Hydrogenation of methyl sorbate and soybean esters with polymer-bound metal catalysts

New polymer-bound hydrogenation catalysts were made by complexing PdCl₂, RhCl₃·3H₂O, or NiCl₂ with anthranilic acid anchored to chloromethylated polystyrene. The Pd(II) and Ni(II) polymers were reduced to the corresponding Pd(O) and Ni(O) catalysts with NaBH₄. In the hydrogenation of methyl sorbate, these polymer catalysts were highly selective for the formation of methyl 2-hexenoate. The diene to monoene selectivity decreased in the order: Pd(II), Pd(O), Rh(I), Ni(II), Ni(O). Kinetic studies support 1,2-reduction of the Δ4 double bond of sorbate as the main path of hydrogenation. In the hydrogenation of soybean esters, the Pd(II) polymer catalysts proved superior because they were more active than the Ni(II) polymers and produced lesstrans unsaturation than the Rh(I) polymers. Hydrogenation with Pd(II) polymers at 50~100 C and 50 to 100 psi H₂ decreased the linolenate content below 3% and increasedtrans unsaturation to 10~26%. The linolenate to linoleate selectivity ranged from 1.6 to 3.2. Reaction parameters were analyzed statistically to optimize hydrogenation. Recycling through 2 or 3 hydrogenations of soybean esters was demonstrated with the Pd(II) polymers. In comparison with commercial Pd-on-alumina, the Pd(II) polymers were less active and as selective in the hydrogenation of soybean esters but more selective in the hydrogenation of methyl sorbate. Presented at ISF-AOCS Meeting, New York, April 1980.     

Efficient Anchorage of Palladium Nanoparticles on the Multi‐Walled Carbon Nanotubes as Electrocatalyst for the Hydrazine Electrooxidation in Strong Acidic Solutions

A facile homogeneous precipitation–reduction reaction method, which involves PdCl₂ → PdO · H₂O → Pd⁰ reaction path, is used to synthesize the multi‐walled carbon nanotubes (MWCNTs) supported Pd nanoparticles (Pd/MWCNTs) catalysts. The particle size of Pd/MWCNTs catalysts can be easily tuned by controlling the hydrolysis temperature of PdCl₂. X‐ray diffraction (XRD) and transmission electron microscopy (TEM) measurements show the particle size of Pd/MWCNTs catalysts increases with hydrolysis temperature of PdCl₂, which is ascribed to the fact that the particle size of PdO · H₂O nanoparticles increases with hydrolysis temperature of PdCl₂. At the lower hydrolysis temperature, the as‐prepared Pd/MWCNTs catalyst possesses the higher dispersion and the smaller particle size. Consequently, the resultant Pd/MWCNTs catalyst exhibits the big electrochemical active surface area and the excellent electrocatalytic performance for hydrazine electrooxidation in strong acidic solutions. In addition, the electrochemical measurement indicate that particle size effect of Pd‐NPs occurs during the N₂H₄ electrooxidation. In brief, the mass activity and specific activity of the Pd/MWCNTs catalyst increases and decreases with decreasing the particle size of Pd‐NPs for the N₂H₄ electrooxidation, respectively.     

On the deactivation of supported palladium hydrogenation catalysts by thiophene poisoning

The deactivation of supported palladium catalysts for ethylbenzene hydrogenation by thiophene was studied. The presence of Pd ⁿ⁺ species on the catalyst surface, in samples prepared from acid solutions of PdCl₂, and reduced at temperatures below 450 °C, was evidenced by XPS. A correlation between the concentration of electron-deficient Pd species and the sulfur resistance was found. Thus, the higher the value of the Pd ⁿ⁺/Pd⁰ ratio, the higher the sulfur resistance. Catalysts prepared from Pd(NO₃)₂ or from PdCl₂ reduced at 450 °C, which essentially contain Pd⁰, are more quickly deactivated. Furthermore, our results also suggest that while the influence of the metal dispersion on the stability of the palladium catalysts toward sulfur is not significant, the nature of the support, on the other hand, plays an important role.     

