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1.
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
2.
Ching-Shiun Chen Jarrn-Horng Lin Hsiu-Wei Chen Chien-Yuan Wang 《Catalysis Letters》2005,105(3-4):149-155
FT-IR spectra of the co-adsorption of benzene and CO have been performed to identify the preferred adsorption sites of hydrogen
and benzene on a Pt/SiO2 catalyst for hydrogenation of benzene. Results of CO adsorbed on atop sites on Pt/SiO2 includes: an α peak at 2091 cm−1, a β peak at 2080 cm−1 and a γ peak at 2067 cm−1 indicating three kinds of adsorption sites for dissociative hydrogen on Pt/SiO2. The site of lowest CO stretching frequency offers stronger adsorbates–metal interaction for benzene and hydrogen. Hydrogen
binding on the site of lowest CO stretching frequency before benzene adsorption significantly enhances the reaction rate of
benzene hydrogenation. 相似文献
3.
Surendra P. Verma Jean R. Philippot Bernard Bonnet Josette Sainte-Marie Yves Moschetto Donald F. H. Wallach 《Lipids》1985,20(12):890-896
Raman and resonance Raman spectra of plasma lipoproteins ± malondialdehyde were studied at concentrations which block the
normal receptor-mediated uptake by cells. The strong resonance Raman bands at about 1010, 1162 and 1530 cm−1, due to the presence of carotenoids in the lipoproteins, are envisaged as structural probes. High resolution resonance Raman
spectra of the 1500–1600 cm−1 region reveal multiple features suggesting the coexistence of several structural populations of β-carotene whose precise
assignment is complex. When plasma lipoproteins are reacted with malondialdehyde, a complex change occurs in the resonance
Raman banding of β-carotene in the 1500–1600 cm−1 region. Malonaldehyde (MDA) also modifies the acoustical region (70–200 cm−1 of low density lipoprotein (LDL) lipids. We suggest that malondialdehyde association with plasma lipoproteins alters the
lipid structure via apoprotein or apoprotein/lipid associations. 相似文献
4.
Abstract
Nanosized CexM1−xO2−δ (M = Zr, Hf, Tb and Pr) solid solutions were prepared by a modified coprecipitation method and thermally treated at different temperatures from 773 to 1073 K in order to ascertain the thermal behavior. The structural and textural properties of the synthesized samples were investigated by means of X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), BET surface area, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy (RS) techniques. The catalytic efficiency has been performed towards oxygen storage/release capacity (OSC) and CO oxidation activity. The characterization results indicated that the obtained solid solutions exhibit defective cubic fluorite structure. The solid solutions of ceria–hafnia, ceria–terbia and ceria–praseodymium exhibited good thermal stability up to 1073 K. A new Ce0.6Zr0.4O2 phase along with Ce0.75Zr0.25O2 was observed in the case of ceria–zirconia solid solution due to more Zr4+ incorporation in the ceria lattice at higher calcination temperatures. The reducibility of ceria has been increased upon doping with Zr4+, Hf4+, Tb3+/4+ and Pr3+/4+ cations. This enhancement is more in case of Hf4+ doped ceria. Among various solid solutions investigated, the ceria–hafnia combination exhibited better OSC and CO oxidation activity. The high efficiency of Ce–Hf solid solution was correlated with its superior bulk oxygen mobility and other physicochemical characteristics. 相似文献5.
FTIR spectra are reported of CO and formic acid adsorption on a series of Cu/ZnO/SiO2 catalysts. Peaks due to linear CO adsorbed on copper diminished in intensity as the loading of ZnO was increased. This behaviour was explained in terms of ZnO island growth on the copper surface. Similarly, reduction of the copper concentration while maintaining a constant ZnO loading also resulted in further attenuation in bands ascribed to CO chemisorbed on copper. Formic acid exposure to a Cu/SiO2 sample produced a formate species displaying a as(COO) mode at 1585 cm–1. Addition of a small quantity of ZnO to the catalyst resulted in substantial promotion of formate growth, which was accompanied by a shift (and broadening) of the as(COO) vibration to 1660–1600 cm–1. Since further ZnO incorporation poisoned formate creation it was concluded that formate species bonded to Cu and Zn sites located at interfacial positions had been formed. The role of such species in methanol synthesis is discussed. 相似文献
6.
