Heats of xenon adsorption on Nax zeolite at high pressures and various temperatures

The heats of xenon adsorption on zeolite NaX at 299–467 K and 0–21 MPa were measured on a Tian-Calvet differential calorimeter. A significant temperature dependence of the heats measured at high occupancies of the adsorption surface was demonstrated.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 223–226, January, 1991.     

Investigations of TsVM zeolite acidities with different degrees of exchange of Na+ by H+

The method of programmed thermal desorption of ammonia has been used to establish that on the surface of the sodium form of type TsVM zeolite having a modulus SiO₂/Al₂O₃= 34.5 there are two types of acidic centers having ammonia desorption activation energies E_d equal to 40–45 and 80–100 kJ/mole. Replacement of Na⁺ by H⁺ leads to the appearance of a third type of center with a value E_D=130–150 kJ/mole. In this case in the IR spectra of specimens saturated with ammonia a band appears at 1410 cm_–1, which is evidence for the presence of NH ₄ ⁺ ions. Increasing the degree of Na⁺ replacement by H⁺ leads to a nonproportional rapid increase in the concentration of highly energetic centers, which may be explained by the partial transfer of aluminum into cationic positions with the formation of additional acidic centers.Translated from Teoreticheskie i Éksperimental'naya Khimiya, Vol. 22, No. 6, pp. 752–755, November–December, 1986.     

Relationship of the critical parameters of adsorbed gases with the initial heats of adsorption on carbon adsorbents

Conclusions The initial heats of adsorption on microporous carbon adsorbents (Saran and S charcoals) are proportional to the critical parameters of the adsorbates. Doubling of the initial heat of adsorption in the slit micropore of S-band charcoal relative to the initial heat of absorption on the basis graphite face was established experimentally.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2803–2805, December, 1985.     

Complex formation equilibrium and absorption on unmodified and modified silicas

We consider the relation between the equilibrium constants for complex formation and absorption involving the surface centers of silica and the parameters used in various fields of application of modified adsorbents.Institute for Surface Chemistry, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 3, pp. 361–370, May–June, 1991. Original article submitted March 5, 1991.     

Adsorption characteristics of chloroform on modified zeolites from gaseous phase as well as its aqueous solution

Adsorption characteristics of chloroform from its aqueous solution on Na–Y and Li–Na–Y modified by SiCl₄ were measured and compared with those on Na–ZSM-5 and Na-Mordenite.No adsorption occurred on Na–Y with high hydrophilicity, while the siliceous faujasites became capable of adsorption and its amount increased with increase in the Si/A1 ratio. Adsorption isotherms are of Langmuir type, suggesting that adsorption proceeds by pore filling. The adsorption amounts expressed in volume on Na–Y with high hydrophobicity corresponded to their pore volumes.Adsorption characteristics of chloroform from gaseous phase on Na–Y with different Si/A1 ratio were also measured. The adsorption capability decreased with increasing Si/A1 ratio.Immersional heats of zeolites into water or chloroform were measured in order to evaluate the surface affinity to both solvents. Immersional heats into water were almost constant (about 500 mJ·m^–2) for zeolites with their Si/A1 ratio below 10. The heats decreased with an increase in the Si/A1 ratio above 10, then became almost constant (about 120 mJ·m^–2) over 30 in their ratio. Heats of immersion of Na–Y series into chloroform were almost constant irrespective of their Si/A1 ratio, but decreased slightly when the ratio exceeded 20.Adsorption characteristics of chloroform could be well related to immersional heats into both solvents.     

Heats of adsorption of CO2 on high-silicon zeolites ZSM-5 and silicalite

The heat of adsorption of C0₂on NaZSM-5 at zero occupancy is 50.0 kJ/mole. The differential heats have two linearly descending segments, corresponding to the formation of two types of adsorption complexes with one or two C0₂ molecules, on the average. The heat of adsorption on silicalite coincides with the heat of adsorption of CO₂ on the noncationic segment of the NaZSM-5 zeolite structure (28–29 kJ/mole). The adsorbate-adsorbate interaction forces are not evident on the zeolites up to 1.5 mmole/g occupancy. The isotherms for the adsorption of C0₂ on zeolite NaZSM-5 and silicalite at 303 K in the occupancy region of 0–1.5 and 0–0.5 mmole/g are completely described by VMOT equations.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2636–2638, November, 1989.     

Cluster structures for water adsorbed on SiO2

The MO LCAO SCF method has been used in the MNDO approximation to examine the electronic structures and formation energies for adsorption complexes for water on SiO₂ stabilized by hydrogen and coordination bonds. Stabilization by several hydrogen bonds cannot explain the high initial heats of adsorption for dehydrated silica. H₂O coordination complexes give higher energies, and hydroxylated silicon atoms on SiO₂ are considered as primary water-adsorption centers.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 5, pp. 532–545, September–October, 1988.     

