Catalytic conversions of coumarans

The dehydrogenation of 2-methylcoumaran on platinum, palladium, and rhodium catalysts deposited on carbon (content of the metal 5%), has been studied. The maximum yields of 2-methylbenzofuran at 300–350° C were 89, 95, and 81%, respectively, for Pt, Rh, and Pd, the yield of catalyzates being 98–99%.     

Hydrogermylation of phenylacetylene catalyzed by onium chlorometallates

Triethylbenzylammonium chlorometallates [Et₃NCH₂Ph][MCl_n]^m? (M = Pt, Pd, Rh, Ir, Fe, Co, Cu, m = 1–3, n = 3–6), polymer-anchored ionic metal complexes [?—CH₂PBu₃][MCl_n]^n? and some other chlorometallates and complexes of platinum, rhodium, ruthenium and osmium were studied as catalysts in the hydrogermylation of phenylacetylene with triethylgermane. All the complexes containing platinum, palladium and rhodium were found to be effective catalysts. The cis/trans ratio of the products obtained is determined by the metal atom involved and decreases in the following order: Ir > Rh ? Pd > Pt.     

Heterogenization of palladium(II) chelates on a sibunite

Summary Heterogenized palladium(II) chelates have been prepared by a sibunite treatment of acetone or aqueous solutions of palladium complexes with alizarin red C, 4- anilino-pent-3-en-2-one,N, N-bis(acetylacetone)ethylenediamine, 1-phenyl-4-methylpent-4-en-1,3-dione and 1-phenyl-3-anilino-4-methylpent-4-en-1-one. The catalytic properties of these chelates in chloronitrobenzene hydrogenation have been studied. It was found that the catalytic activity approaches 159 mol H₂ (mol Pd min)^–1 depending on the chlorine atom position in the aromatic ring and the nature of the solvent. The catalysts do not lose their activity after five cycles. The products of chloronitrobenzene hydrogenation are chloroanilines (up to 90%), azo- and azoxychlorobenzenes (5–7%) as a result of incomplete reduction as well as small quantities (2–5%) of dehalogenated azo-, azoxybenzenes and aniline.     

The investigation of redox properties of palladium-zeolite catalysts

Palladium catalysts based on A, X, Y, chabazite, erionite, mordenite, TsVM, and TsVK zeolites are studied by the methods of temperature-programmed reduction and hydrogen desorption. Palladium is shown to be located in zeolite pores in all catalysts except Pd/mordenite for which 24 % of the palladium is located on the external surface of the zeolite. The dispersity of the palladium on the zeolites is determined by the amount of H₂ evolved in the decomposition of the -phase of PdH and by the value of the O/Pd ratio obtained by palladium oxidation in the 100 to 500 °C temperature range. According to the O/Pd ratio, the catalysts are divided into two groups: samples based on X, Y, chabazite, erionite, and mordenite (O/Pd=0.4 to 0.7), and catalysts containing A, TsVM, and TsVK zeolites (O/Pd=0.2 to 0.3). The catalysts of the first group are weakly active in the oxidative acetoxylation of propylene, while all of the catalysts of the second group except Pd/NaA are very active. The conclusion is drawn that the oxidation of palladium is not the limiting stage in the oxidative acetoxylation of propylene.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 642–648, April, 1995.     

Pt/Pd/C catalysts with ultra low platinum content for oxygen reduction reaction

The activity of Pt/Pd/C ETEK catalysts of the core-shell type with an ultralow content of platinum (0.5–15 μg cm^?2) based on a commercial palladium catalyst is shown to exceed the activity of commercial Pt/C ETEK catalysts in the oxygen reduction reaction. The activity sharply increases with the decrease in the platinum content down to values corresponding to monolayer and submonolayer of platinum on palladium. This dependence wasn’t observed for the same amounts of platinum deposited on the carbon support Vulcan XC-72. This makes it possible to conclude that the most probable factor responsible for the high catalytic activity of Pt/Pd/C ETEK is the effect of palladium on the electronic properties of platinum rather than the effect of structural modification of the platinum deposit induced by the decrease in the platinum amount deposited on a foreign metal or a carbon support.     

