Palladium Metal Catalysts Research Articles

Selective hydrogenation of vegetable oil over supported noble metal nanocatalyst

Selective hydrogenation of canola oil was tested using a palladium metal catalyst on the graphene layer (G/Pd) nanocatalyst. The reaction was carried out in a batch reactor under mild operating conditions. G/Pd nanocatalyst was studied for the promotion of selectivity instearic acid (C18:0). The Pd catalysts were found to be much more active without the generation isomer such as transfatty acids, due to also the coating on the surface of Pd nanoparticles, during the hydrogenation experiment. The maximum conversion was obtained after 3 h of reaction at 100 °C, with a percentage of stearic acid of > 90 %.

Liquid-phase hydrogenation of carbon tetrachloride catalyzed by three-dimensional graphene-supported palladium catalyst

Abstract In this article, a three-dimensional graphene (3DGN)-supported palladium metal catalyst was prepared by the impregnation method with noble metal palladium as the active component, aiming to synthesize a catalyst with high activity and high selectivity. Its catalytic performance in liquid-phase hydrochlorination of carbon tetrachloride (TTCM) was investigated. The influences of different Pd loadings, reduction temperatures, and reaction temperatures on the catalytic hydrogenation reaction were studied. The purpose is to explore the best operating conditions for the preparation of chloroform. The results show that the 3DGN-supported palladium catalyst exhibits excellent catalytic performance and high selectivity to chloroform in the hydrogenation of TTCM. When the Pd loading was 1.0 wt%, the reduction temperature was 773 K, and the hydrochlorination reaction temperature was 398 K, the conversion of TTCM was as high as 98.12%, and the selectivity of chloroform was 85.23%. The main by-product is dichloromethane. The selectivity of chloroform is affected by the increasing temperature but remains above 80%.

Inexpensive Alkaline Fuel Cell for Introductory Chemistry Classes

Chemical energy storage and use is a critical part of a sustainable world. In this laboratory experiment, students construct and use an inexpensive hydrogen fuel cell to power a calculator or a clock. The reusable cells are prepared from plastic syringes and a nickel mesh that is coated with a palladium metal catalyst by electroless deposition. One syringe is filled with hydrogen gas and the other with air. A sodium hydroxide solution is the bridge between the cells. Students measure the produced voltage and combine two fuel cells to power electronics requiring 1.5 V. The goal is for students to make the connection between theory and practice for symbolic representations of redox reactions and their macroscopic and atomic/molecular interpretations.

Heavy oil viscosity reduction at mild temperatures using palladium acetylacetonate

Metal-ligand compounds (“MLCs”) have been shown to reduce heavy oil viscosity and upgrade oil quality. However, MLCs generally require high treatment temperatures (around 250 °C), which is undesirably energy-intensive. We identified palladium(II) acetylacetonate (“PdA”) as a model MLC that can operate at mild temperatures (<200 °C). We studied its effectiveness on heavy oil viscosity reduction in the range of 80–300 °C using viscometry, SARA analysis, GC–MS, XPS, and XRD to characterize Peace River oil samples thermally treated with and without PdA. This MLC effectively lowered oil viscosity at all treatment temperatures, whereas thermal-only treatments did not reduce viscosity below 160 °C. The thermal treatment with PdA in the 130–250 °C range reduced viscosity by up to ~35% more than the thermal treatment alone. GC–MS and TGA results indicated the PdA partially decomposed at 80 °C and higher temperatures, releasing acetylacetone (“HA”), which lowered oil viscosity. The temperature and HA effects did not completely account for the observed viscosity reduction from thermal treatment with PdA, indicating there were other significant effects. In the 80–130 °C range, the asphaltene fraction increased due to PdA or its decomposition products intercalating into the asphaltene clusters. At temperatures around 250 °C, the resin fraction decreased, correlating to in situ formed metallic Pd that catalytically hydrogenate the resin sulfonyl groups to aliphatic sulfur. This new understanding of the temperature-dependent impact – acetylacetonate ligand, MLC-asphaltene attraction, and palladium metal catalyst formation – on oil viscosity changes provides an improved approach to developing new MLCs for field-relevant conditions.

