Supported Palladium Catalysts Research Articles

Highly Efficient and Reusable Polymer Supported Palladium Catalyst for Copper Free Sonogashira Reaction in Water

AbstractDevelopment of a novel, greener and efficient heterogeneous catalytic system for copper free Sonogashira reaction in water is described. This novel catalyst can be easily prepared by a simple method through synthetic modification of nitrile group in Polyacrylonitrile (PAN) using monoethanolamine (MEA) followed by its complexation with palladium chloride (PdCl2). The resulting polymer Pd complex (mPAN‐Pd) was characterized by means of Fourier Transform Infrared Spectroscopy (FTIR), Energy‐Dispersive X‐ray Spectroscopy (EDAX), Inductively Coupled Mass Spectrometry (ICP‐MS) and X‐ray Photo Electron Spectroscopy (XPS) analyses. mPAN‐Pd was then explored as highly efficient heterogeneous catalyst for Sonogashira coupling reaction under copper and ligand free conditions in water affording the corresponding coupling products up to 97 % isolated yield. Moreover, the catalyst was recovered by simple filtration after the reaction and reused for next 5 cycles with excellent stability and activity. This is the first report on the use of ethanolamine modified PAN Pd (II) complex as an efficient heterogeneous catalyst for a coupling reaction.

Optimizing the Microstructure of SnO2-CeO2 Binary Oxide Supported Palladium Catalysts for Efficient and Stable Methane Combustion.

The preparation of palladium-based catalysts with both high catalytic activity and hydrothermal stability currently appears as a critical topic in methane combustion. Herein, we propose a facile strategy to boost the performance of SnO2-CeO2 binary oxide supported palladium catalysts by tuning the composition of supports. The coexistence of SnO2 and CeO2 phases in an appropriate ratio is favorable for the formation of both PdxCe1-xO2-δ and PdxSn1-xO2-δ solid solutions due to the reduced crystallite size. This unique microstructure could enhance the metal-support interaction to stabilize the active PdO phase and promote its reoxidation, meanwhile generating more oxygen vacancies to improve the reducibility of PdO. On account of the facilitated conversion of PdO ↔ Pd, coupled with the low-temperature dissociation of methane promoted by abundant active oxygen species, the Pd/5Sn5Ce catalyst exhibits a superior catalytic activity with a T99 of ca. 360 °C, a robust stability under both dry and wet conditions, and an excellent thermal stability during heating-cooling light-off tests.

Self-support semi-hollow carbon nanosphere supported palladium catalyst for biomass upgrading

Catalytic removal of oxygen from biomass by hydrodeoxygenation (HDO) as a promising process has been pursued for efficient utilization of biomass resources. Here we report a self-support semi-hollow carbon nanospheres (SHCN) supported palladium (Pd) catalyst for vanillin HDO under mild conditions. The shell-void-core structure of carbon nanospheres originates from the modulation of growth kinetics of resorcinol/formaldehyde resin precursors by a given volume of acetone. Notably, 0.5%Pd/SHCN-60 (acetone of 60 mL) catalyst exhibits >99.9% of vanillin conversion and creosol selectivity under 25 °C and 0.1 MPa of H2. The good catalytic results can derive from the self-support hollow carbon support and active metallic Pd. Raman results show that 0.5%Pd/SHCN-60 possesses the most abundant defect carbon (AD1/AG = 2.02), which leads to the small particle size (mean size of 2.9 nm) and well dispersion (29.5%) of Pd. Higher H2-desorption temperature (∼440 °C) of 0.5%Pd/SHCN-60 by H2-TPD demonstrates the strong interaction of Pd-defect carbon. The strong interaction favors the hydrogen storage and activation of substrates under low pressure of H2 and reaction temperature, which improves the hydrogenation and hydrogenolysis. Additionally, the contribution of unique core structure to support the shell to enhance mechanical stability leads to intact morphology of catalyst and stable catalytic performance after reused six times. This investigation can provide a design idea of carbon-based catalysts for mild HDO.

