Supported Palladium Catalysts Research Articles

Plasma-reconstructed LaMnO3 nanonetwork supported palladium catalyst for methane catalytic combustion

Tuning the metal-support interaction is an effective strategy for improved catalytic performance in catalytic combustion of methane. Herein, we prepared Pd/LaMnO3 catalysts using two types of LaMnO3, that were achieved by plasma treatment or traditional thermal treatment respectively. Contrast to the LaMnO3 (LMO-T) support, the plasma-treated LaMnO3 (LMO-P) support has large surface specific area, porosity and many surface defects. Among these catalysts, the Pd supported on plasma-treated LaMnO3 (Pd/LMO-P) shows the best catalytic activity (T90 = 471 °C) and the lowest Ea value (74 kJ/mol). It reveals that the high performance should be attributed to the large surface area, surface-rich active species and strong metal-support interaction. The XPS techniques also demonstrated that the plasma-treated could boost the electron transfer between PdOx and LaMnO3, improving the redox properties. Moreover, the plasma-treated catalyst exhibits an excellent performance under thermal and water-vapor coexistence environment. The superior performance can arouse interest for the design of advanced catalyst in environmental catalysis.

Funneled Depolymerization of Ionic Liquid-Based Biorefinery "Heterogeneous" Lignin into Guaiacols over Reusable Palladium Catalyst.

The efficient utilization of lignin, the direct source of renewable aromatics, into value-added renewable chemicals is an important step towards sustainable biorefinery practices. Nevertheless, owing to the random heterogeneous structure and limited solubility, lignin utilization has been primarily limited to burning for energy. The catalytic depolymerization of lignin has been proposed and demonstrated as a viable route to sustainable biorefinery, however, low yields and poor selectivity of products, high char formation, and limited to no recycling of transition-metal-based catalyst involved in lignin depolymerization demands attention to enable practical-scale lignocellulosic biorefineries. In this study, we demonstrate the catalytic depolymerization of ionic liquid-based biorefinery poplar lignin into guaiacols over a reusable zirconium phosphate supported palladium catalyst. The essence of the study lies in the high conversion (>80 %), minimum char formation (7-16 %), high yields of guaiacols (up to 200 mg / g of lignin), and catalyst reusability. Both solid residue, liquid stream, and gaseous products were thoroughly characterized using ICP-OES, PXRD, CHN analysis, GC-MS, GPC, and 2D NMR to understand the hydrogenolysis pathway.

An Efficient Recyclable Polymer Supported Palladium Catalyst for Suzuki Reaction in Water

AbstractThis work describes the development of an efficient and reusable heterogeneous polymer supported palladium catalyst for Suzuki reaction in water. This novel catalyst system was designed through monoethanolamine (MEA) modification of nitrile group in Polyacrylonitrile (PAN) followed by metal salt (PdCl2) complexation. The resulting polymer complex (mPAN‐Pd) was then successfully optimised as an efficient heterogeneous catalyst for Suzuki reaction under ligand free conditions. The supported catalyst provided excellent reactivity in the coupling reactions of a series of aryl halides with phenyl boronic acids under mild reaction condition. The reaction proceeded in presence of 2 mol % ofmPAN‐Pdcatalyst at 80 °C in water and the resulting products were isolated in moderate to excellent yields upto 98 %. Furthermore, this catalyst can be conveniently recovered by simple filtration and reused at least five times without an appreciable loss in its activity or Palladium leaching.

The Role of Interstitial Solid Solutions in the Formation of Active Component in Supported Palladium Catalysts for Selective Hydrogenation of Acetylene to Ethylene

The effect of adsorption of the reaction medium components on selective hydrogenation of acetylene to ethylene under the action of supported palladium catalysts is considered. The role of interstitial solid solutions of carbon and hydrogen in palladium, which are formed upon contact of the catalyst with the reaction medium, in the mass-transfer processes between surface and subsurface layer of the active component is revealed. The ratio of activation barriers for ethylene desorption/adsorption processes, which determines the selectivity of acetylene hydrogenation, can change in dependence on the structure of palladium nanoparticles and its electronic state. Therewith, changes in the electronic state affect the energy of activated desorption of ethylene from palladium particles, and their structural features determine the energy of activated adsorption and the subsequent hydrogenation of ethylene to ethane.