Pyrolysis of Polyethylene Terephthalate over Carbon-Supported Pd Catalyst

Pyrolysis of polyethylene terephthalate (PET) produces polycyclic hydrocarbons and biphenyl derivatives that are harmful to human health and the environment. Therefore, a palladium metal catalyst (5 wt.% Pd loaded on activated carbon) was used to prevent the formation of harmful materials. When a Pd catalyst/PET ratio of 0.01 was applied in pyrolysis of PET, it did not show a meaningful difference in the generation of polycyclic hydrocarbons and biphenyl derivatives. However, when a Pd catalyst/PET ratio of 0.05 was used during pyrolysis, it prevented their formation and generation at experimental temperature ranges (400–700 °C). For example, the concentration of 2-naphthalenecarboxylic acid produced, which is a typical polycyclic hydrocarbon material, was reduced by 44%. In addition, the concentration of biphenyl-4-carboxylic acid, which is contained in biphenyl derivatives, was reduced by 79% compared to non-catalytic pyrolysis at 800 °C. This was because the ring-opening reaction and free radical mechanism caused by the Pd catalyst and thermal cracking were dominant during the pyrolysis of PET. Apart from these materials, amine compounds were generated as products of the pyrolysis of PET. Amine concentration showed a similar trend with polycyclic hydrocarbons and benzene derivatives. Based on these results, the total concentration of polycyclic hydrocarbons and biphenyl derivatives was compared; the results confirmed that the concentrations of all substances were reduced. This research suggests that a metal-supported catalyst will help create a more environmentally friendly and reliable method of industrial plastic waste disposal.

Oxidative Addition to Palladium(0) Made Easy through Photoexcited-State Metal Catalysis: Experiment and Computation.

Visible-light induced, palladium catalyzed alkylations of α,β-unsaturated acids with unactivated alkyl bromides are described. A variety of primary, secondary, and tertiary alkyl bromides are activated by the photoexcited palladium metal catalyst to provide a series of olefins at room temperature under mild reaction conditions. Mechanistic investigations and density functional theory (DFT) studies suggest that a photoinduced inner-sphere mechanism is operative in which a barrierless, single-electron transfer oxidative addition of the alkyl halide to Pd0 is key for the efficient transformation.

Oxidative Addition to Palladium(0) Made Easy through Photoexcited‐State Metal Catalysis: Experiment and Computation

AbstractVisible‐light induced, palladium catalyzed alkylations of α,β‐unsaturated acids with unactivated alkyl bromides are described. A variety of primary, secondary, and tertiary alkyl bromides are activated by the photoexcited palladium metal catalyst to provide a series of olefins at room temperature under mild reaction conditions. Mechanistic investigations and density functional theory (DFT) studies suggest that a photoinduced inner‐sphere mechanism is operative in which a barrierless, single‐electron transfer oxidative addition of the alkyl halide to Pd0 is key for the efficient transformation.

Enhanced Electrocatalytic Activity of Branched Pd Nanostructures Decorated Conducting Polymer Nanofibers for Alkaline Fuel Cells

Conducting polymer nanostructures having anisotropic morphology and rich redox properties, employed as support for palladium metal catalysts for electrooxidation of ethanol. Polypyrrole nanofibers have been first synthesized using soft oxidative templates and consequently, a unique Pd-branched structure was nucleated on the polymer surface by photo-reduction method. Polymer supportedelectrocatalystsdemonstratedexcellentethanol oxidation activity (EOR)compared to commercial carbon supported catalysts Pd/Cin terms of current density. This work demonstrates a new and facile approach for the synthesis of electrocatalysts with both the enhanced activity and durability for fuel cell applications.