Simultaneous Potentiostatic Coulometric Determination of Platinum and Palladium

Based on a voltammetric study of the electrochemical behavior of Pt(IV) and Pd(II) in a 1 M HCl + 0.1 M ethylenediamine hydrochloride solution at a carbon–graphite electrode, we have found the optimum conditions for the simultaneous determination of 0.2 to 3 mg of platinum and palladium with a relative standard deviation of less than 0.5%.The oxidation reactions were Pd(0) Pd(II) and Pt(II) Pt(IV). Mass excesses of analytes of 3.5- to 4.5-fold with respect to each other did not interfere with the determination of individual elements. With alternate cathodic and anodic polarization of the electrode, these elements can be multiply determined in a single portion of solution. The procedure was used for the simultaneous determination of platinum and palladium in process solutions of KP-1 platinum concentrate after the separation of gold and silver and also in platinum- and palladium-based alloys.     

Pallatriazo — A sensitive and selective reagent for the spectrometric determination of palladium(II)

Summary Based on an investigation of the functional and active analytical groups, a new trisazo derivative, pallatriazo, is proposed as a reagent for determining Pd(II) spectrometrically. This reagent shows high sensitivity, allowing palladium determination in the concentration range 0.05–4g Pd(II)/ml even if platinum is present up to the ratio Pd(II)Pt(IV)=130.

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Pallatriazo — ein empfindliches und selektives Reagens für die spektrometrische Bestimmung von Palladium(II) (Vorläufige Mitteilung)

Zusammenfassung Auf der Grundlage einer Untersuchung der funktionellen und analytischaktiven Gruppen wurde ein neues Trisazo-Derivat, Pallatriazo, als Reagens für die spektrometrische Bestimmung von Pd(II) vorgeschlagen. Es zeigt hohe Empfindlichkeit und gestattet die Pd-Bestimmung im Gebiet 0,05–4g Pd(II)/ml, auch wenn Platin in 30fachem Überschuß anwesend ist.

     

Coupling of o and/or m-substituted arylamines with the ortho-C–H function of the pendant aryl ring in coordinated arylazopyrimidinepalladium(II) complexes. Spectral and electrochemical characterisation of the products

2-(Arylazo)pyrimidines (aapm) are N,N-chelators which form palladium(II) complexes, Pd(aapm)Cl₂ (1). The reaction of Pd(aapm)Cl₂ (1) with arylamines (ArNH₂) yields Pd(aapm-N-Ar)Cl, (2)–(7), complexes of the tridentate N,N,N-donor system in which arylamines are fused to the ortho C–H function of the pendant aryl ring in the coordinated 2-(arylazo)pyrimidine, leading to the C–N coupled product. Pd(aapm-N-Ar)Cl, complexes (2)–(7), exhibit a broad intense absorption band in n.i.r. region (870–920 nm), while the parent complex, Pd(aapm)Cl₂, shows an intense absorption at 425 nm. Cyclic voltammograms of (2)–(7) exhibit an oxidation couple at positive potential to s.c.e. together with three reductions at negative side. The oxidation may involve conversion of the chelated azoarylamine to semibenzoquinone azoarylamine fragment. The reduction is due to the accommodation of electrons in the azoimine function. The absorption spectra in the n.i.r. region may be regarded as HOMO LUMO intravalence charge transfer (i.v.c.t.) transitions.     

Zur hochspannungselektrophoretischen Trennung anorganischer Ionen unter besonderer Berücksichtigung der Platinmetalle

