Supported Pd Nanoparticles Research Articles

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.

Nanoscale Pd Supported on Layered Co(OH)2 as Efficient Catalysts for Solvent‐Free Oxidation of Benzyl Alcohol

AbstractIn this work, two‐dimensional (2D) Co(OH)2 nanosheets, with large surface areas and wrinkles are obtained, and used to support Pd nanoparticles (NPs) by simple impregnation method as an efficient catalyst for the oxidation of benzyl alcohol under solvent‐free conditions. The resulting 1 wt.% Pd/Co(OH)2 catalyst exhibits a high turnover frequency value of 57999 h−1. The catalysts were characterized by SEM, TEM, AFM, XRD, BET, XPS and CO‐pulse chemisorption. The results of characterizations reveal that the Pd NPs are highly dispersed on the Co(OH)2 nanosheets. The abundant hydroxyl groups on the surface of Co(OH)2 nanosheets promote the reduction of Pd species, resulting in a higher proportion of Pd0 than that of Pd/AC catalyst, which further facilitates the catalytic performances.

Synthesis of yolk-shell magnetic porous organic nanospheres supported Pd catalyst for oxidation of alcohols and Heck reactions

Yolk-shell magnetic porous organic nanospheres (MPONs) supported Pd nanoparticles (Pd@MPONs) were synthesized by encapsulating Fe3O4 and Pd nanoparticles in one cavity of hollow porous organic nanospheres (HPONs) using a continuous “ship-in-bottle” strategy. The obtained Pd@MPONs possessed a hierarchically micro/mesoporous structure, high surface area (354 m2/g) and displayed excellent magnetic response (9 emu/g). They showed high catalytic performance in the oxidation of alcohols under mild conditions and the Heck-Mizoroki reaction, and brilliant magnetic recyclability, they can be removed rapidly from a reaction system using external magnetic fields without any catalytic activity decrease. Hence, the Pd@MPONs are easily recoverable nanocatalysts which have practical significance in the future sustainable industry.

Dehydrogenation of Formic Acid in Liquid Phase over Pd Nanoparticles Supported on Reduced Graphene Oxide Sheets

Reduced graphene oxide sheets (rGO) were used in this study to support Pd nanoparticles through soil-immobilization and impregnation methods. The catalysts were characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray (EDX), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. These nanocatalysts were used as catalysts for the dehydrogenation of formic acid in liquid phase. The results showed that the Pd/rGO samples synthesised via the sol-immobilisation technique exhibited better catalytic activity (TOF = 910 h−1) than those synthesised by the impregnation technique (TOF = 506 h−1) because of the smaller size of Pd particles and higher Pd exposure of the catalysts synthesised by the first technique. The experimental outcomes showed that the graphene sheets provided remarkable support for Pd nanoparticles.

Electron-Enriched Pd Nanoparticles for Selective Hydrogenation of Halonitrobenzenes to Haloanilines

Selective hydrogenation of halonitrobenzenes into haloanilines represents a green process to replace the environmentally unfriendly non-catalytic chemical reduction process in industry. However, this transformation often suffers from serious dehalogenation due to the easy break of carbon-halogen bonds on metal surfaces. Modulations of the electronic structure of the supported Pd nanoparticles on Lewis-basic layered double hydroxides have been demonstrated to promote catalytic activity and selectivity for hydrogenation of halonitrobenzenes into haloanilines. Mechanism studies suggest that Pd with the enhanced electron density not only improves the capability for hydrogen activation, but also generates the partially negative-charged hydrogen species to suppress the electrophilic attack on the carbon-halogen bond and avoid the dehalogenation.