Palladium catalyzed liquid phase oxidation of glycerol under alkaline conditions - Kinetic analysis and modelling

Glycerol is a major by-product of bio-diesel production and hence its utilization has been an area of high interest in the scientific community. Oxidizing glycerol to high-value products can improve the economics of bio-diesel production. In the present work, we study glycerol oxidation in alkaline medium using an activated carbon supported Palladium catalyst. Kinetic studies have been performed in a batch reactor to study the effect of different parameters such as NaOH concentration, temperature, and pressure. Our results point to product inhibition by adsorbing reactant and product species. We also observe a relative insensitivity of product yields at a given conversion, to the temperature. Our observations further suggest that higher NaOH concentration gives better C3 selectivity while higher oxygen pressure results in lower C3 selectivity. Based on our own studies and the literature available, the most likely kinetic pathway and a kinetic model have been proposed. Our results suggest the possibility that C–C cleavage occurs directly from the primary intermediate aldehydic species, as a result of which, carbon chain scission products (including CO2) form from very early stages of the reaction. Various strategies such as pooling temperature data to estimate rate ratios prior to full parameter estimation, use of statistical significance tests to reduce model parameters etc have been used to arrive at a minimalistic model still capable of explaining all features of the oxidation. Confidence bounds on the model parameters have been estimated.

Sulfur-resistant methane combustion invoked by surface property regulation on palladium-based catalysts

Improving sulfur resistance of palladium-based catalysts is crucial for the sustained and efficient methane combustion. Herein, the surface property of catalysts was rationally tailored to tune the dynamic behavior of sulfur species on active sites and supports, which was qualitatively and quantitatively studied through a combination of in-situ and on-line characterizations. Results reveal that the content of accumulated sulfur species in catalysts increased linearly (0.20–0.59 mmol SO2·g−1) with the rise of the surface basic sites, while it was restrained in catalysts with high surface acidity. The zirconium doped alumina supported palladium catalyst exhibited a moderate surface acidity/basicity, meanwhile it showed an excellent catalytic activity in the presence of SO2 and after regeneration. Its enhanced sulfur resistance derived from the proper interaction between supports and sulfur species, the facile decomposition of zirconium sulfates, the suppressed formation of surface/bulk aluminum sulfates, as well as the effective regeneration of PdO phase. The established quantitative correlation between accumulated sulfur species, surface acidity/basicity and catalytic performance paves the way to develop sulfur-resistant palladium-based catalysts for oxidation reactions.

Synthesis of Acid Free Benzaldehyde by Highly Selective Oxidation of Benzyl Alcohol Over Recyclable Supported Palladium Catalyst.

This research work deals with the highly selective oxidation of benzyl alcohol to benzaldehyde by palladium doped graphene oxide catalyst, which was synthesized by a modified Hummer's method. The effect of reaction parameters like temperature, time and catalyst loading were studied. It was found that fine-tuning of reaction temperature and presence of a small amount of benzyl alcohol in a product prevented the undesirable formation of benzoic acid crystals, which form on auto-oxidation of benzaldehyde. Benzoic acid or substituted benzoic acid formation was hindered by the presence of < 2% benzyl alcohol at a reaction temperature of 50˚C, which was further supported by palladium doped graphene oxide catalyst. Modified Hummer's method was used for the synthesis of graphene oxide and palladium doped graphene oxide was synthesized by in-situ method in which graphene oxide dispersed in 20mL of distilled water was ultrasonicated for 2h. Palladium solution was added and it was further ultrasonicated for 30min for homogeneous deposition of palladium on a graphene oxide support. To this, 2 mL of sodium borohydride solution was added and stirred at room temperature for 4h. The resulting solution was centrifuged, and the residue was dried at 60°C for 12 h. The morphological characteristics and the functional groups of supported catalysts were characterized by X-ray diffraction, Field emission scanning spectroscopy, and Fourier transform infrared spectroscopy. The produced benzaldehyde was characterized by gas chromatography. PdGO catalyst was prepared using sodium borohydride as a reducing agent by modified Hummer's method and utilized for the oxidation of benzyl alcohol to benzaldehyde. A maximum conversion of 89% and selectivity of 99% were obtained and the catalyst could be reused up to five times without any compromise on conversion and selectivity.

