Partially exchanged organophilic bentonites

Using a sodium bentonite (VCNa) as substrate differently exchanged organophilic clays were obtained by reaction with hexadecyltrimethylammonium (HDTMA) chloride, at increasing reacting ratios (R) from 20 to 120 meq/100 g of clay (VC20–VC120). The sodium bentonite was previously synthesized from a Verde Claro policationic bentonite (VC) from Bravo, Paraiba State, Brazil. From the thermogravimetric (TG) and derivative thermogravimetric (DTG) analyses of these clays on calcined mass basis and from TG and DTG curves data of VCNa clay, a method was developed to estimate the mass fraction of the exchanged cation present in each organophilic clay (M _org), as a function of R. When all sodium cations of VCNa are exchanged by HDTMA, the obtained organophilic clay presents a maximum value for M _org. From this value and TG and DTG curves data of VC and VCNa clays, the cation exchange capacity of the original VC bentonite can be estimated.     

Partially exchanged organophilic bentonites

Phenol is a pollutant that has caused many problems even when present in low concentrations and still represents an environmental problem with difficult solution. This paper presents a study of phenol adsorption by organophilic clays, obtained from aVerde Claro bentonitic clay, from Bravo, Paraíba State, Brazil, at different partial cation exchange degrees with hexadecyltrimethylammonium (HDTMA) chloride, at increasing reacting ratios, from 20 to 120 mmol/100 g of clay, which were characterized in a previous paper. By using Freundlich isotherms obtained for each case, which presented the best correlation coefficients with experimental data, it can be seen that for equilibrium concentrations up to 0.53 mmol L⁻¹ of phenol, the adsorptive capacity decreases for organophilic bentonites obtained at cation exchange degrees higher than 80 mmol/100 g of clay. This indicates that in these cases, the higher is the exchange by organic cation, the higher is the difficulty for the phenol diffusion and sorption in the interlayer space of the organophilic clays. For higher equilibrium concentrations, the maximum adsorption occurs for the organophilic bentonite obtained at 100 mmol/100 g of bentonite exchange.     

DTA of Pt exchanged vermiculite mineral

DTA curves of Pt and Pd exchanged vermiculite mineral samples are presented. The minor structural changes brought by introduction of these cations in Mg and Ni vermiculites are explained. Results of chemical analysis and XRD are also discussed.

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Zusammenfassung DTA-Kurven von Pt- und Pd-versetzten Vermikulitmineralproben werden beschrieben. Es wird eine Erklärung für kleinere Strukturveränderungen gegeben, die durch den Einbau dieser Kationen in Mg- und Ni-Vermikulit auftraten. Ergebniße aus chemischer und röntgenografischer Analyse werden ebenfalls diskutiert.

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The authors are grateful to Dr H. Pezerat, Groupe cristallochimie CNRS, and Mmes D. Delafosse and Dr M. Kermarec, Laboratoire de cinétique des surfaces et des structures, Université de Pierre et Marie Curie, Paris, France for their valuable associations.     

Surface acidity of cerium exchanged Y-zeolite

Surface acidities of Ce^III, Ce^IV and [Ce^III, Ce^IV] containing Na-Y zeolites were determined by means of n-butylamine titration in benzene using Hammett indicators in the range H_o: +6.8 to H_o: –8.2. Total acidites of Ce^IVNaY zeolites until 51% Ce^IV exchange were found to be small (0.80 mequ/g at H_o: +6.8) but formed preferably strong acidic centers (H_o: –5.6) even at low degrees of exchange. Ce^IIINaY displayed an acidity pattern similar to that which is known from lanthanum exchanged NaY faujasites under the same pretreatment conditions.

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NaY, Ce^III, Ce^IV [Ce^III, Ce^IV], -, H_o: +6,8 H_o:–8,2. Ce^IVNaY 51%- Ce^IV (=0,80 / H_o: +6,8), (H_o: –5,6) . Ce^IIINaY NaY .

     

Some studies on cerium exchanged synthetic faujasites

Radiochemical techniques have been used to measure cation mobilities in samples of NaCeX zeolite which have been subjected to calcinations in air or nitrogen. Thermal analyses and X-ray powder photographs were used to determine changes in water content and/or crystallinity.     

