Supported Palladium Catalysts Research Articles

A Review on the Development of Polymer Supported Heterogeneous Palladium Materials for Organic Synthesis and Electrochemical Applications

Abstract:: This comprehensive review explores the advancements in catalytic transformation, focusing on the use of heterogeneous catalytic systems with a particular emphasis on polymeric-supported palladium (Pd) complexes. This study explores the limitations associated with conventional homogeneous reagents, emphasizes the transition to eco-friendly catalytic systems, and emphasizes the importance of Pd nanoparticles. These nanoparticles are particularly noteworthy for their distinctive properties, including elevated catalytic activity, making them promising for various applications in organic synthesis. The review thoroughly examines the design and synthesis of heterogeneous catalysts, emphasizing the crucial selection of safe and recyclable supports to augment the longevity and reusability of metallic catalysts. Diverse polymer varieties, including polystyrene (PS), polyethylene (PE), polyacrylate derivatives, polyethylene glycol (PEG), and grafted polymers, are investigated as viable supports for Pd complexes. The authors intricately describe the synthesis techniques for these polymer-supported Pd catalysts and furnish illustrative examples showcasing their effectiveness in organic transformation. This comprehensive review additionally highlights the synthesis of polymer-supported palladium (Pd) materials and discusses their applications in electrochemistry. The focus extends to the electrocatalytic properties of Pdbased polymeric nanomaterials, showcasing their effectiveness in glucose sensing, hydrogen peroxide detection, and the sensing of other biological analytes. Furthermore, the catalytic capabilities of Pd nanoparticles in various electrochemical applications, including wastewater treatment and electrochemical capacitors, are explored. Integrating polymer-supported Pd materials into these electrochemical processes underscores their versatility and potential contributions to advancements in catalysis and electrochemical sensing. Catalytic applications featuring polymer-supported palladium complexes with polymeric ligands in organic synthesis processes use the Sonogashira reaction, Suzuki-Miyaura coupling, Heck reaction, Catalytic asymmetric transformations, etc. The subsequent section of the paper focuses on the creation of polymeric palladium complexes, achieved by the complexation of polymeric ligands with palladium precursors. It delves into noteworthy examples of catalytic processes employing polymer-supported palladium complexes featuring polymeric ligands, emphasizing distinct polymers, such as PS, PE, polyacrylate derivatives, PEG, and grafting polymers. The review concludes by exploring catalytic asymmetric transformations using chiral palladium complexes immobilized on polymer supports and discusses various chiral ligands and their immobilization on polymer supports, emphasizing their application in asymmetric allylic alkylation. The review furnishes a comprehensive summary of recent advancements, challenges, and prospective avenues in catalytic oxidation facilitated by polymer- supported palladium catalysts with electrochemical applications.

Determination of palladium content in catalysts based on different carbon supports by inductively coupled plasma — atomic emission spectrometry (ICP-AES)

Catalytic processes and technologies are the structure-forming elements of modern chemical, petrochemical and pharmaceutical industries. Prospects of their development are strongly determined by continuous improvement of the existing catalysts and developing the advanced and more efficient ones. Among the available catalysts, an important place belongs to palladium catalysts with carbon supports. Palladium as an active component exhibits unique catalytic properties in various transformations of organic substances: hydrogenation, dehydrogenation, isomerization, dehydrocyclization, carbonylation, oxidation, etc. To control the content of the active component of a catalyst, precise and rapid physicochemical methods are used. ICP-AES shows a good performance in the analytical practice due to the rapidity, sensitivity, high accuracy and selectivity in determining various elements. The aim of the study was to develop a scientifically grounded methodological approach to estimate the palladium content in the catalysts synthesized on different carbon supports made of carbon black and Sibunit, which combines only the acidic decomposition of a sample and analysis by ICP-AES. A series of palladium catalysts synthesized on the carbon supports with different structural and textural characteristics was studied. An urgent goal is to control the content of the active component in the composition of catalysts. This characteristic affects the phase and electronic state of the metal, the structural and textural characteristics and thus determines the activity and selectivity of catalysts during operation. Therefore, quantitative chemical analysis is one of the main methods used to control the quality of catalysts. A method for quantitative determination of palladium concentration, which combines acidic decomposition of a sample and ICP-AES has been developed. The carbon support type was shown to exert no effect on the accuracy and reproducibility of data obtained by the analysis of supported palladium catalysts. The content of palladium in such catalysts can be measured using analytical lines 340.458 and 360.955 nm without lowering the measurement accuracy. The selected conditions of sample preparation make it possible to carry out a quantitative analysis of metal systems based on the carbon support with high accuracy. The relative error in determining the elements did not exceed 4%, the relative standard deviation was no more than 0.04. The results of this work can be used to analyze catalysts of similar chemical composition by ICP-AES.

