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1.
The hydrogen permeation and stability of tubular palladium alloy (Pd–23%Ag) composite membranes have been investigated at elevated temperatures and pressures. In our analysis we differentiate between dilution of hydrogen by other gas components, hydrogen depletion along the membrane length, concentration polarization adjacent to the membrane surface, and effects due to surface adsorption, on the hydrogen flux. A maximum H2 flux of 1223 mL cm−2 min−1 or 8.4 mol m−2 s−1 was obtained at 400 °C and 26 bar hydrogen feed pressure, corresponding to a permeance of 6.4 × 10−3 mol m−2 s−1 Pa−0.5. A good linear relationship was found between hydrogen flux and pressure as predicted for rate controlling bulk diffusion. In a mixture of 50% H2 + 50% N2 a maximum H2 flux of 230 mL cm−2 min−1 and separation factor of 1400 were achieved at 26 bar. The large reduction in hydrogen flux is mainly caused by the build-up of a hydrogen-depleted concentration polarization layer adjacent to the membrane due to insufficient mass transport in the gas phase. Substituting N2 with CO2 results in further reduction of flux, but not as large as for CO where adsorption prevail as the dominating flow controlling factor. In WGS conditions (57.5% H2, 18.7% CO2, 3.8% CO, 1.2% CH4 and 18.7% steam), a H2 permeance of 1.1 × 10−3 mol m−2 s−1 Pa−0.5 was found at 400 °C and 26 bar feed pressure. Operating the membrane for 500 h under various conditions (WGS and H2 + N2 mixtures) at 26 bars indicated no membrane failure, but a small decrease in flux. A peculiar flux inhibiting effect of long term exposure to high concentration of N2 was observed. The membrane surface was deformed and expanded after operation, mainly following the topography of the macroporous support.  相似文献   

2.
A thin layer (30–40 nm) of a dual-element silica–alumina composition was deposited on a porous alumina support by chemical vapor deposition (CVD) in an inert atmosphere at high temperature. Prior to CVD, an intermediate layer of γ-alumina was coated on the macroporous alumina support. The intermediate layer was prepared by the dip-coating and calcination of boehmite sols of different sizes to give a graded structure that was substantially free of defects. The resulting supported composite membrane had high permeance for hydrogen in the order of 2–3 × 10−7 mol m−2 s−1 Pa−1 at 873 K with selectivities of H2 over CH4, CO and CO2 of 940, 700 and 590, respectively. The membrane operated by a hopping mechanism involving jumps of permeating molecules between solubility sites. The presence of aluminum improved the hydrothermal stability of the membranes for periods in excess of 500 h at 873 K in 16% steam, allowing the permeance to remain above 10−7 mol m−2 s−1 Pa−1, although with decreased selectivities.  相似文献   

3.
The changes in structural organization of the major light-harvesting chlorophyll a/b–protein complex of photosystem II (LHC II) at the level of trimeric subcomplexes were studied in spinach plants grown under low light conditions (50 μmol quanta m−2 s−1) and then acclimated to elevated irradiances. By monitoring photochemical quenching of fluorescence yield (qP), photosystem II (PS II) functional status was assessed in leaves of plants acclimated to a range of elevated irradiances. Three separate acclimative irradiances were selected for the experiments, reflecting: limiting light conditions (150 μmol quanta m−2 s−1), near to the inflexion point on the irradiance curve conditions (300 μmol quanta m−2 s−1) and an excessive light, causing a moderate stress in the form of down regulation of PS II (450 μmol quanta m−2 s−1). An immunoblot analysis showed that there was a clear decline in an abundance on chlorophyll basis of Lhcb1-3 apoproteins as an acclimative irradiance increased from 50 to 450 μmol quanta m−2 s−1, with Lhcb1 decreasing to a lesser extent than Lhcb2 and Lhcb3 (only at excessive irradiance). When analyzed by non-denaturing isoelectric focusing BBY membrane fragments (PSII-enriched, stacked thylakoid membranes) isolated from low light-grown plants were resolved into nine fractions, seven of which (labelled 3–9) were established by us previously [Jackowski and Pielucha, J. Photochem. Photobiol. B: Biol. 64 (2001) 45] to be LHC II subcomplexes representing mixed populations of closely similar trimers, comprising permutations of Lhcb1 and Lhcb2 (subcomplexes 3–7) or Lhcb1-3 (subcomplexes 8 and 9). A heterogeneity with regard to accumulation behaviour of LHC II subcomplexes in response to elevated irradiances was revealed. The subcomplexes 5 and 6 were accumulating at similar level, regardless of the light irradiance experienced. Another group consisting of the subcomplexes 3 and 4 (the most basic ones) showed a progressive increase in relative abundance with increasing an irradiance intensity whereas the subcomplexes 7–9 (the most acidic ones) exhibited a progressive decline in their relative abundance during an acclimation of spinach plants to elevated irradiances thus they may collectively represent an elevated irradiance-responsive subunit of LHCII.  相似文献   