Physico-chemical characterization of ferric exchanged y zeolites

Ferric exchanged Y zeolites are prepared by ion exchange and are characterized by X-ray diffraction, thermal analysis, IR and visible spectroscopy. The number of hexa-aquo complexes, [Fe(OH)(H₂O)₅]²⁺, in supercages is determined from thermal analysis, and cation distribution at different sites is discussed. The visible spectra confirmed the formation of hexa-aquo complexes of iron in freshly prepared hydrated FeNaY zeolites. The migragtion of ferric ions from the supercage to the sodalite cage or hexagonal prism takes place on activation of Fe³⁺Y zeolites at 500°C for 2–10 h. The thermal stability of the activated samples is discussed on the basis of X-ray and thermal analysis.     

Physicochemical properties of alkali-metal exchanged type X zeolites

The changes in the physicochemical properties of a series of faujasite type X zeolites cation exchanged with K⁺, Rb⁺ and Cs⁺ have been studied by XRD, IR, thermoanalytical methods and sorption measurements. As a consequence of the enhanced scattering of X-rays by larger alkali metal cations, the percent relative intensity of the XRD peaks of cation exchanged zeolites was found to have decreased considerably. The framework IR spectra also showed analogous changes. The alkali metal exchange was found to enhance the thermal stability of the parent zeolite. The available void volume and specific surface area (obtained by low temperature nitrogen sorption) also decreased with the increase in the degree of exchange and cationic size. Equilibrium sorption capacities (298 K andP/P ₀=0.5) for water,n-hexane, cyclohexane and 1,3,5-trimethylbenzene also exhibited the same trend.NCL communication no. 6056.     

DTA of some reduceable metal ion exchanged montmorillonites

Stable montmorillonites with exchange of Cu, Ni, Ce, Ag, Pd and Pt are possible to be prepared. Ni²⁺ only migrates into the octahedral space and thus stabilising the structure.     

Characterization of alkali exchanged ZSM5 by IR spectrosopy

The use of time resolved FTIR spectroscopy for characterizing time dependent adsorbate concentrations has been demonstrated with the examples of adsorption/desorption of ammonia and of adsorption and reactions of propan-2-ol. Adsorption sites and adsorbate structures are discussed.     

Thermal and structural properties of rare earth exchanged zeolites

A series of rare earth zeolites of types X and Y were prepared by cation exchange. Thermal analysis curves (TG/DTA) were employed to estimate the structural changes in the zeolite framework. Analogous investigations were carried out by independent methods such as XRD and IR spectroscopy. The results indicate increased thermal stability on the replacement of sodium by rare earth. Partial replacement of rare earth by ammonium/hydrogen enhances the thermal stability. The type Y zeolites are more stable than those of X type.

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Zusammenfassung Eine Reihe von Ionen der Seltenen Erdmetalle enthaltenden Zeolithen des Typs X und Y wurden durch Ionenaustausch hergestellt. Thermoanalytische Kurven (TG/DTA) wurden zur Beurteilung der strukturellen Veränderungen des Zeolithgitters herangezogen. Analoge Untersuchungen wurden mit unabhängigen Methoden (XRD und IR-Spektroskopie) ausgeführt. Es wurde festgestellt, daß ein Ersatz der Natriumionen durch Ionen der Seltenen Erdmetalle zu einer Erhöhung der thermischen Stabilität führt. Ein teilweiser Ersatz der Seltenen Erdmetallionen durch Ammonium-/Wasserstoffionen erhöht die thermische Stabilität. Zeolithe des Typs Y sind stabiler als die des X-Typs.

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X . (/) . - . . . X .

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NCL Communication No: 2186     

Characterization of UO 2 2+ exchanged Y zeolite

The present study discusses the incorporation of uranyl ion into Y-zeolite framework. The UO ₂ ²⁺ sorption was measured by neutron activation analyses. The Y-zeolite framework distorts in response to the cations present in the structure. Hence, depending on the amount and the location of the exchanged cations, the features of the X-ray diffraction pattern may vary. From the Rietveld analysis of these patterns, the positions occupied by the UO ₂ ²⁺ cations in the zeolite network were determined.     

Regularities of oxygen chemisorption on coked exchanged Y zeolites

Two types of paramagnetic centers have been revealed in the composition of coke formation products on zeolite surfaces. The oxygen effect on the paramagnetic properties of these systems is determined by the concentration of these centers, which in turn characterizes the structure of coke precursors on their surface.

