Preparation of polymeric modifier-attached graphene-supported bimetallic Pt–Pd nanocomposites,and their electrochemical properties as electro-catalysts

Graphene-supported bimetallic nanocomposites were synthesized by a modified sodium borohydride reduction method. Poly(diallyldimethylammonium chloride) (PDDA) was used as modifier for good dispersion and higher metal alloy content. The micro-structure and dispersive properties of the electro-catalysts were determined by X-ray diffraction, Fourier-transform-infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. The electrochemical properties of the Pt–Pd electro-catalysts were studied by cyclic voltammetry. This analysis confirmed that functional groups on the graphene oxide (GO) sheet were chemically bonded to the PDDA layer. The average particle diameter of Pt–Pd_{1 to 0.5}–PDDA–reduced graphene oxide (RGO) was found to be 2.4 ± 0.4 nm which is the smallest platinum metal particle size among Pt–Pd–PDDA–RGO electro-catalysts. The electrochemically active surface area was studied and the activity was found to be enhanced by use of the polymeric modifier.     

The catalytic activity of bimetallic Pt—Pd polymer nanocomposites in formic acid oxidation

The platinum-palladium/Nafion metal—polymer nanocomposites were synthesized by chemical reduction of metal ions in water—organic reverse microemulsion solutions. The catalytic activity of the synthesized polymer composites with bimetallic Pt—Pd nanoparticles was estimated in the oxidation of hydrogen and formic acid.     

Characterization and reactivity of γ-Al_2O_3 supported Pd–Ni bimetallic nanocatalysts for selective hydrogenation of cyclopentadiene

Several g-Al2O3 supported Pd–Ni bimetallic nanocatalysts(Pd–Ni(x:y)/Al2O3; where x and y represent the mass ratio of Pd and Ni, respectively) were prepared by the impregnation method and used for selective hydrogenation of cyclopentadiene to cyclopentene. The Pd–Ni/Al2O3 samples were confirmed to generate Pd–Ni bimetallic nanoparticles by X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS) and transmission electron microscopy(TEM). The catalytic activity was assessed in view of the effects of different mass ratios of Pd and Ni, temperature, pressure, etc. Among all the samples, the Pd–Ni(1:1)/Al2O3(PN-1:1) catalyst showed extremely high catalytic ability. The conversion of cyclopentadiene and selectivity for cyclopentene can be simultaneously more than 90%.     

DFT studies of the characteristics of Pd−Pt core-shell clusters

It is reported that Pd?Pt core-shell type nanoclusters in which the inner atoms of the Pd cluster are substituted by Pt significantly enhance the catalytic activity for cycloocatdiene hydrogenation. In order to discuss the electronic states of core-shell clusters, DFT calculations were carried out for Pd₁₃, Pt₁₃, Pt/Pd₁₂, Pd/Pt₁₂ Pd₃₈ and Pd₆/Pt₃₂ clusters. From these calculations, it was found that the charge transfer between the core atoms and the shell atoms played an important role for the modification of the electronic state of the surface atoms in them.     

Characterization and reactivity of γ-Al_2O_3 supported Pd–Cu bimetallic nanocatalysts for the selective oxygenization of cyclopentene

In this work, Pd–Cu/γ-Al_2O_3 is prepared by the impregnation method and investigated for selective oxygenization of cyclopentene to cyclopentanone. A series of bimetallic Pd–Cu/γ-Al_2O_3 nanocatalysts were prepared and the structures characterized by XRD, XPS and TEM. We determined that the obtained Pd–Cu/γ-Al_2O_3(molar ratio Pd:Cu = 5:1) was an efficient catalyst for the oxygenization of cyclopentene to cyclopentanone with 95% selectivity and 85% conversion(100 °C, 1 MPa initial O_2 pressure, 7 h).     

Synthesis and characterization of bimetallic Pt–Fe/polypyrrole–carbon catalyst as DMFC anode catalyst

A novel synthesis route, concerning in situ interfacial polymerization of pyrrole on carbon black and following co-deposition of Pt and Fe on polypyrrole–carbon support, is developed to prepare the bimetallic Pt–Fe/polypyrrole–carbon catalyst. In this synthesis process, ferrous precursor simultaneously functions as an oxidant for the polymerization of pyrrole. The Pt–Fe/polypyrrole–carbon catalyst shows improved catalytic activity towards methanol oxidation compared to commercial Pt/C catalyst, which may be of great potential in direct methanol fuel cells.     

