Pt In Catalysts Research Articles

N-doped carbon supported Pt catalyst for base-free oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid

A new kind of N-doped carbon supported Pt catalyst (Pt/C) has been prepared for the selective oxidation of 5-Hydroxymethylfurfural (HMF) to 2,5-Furandicarboxylic Acid (FDCA) in base-free conditions. The catalyst (Pt/C-EDA-x) prepared by using ethylenediamine (EDA) as nitrogen source showed higher activity than those prepared by N,N-dimethylaniline (DMA), ammonia (NH3) or acetonitrile (ACN) as nitrogen sources. The Pt/C-EDA-4.1 catalyst showed the highest activity in the oxidation of HMF to FDCA and as high as 96.0% FDCA was obtained under optimal reaction conditions (110°C, 1.0MPa O2, 12h). The samples were characterized by XRD, XPS, CO2-TPD, TEM, SEM, and elemental analysis. XPS results showed that the pyridine-type nitrogen (N-6) played a key role in the selective oxidation of HMF, which can be attributed to the basicity of N-6 site. CO2-TPD measurements also showed that the involving of N elements in catalyst preparation introduced a new kind of medium basic site on the support surface. The influence of reaction time, catalyst dosage, and temperature on the HMF oxidation to FDCA catalyzed by Pt/C-EDA-4.1 was studied.

Acceptorless dehydrogenation of N-heterocycles by supported Pt catalysts

Pt metal nanoparticles loaded on various supports and carbon-supported various metal catalysts are tested for dehydrogenation of 6-methyl-1,2,3,4- tetrahydroquinoline to 6-methyl-quinoline under oxidant-free conditions. In the 20 types of the catalysts screened, carbon-supported Pt catalyst (Pt/C) shows the highest activity. Pt/C is reusable after the reaction and is effective for dehydrogenation of various N- heterocycles (tetrahydroquinolines and indoline). Pt/C is also effective for hydrogenation of quinoline under 3bar H2. The results demonstrate that this catalytic method may be useful for an organic hidride–based hydrogen storage system.

Synthesis and Characterization of Bimetallic Ni<SUB>50</SUB>Pt<SUB>50</SUB> Catalyst Supported on SiO<SUB>2</SUB> for N<SUB>2</SUB>O Decomposition

Nanometallic and bimetallic catalyst of Ni, Pt and Ni50Pt50 were studied by the decompositions of N2O. The catalyst were prepared by incipient wetness impregnation of the silica with low superficial area of 50 m2/g supported with aqueous solution of the metal precursors, for Pt H2Pt Cl6 x 6H2O was used and for Ni, Ni(NO3)2 was used to a total metal loading of 1% wt. Catalyst were oxidized for 2 hours at 400 degrees C with O2, then the samples were reduced for 30 minutes with N2 and 2 hours with H2, all at the same temperature. The catalyst was characterized by Transmission Electron Microscopy (TEM), High Angular Annular Dark Field (HAADF), High Resolution Transmission Electron Microscopy (HR-TEM) and Termoprogramed Reduction (TPR). The mean particle sizes obtained by TEM and HAADF were about 12.5 nm for Ni/SiO2, 2.8 nm for Pt/SiO2 and 3.5 nm Ni50Pt50/SiO2 catalysts respectability. HR-TEM and HAADF analysis showed differences between Ni and Pt catalysts displaying mainly cuboctahedral shapes. Stepped surface defects were found in the Ni50Pt50/SiO2 catalyst. Finally Ni50Pt50/SiO2 was more active than Pt/SiO2 and Ni/SiO2 catalysts for the decomposition of N2O.

Ga and In promoters in bimetallic Pt based catalysts to improve the performance in the selective hydrogenation of citral

In this paper, bimetallic PtGa and PtIn catalysts supported on multiwall carbon nanotubes and carbon Vulcan were used to study the hydrogenation of citral (α,β-unsaturated aldehyde) in liquid phase to produce nerol and geraniol (unsaturated alcohols, UA). The catalysts were prepared with different metallic loadings by conventional impregnation. All the catalysts contained a Pt loading of 5wt%. Once reduced under hydrogen flow, the supported catalysts were characterized by test reactions of the metallic phase, H2 chemisorption, temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Hydrogenation results showed that the addition of a second metal to Pt leads to important modifications of the selectivity to UA. The highest selectivities to UA were reached with different promoter/Pt atomic ratios for Ga and In. The catalyst performances in the citral hydrogenation were related to the characteristics of each supported bimetallic phase. It was found that the PtGa catalysts have a typical behavior of an ionic promoter together with a contribution of the Ga reduced species, reaching high selectivities to UA. On the other hand, PtIn catalysts with a metallic phase composed mainly by zerovalent In species in contact with the metallic phase, also showed high activities and selectivities to UA. The best selectivity value to UA (about 97%) was found for PtIn(2.5wt%)/CN-P catalyst with an excellent activity.