Asymmetric transfer hydrogenation of 2,3-diphenylpropenoic acids over heterogeneous palladium catalysts modified by cinchona alkaloids

Asymmetric catalytic methods are among the convenient syntheses procedures of optically pure organic compounds, many of which are valuable pharmaceutical intermediates. Applying heterogeneous catalysts may contribute to their economic and environmentally benign synthesis. Among the easiest and often used methods of introducing chiral centres in molecules are the reduction of prochiral unsaturated compounds. Although, several heterogeneous catalytic systems are known in which in situ chirally-modified metals are used, such catalysts have never been applied in asymmetric transfer hydrogenations. Here we report the enantioselective transfer hydrogenations of (E)-2,3-diphenylpropenoic acids over supported palladium catalysts modified by dihydrocinchonidine carried out in ordinary laboratory glassware using easily available, cheap hydrogen donor, i.e. potassium formate. High conversions and good enantioselectivities were obtained in transfer hydrogenations of various acids substituted on phenyl rings. Results obtained with various acid derivatives and with few cinchona alkaloid modifiers indicated that the transfer hydrogenations occur through a similar surface intermediate as the enantioselective hydrogenations with molecular hydrogen. A deuterium tracer study showed low deuterium incorporation in the product possibly due to dissociation of formate and exchange with the surface mobile hydrogens, however, these processes are strongly influenced by the donor cation. The asymmetric transfer hydrogenation may be carried out at over 2 g scale, thus may be used as an advantageous laboratory synthetic procedure without applying special precautions characteristic of gaseous reactants.

Carbonylative synthesis of 2-(trifluoromethyl)quinazolin-4(3H)-ones from trifluoroacetimidoyl chlorides and amines based on an activated carbon fibers supported palladium catalyst

Activated carbon fibers known for their unique physical and chemical properties, are increasingly utilized in diverse industries ranging including textiles and fabrics, which can serve as ideal supports of heterogeneous...

Palladium Catalysts for Methane Oxidation: Old Materials, New Challenges.

ConspectusMethane complete oxidation is an important reaction that is part of the general scheme used for removing pollutants contained in emissions from internal combustion engines and, more generally, combustion processes. It has also recently attracted interest as an option for the removal of atmospheric methane in the context of negative emission technologies. Methane, a powerful greenhouse gas, can be converted to carbon dioxide and water via its complete oxidation. Despite burning methane being facile because the combustion sustains its complete oxidation after ignition, methane strong C-H bonds require a catalyst to perform the oxidation at low temperatures and in the absence of a flame so as to avoid the formation of nitrogen oxides, such as those produced in flares. This process allows methane removal to be obtained under conditions that usually lead to higher emissions, such as under cold start conditions in the case of internal combustion engines. Among several options that include homo- and heterogeneous catalysts, supported palladium-based catalysts are the most active heterogeneous systems for this reaction. Finely divided palladium can activate C-H bonds at temperatures as low as 150 °C, although complete conversion is usually not reached until 400-500 °C in practical applications. Major goals are to achieve catalytic methane oxidation at as low as possible temperature and to utilize this expensive metal more efficiently.Compared to any other transition metal, palladium and its oxides are orders of magnitude more reactive for methane oxidation in the absence of water. During the last few decades, much research has been devoted to unveiling the origin of the high activity of supported palladium catalysts, their active phase, the effect of support, promoters, and defects, and the effect of reaction conditions with the goal of further improving their reactivity. There is an overall agreement in trends, yet there are noticeable differences in some details of the catalytic performance of palladium, including the active phase under reaction conditions and the reasons for catalyst deactivation and poisoning. In this Account we summarize our work in this space using well-defined catalysts, especially model palladium surfaces and those prepared using colloidal nanocrystals as precursors, and spectroscopic tools to unveil important details about the chemistry of supported palladium catalysts. We describe advanced techniques aimed at elucidating the role of several parameters in the performance of palladium catalysts for methane oxidation as well as in engineering catalysts through advancing fundamental understanding and synthesis methods. We report the state of research on active phases and sites, then move to the role of supports and promoters, and finally discuss stability in catalytic performance and the role of water in the palladium active phase. Overall, we want to emphasize the importance of a fundamental understanding in designing and realizing active and stable palladium-based catalysts for methane oxidation as an example for a variety of energy and environmental applications of nanomaterials in catalysis.