Effect of residual Cl− derived from metal precursors on catalytic activity in the hydrogenation of naphthalene over supported Pd catalysts

Hydrogenation of naphthalene was performed over supported Pd catalysts prepared from precursors that contained Cl⁻ and from precursors that were free of Cl⁻. The activity of catalyst prepared from PdCl₂ was much higher than that prepared from Pd(NH₃)₂(NO₂)₂. The species of Pd precursor strongly affected the activity of Pd/Al₂O₃, whereas no significant influence was observed in the effect of Pd/SiO₂, because residual Cl⁻ was easily removed by calcination and/or reduction. Catalytic activity was increased by addition of NH₄Cl to Cl⁻-free Pd/Al₂O₃. Residual Cl⁻ was concluded to enhance the catalytic activity of the supported Pd catalysts.     

The electrochemical reduction of PdCl4 and PdCl6 in polyaniline: Influence of Pd deposit morphology on methanol oxidation in alkaline solution

The controlled uptake and electrochemical reduction of metal precursors PdCl₄²⁻ and PdCl₆²⁻ in polyaniline (PANI) is demonstrated. The formation of PANI/Pd composites is achieved with a reduction in proton doping and an increase in the oxidation of the polymer with Pd deposits physically blocking the nitrogen groups. High surface area filaments (PdCl₄²⁻) or a rough encapsulation (PdCl₆²⁻) of Pd metal on PANI are obtained. The structural differences highlight the influence of the metal precursor oxidation state on the morphology of the Pd deposits in PANI. Thermal gravimetric analysis provides an estimate of the Pd content for each composite of ∼40%. X-ray Photoelectron Spectroscopy and X-ray-excited Auger Electron Spectroscopy analyses confirm the deposition of Pd metal. The catalytic oxidation of methanol was demonstrated for both PANI/Pd composites in alkaline solutions that prohibit proton doping of the polymer. The data indicates that Pd metal acts as a solid-state dopant that may delocalize the charge on the polymer backbone to maintain conductivity. Methanol oxidation at PANI/Pd composites produced using PdCl₄²⁻ was enhanced relative to the composite produced using PdCl₆²⁻ and a planar Pd electrode. Comparison of PANI/Pd composite produced using PdCl₄²⁻ with other Pd catalysts from the literature indicates surface poisoning is reduced when Pd is coupled with the polymer. The composite is robust and stable in alkaline solution with the charge density decreasing by 5% on the positive scan and 13% on the negative scan after 200 voltammetric cycles. The data also indicates that the reductive desorption of surface contaminants is possible, minimizing the catalytic loss due to surface poisoning.     

Palladium(II) complexes bearing the new pincer ligand 3,5-bis(indazol-2-ylmethyl)toluene; synthesis and catalytic properties

The reaction of 3,5-bis(bromomethyl)toluene with 1H-indazole in toluene, in the presence of triethylamine, yields the ligand 3,5-bis(indazol-2-ylmethyl)toluene (1). Compound 1 reacts with Pd(OAc)₂ in refluxing acetic acid, followed by a metathetic reaction with lithium chloride and with [PdCl₂(cod)] (cod = 1,5-cyclooctadiene) in refluxing acetonitrile to give the complexes [PdCl{3,5-bis(indazol-2-ylmethyl)tolyl-N,C,N}] (2) and [PdCl₂{3,5-bis(indazol-2-ylmethyl)toluene-N,N}] (3), respectively. Compounds 1–3 were characterized by elemental analyses, mass spectra and IR and NMR (¹H, ¹³C) spectroscopies. The molecular structure of 1 was also determined by single-crystal X-ray diffraction. The palladium(II) complexes (2,3) were tested as catalysts in ethylene polymerization and in C–C coupling reactions involving aryl halides substrates.     