Structure of gold nanoparticles formed by physical vapor deposition onto thin ceria films was studied by scanning tunneling
microscopy (STM). Gold preferentially nucleates on point defects present on the terraces of the well-ordered, fully oxidized
films to a low density. The nucleation expands to the terrace step edges, providing a large variety of low-coordinated sites.
Only at high coverage, the Au particles grow homogeneously on the oxygen-terminated CeO2(111) terraces. The morphology of Au particles was further examined by STM in situ and ex situ at elevated (up to 20 mbar) pressures of O2, CO, and CO + O2 at 300 K. The particles are found to be stable in O2 ambient up to 10 mbar, meanwhile gold sintering emerges at CO pressures above ∼1 mbar. Sintering of the Au particles, which
mainly proceeds along the step edges of the CeO2(111) support, is observed in CO + O2 (1:1) mixture at much lower pressure (∼10−3 mbar), thus indicating that the structural stability of the Au/ceria catalysts is intimately connected with its reactivity
in the CO oxidation reaction. 相似文献
7.
Hadjiivanov Konstantin Concepción Patricia Knözinger Helmut 《Topics in Catalysis》2000,11(1-4):123-130
Adsorption of NO on vanadia–titania samples pre-subjected to different reduction treatments has been studied by FTIR spectroscopy.
When the NO adsorption is performed at 85 K on oxidized samples, antisymmetric NONO species, typical for V5+ sites, are detected and characterized by bands at 1779 and 1686 cm−1. At ambient temperature, however, adsorption is negligible and only with time reactive adsorption occurs producing NO+ (2120 cm−1), nitro/nitrato species (bands in the 1650–1100 cm−1 region) and weakly adsorbed NO (broad band at 1915 cm−1). Adsorption of NO at ambient temperature on reduced samples results in the formation of two types of species: (i) V4+(NO)2 dinitrosyls characterized by νs(NO) and νas(NO) at 1903–1880 and 1769–1753 cm−1, respectively, and (ii) V3+(NO)2 complexes, which give rise to νs(NO) at 1834–1822 cm−1 and νas(NO) at 1697–1685 cm−1. At low temperature the dinitrosyls are transformed into species in which more than one (NO)2 dimer is attached to one cationic site. Addition of O2 to NO, preadsorbed on reduced vanadia–titania samples, results in a fast oxidation of the V3+(NO)2 species, whereas the V4+(NO)2 complexes are more stable and do not disappear completely in the presence of oxygen. The results obtained suggest that NO
is a convenient probe molecule for the analysis of the oxidation state of vanadium in vanadia–titania catalysts. To prevent
oxidation of reduced vanadium sites, low equilibrium pressures of NO and registration of the IR spectrum soon after the NO
admission are recommended.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
8.
Thomas Diemant Zhong Zhao Hubert Rauscher Joachim Bansmann R. Jürgen Behm 《Topics in Catalysis》2007,44(1-2):83-93
The interaction of CO with structurally well-defined, planar Au/TiO2 model catalysts at elevated pressures (up to 50 mbar) was studied in-situ by polarization-modulated infrared reflection absorption spectroscopy and ex-situ by X-ray photoelectron spectroscopy performed before and after CO exposure. The results indicate a CO-induced partial reduction
of the oxide surface, which is evidenced by a low frequency C–O vibration at 2060 cm−1, combined with a spreading of the Au nanoparticles due to a modification of the Au-oxide interface energy. In a 2:1 CO:O2 atmosphere, TiO2 support reduction was not observed, and a pre-reduced surface was re-oxidized. The consequences of these results for the
understanding of the CO oxidation mechanism on Au/TiO2 (model) catalysts are discussed. 相似文献
9.
