Supported Pd Nanoparticle Catalyst Research Articles

Model Catalysis with HOPG-Supported Pd Nanoparticles and Pd Foil: XPS, STM and C2H4 Hydrogenation

A surface science based approach was applied to model carbon supported Pd nanoparticle catalysts. Employing physical vapour deposition of Pd on sputtered surfaces of highly oriented pyrolytic graphite (HOPG), model catalysts were prepared that are well-suited for characterization by X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). Analysis of the HOPG substrate before and after ion-bombardment, and of Pd/HOPG before and after annealing, revealed the number of “nominal” HOPG defects (~ 1014 cm−2) as well as the nucleation density (~ 1012 cm−2) and structural characteristics of the Pd nanoparticles (mean size/height/distribution). Two model systems were stabilized by UHV annealing to 300 °C, with mean Pd particles sizes of 4.3 and 6.8 nm and size/height aspect ratio up to ~ 10. A UHV-compatible flow microreactor and gas chromatography were used to determine the catalytic performance of Pd/HOPG in ethylene (C2H4) hydrogenation up to 150 °C under atmospheric pressure, yielding temperature-dependent conversion values, turnover frequencies (TOFs) and activation energies. The performance of Pd nanocatalysts is compared to that of polycrystalline Pd foil and contrasted to Pt/HOPG and Pt foil, pointing to a beneficial effect of the metal/carbon phase boundary, reflected by up to 10 kJ mol−1 lower activation energies for supported nanoparticles.Graphical

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.

Selective Synthesis of Primary Anilines from NH3 and Cyclohexanones by Utilizing Preferential Adsorption of Styrene on the Pd Nanoparticle Surface

AbstractDehydrogenative aromatization is one of the attractive alternative methods for directly synthesizing primary anilines from NH3 and cyclohexanones. However, the selective synthesis of primary anilines is quite difficult because the desired primary aniline products and the cyclohexanone substrates readily undergo condensation affording the corresponding imines (i.e., N‐cyclohexylidene‐anilines), followed by hydrogenation to produce N‐cyclohexylanilines as the major products. In this study, primary anilines were selectively synthesized in the presence of supported Pd nanoparticle catalysts (e.g., Pd/HAP, HAP=hydroxyapatite, Ca10(PO4)6(OH)2) by utilizing competitive adsorption unique to heterogeneous catalysis; in other words, when styrene was used as a hydrogen acceptor, which preferentially adsorbs on the Pd nanoparticle surface in the presence of N‐cyclohexylidene‐anilines, various structurally diverse primary anilines were selectively synthesized from readily accessible NH3 and cyclohexanones. The Pd/HAP catalyst was reused several times though its catalytic performance gradually declined.

Selective Synthesis of Primary Anilines from NH3 and Cyclohexanones by Utilizing Preferential Adsorption of Styrene on the Pd Nanoparticle Surface.

Dehydrogenative aromatization is one of the attractive alternative methods for directly synthesizing primary anilines from NH3 and cyclohexanones. However, the selective synthesis of primary anilines is quite difficult because the desired primary aniline products and the cyclohexanone substrates readily undergo condensation affording the corresponding imines (i.e., N-cyclohexylidene-anilines), followed by hydrogenation to produce N-cyclohexylanilines as the major products. In this study, primary anilines were selectively synthesized in the presence of supported Pd nanoparticle catalysts (e.g., Pd/HAP, HAP=hydroxyapatite, Ca10 (PO4 )6 (OH)2 ) by utilizing competitive adsorption unique to heterogeneous catalysis; in other words, when styrene was used as a hydrogen acceptor, which preferentially adsorbs on the Pd nanoparticle surface in the presence of N-cyclohexylidene-anilines, various structurally diverse primary anilines were selectively synthesized from readily accessible NH3 and cyclohexanones. The Pd/HAP catalyst was reused several times though its catalytic performance gradually declined.

Pd nanoparticle and molecular Pd2+ leaching pathways for a strongly acid versus strongly basic resin supported Pd nanoparticle catalyst in Suzuki coupling

The Pd leaching behaviour of a strongly acid (Lewatit K2629) versus strongly basic (Lewatit MP500 OH) ion exchange resin supported Pd nanoparticle (Pd-NP) catalyst is elucidated in the Suzuki reaction between iodobenzene and phenylboronic acid with K2CO3 as base in 1:1 (v/v) DMF/H2O at 40 °C. Reaction and leaching kinetic analyses combined with hot filtration tests indicated heterogeneous-homogeneous catalysis for both Pd-NP catalysts. More particularly, leaching experiments showed that for Pd-NP Lewatit K2629, Pd-NP as well as molecular Pd2+ leaching (as phenylpalladium(II)hydroxide complexes) occurred due to, respectively, the disturbance of the electrostatic NP stabilization by dissociated K2CO3 and reaction with iodobenzene and hydroxide. For Pd-NP Lewatit MP500 OH, however, molecular Pd2+ leaching induced by iodobenzene, dominates. Hence, the resin functionality determines the contribution of each leaching pathway. Furthermore, at high conversions, Pd re-deposition occurred due to the decreased amount of leaching inducing reagents causing enlarged NPs in the resin which leached less in subsequent runs.