The reaction between Pt- and Pd-cis di-chloro complexes and 4,4′-diethynylbiphenyl: synthesis and characterisation of a ‘zigzag’ metal/poly-yne polymer

The synthesis of poly-yne polymers containing transition metals inserted in the main chain has been attempted by reacting a dialkyne molecule, 4,4′-diethynylbiphenyl (or DEBP), with [PtCl₂(dppe)] and [PdCl₂(dppe)], the platinum- and palladium-cis square-planar di-chlorine complexes containing diphenylphosphine ethane (dppe) as bidentate ligand. The aim of this work was to obtain organometallic polymers ([Pt(dppe)DEBP]_n and [Pd(dppe)DEBP]_n, respectively) having an all-cis ‘zigzag’ structure, by formation of a σ-acetylide bond between the transition metal complexes and the dialkyne molecule. When [PtCl₂(dppe)] was reacted with DEBP, the formation of a chlorine-terminated [Pt(dppe)DEBP]_n oligomer was evidenced; in the reaction involving the Pd(II) complex, on the other hand, [PdCl₂(dppe)] seems to catalyse the polymerisation of DEBP via opening of the triple bond, producing a poly-DEBP polymer containing Pd(II) atoms inserted in the main chain.     

Observation of [Al(OH) n (H2O)6-n ] n (MoO4) in hydrotreating catalyst precursors by solid-state27 Al NMR

A previously unobserved octahedral²⁷Al MAS NMR resonance has been detected in rehydrated calcined Mo/Al₂O₃ hydrotreating catalyst precursors. This resonance is attributed to the presence of hydrated forms of aluminum molybdate such as [Al(OH) _n (H₂O)_6-n ] _n (MoO₄) (n = 1 or 2). The cross-polarization relaxation parameters, obtained from variable contact time experiments, yielded information on the relative sizes of the [Al(OH) _n (H₂O)_6-n ] _n (MoO₄) domains in the catalysts with different molybdenum loadings. Analysis of the²⁷A1 MAS NMR spectra of P-Mo(8)/Al₂O₃ and P-Mo(12)/Al₂O₃ (wt%P = 0.0–12.0) shows that a function of the phosphate in the 12 wt% Mo catalyst is to prevent the re-hydration of the molybdate phases on the calcined catalysts.     

TiOx/Pd interfacial catalysts with controllable geometrical/electronic effects for industrial H2O2 production

Aiming at controllable modulating metal−support interactions to achieve an optimal trade-off of geometric/electronic effect in supported catalysts, we developed a reliable approach based on the typical 2D material layered double hydroxide (LDHs). A series of TiO_x/Pd/MgTiAl-MMO-X catalysts with adjustable interfacial effect were acquired by loading PdCl₄²⁻ precursor and further preciously adjusting the topological reduction temperature, based on the regulatory effect of Mg–O–Ti–O–Al–O structure in the support on the reducibility and mobility of Ti⁴⁺. The catalysts with semi-continuous and accessible TiO_x/Pd interface, confirmed by AC-HAADF-STEM, CO chemisorption, XPS, exhibit much higher H₂O₂ yield than the catalyst with over-encapsulation structure. The TiO_x/Pd/MgTiAl-MMO-450 catalysts possessed optimal geometric and electronic structure exhibited the highest activity with TOF of 9.75 s⁻¹, excellent H₂O₂ yield of 11.4 g/L, as well as good stability.     

Synthesis of polymers having arylene-vinylene units by palladium-catalyzed hydroarylation polymerization of diethynylbenzene derivatives

Summary Arylene-vinylene-containing polymers with fully aromatic backbone structures were prepared by the palladium-catalyzed hydroarylation polymerization of diethynylbenzene derivatives with diiodobenzene and alkylmalonate anions as a hydride source. For instance, the polymerization of 1,4-bis(4'-dodecyloxy)phenylethynylenebenzene, diiodobenzene, and sodium diethyl benzylmalonate was carried out at 80°C for 2 days in 1,4-dioxane in the presence of Pd(OAc)₂ / tri-o-tolylphosphine (7 equiv. to Pd) to produce a polymer (M _n= 6,390, M _w/M _n= 1.53) in high yield (86 %). Using various diethynylbenzene derivatives, polymers having arylene-vinylene units were also obtained in high yields. Received: 16 December 1999/Accepted: 20 January 2000     

Electrodeposition of palladium in a hydrophobic 1-n-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide room-temperature ionic liquid

