Supported Pd Nanoparticles Research Articles

Taking advantage of sulfur impurities present in commercial carbon nanofibers to generate selective palladium catalysts

Achieving high selectivity is one of the major challenges in heterogeneous catalysis, being carbon materials universally employed as catalysts support due to their so-called “inert” nature. However, due to the complexity of its intrinsic characteristics, there are still several factors to bear in mind when selecting the appropriate carbon support. In this work we demonstrate that the remaining sulfur impurities in one type of commercial carbon nanofibers (CNFs) drastically alter the catalytic properties of palladium by triggering electro-deficient active sites. Two as-received CNFs thermally processed at different severity degrees, namely PS and HHT, were used to support Pd nanoparticles through the wet impregnation technique using palladium nitrate as precursor. The proof of principle is demonstrated through two transformation reactions of biomass platform molecules: the hydrogenation of 5-hydroxymethylfurfural, performed in a batch-type reactor, and the ethanol dehydrogenation/decarbonylation reaction, carried out in a continuous flow fixed-bed reactor. In both reactions, Pd/PS was substantially more selective than its sulfur-free counterpart Pd/HHT, and one of the most selective in comparison with the state-of-the-art Pd catalysts. This finding makes available a simple, easy and green strategy to design carbon-supported Pd catalysts for selective hydrogenation and dehydrogenation reactions.

Palladium Nanocatalysts on Hydroxyapatite: Green Oxidation of Alcohols and Reduction of Nitroarenes in Water

A green procedure is described for supporting Pd nanoparticles on hydroxyapatite (HAP), which serves as a highly-stable heterogeneous catalyst displaying excellent activity for the aqueous expeditious reduction of nitroaromatics to the corresponding amines with sodium borohydride, and oxidation of primary and secondary alcohols by hydrogen peroxide with high yields and selectivities. The structural features of the prepared catalyst are confirmed by latest techniques including field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The reusability of the heterogeneous catalyst was affirmed in the aqueous reduction of nitrobenzene and oxidation of cycloheptanol for six consecutive runs without significant loss of catalytic activity.

Probing the origin of the enhanced catalytic performance of sp3@sp2 nanocarbon supported Pd catalyst for CO oxidation

Tuning the fine structure of carbon support is crucial for modifying the metal-support interface (MSI) in order to harvest a high-performance catalysis. Herein, a core–shell sp3@sp2 nanocarbon (nanodiamond@graphene, ND@G) and a pure sp2 carbon derivative (onion-like carbon, OLC) were applied to support Pd nanoparticles. We found that Pd/ND@G displayed a superior catalytic activity for CO oxidation reaction with a TOF of 2.9 times higher than that of Pd/OLC at 46 °C. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and ambient pressure X-ray photoelectron spectroscopy (AP-XPS) revealed that, different with the Pd/OLC system, a unique interface microstructure was formed in Pd/ND@G, which not only provides a high exposure of active sites, but also enhances the Pd surface reactivity toward oxygen species, thus leading to a superior catalytic activity of Pd/ND@G. Moreover, the temperature-programmed surface reaction (TPSR) results showed that CO oxidation on Pd/ND@G undergoes an unusual termolecular Eley–Rideal (TER) mechanism, which has a lower energy barrier as compared to the traditional Langmuir-Hinshelwood (LH) and ER mechanism.

Pd embedded N, S co‐doped graphene wrapped core‐shell magnetic nanospheres: Engineered stable nanocatalyst for Suzuki couplings

Designed nitrogen and sulfur co‐doped graphene wrapped magnetic core‐shell supported Pd nanoparticles were synthesized through the following steps. Firstly, Fe3O4 was prepared, coated with silica and then functionalized with amine groups to create a positive charge on the structure for enhancing the interaction of the Fe3O4@SiO2 with graphene oxide. Secondary, the pre‐catalyst wrapped with graphene to enhance adsorption of aromatic substrates through π–π stacking. Thirdly, graphene was doped with nitrogen and sulfur to increase the grafting of Pd in hybrid. Finally, Pd NPs were attached on the surface of pre‐engineered structure to produce Fe3O4@SiO2@N,S‐wG@Pd which exhibited high performance in Suzuki reactions. This superior activity can be indexed to the incorporation of N and S atoms into graphene led to high anchoring and well‐dispersion of Pd NPs on the nanocomposite surface offering large amounts of active centers, that strongly increased the interaction between Pd and substrates to decreases Pd leaching.

