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1.
Confirmation of sulfur tolerance of bimetallic Pd–Pt supported on highly acidic USY zeolite by EXAFS
Hiroyuki Yasuda Nobuyuki Matsubayashi Toshio Sato Yuji Yoshimura 《Catalysis Letters》1998,54(1-2):23-27
The sulfur tolerance (i.e., degree of sulfidation) of Pd and Pt in sulfided bimetallic Pd–Pt catalysts (Pd : Pt mole ratio
of 4 : 1) supported on USY (ultrastable Y) zeolites (SiO2/Al2O3 = 10.7, 48, and 310) was investigated using an extended X‐ray absorption fine structure (EXAFS) method. The sulfidation of
the catalysts was done in a 1000 ppm H2S–2% H2/N2 stream at 573 K for 0.5 h. In the Fourier transforms of Pd K‐edge and Pt LIII‐edge EXAFS spectra, both of the peaks due to metallic Pd and to metallic Pt for the Pd–Pt/USY (SiO2/Al2O3 = 10.7) catalyst remained most after sulfidation. Further, the results of the Fourier transforms confirmed that the sulfur
tolerance of both Pd and Pt decreased with increasing SiO2/Al2O3 ratio, suggesting that Pd and Pt become sulfur‐tolerant when Pd–Pt bimetallic particles are supported on highly acidic USY
zeolite.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
Jacinto Sá Dana Gasparovicova Konrad Hayek Erich Halwax James A. Anderson Hannelore Vinek 《Catalysis Letters》2005,105(3-4):209-217
Bimetallic Pd–Sn catalysts were synthesized by incipient-wetness impregnation of the metals on alumina and employed for the
reduction of nitrates from aqueous solutions. The catalysts were characterized by FTIR spectroscopy of adsorbed CO, X-ray
diffraction (XRD), transmission electron microscopy (TEM), and H2 chemisorption. The influence of the metal ratio was evaluated in reaction measurements. The bimetallic Pd–Sn catalysts exhibited
high selectivity for nitrate removal forming less NO2− and NH4+ than the Pd–Cu catalysts. 相似文献
3.
Weiwei Si Gang Yu Yuejun Ouyang Lili Tang Xiaomei He Bonian Hu 《Journal of Applied Electrochemistry》2008,38(12):1727-1734
In order to fabricate effective Pd–Ni alloy nanowire arrays with given compositions and size, the process of nucleation and
growth and the dependence of alloy composition on deposition potential were investigated. The results reveal that the compositions
and sizes of Pd–Ni alloy nanowires can be controlled within a desired range through adjusting suitable nucleation and growth
potentials as well as the time. The Ni content in the alloy nanowires was found to vary from 6 to 28% when the deposition
potential was changed from −0.3 to −1.9 V. A growth potential of −0.35 to − 0.50 V was applied to fabricate Pd–Ni alloy nanowires
with 8–15% Ni content. Continuous and parallel nanowire arrays can be successfully fabricated when nucleation is performed
at a potential of −1.2 V for 50 ms with further growth at −0.45 V for 800 s. Pd–Ni crystal phases exist in the alloy structure
forms of 〈111〉, 〈200〉, 〈220〉, 〈311〉. The nanowires have an average diameter of 150 nm and a length of 100–450 μm. 相似文献
4.
Pd–Ru, Pd and Ru nanoparticles supported on Vulcan XC-72 carbon were prepared by chemical reduction of PdCl2 and/or RuCl3 in aqueous solution using NaBH4 as the reducing agent. Transmission electron microscopy measurements showed that Pd–Ru particles were uniformly dispersed
on carbon. The particle size of Pd–Ru is around 5–9 nm. X-ray diffraction analysis indicated that Ru formed alloy with Pd
in Pd–Ru/C catalyst. The electroreduction of hydrogen peroxide on Pd–Ru/C, Pd/C and Ru/C in H2SO4 solution was examined by linear sweep voltammetry and chronoamperometry measurements. Results revealed that Pd–Ru/C catalyst
exhibited higher electrocatalytic activity for hydrogen peroxide reduction than Pd/C and Ru/C. All the catalysts showed good
stability for hydrogen peroxide electroreduction in H2SO4 electrolyte. 相似文献
5.