4.
A silica membrane was produced by chemical vapor deposition using tetraethoxysilane (TEOS), phenyltriethoxysilane (PTES) or diphenyldiethoxysilane (DPDES) as the Si source. Amorphous silica was deposited in the mesopores of a γ-alumina film coated on a porous -alumina tube, by evacuating the reactant through the porous wall. Hydrogen permeance at a permeation temperature of 600°C was of the order of 10−7 mol m−2 s−1 Pa−1, and was not greatly dependent on the Si sources. The silica membrane produced using TEOS contained micropores permeable to both helium and hydrogen, but CO2 and larger molecules were only slightly permeated through those mesopores which were left unplugged. The silica membrane produced from DPDES showed a single-component CO2 permeance equivalent to that of single-component He, and CO2/N2 selectivity was approximately 9 at a permeation temperature of 30°C. When a mixture of CO2 and N2 was fed, however, CO2 permeance decreased to the level of N2 permeance. The H2/N2 selectivity, determined from single-component permeances to H2 and N2, was approximately 100, and these permeances remained unchanged when an equimolar mixture of H2 and N2 was fed. Thus, the DPDES-derived membrane possessed two types of micropores, abundant pores through which helium and hydrogen permeated and a small number of pores in which molecules of CO2 and N2 were permeable but not able to pass one another. Neither meso or macropores remained in the DPDES membrane.  相似文献   

5.
A thin, gas-tight palladium (Pd) membrane was prepared by the counter-diffusion chemical vapor deposition (CVD) process employing palladium chloride (PdCl2) vapor and H2 as Pd precursors. A disk-shaped, two-layer porous ceramic membrane consisting of a fine-pore γ-Al2O3 top layer and a coarse-pore -Al2O3 substrate was used as Pd membrane support. A 0.5–1 μm thick metallic membrane was deposited in the γ-Al2O3 top layer very close to its surface, as verified by XRD and SEM with a backscattered electron detector. The most important parameters that affected the CVD process were reaction temperature, reactants concentrations and top layer quality. Deposition of Pd in the γ-Al2O3 top layer resulted in a 100- to 1000-fold reduction in He permeance of the porous substrate. The H2 permeation flux of these membranes was in the range 0.5–1.0 × 10−6 mol m−2 s−1 Pa−1 at 350–450°C. The H2 permeation data suggest that surface reaction steps are rate-limiting for H2 transport through such thin membranes in the temperature range studied.  相似文献   

