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1.
The study of thiophene adsorption onto La(III)-exchanged zeolite NaY by FT-IR spectroscopy 总被引:3,自引:0,他引:3
Tian F Wu W Jiang Z Liang C Yang Y Ying P Sun X Cai T Li C 《Journal of colloid and interface science》2006,301(2):395-401
Zeolites NaY and LaNaY (ion-exchanged with aqueous lanthanum nitrate solution) were used as adsorbents for removing organic sulfur compounds from model gasoline solutions (without and with toluene) and fluid catalytic cracked gasoline in fixed-bed adsorption equipment at room temperature and atmosphere pressure. The adsorptive selectivity for organic sulfur compounds was significantly increased when Na(+) ions in zeolite NaY were exchanged with lanthanum ions. IR spectra of thiophene adsorption indicate that thiophene is adsorbed onto La(3+) ions via direct S-La(3+) interaction and Na(+) ions via pi-electronic interaction for La(3+)-exchanged zeolite NaY, but only via pi-electronic interaction with Na(+) ions for NaY. The amount of adsorbed thiophene on La(3+)-exchanged zeolite Y was slightly decreased by coadsorption of benzene, but greatly reduced on NaY. The adsorption of thiophene via interaction with La(3+) on La(3+)-exchanged zeolite Y is hardly replaced by benzene coadsorption. The direct S-La(3+) interaction might be the essential reason for the evidently improved adsorptive selectivity of LaNaY for removing organic sulfur compounds from solutions containing large amount of aromatics. 相似文献
2.
Gao W Butler D Tomasko DL 《Langmuir : the ACS journal of surfaces and colloids》2004,20(19):8083-8089
Supercritical carbon dioxide is an efficient solvent for adsorptive separations because it can potentially be used as both the carrier solvent for adsorption and the desorbent for regeneration. Recent results have demonstrated an anomalous peak or "hump" in the adsorption isotherm near the bulk critical point when the adsorption isotherm is plotted as a function of bulk density. This work presents new data for the adsorption and desorption of carbon dioxide in the near-critical region on a crystalline, well-structured adsorbent (NaY zeolite). The results indicate a strong affinity for CO(2) as well as a significant hump near the critical point. The lattice model previously developed by Aranovich and Donohue is applied to analyze the adsorption. 相似文献
3.
Liu X Dilger H Eichel RA Kunstmann J Roduner E 《The journal of physical chemistry. B》2006,110(5):2013-2023
A well-defined cluster containing 12 equivalent platinum atoms was prepared by ion exchange of an NaY zeolite, followed by hydrogen reduction. It was characterized by electron paramagnetic resonance (EPR) spectroscopy, hyperfine sublevel correlation (HYSCORE), and theoretical calculations. Combing the results of the experiments with density functional calculations, the likely structure of this cluster is icosahedral Pt13Hm, possibly with a low positive charge. The adsorbed H/D on the Pt cluster surface can be exchanged reversibly at room temperature. From H/D desorption experiments, an H2 binding energy of 1.36 eV is derived, in reasonable agreement with the calculated value but clearly larger than that for a (111) Pt single-crystal surface, revealing a finite size effect. While the hydrogen-covered cluster should clearly be regarded as a molecule, it is conceivable that the cluster adopts metallic character upon hydrogen desorption. It is likely that up to m=30 H atoms bind to this cluster with 12 surface atoms, which has important implications for the determination of the dispersion of small Pt catalyst particles by hydrogen chemisorption. Calculations as well as experiments give evidence of an interesting magnetic behavior with high-spin states playing a prominent role. There are strong indications that a reservoir of EPR silent but structurally similar clusters exists which can partly be converted to EPR visible species by H/D exchange or by gas adsorption. 相似文献
4.