Covalent organic framework supported palladium catalysts

Covalent organic frameworks (COFs), as highly porous crystalline structures, are newly emerging materials designed with tuneable features.

Ultrahigh stable covalent organic framework-derived carbon–nitrogen-supported palladium nanoparticles for highly efficient electrocatalytic methanol and ethanol oxidation reactions

COF-derived nitrogen-doped-carbon structure supported palladium catalysts exhibited excellent EOR and MOR activities, much higher than those of commercial Pd/C, with good catalytic stability.

Hydrodeoxygenation of vanillin to creosol under mild conditions over carbon nanospheres supported palladium catalysts: Influence of the carbon defects on surface of catalysts

Hydrodeoxygenation (HDO) is a promising process for biomass upgrading. A challenge is designing and developing related efficient catalysts. Here, we developed a defects enhancement engineering to synthesize carbon-based supported Pd catalysts (0.5%Pd/CNS) for vanillin HDO under mild condition. It is found that the degree of carbon defects was negative correlation with the cross-linked degree of resorcinol–formaldehyde (RF) resin sphere (carbon precursor), which can be modulated by amount of ammonium fluoride (NH4F) (0, 0.01, 0.03, and 0.05 g). The RF resin sphere (RF-0.03) with the lowest cross-linked degree was obtained by addition of 0.03 g NH4F, and then 0.5%Pd/CNS-0.03 possessed rich carbon defects obtained by carbonization of RF-0.03. The catalyst possessing the most degree of carbon defects (1.96 of AD1/AG from Raman data, D1 ∼ defective carbon, G ∼ graphitic carbon) exhibited the highest activity among as-prepared catalysts: 100% of vanillin conversion and 100% of yield to creosol in vanillin HDO over 0.5%Pd/CNS-0.03 (0.03 g of NH4F) at 60 °C, 0.1 MPa H2, and 1 h. The excellent performance can be attributed to the rich carbon defects on surface of catalysts, which can play an important role on growth of active metal and activation of reactants. This work improves green catalysis of HDO with a strategy of defect engineering to surface microenvironment modulation.

Hollow Microporous Organic Nanospheres with an Organocatalyst and a Metal Catalyst for Tandem Reactions

AbstractAmino‐functionalized hollow microporous organic nanospheres supported palladium catalysts (Pd@NH2‐H‐MONs) are prepared via the integration of hyper‐crosslinking induced self‐assembly strategy and a simple impregnation method by employing polylactide‐b‐poly(Boc‐aminoethyl acrylamide)‐b‐polystyrene (PLA‐b‐PBOCa‐b‐PS) triblock copolymers as precursors, in which Pd nanoparticles are uniformly anchored on NH2‐H‐MONs based on the strong interaction between Pd nanoparticles and amino functional groups. Combining with the unique micro/mesoporous structure derived from hyper‐crosslinking shell and the degradation of PLA block, the coexistence of free amine moieties produced by the deprotection of PBOCa block and well‐dispersed Pd nanoparticles endows the Pd@NH2‐H‐MONs with excellent catalysis activity for various cascade reactions. The present strategy opens a novel avenue for the multifunctional H‐MONs acting as a superior candidate for the heterogeneous tandem catalysis reactions.

Hydrogenation aging mechanisms of a porous composite with polyethylene as matrix and 1,4-bis(phenylethynyl)benzene as hydrogen getter

Although 1,4-bis(phenylthynyl)benzene (DEB) blended with a carbon supported palladium catalyst (Pd/C) is one of the most widely used irreversible hydrogen getter in a closed environment, it is hard to form and easy to burn. To overcome these deficiencies of this powdery DEB-Pd/C hydrogen getter, a DEB-Pd/C/LDPE porous hydrogen absorbing composite has been developed in our group. In the present work, hydrogen absorption aging mechanisms of this porous hydrogen absorbing composite samples are investigated by using a accelerated aging test method, their hydrogen absorption performances are measured by hydrogen absorption experiments, and their aging mechanisms are studied by X-ray diffraction, attenuated total reflection-Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and field emission transmission electron microscope. The results show that both the hydrogen absorption rate and the hydrogen absorption capability of each aging composite sample decrease with the increasing of storage time. The results also show that the decrease of its hydrogen absorption rate is mainly attributed to both the surface migration of its DEB and the surface oxidation of its Pd catalyst, and the decrease of its hydrogen absorption capacity is mainly attributed to the surface migration of its DEB.