6.
Pentaerythrityl tetraethylenediamine (PETEDA) dendrimer was synthesized from pentaerythrityl tetrabromide and ethylenediamine. Its molecular structure was characterized by elemental analysis, Fourier transform infrared resonance (FT-IR) and hydrogen nuclear magnetic resonance (1H NMR) spectroscopy. The composite membranes for selectively permeating CO2 were prepared by using PETEDA-PVA blend polymer as the active layer and polyethersulfone (PES) ultrafiltration membrane as the support layer and their permselectivity was tested by pure CO2 and CH4 gases and the gas mixture containing 10 vol.% CO2 and 90 vol.% CH4, respectively. For pure gases, the membrane containing 78.6 wt% PETEDA and 21.4 wt% PVA in the blend has a CO2 permeance of 8.14 × 10−5 cm3 (STP) cm−2 s−1 cmHg−1 and CO2/CH4 selectivity of 52 at 143.5 cmHg feed gas pressure. While feed gas pressure is 991.2 cmHg, CO2 permeance reaches 3.56 × 10−5 cm3 (STP) cm−2 s−1 cmHg−1 and CO2/CH4 selectivity is 19. For the gas mixture, the membrane has a CO2 permeance of 6.94 × 10−5 cm3 (STP) cm−2 s−1 cmHg−1 with a CO2/CH4 selectivity of 33 at 188.5 cmHg feed gas pressure, and a CO2 permeance of 3.29 × 10−5 cm3 (STP) cm−2 s−1 cmHg−1 with a CO2/CH4 selectivity of 7.5 at a higher feed gas pressure of 1164 cmHg. A possible gas transport mechanism in the composite membranes is proposed by investigating the permeating behavior of pure gases and the gas mixture and analyzing possible reactions between CO2/CH4 gases and the PETEDA-PVA blend polymer. The effect of PETEDA content in the blend polymer on permselectivity of the composite membranes was investigated, presenting that CO2 permeance and CO2/CH4 selectivity increase and CH4 permeance decreases, respectively with PETEDA content. This is explained by that with increasing PETEDA content, the carrier content increases, and the crystallinity and free volume of the PETEDA-PVA blend decrease that were confirmed by the experimental results of X-ray diffraction spectra (XRD) and positron annihilation lifetime spectroscopy (PALS).  相似文献   

7.
NaY zeolite tubular membranes in an industrial scale of 80 cm long were synthesized on monolayer and asymmetric porous supports. The quality of synthesized membranes were evaluated by pervaporation (PV) experiments in 80 cm long at 75 °C in a mixture of water (10 wt.%)/ethanol (90 wt.%), resulting in higher permeation fluxes of 5.1 kg m−2 h−1 in the monolayer type membrane and of 9.1–10.1 kg m−2 h−1 in the asymmetric-type membranes, respectively. The uniformity with small performance fluctuation in longitudinal direction of the membranes were observed by PV for 10–12 cm long samples at 50 °C in a mixture of methanol (10 wt.%)/MTBE (90 wt.%). The ethanol single component permeation experiments in PV and vapor permeation (VP) up to 130 °C and 570 kPa were performed to determine the relations between the ethanol flux and the ethanol pressure difference across the membrane which is represented by permeance (Π, mol m−2 s−1 Pa−1) for estimate of potential of ethanol extraction through the present NaY zeolite membranes applying feasible studies. Results indicate that (1) the permeation fluxes are linearly proportional to the driving force of vapor pressure for each sample in VP and PV. The permeances through an asymmetric support type membrane were rather constant of 0.6–1.2 × 10−7 mol m−2 s−1 Pa−1 in the wide temperature range of 90–130 °C in PV and VP, indicating that the ethanol permeances have weak temperature dependency with the feed at the saturated vapor pressure.

The results of superheating VP experiments showed that ethanol permeation fluxes are increased with increasing of the degree of superheating at a given constant feed vapor pressure. The ethanol permeances are increased with increasing of temperature at a given feed vapor pressure. The superheating VP could be a feasible process in industry.  相似文献   


8.
A double layered hydroxy sodalite membrane was synthesised directly onto a tubular -alumina support without seeding using a conventional hot-air oven. The effect of different synthesis parameters including the water content, ageing period, synthesis time and temperature, on the purity and continuity of the membrane was investigated. The water content was an important factor in controlling the presence of contaminating zeolite phases in the membrane. The optimised membrane which was contaminant free was characterised by XRD, SEM and single gas permeation using He, N2 and SF6. The permeance of the three gases through the membrane ranged from 0.8 to 8 × 10−8 mol m−2 s−1 Pa−1. The selectivity ( = 2.5–2.7) compared well to the Knudsen diffusion ratio for He/N2.  相似文献   

