agents chemical reduction approach. Herein, for the first time N-functionalized CMK-9 is explored as supports to immobilize Pd NPs and use as multifunctional catalysts for Suzuki-Miyaura cross-coupling reaction, reduction of 4-nitrophenol and hydrodechlorination of chlorobenzene. The Pd@N-CMK-9 catalysts show excellent activities with 100% conversion for Suzuki-Miyaura reaction between iodobenzene and phenylboronic acid and turnover frequency up to 1992 h−1. When use as catalyst for reduction of 4-nitrophenol to 4-aminophenol, it delivers an outstanding rate constant of 4.22 × 10-2 s−1 with activity parameter of 51719 s-1g−1 with respect to only Pd content. The nanocatalysts also demonstrate 100% conversion of chlorobenzene to benzene within 1 h. In addition, the catalyst exhibits remarkable catalytic stability for several cycles without any significant loss of products. The excellent catalytic activities can be attributed to synergistic effect of uniformly dispersed Pd NPs, favorable interaction between metal and support, and tubular interconnected mesoporous framework of N-functionalized CMK-9 that accelerate mass transportation. The present work signifies the versatility of Pd@N-CMK-9 nanocatalysts for various catalytic reactions.

Pd–Co nanoparticles decorated on different carbon based substrates as electrocatalyst for O2 reduction reaction

In this study, a facile process for the synthesis of bimetallic Pd–Co nanotubes on multi-walled carbon nanotubes (MWCNTs) and chemically reduced graphene oxide (rGO) is reported. The synthesized nanocatalysts are characterized by field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX). Catalysts are evaluated for the oxygen reduction reaction (ORR) in basic media. The electrocatalytic performance of Pd–Co supported on rGO and MWCNTs toward ORR is compared with bimetallic and single Pd nanoparticles decorated on Vulcan carbon (XC-72R) by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and rotating disk electrode (RDE) in 0.1 M NaOH solution. The specific electrochemical surface areas of Pd–Co supported on rGO is higher than the corresponding carbon-supported Pd nanoparticles (222.09 vs. 41.57 m2 g−1, respectively). The RDE results confirm that the final product of the oxygen reduction is water and the proposed main path is direct 4 electron transfer process with smooth transfer kinetic rate on the Pd–Co/rGO in comparison to Pd–Co/C. Furthermore, the lower charge transfer resistance of the particles in ORR process for the Pd–Co/rGO compared to single Pd/C catalyst, indicating it could be excellent candidate for ORR in alkaline media.

How Nitrogen Doping Affects Hydrogen Spillover on Carbon-Supported Pd Nanoparticles: New Insights from DFT

The process of hydrogen spillover on metal nanoparticle decorated carbon surfaces has been discussed for many years due to its importance for heterogeneous catalysis and hydrogen storage. The present density functional theory (DFT) study supports recent experimental observations of the hydrogen spillover process. By use of model systems of carbon-supported palladium nanoparticles, the details of hydrogen spillover are investigated and the effects of nitrogen doping on such processes are elucidated. It is found that graphitic nitrogen atoms and water molecules significantly facilitate the hydrogen spillover reaction and serve as anchoring sites for the spillover hydrogen atoms.

Lignin-derived hierarchical porous carbon supported Pd nanoparticles as an efficient electrocatalyst for ethanol oxidation

Herein, lignin derived hierarchical porous carbon (LHPC) supported Pd nanoparticles (Pd/LHPC) were synthesized and developed as advanced electrocatalysts for ethanol oxidation. In the Pd/LHPC, the special hierarchical porous carbon with the interconnected micropores and mesopores uniformly distribute on the surface and walls of macropores can provide facile transport for electroactive species and more reaction available surface. The Pd/LHPC exhibits larger specific electrochemically active surface area, higher electrocatalytic activity and better stability toward the oxidation of ethanol than the black carbon (Vulcan XC-72) supported Pd (Pd/XC-72) and commercial Pd/C electrocatalysts. The strategy reported will open a new road to effectively use industrial waste to synthesize advanced carbon material for efficient electrocatalysts and other electrochemical energy-conversion devices.

Nanostructured Pd/Sb2O3: A new and promising fuel cell electrocatalyst and non-enzymatic amperometric sensor for ethanol

Abstract This manuscript describes the synthesis and structural/morphological characterization of Sb2O3 nanostructures modified by Pd nanoparticles and its use as a Fuel Cells electrocatalyst and as non-enzymatic amperometric sensor for ethanol. Interesting Sb2O3 surface modifications due to Pd nanoparticles were observed, such as the loss of spherical shape and the appearance of superficial pores. As an electrocatalyst Pd/Sb2O3 exhibited two times higher catalytic activity at a constant potential than carbon-supported Pd nanoparticles to oxidize ethanol in alkaline media (current densities of 348 μA cm−2 and 165 μA cm−2 at −0.3 V vs. Ag/AgCl 3.0 M, respectively). To the extent of our knowledge this result is the first one describing such an enhancement of the Pd activity only by means of alteration of the support. Moreover, as an amperometric sensor for ethanol, the electrode showed a linear response in a broad range of concentrations with a detection limit of 0.10 μM and sensitivity between of 1.47 to 1.00 μA mM−1 cm−2. The combined findings presented in this work revealed Pd/Sb2O3 can be a promising material for Direct Ethanol Fuel Cells and as a non-enzymatic amperometric sensor for ethanol.