Iodo Derivatives of Bimetallic Fe—Pd and Fe—Pt Complexes. Crystal Structures of

Summary.  Iodo derivatives of diphosphine-bridged heterobimetallic Fe—Pd and Fe—Pt complexeshave been prepared in which an alkoxysilyl ligand bridges the two metals in a μ₂−η²-SiO manner. In the course of their synthesis by halide exchange from (dppx = dppm (Ph₂ PCH₂ PPh₂) or dppa (Ph₂PNHPPh₂); M = Pd or Pt), loss of the alkoxysilyl ligand occurred resulting in the formation of complexes in which a bridging iodide has replaced, as a 3e⁻-donor, the bridging alkoxysilyl ligand. These complexes of formula (M = Pd, Pt are better prepared by reaction of with [MI₂(cod)]. The crystal structures of (2a), (2b), and  · CH₂Cl₂ (3b · CH₂Cl₂) have been determined by X-ray diffraction. Received January 24, 2001. Accepted February 12, 2001     

Preparation and electrochemical performance of graphene–Pt black nanocomposite for electrochemical methanol oxidation

This work reports the preparation, characterization, and electrocatalytic characteristics of a new metallic nanocatalyst. The catalyst, Pt black–graphene oxide (Pt-GO), was prepared by deposition of Pt black on the surface of graphene oxide nanosheet and characterized by transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), and voltammetry. The Pt-graphene (Pt-GR) composite modified glassy carbon electrode (Pt-GR/GCE) was prepared with cyclic voltammetric scanning of Pt-GO/GCE in the potential range from ?1.5 to 0.2 in 0.1 M phosphate buffer solution at 50 mV·s^?1 for 5 cycles. The electrocatalytic properties of the Pt-GR/GCE for methanol (CH₃OH) oxidation have been investigated by cyclic voltammetry (CV); high electrocatalytic activity of the Pt-GR/GCE can be observed. This may be attributed to the high dispersion of Pt catalyst and the particular properties of GR support. The long-term stability of Pt-GR composite was investigated in 0.05 M CH₃OH in 0.1 M H₂SO₄ solution. It can be observed that the peak current decreases gradually with the successive scans. The loss may result from the consumption of methanol during the CV scan. It also may be due to the poisoning organic compounds. The results imply that the Pt-GR composite has good potential applications in fuel cells.     

Preparation and characteristics of hydroxypropyl-β-cyclodextrin polymeric nanocapsules loading nimodipine

Nimodipine loaded hydroxypropyl-β-cyclodextrin polymeric nanocapsules were prepared by interfacial polyaddition of hydroxypropyl-β-cyclodextrin and isophorone diisocyante in a miniemulsion system. The effects of ultrasonicate times on the preparation of miniemulsion, the total amount of hydroxypropyl-β-cyclodextrin and isophorone diisocyante, and the molar ratio of isophorone diisocyante to hydroxypropyl-β-cyclodextrin on the capsule size and drug release behavior from capsule were investigated. The chitosan based polymeric nanocapsules were prepared as a control to study the effect of hydroxypropyl-β-cyclodextrin molecules in capsule matrix on the drug release. The results indicated that the droplet size of miniemulsion and capsule size decreased with increasing sonicate times. When the total amount of hydroxypropyl-β-cyclodextrin and isophorone diisocyante, and the molar ratio of isophorone diisocyante to hydroxypropyl-β-cyclodextrin were increased, the capsule as well, but the drug release rates from capsules became slower. The drug release behaviors from hydroxypropyl-β-cyclodextrin polymeric nanocapsules were affected by the drug diffusion through the polymer matrix and the formation of inclusion complex between drug and hydroxypropyl-β-cyclodextrin.     

A pseudo triple-enzyme electrochemical aptasensor based on the amplification of Pt–Pd nanowires and hemin/G-quadruplex

Our present work aimed at developing a pseudo triple-enzyme cascade electrocatalytic electrochemical aptasensor for determination of thrombin with the amplification of alcohol dehydrogenase (ADH)-Pt–Pd nanowires bionanocomposite and hemin/G-quadruplex structure that simultaneously acted as NADH oxidase and HRP-mimicking DNAzyme. With the addition of ethanol to the electrolyte, the ADH immobilized on the Pt–Pd nanowires catalyzed ethanol to acetaldehyde accompanied by NAD⁺ being converted to NADH. Then the hemin/G-quadruplex firstly served as NADH oxidase, converting the produced NADH to NAD⁺ with the concomitant local formation of high concentration of H₂O₂. Subsequently, the hemin/G-quadruplex acted as HRP-mimicking DNAzyme, bioelectrocatalyzing the produced H₂O₂. At the same time, the Pt–Pd nanowires employed in our strategy not only provided a large surface area for immobilizing thrombin binding aptamer (TBA) and ADH, but also served as HRP-mimicking DNAzyme which rapidly bioelectrocatalyzed the reduction of the produced H₂O₂. Thus, such a pseudo triple-enzyme cascade electrochemical aptasensor could greatly promote the electron transfer of hemin and resulted in the dramatic enhancement of electrochemical signal. As a result, a wide dynamic concentration linear range from 0.2 pM to 20 nM with a low detection limit of 0.067 pM for thrombin (TB) determination was obtained. The excellent performance indicated that our strategy was a promising way for ultrasensitive assays in electrochemical aptasensors.     

