Adsorption properties of oxidized gallium-modified zeolite ZSM-5 from diffuse reflectance IR and quantum-chemical data: 1. Interaction with hydrogen and ethane

Diffuse reflectance IR spectroscopy was used to study adsorption and subsequent high-temperature hydrogen and ethane transformations on gallium ions in gallium-modified ZSM-5 zeolite. The results were correlated with the corresponding quantum-chemical calculations. From the experimental and calculated data, it follows that trivalent gallium oxo ions are reduced to the univalent state in a hydrogen or ethane atmosphere even at moderate temperatures. Therefore, gallium oxo ions can function as active sites only at the early stages of light-paraffin aromatization. At the later stages, the dehydrogenation of light paraffins involves univalent gallium ions through the formation of intermediate gallium and alkylgallium hydrides.     

ZSM-5分子筛的脱硅改性及加氢改质性能

考察了水热与碱联合处理过程中两者的先后顺序对ZSM-5分子筛酸性和孔结构的影响,并与单独的水热和碱处理进行了比较。结果表明,水热后的碱处理对ZSM-5分子筛具有骨架脱硅、骨架补铝和清除非骨架铝物种三重作用,而碱处理后的水热处理具有骨架脱铝和部分骨架稳定化双重作用。与先水热处理再碱处理相比,先碱处理后的水热处理在优化分子筛酸性和产生介孔方面更加有效。基于水热-碱联合处理的HZSM-5分子筛所制备的催化剂对催化裂化汽油的加氢改质表现出适中的异构化活性、较高的烯烃芳构化活性以及最高的稳定性。     

Microwave synthesis,characterization and catalytic properties of titanium-incorporated ZSM-5 zeolite

Titanium-incorporated ZSM-5 zeolites (Si/Al = 50–200 and Si/Ti = 70) were successfully synthesized in a one-step sol-gel process under microwave irradiation. The characteristics of Ti-ZSM-5 zeolites were investigated using X-ray power diffraction, UV/Vis-DRS, FT-IR spectroscopy and solid-state ²⁷Al-NMR to monitor the physico-chemical properties. Simultaneously, the acidic properties were characterized by the NH₃-TPD profile. The characterization results revealed that the Ti⁴⁺ and Al³⁺ ions were well incorporated into the framework of Ti-ZSM-5 zeolite. The prepared zeolite was moderately active but selective in the dehydration of methanol to dimethyl ether.     

Molecular and dissociative adsorption of H2O on zeolite Zn/ZSM-5 studied by diffuse-reflectance IR spectroscopy and quantum chemical calculations

Interest in water adsorption on cation-substituted zeolites is due to the possibility of the M ⁿ⁺ (H₂O) + [Si-O-Al]^?1 → MOH^{(n ? 1)+} + Si-O(H)-Al (M = metal, n = 1–3) reaction taking place. As a result of this reaction, the cation-substituted zeolite can exhibit Brønsted acid activity. The molecular adsorption of water on Zn/ZSM-5 zeolite at room temperature and the subsequent heterolytic dissociation of adsorbed water under heating have been investigated by diffuse-reflectance IR spectroscopy. For theoretical simulation of these processes, three different fragments of the ZSM-5 lattice corresponding to possible variants of the structure of the ionic site of the substituting cation have been examined. Calculations on the molecular and dissociative adsorption of water molecules on substituting Zn²⁺ cations have been performed by the DFT method. Two pathways of the dissociation of adsorbed H₂O molecules-endothermic and exothermic ones-have been discovered, and it has been demonstrated that the spatial separation of two lattice Al ions at the Zn²⁺ cation site significantly affects the adsorption energy.     