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生物质乙醇在 Fe-HZSM-5分子筛催化剂上脱水制乙烯

乙烯是一种重要的大宗化工原料.目前国内外乙烯的生产方法主要是石脑油裂解法.但是,随着全球性石油资源供求关系日趋紧张,以及该生产过程存在较大环境污染,该工艺面临严峻挑战.生物乙醇是一种可以通过生物质发酵获得的可再生资源.因此,生物质乙醇催化脱水制乙烯工艺受到越来越多研究者关注.该技术的关键在于高性能乙醇脱水制乙烯催化剂的开发.研究发现, Si/Al比大于40的 Fe改性 ZSM-5分子筛在乙醇转换制碳氢化合物的催化反应中具有较高活性,当反应温度大于400oC时,可生成 C1-C9的烷烃、烯烃和芳香烃,其中以 C3产物和芳香烃产物为主.本文研究了 Si/Al比为25-300的 Fe离子交换 ZSM-5分子筛在乙醇脱水制乙烯反应中的催化活性,并利用 XRD, NH3-TPD,吡啶吸附 FT-IR和DRS UV-VIS等表征手段,研究了催化剂的晶相结构、表面组成及酸性位点等,进而探究了该催化反应的反应机理.我们首先考察了 Si/Al比为25-300的 HZSM-5分子筛.随着分子筛 Si/Al比增大,乙醇转化率先增加后降低,在 Si/Al比为100时获得最高值;但是乙烯收率随着 Si/Al比的增加而持续下降, Si/Al比为25时有其最高值47%.经产物分析, HZSM-5(25)和 HZSM-5(300)虽具有相似的乙醇转化率,但前者产生大量 C3+产物,而后者产物只有乙烯和乙醚.据文献报道,乙醚是乙醇脱水制乙烯的中间产物,它的进一步脱水产生乙烯,而乙烯可进一步转化生成 C3+产物.因此,由于 HZSM-5(300)表面酸性较弱,主要生成反应中间体,而 HZSM-5(25)较强的表面酸性又导致乙烯进一步转化,生成 C3+产物.然后我们考察了经过3次离子交换处理的 Fe-ZSM-5催化剂.随着 Si/Al比上升(25-300),乙醇转化率和乙烯收率下降, Si/Al比为25时为其最高值;随着反应温度上升,乙醇转化率在260oC时达到近100%,之后维持不变,乙烯收率也在260 oC时为其峰值,温度继续上升造成乙烯收率再次下降;催化剂空速增大降低乙醇转化率和乙烯收率.经产物分析,温度较低和空速较大时产生大量的反应中间体乙醚,而温度较高时导致乙烯进一步转化生成 C3+产物.在反应温度为260oC、空速为0.81 h-1时, Fe-HZSM-5(25)催化剂上乙醇转化率为98%-99%、乙烯收率为97%-99%,并可实现长达1440 h的单程使用寿命,该值是 HZSM-5(25)催化剂的20余倍,具有很好的工业应用前景.为探究 Fe-ZSM-5(25)催化剂高催化活性和长催化寿命的原因,我们表征了催化剂.从 XRD结果可以看出,离子交换没有损坏 HZSM-5的晶体结构,也没有新的可检测到的物相产生.从 NH3-TPD结果看, HZSM-5(25)的CH/CL(强酸/弱酸)比为0.7, Fe-ZSM-5(25)的CH/CL比为0.29,可知 Fe离子交换降低了分子筛的表面酸性,特别是强酸性位.从吡啶吸附 FT-IR结果看, HZSM-5(25)的 B/L (Br?nsted酸性位/Lewis酸性位)比为1.42, Fe-ZSM-5(25)的 B/L比为0.25,可知 Fe离子交换主要减少的是分子筛表面的 Br?nsted酸性位.文献报道,乙醇脱水制乙烯主要发生在弱酸性位上,而乙烯进一步转化为 C3+产物发生在强酸性位上.所以,催化剂上强酸性位的减少有利于乙烯的生成反应.另据文献报道, Br?nsted酸性位是乙烯聚合、迅速覆盖催化活性位点产生积炭的催化活性中心.因此, Br?nsted酸性的降低可认为是 Fe-HZSM-5(25)催化剂单程使用寿命长较 HZSM-5(25)分子筛显著延长的原因.从 UV-VIS结果得知, Fe-ZSM-5上的 Fe物种主要以骨架内和骨架外 Fe3+为主,此外含有少量低聚合的 FexOy,但几乎没有 Fe2O3颗粒存在.文献记载, Fe3+物种是乙烯形成的活性物种,而 FeOx催化产生乙烯和乙醛.因此,催化剂中大量骨架内和骨架外 Fe3+物种的存在也可认为是该催化剂具有较强乙醇脱水制乙烯催化活性的原因之一.     

