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1.
Marin Senila Emilia Neag Oana Cadar Maria-Alexandra Hoaghia Marius Roman Ana Moldovan Alexandru Hosu Angela Lupas Emoke Dalma Kovacs 《Molecules (Basel, Switzerland)》2022,27(11)
In the present work, the capability of the volcanic tuff from Macicasu (Romania) to remove ammonia (NH3) from air with different contamination levels during 24 h of adsorption experiments was investigated. The natural zeolitic volcanic tuff was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), the Brunauer–Emmett–Teller (BET) method, inductively coupled plasma optical emission spectrometry (ICP-OES), and thermogravimetric analysis (TGA). The adsorption capacities varied between 0.022 mg NH3 g−1 zeolite and 0.282 mg NH3 g−1 zeolite, depending on the NH3 concentrations in the air and at the contact time. The nonlinear forms of the Langmuir and Freundlich isotherm models were used to fit the experimental data. Additionally, the adsorption of NH3 was studied using nonlinear pseudo-first-order (PFO), pseudo-second-order (PSO), and Elovich kinetic model. Based on the total volume of pores of used volcanic tuff, the NH3 was removed from the air both due to the physical adsorption of NH3 gas and the ion exchange of NH4+ (resulted from a reaction between NH3 and H2O adsorbed by the zeolite). Depending on the initial NH3 concentration and the amount of volcanic tuff, the NH3 concentrations can be reduced below the threshold of this contaminant in the air. The adsorption capacity of NH3 per unit of zeolite (1 g) varied in the range of 0.022–0.282 mg NH3 g−1 depending on the NH3 concentration in the air. 相似文献
2.
We have studied experimentally and theoretically the exchange of NH4 +, Na+, K+, Ca++, Mg++, and H+ ions in zeolite beds, weakly-acidic resin beds, and mixed beds of the zeolite and the resin. The zeolite is highly selective for NH4 + and K+, whereas the resin with carboxyl functional groups is highly selective for Ca++ and Mg++. The effluent histories of single exchanger beds can be well predicted by the Multicomponent Chromatography Theory developed by Helfferich and Klein (1970). These histories are mainly the result of ion competition for ion exchanger sites; they can not be adjusted to meet the goal that NH4 + ions are removed and simultaneously the pH and concentrations of all the major physiological cations are maintained at normal values. The effluent histories of mixed beds, on the other hand, can be adjusted. We have designed a mixed bed which can meet the goal except that for each equivalent of NH4 + removed, 0.3 equivalents of Na+ are returned. The effluent histories of K+ and NH4 + for the mixed beds are similar to those of the zeolite beds, whereas the Ca++ and Mg++ histories are similar to those of the resin beds. 相似文献
3.
A.W. Castleman 《Chemical physics letters》1978,53(3):560-564
Thermodynamic data are reported for NH3 clustered about Bi+, Rb+, and K+ in the gas phase. Unusually strong bondings of NH3 to Bi+ suggests the probable importance of partial covalent bonding in stabilizing the first ligand cluster. Differences in relative bond strengths for NH3 and H2O about Rb+ andK+ are consistent with the results of extended Hückel calculations reported herein. 相似文献
4.
NH4Y and NH4LaY-type zeolite catalysts were prepared by cyclic ion-exchange of a synthetic Linde Y-zeolite. The release of ammonia and water were followed by evolved gas analysis (automatic thermogastitrimetric equipment) as well as with a continuous selective water detector. The ion-exchangeability of NH 4 + for La3+ on the zeolite was also investigated. The capacity of the NH4Y-zeolite was found to be 3.60 mequiv./g calcined zeolite. After a three times repeated ion-exchange process, 88.9 % of the ammonia was replaced by lanthanum. 相似文献
5.
6.
Uzi Kaldor 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1994,31(4):279-282
The geometries of the Cl–NH3, Cl–H2O, F–NH3 and F–H2O clusters are optimized using the coupled cluster method. The four lowest ionization potentials are then calculated, leading to the ground and low excited states of the neutral species. The first three IPs describe ionization from the externalp state of the halogen atom, whereas the fourth corresponds to ionization from the NH3 or H2O moiety, leading to charge transfer complexes. These complexes were recently observed in the photoelectron spectrum of Cl–NH3, in full accord with our calculations.Supported in part by the U.S.-Israel Binational Science Foundation 相似文献
7.
《Journal of Molecular Catalysis #》1981,10(2):177-185
The CNDO/2 method was employed in the study of the electronic structure of the HX zeolite using cluster models Si2Al2O4H(OH)−8, Si2Al2O4H2-(OH)8 and Si2Al2O4H(OH)8Na for various types of skeletal hydroxyl groups. It is shown that the hydroxyl groups of the O1 and O3 types are most likely to be formed among all studied groups even if formation of the remaining types of hydroxyl groups cannot be excluded. The calculations indicate that the hydroxyl groups of the HX zeolite are of a less acidic character than those of the HY zeolite and that the location of an Na+ cation in the S1 position excludes the formation of O—H groups of the O3 type. 相似文献
8.