Zusammenfassung Die hochspannungselektrophoretische Wanderung der Halogenokomplexe der Platinmetalle und verschiedener Begleitelemente wurde in verschiedenen Puffergemischen (Glycin+NaCl+HCl), bei denen teilweise NaCl durch Amine und aminartige Verbindungen [NH₄Cl, HONH₃Cl, N₂H₄·2 HCl, CH₃NH₃Cl, (CH₃)₃ NHCl, Pyridin] ersetzt war, sowie in Asparagin-, Asparaginsäure- bzw. Alanin-NaCl-Elektrolytlösungen untersucht. Dabei wurde auch der Einfluß des p _h -Wertes der Glycinpuffer auf die Wanderungsgeschwindigkeiten und Zonenbreiten gemessen und die Abhängigkeit der Wanderung von der Konzentration der Auftragslösungen geprüft.Die Untersuchungen zeigen, daß die Wanderungsgeschwindigkeiten der Halogenokomplexe der Platinmetalle und vieler anderer zwei- und dreiwertiger Ionen sehr unterschiedlich sind. Die Anwendbarkeit der Elektrolyte für Trennungen wurde an Hand von Trennbeispielen (Pd, Pt, Cu,Bi,Zn;Os,Ru,Fe,Ni;Re,Se,Te,Cu u. a.) demonstriert. In den Mischungen aus 0,1–m Glycin+(0,1–m NaCl0,1–m HCl=82,117,9) [p _h =3] und 0,1-m Asparaginsäure+0,1-m NaCl konnten Elektrolytlösungen für die ionophoretische Trennung der Bromokomplexe bzw. Bromverbindungen aller Platinmetalle gefunden werden. Die Beweglichkeiten der scharf wandernden Zonen zeigen hierbei die Abstufung: Ir > Pt > Os > Rh > Pd > Ru.

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The high tension electrophoretic separation of inorganic ions with special consideration of the platinum metals. IV

Summary The high tension electrophoretic migration of the halogen complexes of the platinum metals and various accompanying elements was studied in various buffer mixtures (glycine + NaCl + HCl), in which NaCl was partially replaced by amines and amine-like compounds [NH₄Cl, HONH₃Cl, N₂H₄ · 2 HCl, CH₃NH₃Cl, (CH₃)₃NHCl, pyridine], as well as in asparagine, aspartic acid- or alanine-NaCl-electrolyte solutions. The influence of theph-value of the glycine buffer on the migration velocities and the zone widths was also measured and the dependence of the migration on the concentration of the coating solutions was checked.The studies showed that the migration velocities of the halogen complexes of the platinum metals and many other 2- and 3-valent ions differ greatly. The applicability of the electrolytes for separations was demonstrated by means of separation examples (Pd, Pt, Cu, Bi, Zn; Os, Eu, Fe, Ni, Re, Se, Te, Cu and others). In the mixtures consisting of 0.1M glycine + (0.1M NaCl: 0.1M HCl=82.117.9) [ph=3] and 0.1M aspartic acid + 0.1M NaCl it was found possible to find electrolyte solutions for the ionophoretic separation of the bromo complexes or the bromine compounds of all the platinum metals. The mobilities of the sharply migrating zones showed here the gradations Ir > Pt > Os > Rh > Pd > Ru.

     

Bimetallic Pd—Pt/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for complete methane oxidation: the effect of the Pt: Pd ratio

Alumina-supported bimetallic Pt—Pd catalysts proved to be more active in the complete oxidation of methane than monometallic systems (Pt/Al₂O₃, Pd/Al₂O₃). The maximum activity of the bimetallic catalysts was achieved at ~40 at.% Pt in Pd on the catalyst surface. After the oxidation reaction, redistribution of platinum and palladium was observed in the active component of the catalysts with the degree of redistribution depending on the initial Pt: Pd ratio.     

Catalytic Oxidation of Small Molecules in a Gas Phase in the Presence of Heterogenized Platinum and Palladium Complexes with Chemically Different Ligands

This work is devoted to the study of catalytic properties of the metal complexes of platinum and palladium with acetylacetone and N-allyl-N"-propylthiourea heterogenized on the surface of silica in the oxidation reactions of H₂ and CO in a gas phase. We found that the acetylacetonate complexes were not degraded under catalytic reaction conditions, whereas the metal complexes withN-allyl-N"-propylthiourea exhibited a high activity only after partial degradation of the ligand. We demonstrated that the catalytic activity of the grafted metal complexes was higher than that of traditional supported platinum and palladium catalysts with the same metal content. Taking into account the structure of active centers in Pt and Pd complexes grafted on SiO₂ and the interaction of these centers with reactants, we proposed a detailed mechanism for the catalytic action, which adequately describes the entire set of experimental data.     