The interactions of sorbates with gallosilicates and alkali-metal exchanged gallosilicates

Structures, energetics and vibrational frequencies of the interaction of adsorbates with H-aluminosilicates (H-AlZ), H-gallosilicates (H-GaZ), alkali-metal exchanged aluminosilicates (X-AlZ) and alkali-metal exchanged gallosilicates (X-GaZ), where X being Li, Na, or K, have been carried out at B3LYP and HF levels of theory with 6-31G(d) as the basis set. The charge compensating alkali-metal ions can affect the catalytically active site (Si–O–T where T=Al or Ga) by weakening the Si–O, Al–O, and Ga–O bonds as compared to their anionic frameworks. Comparing the net stabilization energies, ΔE_NSE, of the naked alkali-metal/H₂O adducts with those of the alkali-metal exchanged zeolite/H₂O systems, the latter amounts only to about 50% of the former, which is partly due to the destabilizing role of the negative zeolitic oxygen frameworks surrounding the cations. The interaction of sorbates with the alkali-metal exchanged gallosilicates can be employed to probe the field strength inside the catalytic frameworks as indicated by the plot of the binding energy, ΔE, versus 1/R_X–Ow², with R_(X–Ow) being the distance between the cationic nucleus and the oxygen atom of the adsorbate. The IR spectra of H₂O adsorbed on Na-AlZ are calculated to be 3584, 3651, and 1686 cm⁻¹. The obtained results are in excellent agreement with the very recent experimental IR spectra of water adsorbed on Na-ZSM-5 of Zecchina et al. (J. Phys. Chem., 100 (1996) 16 484). Other important features, i.e. the correlation between Δν_OH and, ΔE, R_(X–Ow), and 1/R_X–Ow², cationic size, demonstrate that the interactions of sorbates with alkali-metal exchanged gallosilicates are well approximated by electrostatic contribution.     

Quantum chemical and vibrational investigation of sodium exchanged gamma-alumina surfaces

The sodium cation is well known as an efficient poison of gamma-alumina surface acidity. This poisoning effect has been revealed both by characterization methods and catalytic tests. In this work, we propose an accurate model of sodium exchanged gamma-alumina surfaces. On realistic models of hydroxylated gamma-alumina surfaces, the location of sodium cation is determined by the use of density functional theory (DFT) methods. For the (100) and (110) surfaces of gamma-alumina, the sodium cation is found in a solvated state within an inner solvation sphere complex. Its coordination sphere is constituted by O-mu(2), O-mu(3) and HO-mu(1) surface groups. The stretching frequency of these HO-mu(1) groups is shifted, leading to the appearance of a new band predicted and observed at about 3754 cm(-1) on the IR spectrum.     

Why relevant chemical information cannot be exchanged without disclosing structures

Both society and industry are interested in increasing the safety of pharmaceuticals. Potentially dangerous compounds could be filtered out at early stages of R&D by computer prediction of biological activity and ADMET characteristics. Accuracy of such predictions strongly depends on the quality & quantity of information contained in a training set. Suggestion that some relevant chemical information can be added to such training sets without disclosing chemical structures was generated at the recent ACS Symposium. We presented arguments that such safety exchange of relevant chemical information is impossible. Any relevant information about chemical structures can be used for search of either a particular compound itself or its close analogues. Risk of identifying such structures is enough to prevent pharma industry from relevant chemical information exchange.     

Copper exchanged beta zeolites for the catalytic oxidation of ammonia

Copper exchanged on beta zeolites are extremely active and selective for the catalytic oxidation of ammonia to nitrogen and water and this activity correlates to the ease of reduction of the copper species.     

微波条件下ZnCl2改性离子交换树脂催化改质生物油的研究

在微波加热条件下,以732型阳离子交换树脂和ZnCl2改性离子交换树脂为催化剂,添加乙醇为溶剂,对生物油进行催化酯化改质.比较研究了两种催化剂随催化剂用量、反应时间及反应温度改变对生物油改质效果的影响,同时考察了微波加热与传统水浴加热条件下催化剂的活性.结果表明,酯化过程中ZnC12改性离子交换树脂比732型树脂活性有...     

Anomalous adsorption of nitrogen and argon in silver exchanged zeolite A

A new adsorbent based on zeolite AgA having N2 adsorption capacity of 22.3 cc g(-1) at 101.3 kPa and N2/O2 selectivity in the range of 5 to 14.6 at 303 K, the highest known so far for any zeolite A type of adsorbent, is reported; furthermore, this adsorbent also shows argon selectivity over oxygen.