Potassium regulating electronic state of zirconia supported palladium catalyst and hydrogen spillover for improved acetylene hydrogenation

High-selectivity acetylene hydrogenation to produce ethylene is an important issue of removing acetylene impurity in ethylene for industrial polyethylene production. Developing high-efficiency catalyst with excellent ethylene selectivity and catalytic durability is desirable but still challenging. In this work, potassium doped palladium catalysts supported on zirconia with different K contents (Pd/ZrO2-xK) have been developed to catalyze acetylene hydrogenation, the Pd/ZrO2-16K exhibits impressive catalytic performance with acetylene conversion of 100 %, ethylene selectivity of 81 % and high catalytic durability. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), in situ synchrotron radiation photoionization mass spectrometry (SR-PIMS) and density functional theory (DFT) calculations reveal that K doping effectively weakens the adsorption of ethylene by regulating the electronic state of catalyst to improve ethylene selectivity and substantially lowers the barriers of hydrogen activation and transfer reactions to favor hydrogen spillover, thus conferring a remarkably improved durability on the Pd/ZrO2-16K catalysts.

Catalytic removal of harmful volatile organic compounds by reutilizing zinc rods waste from spent batteries as a palladium catalyst support

The emission of volatile organic compounds (VOCs) has led to significant deterioration in air quality, making it imperative to ensure that these compounds are removed from emission sources before they are released into the atmosphere. In this context, the present study recycled spent primary batteries to use their zinc rods waste (ZRW) as a palladium catalyst support for the removal of harmful VOCs. To this end, palladium supported on ZRW (Pd/ZRW) catalysts were prepared and tested for the catalytic oxidation of benzene, methylbenzene and 1,2-dimethylbenzene. The physicochemical properties of the Pd/ZRW catalysts were carefully characterized by ICP-OES, BET, SEM, XRD, FE-TEM, XPS, and H2-TPR analyses. The main component of ZRW was identified as ZnO. Consistent with expectations, increases in the loading of Pd from 0.1 to 1.0 wt% in the Pd/ZRW catalysts resulted in enhanced VOCs removal efficiency. The reaction temperature required for the complete oxidation (100% removal efficiency) of methylbenzene and 1,2-dimethylbenzene on the 1.0 wt% Pd/ZRW catalyst was below 340 °C at a gas hourly space velocity of 50,000 h−1. TEM, XPS, and H2-TPR results implied that the enhancement of catalytic activity with the addition of Pd could be attributed to the readily movable surface lattice oxygen as well as the active component (Pd species). Ultimately, ZRW of spent primary batteries appear to show promise as a catalyst support for VOCs removal. This study has introduced a novel strategy for reducing air pollutants by utilizing waste, which promotes the disposal of hazardous solid waste and ensures clean air quality.

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

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

Carbonized Melamine Cyanurate as a Palladium Catalyst Support for the Dehydrogenation of N-heterocyclic Compounds in LOHC Technology