Ethylene hydrogenation on supported Pd nanoparticles: Influence of support on catalyst activity and deactivation

Palladium based systems are used extensively in a wide range of catalytic hydrogenation reactions. Here, electronic modifications of two amorphous SiO2 thin films are used to influence the properties of supported Pd nanoparticles (≈1 nm). Negative charging of the metal particles leads to destabilization of both, surface and subsurface hydrogen species, whereas positive charging leads to stabilization of both hydrogen species as evidenced by temperature-programmed desorption (TPD) measurements. The impact of this finding for general hydrogenation reactions is illustrated for ethylene hydrogenation at 300 K using a pulsed molecular beam technique, where an increase in turnover frequency (TOF) over one order of magnitude is observed for positively charged particles, compared to negative ones. The difference in hydrogenation TOF can be rationalized by two reasons: (i) increased hydrogen coverage on the metal surface due to stabilization and (ii) reduction in activation barrier for hydrogenation, both caused by metal-support interactions. In addition, the active phase of the metal particles during catalysis is proposed to be influenced by two mechanisms, formation of a carbide phase and a dehydrogenated carbonaceous overlayer on the surface.

Selective hydrogenation of ethyne with highly-dispersed sub-2 nm Pd nanoparticles in a hemicellulosic gel-based microreaction chamber

Ethyne is often an unwanted impurity in ethene streams used in plastics industry. Supported Pd catalysts offer high ethyne conversion, but poor ethene selectivity due to over-hydrogenation which leads to the formation of carbonaceous deposits. In this paper, acrylamide was grafted by free radical polymerization onto bagasse pith hemicellulose (to form HEMI-g-AAMs), which was then used as a porous bio-based carrier of Pd nanoparticles. The obtained Pd/HEMI-g-AAMs catalyst showed an ethyne conversion and ethene selectivity of 100% and 94.70%, respectively, at 100 °C and a space velocity of 70,000 h−1. The nitrogen-rich bio-based support regulated the physicochemical properties and catalytic activity of the supported Pd nanoparticles. Results guide the development of new and improved Pd-based catalysts for the partial catalytic hydrogenation of ethyne to ethene.

Pd nanoparticles supported on amine-functionalized SBA-15 for the selective hydrogenation of phenol

In this paper, a stable Pd/NH2-SBA-15 catalyst was prepared by an ammonia evaporation method using amino-functionalized SBA-15 as support. Pd/NH2-SBA-15 showed excellent catalytic performance in the selective hydrogenation of phenol to produce cyclohexanone. Furthermore, this Pd/NH2-SBA-15 catalyst kept the conversion of phenol and selectivity of cyclohexanone both over 90 % even after 10 runs, much better than Pd/SBA-15 and the previously reported Pd-based catalysts, demonstrating the benefit of amine functionalization on the activity of supported Pd nanoparticles. TEM and XPS results indicate that small Pd particles were highly dispersed on the NH2-SBA-15 support and a stronger interaction occurred between the active Pd particles and the amine functionalized SBA-15 support, which could effectively inhibit the agglomeration of the active Pd particles during the reaction and then improve the stability of this catalyst.

Latent Representation Learning for Structural Characterization of Catalysts.

Supervised machine learning-enabled mapping of the X-ray absorption near edge structure (XANES) spectra to local structural descriptors offers new methods for understanding the structure and function of working nanocatalysts. We briefly summarize a status of XANES analysis approaches by supervised machine learning methods. We present an example of an autoencoder-based, unsupervised machine learning approach for latent representation learning of XANES spectra. This new approach produces a lower-dimensional latent representation, which retains a spectrum-structure relationship that can be eventually mapped to physicochemical properties. The latent space of the autoencoder also provides a pathway to interpret the information content "hidden" in the X-ray absorption coefficient. Our approach (that we named latent space analysis of spectra, or LSAS) is demonstrated for the supported Pd nanoparticle catalyst studied during the formation of Pd hydride. By employing the low-dimensional representation of Pd K-edge XANES, the LSAS method was able to isolate the key factors responsible for the observed spectral changes.

Catalytic reduction of 4-nitrophenol to 4-aminophenol using an efficient Pd nanoparticles

Highly stable catalytically active polyvinyl alcohol supported Pd nanoparticles (Pd NPs) are synthesized and used as catalysts in reduction of 4-nitrophenol in aqueous phase by sodium borohydride as reducing agent. The as—synthesized Pd NPs are characterized with the help of UV—vis. absorption spectroscopy, X—ray diffraction (XRD), transmission electron microscopy (TEM). The TEM and high resolution TEM images reveal that the synthesized Pd NPs are mostly global shaped with mean radius of c.a. 2.1 nm. The progress of the reaction is conveniently monitored by UV—vis. spectroscopy. The rate constant of the pseudo—first—order reaction increases with temperature up to 318 K. The rate constant and the activation energy for the reduction of 4-nitrophenol by using Pd nanoparticles were found as 0.013 s−1 and 14.12 kJ mol−1 respectively at 318 K. The as-prepared Pd NPs are stable, easy to prepare, cost effective and have significant efficiency for reduction of 4—nitrophenol in green protocol.

