IR observation of adsorption and initial reactions of olefins on Brønsted acid sites of a deuterated ZSM-5

Adsorption of linear olefins (C₂?C₄) on a deuterated H-ZSM-5 (D-ZSM-5) was studied by infrared (IR) spectroscopy. The initial interaction of the olefins with Brønsted acidic OD groups was hydrogen-bonding to form π-complexes at low temperatures. The adsorbed ethene and propene desorbed by heating under evacuation, while various reactions took place for adsorbed 1-butene; double bond migration (DBM) to 2-butene below 230 K followed by dimerization at room temperature. An unusual reaction path was deduced for DBM of 1-butene, where proton transfer from Brønsted acid sites (BAS) to the adsorbed 1-butene was not essential.     

The homogeneous pyrolysis of 2-butenes

The homogeneous pyrolysis of 2-butene subjected to shock heating was studied in the limit of high pressures by a relative rate technique. Over the temperature range of 1150–1325°K nearly equal amounts of methane, propylene, and butadiene were formed starting with either the cis- or trans-2-butene, while isomerization remained far from equilibrium. The results are consistent with a simple free radical mechanism for which we find as the initial rate-limiting step.     

Steric factors in the gas-phase elimination of esters: The pyrolysis of 2,3-dimethyl-3-pentyl acetate

The kinetics of the thermal decomposition of 2,3-dimethyl-3-pentyl acetate have been studied at a temperature range of 212–260°C and a pressure range of 30–300 mm Hg. The olefins produced are 2-ethyl-3-methyl-1-butene, 3,4-dimethyl-trans-2-pentene, 3,4-dimethyl-cis-2-pentene, and 2,3-dimethyl-2-pentene. The reaction is homogeneous, obeys first-order law, and the value of the rate constant is given by the Arrhenius equation The directions of elimination and their corresponding partial rates are best explained in terms of purely steric factors.     

C2-C2直链烯烃在HY 和H-ZSM-5分子筛上的吸附

采用ONIOM(B3LYP/6-311++G(d,p):UFF)分层计算方法, 研究了C₂-C₅直链烯烃在HY 和H-ZSM-5 分 子筛上的吸附性质. 理论计算结果表明: 烯烃与分子筛的Br?nsted 酸性位相互作用形成π配位超分子复合物; 随着碳链的增长, 烯烃的吸附能增加, 增加量近似为一个常数(HY 分子筛: 约12 kJ·mol^-1; H-ZSM-5 分子筛: 约 25 kJ·mol^-1), 与烷烃在分子筛上的吸附具有相同的规律. 双键位置对烯烃的吸附能影响很大, 2位烯烃的吸附能 要远大于1 位烯烃的吸附能. 不同类型分子筛对烯烃的吸附性能也有很大差别, 由于局域效应的影响, 小孔径 H-ZSM-5分子筛上的吸附能大于大孔径的HY分子筛,而且碳链越长,这种差别越大.从微观结构上看,吸附的烯 烃与H-ZSM-5分子筛酸性位的距离要远大于它们与HY分子筛酸性位的距离, 这是由于不同类型分子筛的微孔 结构产生的范德华作用是不同的,这种作用随着孔径的减小而增强.前线轨道分析表明, 对于小分子烯烃,大孔径 HY分子筛对其催化活性相近,而小孔径H-ZSM-5分子筛随着烯烃碳原子数的增加催化活性有减弱的趋势.     

Transformations of isobutylene in the presence of various types of zeolites

Conclusions In contrast to zeolites with ultrahigh silica content, type A, X, Y, and M zeolites in the Na form and also those modified by decationization, cation exchange, and addition of-Al₂O₃, Al₂O₃-SiO₂, Pt, and Rh show a low activity in the aromatization reaction of C₃-C₄ olefins at 450–550°C at times of contact of 2–14.4 sec. The zeolites studied become rapidly deactivated as the result of intense coke formation.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1300–1304, June, 1981.     

