Interaction between propene and CoNaX zeolite and exchange of propene hydrogens

Interaction of propene with CoNaX and NaX zeolites and exchange of propene hydrogens with CoNaX zeolite was studied at the temperature of the IR beam and at 300°C by means of IR and MS analysis. In addition, the heats of adsorption were measured. The structure of adsorbed propene complexes was found to be influenced by the presence of Co²⁺ ions. The mechanism of the exchange is discussed and the properties of the OH groups of HY, HX and CoNaX zeolites are compared.

---

CoNaX NaX CoNaX 300°C . . , Co²⁺ . OH , CoNaX .

     

Exchange of deuterium with OH groups of HY zeolites

The exchange reaction of D₂ with OH groups of HY zeolites was followed both in the solid and gas phase by IR and MS. The rates of D₂–OH and D₂–H₂ exchange increase considerably with dehydroxylation of the sample. The active centers are probably vacancies formed by removal of oxygen from the lattice, they catalyze the dissociation of D₂. Dehydroxylation of the sample is accompanied by the formation of 3 740 cm^–1 hydroxyls, whose exchange with D₂ is slower than that with other OH groups and which affect the kinetics in the gas phase.

---

D₂ OH HY - O₂–OH O₂–H₂ . , , , O₂. OH, 3740 ^–1, , OH .

     

Aromatization of propene on ZSM-5 zeolites

Cu-ZSM-5, CuZn-ZSM-5 and H-ZSM-5 have been studied for propene aromatization at comparable conditions. It was established that all samples are active for aromatization (yields 50%) and demonstrate high selectivity for benzene, toluene and xylenes formation ( 90%). The role of acid centers in all stage of the aromatization is discussed.

---

Cu-ZSM-5, CuZn-ZSM-5 H-ZSM-5 . ( 50%) , ( 90%). .

     

Vibrational analysis of propene adsorbed in zeolites Y

Normal coordinate analysis was performed for propene adsorbed in faujasites NaY, CaY and MgY applying a valence force model. The force fields obtained were compared with that of the free molecule. Only small shifts of the fundamentals are observed due to the weak interaction with the zeolites. Although in general the results are comparable to those of propene adsorbed in different zeolites A, some distinct features such as a stronger influence on the CC stretching vibration, a smaller hindrance of the CH bending vibration and a higher reduction of the CH (CH₃) bond strength are detectable, which must be attributed to both the different composition and structure of the zeolite framework. The frequency shifts and the corresponding changes of the force constants are related to the geometry of the sorption complex of propene on the zeolite surface.     

碱金属卤化物与NaA分子筛之间的固态离子交换反应

在低于碱金属卤化物熔点的温度下热处理碱金属卤化物和脱水NaA分子筛干混样品时,一部分分散到分子筛内孔的金属离子能够与脱水分子筛进行程度不同的固态离子交换反应,生成的非挥发性NaCl产物将扩散到分子筛笼外单独结晶或剩余的原卤化物形成溶体.热处理温度愈度,离子交换度愈大;在一定温度下热处理干混样品,存在最大离子交换度.     

Chemical composition and ion exchange properties of zeolites

Series of exchange selectivity for alkali cations in zeolites change in a regular manner in dependence on the ratio (z) between the number of particles capable of solvating cations in the frameworks of zeolites (molecules of zeolite water, one-fourth of the framework oxygen ions) and the number of zeolite cations. For z=5–6 zeolites have maximum selectivity for large cations, for z<3–4 they selectively absorb sodium, while if z<2 they selectively absorb lithium. An analysis is given of the reasons of this dependence of the ion exchange selectivity of zeolites on the chemical composition of their frameworks. It is shown that the free energy of solvation of cations in zeolites is less than the free energy of their hydration. The effect of transformation of the selectivity series of zeolites can be connected with the contribution, on the part of the effect of redistribution of water between the solid and liquid phases of the ion exchange system, to the free energy of ion exchange reactions, which differs in dependence on the composition and structure of the crystals.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 3, pp. 378–382, May–June, 1990.     

Ion exchange of radium and barium in zeolites

The sorption of radium, barium and mixture of both elements has been studied in the zeolites 3A, 5A and Y. The ratio zeolite; solution was 100 mg: 10 cm³ and the pH was 3. Carrier-free radium was completely retained in all studied zeolites. When 0.0016 meq of barium/cm³ were added, the sorption of radium decreased in the zeolite 5A only and when 0.014 meq of barium/cm³, the radium sorption was reduced in all the studied zeolites. The sorption of barium was similar to that of radium. The amounts of sodium and calcium removed from the zeolites and the proton quantity fixed to them allowed us propose the ion exchange mechaniosm. The changes and ionic radii of the species exchanged did not play an important role. However, the location of the ions in the crystalline network of each zeolite is probably an important parameter for the exchange.     