9.
Hydrogen production by steam reforming of methane using catalytic membrane reactors was investigated first by simulation, then by experimentation. The membrane reactor simulation, using an isothermal and plug-flow model with selective permeation from reactant stream to permeate stream, was conducted to evaluate the effect of permselectivity on membrane reactor performance – such as methane conversion and hydrogen yield – at pressures as high as 1000 kPa. The simulation study, with a target for methane conversion of 0.8, showed that hydrogen yield and production rate have approximately the same dependency on operating conditions, such as reaction pressure, if the permeance ratio of hydrogen over nitrogen ((H2/N2)) is larger than 100 and of H2 over H2O is larger than 15. Catalytic membrane reactors, consisting of a microporous Ni-doped SiO2 top layer and a catalytic support, were prepared and applied experimentally for steam reforming of methane at 500 °C. A bimodal catalytic support, which allows large diffusivity and high dispersion of the metal catalyst, was prepared for the enhancement of membrane catalytic activity. Catalytic membranes having H2 permeances in the range of 2–5 × 10−6 m3 m−2 s−1 kPa−1, with H2/N2 of 25–500 and H2/H2O of 6–15, were examined for steam reforming of methane. Increased performance for the production of hydrogen was experimentally obtained with an increase in reaction-side pressure (as high as 500 kPa), which agreed with the theoretical simulation with no fitting parameters.  相似文献   

10.
Changes in the accumulation of cAMP levels were measured by the isotope dilution assay using protein kinase A in the lichen Evernia prunastri at varying light conditions. cAMP levels decreased following exposure to low irradiance (20 μmol quanta m−2 s−1, and below the compensation point for photosynthesis) of red light (600–710-nm wave length) and increased by 50% after far-red light illumination (15 μmol quanta m−2 s−1, 710–800-nm wavelength). Far-red partially reverted the effect of red light when the former was supplied after the latter. cAMP increased to its maximum level under high irradiance supplied by a non-photomorphogenic yellow light source (400 μmol quanta m−2 s−1, reaching photosynthetic saturation). The addition of small quantities of red and far-red light, however, had profound restricting effects on cAMP accumulation. The addition of inhibitors of electron transport chains did not promote any significant change in cAMP levels in any of the treatments, indicating that cAMP accumulation could not depend on ATP synthesis. We propose that the response of cAMP accumulation at low irradiance comprises the activation of a morphogenic pathway through a red/far-red photoreceptor. In addition, at high irradiance the response would occur most likely through photosystems II and I acting as sensors of light quantity, that can be strongly modified by the red/far-red photomorphogenic system. Thus, cAMP would be involved in sensing the overall light environment.  相似文献   