Reactions of Group 3 Metal Alkyls in the Gas Phase. Part 10: The addition of olefins to the monomeric diisobutylaluminiumhydride

The relative rate constants for adding ethylene (k₁), propylene (k₂) and 2-methyl-but-1-ene (k₃) to gaseous diisobutylaluminium hydride produced in situ from AlⁱBu₃ have been measured in the temperature range 104–169° in the presence of an excess of equimolar olefin mixtures. The following temperature dependences of the relative rate constants have been obtained: Two compensating factors determine the rate of addition of olefins to Al? H and Al? C bonds: (a) the steric effect, reflected in the differences in the preexponential factors and (b) the polar effects, reflected in differences in the activation energies. In the addition of olefins to R₂Al? H bonds in contrast to R₂Al? C bonds, the steric effect (a) does not always overrule the opposing energy effect. At temperatures below 125° e.g., isobutene adds slightly faster to HAlⁱBu₂, than ethylene. These results are in perfect agreement with expectations based on a reaction mechanism involving a tight asymmetric quadrupolar 4-centre transition state similar to that postulated earlier for the addition of olefins to Al? C bonds.     

The reaction of hydrogen atoms with 1-butanethiol and thiolane the role of chemically activated 1-butanethiol

The reaction of 1-butanethiol with hydrogen atoms has been studied at temperatures of 295° and 576° K under the pressure of 660 Pa, using a conventional discharge-flow apparatus. The reaction products (besides hydrogen sulfide and methane) under the low conversion range (～10%) consisted mainly of n-butane, 1-butene, and propylene-propane, with the relative yields of 70, 25, and 5% at 295° K and 25, 50, and 10% at 576°K. Analysis of kinetic equations by numerical integration indicates that the following initial steps are consistent with the experimental results: where the following expressions have been derived for k₁ and k₂: The subsequent reaction of the butylthio radical with hydrogen atoms leads to the chemically activated 1-butanethiol which either stabilizes to 1-butanethiol or decomposes to 1-butene and hydrogen sulfide, depending on the experimental conditions. A similar analysis of the data on the thiolane-H system has yielded the following rate parameters for the initial step to form the 4-mercapto-1-butyl radical: .     

CeY分子筛中有效脱硫物种活性位的构建及其吸附机理研究

以不同焙烧温度和Ce负载量的CeY分子筛为研究对象,运用XRD及N_2吸附表征其织构性质;运用吡啶吸附红外光谱法剖析了分子筛中活性位的化学属性;采用固定床评价其对噻吩模拟油的吸附脱硫性能及芳烃和烯烃对噻吩脱除的影响;并结合红外光谱和GC-SCD技术分析了其脱硫机制。结果表明,CeY样品经150℃焙烧后,其超笼中具备高含量的B酸和Ce羟基化物种活性位,两者协同增强了噻吩低聚反应能力,进而提高了其吸附穿透硫容量(18.45 mg (S)/g);而提升焙烧温度和Ce负载量会严重降低其有效活性位的数量,削弱了噻吩低聚反应能力,其吸附穿透硫容量显著减小(4.03 mg (S)/g)。当加入烯烃和芳烃后,CeY-12.3-150吸附剂对含低浓度(质量分数)1-己烯(1.0%)和苯(0.1%)的噻吩模拟油依旧保持较高吸附穿透硫容量;但随两者含量的持续增加,其硫容量急剧下降。其主要分别归因于噻吩烷基化反应的发生及“S-H”键的作用模式。     

Derivative Enthalpies of Adsorption of p-Xylene and m-xylene onto NaY and BaY Zeolites at 150°C: Contribution to the prediction of adsorption selectivity

The derivative enthalpies of adsorption of m-xylene and p-xylene onto the NaY and BaY zeolites were measured at 150°C, then compared with those obtained at 25°C, and finally used to predict the selectivity of adsorption of xylene mixtures. Significant differences were observed as the temperature was elevated: for the NaY zeolite, the adsorbate-adsorbate interactions became prevalent, in contrast with the BaY zeolite, between zeolite and derivative interactions were stronger. The difference between the adsorption derivative enthalpies of the two xylenes displayed an abrupt variation from 2 molec. ^–1 for both zeolites, the filling from which selectivity towards m-xylene for the NaY zeolite and towards p-xylene for the BaY zeolite appeared. The preferentially adsorbed xylene was closely connected with the sense of this difference, which changed with the zeolite.This revised version was published online in November 2005 with corrections to the Cover Date.     