Potential-dependent chemisorption of carbon monoxide on platinum electrodes: new insight from quantum-chemical calculations combined with vibrational spectroscopy

Density functional theory (DFT) using the finite cluster approach is utilized to compute binding energies, bond geometries, and vibrational properties of carbon monoxide adsorbed on Pt(111) as a function of the external interfacial field, focusing attention on the metal–CO bond itself. Comparison with electrode potential-dependent frequencies for the metal–CO (ν_M–CO) as well as the much-studied intramolecular C---O (ν_CO) vibration, as measured by in-situ Raman and infrared spectroscopy, facilitate their interpretation in terms of metal-chemisorbate bonding for this archetypal electrochemical system. Decomposing the calculated metal–CO binding energy and vibrational frequencies into individual orbital and steric repulsion components enables the role of such quantum-chemical interactions to the field- (and hence potential-) dependent bonding to be assessed. No simple relationship between the field(F)-dependent binding energies and the ν_M–CO frequencies is evident. While the DFT ν_M–CO–F slopes are negative at positive and small–moderate negative fields, reflecting the prevailing influence of back-donation, a ν_M–CO–F maximum is obtained at larger negative fields for atop CO, and a plateau for hollow-site CO. This Stark-tuning behavior reflects largely offsetting field-dependent contributions from π and σ surface bonding, and can also be rationalized on the basis of changes in the electrostatic component of ν_M–CO from increasing M–CO charge polarization. A rough correlation between the field-dependent ν_M–CO frequencies and the corresponding bond distances, r_M–CO, is observed for hollow and atop CO in that r_M–CO shortens towards less positive fields, but becomes near-constant at moderate–large negative fields. A more quantitative correlation between the field-dependent C---O frequencies and bond lengths is also evident. In harmony with earlier findings (and unlike the ν_M–CO–F behavior), the ν_CO–F dependence is due chiefly to changes in the back-donation bonding component. The overall vibrational frequency-field behavior predicted by DFT is also in semi-quantitative concordance with experimental potential-dependent spectra.     

Interaction of O+ ion with water molecules: A quantum-chemical study

The interaction of O⁺ ion with several (from one to four) water molecules was studied by theab initio (UMP4/4-31G^*) and semiempirical (AM1) quantum-chemical methods. It was found that the energy of binding the O⁺ ion to the first water molecule is appreciably higher than those of binding to the subsequent water molecules. In the complex with a water molecule, whose structure corresponds to that of water oxide, the O⁺ ion retains high reactivity. The barrier to the transfer of O⁺ ion to another water molecule is much lower than the barrier to analogous transfer of O atom from the molecule of water oxide, despite the lower dissociation energy of the H₂O−O bond. Consideration of subsequent interactions with water molecules leads to an increase in the barrier to the transfer of O⁺ ion. The doublet and quadruplet excited states of the O⁺+2 H₂O system were also studied. In these cases, the formation energies are well described by the ion-dipole model. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 981–988, June, 2000.     

Adsorption of n-hexane in zeolite-5A: a temperature-programmed desorption and IR-spectroscopic study

The adsorption and desorption of n-hexane over Zeolite-5A has been investigated as a function of loading using simultaneous Fourier transform infrared (FTIR)-temperature-programmed desorption (TPD) measurements. The TPD profiles show a second peak developing at lower temperatures when loading exceeds 16 hexane molecules per Zeolite-5A unit cell or two molecules per alpha-cavity of the Zeolite-5A structure. The infrared spectra rule out two types of adsorption sites as the origin of the two peaks in the TPD. Changes in the conformation of the adsorbed hexane as a function of loading and temperature were followed by monitoring the position of the methylene stretching modes in the infrared spectra. With increasing loading, the adsorbed hexane adopts a stretched trans conformation. These changes occur at loading levels below 12 hexane molecules per Zeolite-5A unit cell. No change is observed above this loading, ruling out any conformational change at loadings where the second peak is seen in the TPD. The second peak in the TPD arises, therefore, from a combination of steric repulsion and loss of translational entropy.     

Synthesis and physicochemical study of ZSM-5 high-silica zeolite from natural raw materials

ZSM-5 high-silica zeolite was obtained from metakaolinite, Dzhenranchel’sk volcanic ash, and silica gel at T = 150–220°C, pH 9–13, and τ = 48–240 h with the use of an organic structure-forming additive, butanediol-1,4, in an alkaline solution. Optimum conditions for the synthesis of ZSM-5 zeolite were found (T = 200°C, pH 10, τ = 144 h). The catalytic properties of its H-form in vapor-phase esterification of acetic acid (I) with ethanol (II) were studied at 140–180°C and a I: II molar ratio from 1 to 2. Synthesized HZSM-5 showed high activity and selectivity in this reaction.     