Shock tube/laser absorption measurements of the reaction rates of OH with ethylene and propene

Reaction rates of hydroxyl (OH) radicals with ethylene (C?H?) and propene (C?H?) were studied behind reflected shock waves. OH + ethylene → products (rxn 1) rate measurements were conducted in the temperature range 973-1438 K, for pressures from 2 to 10 atm, and for initial concentrations of ethylene of 500, 751, and 1000 ppm. OH + propene → products (rxn 2) rate measurements spanned temperatures of 890-1366 K, pressures near 2.3 atm, and initial propene concentrations near 300 ppm. OH radicals were produced by shock-heating tert-butyl hydroperoxide, (CH?)?-CO-OH, and monitored by laser absorption near 306.7 nm. Rate constants for the reactions of OH with ethylene and propene were extracted by matching modeled and measured OH concentration time-histories in the reflected shock region. Current data are in excellent agreement with previous studies and extend the temperature range of OH + propene data. Transition state theory calculations using recent ab initio results give excellent agreement with our measurements and other data outside our temperature range. Fits (in units of cm3/mol/s) to the abstraction channels of OH + ethylene and OH + propene are k? = 2.23 × 10? (T)(2.745) exp(-1115 K/T) for 600-2000 K and k? = 1.94 × 10? (T)(2.229) exp(-540 K/T) for 700-1500 K, respectively. A rate constant determination for the reaction TBHP → products (rxn 3) was also obtained in the range 745-1014 K using OH data from behind both incident and reflected shock waves. These high-temperature measurements were fit with previous low-temperature data, and the following rate expression (0.6-2.6 atm), applicable over the temperature range 400-1050 K, was obtained: k? (1/s) = 8.13 × 10?12 (T)(7.83) exp(-14598 K/T).     

Electrostatic model and selectivity of cation exchange in zeolites

The agreement of the Eisenman theoretical selectivity series with the experimental ones cannot be considered as a justification of the reality of the mechanism (used in the electrostatic model) of transformation of the selectivity series because the changes of the free energy and enthalpy of this ion-exchange reaction in compositionally and structurally different ion exchangers are independent, the enthalpies postulated by the model and the experimental enthalpies of the ion-exchange reactions differ significantly, and the entropy of the ion-exchange reaction depends on the structure and composition of the ion exchanger. It was determined that the entropy of the ion-exchange reactions of zeolites agrees in sign with the difference of the entropies of hydration of the corresponding cations, but the differences of the entropiers of hydration and solvation of the exchanging cations can differ with respect to sign. An explanation of the effect of concentration of rare alkali metals (cesium, rubidium, and lithium) by some natural aluminosilicates is presented.L. V. Pisarzhevskii Institute of Physical Chemistry, Ukrainian Academy of Sciences, Kiev. Translated from Teoretischeskaya i Éksperimental'naya Khimiya, Vol. 27, No. 5, pp. 619–627, September–Ocotber, 1991. Original article submitted May 31, 1990.     

Ion exchange and pH tolerance in molecular sieve zeolites

We report here on the effect of nitric acid solutions on the structural stability and ion-exchange properties of a series of natural and synthetic zeolite molecular sieves. The implications of this work for the industrial application of zeolites in acidic aqueous systems are discussed.     

Cesium exchange reaction on natural and modified clinoptilolite zeolites

Cesium cation exchange reaction with K, Na, Ca and Mg ions on natural and modified clinoptilolite has been studied. Batch cation-exchange experiments were performed by placing 0.5 g of clinoptilolite into 10 ml or 20 ml of 1·10⁻³M CsCl solution for differing times. Two type deposits of clinoptilolite zeolites from, Nižny Hrabovec (NH), Slovakia and Metaxades (MX), Greece were used for ion-exchange study. The distribution coefficient (K _d ) and sorption capacity (Γ) were evaluated. For the determination of K, Na, Ca and Mg isotachophoresis method, the most common cations in exchange reaction was used. Cesium sorption was studied using ¹³⁷Cs tracer and measured by γ-spectrometry.     

Ion exchange studies on natural and modified zeolites and the concept of exchange site accessibility

In the present study natural and Na-rich form of clinoptilolite are examined, in respect to ion exchange of Pb2+, Cu2+, Cr3+, and Fe3+. Equilibrium and kinetic studies performed, under the same normality (0.01 N). Equilibrium studies demonstrate that Na+ enrichment of clinoptilolite is beneficial in respect to metal uptake for all metals, except Cr3+, which is shown to have the same equilibrium behavior in both materials. Kinetic study shows that diffusion coefficients are in the range of 0.16 to 9 x 10(-9) cm2/s, and are not always improved in Na-rich form of clinoptilolite. The effect of temperature on diffusion coefficients is also examined, and Arrhenius activation energy is determined to be in the range of 3.02 to 13.9 kcal/mol, for all metals and materials, except Cu2+, which have extremely low activation energy in the natural sample, equal to 0.04 kcal/mol.     

Isotactic-specific polymerization of propene with an iron-based catalyst: polymer end groups and regiochemistry of propagation

Prevailingly isotactic poly(propylene) samples were prepared with a homogeneous catalytic system based on a bis(imino)pyridyl Fe(II) derivative and methylaluminoxane. The polymer microstructure is in agreement with Bernoullian statistics of dyad formation, implicating a “chain-end” mechanism of steric control. The latter is operative even at polymerization temperatures as high as +50°C. NMR analysis of polymer end groups indicates that chain growth proceeds via 2,1 monomer insertion. The last two findings are unprecedented for isotactic-specific polymerization of propene and are reasonably related to each other.     

An anion receptor with NH and OH groups for hydrogen bonds

An anion receptor with NH and OH groups as hydrogen bond donors has been prepared, and both groups are simultaneously involved in hydrogen bonding with anions.