Suppressing the Pd-C interaction through B-doping for highly efficient oxygen reduction

As a potential alternative to commercial Pt/C, carbon supported Pd nanoparticles (NPs) is powerful in facilitating ORR. However, a strong interaction usually existing between Pd and carbon probably hinders the expression of ORR activity. This work focuses on tuning the interaction between Pd and graphene for architecting high-performance ORR catalyst. The strong interaction between Pd and graphene was confirmed, rendering significant microstructural variation, e.g., the dramatic change of lattice disorder and vibration of surface C-H/C-O bond for the graphene support. Boron (B)-doping enables reversing such structural evolution and suppressing the Pd-C interaction. It literates the Pd from the interaction, increases its electrochemical specific surface area (ECSA) from 68 to 125 m2 g−1 and thereof contributes to the highly efficient ORR performance in alkaline solution with more feasible 4e− pathway on a 2.8 wt% Pd/C catalyst. Moreover, theoretical simulations further proved that B-doping enhances the electron transfer between Pd and the graphene support and probably benefits a 4e− pathway for ORR.

Conversion of Biomass-Derived Furanics to Fuel-Range Hydrocarbons: Use of Palm Oil Empty Fruit Bunches

In the search of hydrocarbon fuels derived from biomass, the increase in the chain length with the elimination of oxygenated species is a hard task. The simultaneous conversion of furfural and cyclopentanone to fuel range hydrocarbons has been investigated on a series of solid base catalysts. Furfural represents the family of sugars, typically obtained from the hemicellulose biomass fraction by different catalytic routes. Cyclopentanone can be readily obtained from the catalytic conversion of furfural via Piancatelli ring-rearrangement under reducing conditions. Aimed to enlarge the carbon chain length of these oxygenates, the aldol-condensation reaction between furfural and cyclopenanone was studied over MgAl mixed oxides, among which the MgAl-3 mixed oxide exhibited the best catalytic activity to produce C10–C14 oxygenates, a suitable range for transportation fuel precursors (C7–C15). After this C–C coupling reaction, the large oxygenates were successfully upgraded via hydrodeoxygenation on carbon-supported Ru and Pd nanoparticles to produce a mixture of linear alkanes and saturated cyclic hydrocarbons, which in practice would be direct drop-in components for transportation fuels. As an illustration of the potential implementation of this strategy for biofuel production, palm oil empty fruit bunches were experimentally evaluated using different acid pretreatments to extract the furfural, which was further employed to perform the aldol-condensation reactions. It was found that the proposed catalytic strategy is an environmentally-friendly route to add value to the palm oil industry wastes by producing value-added chemicals and fuel precursors.

Quantitative structural determination of active sites from in situ and operando XANES spectra: From standard ab initio simulations to chemometric and machine learning approaches

• Different theoretical methods in the simulation of the XANES spectra are discussed. • An extended list of available codes for XANES spectra simulation is provided. • The potential of operando XANES in catalysis is described with relevant examples. • Chemometric methods in the treatment of operando XANES spectra is discussed. • Machine learning approaches are used to provide structural determination from XANES. In the last decade the appearance of progressively more sophisticated codes, together with the increased computational capabilities, has made XANES a spectroscopic technique able to quantitatively confirm (or discard) a structural model, thus becoming a new fundamental diagnostic tool in catalysis, where the active species are often diluted metal centers supported on a matrix. After providing a brief historical introduction and the basic insights on the technique, in this review article, we provide a selection of four examples where operando XANES technique has been able to provide capital information on the structure of the active site in catalysts of industrial relevance: (i) Phillips catalyst for ethylene polymerization reaction; (ii) TS-1 catalyst for selective hydrogenation reactions; (iii) carbon supported Pd nanoparticles for hydrogenation reactions; (iv) Cu-CHA zeolite for NH 3 -assisted selective reduction of NO x and for partial oxidation of methane to methanol. The last example testifies how the multivariate curve resolution supported by the alternating least-squares algorithm applied to a high number of XANES spectra collected under operando conditions allows to quantitatively determine different species in mutual transformation. This approach is particularly powerful in the analysis of experiments where a large number of spectra has been collected, typical of time- or space-resolved experiments. Finally, machine learning approaches (both indirect and direct) have been applied to determine, from the XANES spectra, the structure of CO, CO 2 and NO adsorbed on Ni 2+ sites of activated CPO-27-Ni metal-organic framework.

A novel electrochemical cell for operando X-ray absorption measurements at low energies: Probing electrochemically induced electronic changes in palladium

Operando assessment of electronic properties near the Fermi level is essential to gain new insights into the mechanisms of electrochemical reactions as well as for the development of more efficient electrocatalysts. However, the high vacuum ambient needed for X-ray absorption measurements at low energies has made studies under electrochemical conditions quite challenging. Here, we describe an out-of-chamber setup with a new electrochemical cell that allowed us to performed operando X-ray absorption studies at the low energy of the Pd L3 edge. Using the new electrochemical cell, we were able to probe, for the first time, the changes in electronic properties of carbon-supported Pd nanoparticles induced by the electrochemical oxidation of the Pd surface. Our results demonstrate that the oxidation process produces an increase in the Pd 4d band vacancy, which indicates that charge is transferred from the metal to the adsorbed oxygenated species.

Functionalized Silica Facilitated Proton-Coupled Electron Transfer in Electrochemical Reduction of CO2

This work considers composite electrocatalysts including functionalized silica and carbon-supported Pd nanoparticles to facilitate directed proton coupled electron transfer (PCET) CO2 reduction reactions. Results show ligands may improve hydrogenation of CO leading to increased selectivity and yields of CH3OH.