Adsorption isotherms for Ar, 02, N2, CO, CO2, CH4, and C2H6 on 4A zeolite at three or more temperatures were determined. An adsorption equation based on a 2-dimensional virial equation in terms of integer powers of the reciprocal of (A - σ) was shown to fit the equilibrium data accurately with three constants for C2H6 and two constants for other gases. Here A is the area per molecule and σ is the area of the molecule in a close-packed situation.Rates of adsorption and desorption of Ar, N2, CO, CH4, and C2H6 on 4A zeolite were determined over ranges of temperature in which the rate was moderately fast. Electron microscopy showed that the particles were cubes, and their size-distribution was determined. The conventional Fick's law rate equation for cubes was used to produce a generalized rate curve for the particle size distribution of the adsorbent. This curve was applied to the last 20% of the rate curve to obtain a diffusivity that could be related to the final amount adsorbed. This procedure also avoids the initial rapid portion of the adsorption, in which large variations of adsorbent temperature from that of the bath often occur.The diffusivities increased with amount adsorbed by a small extent for Ar and CH4 and by larger amounts for N2, CO, and C2H6. The activation energy for diffusion, as well as the heat of adsorption, were nearly independent of amount adsorbed for Ar and CH4, but these quantities decreased substantially with coverage for N2, CO, and C2H6. The dependence upon amount adsorbed of diffusivity and activation energy seemed related to the shape of the adsorption isotherm; those for Ar and CH4 were nearly linear, whereas isotherms for the other gases had large curvatures. The activation energy for diffusion varied with coverage in the same way as heat of adsorption. 相似文献
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Cation mobility and the sorption of chloroform in zeolite NaY: molecular dynamics study 总被引:1,自引:0,他引:1
Molecular dynamics simulations at temperatures of 270, 330, and 390 K have been carried out to address the question of cation migration upon chloroform sorption in sodium zeolite Y. The results show that sodium cations located in different sites exhibit different types of mobility. These may be summarized as follows: (1) SII cations migrate toward the center of the supercage upon sorption, due to interactions with the polar sorbate molecules. (2) SI' cations hop from the sodalite cage into the supercage to fill vacant SII sites. (3) SI' cations migrate to other SI' sites within the same sodalite cage. (4) SI cations hop out of the double six-rings into SI' sites. In some instances, concerted motion of cations is observed. Furthermore, former SI' and SI cations, having crossed to SII sites, may then further migrate within the supercage, as in (1). The cation motion is dependent on the level of sorbate loading, with 10 molecules per unit cell not being enough to induce significant cation displacements, whereas the sorption of 40 molecules per unit cell results in a number of cations being displaced from their original positions. Further rearrangement of the cation positions is observed upon evacuation of the simulation cell, with some cations reverting back to sites normally occupied in bare NaY. 相似文献
7.
Zhuo Guo Li Feng Wang Zhan Gao Wei Wei Zhang School of Materials Science Engineering Shenyang Institute of Chemical Technology Shenyang China State Key Laboratory of Inorganic Synthesis Preparative Chemistry Jilin University Changchun China 《中国化学快报》2007,18(2):233-236
The adsorption of VB12 onto CMK-3 was studied as a function of temperature and initial VB12 concentration. The highest VB12 adsorption capacity was determined as 353.4 mg/g at 40℃. Adsorption data were well described by the Langmuir model, although they could be modelled by the Freundlich equation. The pseudo-first-order and pseudo-second-order kinetic models were applied to test the experimental data. The pseudo-second-oider kinetic model provided the best correlation of the experimental data compared to the pseudo-nrsi-order model. 相似文献
8.
Tomohito Kameda Saya Ito Toshiaki Yoshioka 《Journal of Dispersion Science and Technology》2017,38(7):1063-1066
We found that activated carbon effectively removed urea from solution and that urea adsorption onto activated carbon followed a pseudo-second-order kinetic model. We classified the urea adsorption on activated carbon as physical adsorption and found that it was best described by the Halsey adsorption isotherm, suggesting that the multilayer adsorption of urea molecules on the adsorption sites of activated carbon best characterized the adsorption system. The mechanism of adsorption of urea by activated carbon involved two steps. First, an amino (–NH2) group of urea interacted with a carbonyl (–C?O) group and a hydroxyl (?OH) group on the surface of activated carbon via dipole–dipole interactions. Next, the –C?O group of the urea molecule adsorbed to the activated carbon interacted with another –NH2 group from a second urea molecule, leading to multilayer adsorption. 相似文献
9.