吸附与润湿II.Triton X-100和Triton x-305在炭黑/水和炭黑/环己烷界面上的吸附层结构

测定了15℃和30℃时炭黑自水和环己烷中吸附非离子型表面活性剂TritonX-100和Triton X-305的等温线;计算了吸附过程的标准热力学函数;测定了石墨/水/环己烷和石墨/水/空气的接触角与表面活性剂浓度的关系, 分析所得结果,可得结论:在炭黑/水或石墨/水界面上,Triton型表面活性分子形成单分子吸附层,分子以憎水的iso-C8H17C6H4基团附着在表面,而以亲水的聚氧乙烯链伸入水相的方式取向;在炭黑/环已烷或石墨/环己烷界面上,分子是通过聚氧乙烯链吸附到表面上的,当浓度增加时分子在表面可能通过聚氧乙烯链间的相互作用而发生聚集,即可能形成表面反式胶团。     

Synthesis and properties of copolymers of ethylene/carbon monoxide with styrene/carbon monoxide

The terpolymerization of ethylene, styrene, and carbon monoxide was accomplished by two different palladium‐based catalysts: a phosphine‐based ligand system and a nitrogen‐based ligand system. The range of possible compositions and the composition dependence of the properties of the resulting polymers were determined. These polymers were essentially carbon monoxide versions of the ethylene styrene interpolymers recently presented by Dow. A comparison between the two families of polymers is attempted. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 752–757, 2000     

不同形貌ZSM-5分子筛的合成及苯-乙醇烷基化反应性能

采用水热法制备了环状、薄片、类球状聚集体和小晶粒4种不同形貌和尺寸的纳米ZSM-5分子筛,用XRD、SEM、BET和NH3-TPD对所合成分子筛进行了表征,并考察分子筛形貌对苯和乙醇烷基化性能的影响。实验结果表明：在相同的硅铝比下,不同形貌的分子筛具有相似的弱酸峰强度,短b轴和中空结构的存在会降低分子筛的强酸峰强度,分子筛的强酸峰强度直接影响烷基化性能;分子筛颗粒形貌对催化烷基化性能有较大影响,四种形貌分子筛催化苯和乙醇烷基化性能优劣顺序为：薄片ZSM-5>环状ZSM-5>类球状团聚体ZSM-5>小晶粒ZSM-5。其中,具有薄片结构的H-ZSM-5分子筛在烷基化反应过程中表现出最佳的催化性能。综合对比结果表明：较低的强酸强度、较大的比表面积和孔容、较多的直形孔道占比下,分子筛的烷基化性能最佳,产物乙苯的选择性越高。     

Thermal behaviour of the tpa IONS in ZSM-5 zeolite: II. Effect of crystal size and grinding of silicalite-1

Thermal decomposition of Silicalite-1 crystals of various size was studied. The crystals were in as-made form and upon grinding. The DTA and DTG curves show differences in the temperature of thermal decomposition of TPA species occluded in the as-made crystals. These differences disappear upon grinding. The explanation of this phenomena is given.

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Zusammenfassung Die thermische Zersetzung von Silikalit-1 Kristallen verschiedener Größe wurde untersucht. Es wurden ursprüngliche als auch zerkleinerte Kristalle einbezogen. DTA- und DTG-Kurven zeigen für die einzelnen TPA Spezies in den unzerkleinerten Kristallen verschiedene Zersetzungstemperaturen. Diese Unterschiede werden jedoch durch die Zerkleinerung beseitigt. Eine Erklärung für diese Erscheinung wird gegeben.

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Work supported by Italian C. N. R. (progetto finalizzato Energetica 2).     