FTIR spectra are reported of CO2 and CO2/H2 on a silica-supported caesium-doped copper catalyst. Adsorption of CO2 on a “caesium”/silica surface resulted in the formation of CO2
− and complexed CO species. Exposure of CO2 to a caesium-doped reduced copper catalyst produced not only these species but also two forms of adsorbed carboxylate giving
bands at 1550, 1510, 1365 and 1345 cm−1. Reaction of carboxylate species with hydrogen at 388 K gave formate species on copper and caesium oxide in addition to methoxy
groups associated with caesium oxide. Methoxy species were not detected on undoped copper catalyst suggesting that caesium
may be a promoter for the methanol synthesis reaction. Methanol decomposition on a caesium-doped copper catalyst produced
a small number of formate species on copper and caesium oxide. Methoxy groups on caesium oxide decomposed to CO and H2, and subsequent reaction between CO and adsorbed oxygen resulted in carboxylate formation. Methoxy species located at interfacial
sites appeared to exhibit unusual adsorption properties. 相似文献
10.
The adsorption of CO at low temperatures (130–293 K) has been investigated on Rh/Al2O3 catalysts of low (0.001–1 wt%) Rh loadings by means of Fourier transform infrared spectroscopy. The surface structure of
Rh produced at different reduction temperatures (573 and 1173 K) was shock-cooled to 130 K, where the addition of CO caused
the appearance of the band due to bridge-bonded CO ((Rh0)2–CO) on all samples. The appearance of the bands due to gem-dicarbonyl (Rh+(CO)2) and linearly bonded CO (Rhx–CO) depended on the Rh content and the reduction temperature of the catalysts. The positions and the integrated absorbances
of the symmetric and asymmetric stretchings of the Rh+(CO)2 changed with temperature. On the basis of the above findings the rearrangement of the adsorbed CO species (indirectly that
of surface Rh) is discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
Using chemical reduction-deposition method, a type of metallic cobalt-decorated multi-walled carbon nanotubes, noted as y%(mass percentage)Co/MWCNTs, was prepared. TEM, SEM and XRD measurements demonstrated that the metallic cobalt was evenly
coated on the MWCNT substrate, with granule-diameter of the Co
x
0
-crystallites of 5–8 nm. Using the y%Co/MWCNTs as support, a type of supported Co–Mo–K sulfide catalysts, noted as x%(Co
i
Mo
j
K
k
)/(y%Co/MWCNTs), for higher alcohol synthesis (HAS) was developed. It was experimentally shown that using the Co-modified MWCNTs
in place of simple MWCNTs or activated carbon (AC) as the catalyst support led to a significant increase in activity of CO
hydrogenation conversion and improvement in the selective formation of C2+-alcohols. Under the reaction condition of 5.0 MPa, 613 K, CO/H2/N2 = 45/45/10 (v/v) and GHSV = 3600 mlSTPh−1 g
−cat.
−1
, the observed STY of C1–4-alcohols reached 154.1 mgh−1g
−cat.
−1
at 12.6% conversion of CO over the 11.6%(Co1Mo1K0.6)/(6.4%Co/MWCNTs) catalyst, which was 1.76 and 2.33 times as high as that (87.7 and 66.1 mgh−1g
−cat.
−1
) of the reference systems supported by simple MWCNTs and AC respectively. Ethanol became the predominant product of the CO
hydrogenation, with carbon-based selectivity ratio of C2–4-alcohols to CH3OH reaching 3.6 in the products. It was experimentally found that using the Co-modified MWCNTs in place of simple MWCNTs or
AC as the catalyst support caused little change in the apparent activation energy for the conversion of CO, but led to a slight
increase in the molar percentage of catalytically active Mo-species (Mo4+) in the total Mo-amount at the surface of the functioning catalyst. Based upon the results of TPD investigation, it could
be inferred that, under the reaction condition of HAS, there existed a considerably larger amount of adsorbed H-species and
CO-species on the functioning catalyst, thus in favour of increasing the rate of a series of surface hydrogenation reactions
in HAS. 相似文献
12.