Arylation of indole at C2 catalyzed by palygorskite grafted covalent organic frameworks supported palladium catalyst

A heterogeneous palladium catalyst, palygorskite grafted covalent organic frameworks supported palladium (Pd-Pal/COF), was successfully prepared by a simple method. A series of C2 aromatic indole derivatives were synthesized under mild reaction conditions. Pd-Pal/COF catalyst can be reused at least 5 times with inappreciable metal leaching. Undoubtedly, facile synthesis, mild reaction conditions, a wide scope of reactants, and recyclability make the catalyst systems potentially useful in organic synthesis. For the synthesized heterogeneous catalysts, palygorskite as a matrix, the unique structure and good dispersion of palygorskite result in the excellent catalytic activity and good cycle stability of the Pd-Pal/COF catalyst, comparing with the traditional clay catalyst. The result further expands the application scope of clay in the catalytic field.

Recyclable Palladium-Catalyzed Carbonylative Cyclization of Aryl Iodides and 2-Hydroxyacetophenones towards Flavones

AbstractA highly efficient heterogeneous palladium-catalyzed carbonylative cyclization of aryl iodides and 2-hydroxyacetophenones is developed. The reaction proceeds efficiently in DMSO at 120 °C under 3 bar of carbon monoxide by using 2 mol% of an MCM-41-immobilized bidentate phosphine palladium complex [MCM-41-2P-Pd(OAc)2] as the catalyst and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as the base, providing a general, efficient and practical approach for the assembly of a wide variety of flavones in mostly good to high yields from readily available starting materials. This supported palladium catalyst can be easily recovered via centrifugation of the reaction mixture and recycled more than nine times without any significant loss of its catalytic efficiency.

Hydrogenetion of 4-Nitro-2'-Hydroxy-5'-Methylazobenzene on Supported Palladium Catalysts and Skeletal Nickel

Hydrogenetion of 4-Nitro-2'-Hydroxy-5'-Methylazobenzene on Supported Palladium Catalysts and Skeletal Nickel

Correlation ofo-Ps annihilation properties with catalytic activities of palladium species immobilized on functionalized MCM-41 supports

Design and preparation of highly active and stable supported palladium catalysts have garnered increased attention for their easy separation and reusability. Herein, MCM-41 mesoporous materials functionalized by four different amino functional groups were synthesized by using four commercially available siloxanes and then used to support palladium catalysts. The Fourier transform infrared spectroscopy (FT-IR) was used to analyze the chemical structures of functionalized MCM-41 supports. The thermogravimetric analysis (TGA) and element analysis (EA) were employed to determine the grafting densities of functional groups on MCM-41 supports. The mesoporous structures of functionalized MCM-41 supports and dispersion of palladium species were characterized by high resolution transmission electron microscopy (TEM) and X-ray diffraction patterns (XRD). A study of the materials using positron annihilation lifetime spectroscopy (PALS) reveals the different ortho-positronium (o-Ps) annihilation properties of the supported palladium species on the four supports. Meanwhile, the catalytic activities of supported palladium species on the four supports were evaluated by the Heck reactions of iodobenzene with n-butyl acrylate. At last, the annihilation properties of the supported palladium species on the four supports were successfully correlated with their catalytic activities. The result suggests a facile method to determine and predict the catalytic activities of supported palladium species by using PALS, which may hold great potential in the preparation of rationally designed and highly active supported palladium catalysts.

Palladium Decorated, Amine Functionalized Ni-, Cd- and Co-Ferrite Nanospheres as Novel and Effective Catalysts for 2,4-Dinitrotoluene Hydrogenation.

2,4-diaminotoluene (TDA) is one of the most important polyurethane precursors produced in large quantities by the hydrogenation of 2,4-dinitrotoluene using catalysts. Any improvement during the catalysis reaction is therefore of significant importance. Separation of the catalysts by filtration is cumbersome and causes catalyst loss. To solve this problem, we have developed magnetizable, amine functionalized ferrite supported palladium catalysts. Cobalt ferrite (CoFe2O4-NH2), nickel ferrite (NiFe2O4-NH2), and cadmium ferrite (CdFe2O4-NH2) magnetic catalyst supports were produced by a simple coprecipitation/sonochemical method. The nanospheres formed contain only magnetic (spinel) phases and show catalytic activity even without noble metals (palladium, platinum, rhodium, etc.) during the hydrogenation of 2,4-dinitrotoluene, 63% (n/n) conversion is also possible. By decorating the supports with palladium, almost 100% TDA selectivity and yield were ensured by using Pd/CoFe2O4-NH2 and Pd/NiFe2O4-NH2 catalysts. These catalysts possess highly favorable properties for industrial applications, such as easy separation from the reaction medium without loss by means of a magnetic field, enhanced reusability, and good dispersibility in aqueous medium. Contrary to non-functionalized supports, no significant leaching of precious metals could be detected even after four cycles.