Yaokun Xiao Baicheng Weng Gang Yu Jinyin Wang Bonian Hu Zongzhang Chen 《Journal of Applied Electrochemistry》2006,36(7):807-812
This paper reports findings of an investigation of Pd–Ag alloy nanowires on the step edges of highly oriented pyrolytic graphite (HOPG) by electrochemical deposition at room temperature. Scanning electron microscopy (SEM) images reveal that these alloy nanowires (109–430 nm) are uniform in diameter, and have lengths up to 100–500 μm. The electrodeposition process involves the initial formation of nanowires induced at the step edges of the oxidized HOPG substrate at a very negative potential and subsequent growth at a constant low current density to coalesce the discontinuous nanowires. Alloy nanowires with a 20–25% silver content can be obtained when the ratio of Pd and Ag in the solution is carefully controlled. The SEM images demonstrate that the alloy nanowire arrays are continuous, parallel, ordered, well-aligned and have a narrow distribution of diameters. The Pd–Ag alloy nanowire arrays are promising materials for fabricating hydrogen nanosensors. 相似文献
6.
Olga P. Tkachenko Alexander Yu. Stakheev Leonid M. Kustov Igor V. Mashkovsky Maurits van den Berg Wolfgang Grünert Natalya Yu. Kozitsyna Zhanna V. Dobrokhotova Valery I. Zhilov Sergei E. Nefedov Michael N. Vargaftik Ilya I. Moiseev 《Catalysis Letters》2006,112(3-4):155-161
The heterobimetallic lantern complex Pd(μ-OOCMe)4Zn(OH2) was found to be readily reduced with H2 under fairly mild conditions (150–250 °C, 5–10% H2/He) both in the carbon-supported and crystalline states to afford a Pd–Zn nanoalloy as evidenced by the ICP elemental analysis,
EXAFS, XANES and XRD data.
相似文献
7.
Infrared spectra of adsorbed CO have been used as a probe to monitor changes in Pt site character induced by the coking of
Pt/Al2O3 and Pt–Sn/Al2O3 catalysts by heat treatment in heptane/hydrogen. Four distinguishable types of Pt site for the linear adsorption of CO on
Pt/Al2O3 were poisoned to different extents showing the heterogeneity of the exposed Pt atoms. The lowest coordination Pt atoms (ν(CO)
< 2030 cm−1) were unpoisoned whereas the highest coordination sites in large ensembles of Pt atoms (2080 cm−1) were highly poisoned, as were sites of intermediate coordination (2030–2060 cm−1). Sites in smaller two‐dimensional ensembles of Pt atoms (2060–2065 cm−1) were partially poisoned, as were sites for the adsorption of CO in a bridging configuration. The addition of Sn blocked
the lowest coordination sites and destroyed large ensembles of Pt by a geometric dilution effect. The poisoning of other sites
by coke was impeded by Sn, this effect being magnified for Cl‐containing catalyst. Oxidation or oxychlorination of coked catalyst
at 823 K followed by reduction completely removed coke from the catalyst surfaces.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
A. Di Blasi C. D’Urso V. Baglio V. Antonucci A. S. Arico’ R. Ornelas F. Matteucci G. Orozco D. Beltran Y. Meas L. G. Arriaga 《Journal of Applied Electrochemistry》2009,39(2):191-196
IrO2–RuO2, IrO2–Pt and IrO2–Ta2O5 electrocatalysts were synthesized and characterized for the oxygen evolution in a Solid Polymer Electrolyte (SPE) electrolyzer.
These mixtures were characterized by XRD and SEM. The anode catalyst powders were sprayed onto Nafion 117 membrane (catalyst
coated membrane, CCM), using Pt catalyst at the cathode. The CCM procedure was extended to different in-house prepared catalyst
formulations to evaluate if such a method could be applied to electrolyzers containing durable titanium backings. The catalyst
loading at the anode was about 6 mg cm−2, whereas 1 mg cm−2 Pt was used at the cathode. The electrochemical activity for water electrolysis was investigated in a single cell SPE electrolyzer
at 80 °C. It was found that the terminal voltage obtained with Ir–Ta oxide was slightly lower than that obtained with IrO2–Pt and IrO2–RuO2 at low current density (lower than 0.15 A cm−2). At higher current density, the IrO2–Pt and IrO2–RuO2 catalysts performed better than Ir–Ta oxide. 相似文献
9.