This article investigates a method in further improvement of a (La0.8,Sr0.2)MnO3 (LSM)-Yttria-stabilized zirconia (YSZ) dual composite cathode by adding material with high ionic conductivity such as gadolinia-doped
ceria (GDC). A nano-porous composite cathode containing LSM, YSZ, and GDC was prepared by a two-step polymerizable complex
(PC) method which minimizes the formation of YSZ–GDC solid solution. The structure of the resulting LSM/GDC–YSZ dual composite
cathode was such that the LSM and GDC phases were present on the YSZ core particles without formation of the La2Zr2O7, SrZrO3, and GDC–YSZ solid solution. At 800 °C, the electrode polarization resistance of the LSM/GDC–YSZ dual composite cathode decreased
to 0.266 Ω cm2, compared with 0.385 Ω cm2 for the LSM/YSZ–YSZ dual composite cathode. In addition, the Ni–YSZ anode-supported single cell using a LSM/GDC–YSZ dual
composite cathode with H2 as the fuel achieved a maximum power density of 0.65 W cm−2 at 800 °C. 相似文献
13.
Harold N. Evin Gary Jacobs Javier Ruiz-Martinez Uschi M. Graham Alan Dozier Gerald Thomas Burtron H. Davis 《Catalysis Letters》2008,122(1-2):9-19
Doping Pt/ceria catalysts with the Group 1 alkali metals was found to lead to an important weakening of the C–H bond of formate
and methoxy species. This was demonstrated by a shift to lower wavenumbers of the formate and methoxy ν(CH) vibrational modes
by DRIFTS spectroscopy. Li and Na-doped Pt/ceria catalysts were tested relative to the undoped catalyst for low temperature
water–gas shift and methanol steam reforming using a fixed bed reactor and exhibited higher catalytic activity. Steaming of
formate and methoxy species pre-adsorbed on the catalyst surface during in-situ DRIFTS spectroscopy suggested that the species
were more reactive for dehydrogenation steps in the catalytic cycle for the Li and Na-doped catalysts relative to undoped
Pt/ceria. However, with increasing atomic number over the series of alkali-doped catalysts, the stability of a fraction of
the carbonate species was found to increase. This was observed during TPD-MS measurements of the adsorbed CO2 probe molecule by a systematic increase of a high temperature peak for a fraction of the CO2 desorbed. This result indicates that alkali-doping is an optimization problem—that is, while improving the dehydrogenation
rates of methoxy and formate species, the carbonate intermediate stability increases, making it difficult to liberate the
CO2. Infrared spectroscopy results of CO adsorbed on Pt and ceria suggest that the alkali dopant is located on, and electronically
modifies, both the Pt and ceria components. The results not only lend further support to the role that methoxy and formate
species play as intermediates in the catalytic mechanisms, but also provide a path forward for improving rates by means other
than resorting to higher noble metal loadings. 相似文献
14.
The nature of the Keggin ions of tungstophosphoric acid interacting with Ce0.5Zr0.5O2 solid solution has been investigated. The vibrational study shows additional IR features at 1051 and 957 cm−1 which are correlated to the primary Keggin anions interacting with Lewis sites involving Ce4+ and Zr4+ ions, and thus affecting the P–O and W=Oterminal bonds. The IR study indicates the formation of interfacial Ce4+–O–W and Zr4+–O–W bonds. The chemisorbed Keggin molecular layers on Ce0.5Zr0.5O2 show activity towards conversion of acetophenone to styrene by Meerwein–Ponndorf–Verley reduction followed by dehydration.