Catalytic conversion of cellulose into polyols using carbon-nanotube-supported monometallic Pd and bimetallic Pd–Fe catalysts

A series of carbon nanotube (CNT)-supported monometallic Pd and bimetallic Pd–Fe catalysts were synthesized and employed for catalytic hydrogenolysis of cellulose into polyols, including hexitol, ethylene glycol (EG), 1,2-propanediol (1,2-PG), and glycerol (Gly). The physicochemical properties of the catalysts were characterized by nitrogen physical adsorption measurements, X-ray diffraction analysis, transmission electron microscopy, and X-ray photoelectron spectroscopy. The total yield of hexitol, EG, 1,2-PG, and Gly in hydrolytic hydrogenation of cellulose was 37, 55, and 53% for Pd/CNTs, Pd–Fe/CNTs (Pd:Fe = 1:1), and Pd–Fe/CNTs (Pd:Fe = 1:2), respectively. Addition of Fe to Pd significantly modified the physicochemical properties of the nanoparticles and their catalytic performance, especially regarding hexitol selectivity. The promoting effect of Fe, especially for hexitol selectivity, compared with the monometallic catalyst is due to the fact that incorporation of Fe may stabilize Pd⁰ nanoparticles and lead to downshift of the d-band center of Pd metal nanoparticles by charge transfer from Fe to Pd. Recycling experimental results showed that leaching of Fe resulted in a significant decrease in the hexitol yield obtained using the Pd–Fe/CNTs after the first recycle, further demonstrating that Fe element plays a promoting role for hexitol formation.     

Hydrogen evolution on Pt and polyaniline modified Pt electrodes—a comparative electrochemical impedance spectroscopy study

Kinetic of hydrogen evolution reaction, HER, at Pt and polyaniline, PANI, polymer film modified Pt electrodes in the sulphuric acid solution was investigated within the context of possible inhibition of HER by conducting polymers. Pt/PANI electrodes were prepared by electro-polymerization procedure with different quantities of PANI and electrochemically aged in the insulating state prior polarization and electrochemical impedance spectroscopy experiments. Polarization and impedance data obtained in the hydrogen (0.30 to 0.05 V_RHE) and HER (0.00 to ?0.155 V_RHE) potential regions of bare Pt-poly electrode were compared with those of Pt/PANI electrodes. Significant differences of impedance spectra in the hydrogen region of potentials pointed toward domination of hydrogen under-potential deposition, H UPD, at Pt-poly surface and domination of PANI impedance at Pt/PANI electrodes, respectively. Quite similar impedance spectra obtained in the HER region of potentials and Tafel slopes of about 30 mV decade^?1 evaluated from polarization measurements indicated that HER is proceeding by the same mechanism at Pt-poly and Pt/PANI electrodes, respectively. Analysis of respective impedance parameters showed that HER which is easily driven at Pt-poly electrode becomes inhibited to a certain extent at both Pt/PANI electrodes, but more for the one with higher quantity of PANI. These results can commonly be interpreted by HER that is taking place on the Pt substrate underlying more or less porous PANI film acting as a barrier toward electrolyte solution.     

Synthesis and characterization of a one-dimensional polymeric copper(Ⅱ)-tetrathioporphyrazine

The title polymer PCuS4Pz was synthesized by reaction of 2,3-dicyano-5,6-dihydro-1,4-dithiin,pyromellitic dianhydride and urea with cuprous salt in optimized gentle method.The structure and properties of the PCuS4Pz were characterized by elemental analysis,X-ray powder diffraction,IR,UV-Vis,fluorescence and EPR spectra and variable-temperature magnetic susceptibility.The polymer is black sublimable crystallite and the degree of polymerization has been found to be n>4.The PCuS4Pz in H2SO4 exhibits intensive absorption bands at 236,342,656 and 767 nm and intensive fluorescence band at 410 nm or 464 nm under the excitation of the ultraviolet light of a determined wavelength at room temperature.It has been found that the polymer exhibits a weaker antiferromag-netic interaction (J=-2.cm-1,εff=1.68 B.M.) with an apparent spin S<1/2 in the ground state and its conductivity 298K is 1.01×10-5 S-cm-1 at 13.73 MPa.     