J. C. Greer R. Ahlrichs I. V. Hertel 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1991,18(4):413-426
A theoretical study of the energetics and intramolecular dynamics for ammonia cluster cations (NH3) 2 + and (NH3) 3 + is presented. The proton transfer mechanism after a vertical ionisation is followed in detail. Structural and energetic calculations are performed near the Hartree-Fock self consistent field (HF-SCF) limit; all open shell calculations are spin restricted (RHF). The calculations reconcile experimental results from thermochemical and photoionisation measurements: discrepancies in the energetics are shown to be due to the probing of different regions of the potential energy surface (PES). For the dynamics calculations, it is impractical to determine a large region of the multidimensional PES and then integrate Newton's equations. The calculations therefore incorporate a quantum mechanical determination of the electronic energy of the system after each time increment while nuclear degrees of freedom are handled classically. In this way, the classical reaction path across the Born-Oppenheimer surface is obtained. 相似文献
9.
Rania Charrad Dr. Hanna E. Solt Dr. József Valyon László Trif Dr. Faouzi Ayari Dr. Mourad Mhamdi Jenő Hancsók Dr. Ferenc Lónyi 《ChemistryOpen》2020,9(11):1123-1134
Co/SSZ-13 zeolites were prepared by heating the finely dispersed mixture of NH4-SSZ-13 and different cobalt salts up to 550 °C. Investigations by thermogravimetry – differential scanning calorimetry – mass spectrometry provided new insight into details of the solid-state reaction. Formation of Co carrying hydrate melt or volatile species was shown to proceed from chloride, nitrate, or acetylacetonate Co precursor salts upon thermal treatment. This phase change allows the transport of the Co species into the zeolite pores. The reaction of the NH4+ or H+ zeolite cations and the mobile Co precursors generates vapor or gas products, readily leaving the zeolite pores, and cobalt ions in lattice positions suggesting that solid-state ion-exchange is the prevailing process. The obtained catalysts are of good activity and N2 selectivity in the CH4/NO-SCR reaction. The thermal treatment of acetate or formate salts give solid intermediates that are unable to get in contact and react with the cations in the zeolite micropores. These catalysts contain mainly Co-oxide clusters located on the outer surface of the zeolite crystallites and have poor catalytic performance. 相似文献
10.
通过过量浸渍Cu(NO_3)_2溶液于Y分子筛载体上,制备出Cu负载量为6.4%的CuY催化剂,考察了甲醇氧化羰基化反应的催化性能,并采用X射线衍射(XRD)、H2程序升温还原(H2-TPR)、透射电子显微镜(TEM)和NH3程序升温脱附(NH3-TPD)等手段对催化剂表面微观结构进行了表征。研究表明,随Y分子筛载体H+含量的增加,可使更多Cu物种落位于分子筛微孔笼结构中,且高度分散,而笼内未交换的Na+能进一步促进铜物种更多落位于载体超笼结构中,形成更多甲醇氧化羰基化反应的Cu+活性中心。同时随铜物种引入,催化剂中产生了明显的中强酸,酸量随落位于载体笼结构中的Cu物种的增加而增加,催化剂总酸量随之增加,导致甲醇氧化羰基化产物分布发生改变,碳酸二甲酯(DMC)选择性明显降低。对比等体积浸渍法制备的92.3%的高DMC选择性CuY催化剂,以不含H+的NaY分子筛为载体,过量浸渍法制备的CuY催化剂酸量少、Cu物种活性中心多,在保持82.4%的高DMC选择性时,其DMC的时空收率(STY)也高达109.1mg·g~(-1)·h-1。 相似文献
11.
El-Mekki El-Malki Pascale Massiani Michel Che 《Research on Chemical Intermediates》2007,33(8):749-774
V-containing β zeolites were prepared by solid-state reaction between V2O5 and β zeolite. The zeolite structure was analysed by XRD and N2 physisorption. The V speciation was studied by chemical analysis and different spectroscopies (FT-IR, 27Al-NMR, UV-Vis, EPR, photoluminescence). After calcination of V2O5-β zeolite mechanical mixtures at 500°C, three kinds of V species were identified: (i) oligomeric vanadates with octahedral
V5+ easily removed by treatment with NH4OAc, (ii) isolated vanadyl (V=O)2+ ions in axially distorted octahedral or square pyramidal environment, interacting with framework and/or extraframework Al
nuclei and (iii) isolated V5+ in tetrahedral and octahedral environments, localized in framework defect sites. The amount of the latter species is higher
when water vapor is present during calcination and when parent β zeolite contains a high concentration of defect sites generated by a strong acid pretreatment. Isolated V5+ are easily reduced to tetrahedral V4+ or to square pyramidal (V=O)2+. Possible models of the mechanism of formation of V species by solid-state reaction and further reduction are proposed. 相似文献
12.