The electrochemical reduction of palladium halide complexes such as PdBr₄²⁻ and PdCl₄²⁻ was investigated in a hydrophobic room-temperature ionic liquid (RTIL), 1-n-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPTFSI). The irreversible electrode reaction between Pd(II) and Pd(0) was observed in BMPTFSI containing PdBr₄²⁻ or PdCl₄²⁻ by cyclic voltammetry. The diffusion coefficient of PdBr₄²⁻ was estimated to be (1-2) × 10⁻⁷ cm² s⁻¹ by choronopotentiometry and chronoamperometry. The deposition of crystalline Pd metal was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy. It was suggested by the chronoamperometric measurements on PdBr₄²⁻ in BMPTFSI that the initial stage of the electrodeposition of Pd on the polycrystalline Pt electrode surface involves three-dimensional progressive nucleation under diffusion control. The reduction potential of PdCl₄²⁻ was more negative than that of PdBr₄²⁻, reflecting the difference in the donor property between chloride and bromide.     

Oxidative carbonylation of phenol to diphenyl carbonate catalyzed by Pd complex with diimine ligands

Pd complexes with diimine ligands were investigated as novel Pd catalysts for direct synthesis of diphenyl carbonate by oxidative carbonylation of phenol using carbon monoxide and air. Best efficiency was obtained by using a PdCl₂(ArN=CH–)₂ or PdCl₂(ArN=CMe–)₂/Mn(TMHD)₃/(Ph₃P=)₂NBr system where TOF reached 8.08 and 8.00 mol-DPC/mol-Pd h, respectively. The efficiency was increased with increases in the CO pressure.     

Synthesis and physicochemical characterization of nanostructured Pd/ceria‐clinoptilolite catalyst used for p‐xylene abatement from waste gas streams at low temperature

BACKGROUND: The effect of Pd loading, xylene concentration and GHSV on xylene oxidation was tested over Pd/CeO₂(30%)‐clinoptilolite nanocatalysts at low temperatures. The catalysts were prepared by acid treatment of clinoptilolite, followed by the incipient wetness method of synthesized ceria and modified clinoptilolite in PdCl₂ solution. The synthesized nanocatalysts were characterized by XRD, FESEM, EDAX, TEM, BET, FTIR and TG‐DTG analysis. RESULTS: The XRD patterns confirmed the formation of crystalline ceria with an average crystallite size of 11.8 nm. FESEM images showed nanostructures in cavities of natural zeolite, brought about by ceria incorporation and acid activation. TEM analysis showed high dispersion of Pd with a size distribution between 6.6 and 36.7 nm. The quantitative analysis showed that the specific surface area of Pd(1%)/CeO₂(30%)‐clinoptilolite was 77 m² g^?1. The results showed that Pd(1%)/CeO₂(30%)‐clinoptilolite is the most appropriate catalyst, with the conversion more than 90% at 275 °C. CONCLUSIONS: Experimental results established effective performance and durability for the catalysts. As a result, clinoptilolite modification and ceria incorporation significantly altered the samples' morphology at nanoscale, improving the structure of composites and distribution of noble metals. A reaction path was suggested based on the adsorption‐migration of species to reveal the mechanism of p‐xylene oxidation over nanocatalysts. © 2012 Society of Chemical Industry     

Homogenous catalysis in the reactions of olefinic substances. V. Hydrogenation of soybean oil methyl ester with triphenylphosphine and triphenylarsine palladium catalysts