Promoting Effect of Tin in Platinum Electrocatalysts for Direct Methanol Fuel Cells (DMFC)

Pt-Sn anodic catalysts supported on multiwall carbon nanotubes, mesoporous carbon and Vulcan carbon were prepared using a deposition-reduction technique with sodium borohydride, characterized by different techniques and tested as anodes in a single direct methanol fuel cell at low temperatures. Characterization and CO stripping results indicate the presence of promoting effects of Sn over Pt in catalysts supported on Vulcan carbon and carbon nanotubes. This would mainly be caused both by geometric modifications induced by Sn placed in the surroundings of the active metal phase and probable electronic effects. These promoting effects make the oxidation of CO to CO2 at low potentials easier, thus improving the CO tolerance of the anodic electrocatalyst. On the other hand, Pt-Sn catalysts supported on mesoporous carbon do not show a proper metallic phase needed for a good electrochemical behavior. When catalysts were tested in a DMFC, Pt-Sn catalysts supported on Vulcan carbon and carbon nanotubes gave a better power density than a commercial one mainly when working at low current densities.

Ethanol electro-oxidation on partially alloyed Pt-Sn-Rh/C catalysts

Ternary Pt-Sn-Rh/C catalysts of Pt:Sn:Rh=1:0.8:0.2 and 1:1:0.33 atomic ratios were synthesized using the formic acid method and their electrochemical activities were compared for ethanol oxidation with that of binary Pt-Sn/C (1:1) and Pt-Rh/C (1:0.11) catalysts. XRD analysis indicated the presence of Sn in both alloyed and oxide form and suggested the formation of a ternary Pt-Sn-Rh alloy in both catalysts. The particle size by TEM was around 3.5nm for all catalysts. The efficiency for Pt utilization increased with Rh content. Pt-Sn-Rh/C catalysts exhibited higher catalytic activity for ethanol oxidation than Pt-Rh/C, but lower than Pt-Sn/C. Among ternary catalysts, Pt-Sn-Rh/C (1:0.8:0.2) was the most active. In situ IRRAS showed Rh plays a dual counteracting role during ethanol electro-oxidation on Pt-Sn-Rh/C catalysts, once it promotes C-C bond breaking, thus favouring CO2 formation, but hinders adsorption of ethanol, decreasing the production of acetic acid.

Kinetic Studies on the Selective Oxidation of Benzyl Alcohols in Organic Medium under Phase Transfer Catalysis

Kinetic studies on the oxidation of benzyl alcohol and substituted benzyl alcohols in benzene as the reaction medium have been studied by using potassium dichromate under phase transfer catalysis (PTC). The phase transfer catalysts (PT catalysts) used were tetrabutylammonium bromide (TBAB) and tetrabutylphosphonium bromide (TBPB). Benzyl alcohols were selectively oxidised to corresponding benzaldehydes in good yield (above 90%). The order of reactivity among the studied benzyl alcohols is p - OCH3 > p - CH3 > - H > p - Cl. Plots of log k2 versus Hammett's substituent constant (s) has been found to be curve shaped and this suggests that there should be a continuous change in transition state with changes in substituent present in the substrate from electron donating to electron withdrawing. A suitable mechanism has been suggested in which the rate determining step involves both C - H bond cleavage and C - O bond formations in concerted manner. © 2014 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)

Catalytic Asymmetric Darzens Reactions

Optically active α,β-epoxy derivatives can be converted into many types of useful chiral compounds, such as chiral building blocks and synthetic intermediates for biologically active compounds. The most up-to-date and most economical method for the preparation of enantiomeric pure epoxides is the catalytic asymmetric Darzens condensation. The homogeneous phase and heterogeneus phase (phase-transfer [PT]) catalytic methods for the synthesis of chiral α,β-epoxycarbonyl, epoxysulfonyl and epoxy-amide compounds are reviewed. The effect of chiral catalysts on the yields and enantioselectivities of the epoxides was studied in homogeneous phase and under PT conditions. The use of the most important chiral PT catalysts (ephedrinium salts, cinchona-derived salts and chiral crown ethers) in Darzens condensation is also summarized. In some cases, the relationship between the structure of catalyst and its activity is also studied. Keywords: Asymmeric reactions, Darzens condensation, phase-transfer catalysis.