X.-M. Yan S. Kwon A.M. Contreras M.M. Koebel J. Bokor G.A. Somorjai 《Catalysis Letters》2005,105(3-4):127-132
High-density arrays of platinum nanowires with dimensions 20 nm × 5 nm × 12 μm (width × height × length) have been produced
on planar oxide thin films of silica, alumina, zirconia, and ceria. In this multi-step fabrication process, sub-20 nm single
crystalline silicon nanowires were fabricated by size reduction lithography. The Si nanowire patterns were then replicated
to produce a high density of Pt nanowires by nanoimprint lithography. The width and height of the Pt nanowires are uniform
and are controlled with nanometer precision. The Pt surface area is larger than 2 cm2 on a 5 × 5 cm2 oxide substrate. The catalytic oxidation of CO was carried out on zirconia-supported Pt nanowires. The reaction conditions
(100 Torr O2, 40 Torr CO, 513–593 K) and vacuum annealing (1023 K) did not change the nanowire structures. 相似文献
10.
Ngoc Trung Trinh Jong Hyeok Park Byung-Woo Kim 《Korean Journal of Chemical Engineering》2009,26(3):748-753
The microbial fuel cell (MFC) has attracted research attention as a biotechnology capable of converting hydrocarbon into electricity
production by using metal reducing bacteria as a biocatalyst. Electricity generation using a microbial fuel cell (MFC) was
investigated with acetate as the fuel and Geobacter sulfurreducens as the biocatalyst on the anode electrode. Stable current production of 0.20–0.24 mA was obtained at 30–32 °C. The maximum
power density of 418–470 mW/m2, obtained at an external resistor of 1,000 Ω, was increased over 2-fold (from 418 to 866 mW/m2) as the Pt loading on the cathode electrode was increased from 0.5 to 3.0 mg Pt/cm2. The optimal batch mode temperature was between 30 and 32 °C with a maximum power density of 418–470 mW/m2. The optimal temperature and Pt loading for MFC were determined in this study. Our results demonstrate that the cathode reaction
related through the Pt loading on the cathode electrode is a bottleneck for the MFC’s performance. 相似文献
11.
Sébastien Clément Shawkat Mohammed Aly Karl Gagnon Alaa S. Abd-El-Aziz Michael Knorr Pierre D. Harvey 《Journal of Inorganic and Organometallic Polymers and Materials》2008,18(1):104-110
Abstract ClPd(μ-dppm)2PtCl (1) reacts with (CNC6H4–2-OCH2–)2 to form a sparingly soluble and thermally stable orange polymeric material 4. 1 reacts with 1 or 2 equivalents of CNC6H4–2-OCH3 to form the soluble A-frame d8–d8 model complexes 2 [ClPd(μ-dppm)2(μ-CNR)PtCl], and 3 [ClPd(μ-dppm)2(μ-CNR)Pt(CNR)](Cl) (R = C6H4–2-OCH3), respectively. IR (ν(NC) bridging versus terminal) and NMR data reveal an A-frame structure where the terminal CNR ligands
are bonded to Pt. 4 which is amorphous (XRD) appears stable up to 290 °C (TGA), but exhibits an exothermic process between 215 and 255 °C upon
the first scan in DSC, but disappears upon the second. Two compounds, model 2 (λe = 674 nm; τe = 0.38 ± 0.01 μs; Φe = 0.0079 (±10%)) and polymer 4 (λe = 660 nm; τe = 0.18 ± 0.01 μs; Φe = 0.0056 (±10%)) are luminescent at 77 K in the solid state and in fluid solution (PrCN).
Graphical abstract
The First A-Frame-Containing Organometallic Polymer: Taking Advantage of the Site Selectivity in PdPt-Mixed Metal Bimetallics
Sébastien Clément, Shawkat Mohammed Aly, Karl Gagnon, Alaa S. Abd-El-Aziz, Michael Knorr, Pierre D. Harvey
ClPd(μ-dppm)2Cl2 reacts with (CN–C6H4–O–CH2–)2 to form the first A-frame-containing organometallic polymer, which is unambiguously characterized with the use of model compounds.
This polymer does not experience any weight loss up to 290 °C based on TGA measurements, but DSC traces reveal an irreversible
process at 215 °C (DSC). The novel material is also luminescent at 77 K. For example, λe = 660 nm; τe = 0.18 ± 0.01 μs; Φe = 0.0056 (±10%) in PrCN.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
This article is dedicated to Professor Astruc. 相似文献
12.