Development and Evaluation of a Borohydride-palladium System for Selective Reduction of the C=C Bond of α,β-unsaturated Carbonyl Compounds

Selective reduction of the carbon-carbon double bond of α,β-unsaturated carbonyl compounds is most commonly and reliably effected using a palladium metal catalyst together with molecular hydrogen from a pressurized tank. Sodium borohydride, like other hydrides, is ordinarily associated with reduction of the more polarized carbonyl of such compounds. However, we have developed an alternative means of employing sodium borohydride in combination with palladium metal to selectively reduce the carbon-carbon double bonds of these compounds. In this survey study, we introduce sodium borohydride as an alternative hydrogen source for such selective, palladium-catalyzed reductions. We also compare the results of this new, heterogeneous borohydride-palladium method with that of traditional palladium-catalyzed hydrogenation. A third method using only sodium borohydride with no palladium is included for comparison.

Selective Hydrogenation of Naphthols to Tetralones over Supported Palladium Catalysts in Supercritical Carbon Dioxide Solvent

Abstract Naphthols were selectively hydrogenated to the corresponding tetralones over supported palladium metal catalysts in supercritical carbon dioxide solvent.

Functional resins in palladium catalysis: promising materials for Heck reaction in aprotic polar solvents

The performances of palladium metal catalysts supported by organic resins containing tertiary amino, cyano, carboxyl, and pyridyl groups have been investigated in standard Heck reactions. The catalysts were prepared by either immobilization in the resins of palladium(II) precursors and chemical reduction thereof or by deposition of solvated metal atoms obtained by means of metal vapor synthesis (MVS). Particular attention was paid to the nature of catalysis in the presence of these materials. As the observed catalytic activity turned out to be generally associated with metal leaching, the reaction was most likely catalyzed in solution by soluble, active palladium species. However, a MVS 1% (w/w) catalyst supported by a commercial polyvinylpyridine resin cross-linked with divinylbenzene exhibited an appreciable catalytic activity with a possible partial contribution from supported active palladium species.

Generating palladium nanoclusters inside very lipophilic gel-type functional resins: preliminary catalytic tests in the hydrogenation of 2-ethyl-anthraquinone to 2-ethylanthrahydroquinone

Four lipophilic polystyrene–methacryloylethylensulfonic acid–divinylbenzene gel-type resins, with 2 and 4% cross-linking degree, are synthesized and used as supports for “atomic” dispersion of Pd(II) finalized to the preparation of resins-supported palladium metal catalysts. Properly performed reduction of Pd(II) to Pd(0) achieves homogeneous dispersion of ca. 3 nm metal nanoclusters inside the supports particles in the more cross-linked resin. Resulting resin-supported palladium catalysts are efficient and moderately chemoselective in the hydrogenation of 2-ethylanthraquinone to 2-ethylanthrahydroquinone.

Oscillatory behaviour during the oxidation of methane over palladium metal catalysts

Oscillatory reactions over palladium foil and wire catalysts during the oxidation of methane have been investigated over a wide range of reaction temperatures and argon/methane/oxygen feed gas compositions. Characterisation of the catalyst has also been carried out using scanning electron microscopy (SEM) techniques, which revealed the presence of a porous surface. This suggested that the metal surface has undergone a change since the reaction commenced, and using X-ray powder diffraction (XRD) techniques the palladium phase was shown to be the dominant phase present. Hysteresis phenomena were observed in the activity of the reaction as the temperature was cycled up and down, showing that the metal surface was continually changing throughout the reaction. The activation energies of the reaction during the high reactivity mode, PdO, and low reactivity mode, Pd, were also calculated. Oscillation rates were observed to depend on the dominant surface. Oscillations were frequent when the high reactivity mode was dominant while the activation energy of this mode was found to be low. When the low reactivity mode was dominant, the oscillations were slower and the activation energy was three times larger. The results obtained imply that the behaviour of the palladium surface, switching back and forth from the reduced state to the oxidised state, is responsible for the oscillatory behaviour seen in this system.