Visible light assisted thermocatalytic reaction of CO + NO over Pd/LaFeO3

A LaFeO3 supported Pd nanoparticle catalyst Pd/LaFeO3 was prepared by a two-step precipitation–deposition method. Its catalytic performance for the reduction of NO by CO was subsequently evaluated in the lower temperature under visible light irradiation or not. It was found that visible light could boost the progress of the reaction and the selectivity of forming N2. The results of temperature-programmed desorption (TPD) of CO and in-situ diffuse reflectance infrared Fourier transform spectra (in-situ DRIFTS) showed that visible light could enhance the adsorption of NO and its activation at Pd or LaFeO3 site and that of CO at Pd site, respectively. Co-adsorption results of NO + CO suggested that the activated intermediates of CO and NO would further interact to form the isocyanate (–NCO) and N2O species, which finally transformed to N2 and CO2. Based on the results of Raman spectrum, H2-temperature programmed reduction (TPR), the X-ray photoelectron spectroscopy (XPS), photoluminescence spectra (PL) and photocurrent testing, it was proposed that visible light irradiation could cause the increase in surface electron density of Pd nanoparticles by the photo-induced electron (from O2p to Fe3d orbit) transfer from LaFeO3 to Pd. Moreover, the valence exchange of Fe4+ and Fe3+ induced by visible light could promote the formation of oxygen vacancies and then the adsorption and activation of CO and NO. This result also indicated that the photo-excitation of supports could strengthen the strong interaction between support and metal nanoparticles, and then promote the thermo-catalytic reactivity of catalysts.

Structural selectivity of supported Pd nanoparticles for catalytic NH3 oxidation resolved using combined operando spectroscopy

The selective catalytic oxidation of NH3 to N2 presents a promising solution for the abatement of unused NH3-based reductants from diesel exhaust after treatment. Supported Pd nanoparticle catalysts show selectivity to N2 rather than NOx, which is investigated in this work. The link between Pd nanoparticle structure and surface reactivity was found using operando X-ray absorption fine structure spectroscopy, diffuse reflectance infrared Fourier-transformed spectroscopy and on-line mass spectrometry. Nitrogen insertion into the metallic Pd nanoparticle structure at low temperatures ( 280 °C). Our work demonstrates the ability of combined operando spectroscopy and density functional theory calculations to characterize a previously unidentified PdNx species, and clarify the selectivity-directing structure of supported Pd catalysts for the selective catalytic oxidation of NH3 to N2.

Pd0-PyPPh2@porous organic polymer: Efficient heterogeneous nanoparticle catalyst for dehydrogenation of 3-methyl-2-cyclohexen-1-one without extra oxidants and hydrogen acceptors

In this contribution, we have developed an efficient and recyclable porous organic polymer (POP) supported Pd nanoparticle catalyst (Pd°-PyPPh2@POP) for dehydrogenation of 3-methyl-2-cyclohexen-1-one. This heterogeneous catalytic system represents a totally clean process without using any extra oxidant and hydrogen acceptors. The SEM-EDS mapping images of the Pd°-PyPPh2@POP catalyst reveal the highly uniformly dispersed character of C, Pd, P and N elements. The coordination bonds between Pd nanoparticle and exposed P atom as well as N atom on the surface of PyPPh2@POP polymer are confirmed by means of solid-state 31P NMR and XPS. Importantly, both P atom and pyridyl ring on the PyPPh2@POP polymer are themselves used as solid base over the Pd°-PyPPh2@POP catalyst, leading to a catalytic conversion of 88.2% even without the employment of inorganic base additives (K2CO3). Our results have provided a strategy for designing highly active bifunctional POP supported nanoparticle catalysts.