11.
Polyallylamine (PAAm) was synthesized by free radical polymerization and characterized by Fourier transform infrared resonance (FT-IR) spectroscopy, hydrogen nuclear magnetic resonance (1H NMR) spectroscopy and differential scanning calorimetry (DSC). The composite membranes were prepared by using PAAm–poly(vinyl alcohol) (PVA) blend polymer as the separation layer and polysulfone (PSF) ultrafiltration membranes as the support layer. The surface and cross-section morphology of the membrane was inspected by environmental scanning electron microscopy (ESEM). The gas transport property of the membranes, including gas permeance, flux and selectivity, were investigated by using pure CO2, N2, CH4 gases and CO2/N2 gas mixture (20 vol% CO2 and 80 vol% N2) and CO2/CH4 gas mixture (10 vol% CO2 and 90 vol% CH4). The plots of gas permeance or flux versus feed gas pressure imply that CO2 permeation through the membranes follows facilitated transport mechanism whereas N2 and CH4 permeation follows solution–diffusion mechanism. Effect of PAAm content in the separation layer on gas transport property was investigated by measuring the membranes with 0–50 wt% PAAm content. With increasing PAAm content, gas permeance increases initially, reaches a maximum, and then decreases gradually. For CO2/N2 gas mixture, the membranes with 10 wt% PAAm content show the highest CO2 permeance of about 1.80 × 10−5 cm3 (STP) cm−2 s−1 KPa−1 and CO2/N2 selectivity of 80 at 0.1 MPa feed gas pressure. For CO2/CH4 gas mixture, the membranes with 20 wt% PAAm content display the highest CO2 permeance of about 1.95 × 10−5 cm3 (STP) cm−2 s−1 KPa−1 and CO2/CH4 selectivity of 58 at 0.1 MPa feed gas pressure. In order to explore the possible reason of gas permeance varying with PAAm content, the crystallinity of PVA and PAAm–PVA blend polymers was measured by X-ray diffraction (XRD) spectra. The experimental results show an inverse relationship between crystallinity and gas permeance, e.g., a minimum crystallinity and a maximum CO2 permeance are obtained at 20 wt% PAAm content, indicating that the possibility of increasing CO2 permeance with PAAm content due to the increase of carrier concentration could be weakened by the increase of crystallinity.  相似文献   

12.
Methanol diffusion in two polymer electrolyte membranes, Nafion 117 and BPSH 40 (a 40% disulfonated wholly aromatic polyarylene ether sulfone), was measured using a modified pulsed field gradient NMR method. This method allowed for the diffusion coefficient of methanol within the membrane to be determined while immersed in a methanol solution of known concentration. A second set of gradient pulses suppressed the signal from the solvent in solution, thus allowing the methanol within the membrane to be monitored unambiguously. Over a methanol concentration range of 0.5–8 M, methanol diffusion coefficients in Nafion 117 were found to increase from 2.9 × 10−6 to 4.0 × 10−6 cm2 s−1. For BPSH 40, the diffusion coefficient dropped significantly over the same concentration range, from 7.7 × 10−6 to 2.5 × 10−6cm2 s−1. The difference in diffusion behavior is largely related to the amount of solvent sorbed by the membranes. Increasing the methanol concentration results in an increase in solvent uptake for Nafion 117, while BPSH 40 actually excludes the solvent at higher concentrations. In contrast, diffusion of methanol measured via permeability measurements (assuming a partition coefficient of 1) was lower (1.3 × 10−6 and 6.4 × 10−7 cm2 s−1 for Nafion 117 and BPSH 40 respectively) and showed no concentration dependence. The differences observed between the two techniques are related to the length scale over which diffusion is monitored and the partition coefficient, or solubility, of methanol in the membranes as a function of concentration. For the permeability measurements, this length is equal to the thickness of the membrane (178 and 132 μm for Nafion 117 and BPSH 40 respectively) whereas the NMR method observes diffusion over a length of approximately 4–8 μm. Regardless of the measurement technique, BPSH 40 is a greater barrier to methanol permeability at high methanol concentrations.  相似文献   

13.
A highly hydrogen permeable silica membrane, referred to as Nanosil, was obtained by chemical vapor deposition of a thin SiO2 layer on a porous Vycor glass support. This composite membrane showed good permeance (10−8 mol m−2 s−1 Pa−1) for the small gas molecules (He, Ne, and H2) at 873 K with high selectivity (104) over other larger gas molecules (CO2, CO, and CH4). The characteristics of gas transport on the Vycor and Nanosil membrane were investigated with several gas diffusion models. The experimental gas permeation data on Vycor glass could be explained by the occurrence of Knudsen diffusion in parallel with surface diffusion. The permeance of the small gas molecules (He, Ne, and H2) on the Nanosil membrane was activated, and increased as temperature increased. However, this permeance was limited at high temperature because of the limited permeance on the Vycor support. The gas permeance on the deposited silica layer was obtained by applying a series analysis of gas permeation on the combined silica layer and Vycor support composite system. The order of permeance through the silica layer was He>H2>Ne which was the same as that through vitreous silica glass, but occurred with lower activation energies. The order of permeation of these small gas molecules did not follow either mass or molecular size but could be explained using a statistical gas permeance model.  相似文献   