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.

Facile synthesis of supported Pd catalysts by chemical fluid deposition method for selective hydrogenation of biomass-derived furfural

In this work, we reported the facile synthesis of the supported Pd nanoparticles on various supports (MCM-41, TiMCM-41, ZrMCM-41, SnMCM-41, SiO2, Al2O3) by chemical fluid deposition (CFD) methods, which were highly selective for the hydrogenation of biomass-derived furfural. A combination analysis of various characterization techniques was used to study the physical properties of the synthesized metal Pd nanoparticles. The different product distribution was strongly related to the type of supports, and the strength of interaction between the furan ring and the metal surface. It was found that the fabricated Pd nanoparticles supported on amorphous supports (SiO2, Al2O3) were efficient for the synthesis of furfuryl alcohol. In contrast, Pd supported on mesoporous supports (TiMCM-41, ZrMCM-41, SnMCM-41) were highly selective for the production of furfuryl alcohol and tetrahydrofurfuryl alcohol. Besides, Pd nanoparticles confined in the mesoporous channel was more stable, displaying no clear difference even recycle for three times. This works further documents the strategy to confine Pd nanoparticles is beneficial for the utilization of precious metal, enhancement of mass transportation with less resistance, higher activities and the improved stability.

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.

Electronic Metal–Support Interaction To Modulate MoS2-Supported Pd Nanoparticles for the Degradation of Organic Dyes

Electronic modulation of heterogeneous metal catalysts has been considered as an effective means to optimize their catalytic performance. Two-dimensional nanomaterials, typically used as the supporting substrates for anchoring the active metal nanoparticles, are well-known to profoundly influence the electronic structure of metals through interfacial electronic metal–support interaction (EMSI). However, the detailed investigation of EMSI for catalytic enhancement still remains obscure at the microscopic level. Herein, we propose to utilize MoS2 nanosheets to modulate the electronic structure of Pd through EMSI and investigate the influence of “support effect” of MoS2 on the catalytic activity of Pd utilizing degradation of methylene blue (MB) with the electron donor NaBH4 as a simple model reaction. Mechanistic investigations reveal that the electron transfer from Pd to MoS2 makes a highly electron-deficient Pd surface. During the target catalysis, this interfacial electronic structure makes the surface o...

Mesoporous Sn(IV) doping MCM-41 supported Pd nanoparticles for enhanced selective catalytic oxidation of 1,2-propanediol to pyruvic acid

The conversion of biomass derivative 1,2-propanediol (PDO) to value-added chemicals by selective catalytic oxidation is of great research interest. Herein, we provide an alternative and effective strategy for selectively catalyzing the PDO oxidation to pyruvic acid using Sn(IV) doping MCM-41 (SnM) supported Pd nanoparticles (2%Pd/SnM) as catalyst, in which the SnM with the Si/Sn ratios ranging from 6 to 50 are prepared by direct hydrothermal synthesis (DHS) method and the Pd nanoparticles are in situ reduced on the SnM surfaces. When the Si/Sn ratios are above 12, decreasing the Si/Sn ratio favors the incorporation of more Sn(IV) species into the framework, the formation of smaller Pd nanoparticles with higher distribution and the increment of basicity, contributing to the significant enhancement in the selective oxidation of PDO to pyruvic acid, but if the ratio is further reduced to 6, larger Pd nanoparticles are formed in the 2%Pd/SnM6 with less ordered mesostructure due to excess Sn(IV) resulting in the formation of SnO2 crystallites, displaying much lower catalytic activity than the 2%Pd/SnM12. The Sn(IV) species incorporated into MCM-41 can be used as effective promoter for enhancing the selective oxidation of PDO to pyruvic acid over the Pd/SnM catalyst.

Pyrolysis of functional cellulose by ionothermal method to synthesis of mesoporous triazine carbon for supporting of Pd and its application

A mesoporous triazine-based carbon (MTC) supported Pd nanoparticles was synthesized and found to be a retrievable and efficient heterogeneous catalyst for Heck cross-coupling reaction between various aryl halides and alkenes. The MTC-supported Pd catalyst is synthesized by ionothermal methodology followed by high temperature pyrolysis of functional cellulose (Cell-CN) and trimerization of nitrile groups in the presence of ZnCl2. A combination of different analysis such as FT-IR, Raman, XRD, FE-SEM, HRTEM, N2 adsorption-desorption isotherm and TGA confirm the successfully preparation of catalyst. The presence of ZnCl2 and also nitrile groups during pyrolysis process is proved to create a mesoporous structure with high specific surface area (1216.8 m2 g−1) which achieved from BET analysis. This heterogeneous catalyst represents a high stability and catalytic activity towards Heck cross-coupling reaction in optimized reaction condition.