Aromatic reduction of residue oil of naphtha cracking over bimetallic Pt−Pd catalysts supported on mesoporous molecular sieve

An Al-containing mesoporous molecular sieve (Al-MMS) was prepared by hydrolysis of H₂SiF₆ and Al(NO₃)₃·9H₂O. NH₃-TPD results suggest that the acidity of Al-MMS was less than that of dealuminated zeolite. Y. The potential use of mesoporous molecular sieve as a new support material for dearomatization of residue oil of naphtha cracking was described. In case of C₉ ⁺ and PGO feed, Pt?Pd/Al-MMS showed a higher activity than Pt?Pd/dealuminated zeolite Y catalyst. This is ascribed to its better accessibility of bulky molecules, and much less cracking activity due to mild acidity, indicating high yield of liquid. Thus, Pt?Pd/Al-MMS catalyst can be applied effectively to the hydrogenation of aromatic compounds in the residue oil of a commercial naphtha cracker.     

Phosphine σ-sydnonyl complexes of Ni,Pd, and Pt

3-R"-4-Bromosydnones 1 (R" = Me) and 2 (R" = Ph) react with complexes Ì(PR₃)_n (M = Ni, Pd, Pt) to form mononuclear phosphine -sydnonyl d⁸-complexes of trans-configuration MBr(3-R"-sydnon-4-yl)(PR₃)₂: 3, 4 (Ì = Ni, R" = Ph); 5 (M = Pd, R" = Me); 6a (M = Pd, R" = Ph); 7 (M = Pt, R" = Ph). In the reaction of bromosydnone 2 with Pd(PPh₃)₄, the cis-complex PdBr(3-Ph-sydnon-4-yl)(PPh₃)₂ (6b) is formed initially; 6b rearranges in solution to give trans-complex 6a. On heating in THF, complex 6a is converted into the binuclear [PdBr(3-phenylsydnon-4-yl)(PPh₃)]₂ complex (8). The reaction of 4-chloromercurio-3-phenylsydnone (10) with Ni(PEt₃)₄, Pd(PPh₃)₄, and Pt(PPh₃)₄ gives mononuclear NiCl(3-phenylsydnon-4-yl)(PEt₃)₂ complex (11), binuclear [PdCl(3-phenylsydnon-4-yl) (PPh₃)]₂ complex (14), and cis- and trans-bimetallic PtCl(3-phenylsydnon-4-ylmercurio)(PPh₃)₂ complexes 15a and 15b, respectively. UV irradiation of 15a and 15b in a benzene solution induces redox demercuration to yield the PtCl(3-phenylsydnon-4-ylcarbonyl)(PPh₃)₂ complex (16). In carbonylation of complexes 3, 6, and 7, CO insertion into the M--C bond occurred to form the corresponding acyl derivatives MBr(3-phenylsydnon-4-ylcarbonyl)(PR₃)₂ (17--19).     

Synthesis, electrochemical and photophysical properties of β-carboxy triaryl corroles

An unswerving one-pot conversion of 3-formyl-5,10,15-triaryl substituted corroles and their copper(III) derivatives to the corresponding 3-carboxy-5,10,15-triaryl substituted corroles was achieved by adopting mild reaction conditions by using hydroxylamine hydrochloride and phthalic anhydride. All these substituted carboxy corroles were completely characterized by using Mass, CHN analysis, IR, ¹H NMR, UV-vis., Fluorescence spectroscopies, and cyclic voltammetry. Both the absorption maxima and emission maxima of carboxy corroles were red shifted by 5-13 nm. The LUMO level of these corroles is above the TiO₂ conduction band and HOMO level was below the redox electrolytes. These β-carboxy corroles confined with may find applications as sensitizers in dye-sensitized solar cells.     

Synthesis of 3,4-dihydroxyphenyl-containing polymeric materials from 1,2-polybutadiene and eugenol via thiol—ene addition

Russian Chemical Bulletin - In a search for routes to new promising adhesive materials, 3,4-dihydroxyphenyl groups were introduced for the first time into syndiotactic polybutadiene (1,2-unit...     

Geometrical structures of trimetallic Ag–Pd–Pt and Au–Pd–Pt clusters up to 147 atoms

Structural Chemistry - The core-shell morphologies of (PdPt)coreAgshell and (PdPt)coreAushell up to 147 atoms are investigated. The structural optimization of M–Pd–Pt (M = Ag or Au) is...