Supported Pd nanoparticle catalysts with high activities and selectivities in liquid-phase furfural hydrogenation

Highly dispersed and ultrafine Pd nanoparticles (NPs) deposited on carbon, silica, and alumina supports were prepared by chemical reduction (CR) using sodium borohydride, in the presence of trisodium citrate as a stabilizer. For comparison, supported Pd catalysts were also prepared through impregnation followed by thermal reduction (TR) and capillary inclusion of the colloidal Pd NPs (CI). The activities and selectivities of the prepared catalysts were evaluated in the liquid-phase furfural (FAL) hydrogenation reaction under 20 bar H2 at 180 °C. Under these conditions, FAL was converted via two distinct pathways to produce either furan via decarbonylation or furfuryl alcohol (FA) via aldehyde hydrogenation. Subsequently, furan and FA were converted to tetrahydrofuran and tetrahydrofurfuryl alcohol (THFA), respectively, via ring hydrogenation. 2-Methylfuran was also produced from the hydration of FAL. To verify the efficiency of the preparation methods, the size of the Pd NPs, the degree of metal dispersion, and the type of supports were correlated with the catalytic conversions and selectivities of FAL hydrogenation. It was confirmed that the 5 wt% Pd/C catalysts possessed highly dispersed small Pd NPs with large metallic Pd surface areas, which resulted in high conversions and selectivities towards THFA in the FAL hydrogenation reaction compared to conventional supported catalysts.

The controllable preparation of electrospun carbon fibers supported Pd nanoparticles catalyst and its application in Suzuki and Heck reactions

Abstract The palladium nanoparticles/carbon nanofibers (Pd NPs/CNFs) catalyst was prepared by the electrospinning method, the hydrazine hydrate solution reduction in an ice bath environment, the high temperature carbonization. The catalyst was characterized by X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), and transmission electron microscopy (TEM). The nanofibers are not cross-linked and arranged in order. The surface of Pd NPs/CNFs is smooth, and it can be observed that a large number of particles were loaded and well-dispersed in carbon fiber matrix, and the particle distribution is uniform. The activity center of catalyst is Pd(0). The Pd NPs/CNFs exhibited a high efficiency, good reusability and stability in the Suzuki and Heck reactions. It can be used for at least five consecutive runs without significant loss of its catalytic activity. The good recyclability of Pd NPs/CNFs provides a way to greatly reduce the cost of the catalyst.

Hydrogenation of cinnamaldehyde to hydrocinnamaldehyde over Pd nanoparticles deposited on nitrogen-doped mesoporous carbon

Nitrogen-doped mesoporous carbon (NMC) supported Pd nanoparticles catalyst exhibited an admirable catalytic activity in cinnamaldehyde hydrogenation to produce hydrocinnamaldehyde.

Synergistic effect of mesoporous Mn2O3-supported Pd nanoparticle catalysts for electrocatalytic oxygen reduction reaction with enhanced performance in alkaline medium

We synthesized a novel mesoporous Mn2O3 nanostructure as an electrocatalyst support, then Pd–Mn2O3 with different Pd loading amounts were obtained by a facile solvothermal method. The Pd–Mn2O3 demonstrated a good competitive ORR activity and a high selectivity in alkaline medium, which can be comparable to commercial Pt/C catalysts.

ChemInform Abstract: Polymerized Functional Ionic Liquid Supported Pd Nanoparticle Catalyst for Reductive Homocoupling of Aryl Halides.

AbstractAryl iodides and bromides react selectively to the reductive homocoupling products.

Green and facile synthesis of carbon nanotube supported Pd nanoparticle catalysts and their application in the hydrogenation of nitrobenzene

Abstract

Dispersion-Enhanced Supported Pd Catalysts for Efficient Growth of Carbon Nanotubes through Chemical Vapor Deposition

Supported Pd nanoparticle catalysts over Mg–Al mixed metal oxides derived from layered double hydroxides were prepared by three different approaches, including coprecipitation, anion-exchange, and impregnation, in order to enhance the metal dispersion and thus facilitate the growth of uniform multiwalled carbon nanotubes (CNTs) via catalytic chemical vapor deposition of methane. The effects of preparation methods for supported Pd catalysts on the morphologies and microstructures of CNTs formed were investigated. The results revealed that the characteristics of CNTs were strongly correlated to the dispersion of active Pd species in the catalysts, and the structural defects and the diameter of CNTs were reduced with the increasing metal dispersion. Especially, the anion-exchange route for preparation of supported Pd catalyst was appropriate for the growth of uniform bamboo-like CNTs with fewer defects, which could be contributed to the presence of more uniform and smaller Pd0 nanoparticles highly dispersed over Mg–Al mixed-metal oxides.

Synthesis and characterization of supported polysugar-stabilized palladium nanoparticle catalysts for enhanced hydrodechlorination of trichloroethylene