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.

Metal–Organic Framework Supported Palladium Nanoparticles: Applications and Mechanisms

AbstractHeterogeneous palladium (Pd)‐based catalysts are extensively applied to improve the catalytic performance and/or expand the reaction scope in many catalytic processes, involving the cross‐coupling, hydrogenation, reduction, and oxidation reactions. Among them, metal–organic framework (MOF)‐supported Pd nanoparticles (Pd NPs) are becoming the most popular one for their excellent catalytic performance and reusable property. To motivate the development of this technology, the applications of MOF‐supported Pd NPs (Pd NPs/MOFs) in heterogeneous catalysis are critically summarized herein, including the hydrogenation reduction of nitro‐ and polyunsaturated compounds, synthesis of carbon–carbon (CC) bonds compounds, chromium (Cr(VI)) reduction, dehalogenation, alcohol oxidation, CO2 conversion, and CO oxidation. The influences of base, solvents, electron character of substitutes, and type of halogen on the catalytic performance are comprehensively discussed. Finally, the application prospects of Pd NPs/MOFs and existing shortcomings in the catalytic field are proposed.

Denitrative Cyclizations of β-Nitrostyrenes on Supported Pd Nanoparticles

Denitrative Cyclizations of β-Nitrostyrenes on Supported Pd Nanoparticles

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.

High Activity of Helical Carbon Nanotube supported Pd Nanoparticles for Ethanol Electro-oxidation in Alkaline Media

High Activity of Helical Carbon Nanotube supported Pd Nanoparticles for Ethanol Electro-oxidation in Alkaline Media

Suzuki–Miyaura reaction by heterogeneously supported Pd nanoparticles on thio-modified multi walled carbon nanotubes as efficient nanocatalyst

The palladium (Pd) supported on thio-modified multi walled carbon nanotubes (MWCNTs/CC-SH/Pd) was utilized as a useful and reusable nanocatalyst in Suzuki–Miyaura coupling reactions. The catalyst was really efficient for the Suzuki–Miyaura reaction of aryl halides (Ar–I, Ar–Br, Ar–Cl) with phenylboronic acid and conversion was good in most cases. The aryl iodides and aryl bromides reactions take place at room temperature, while reaction of aryl chlorides occurs at temperature of 80 °C. The products yields ranged between70% and 96%. The catalyst indicated excellent constancy and could be recycled and reused up to four cycles with no considerable change in its catalytic behavior.

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.

Black Phosphorus-Graphene Heterostructure-Supported Pd Nanoparticles with Superior Activity and Stability for Ethanol Electro-oxidation.

Rational design supporting material for palladium (Pd)-based catalyst can maximize its electrocatalytic performance for ethanol oxidation reaction (EOR) catalyst in alkaline condition. Utilizing the unique two-dimensional structures and outstanding physicochemical property of graphene and black phosphorus (BP), herein, we proposed and designed a black phosphorus-graphene heterostructure for supporting Pd nanoparticles. Through merely ball-milling of activated graphene (AG) and black phosphorus (BP), the AG-BP hybrid with a linkage of P-C bonding is used as supports of Pd. The obtained Pd/AG-BP hybrid exhibits ultrahigh electrochemical activity toward EOR. Remarkably, it can achieve a high mass peak current density of ∼6004.53 and ∼712.03 mA mgPd-1 before and after the durability tests of 20 000s on EOR, which are ∼7.19 and 80 times higher than those of commercial Pd/C. The experimental analysis and density-functional-theory calculation show that Pd becomes more positive with electrons transfer from Pd to AG-BP supports and is liable to absorb the OH radicals for removing COads intermediate to release active sites on EOR, together with the excellent ability to generate additional OH militants after combining with the AG-BP heterostructure.

Ethanol electrooxidation on high-performance mesoporous ZnFe2O4-supported palladium nanoparticles

As a catalyst for the electrooxidation of ethanol, a well-dispersed mesoporous ZnFe2O4 powder (ZnFe2O4MP) as a support for Pd nanoparticles (PdNPs) was fabricated using solution combustion synthesis, which is an easy and environmentally friendly method.