14.
The one-electron oxidation of Mitomycin C (MMC) as well as the formation of the corresponding peroxyl radicals were investigated by both steady-state and pulse radiolysis. The steady-state MMC-radiolysis by OH-attack followed at both absorption bands showed different yields: at 218 nm Gi (-MMC) = 3.0 and at 364 nm Gi (-MMC) = 3.9, indicating the formation of various not yet identified products, among which ammonia was determined, G(NH3) = 0.81. By means of pulse radiolysis it was established a total κ (OH + MMC) = (5.8 ± 0.2) × 109 dm3 mol−1 s−1. The transient absorption spectrum from the one-electron oxidized MMC showed absorption maxima at 295 nm (ε = 9950 dm3 mol−1 cmt-1), 410 nm (ε = 1450 dm3 mol−1 cm−1) and 505 nm ( ε = 5420 dm3 mol−1 cm−1). At 280–320 and 505 nm and above they exhibit in the first 150 μs a first order decay, κ1 = (0.85 ± 0.1) × 103 s−1, and followed upto ms time range, by a second order decay, 2κ = (1.3 ± 0.3) × 108 dm3 mol-1 s−1. Around 410 nm the kinetics are rather mixed and could not be resolved.

The steady-state MMC-radiolysis in the presence of oxygen featured a proportionality towards the absorbed dose for both MMC-absorption bands, resulting in a Gi (-MMC) = 1.5. Among several products ammonia-yield was determined G(NH3) = 0.52. The formation of MMC-peroxyl radicals was studied by pulse radiolysis, likewise in neutral aqueous solution, but saturated with a gas mixture of 80% N2O and 20% O2. The maxima of the observed transient spectrum are slightly shifted compared to that of the one-electron oxidized MMC-species, namely: 290 nm (ε = 10100 dm3 mol−1 cm−1), 410 nm (ε = 2900 dm3 mol−1 cm−1) and 520 nm (ε = 5500 dm3 mol−1 cm−1). The O2-addition to the MMC-one-electron oxidized transients was found to be at 290 to 410 nm gk(MMC·OH + O2) = 5 × 107 dm3 mol−1 s−1, around 480 nm κ = 1.6 × 108 dm3 mol−1 s−1 and at 510 nm and above, κ = 3 × 108 dm3 mol−1 s−1. The decay kinetics of the MMC-peroxyl radicals were also found to be different at the various absorption bands, but predominantly of first order; at 290–420 nm κ1 = 1.5 × 103 s−1 and at 500 nm and above, κ = 7.0 × 103 s−1.

The presented results are of interest for the radiation behaviour of MMC as well as for its application as an antitumor drug in the combined radiation-chemotherapy of patients.  相似文献   


15.
The far-UV (193 nm) laser flash photolysis of nitrogen-saturated isooctane solutions of 1,1-dimethylsiletane allows the direct detection of 1,1-dimethylsilene as a transient species, which (at low laser intensities) decays with pseudo-first-order kinetics (τ 10 μs) and exhibits a UV absorption spectrum with λmax 255 nm. Characteristic rapid quenching is observed for the silene with methanol (kMcOH = (4.9 ± 0.2) × 109 M−1 s−1), tert-butanol (kBuOH = (1.8 ± 0.1) × 109 M−1 s−1) and oxygen (kO2 = (2.0 ± 0.5) × 108 M−1 s−1). The Arrhenius activation parameters for the reaction with methanol have been determined to be Ea = −2.6 ± 0.6 kcal mol−1 and log A = 7.7 ± 0.3.  相似文献   