Some palladium complexes containing coordinated triphenylphosphine or arsine have been found to be effective and selective catalysts in the homogeneous hydrogenation of soybean oil methyl ester. The characteristic features of the catalysis are 1) isomerization ofcis double bonds totrans double bonds, 2) migration of isolated double bonds to form conjugated dienes, 3) selective hydrogenation of poly olefines to mono olefines without hydrogenation of mono olefine, 4) ester exchange of methyl ester to butyl ester, 5) effective hydrogenation and isomerization by methanol in the absence of elemental hydrogen. The catalytic activity of a variety of palladium complexes decreases in the following order: (ϕ₃P)₂PdCl₂+SnCl₂·2H₂O>(ϕ₃P)₂PdCl₂+GeCl₂>(ϕ₃P)₂Pd(CN)₂> (ϕ₃As)₂Pd(CN)₂>(ϕ₃P)₂PdCl₂≫(ϕ₃As)₂PdCl₂. However, neither K₂PdCl₄ with SnCl₂·2H₂O nor (ϕ₃P)₂Pd(SCN)₂ was effective for hydrogenation. The hydrogenation and isomerization of soybean oil methyl ester have been examined under various conditions using a mixture of (ϕ₃P)₂PdCl₂ and SnCl₂·2H₂O. Under nitrogen pressure, in benzene and methanol as a solvent, both isomerization and hydrogenation of soybean oil methyl ester proceeded less effectively than under hydrogen pressure. This work was done under contract with the USDA. Earlier articles in the series are: I, Inorg. Chem.4, 1618 (1965): II, Proceedings of the Symposium on Coordination Chemistry (Tihany, Hungary, 1964), Edited by M. T. Beck, Budapest, 1965; III, JAOCS43, 337 (1966); IV, Advances in Chemistry Series, American Chemical Society, in press.     

MECHANISTIC STUDIES ON THE EXTRACTION OF PALLADIUM(II) WITH DIOCTYL SULPIDE

ABSTRACT The equilibrium and kinetics of the extraction of palladiura(II) ion with dioctyl sulfide (R-S) in chloroform have been studied at 25 C and an ionic strength of 1.0 M. The extracted species was found to be pdcl₂ (R₂S) and to have an extraction constant log K_ex. =9.84 The observed rate expression for the extraction:

-d[Pd]_T/dt = k [Pd]_T[R₂S]_o/[cl^-],

supports a mechanism in which the rate-determining step is the reaction of PdCl₃(H₂O) ^- with R₂ S in the aqueous phase.     

Methanol Decomposition to Synthesis Gas Over Supported Pd Catalysts Prepared from Hydrotalcite Precursors

Supported Pd catalysts were prepared by solid-phase crystallization (spc) starting from MgAl hydrotalcite anionic clay minerals as the precursors, and were tested for the methanol decomposition to synthesis gas. The precursors based on [Mg₆Al₂(OH)₁₆CO₃ ^2-] · 4H₂O were prepared by coprecipitation from raw materials containing Pd²⁺, Mg²⁺ and Al³⁺ ions as the components of hydrotalcite. The precursors were thermally decomposed and reduced to afford supported Pd catalysts on MgAl mixed oxide. Pd-supported catalysts as a reference were also prepared by the impregnation (imp) method. The spc-Pd catalysts thus prepared afforded highly dispersed Pd metal particles and showed higher activity as well as lower activation energy than the imp-Pd catalysts. When the precursor was prepared under mild conditions, finer particles of Pd metal were formed over the catalyst, resulting in a high activity. In the case of spc-Pd catalysts, carbon monoxide adsorbed on Pd easily desorbed, compared with imp-Pd catalysts. It is likely that the high activity is due to the highly dispersed and stable Pd metal particles and the easy desorption of carbon monoxide.     

Amphiphilic ionic palladium complexes for aqueous–organic biphasic Sonogashira reactions under aerobic and CuI-free conditions

The ionic Pd(II)-complexes of 2 (ammonium-[1-(2-hydroxyethyl)-3-methylimidazolium] bis[3-(diphenylphosphino)benzenesulfonate]-dichloropalladium(II) ([(NH₄)(Hemim)][PdCl₂(TPPMS)₂])) and 3 (bis[1-n-butyl-3-methylimidazolium] bis[3-(diphenylphosphino)benzenesulfonate]-dichloropalladium(II) ([Bmim]₂[PdCl₂(TPPMS)₂])) were synthesized and fully characterized. The single crystal X-ray diffraction analyses show that 2 and 3 are composed of the imidazolium-based cations and [PdCl₂(TPPMS)₂]^2 − anions. The properties of such imidazolium-based Pd-complexes of 2 and 3, in terms of the aqueous solubilities and the catalytic behaviors in water, could be dramatically varied. When 2 and 3 were applied as the precatalysts for the Sonogashira coupling of iodobenzene with phenylacetylene under aerobic and CuI-free conditions, the much higher yields of 1,2-diphenylethyne were obtained due to their amphiphilicity. The wide generality of 2 was available for aqueous–organic biphasic Sonogashira reactions.     