Isomerization of alkenes during drying over zeolites

We observed that zeolite 5A, a zeolite commonly used for drying, isomerized 1-butene and 1-hexene at room temperature. The activity for 1-butene isomerization on 3A, 4A, 5A and 13X zeolites at temperatures of 300 to 565 K is reported.     

Adsorption of Nitrogen, Oxygen and Argon on Na-CeX Zeolites

Commercial type X zeolites (Linde 13X) are nitrogen selective. Oxygen is the less abundant component in air; hence oxygen selective sorbents are desired for air separation. Mixed Na-Ce type X zeolites containing different ratios of Ce³⁺/Na⁺ ions are prepared by partial ion exchange of commercial X zeolite. The adsorption isotherms of nitrogen, oxygen and argon are measured and the pure-component selectivity ratios are compared and analyzed against commercial zeolites (13X) for air separation. Oxygen selectivity over nitrogen (1.5) and argon (4.0) are seen for mixed Na-Ce type X zeolite (Si/Al = 1.25; Ce³⁺/Na⁺ < 4.0) from Henry's constant determined from low pressure adsorption measurements. The oxygen and nitrogen isotherms cross over for mixed Na-Ce type X zeolite (Si/Al = 1.25; Ce³⁺/Na⁺ < 4.0), and the pressure at which cross they over increases as Ce³⁺/Na⁺ approaches 1. The oxygen selectivity as claimed in the patent by N.V. Choudary, R.V. Jasra, and S.G.T. Bhat (US Patent no. 6,087,289, 2000) is seen only at very low pressures in the volumetric adsorption measurement and the hydrogen treatment of the Ce-exchanged samples have no effect on the adsorption characteristics.     

A radiochemical study on the thermodynamics of cesium adsorption on potassium copper nickel hexacyanoferrate(II) from aqueous solutions

This paper reports a radiochemical study on the themodynamics of cesium adsorption on potassium copper nickel hexacyanoferrate(II) (KCNF) using¹³⁴Cs radionuclide as a radiotracer. The values of themodynamic parameters like H ^o , S ^o and G ^o have been calculated using the temperature dependence of cesium adsorption on KCNF. These values indicate the endothermic nature of the adsorption process. Freundlich and Langmuir izotems have shown their applicability for the adsorption of cesium on KCNF at different temperatures and their corresponding constants have been calculated and interpreted. The Dubinin-Radushkevich (D-R) equation has also been applied to the adsorption data and the values of mean free energies of the adsorption process at different temperatures have been evaluated. These values indicate that the adsorption of cesium on KCNF is expected to follow an ion exchange process.     

Steric Factors in Liquid-Phase Oxidation of Olefins with iso Structure

Products of liquid-phase oxidation of 2-methyl-2-butene and 2-methyl-2-pentene were studied by NMR and IR spectroscopy. Steric hindrances in liquid-phase oxidation of olefins with iso structure were shown to arise from branching of the alkyl group at the -carbon atom.     

Intramolekularer Carbonylgruppenaustausch in Tetracarbonyleisen-Komplexen von Äthylen und einfachen (E)-konfigurierten Olefinen

Intramolecular Exchange of Carbonyl Group Sites in Tetracarbonyliron Complexes of Ethylene and Simple (E)-Configurated Olefins The activation parameters of the intramolecular exchange of carbonyl group sites in the tetracarbonyliron complexes 2–5 of ethylene, (E)-2-butene, (E)-4-octene and (E)-cyclooctene, respectively have been determined between 180 and 115 K by a complete line shape analysis of the ¹³C-NMR, signals of the CO-groups. The temperature dependence of the rates (k (2) , k (3) , k (4) and k (5) , respectively) of this intramolecular exchange process can be described by the following equations (E_a in J/mol): Further data are given in Tables 3 and 4. Furthermore, a good linear correlation between the energies of activation of the carbonyl exchange process in 1,2-disubstituted olefins and the corresponding averaged wavenumbers ( (CO)) of the carbonyl stretching vibrations or of the corresponding chemical ¹³C-shifts (δ (CO)) of the carbonyl group at fast exchange in the complexes seems to exist.     