Synthesis and properties of alternating copolymers of carbon monoxide with 5-vinyl-2-norbornene

The alternating cooligomers of carbon monoxide and 5-vinyl-2-norbornene have been first synthesized in the presence of catalysts based on palladium complexes containing N^N and P^P ligands. It has been shown that the insertion of carbon monoxide proceeds for the most part via a C(2)-C(3) bond of the norbornene ring. The degree of involvement of both olefinic bonds of diene in alternating copolymerization is decreased when the reaction is carried out in a protic solvent (methanol). The structure of terminal groups of the copolymers depends on the nature of a bidentate ligand and acid.     

NMR-spectroscopic evidence of intermediate-dependent pathways for acetic acid formation from methane and carbon monoxide over a ZnZSM-5 zeolite catalyst

Two ways: a Zn-modified ZSM-5 zeolite catalyst was developed for the reaction of methane with carbon monoxide to directly produce acetic acid under mild conditions (573-623 K), and two different intermediate-dependent reaction pathways were unambiguously identified for acetic acid formation by in situ solid-state NMR spectroscopy.     

Adsorption and mobility of water molecules and organic substances in carbon adsorbents 5. Self-diffusion of adsorbed molecules and fractal properties of carbon adsorbents

The self-diffusion coefficients of molecules of C₆H₆ and C₆H₁₄ adsorbed in two active carbons (AC) are not a function of the observation time in the time range from 1 to 600 msec. These AC have extensive microporous zones, and the AC studied do not exhibit fractal properties in the range of movements of 2–40 m for one and 1–100 m for the other.For previous communication, see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2189–2192, October, 1989.     

Adsorption of alkali and alkaline earth radionuclides on zeolite from water solutions

The adsorption of cesium and strontium ions from water solutions on zeolite has been investigated in presence of sodium, potassium, magnesium and calcium ions. Distribution ratios of cesium and strontium on the zeolite were determined in solutions of various compositions and solution volume to sorbent weight ratios (batch factor). Breakthrough curves for zeolite layers are reported.     

Adsorption of fluorinated ethers and alcohols on fresh and oxidized carbon overcoats for magnetic data storage

Temperature programmed desorption has been used to study the desorption kinetics and desorption energies of perfluorodiethylether, (CF3CF2)2O, and 2,2,2-trifluoroethanol, CF3CH2OH, adsorbed on fresh and oxidized hydrogenated amorphous carbon (a-CHx) films. (CF3CF2)2O and CF3CH2OH serve as models for the ether backbone and hydroxyl end-groups of Fomblin Zdol, the lubricant most commonly used to lubricate the surfaces of amorphous carbon overcoats on magnetic data storage hard disks. Our measurements clearly reveal, for the first time, the effects of surface oxidation on the adsorption of fluorocarbon lubricants such as Fomblin Zdol on a-CHx films. Oxidation of the a-CHx surface increases the desorption energy of CF3CH2OH but has no observable impact on the desorption energy of (CF3CF2)2O. These results support the suggestion that the alcohols interact with the surface via hydrogen bonding. From a practical perspective, these results imply that the oxidation of the fresh a-CHx film may serve as a means to control or tailor the a-CHx surface to optimize the properties of the lubricant-overcoat interface in hard disks.     

Molecular structure of 5-fluorouracil from gas-phase electron diffraction data and quantum-chemical calculations

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Adsorption of carbon monoxide on Li-ZSM-5: theoretical study of complexation of Li+ cation with two CO molecules

The Li+ cation complexes with one and two CO molecules have been studied computationally. The calculations reveal the conditions when two CO molecules could bind to one Li+ cation in zeolite Li-ZSM-5. In the absence of dicarbonyls (at low adsorbate coverage or at high temperatures), the IR absorption bands can be assigned only on the basis of the Li+ coordination number to the framework oxygen atoms.     

Reduction of nitrobenzene to aniline with carbon monoxide and water

Modified catalytic system composed of selenium and cocatalysts such as pyridine and aniline, applied in the reduction of nitrobenzene to aniline in the presence of carbon monoxide and water is described. The reaction proceeds at 150–200°C and 3–4 MPa gauge pressure. After 1–2 h the reaction is complete, reaching nitrobenzene conversions of up to 98% with selectivity to aniline near 100%.