Effect of supports on activity and stability of Pt–Pd catalysts for oxygen reduction reaction in proton exchange membrane fuel cells

The platinum–palladium alloy (Pt–Pd) catalysts were prepared on various supports including Vulcan XC72, Hicon Black (HB), multiwalled carbon nanotubes (MWCNTs), and titanium dioxide (TiO₂) by a combined approach of impregnation and seeding using NaBH₄ reduction at low temperature. Their oxygen reduction reaction (ORR) activities in single proton exchange membrane fuel cell (PEMFC) under a H₂/O₂ environment and their stability in an acid electrolyte (0.5 M H₂SO₄) were tested and compared with the Vulcan XC72-supported Pt (Pt/C) catalysts. The presence of the Pd metal as well as different types of supports affected the ORR activity in H₂/O₂ environment and stability in the acid electrolyte. Overall, the HB-supported Pt–Pd (Pt–Pd/HB) catalysts provided the highest current density at 0.6 V under a H₂/O₂ environment, while the MWCNT-supported Pt–Pd (Pt–Pd/MWCNT) catalyst provided the best stability in an acid electrolyte.     

C–HPt(II) interaction-controlled self-assembly and photophysics of chiral bis(pyrrol-2-ylmethyleneamino)cyclohexane platinum(II) complexes

Reaction of (R,R)-(−)- and (S,S)-(+)-1,2-bis(pyrrol-2-ylmethyleneamino)cyclohexane with K₂PtCl₄ afforded chiral, neutral platinum(II) Schiff base complexes of (R,R)-PtL and (S,S)-PtL with high yields. The rare C–HPt(II) intermolecular interaction was found to show considerable strength and directionality for controlling M and P helical supramolecular architectures of (R,R)-PtL and (S,S)-PtL, respectively, in crystal lattices. More importantly, the open square-planar geometry of platinum(II) complexes allows axial C–HPt(II) interaction, resulting in the ³(ππ^*) excited state with some mixing of the Pt(II) metal character observed both in concentrated solutions and in the solid state at room temperature.     

Synthesis and characterization of some methyl complexes of palladium(II). Part 2(1)

Summary Dichloro complexes of Pd^II, [Pd(L–L)Cl₂], where L–L=1-(thiomethyl)-2-(diphenylarsino)ethane (S–As) or 1-(thiomethyl)-2-(diphenylphosphino)ethane (S–P) andtrans-[PdL₂Cl₂], where L=diphenyl(2-phenylethyl)-phosphine (PE), diphenyl(1-naphthyl)phosphine (PN) orN-methyl-2-thiophenealdimine (SN), have been prepared and characterized. The reactions of these complexes with MeLi were investigated. The dimethyl complexes [Pd(L–L)Me₂] (L–L=S–As, S–P) and [Pd(PE)Me₂] were isolated and characterized. Reaction of [Pd(L–L)Me₂] (L–L=S–As, S–P) with HCl affords the monomethyl derivatives [Pd(L–L)Me(Cl)]. In contrast to the Pt analogues, [Pd(L–L)Me₂] and [Pd(L–L)Me(Cl)] are relatively less stable than [Pt(L–L)Me₂] and [Pt(L–L)Me(Cl)].     

Platinum concentration in silicone breast implant material and capsular tissue by ICP-MS

Inductively coupled plasma-mass spectrometry (ICP-MS) was used to determine the concentration of platinum (Pt) in silicone breast implant gel (range, 0.26–48.90 g g^–1 Pt; n=15), elastomer (range, 3.05–28.78 g g^–1 Pt; n=7), double lumen (range, 5.79–125.27 g g^–1 Pt; n=7), foam (range, 5.79–8.36 g g^–1 Pt; n=2), and capsular tissue (range, 0.003–0.272 g g^–1 Pt; n=15). The results show that very high levels of Pt are present in the encasing elastomer, double lumen, and foam envelope materials. Silicone breast implants can be a source of significant Pt exposure for individuals with these implants.     