A study of the Pd/C catalyst for synthesis of hydroxylamine

Palladium dispersed on active carbon (Pd/C) is used as a catalyst in the synthesis of hydroxylamine. Alkaline precipitation was used to prepare the catalyst. It was found that the controlling factor was the size of palladium crystal, which in turn was chiefly determined by the PdCl₄^2-/Pd(OH)₂ conversion stage. The sintering and crystal growth of Pd was the main reason for the decay of the catalyst. The sintering mechanism was found to follow the Ostwald ripening model.     

SEPARATION OF PALLADIUM(II) FROM PLATINUM(II), IRIDIUM(III), AND RHODIUM(III) USING CENTRIFUGAL PARTITION CHROMATOGRAPHY

The separation of Pd(II) from Pt(II), Ir(III) and Rh(III) with trioctylphosphine oxide (TOPO) in heptane using centrifugal partition chromatography (CPC) has been investigated for the first time. The extraction of Pd(II) has been studied by CPC and batch solvent extraction. The distribution ratios for Pd(II) determined by both methods agree well. In low HCl concentrations (<0.1 M), the extracted species was PdCl₂.(TOPO)₂, irrespective of the chloride concentration, while at acid concentrations above 0.1 M, the Pd was extracted as the ion pair, 2(TOPO.H⁺).PdCl₄ ^2-. Base line separation of Pd(II) and Pt(II) in CPC was obtained under a variety of chloride and HCl concentration with the average number of theoretical plates being 390 ± 40 at a flow rate of 0.47 ± 0.05 mL/min.     

Catalytic conversions in water. Part 5: Carbonylation of 1-(4-isobutylphenyl)ethanol to ibuprofen catalysed by water-soluble palladium–phosphine complexes in a two-phase system

1-(4-Isobutylphenyl)ethanol (IBPE) was carbonylated to 2-(4-isobutylphenyl)propionic acid (ibuprofen) in an aqueous/organic two phase system using the water-soluble Pd(tppts)₃ catalyst [tppts = P(C₆H₄-m-SO₃Na)₃] in the presence of p-CH₃C₆H₄SO₃H at 363 K, 15 MPa CO pressure and a palladium concentration of 150 ppm without addition of organic solvents. Under these conditions the conversion of IBPE was 83% and the selectivity to ibuprofen 82% with no decomposition of the Pd(tppts)₃ catalyst. Both the activity and selectivity were strongly influenced by the tppts/Pd molar ratio and the nature of the added Brønsted acid. Maximum efficiency was observed for P/Pd = 10. Acids of weakly or non-coordinating anions, such as p-CH₃C₆H₄SO₃H, CF₃COOH or HPF₆ afforded carbonylation. No catalytic activity was observed in the presence of acids of strongly coordinating anions, such as HI. The water-soluble Pd/dppps catalyst [dppps = Ar_2-nPh_nP-(CH₂)₃-PPh_n′Ar_2-n′; Ar = C₆H₄-m-SO₃Na; n = nń = 0: 86% and n = 0, nń = 1: 14%] exhibited low catalytic activity and the major product obtained was the linear isomer of ibuprofen, 3-(4-isobutylphenyl)propionic acid (3-IPPA) with selectivities up to 78%. Replacement of tppts by a ligand containing less −SO₃Na groups such as monosulphonated triphenylphosphine (tppms) gives rise to a dramatic drop in the catalytic activity and selectivity to ibuprofen. No catalytic activity was observed using palladium catalysts modified with 2-pyridyldiphenylphosphine (PyPPh₂) and tris(2-pyridyl)phosphine (PPy₃) which are both water soluble in their protonated form. A catalytic cycle is proposed to explain the observed results. ©1997 SCI