A novel derivatization method for the determination of Fosfomycin in human plasma by liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometric detection via phase transfer catalyzed derivatization

An analytical method employing novel sample preparation and liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometric detection (LC–APCI/MS) was developed for the determination of fosfomycin in human plasma. Sample preparation involves derivatization through phase transfer catalysis (PTC) which offers multiple advantages due to the simultaneous extraction, preconcentration and derivatization of the analyte. Using a PT catalyst, fosfomycin was extracted from plasma in an organic phase and, then converted to a pentafluorobenzyl ester with the use of pentafluorobenzyl bromide (PFBBr) derivatization reagent. The method was fully optimized by taking into account both PTC and derivatization parameters. Several catalysts, in a wide range of concentrations, with different counter ions and polarities were tested along with different extraction solvents and pH values. Thereafter, the derivatization procedure was optimized by altering the amount of the derivatization reagent, the temperature of the reaction and finally, the derivatization duration. As internal standard (I.S.) ethylphosphonic acid was chosen and underwent the same pretreatment. The derivatives were separated on a pentafluorophenyl (PFP)-C18 analytical column, which provides unique selectivity, using an isocratic elution with acetonitrile–water (70–30, v/v). The method was validated according to US Food and Drug Administration (FDA) guidelines and can be used for a bioequivalence study of fosfomycin in human plasma. The correlation coefficient (r2) of the calibration curve of spiked plasma solutions in the range of 50–12000ng/mL was found greater than 0.999 with a limit of quantitation (LOQ) equal to 50ng/ml (for 500μL plasma sample).

Development of PtGe and PtIn anodic catalysts supported on carbonaceous materials for DMFC

Bimetallic PtGe and PtIn catalysts (Ge/Pt and In/Pt molar ratios = 0.33, 17 wt.% Pt loading) were prepared over carbonaceous supports (carbon Vulcan, carbon nanotubes and structured mesoporous carbon). The liquid phase deposition–reduction method by using 0.4 M sodium borohydride as a reducing agent was employed. The electrocatalytic activity for methanol oxidation was compared with a commercial Pt/CV E-TEK catalyst. The onset potential of the CO oxidation was shifted to less positive values for carbon Vulcan and carbon nanotubes supported catalysts and with a smaller effect in the case of mesoporous carbon supported ones. The best electrocatalytic performance was obtained by using carbon Vulcan as support of bimetallic catalysts, followed by carbon nanotubes. The performance of mesoporous carbon as a support was not adequate. PtGe/CV, PtGe/NT and PtIn/CV catalysts displayed the best performance in DMFC. The good performance of these catalysts could be due to the presence of small particle sizes with a narrow distribution, and to geometric effects (observed from different characterization techniques) related to a probable decoration of Ge or In around the small Pt particles.

Kinetics and mechanism of the selective oxidation of primary aliphatic alcohols under phase transfer catalysis

Article history: Received March 28, 2013 Received in Revised form August 28, 2013 Accepted 27 November 2013 Available online 28 November 2013 Kinetics of the oxidation of primary aliphatic alcohols has been carried out using phase transferred monochromate in benzene. Tetrabutylammonium bromide (TBAB) and tetrabutylphosphonium bromide (TBPB) are used as phase transfer catalysts (PT catalyst). The reaction shows first order dependence on both [alcohol] and [monochromate ion]. The oxidation leads to the formation of corresponding aldehyde and no traces of carboxylic acid has been detected. The reaction mixture failed to induce the polymerization of added acrylonitrile which rules out the presence radical intermediates in the reaction. Various thermodynamic parameters have been evaluated and a suitable mechanism has been proposed. © 2014 Growing Science Ltd. All rights reserved.