The equilibrium and dynamics of levulinic acid sorption on two weakly basic anion exchangers, in free base form, in single-component aqueous solutions were investigated. Adsorption isotherms such as Langmuir, Sips, Radke-Prausnitz, and Toth were applied to correlate the experimental data in the temperature range 285-315 K. Modeling results showed that the Toth model is the best one to correlate the sorption isotherms. The resulting Toth equations were used with the Clausius-Clapeyron equation to determine the isosteric heat of sorption. The sorption kinetics was experimentally measured via a completely stirred finite-bath batch experiment under different initial concentrations and at varying solution temperatures. The pseudo-second-order kinetic model and the Elovich equation were used to represent the kinetic data and the equation parameter values were also evaluated. The pseudo-second-order equation cannot simulate the experimental kinetic data, while the Elovich equation fitted the sorption dynamic data very well under all the operating conditions studied. Finally, the apparent activation energy of sorption was also determined. 相似文献
10.
1. | The adsorption isotherms of krypton, xenon, and nitrogen in the 140–270K temperature range and the 0.3 Pa-65 kPa pressure range were calculated with the equations from a quasi-chemical model of adsorption. |
2. | The phase diagrams of krypton-xenon adsorption solutions for 170 and 220 K were plotted for a binary mixture of gases. The limit of applicability of the given model was substantiated, and its drawbacks were noted.Fig. 1. Adsoprtion isotherms of Kr, Xe (a) and N2 (b) at T, K: 1) 170, 2) 220, 3) 235,4) 160. Points: experimental; lines: calculated.Fig. 2. Diagrams of equilibrium adsorption solutions of Kr-Xe for T, K: a) 170, b) 220, and with Ptot, kPa: 1) 20, 2) 14, 3) 50, CXe(Kr): adsorption, atoms/cavity. Points: experimental: lines: calculated. |
3. | The equations of the quasichemical model can be successfully used in engineering calculations of adsorption systems with properties similar to the Kr-Xe-NaX system in the range of degrees of filling of 0.01 1 0.50 and 0.10 2 0.70. |
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Kinetics and equilibrium adsorption study of lead(II) onto activated carbon prepared from coconut shell 总被引:9,自引:0,他引:9
Removal of lead from aqueous solutions by adsorption onto coconut-shell carbon was investigated. Batch adsorption experiments were performed to find out the effective lead removal at different metal ion concentrations. Adsorption of Pb2+ ion was strongly affected by pH. The coconut-shell carbon (CSC) exhibited the highest lead adsorption capacity at pH 4.5. Isotherms for the adsorption of lead on CSC were developed and the equilibrium data fitted well to the Langmuir, Freundlich, and Tempkin isotherm models. At pH 4.5, the maximum lead adsorption capacity of CSC estimated with the Langmuir model was 26.50 mg g(-1) adsorbent. Energy of activation (Ea) and thermodynamic parameters such as DeltaG, DeltaH, and DeltaS were evaluated by applying the Arrhenius and van't Hoff equations. The thermodynamics of Pb(II) on CSC indicates the spontaneous and endothermic nature of adsorption. Quantitative desorption of Pb(II) from CSC was found to be 75% which facilitates the sorption of metal by ion exchange. 相似文献
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14.
Yu-Wen Chen 《Reaction Kinetics and Catalysis Letters》1987,34(1):219-224
A series of NaY zeolites with different Si/Al ratios were used to support the Ru catalysts. Both the activity/selectivity of Ru in F–T synthesis and the suppressing of hydrogen may be related to the acid strength of the OH groups present, which is a function of the Si/Al ratio of the zeolite.
NaY Si/Al Ru. / Ru -, OH-, Si/Al .相似文献
15.
Amir Khosravi Majid Esmhosseini Somayeh Khezri 《Research on Chemical Intermediates》2014,40(8):2905-2917
The aim of the present study is to investigate the removal of ammonium ions from aqueous solutions using the natural Western Azerbaijan zeolite by utilizing ion exchange process. Batch experimental studies were conducted to evaluate by changing relevant parameters such as pH, dosage of adsorbent, stirring time, initial ammonium concentration, and temperature. The results clearly confirmed that all mentioned parameters have vital affects on removing ammonium ions from wastewater and effluents, so got optimized. Adsorption kinetics and equilibrium data for the removal of ammonium ion were analyzed using Langmuir and Freundlich equations. The Langmuir model fits the equilibrium data better than the Freundlich model. According to the Langmuir equation, the maximum uptake for ammonium ion was 43.47 (mg g?1). Pseudo-first-order and pseudo-second-order models were used to represent the kinetics of the process. Kinetic studies showed that the adsorption followed a pseudo-second-order reaction. The calculated thermodynamic parameters (ΔG°, ΔH°, and ΔS°) indicate that the adsorption process is feasible, spontaneous, and endothermic at 20–50 °C. Based on the experimental results, it can be suggested that the natural Western Azerbaijan zeolite has the potential of application as an efficient adsorbent for the removal of ammonium ions from aqueous solutions, and is suggested for wastewater treatment purposes. 相似文献
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17.