Easy approach for decorating of poly 4-aminithiophenol with Pd nanoparticles: an efficient electrocatalyst for ethanol oxidation in alkaline media

In this work, a polymer composite based on poly 4-aminothiophenol (p-ATP) is prepared via a facile electrochemical route and is used as an appropriate support for Pd nanoparticles. The morphological studies reveal that a nanofiber structure patterned on the multiwalled carbon nanotubes (MWCNT) structure is obtained for the synthesized catalyst viz. Pd/p-ATP/MWCNT. The Pd/p-ATP/MWCNT catalyst delivers a mass activity of 3245 $$ \mathrm{mA}\ {\mathrm{mg}}_{\mathrm{Pd}}^{-1} $$ manifesting its superb electrocatalytic activity for ethanol oxidation in the alkaline media. The vital role of the polymeric substrate on the electrocatalytic activity of Pd nanoparticles is established by comparing the catalytic performance of Pd/p-ATP/MWCNT with Pd/MWCNT. Finally, the superb activity of the synthesized catalyst is explicated according to the mechanism of ethanol oxidation on the synthesized catalyst.

Tandem synthesis of tetrahydroquinolines and identification of the reaction network by operando NMR

Bifunctional MOF supported Pd nanoparticles for the one-pot tandem synthesis of substituted tetrahydroquinolines were developed, and operando high-pressure MAS-NMR were performed to understand the complex reaction network.

Catalytic Consequences of Supported Pd Catalysts on Dehydrogenative H2 Evolution from 2-[(n-Methylcyclohexyl)methyl]piperidine as the Liquid Organic Hydrogen Carrier

Herein, nanoporous Al2O3, CeO2, TiO2, ZrO2, and SnO2 were used as the supports for Pd nanoparticles, and effects of surface characteristics on catalytic performances for dehydrogenation of 2-[(n-methylcyclohexyl)methyl]piperidine (H12-MBP) as the H2-rich liquid organic hydrogen carrier were investigated. The H2 yield, dehydrogenation rate, product selectivity, and recyclability of the supported Pd catalysts depended on the metal oxide support and Pd loading. The H2 yield and reaction rate of the Al2O3 supporting 5 wt % Pd with a mean size of 5.76 nm were the highest (75.8%) and the fastest (k1 = 0.076 min–1), respectively, of all the catalysts. CeO2 exhibited the highest reducibility and the best supporting ability for Pd nanoparticles, which thus dispersed Pd with the smallest mean size of 3.45 nm. Although this catalyst exhibited a lower H2 yield (67.1%) and a slower reaction rate (k1 = 0.030 min–1) than Al2O3, it showed the best recyclability without a significant loss of activity during four consecutive runs, which could be attributed to the strong metal–support interaction of Pd to the surface of CeO2. The H2 yield and the dehydrogenation rate were systematically correlated with the surface characteristics of the metal oxides, such as acidity, adsorption affinity (adsorption energy), and charge transfer value of H12-MBP, which were determined via combined experimental and theoretical studies.

Hydrophilic role of deep eutectic solvents for clean synthesis of biphenyls over a magnetically separable Pd-catalyzed Suzuki-Miyaura coupling reaction