在静态条件下, 采用不同浓度的氟硅酸铵溶液对纳米ZSM-5分子筛进行了改性处理. 利用粉末X射线衍射(XRD)、27Al 魔角旋转固体核磁共振(27Al MAS NMR)、X射线荧光光谱(XRF)、X射线光电子能谱(XPS)、N2 吸附、透射电镜(TEM)、NH3程序升温脱附(NH3-TPD)、吡啶吸附红外光谱(Py-IR)等技术对改性前后纳米ZSM-5分子筛的骨架结构、织构性质、酸性质进行了表征. 并在常压、反应温度为450℃、甲醇质量空速(WHSV)为1 h-1的条件下, 研究了改性前后纳米HZSM- 的甲醇制丙烯(MTP)催化性能. 结果表明, 合适浓度的氟硅酸铵处 理能够选择性地脱除纳米ZSM-5 分子筛的外表面铝, 从而使得HZSM-5 的酸密度降低, 比表面积和孔容增大, MTP催化性能显著提高. 氟硅酸铵改性后纳米HZSM-5 的丙烯选择性和丙烯/乙烯(P/E)质量比分别由原来的 28.8%和2.6提高到45.1%和8.0, 催化剂寿命增加了近2倍. 相似文献
13.
14.
Rozanska X van Santen RA Hutschka F Hafner J 《Journal of the American Chemical Society》2001,123(31):7655-7667
A periodic density functional theory (DFT) study of the isomerization reactions of toluene and xylene catalyzed by acidic mordenite is reported. Monomolecular isomerization reactions have been considered and analyzed. The different reaction pathways have been discussed in detail. The use of periodic structure calculations allows consideration and analysis of zeolite electrostatic contributions and steric constraints that occur within zeolite micropores. Major differences in the details of protonation reaction pathways are found when periodic structures are used rather than small cluster models of the Br?nsted acidic site. Complex relationships are found between zeolite topology and reaction pathways. 相似文献
15.
Bartosz Mozgawa Dr. Filip Zasada Dr. Monika Fedyna Prof. Kinga Góra-Marek Dr. Edyta Tabor Dr. Kinga Mlekodaj Dr. Jiří Dědeček Prof. Zhen Zhao Dr. Piotr Pietrzyk Prof. Zbigniew Sojka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(68):17159-17180
NH3 temperature-programmed desorption (NH3-TPD) is frequently used for probing the nature of the active sites in CuSSZ-13 zeolite for selective catalytic reduction (SCR) of NOx. Herein, we propose an interpretation of NH3-TPD results, which takes into account the temperature-induced dynamics of NH3 interaction with the active centers. It is based on a comprehensive DFT/GGA+D and first-principles thermodynamic (FPT) modeling of NH3 adsorption on single Cu2+, Cu+, [CuOH]+ centers, dimeric [Cu-O-Cu]2+, [Cu-O22−-Cu]2 species, segregated CuO nanocrystals and Brønsted acid sites (BAS). Theoretical TPD profiles are compared with the experimental data measured for samples of various Si/Al ratios and distribution of Al within the zeolite framework. Copper reduction, its relocation, followed by the intrazeolite olation/oxolation processes, which are concomitant with NH3 desorption, were revealed by electron paramagnetic resonance (EPR) and IR. DFT/FPT results show that the peaks in the desorption profiles cannot be assigned univocally to the particular Cu and BAS centers, since the observed low-, medium- and high-temperature desorption bands have contributions coming from several species, which dynamically change their speciation and redox states during NH3-TPD experiment. Thus, a rigorous interpretation of the NH3-TPD profiles of CuSSZ-13 in terms of the strength and concentration of the active centers of a particular type is problematic. Nonetheless, useful connections for molecular interpretation of TPD profiles can be established between the individual component peaks and the corresponding ensembles of the adsorption centers. 相似文献
16.
《Chemical physics》2005,318(3):180-190
Hartree–Fock and DFT calculations are reported for the CO/CeO2(1 1 0) surface system. The electron density, electrostatic potential, atomic charges and projected electronic density of states have been calculated from an ECP-and-point-charge-embedded cluster model and is compared with periodic calculations. The agreement between the two surface models is reasonably good. A number of weakly bonding CO adsorption sites were found, with Eads (BSSE-corrected) ranging from 0.01 to 0.22 eV per adsorbed molecule. The two most favourable sites are found in the vicinity of surface cerium ions, with the CO molecule oriented in a tilted fashion, C-end down. The surface-induced CO stretching vibrational frequency shifts on these sites are a redshift of ≈−30 cm−1 and a blueshift of ≈25 cm−1, respectively. 相似文献
17.