Facile synthesis strategy for the development of carbon fiber cloth supported palladium catalyst from spent Pd catalyst for low-temperature CO oxidation

Metal supported catalysts are well-known for the effective conversion of carbon monoxide. Among different support materials that are generally employed, activated carbon-based materials are important because of their well-developed structural characteristics. This paper investigates the development of palladium (Pd) catalyst supported on activated carbon fiber cloth (CFC) as a potential scalable material for mitigation of environmental pollution by studying its carbon monoxide (CO) removal efficiency under ambient conditions. As a Pd source, the deactivated Pd/C catalyst was employed for the development of the Pd/CFC catalyst. Palladium was reduced using reducing agents of different reduction potential, i.e. , sodium borohydride and formaldehyde. The catalysts were characterized using atomic absorption spectrometry, scanning electron microscopy, energy dispersive X-ray spectrometry, X-ray powder diffraction, BET surface area analyzer, temperature-programmed reduction and desorption, X-ray photoelectron spectroscopy, H 2 chemisorption followed by CO efficiency studies. It was observed that the microporous nature of activated CFC affects the surface metal concentration of Pd 0 and Pd +2 and accordingly, the CO conversion activity. The study involves testing the dependency of moisture towards the catalyst and noticed that a higher moisture level causes a reduction in the CO conversion efficiency due to pore blockage. • Carbon Monoxide removal studies using Palladium impregnated activated carbon fiber cloth (Pd/CFC) was conducted. • A spent Pd/C catalyst was re-used as a metal precursor for catalyst preparation to make the process economically viable. • The Pd/CFC catalyst was prepared by incipient wetness impregnation method followed by liquid media reduction. • The effect of different reducing agents on the efficacy of cloth catalyst was studied. • The structural characteristics of Pd/CFC catalysts and its dependency on moisture for the catalytic activity was studied.

Supported Palladium Catalyzed Carbonylative Coupling Reactions using Carbon Monoxide as C1 Source.

The carbonylative reactions of aryl halides, boronic acids, amines, activated alkene and alkynes under CO and supported palladium catalyzed conditions are very popular reactions for the synthesis of bioactive molecules, pharmaceuticals, polymers, peptides, intermediates and fine chemicals synthesis. Due to cost effectiveness and easy handling of recyclable supported palladium catalyst, it became more popular among researchers either working in academic institute or industry. In recent years, irrespective of poisoning effect of CO with palladium as major limitation, several advancements have been done through surface selection, designing and condition improvement to achieve high yield in the area of carbonylative coupling reactions. We hope this review will be helpful as a ready reference of last 20 years in the field of CO insertion reactions using diverse range of supported palladium catalysts under carbon monoxide or its sources as C1 source.

Iron-iron oxide supported palladium catalyst for the interconversion of formate and carbon dioxide