The development of an efficient and sustainable catalytic system for the preparation of biphenyls through the Suzuki-Miyaura coupling reaction is still a great challenge to green chemistry. Encouraging the prevailing challenge, in the present work, a heterogeneous Pd catalyst was synthesized through a green method and used for the production of biphenyls in deep eutectic solvents (DESs) as green reaction media. In order to prepare the catalyst, magnetite-graphene oxide nanocomposite was modified with cellulose via the click reaction and applied as support for Pd nanoparticles. Cellulose acted as both reducing and stabilizing agent for Pd nanoparticles and eliminated the requirement of a reducing agent. The prepared catalyst was characterized by different methods such as FT-IR, EDX, EDX-mapping, XPS, SEM, TEM, XRD, VSM, and ICP-OES analyses. Catalytic properties of the obtained catalyst was explored in the coupling reaction of aryl halides with aryl boronic acids in different hydrophilic and hydrophobic DESs. The presence of cellulose with hydrophilic character on the structure of catalyst offered well dispersion of the catalyst in hydrophilic DESs, which led to enhancement of its catalytic activity. Among various hydrophilic DESs, the DES composed of dimethylammonium chloride and glycerol was verified as the most effective solvent for the preparation of biphenyls. The catalyst was compatible with a variety of substrates, with which all the Suzuki coupling products were achieved in high to excellent yields. Thanks to the low solubility of catalyst and DES in organic solvents, the separated aqueous phase containing both of the catalyst and DES could be readily recovered by evaporating water and reused up to five successive runs with a stable activity. This simple and new separation strategy provided a clean and highly efficient synthetic methodology for the synthesis of various biphenyls. Moreover, hot filtration test efficiently confirmed that the catalyst is heterogeneous and completely stable under reaction conditions.

Liquid-phase synthesis of methyl isobutyl ketone over bifunctional heterogeneous catalysts comprising cross-linked perfluorinated sulfonic acid Aquivion polymers and supported Pd nanoparticles

The solvent-free hydrogenation reaction of acetone over bifunctional heterogeneous catalysts, comprising cross-linked perfluorosulfonic acid (PFSA) resins and supported Pd nanoparticles, was investigated in the liquid phase under batch conditions. A systematic study was performed by analyzing separately the effect of the main reaction parameters on the reaction outputs. Acetone conversion, selectivity and productivity to methyl isobutyl ketone (MIBK) were measured as a function of the reaction temperature, the amount of catalyst, the Pd loading, the H2 pressure, the reaction time and the cross-linkage of the polymeric support. Reproducible trends were observed that could be explained in terms of properties of the catalyst, conversion path and kinetics. Best compromise results between selectivity (92 %) and productivity (37.0 mmolMIBK gcat−1 h-1) at 19.7 % acetone conversion were obtained for the 0.26Pd@X-link-08-PW79 catalyst, based on 0.8 % cross-linked PFSA support and 0.26 % wt Pd content.

Ternary Al–Mg–Ag alloy promoted palladium nanoparticles as potential catalyst for enhanced electro-oxidation of ethanol

In this report, ternary Al–Mg–Ag alloy is introduced as novel support material as well as active promoter for palladium nano catalyst. The catalytic activity is explored with respect to ethanol oxidation reaction (EOR) in alkali. Pd nanoparticles supported on Al–Mg–Ag alloy is synthesized using a facile rapid solidification of melt method followed by chemical reduction. X-ray diffraction and microscopic analysis revealed uniformly distributed spherical Pd particle of nano dimension is formed on the support material. The application of the prepared catalysts for electro-chemical oxidation of ethanol is assessed by cyclic voltammetry (CV), chronoamperometry (CA) and impedance spectroscopy (EIS) study. Pd/Al–Mg–Ag catalyst show remarkably high peak current density (1971 mA mg−1Pd) for EOR which is 3.36 times higher than commercial Pd/C (20%) catalyst. In addition, the synthesized catalyst show low onset potential and excellent stability towards long-term application as anode catalyst for fuel cells. The study portrays Al–Mg–Ag trimetallic alloy as a promising support material and an effective promoter. The boosted catalytic activity may be attributed to the high dispersion, high Pd utilization, synergy between metals and superior conduction between support material and Pd nanoparticles.

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.

Interfacial Pd-O-Ce Linkage Enhancement Boosting Formic Acid Electrooxidation.