The concentrations of arsenic, selenium, iodine and bromine in a series of fish, plant and mammalian oils have been determined
by cyclic instrumental neutron activation analysis (CINAA). Crude fish oils contain between 0.047 and 0.151 μg Se g−1, 2.36–14.5 μg As g−1, 2.36–9.63 μg Br g−1 and 0.97–4.76 μgI g−1. Seal oil contains the same four elements, but at levels below the lower end of the fish oil ranges. Iodine, bromine and
arsenic were not detected in rape-seed or soybean oils and the concentration of selenium varied from < 0.010 to 0.042 μg g−1. The levels of selenium, iodine and bromine are reduced markedly by hydrogenation of the menhaden oils. The CINAA method
yielded results which were in agreement with pub-lished values obtained by other methods. The technique was rapid, requiring
minimal sample manipulation, and was essentially free from interferences. 相似文献
13.
The kinetics of the thermal decomposition reaction of diethylketone triperoxide (3,3,6,6,9,9-hexaethyl-1,2,4,5,7,8-hexaoxacyclononane,
DEKTP) in ethylbenzene solution were studied in the temperature range of 120.0–150.0 °C and at an initial concentration range
of 0.01–0.10 M. This peroxide was used as a new initiator in methyl methacrylate (MMA) polymerization process at high temperatures
(110.0–140.0 °C) in ethylbenzene solution. The effects of initiator concentration and reaction temperature on the polymerization
rate were investigated in detail. Thus, activation parameters of the solution polymerization process (ΔE
d* = 83.3 kJ mol−1 and ΔE
p* − ΔE
t*/2 = 54.0 kJ mol−1) will be obtained. DEKTP can effectively act as initiator in MMA polymerization and its performance is similar to that presented
by a multifunctional initiator resulting in high-molecular weight polymethylmethacrylate with a high reaction rate. 相似文献
14.
A series of well-defined dendritic star-block copolymers were successfully synthesized by combination of living ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP) with the hydroxyl-terminated dendrimer polyester. Dendritic star-shaped poly(l-lactide)s (PLLAs) were prepared by bulk polymerization of l-lactide (l-LA) with dendrimer polyester initiator and tin 2-ethylhexanoate catalyst. The number-average molecular weight of these polymers linearly increased with the molar ratio of l-LA to dendrimer initiator. Dendritic star-shaped PLLA was converted into a PLLABr macroinitiator with 2-bromopropionyl bromide. Dendritic star-block copolymers could be obtained via ATRP of 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA). The molecular weight distributions of these copolymers were narrow. The molecular weights of dendritic star-shaped polymers and star-block copolymers could be controlled by the molar ratios of monomer to initiator and monomer conversion. The thermal properties of these dendritic star-shaped polymers and star-block copolymers were investigated. The behavior of model drug chlorambucil release from the copolymer indicated that the rate of drug release could be effectively controlled by altering the pH values of the environment. 相似文献
15.
Direct current (DC) and pulse current (PC) electrodeposition of Pt–Co alloy onto pretreated electrodes has been conducted
to fabricate catalyst electrodes for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFC). The effect
of plating mode and pulse plating parameters on the Pt–Co alloy catalyst structure, composition and electroactivity for the
ORR in PEMFC has been investigated. The electrodeposited Pt–Co alloy catalyst indicates higher electrocatalytic activity towards
the ORR than the electrodeposited Pt catalyst. The activity of the electrodeposited Pt–Co catalysts is further improved by
applying the current in a pulse waveform pattern. The electrodeposition mode and the pulse plating parameters do not have
the significant effect on the Pt:Co composition of deposited catalysts, but show the substantial effect on the deposit structures
produced. The Pt–Co catalysts prepared by PC electrodeposition have finer structures and contain smaller Pt–Co catalyst particles
compared to that produced by DC electrodeposition. By varying the Pt concentration in deposition solution, the Pt:Co composition
of the electrodeposited catalyst that exhibits the highest activity is found. The Pt–Co alloy catalyst with the Pt:Co composition
of 82:18 obtained at the charge density of 2 C cm−2, the pulse current density of 200 mA cm−2, 5% duty cycle and 1 Hz was found to yield the best electrocatalytic activity towards the ORR in PEMFC. 相似文献
16.