Efficient Hydrogen Production by Catalytic Dehydrogenation of Methylcyclohexane over Ni-Pt/ Nano-Film Alumina Catalyst

The Ni-Pt bimetallic catalyst supported on nanofilm alumina was prepared by coprecipitation method under the assistance of ultrasonic vibration. The characterization result revealed that the prepared catalyst had a good dispersion with an average particle size around 7nm. The activities of supported catalyst of Ni, Pt and Ni-Pt were compared through using the dehydrogenation of methylcyclohexane (MCH) to produce toluene in Microreactor-Gas Chromatography System (MGCS). The conversion and the selectivity of the Ni-Pt catalyst at 350°C for the dehydrogenation of MCH was 97.0% and 100%, respectively. It was found that the bimetallic synergistic effect between Ni and Pt particles would affect the catalyst performance. The addition of Ni into Pt/γ-Al2O3 catalyst was beneficial to decrease the use of Pt in the dehydrogenation.

Efficiency of selected phase transfer catalysts for the synthesis of 1,2-epoxy-5,9-cyclododecadiene in the presence of H2O2/H3PW12O40 as catalytic system

Abstract The results of the studies on the influence of the phase transfer catalyst on the epoxidation of (Z,E,E)-1,5,9-cyclododecatriene (CDT) to 1,2-epoxy-5,9-cyclododecadiene (ECDD) in the H2O2/H3PW12O40 system by a method of phase transfer catalysis (PTC) were presented. The following quaternary ammonium salts were used as phase transfer catalysts: methyltributylammonium chloride, (cetyl)pyridinium bromide, methyltrioctylammonium chloride, (cetyl)pyridinium chloride, dimethyl[dioctadecyl(76%)+dihexadecyl(24%)] ammonium chloride, tetrabutylammonium hydrogensulfate, didodecyldimethylammonium bromide and methyltrioctylammonium bromide. Their catalytic activity was evaluated on the basis of the degree of CDT and hydrogen peroxide conversion and the selectivities of transformation to ECDD in relation to consumed CDT and hydrogen peroxide. The most effective PT catalysts were selected based on the obtained results. Among the onium salts under study, the epoxidation of CDT with hydrogen peroxide proceeds the most effectively in the presence of methyltrioctylammonium chloride (Aliquat® 336) and (cetyl)pyridinium chloride (CPC). The relatively good results of CDT epoxidation were also achieved in the presence of Arquad® 2HT and (cetyl)pyridinium bromide

Performance of the Direct Methanol Carbonate Fuel Cell Using Anion Exchange Materials and Non‐Noble Metal Cathode Catalyst

AbstractA direct methanol fuel cell using a mixture of O2 and CO2 at the cathode was evaluated using anion exchange materials and cathode catalysts of Pt and a non‐Pt catalyst. The MEA based on non‐noble metal catalyst Acta 4020 showed superior performance than Pt/C based MEA in terms of open circuit potential and power density in carbonate environment. The fuel cell performance was improved by applying anion exchange ionomer in the catalyst layer. A maximum power density of 4.5 mW cm–2 was achieved at 50 °C using 6.0 M methanol and 2.0 M K2CO3.

Enhanced-electrocatalytic activity of Pt nanoparticles supported on nitrogen-doped carbon for the oxygen reduction reaction

Spillover, a well-known phenomenon in heterogeneous catalysis referring to the transport of the adsorbed intermediates over the catalyst/support interface, could enhance the catalytic performance by providing additional active sites. Here, we report the spillover-promoted electrocatalytic activity of Pt supported on nitrogen-doped carbon black (NCB) for the oxygen reduction reaction (ORR). By treating Vulcan XC-72R carbon black (CB) at 600 °C under gaseous NH3, NCB of near 1 at% surface nitrogen content is obtained. The catalyst of Pt supported on NCB (Pt/NCB) exhibits simultaneously smaller particle sizes and higher electrochemical surface area and electrocatalytic activity for the ORR than the catalyst of Pt supported on pristine CB (Pt/CB) prepared with the same impregnation method. Particularly, the activity enhancement of Pt/NCB over Pt/CB surpasses that expected due to the surface area increase, which seems to conflict with the common belief that Pt nanoparticles of smaller sizes would have lower area specific activities for the ORR. Cyclic voltammetric responses of these catalysts implied that the oxygenated adsorbates formed on Pt can transport to surface of the NCB support, which may be responsible for the increased area specific activity of the Pt/NCB catalyst.

Enhancement of methanol electrocatalytic oxidation on platinized WO3–TiO2 composite electrode under visible light irradiation

A ternary composite catalyst of Pt–WO3–TiO2 has been successfully prepared by a chemical method. The prepared composite was systematically characterized by UV–vis diffuse reflectance absorption spectra (DRS), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). The electrocatalytic properties of Pt–WO3–TiO2 for methanol oxidation in an alkaline medium were evaluated by the cyclic voltammetry (CV) and chronoamperometry (CA) with or without visible light irradiation. Compared with the pure TiO2, the introduction of WO3 extends its absorption edge to visible light region. Under visible light illumination, the Pt–WO3–TiO2 composite catalyst exhibits higher electrocatalytic activity toward methanol oxidation in comparison with its counterpart, the pure Pt–TiO2 catalyst.