《Green Chemistry Letters and Reviews》2013,6(3-4):1-12
ABSTRACTThis study reports on the adsorption of 2-chlorophenol from an aqueous solution using activated carbon prepared by H2SO4 activation of the pericarp of Ricinus communis (RCAC). The pericarp was carbonized and activated by treating with H2SO4 solution followed by heating in an oven at 105°C for 12 hrs. Batch adsorption experiments were carried out as a function of pH, contact time, initial concentration of the adsorbate, adsorbent dosage and temperature of the solution. Kinetic data were best fit to a pseudo-first-order rate equation for the adsorption of 2-chlorophenol on RCAC. Thermodynamic parameters ΔHo, ΔSo and ΔGo for the adsorption were also determined which shows that adsorption on the surface of RCAC was spontaneous in nature, and exothermic between temperatures of 20°C and 80°C. The equilibrium data better fit the Langmuir isotherm model for 2-chlorophenol adsorption on RCAC. IR spectrum for loaded and unloaded RCAC was obtained and found to be in good agreement. 相似文献
18.
O. A. Vlasova K. G. Ione L. G. Karakchiev L. M. Plyasova 《Russian Chemical Bulletin》1972,21(3):487-488
Conclusions Mechanical pulverization of NaY zeolite crystals leads to a decrease in the adsorption volume and a decrease in the intensities of the lines on the x-ray diffraction patterns, which indicates a breakdown of their crystal structure.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 534–536, March, 1972. 相似文献
19.
Polyaniline sulfate‐zeolite composite was prepared by emulsion polymerization. Epoxy resin was cured using polyaniline‐sulfate salt and various amounts of polyaniline sulfate‐zeolite composite. The kinetics of the cure reaction for an epoxy resin based on the diglycidyl ether of bisphenol A (DGEBA) with polyaniline‐sulfate and polyaniline sulfate‐zeolite composite have been studied using differential scanning calorimetry (DSC) under isothermal and dynamic conditions. Isothermal kinetics analysis was performed using the phenomenological model of Kamal. Dynamic kinetic analysis was performed using Kissinger's method. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
20.
Electrochemical quartz crystal microbalance study of azurin adsorption onto an alkanethiol self-assembled monolayer on gold 总被引:1,自引:0,他引:1
Fleming BD Praporski S Bond AM Martin LL 《Langmuir : the ACS journal of surfaces and colloids》2008,24(1):323-327
A quartz crystal microbalance coupled with electrochemistry was used to examine the adsorption of azurin on a gold electrode modified with a self-assembled monolayer of octanethiol. Azurin adsorbed irreversibly to form a densely packed monolayer. The rate of azurin adsorption was related to the bulk concentration of azurin in solution within the concentration range studied. At a high azurin concentration (2.75 muM), adsorption was rapid with a stable adsorption maximum attained in 2-3 min. At a lower azurin solution concentration (0.35 muM), the time to reach a stable adsorption maximum was approximately 30 min. Interestingly, the maximum surface concentration attained for all solution concentrations studied by the QCM method was 25 +/- 1 pmol cm-2, close to that predicted for monolayer coverage. The dissipation was monitored during adsorption, and only small changes were detected, implying a rigid adsorption model, as needed when using the Sauerbrey equation. Cyclic voltammetric data were consistent with a one-electron, surface-confined CuII/CuI azurin process with fast electron-transfer kinetics. The electroactive surface concentration calculated using voltammetry was 7 +/- 1 pmol cm-2. The differences between the QCM and voltammetrically determined surface coverage values reflect, predominantly, the different measurement methods but imply that all surface-confined azurin is not electrochemically active on the time scale of cyclic voltammetry. 相似文献