The activity is correlated with the relative intensities of IR peaks at 1051 and 957 cm−1 of the perturbed Keggin molecular layers. 相似文献
15.
N. Droushiotis A. Torabi M. H. D. Othman T. H. Etsell G. H. Kelsall 《Journal of Applied Electrochemistry》2012,42(7):517-526
Single layer La0.6Sr0.4Co0.2Fe0.8O3 hollow fibre (HF) precursors (<1 mm ID) produced by phase inversion (PI) were sintered at 1,200, 1,350 and 1,400 °C. The increase in sintering temperature resulted in microstructural changes in the LSCF fibres, reflected in their electrical conductivities. LSCF-based cathodes with different designs were brushed onto co-extruded nickel–gadolinium-doped ceria (CGO) anode/CGO electrolyte dual-layer HFs (<1 mm ID) fabricated by PI. The effect of cathode layers on the overall performance of the fuel cells (FCs) was assessed using nearly identical anode and electrolyte compositions, thicknesses, and microstructures. Cathode microstructure design caused cells to perform differently producing peak power densities of 0.35–0.7 W cm−2 at 600 °C. Impedance spectroscopy analysis at 600 °C on the FCs produced 0.12–0.24 Ω cm2 confirming the cathode’s structural effect on the overall area-specific resistance of the FCs. The best performing FC with a brush-deposited cathode was compared to a similar FC where cathode was deposited by dip coating; at 600 °C the first produced 0.6 W cm−2 while the second cell 0.7 W cm−2. Co-extruding anodes and electrolytes by using PI and combining dip coating for cathode deposition could lead to the fabrication of FCs with enhanced microstructures and improved performances. 相似文献
16.
Yudai Huang Rongrong Jiang Shu-Juan Bao Yali Cao Dianzeng Jia 《Nanoscale research letters》2009,4(4):353-358
LiMn2O4–y
Br
y
nanoparticles were synthesized successfully for the first time by a room temperature solid-state coordination method. X-ray
diffractometry patterns indicated that the LiMn2O4–y
Br
y
powders were well-crystallized pure spinel phase. Transmission electron microscopy images showed that the LiMn2O4–y
Br
y
powders consisted of small and uniform nanosized particles. Synthesis conditions such as the calcination temperature and
the content of Br− were investigated to optimize the ideal condition for preparing LiMn2O4–y
Br
y
with the best electrochemical performances. The optimized synthesis condition was found in this work; the calcination temperature
is 800 °C and the content of Br− is 0.05. The initial discharge capacity of LiMn2O3.95Br0.05 obtained from the optimized synthesis condition was 134 mAh/g, which is far higher than that of pure LiMn2O4, indicating introduction of Br− in LiMn2O4 is quite effective in improving the initial discharge capacity. 相似文献
17.
Co–Mo/γ-Al2O3 oxide containing 9.8 wt% Mo and 2.9 wt% Co was prepared by high-intensity ultrasonic irradiation of Mo(CO)6, Co2(CO)8, and γ-Al2O3 in decahydronapthalene under air flow. The oxidic Co–Mo catalyst thus formed was characterized by elemental analysis, BET
N2 adsorption and XRD. The surface sites on the sulfided Co–Mo/γ-Al2O3 catalyst were characterized by infrared spectroscopy of CO adsorption. Hydrodenitrogenation (HDN) and hydrodesulfurization
(HDS) activities were evaluated for heavy gas oil derived from Athabasca bitumen in a trickle bed reaction system using the
following conditions: temperatures ranging from 370 to 400 °C, a pressure of 8.8 MPa, a liquid hourly space velocity of 1 h−1, and a H2/feed ratio of 600 ml/ml. The dispersion, nature of active sites and hydrotreating activity of this catalyst were compared
with the conventionally prepared Co–Mo/γ-Al2O3 catalyst containing similar wt% of Mo and Co. The Co–Mo catalyst prepared by sonochemical method has higher HDN and HDS rate
constants than the conventional catalyst due to an improved dispersion of MoS2. 相似文献
18.