Predicting adsorption enthalpies on silicalite and HZSM‐5: A benchmark study on DFT strategies addressing dispersion interactions
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Cheng‐chau Chiu Georgi N. Vayssilov Alexander Genest Armando Borgna Notker Rösch 《Journal of computational chemistry》2014,35(10):809-819
We evaluated the accuracy of periodic density functional calculations for adsorption enthalpies of water, alkanes, and alcohols in silicalite and HZSM‐5 zeolites using a gradient‐corrected density functional with empirical dispersion corrections (PBE‐D) as well as a nonlocal correlation functional (vdW‐DF2). Results of both approaches agree in acceptable fashion with experimental adsorption energies of alcohols in silicalite, but the adsorption energies for n‐alkanes in both zeolite models are overestimated, by 21?46 kJ mol?1. For PBE‐D calculations, the adsorption of alkanes is exclusively determined by the empirical dispersion term, while the generalized gradient approximation‐DFT part is purely repulsive, preventing the molecule to come too close to the zeolite walls. The vdW‐DF2 results are comparable to those of PBE‐D calculations, but the latter values are slightly closer to the experiment in most cases. Thus, both computational approaches are unable to reproduce available experimental adsorption energies of alkanes in silicalite and HZSM‐5 zeolite with chemical accuracy. © 2014 Wiley Periodicals, Inc. 相似文献
18.
Ab initio SCF-MO calculations of 14N quadrupole coupling constants are reported for HCN, HNC, CH3CN, CH3NC, NH3, NH2NH2, FCN, N2O, (CN)2, BrCN, pyridine and pyrazine. There is excellent correlation between calculation and experiment yielding Q = 1.503 ± 0.159 × 10?26 cm2 for the 14N nuclear quadrupole moment. Dunning sp basis sets are more than adequate for such calculations, STO/4G basis sets yielding almost identical results for pyridine and pyrazine. Unsuccessful attempts were made to correlate coupling constants with electronic population analysis indices. 相似文献
19.
N. Cohen 《国际化学动力学杂志》1987,19(4):319-362
Experimental data for the reaction of O atoms with NH3 have been reviewed with particular attention to the possible effects of secondary reactions on the deduced rate coefficient. A reaction mechanism was assembled and computer calculations carried out to simulate several sets of experiments. The sensitivity of the calculations to uncertainties in the various rate coefficients was assessed. Transition-state theory calculations were carried out on the rate coefficient k1 for the O + NH3 → OH + NH2 reaction. These studies suggest that the reaction stoichiometry is dependent on temperature, initial reagent ratios, and extent of reaction; that available data are not sufficient to determine whether the initial step is H-atom abstraction (producing OH and NH2 radicals) or O-atom addition (producing an NH3O* complex): and that the low temperature values of k1 (T ? 400 K) are not consistent with values deduced at higher temperatures if the reaction proceeds by H-atom abstraction. Taking all the evidence into account, it is recommended that the expression 1.1 × 103 T2.1 exp(?2620/T) L mol?1 s?1 be used for k1 until more definitive experimental measurements are made at low temperatures. 相似文献
20.
M.R. Harrison P.P. Edwards J. Klinowski J.M. Thomas D.C. Johnson C.J. Page 《Journal of solid state chemistry》1984,52(3):330-331
Dehydrated samples of zeolite Y containing alkali-metal cations have been reacted with alkali-metal vapor in sealed silica tubes, and the products studied by electron-spin resonance (ESR) spectroscopy. Two distinct species were detected following the reaction of sodium-exchanged zeolite Y with sodium, potassium, or rubidium vapor. Exposure to a low concentration of metal vapor resulted in brightly colored samples with ESR signals characteristic of a stable ionic cluster species Na3+4, in which an unpaired electron is trapped on four equivalent sodium cations in the sodalite cages of the zeolite. Exposure to higher concentrations of metal vapor resulted in dark-colored samples with ESR signals characteristic of small metallic particles located inside the zeolite cavities. A similar ionic cluster species K3+4 was detected following the reaction of potassium-exchanged zeolite Y with sodium or potassium vapor although the potassium cluster was less stable than its sodium counterpart and an ESR signal from small metallic particles was observed at the same time. The corresponding Rb3+4 ionic cluster species was not detected following the reaction of rubidium-exchanged zeolite Y with rubidium vapor; only an ESR signal from small metallic particles was observed. The narrow linewidths of the ESR signals from the small metallic particles suggest an inhibition of the spin-relaxation mechanisms in the bulk metals. 相似文献