Palladium supported on pyrrole functionalized hypercrosslinked polymer: Synthesis and its catalytic evaluations towards Suzuki-Miyaura coupling reactions in aqueous media

Bearing the merits of convenient functionalization and versatile framework composition, hypercrosslinked polymers are employed as promising candidates in green catalysis. In this study, a new hypercrosslinked polymer supported palladium catalyst has been synthesized based on pyrrole functionalization from triphenyl benzene and pyrrole via Scholl reaction and palladium anchoring on the polymer surface. The structure of prepared Pd catalyst was confirmed by TEM, SEM, EDX, XRD, N2 adsorption–desorption, solid state 13C NMR, TGA, FT-IR, XPS, and ICP analyses. The novel complex can be served as an effective catalyst for the preparation of biphenyl compounds with the yields up to 100 % in EtOH: H2O (1:1) at 60 °C by using 0.07 mol% of catalyst in air. More importantly, the catalyst also has significant advantages in terms of facile availability of raw materials, chemical and thermal stability, and cost-effective synthesis. Due to the high specific surface area, and the coordination of pyrrole groups with palladium on the surface of this polymer, this catalyst could effectively prevent palladium leaching (<1.1 %). Furthermore, the catalyst could be recovered by simple centrifugation for four consecutive times. The study provides new insight into the immobilization of palladium on such polymer surface in other heterogeneous catalysis systems.

A layer-like FAU zeolite with palladium particles embedded in situ as catalyst for hydrogenation of 1,4-bis(phenylethynyl) benzene

The active carbon supported palladium catalyst (Pd/C) is commonly used for hydrogenation of 1,4-bis(phenylethynyl) benzene (DEB), to avoid its disadvantage of easy combustion, a nonflammable Pd-containing zeolite was developed as a novel catalyst for the DEB hydrogenation. In the present work, this Pd-containing zeolite catalyst was synthesized via a one-pot hydrothermal technique, and its structure and catalytic performance were investigated. The results show that the support of this prepared Pd-containing zeolite catalyst is a layer-like FAU zeolite with a hierarchical pore structure, and the Pd particles is embedded uniformly inside the layer-like FAU zeolite with an average size of 2.02 ± 0.41 nm. The results also show that the catalytic performance of this prepared Pd-containing zeolite catalyst (Pd@FAU) is much better than that of the traditional Pd/C catalyst with the same content of Pd particles, the DEB-Pd@FAU mixture can reach its maximal hydrogen uptake capacity of 257.41 ml/g in 20 h, and the DEB-Pd/C mixture can only reach its maximum of 223.81 ml/g in 45 h. These differences are mainly caused by that the Pd particles in the prepared Pd@FAU catalyst has a smaller size, a better dispersion and a more metallic Pd species than those in the Pd/C catalyst. All these results indicate that the Pd@FAU catalyst would be a promising substitute for the traditional Pd/C catalyst for hydrogenation of DEB.

Synthesis of 3-Aryl- and 3-Alkynylbenzofurans in the Presence of a Supported Palladium Catalyst

AbstractSuzuki and Sonogashira coupling reactions of 3-iodo-2-phenylbenzofuran, leading to the corresponding 3-aryl- and 3-alkynyl derivatives, respectively, were carried out using a silica supported pyridinium ionic liquid-based heterogeneous catalyst. Under optimized reaction conditions, arylboronic acids with either electron-withdrawing or -donating substituents as well as terminal alkynes with aromatic or aliphatic groups could be coupled to the benzofuran skeleton efficiently. The application of this catalyst made it possible to carry out the reaction under phosphine-free and, in the case of the Sonogashira coupling, under copper-free conditions. The catalyst retained its activity in at least 7 subsequent runs in both types of reactions. Palladium leaching of less than 1% of the original amount used in the catalytic reaction was observed under optimized conditions in most cases. The methodology was applied successfully to the synthesis of nine different 3-aryl- and ten different 3-alkynylbenzofuran derivatives in moderate to high yields.