Bimetallic lanthanide (Ln: Eu or Yb)–Ni/SiO2 catalysts prepared by the use of dissolution of lanthanide metals in liquid ammonia have been studied by infrared spectroscopy
for dinitrogen adsorption. The infrared spectra were measured at 133–300 K using Ln–Ni/SiO2 obtained when the Eu or Yb metal dissolved in liquid ammonia reacted with 20 mass% Ni/SiO2 in different ratios. Infrared spectra for Eu–Ni/SiO2 showed absorption bands at 2336, 2265, 2254 and 2227 cm−1 at 133 K, which disappeared upon evacuation. The adsorbed state was found to be all molecular from the isotope shift using
28N2 and z30N28. The bands at 2254 and 2227 cm−1 of them were assigned to new adsorbed dinitrogen species resulting from synergetic interactions between the europium and
nickel metal. The concentration of adsorbed dinitrogen on Eu–Ni/2 varied markedly with the Eu/Ni ratios, and particularly, it increased in the region of high Eu content. Upon introduction
of ytterbium onto nickel, new bands at 2254 and 2226 cm−- similarly appeared. However, the dependence of dinitrogen adsorption as a function of Yb content in Yb–Ni/SiO2> was somewhat different from that for Eu–Ni/SiO2. The effects of lanthanide on the surface of Ln–Ni/SiO2 were discussed in connection with the variation in catalytic properties.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
N-vinyl pyrrolidone (NVP) was polymerized in dioxan at 60 ± 0.1°C for 1 h using diphenyl ditelluride as radical initiator.
The system follows ideal kinetics i.e. R
p
α [DPDT]0.5[NVP]. The activation energy and dissociation constant is computed as 46 kJ mol−1 and 1.1 × 10−11 s−1, respectively. The polymer was characterized with the help of FTIR, 1H-NMR, 13C-NMR, ESR spectroscopy. The FT-IR spectrum showed bands at 1660–1680 cm−1 due to combination of >C = O and C–N stretching. The gyromagnetic constant ‘g’ has been computed as 2.2203. The main product of this reaction were poly(N-vinylpyrrolidone)s with phenyl tellanyl ends. The presence of tellurium in polymer is confirmed by ICP analysis. The DSC
shows the T
g
of poly(N-vinylpyrrolidone) is 168°C due to rigid pyrrolidane group. The TGA showed that polymer was stable up to 380°C.The GPC studies
showed that the weight average molecular weight decreases with increase of [DPDT]. 相似文献
20.
Lihua Wang Xiaodong Yi Weizheng Weng Chunxi Zhang Xin Xu Huilin Wan 《Catalysis Letters》2007,118(3-4):238-243
By using the in situ IR spectroscopy, the superoxide species (O2−), characterized by the O–O stretching peak at 1130 cm−1, was detected on the SrF2/La2O3 catalyst at temperatures up to 973 K. The introduction of 18O2 isotope caused the 1130 cm−1 peak to shift to lower wavenumbers (1095 and 1064 cm−1), consistent with the assignment of the spectra to the superoxide species. A good correlation between the rate of the disappearance
of the O2− species and that of the formation of C2H4 was observed, suggesting that O2− was the active oxygen species responsible for the oxidative coupling of methane (OCM) on the SrF2/La2O3 catalyst. This conclusion was reinforced by the EPR experiments (gxx = 2.0001, gyy = 2.0045, gzz = 2.0685), showing that O2− was the only paramagnetic oxygen species detectable on the O2-preadsorbed SrF2/La2O3 catalyst. These results suggest that superoxide O2− can be a stable active oxygen species, whose role in the OCM reaction cannot be overlooked. 相似文献