16.
This Letter reports the first kinetic study of 2-butoxy radicals to employ direct monitoring of the radical. The reactions of 2-butoxy with O2 and NO are investigated using laser-induced fluorescence (LIF). The Arrhenius expressions for the reactions of 2-butoxy with NO (k1) and O2 (k2) in the temperature range 223–311 K have been determined to be k1=(7.50±1.69)×10−12×exp((2.98±0.47) kJmol−1/RT) cm3 molecule−1 s−1 and k2=(1.33±0.43)×10−15×exp((5.48±0.69) kJmol−1/RT) cm3 molecule−1 s−1. No pressure dependence was found for the rate constants of the reaction of 2-butoxy with NO at 223 K between 50 and 175 Torr.  相似文献   

17.
The rate constant for the reaction between the sulphate radical (SO4√−) and the ruthenium (II) tris-bipyridyl dication (Ru(bipy)32+) is (3.3±0.2)×109 mol−1 dm3 s−1 in 1 mol dm−3 H2SO4 and (4.9±0.5)×109 mol−1 dm3 s−1 in 0.1 mol dm−3, pH 4.7 acetate buffer. The SO4√−radical produced by the electron transfer quenching of Ru(bipy)32+* by S2O82− reacts rapidly with both acetate buffer and chloride ions. These side reactions result in a reduction in the overall quantum yield of Ru(bipy)33+ production and reduced reaction selectivity when Ru(bipy)32+* is quenched by persulphate.  相似文献   

18.
Pulse radiolysis of epicatechin in aqueous solution has been done to investigate the reactions of epicatechin derived phenoxy radical (EpO) at neutral pH. EpO was generated by N3 reacting toward EpOH, the rate constant was measured to be 3 × 108 dm3 mol−1 s−1. The biomolecular termination of EpO is rather slow ((2k < × 106 dm3 mol−1 s−1) and results in products exhibiting strong visible absorption around 450 nm. No reactions have been observed for EpO with O2 and O2 in the time scale of pulse radiolysis (0.01 s), suggesting the bimolecular rate constant are less than 104 and 5 × 106 dm3 mol−1 s−1, respectively.  相似文献   

19.
The state-selected reaction of CH(X2Πν″ = 0, 1) with H2 has been studied, in which CH was generated by IRMPD of a precursor gas, CH3OH. The subsequent evolution of CH (ν″ = 0, 1) was monitored by the sensitive LIF technique. For the ground state and vibrationally excited state CH, the reaction with H2 is found to depend on the total pressure in the sample cell at room temperature, which suggests that the reaction proceeds through an intermediate adduct, CH3. The backward dissociation process is found to depend on the buffer pressure, which can be rationalized via a collision-induced backward dissociation. The decay rates of CH (ν″ = 0, 1) due to collisions with H2 and Ar at a buffer pressure of 10 Torr are kH2 (ν″ = 1) = (2.3±0.1) × 10−1 cm3 molecule−1 s−1 and kAr (ν″ = 1) = (4.4±0.1) × 10−13 cm3 molecule−1 s−1. Possible effects of the vibrational excitation on the reaction rate of CH (ν″ = 1) are discussed.  相似文献   

20.
Wang Q  Li N 《Talanta》2001,55(6):243-1225
The thiolactic acid (TLA) self-assembled monolayer modified gold electrode (TLA/Au) is demonstrated to catalyze the electrochemical response of norepinephrine (NE) by cyclic voltammetry. A pair of well-defined redox waves were obtained and the calculated standard rate constant (ks) is 5.11×10−3 cm s−1 at the self-assembled electrode. The electrode reaction is a pseudo-reversible process. The peak current and the concentration of NE are a linear relationship in the range of 4.0×10−5–2.0×10−3 mol l−1. The detection limit is 2.0×10−6 mol l−1. By ac impedance spectroscopy the apparent electron transfer rate constant (kapp) of Fe(CN)3−/Fe(CN)4− at the TLA/Au electrode was obtained as 2.5×10−5 cm s−1.  相似文献   

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