Calorimetric and IR-spectroscopic study of adsorption of methanol on zeolite-like aluminophosphates

Electrostatic properties of zeolite-like aluminophosphates are intermediate between those of zeolites and zeolite-like silica modifications. The adsorption measurements and IR spectroscopic investigations of the framework vibrations demonstrate that the number of the adsorption complexes of CH₃OH with Al atoms increases in the following order: AlPO₄-5 < AlPO₄-17 AlPO₄-18.The OH vibrations of methanol molecules in the first coordination sphere of the Al atoms are reflected in the IR spectra as an absorption band at 3200 cm^–1, which is not observed for the adsorption of CH₃OH on zeolites.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1937–1942, October, 1995.     

EPR study of the mechanism of interaction of NO and NO2 molecules with zeolite surfaces

The adsorption of the paramagnetic molecules of NO and NO₂ by zeolites in the alkali and alkaline earth cationic forms has been studied by EPR and reflectance spectroscopic methods. The change in the EPR spectra of adsorbed nitric oxide with increase in the degree of covering of the surface of the alkali cationic form of the zeolites, and also the nature of the change in the spectra when oxygen is adsorbed on zeolites on which NO has previously been adsorbed, indicate the existence of two types of adsorption center. At low degrees of covering of the surface, on the order of 10¹⁸ g^–1, as can be judged from the EPR spectra, the adsorbed NO molecule is strongly polarized and the unpaired electron is almost completely localized on the oxygen atom. At high degrees of covering, for an appreciable proportion of the NO molecules, the bond with the surface is weaker. In this case, the EPR spectra show a hyperfine structure (HFS) with a constant which changes with change in the cation in the order Li⁺ Na⁺ K⁺. The replacement of the singly charged Na⁺ by the doubly charged Ca²⁺ produces a marked change in the adsorption properties of the zeolite. The adsorption of NO on CaA leads not only to polarization of the adsorbed molecule but also to transfer of the electron from the nitrogen atom to the atoms of the adsorbent; this is recorded in the EPR spectrum in the form of an F-center. On further adsorption, the NO molecules are adsorbed both on the nitrogen atom and on the oxygen atom of the first molecule; thus, NO₂ and N₂O are formed.     

Differential calorimetric enthalpies of adsorption ofp-xylene andm-xylene on y faujasites at 25°C

The differential enthalpies of adsorption ofp-xylene andm-xylene on NaY, KY and BaY zeolites were measured by isothermal calorimetry coupled with isothermal volumetry at 25C. Whatever the zeolite, the enthalpies of adsorption ofp-xylene andm-xylene at low filling were of the same order of magnitude. They did not show significantly the effect of the dipolar moment ofm-xylene. Their absolute values varied in the sequence Q ₀(pX/NaY)<Q ₀(pX/KY) =Q ₀(mX/KY)<Q ₀(pX/BaY)<Q ₀(mX/NaY) =Q ₀(mX/BaY)During the adsorption of the third molecule of xylene per -cage, BaY zeolite exhibited specific behaviour: the differential enthalpies of adsorption decreased with the filling of the -cages in such a way that they became lower than those of the other two zeolites. Some arguments concerning the structures of the zeolite and xylene molecules can explain such behaviour. Whatever the zeolite, the adsorption capacity of the -cages was 3.5 molec.^–1. For relative pressures ranging from 0.2 to 0.5, an additional adsorption of about 0.1 molec.^–1 occurred on the external surface.