In this work, the use of graphite-like carbon nitride (g-C3N4) with improved texture characteristics for the synthesis of supported palladium catalysts of dehydrogenation of nitrogen-containing heterocycles was studied. This process is key to the creation of liquid organic carrier technology (LOHC) using N-heterocycles as reversibly hydrogenated/dehydrogenated substrates. For the preparation of graphite-like carbon nitride supports with advanced textural characteristics, well-established technology of the melamine cyanurate complex carbonization and standard techniques of adsorption precipitation together with wet impregnation were used for the synthesis of Pd-containing systems. The activity of the synthesized catalysts was studied in decahydroquinoline dehydrogenation. The high weight content of extractable hydrogen (7.2 wt%) and the high extraction rate, respectively, make it possible to consider these substances as the most promising N-heterocyclic compounds for this technology. It was shown that an increase in the specific surface area of g-C3N4 allows for achieving a slightly lower but comparable fineness of palladium particles for the 1 wt% Pd/MCA-500 sample, compared to the standard 1 wt% Pd/C. In this case, the catalytic activity of 1 wt% Pd/MCA-500 in the dehydrogenation of both substrates exceeded the analogous parameter for catalysts supported by nitrogen-free supports. This regularity is presumably associated with the electron-donor effect of surface nitrogen, which favorably affects the dehydrogenation rate as well as the stability of catalytic systems.

Methane Combustion over Zeolite-Supported Palladium-Based Catalysts

The emission of methane leads to the increase in the methane concentration in the atmosphere, which not only wastes resources but also intensifies the greenhouse effect and brings about serious environmental problems. Catalytic combustion can completely convert methane into carbon dioxide and water at low temperatures. However, the catalytic activities of the conventional supported palladium catalysts (e.g., Pd/Al2O3 and Pd/ZrO2) are easy to decrease or the two catalysts can even be deactivated under actual harsh reaction conditions (high temperatures, steam- and sulfur dioxide-containing atmospheres, etc.). Recently, noble metal catalysts supported on zeolites with ordered pores and good thermal stability have attracted much attention. This review article summarizes the recent progress on the development and characteristics of zeolite-supported noble metal catalysts for the combustion of methane. The effects of framework structures, silica/alumina ratios, acidity, doping of alkali metals or transition metals, particle sizes and distributions, and their locations of/in the zeolites on methane combustion activity are discussed. The importance of developing high-performance catalysts under realistic operation conditions is highlighted. In addition, the related research work on catalytic methane combustion in the future is also envisioned.

Anodic TiO2 nanotubes supported palladium catalysts for Heck coupling reactions: Excellent catalytic activity and reusability

A convenient method for preparing palladium nanocatalyst and its application in the Heck coupling reactions between various aryl halides and olefins are presented. Pd nanoparticles were photoreduced on anodic TiO2 nanotubes (ATNTs) to prepare the Pd@ATNTs catalyst by utilizing the large specific surface area of the ATNTs' hollow tubes. Pd nanoparticles were found to be highly dispersed on the walls of the nanotubes with an average particle size of 8.01 nm by characterization techniques. The heterogeneous Pd@ATNTs catalyst showed excellent catalytic efficiency (TOF up to 1010 h−1) due to the highly dispersed Pd within the ATNTs. Pd@ATNTs has remarkable properties of ease of separation and good reusability, allowing for at least 10 cycles of recovery and reuse without a significant decrease in catalytic activity.

Dioxin-Linked Covalent Organic Framework-Supported Palladium Complex for Rapid Room-Temperature Suzuki–Miyaura Coupling Reaction

Covalent organic framework (COF)-supported palladium catalysts have garnered enormous attention for cross-coupling reactions. However, the limited linkage types in COF hosts and their suboptimal catalytic performance have hindered their widespread implementation. Herein, we present the first study immobilizing palladium acetate onto a dioxin-linked COF (Pd/COF-318) through a facile solution impregnation approach. By virtue of its permanent porosity, accessible Pd sites arranged in periodic skeletons, and framework robustness, the resultant Pd/COF-318 exhibits exceptionally high activity and broad substrate scope for the Suzuki–Miyaura coupling reaction between aryl bromides and arylboronic acids at room temperature within an hour, rendering it among the most effective Pd/COF catalysts for Suzuki–Miyaura coupling reactions to date. Moreover, Pd/COF-318 demonstrates excellent recyclability, retaining high activity over five cycles without significant deactivation. The leaching test confirms the heterogeneity of the catalyst. This work uncovers the vast potential of dioxin-linked COFs as catalyst supports for highly active, selective, and durable organometallic catalysis.