Palladium (Pd) nanoparticle catalysts were successfully synthesized within an aqueous phase using sodium carboxymethyl cellulose (CMC) as a capping ligand which offers a green alternative to conventional nanoparticle synthesis techniques. The CMC-stabilized Pd nanoparticles were subsequently dispersed within support materials using the incipient wetness impregnation technique for utilization in heterogeneous catalyst systems. The unsupported and supported (both calcined and uncalcined) Pd nanoparticle catalysts were characterized using transmission electron microscopy, energy dispersive x-ray spectrometry, x-ray diffraction, and Brunauer–Emmett–Teller surface area measurement and their catalytic activity toward the hydrodechlorination of trichloroethylene (TCE) in aqueous media was examined using homogeneous and heterogeneous catalyst systems, respectively. The unsupported Pd nanoparticles showed considerable activity toward the degradation of TCE, as demonstrated by the reaction kinetics. Although the supported Pd nanoparticle catalysts had a lower catalytic activity than the unsupported particles that were homogeneously dispersed in the aqueous solutions, the supported catalysts retained sufficient activity toward the degradation of TCE. In addition, the use of the hydrophilic Al2O3 support material induced a mass transfer resistance to TCE that affected the initial hydrodechlorination rate. This paper demonstrates that supported Pd catalysts can be applied to the heterogeneous catalytic hydrodechlorination of TCE.

Palladium Nanoparticles Supported on γ-Al2O3 for Hydrogenation of 2-Tertiary Butyl Anthraquinone to Produce H2O2

The supported palladium catalysts were prepared by depositing Pd colloidal particles on boehmite, and then promoted by lanthanum oxide. The samples were characterized by transmission electron microscopy, powder x-ray diffraction, scanning electron microscopy, and energy dispersive x-ray spectroscopy, and studied in hydrogenation of 2-tertiary butyl anthraquinone (BAQ) to 2-tertiary butyl anthrahydroquinone (BAQH4) for H2O2 production. Compared to the catalyst prepared by metal salt impregnation method, the supported Pd nanoparticles catalyst showed high catalytic activity. Superior catalytic activity of the catalyst was related to the high dispersion of the active components and the existence of lanthanum oxide as an effective promoter, which may promote the catalytic activity both electronically and morphologically. The reaction kinetics for the catalytic hydrogenation of BAQ to BAQH2 can be described by equation r = kC BAQ · p H 2 , and the apparent activation energy is 38 kJ · mol−1.

Pt monolayer on Pd/C as electrocatalyst for oxygen reduction reaction

Carbon supported Pd nanoparticle catalysts (Pd/C) for oxygen reduction reaction (ORR) were synthesized by using the liquid-phase pyrolysis method and the impregnation method respectively. Although the Pd/C catalysts produced in liquid phase method possessed larger particle sizes, they exhibited higher activity for ORR and much better durability as compared with Pd/C prepared by the impregnation-reduction method. By galvanic displacement of the monolayer Cu formed on Pd nanoparticle surface through under potential deposition, Pt monolayer decorated Pd/C catalysts (Pt_ML/Pd/C) were fabricated. The thus prepared Pt monolayer catalysts exhibited ORR activity close and durability superior to the state-of-the-art commercial Pt/C. The Pt mass activity of the PtML/Pd/C catalyst for ORR was more than 4 times higher than that given by the Pt/C, showing a great perspective of the Pt monolayer electrocatalysts in fuel cells applications.

Magnetically Recyclable Pd Nanoparticles Immobilized on Magnetic Fe3O4@C Nanocomposites: Preparation, Characterization, and Their Catalytic Activity toward Suzuki and Heck Coupling Reactions

An efficient magnetic carbon nanocomposite supported Pd nanoparticle catalyst has been prepared by a three-step process in this report. The morphology, inner structure, and magnetic properties of all products were studied with transmission electron microscopy, X-ray powder diffraction, Fourier translation infrared spectroscopy, X-ray photoelectron spectroscopy, and vibrating sample magnetometer. The Suzuki and Heck coupling reactions were used to demonstrate the catalytic efficiency of the as-prepared Pd/Fe3O4@C (Pd/MFC) nanocomposite catalyst. The results showed that the catalyst is completely recoverable with the simple application of an external magnetic field and the catalytic efficiency shows no obvious loss for Suzuki and Heck coupling reactions even after five repeated cycles.

Selective hydrogenation of 3,3-dimethylbutanoyl chloride to 3,3-dimethylbutyraldehyde with silica supported Pd nanoparticle catalyst

Abstract A novel method for selective hydrogenation of 3,3-dimethylbutanoyl chloride (DMBC) to 3,3-dimethylbutyraldehyde (DMBA) with silica supported Pd nanoparticle catalyst (Pd/SiO2) is developed. The catalysts were characterized by Fourier transform infrared spectroscopy, X-ray powder diffraction, N2 physisorption and transmission electron microscopy. The performance of the Pd/SiO2 catalyst was compared with Pd/C and Pd/BaSO4 catalysts with or without being pretreated by quinoline–sulfur. The Pd/SiO2 catalyst activated at 80 °C by bubbling hydrogen in cyclohexane for 1 h showed the highest yield of DMBA. For 3 wt.% Pd/SiO2, the yield of DMBA reached 84.6%, which exhibited much higher value than Pd/C and Pd/BaSO4 catalysts.