Catalytic reactivity and surface chemical effects induced by the presence of water in the molecular system polyaniline(EB)–Pd–H2O were investigated. The polyaniline(EB) doped with palladium reveals its high activity and selectivity in the semihydrogenation:
hexyne → hexenes (→ hexane). However, to demonstrate these effects, the specimen has to be submitted to a special treatment
to lose most of its water. The XPS analysis allowed identification of the catalytically active sites of the studied system.
They were ascribed to the [PdCl4]2− complex anions present at the surface of the dry specimens.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
17.
Two forests and two croplands, converted from the forest ecosystem were studied for 2 years to quantify inorganic N, nitrification,
N-mineralization and microbial-N. The available N-pool ranged from 15.23 μg g−1 to 19.84 μg g−1, microbial-N from 20.6 μg g−1 to 80.02 μg g−1 with maximum values in summer season and minimum values in the rainy season. The trend for nitrification and N-mineralization
was opposite to that of the size of available N-pool. Mean annual net nitrification rates ranged from 7.07 μg g−1 month−1 to 44.84 μg g−1 month−1 (0.17–1.39 μg g−1 day−1) and net N-mineralization from 6.56 μg g−1 month−1 to 48.53 μg g−1 month−1 (0.21–1.56 μg g−1 day−1). On an average, the pool of available N was slightly higher by 4.81%, while the microbial-N was declined substantially by
41.78% after the conversion of forest into cropland. Cultivation reduced the mean annual net nitrification and net N-mineralization,
respectively by 50.71% and 47.67%. Interestingly, seasonal moisture content is negatively correlated to microbial-N and inorganic
N and positively related to nitrification and N-mineralization. 相似文献
18.
C. Koutsodontis A. Katsaounis J. C. Figueroa C. Cavalca Carmo J. Pereira C. G. Vayenas 《Topics in Catalysis》2006,38(1-3):157-167
The effect of catalyst film thickness on the magnitude of the effect of electrochemical promotion was investigated for the
model catalytic reaction of C2H4 oxidation on porous Pt paste catalyst-electrodes deposited on YSZ. It was found that the catalytic rate enhancement ρ is up to 400 for thinner (0.2 μm) Pt films (40,000% rate enhancement) and gradually decreases to 50 for thicker (1 μm) films. The Faradaic efficiency Λ was found to increase moderately with increasing film thickness and to be described semiquantitatively
by the ratio 2Fr
o/I
0, where r
o is the unpromoted rate and I
0 is the exchange current of the catalyst–electrolyte interface. The results are in good qualitative agreement with model predictions
describing the diffusion and reaction of the backspillover O2- species, which causes electrochemical promotion. 相似文献
19.
A sensitive hydroxylamine sensor was developed based on electrodeposition of Pt nanoclusters on choline film modified glassy
carbon electrode (nano-Pt/Ch/GCE). The properties of the composites were characterized by field emission scanning electron
microscope, X-ray photoelectron spectroscopy, powder X-ray diffraction, and electrochemical investigations. The designed nano-Pt/Ch/GCE
showed a high sensing performance for hydroxylamine in a wide concentration ranges of 5.0 × 10−7–1.1 × 10−3 M and 1.1 × 10−3–19 × 10−3 M. The detection limit was 0.07 μM (s/n = 3). The proposed electrode presented excellent operational and storage stability for the determination of hydroxylamine.
Moreover, the sensor showed good sensitivity, selectivity, and reproducibility properties. All the results indicated the designed
sensor had a good potential application in the determination of hydroxylamine. 相似文献
20.
Hirofumi Ohtsuka 《Catalysis Letters》2003,87(3-4):179-186
The effects of adding iron to Pd–Pt/sulfated zirconia (SZ) on the selective NO
x
reduction by methane were examined based on durability tests under conditions simulating natural gas combustion exhaust. While Pd–Pt/SZ was severely deactivated at 500 °C, Pd–Pt/Fe-SZ maintained a NO
x
conversion higher than 70% for over 2400 h under the same conditions. Methane conversion on Pd–Pt/Fe-SZ was significantly lower than that on Pd–Pt/SZ. XRD analysis of fresh and used catalysts showed that a part of the SZ had transformed to monoclinic ZrO2 and that adding Fe suppressed the transformation. These results suggested that the improvement in NO
x
conversion by adding Fe was due to the suppression of methane combustion and the stabilization of SZ against transformation to ZrO2. 相似文献