Molybdenum-containing carbon nanofiber supported palladium catalyst for formic acid oxidation reaction

Numerous studies have reported the development of Pd-based catalyst for the anode direct formic acid fuel cell (DFAFC) that improves the electrocatalytic activities. We have now developed a carbon nanofiber embedded with carbon black (Vulcan) and molybdenum sulfide (MoS2) nanoparticles as the Pd support for the FAOR catalyst. The MoS2-Vulcan embedded carbon nanofiber (MoS-VECNF) was first prepared by electrospinning and heat treatment. The MoS-VECNF was prepared with different weight ratios of MoS2 to polyacrylonitrile (PAN). The prepared support was then loaded with 20 wt% Pd nanoparticles by the polyol method. The Pd/MoS-VECNF catalyst demonstrated a better FAOR activity and stability as compared to the Pd/VECNF catalyst with 0.10 as the optimum weight ratio. The achieved peak current density was 1.46 times higher than that of the Pd/VECNF catalyst. The presence of MoS2 nanoparticles in the carbon support produced a strong metal-support interaction which improved the FAOR activity and stability of the catalyst. Therefore, the Pd/MoS-VECNF catalyst is suggested to be promising for DFAFC applications.

Selective hydrogenation of phenylacetylene over high-energy facets exposed nanotubular alumina supported palladium catalysts

High-energy facets exposed nanotubular alumina as well as conventional alumina supported Pd catalysts were synthesized and applied to the selective hydrogenation of phenylacetylene. Novel alumina supported catalyst presented higher selectivity at complete conversion of phenylacetylene. This could be related to the well dispersion of Pd and strong metal-support interaction, which are the consequences of the unique structural properties of the crystal plane regulated alumina. It helps create more active sites for hydrogenation meanwhile facilitates the desorption of alkene and thus suppresses the excess hydrogenation towards ethylbenzene.

Stabilization of a Carbon Support by Surface Oxygen with Respect to Nitrogen Dioxide in the Pd/HOPG Model System

X-ray photoelectron spectroscopy (XPS) method has been used to study the effect of oxygen on the surface of a carbon support on the result of NO2 interaction with model systems prepared by evaporation of palladium on highly oriented pyrolytic graphite (HOPG). For Pd/HOPG samples with an atomic ratio [O]/[C] ≤ 0.0035, graphite oxidized with the destruction of its structure to a depth of 10–15 graphene layers. In this case, palladium particles remained in the metallic state and penetrated into the subsurface layer of the support due to the deep oxidation of the adjacent carbon atoms. At the atomic ratio [O]/[C] ≈ 0.01–0.02, the result of the interaction changed dramatically. In this case, the HOPG remained stable, and the palladium particles were oxidized to form an oxide. This finding explained the high stability of supported palladium catalysts prepared on Sibunit carbon supports in reactions of oxidation catalysis.

Selective Hydrogenation of Benzylidenethiazolidinedione Exocyclic Alkene with Anti-poisoning Nitrogen-Doped Carbon Supported Palladium Catalysts

Selective Hydrogenation of Benzylidenethiazolidinedione Exocyclic Alkene with Anti-poisoning Nitrogen-Doped Carbon Supported Palladium Catalysts

The Effect of Polymer Matrix on the Catalytic Properties of Supported Palladium Catalysts in the Hydrogenation of Alkynols

Palladium catalysts were obtained by the adsorption method involving the sequential deposition of polyvinylpyrrolidone (PVP) and then palladium ions on a modified zinc oxide surface without high-temperature calcination and reduction stages. The immobilized PVP-palladium catalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), infrared spectroscopy (IRS), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and elemental analysis methods. It was found that the introduction of polymer into the catalyst’s composition promotes the dispersion and uniform distribution of active phase nanoparticles (PdO, Pd0) on the surface of zinc oxide. The catalysts were tested in the hydrogenation of complex acetylene alcohol, 3,7,11-trimethyldodecyn-1-ol-3 (C15-yn) under mild conditions (0.1 MPa, 40 °C). For comparison, studies on stereoselective hydrogenation of the short-chain alcohol 2-hexynol-1 were performed. It was shown that modification of the catalyst with polymer improves its catalytic properties. High C15-alkenol selectivity (98%), activity (W = 70 × 10−6 mol/s), and stability (turnover number (TON) 62,000) were achieved on a Pd-PVP/ZnO catalyst. Varying the active phase made it possible to reduce the metal content without deteriorating the catalytic performance of the catalyst.

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.