Synthesized palladium-coated iron-iron oxide (Fe@FeOx/Pd) nanoparticles (NPs) using the successive salt reduction method are tested for their activity and stability toward formate oxidation (FO) and electrochemical CO2 reduction to formate (eCO2RF). The experimental results for FO show a current density at 0.12 V vs. Ag/AgCl of 1.65 mA/cm2 over 1 h, which is 16 times higher than that for Pd NPs. Furthermore, the same catalyst displays a higher current density with a faradaic efficiency (FE) of 95.6 % toward the eCO2RF, and exhibits a lower degree of CO adsorption. The iron-iron oxide interaction with the overlayer palladium is characterized by TEM/EDX, XPS/UPS, Mössbauer spectroscopy, and electrochemical techniques such as cyclic voltammetry (CV) and chronoamperometry (CA). NMR is used to estimate the amount of formate produced by the eCO2RF. A positive binding energy shift of the Pd 3d peak and the upshift of the d-band center as measured by XPS compared to monometallic homemade Pd NPs confirm that the electronic perturbation of the catalyst surface plays a major role in enhancing the performance of Fe@FeOx/Pd for both FO and eCO2RF. Furthermore, the work function as measured by UPS for the Fe@FeOx/Pd material is lower than that for monometallic Pd confirming a change in chemical properties of the catalyst surface. Finally, Mössbauer spectroscopy is used to determine the composition, structure and nature of all sites of the Fe@FeOx substrate before use and the perturbation of their intrinsic properties by the Pd overlayer. This change in intrinsic properties of the Pd coated material provides additional explanations for the electrochemical improvement measured for this catalyst toward both FO and eCO2RF

Synergistic tuning of the phase structure of alumina and ceria-zirconia in supported palladium catalysts for enhanced methane combustion

CeO2–ZrO2–Al2O3 composite oxides supported palladium catalysts (Pd/CZA) are promising candidates for catalytic oxidation reactions. However, the efficient and stable oxidation of methane over Pd-based catalysts remains a longstanding challenge. Herein, we present a facile strategy to boost the catalytic performance of Pd/CZA through elaborately tuning the phase structure of supports. Calcining supports at relatively high temperatures (1200, 1300 °C) induced the phase transition of alumina (from γ-to α-) and the development of CeO2–ZrO2 solid solution (CZ). The weak interaction between α-Al2O3 and PdO resulted in an improved reducibility of catalysts. Meanwhile, the higher oxygen mobility originated from well-crystallized CZ phase contributed to the reoxidation of Pd to PdO, giving rise to abundant surface active Pd2+ species. Coupled with the hydrophobicity of α-Al2O3, the catalyst prepared with CZA supports calcined at 1300 °C demonstrated an excellent low-temperature activity, astounding stability and greatly enhanced water resistance towards methane combustion.

Facile fabrication of TiO2 with 3D hierarchical structure and its supported Pd catalysts for high catalytic hydrogenation performance of 4-Nitrophenol to 4-Aminophenol

TiO2 with different morphology as supports can lead to different surface properties and catalytic activities of catalysts. Herein, we reported a novel facile evaporation-induced assisted hydrothermal approach to synthesize three-dimensional hierarchical structure TiO2 assembled from needle flakes by using Brij-35 as the morphology-directing agent. The morphology of the prepared TiO2 from flower-like (TiO2-FT), sea urchin-like (TiO2-SUT), to ball-like (TiO2-BT), as well as the size of needle flakes, were controlled by adjusting the amount of Brij-35. These TiO2 supported palladium catalysts were facilely prepared using a green bio-reductive method with Catalpa Fruit extract as reducing agent, where they showed remarkable catalytic activity in selective hydrogenation of 4-nitrophenol by sodium borohydride. Especially, 1 wt%Pd/TiO2-SUT with sea urchin-like exhibited higher reaction rate constant (1.44 min−1) than 1 wt%Pd/TiO2-FT (1.08 min−1) and 1 wt%Pd/TiO2-BT (0.72 min−1). Furthermore, XRD, N2 adsorption–desorption, SEM, TEM, CO-FTIR, XPS and CO chemisorption measurements were performed to study the effects of different surface morphologies on the surface properties of catalysts. It reveals that the high catalytic performance of 1 wt%Pd/TiO2-SUT can be attributed to its specific hierarchical structure and much higher surface area, improving the uniform dispersion of Pd nanoparticles on the support to expose extra active surface Pd atoms (Pd0 species) over 1 wt%Pd/TiO2-SUT.