Bis[N-(2,6-di-t-butyl-1-hydroxyphenyl)salicylideneaminato]palladium(II) complexes and their radical intermediates generated by PbO2 and PPh3

New bis[N-(2,6-di-t-butyl-1-hydroxyphenyl)salicylideneminato]palladium(II) [Pd(L ^x )₂] complexes bearing HO and MeO substituents on the salicyaldehyde moiety were prepared, and their spectroscopic properties, as well as redox reactivity towards PbO₂ and PPh₃, examined by e.s.r. and u.v. spectroscopy. The complexes display charge-transfer bands in the 670–692 nm range in polar solvents, which are assigned to the d(Pd) * (chelated quinoid) transition. One-electron oxidation of Pd(L ^x )₂ produces Pd^II-stabilized radicals in which the unpaired electrons are localized on the phenoxy fragments and do not couple with the two radical centers. The complexes are easily reduced with PPh₃ via intramolecular electron-transfer from ligand to metal to give various radical intermediates and Pd. All detected radical species have been characterized by e.s.r. spectroscopy.     

NOx-Sorbing Metal Oxides, MnOx–CeO2. Oxidative NO Adsorption and NOx–H2 Reaction

(n)MnO_x–(1–n)CeO₂ binary oxides have been studied for the sorptive NO removal and subsequent reduction of NO_x sorbed to N₂ at low temperatures (150 °C). The solid solution with a fluorite-type structure was found to be effective for oxidative NO adsorption, which yielded nitrate (NO^– ₃) and/or nitrite (NO^– ₂) species on the surface depending on temperature, O₂ concentration in the gas feed, and composition of the binary oxide (n). A surface reaction model was derived on the basis of XPS, TPD, and DRIFTS analyses. Redox of Mn accompanied by simultaneous oxygen equilibration between the surface and the gas phase promoted the oxidative NO adsorption. The reactivity of the adsorbed NO_x toward H₂ was examined for MnO_x–CeO₂ impregnated with Pd, which is known as a nonselective catalyst toward NO–H₂ reaction in the presence of excess oxygen. The Pd/MnO_x–CeO₂ catalyst after saturated by the NO uptake could be regenerated by micropulse injections of H₂ at 150 °C. Evidence was presented to show that the role of Pd is to generate reactive hydrogen atoms, which spillover onto the MnO_x–CeO₂ surface and reduce nitrite/nitrate adsorbing thereon. Because of the lower reducibility of nitrate and the competitive H₂–O₂ combustion, H₂–NO reaction was suppressed to a certain extent in the presence of O₂. Nevertheless, Pd/MnO_x–CeO₂ attained 65% NO-conversion in a steady stream of 0.08% NO, 2% H₂, and 6% O₂ in He at as low as 150 °C, compared to ca. 30% conversion for Pd/–Al₂O₃ at the same temperature. The combination of NO_x-sorbing materials and H₂-activation catalysts is expected to pave the way to development of novel NO_x-sorbing catalysts for selective deNO_x at very low temperatures.     

Effect of Thermal Activation of Supported Catalysts Pt/MeOx,Where MOx = Al2O3, CeO2, La2O3, and ZrO2, for Complete Oxidation

A sharp increase in the atomic catalytic activity (ACA) of supported platinum catalysts in the model reaction of n-pentane complete oxidation is found on going from the preliminary calcination temperature of 500–600°C to a temperature of 700°C. ACA increases by an order of magnitude for the Pt/-Al₂O₃ system, 3 times for Pt/ZrO₂, and 1.5 times for Pt/CeO₂. The per-gram activities of all catalysts decrease because of a decrease in the dispersion of supported platinum with an increase in the temperature of preliminary calcination.     

Synthesis and structure of mixed-metal thiolate complex Cp′Cr(CO)2(μ-SBu)Pt(PPh3)2: Side-on-coordination of Cr–S double bond with platinum

The reaction of [Cp′Cr(CO)₂(μ-SBu)]₂ (1) (Cp′ = MeC₅H₄) with (PPh₃)₂Pt(PhCCPh) gives Cp′Cr(CO)₂(μ-SBu)Pt(PPh₃)₂ (2) which could be regarded as a product of the substitution of acetylene ligand at platinum by a monomeric chromium–thiolate fragment. According to the X-ray diffraction analysis 2 contains single Cr–Pt (2.7538(15)) and Pt–S (2.294(2) Å) bonds while Cr–S bond (2.274(3) Å) is shortened in comparison with ordinary Cr–S bonds (2.4107(4)–2.4311(4) Å) in 1. The bonding between Cr–S fragment and platinum atom is similar to the olefine coordination in their platinum complexes.