Palladium metal catalysts in Heck CC coupling reactions

This review is devoted to the application of palladium metal catalysts to the Heck reaction (arylation or vinylation of alkenes with aryl or vinyl halides and pseudohalides). The number of relevant articles published in recent years shows steadily increasing interest in this field. A brief outline of the historical development of heterogeneous catalysis as applied to the Heck reaction is given ( Section 2). Both supported metal catalysts ( Section 3) and stabilized colloidal palladium catalysts ( Section 4) are included. Heterogeneous catalysts supported over different kinds of supports (carbon, inorganic oxides, molecular sieves, polymeric materials, etc.) are reviewed under separate headings. Particular attention is paid to the metal leaching and the nature of catalysis, two tightly connected problems which appear to be still controversial ( Section 5). Some perspectives are shortly discussed in the final section ( Section 6).

Metallic Palladium in the Heck Reaction: Active Catalyst or Convenient Precursor?

Novel experimental evidence is presented pointing out that “heterogeneous” palladium metal catalysts employed in Heck-type reactions mainly act as sources of soluble palladium(II) complexes, which are the true catalytically active species.

Combination Catalysts Consisting of a Homogeneous Catalyst Tethered to a Silica-Supported Palladium Heterogeneous Catalyst: Arene Hydrogenation

Combination Catalysts Consisting of a Homogeneous Catalyst Tethered to a Silica-Supported Palladium Heterogeneous Catalyst: Arene Hydrogenation

The preparation of palladium metal catalysts supported on carbon part II: Deposition of palladium and metal area measurements

Four techniques for Pd deposition were compared and various carbons from Part I were used. Increasing burnoff produced higher area of the support and higher available metal area. However, excessive removal of carbon resulted in a decrease in Pd area for a given loading. Although HNO 3 treatment did not produce an increase in carbon area, there were significant increases in catalyst areas for some deposition techniques. Carbon deposition appeared to block micropores to some extent, but was disappointing in the areas of Pd found on these samples. A favorable technique would seem to be to use 15 to 20% burnoff followed by HNO 3 acid washing and the impregnation adsorption deposition method.

The preparation of palladium metal catalysts supported on carbon part I: Selection and treatment of the carbons

Carbons are widely used as supports for precious metal catalysts. The carbon should be carefully chosen to have a high area and a minimum of micropores. A number of commercial carbons have been chosen and examined by nitrogen adsorption to determine their surface properties. Some of the carbons have been subjected to carbon burnoff, acid soaking, and/or deposition of carbon via a polymer. Changes in surface properties are brought about by burnoff, but the carbons retain a large proportion of microporosity, although mesopore volume is increased. Acid washing does not have a significant effect on area or pore volume. Deposition of carbon results in pore volume decrease including volume of micropores.

Antimony-doped stannic oxide-based thick-film gas sensors

The use of stannic oxide thick films that incorporate antimony as a structural dopant for sensing combustible gases in oxidizing and fixed water vapor-containing atmospheres in described. Data on the hydrogen and carbon monoxide responses of thick films that were made with one of the most electronically conductive and chemically-stable antimony-doped compositions of stannic oxide are presented. The reliability and accuracy of the gas response were ensured by the addition of 5 wt.% palladium metal catalyst and/or other film matrix diluents, such as 5 wt.% magnesium oxide and 9 wt.% oxidation-resistant nickel silicide. The data were obtained at selected temperatures, within the range 250 – 500 °C, and with film support configurations adaptable to industrial units where in situ combustible gas monitoring is required for combustion control. Calibration procedures simulating field test conditions are also discussed.

Hydrodehalogenation of bromo- and chloropyridines over palladium complex and palladium metal catalysts

The hydrodehalogenation of 2-chloro-, 2-bromo-, 3-bromo, and 3,5-dibromopyridine has been studied in the presence of a palladium complex catalyst immobilized on silica gel, and a Pd/C catalyst. Cleavage of bromine from bromopyridines over the Pd complex is significantly faster than from the bromo-substituted furanes and thiophenes previously studied. Debromination over Pd/C is faster than over the complex catalyst. Over both catalysts 3-bromopyridine debrominates faster than the 2-isomer. When molecular deuterium is used, the respective deuterated pyridines can be obtained.