Development of magnetic, ferrite supported palladium catalysts for 2,4-dinitrotoluene hydrogenation

Cobalt, copper, and nickel ferrite spinel nanoparticles have been synthesized by using a combination of sonochemical treatment and combustion. The magnetic nanoparticles have been used as supports to prepare ~4 wt% palladium catalysts. The ferrites were dispersed in an ethanolic solution of Pd(II) nitrate by ultrasonication. The palladium ions were reduced to metallic Pd nanoparticles, which were then attached to the surface of the different metal oxide supports. Thus, three different catalysts (Pd/CoFe2O4, Pd/CuFe2O4, Pd/NiFe2O4) were made and tested in the hydrogenation of 2,4-dinitrotoluene (DNT). A possible reaction mechanism, including the detected species, has been envisaged based on the results. The highest 2,4-diaminotoluene (TDA) yield (99 n/n%) has been achieved by using the Pd/NiFe2O4 catalyst. Furthermore, the TDA yield was also reasonable (84.2 n/n%) when the Pd/CoFe2O4 catalyst was used. In this case, complete and easy recovery of the catalyst from the reaction medium is ensured, as the ferrite support is fully magnetic. Thus, the catalyst is very well suited for applicationy in the hydrogenation of DNT or other aromatic nitro compounds.

Applications of Neutron Scattering in Technical Catalysis: Characterisation of Hydrogenous Species on/in Unsupported and Supported Palladium

Recent results from inelastic neutron scattering (INS) measurements are reviewed that show the synergy between research on hydrogen adsorption/absorption on/in catalysts and chemical engineering. The proton dynamics of catalysts for large scale reactor technology are compared. The focus is the identification and quantification of hydrogenous species on, and inside, fresh, hydrogenated and dehydrogenated palladium black and supported palladium catalysts of different particle size, type of support and, therefore, morphology. INS studies of in-situ hydrogenation/ dehydrogenation of catalysts of 25–60 g size per sample are carried out in stainless steel cans as a function of varying hydrogen pressures. Differences in hysteresis effects in retaining hydrogen inside the catalyst in desorption from palladium hydrides and hydrogen bonding in adsorption sites in varying particle morphologies on different supports were evaluated. This aids the understanding of hydrogen/palladium interactions in catalytic processes with varying local hydrogen partial pressure, e.g. in loop reactors. The importance of the measured on-top Pd–H site in catalytic hydrogenation reactions is discussed together with previous INS results on the degree of deactivation of a technical catalyst by molecular blocking of the on-top site.

Onset of High Methane Combustion Rates over Supported Palladium Catalysts: From Isolated Pd Cations to PdO Nanoparticles

Industrial low-temperature methane combustion catalyst Pd/Al2O3 suffers from H2O-induced deactivation. It is imperative to design Pd catalysts free from this deactivation and with high atomic efficiency. Using a small-pore zeolite SSZ-13 as support, herein we report well-defined Pd catalysts with dominant active species as finely dispersed Pd cations, uniform PdO particles embedded inside the zeolite framework, or PdO particles decorating the zeolite external surface. Through detailed reaction kinetics and spectroscopic and microscopic studies, we show that finely dispersed sites are much less active than PdO nanoparticles. We further demonstrate that H2O-induced deactivation can be readily circumvented by using zeolite supports with high Si/Al ratios. Finally, we provide a few rational catalyst design suggestions for methane oxidation based on the new knowledge learned in this study.

Enhancing stability by trapping palladium inside N-heterocyclic carbene-functionalized hypercrosslinked polymers for heterogeneous C-C bond formations

Catalyst deactivation caused by the aggregation of active metal species in the reaction process poses great challenges for practical applications of supported metal catalysts in solid-liquid catalysis. Herein, we develop a hypercrosslinked polymer integrated with N-heterocyclic carbene (NHC) as bifunctional support to stabilize palladium in heterogeneous C-C bond formations. This polymer supported palladium catalyst exhibits excellent stability in the one-pot fluorocarbonylation of indoles to four kinds of valuable indole-derived carbonyl compounds in cascade or sequential manner, as well as the representative Suzuki-Miyaura coupling reaction. Investigations on stabilizing effect disclose that this catalyst displays a molecular fence effect in which the coordination of NHC sites and confinement of polymer skeleton contribute together to stabilize the active palladium species in the reaction process. This work provides new insight into the development of supported metal catalysts with high stability and will also boost their efficient applications in advanced synthesis.