나노입자가 코팅된 그래핀 기반 수소센서의 제작과 그 특성

This paper presents the fabrication and characterization of graphene based hydrogen sensors. Graphene was synthesized by annealing process of Ni/3C-SiC thin films. Graphene was transferred onto oxidized Si substrates for fabrication of chemiresistive type hydrogen sensors. Au electrode on the graphene shows ohmic contact and the resistance is changed with hydrogen concentration. Nanoparticle catalysts of Pd and Pt were decorated. Response factor and response (recovery) time of hydrogen sensors based on the graphene are improved with catalysts. The response factors of pure graphene, Pt and Pd doped graphenes are 0.28, 0.6 and 1.26, respectively, at 50 ppm hydrogen concentration.

Gasochromic property of dehydrogenation-catalyst loaded tungsten trioxide

The gasochromic property of dehydrogenation-catalyst loaded tungsten trioxide (M/WO3) powders was examined in exposure to gaseous cyclohexane under different kinds and contents of catalysts, catalyst temperatures, and cyclohexane concentrations. The change in the intensity of visible lights reflected from the M/WO3 powders was in situ obtained using a portable visible-light spectrometer associating with the analysis of dehydrogenation products when M/WO3 powders were exposed to cyclohexane gas. The catalyst of Pt was a catalyst initiating dehydrogenation and change of reflected light intensity at lower temperatures in comparison with the catalysts of Pd and Rh. Among 0.1, 0.5, and 1wt% Pt/WO3 powders, 0.5wt% Pt/WO3 powders demonstrated large change of reflected 640-nm lights, 5.4%, to visually detect their coloration at lower temperatures. The heating of 0.5wt% Pt/WO3 powders at temperatures higher than 130°C was required to visually detect cyclohexane at a concentration of 1vol%, lower than the combustion lower limit (1.3vol%). The quantitative analysis of hydrogen species such as hydrogen atoms and ions absorbed in 0.1–1wt% Pt/WO3 powders demonstrated that Pt/WO3 powders would absorb the same amount of hydrogen species independent of loaded-Pt contents.

The use of nitrogen-doped graphene supporting Pt nanoparticles as a catalyst for methanol electrocatalytic oxidation

Nitrogen-doped graphene (N-G) was prepared by thermal annealing of graphene oxide in ammonia at different temperatures. The resultant N-G was used as a conductive support for Pt nanoparticles (Pt/N-G) and the electrocatalytic activity of the Pt/N-G catalysts towards methanol oxidation was examined. To investigate the microstructure and morphology of the synthesized catalysts, X-ray diffraction, scanning and transmission electron microscopy and X-ray photoelectron spectroscopy were used. The catalytic activity of the catalysts towards the oxidation of methanol was evaluated by cyclic voltammetry. Compared to a control catalyst of Pt loaded on undoped graphene, the Pt/N-G materials show higher electrochemical activity towards methanol oxidation. The excellent electrochemical performance of Pt/N-G is mainly attributed to the nitrogen doping and the uniform distribution of Pt particles on the doped graphene support. These results indicate that N-doped graphene has great potential as a high-performance catalyst support for fuel cell electrocatalysis.

A study of different polyphosphazene-coated carbon nanotubes as a Pt–Co catalyst support for methanol oxidation fuel cell

The composite of polyphosphazene-coated carbon nanotubes is prepared by a simple and efficient synthesis method and regarded as an improved catalyst support for direct methanol fuel cell. Catalyst of Pt–Co supported on polyphosphazene-coated carbon nanotubes is prepared using mixed reducing agents. The PZAF/MWCNTs, PZS/MWCNTs, Pt–Co/PZAF-MWCNTs and Pt–Co/PZS-MWCNTs are measured by transmission electron microscopy, X-ray diffraction and inductively coupled plasma. The electrocatalytic activity of Pt–Co/PZAF-MWCNTs, Pt–Co/PZS-MWCNTs catalysts for methanol oxidation has been investigated by cyclic voltammetry. The composite of Pt–Co/PZAF-MWCNTs shows a good distribution, small particle size and high mass activity.