Water inhibition and role of palladium adatoms on Pd/Al2O3 catalysts during methane oxidation

Supported palladium catalysts are the most active ones toward the complete oxidation of methane. However, the presence of relevant amounts of water hinders the catalytic activity and long-term stability, due to competition between methane and water for the active sites. Hence, understanding the inhibition effect of water on methane oxidation is mandatory to improve these catalysts. We present an in situ ambient pressure X-ray photoelectron spectroscopy study of methane oxidation on Pd/Al2O3 in presence and in absence of water. The inhibition effect of water is demonstrated by combining reactivity tests with electron microscopy and photoelectron spectroscopy measurements. In the presence of water, the redox activity of palladium decreases. Water competes with methane for the catalytically active sites, poisoning the surface with hydroxyl groups and hindering the generation of the coordinatively unsaturated palladium active sites. Multiple palladium oxide species displaying different reactivity are identified. A new cationic palladium species, assigned to adatoms, is detected, which shows higher reactivity with methane than particulate palladium oxide but also high inhibition by water.

Recent Progress on the Application of the Polyaniline-Pd Catalysts for C-C Cross-coupling Bond Forming Reactions: Trend and Future Analysis

Abstract: In this review recent progress on the application of the polyaniline supported palladium catalysts in different organic transformations focusing on different C-C bond forming reactions such as Suzuki coupling, Heck reactions, oxidative Heck coupling, Ullmann coupling, Sonogashira and related chemistry. Effect of catalyst preparation, characteristic of the support and supported palladium species on the outcome of the catalyst efficiency are also highlighted. Finally, the emerging trend is summarized for the future of this unique modular catalytic system.

The effects of alkali metal ions on the physiochemical and catalytic properties of Pd/NiAlOx catalysts for lean methane oxidation

Self-assembled nickel-aluminum mixed oxides (NiAlOx) were prepared by using alkali metal ions as modifiers in a hydrothermal system and employed as the support materials for palladium catalysts. Via tuning the preparation procedure, both the ‘bonded’ and ‘deposited’ alkali metal ions were introduced to the NiAlOx materials for elucidating their effects on the physiochemical and the catalytic properties of Pd/NiAlOx catalysts for lean methane oxidation. Benefiting from the well-dispersed palladium nanoparticles, optimized electronic state of palladium phases, and the favorable structure of host materials, the optimal Pd/NiAl-Na sample exhibited excellent catalytic performance for methane oxidation. Over this sample, complete methane conversion was realized at 401 °C in the presence of 15 vol % water vapor, which was 26 °C lower than that of the Pd/NiAl catalyst (427 °C) at same reaction conditions. Due to the relatively small size of Li+ ions, certain amounts of Li+ incorporated into the NiAlOx lattice and improved the redox properties of NiAl-Li. However, its supported palladium catalysts did not show improved performance in the oxidation of methane. Furthermore, systematic characterizations revealed that the ‘deposited’ alkali metal ions resulted in the agglomeration of palladium nanoparticles and the formation of electron-deficient palladium component, thus exerting negative effect on the activities of palladium phases. It was hoped that this work could provide some fundamental understandings on the roles of alkali metal played in catalytic reaction.

Palladium catalysts based on porous aromatic frameworks for vanillin hydrogenation: Tuning the activity and selectivity by introducing functional groups

The aim of the current work was to study the activity of supported palladium catalysts based on porous aromatic frameworks (PAF) in vanillin hydrogenation, and to develop the methods for controlling their activity and selectivity by modifying the PAF structure with various functional groups. Using unmodified PAF-30, its sulfonated derivative PAF-30-SO3H, and that of PAF-30-TEA modified with CH2N+(C2H5)3 groups, palladium catalysts were synthesized and tested for HDO of lignin components. This investigation provides one potential route for the development of efficient catalysts for hydrodeoxygenation by the adjustment of the composition of the catalyst and its appropriate derived properties.

The effects of facet-dependent palladium-titania interactions on the activity of Pd/Rutile catalysts for lean methane oxidation

Rod-shaped rutile materials with different proportions of (110) and (111) facets exposed were hydrothermally prepared, and the facet-dependent effects of rutile on the activity of supported palladium phases in lean methane oxidation were elucidated. Although a stronger interaction between palladium and the rutile (111) facet was confirmed by systematic characterizations, performance evaluation and in situ DRIFTS revealed deteriorated catalytic efficiencies of palladium catalysts. Specifically, while complete methane oxidation was achieved at temperature below 450 °C over a Pd/Rutile-(110) catalyst, only 39% of methane were eliminated at 500 °C over its counterpart supported on Rutile-(111). Investigations on rutile supported palladium catalysts further revealed that the facet-dependent palladium-titania interactions profoundly affected the particle sizes and chemical states of the deposited palladium species. In combination with DFT calculations, it was then found that Pd4+ species that might function synergistically with Pd2+ in methane activation were not as stable on the rutile (111) facet, due to the strong electron transfer from this substrate. It is hoped that the conclusions drawn in this work would provide supplementary understanding of the facet-dependent metal-TiO2 interactions and some inspirations on the further rutile-related catalyst design.