Metal-support interaction enhancement is critical in the fuel cell catalyst design and fabrication. Herein, taking the Pd@CeO2 system as an example, we revealed the substrate morphology coupling effect and the thermal annealing-induced Pd-O-Ce linkage enhancement in the improved catalytic capability for formic acid electrooxidation. Three well-defined CeO2 nanocrystals were employed to support Pd nanoparticles, and the best catalytic performance for formic acid oxidation and anti-CO poisoning ability was found on CeO2 plates because of the high oxygen vacancy, Ce3+, and more Pd-O-Ce linkages resulting from the more edge/corner defects. This interaction of Pd-O-Ce linkages could be largely enhanced by thermal annealing in the N2 atmosphere, as confirmed by a series of crystal structures, surface chemical state, and Raman analysis because the oxygen vacancies and lattice oxygen resulting from the oxygen atoms leaching from the CeO2 lattice would trap the mobile Pd nanocrystals by forming strengthened Pd-O-Ce linkages. Due to the high oxygen vacancy and strong Pd-O-Ce linkages, largely increased catalytic activity and stability, catalytic kinetics, and rapid charge transfer were found for all the thermal annealed Pd@CeO2 catalysts. A nearly 1.93-fold enhancement in the mass activity was achieved on the Pd@CeO2-plate catalysts demonstrating the significance of Pd-O-Ce linkage enhancement. The formation mechanism of Pd-O-Ce linkage was also probed, and a valid Pd-O-Ce linkage can only be formed in the inert atmosphere because of the reaction between metallic Pd and CeO2. This finding sheds some light on the more efficient catalyst interface construction and understanding for the fuel cell catalysis via metal-support interaction enhancement.

High efficient rGO-modified Ni foam supported Pd nanoparticles(PRNF) composite synthesized using spontaneous reduction for hydrogen peroxide electroreduction and electrooxidation

Constructing efficient, low-cost and durable catalyst for hydrogen peroxide (H2O2) reduction and oxidation is of significant importance for fuel cells with H2O2 as oxidant or fuel. Herein, a novel approach of two-step spontaneous reduction is developed to fabricate the 3D rGO-modified Ni foam supported Pd nanoparticles (PRNF) composite for H2O2 electroreduction and electrooxidation. The structure, morphology and composition of the PRNF composite are characterized using XRD, SEM, TEM, XPS and Raman analysis. Reduced graphene oxidation (rGO) film with ripple-liked wrinkles improves the surface area, electronic conductivity and corrosion resistance in acidic media of Ni substrate and the dispersing degree of Pd particles. The PRNF electrode exhibits excellent catalytic activity and stability towards H2O2 electroreduction in NaOH or H2SO4 solutions and electrooxidation in NaOH solutions. In addition, the Al–H2O2 semi-fuel cell and the H2O2–H2O2 fuel cell equipped with the PRNF electrode both deliver a higher power density (278 and 67.2 mW cm−2, respectively) and a long term cycle stability (over 50 h). This study introduces a facile and low-cost electrode preparation method which may provide new opportunities to develop high-performance electrodes for energy storage/conversion devices.

Efficient hydro-finishing of polyalfaolefin based lubricants under mild reaction condition using Pd on ligands decorated halloysite

To achieve efficient hydrofinishing of polyalfaolefin based lubricants under mild reaction condition, a novel catalyst is designed and fabricated through supporting Pd nanoparticles on ligand functionalized halloysite clay. In this line, first, using DFT calculations a scan of a library of 36 diamines was performed to find the most proper ligand that can provide the best interactions with Pd nanoparticles, improve Pd anchoring and supress Pd leaching. Characterization of the rather strong covalent and ionic interactions by a Mayer Bond Order analysis, and the non-covalent interactions by NCI plots as well, unveiled the preference for a particular system. The perfect in silico candidate was then studied on an experimental level, and also by studying its reaction profile for the hydrogenation of ethylene by calculations. In the experimental section, halloysite was functionalized with the selected ligand in simulation part and employed for the hydrofinishing of polyalfaolefin type lubricants. Characterization results revealed successful synthesis of the nano catalyst containing tiny Pd nanoparticles with a mean diameter in the range of 2.37 ± 0.5 nm, which homogeneously dispersed on the functionalized halloysite. The synthesized catalyst exhibited excellent activity (98% hydrogenation yield after 6 h) under mild reaction condition (T = 130 °C and PH2 = 6 bar). Furthermore, the catalyst can be recycled for several times with insignificant Pd leaching and loss of its activity.