N-doped carbon-modified palladium catalysts with superior water resistant performance for the oxidative removal of toxic aromatics

The supported palladium catalysts perform well in the oxidative removal of hazardous aromatic hydrocarbons. However, water vapor can seriously deactivate the catalysts especially in the low-temperature regime. Hence, improving moisture resistance of the Pd-based catalysts is full of challenge in the removal of aromatics. Herein, we report a new type of Pd@NC/BN catalysts featured with nitrogen-doped carbon layers modified Pd supported on hexagonal boron nitride (h-BN), and the relationship between structure and water resistance of the catalysts. The results show that in the presence of 10 vol% H2O in the feedstock, the Pd@NC/BN catalyst could effectively oxidize o-xylene (with an almost 87% removal efficiency), whereas o-xylene conversion declined from 69% to 20% over the conventional Pd/Al2O3 at a reaction temperature of 210 °C and a space velocity of 40,000 mL/(g h). The adsorption of H2O was significantly inhibited on the nitrogen-doped carbon layers due to the hydrophobic nature. Meanwhile, the oxygen species active for o-xylene oxidation were not only from the adsorbed gas-phase oxygen but also from the new active oxygen (*OOH and *OH) species that were generated via the interaction of O2 and H2O in the presence of water in the feedstock. It is concluded that the reactive oxygen species that accelerated the activation and cleavage of C−H bonds significantly facilitated the conversion of key intermediate species (from benzaldehyde to benzoic acid), thus playing a decisive role in o-xylene oxidation. The present work provides a direction for developing the superior water resistance catalysts with hydrophobic nature and good water activation ability in the oxidative removal of volatile organic compounds.

Plasma-enabled synthesis of Pd/GO rich in oxygen-containing groups and defects for highly efficient 4-nitrophenol reduction

Effective catalytic removal of 4-nitrophenol (4-NP) in industrial wastewater remains a significant challenge due to the lack of highly efficient and stable catalysts. Herein, we demonstrated a promising plasma method for the facile, ultra-fast and low-temperature synthesis of graphite oxide (GO)-supported palladium catalyst (Pd/GO-P) rich in oxygen-containing groups (OCGs) and defects with smaller Pd nanoparticles (NPs) for highly efficient 4-NP reduction. The plasma method limited the damage to the OCGs and retained more OCGs (mainly alkoxy and hydroxyl groups) on the GO surface. In addition, plasma treatment can increase the active sites and the density of GO surface defects. These OCGs and defects promoted the 4-NP adsorption and improved the catalyst dispersion in the aqueous solution of 4-NP, thereby enhancing the catalytic reduction performance. The Pd/GO-P catalyst showed the highest reduction of 4-NP reported thus far, with a concentration-normalized rate constant of 5576 min−1 g−1 L. This value was 51.6 and 20.5 times greater than that using Pd/rGO-H prepared by a traditional thermal reduction method and a commercial Pd/AC catalyst, respectively. This work opens the avenue of exploring the use of plasma for the rational design of supported Pd catalysts with superior performance for the reduction and recycling of 4-NP in wastewater.

Nano-sized alumina supported palladium catalysts for methane combustion with excellent thermal stability

Pd/Al2O3 catalysts supported on Al2O3 of different particle sizes were synthesized and applied in methane combustion. These catalysts were systematically characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), high resolution-transmission electron microscopy (HR-TEM), high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM), H2-temperature-programmed reduction (H2-TPR), O2-temperature-programmed oxidation (O2-TPO), X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure (XAFS). The characterization results indicated that nano-sized Al2O3 enabled the uniform dispersion of palladium nanoparticles, thus contributing to the excellent catalytic performance of these nano-sized Pd/Al2O3 catalysts. Among them, Pd/Al2O3-nano-10 (Pd/Al2O3 supported by alumina with an average particle size of 10 nm) showed superior catalytic activity and stability for methane oxidation under harsh practical conditions. It maintained excellent catalytic performance for methane oxidation for 50 hr and remained stable even after harsh hydrothermal aging in 10 vol.% steam at 800°C for 16 hr. Characterization results revealed that the strong metal-support interactions and physical barriers provided by Al2O3-nano-10 suppressed the coalescence ripening of palladium species, and thus contributed to the superior sintering resistance of the Pd/Al2O3-nano-10 catalyst.