ESR study of electron interaction in a Tc/Al2O3 system

An investigation was made into the nature of paramagnetic centers in a Tc/Al₂O₃ system under varying conditions as to heat treatment and technetium content, and in O₂ and CO adsorption environments. It was found that in the case of reduction at 573 K Tc²⁺ ions and, conceivably, other ionic forms developed and stabilized on the carrier surface. After reduction at 973 K two types of electron center appeared, whose concentration increased as reduction was prolonged. Signals were observed in the low fields (3–20 mT) of the ESR spectra having g₁ 13.5 and g₂>30, which could be assigned to free charge carriers in a cluster of metal atoms or ions. Adsorption of O₂ at 300 K caused O ₂ ^– ion radicals to form on the surface of the reduced Tc/Al₂O₃ samples, both electron centers and technetium ions constituting the electron donors. In the case of CO adsorption paramagnetic (CO) ₂ ^– particles appeared on the Tc/Al₂O₃ samples after prolonged exposure. On reaction with O₂ two types of O ₂ ^– ion-radical with differing thermal stability were formed.Institute of Physical Chemistry, Russian Academy of Sciences, Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 9, pp. 1972–1978, September, 1992.     

Structure of silica

Summary 1) Preliminary data have been obtained, indicating the existence of structures of two types in silicathree-dimensional framework and double-chain. 2) A model has been proposed for the structure of silica, which resembles the structure of layer clay minerals. 3) The absorption bands in the range of the OH and (Si–(OH) stretching vibrations have been interpreted. 4) The adsorption centers on silica for proton-donor molecules are the oxygen atoms of OH^– ions and SiOH groups; the adsorption centers for electron-donor molecules are the hydrogen atoms of the accessible SiOH groups. 5) It has been shown that the solid-state lattice vibrations are changed under the influence of adsorption.All-Union Scientific-Research Institute for Petroleum Refining, Moscow. Translated from Zhurnal Strukturnoi Khimii, Vol. 18, No. 1, pp. 97–106, January-February, 1977.     

A Microcalorimetric Study of Water Vapor Sorption on Morphine Sulphate

Water vapor sorption on morphine sulphate was studied in a twin double sorption microcalorimeter at 25°C. The vapor sorption isotherm and the differential heats of sorption were determined simultaneously from dry condition to a water activity of 0.99. Two well resolved hydration steps were obtained on the sorption isotherm at water activities of 0.01 and 0.22 corresponding to the formation of dihydrate and pentahydrate of morphine sulphate. They were accompanied by constant values of the differential heats of sorption: –24 kJ mol^–1(H₂O) for the dihydrate formation and –10 kJ mol^–1(H₂O) for the pentahydrate formation.The calorimetrically obtained sorption isotherms were compared with the results of Karl Fisher titrations of morphine sulphate samples equilibrated at different water activities. The appearance of a liquid phase in the morphine sulphate at high water activities is discussed on the basis of the obtained differential heats of sorption and measured heat capacities of morphine sulphate at different water activities.This revised version was published online in November 2005 with corrections to the Cover Date.     

Dehydration of the surface of pyrogenic silica by 1H nuclear magnetic resonance

The proton magnetic resonance method has been used at a frequency of 500 MHz in the temperature ranee 290–870 deg K to investigate dehydration of Aerosil surface. Conclusions have been drawn in relation to the nonhydroxylic nature of the primary water adsorption centers.Translated from Teoreticheskayi i Eksperimental'naya Khimiya, Vol. 24, No. 2, pp. 235–238, March–April 1988.     

Influence of packing of the reactants and products in solution on the volume parameters of the Diels-Alder reaction

The possible causes of a dramatic difference in the volume parameters (by up to 15–20 cm³ mol^–1) of the Diels-Alder reactions involving bulky and small reactants are discussed. The partial molar volumes of anthracene and 9,10-dihydroanthracene and the heats of their solution in six solvents were determined.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 10, 2004, pp. 1674–1680.Original Russian Text Copyright © 2004 by Kiselev, Kashaeva, Potapova, Shikhab, Konovalov.This revised version was published online in April 2005 with a corrected cover date.     

Thermochemistry of nonaqueous solutions of electrolytes: II. Heat of solution of sodium iodide in water-dioxane

The heats of solution of sodium iodide in water and water-dioxane (45. 95, 52. 55, and 68. 15% by wt dioxane at 25° (also for 2° for the first of these mixtures) are reported. The process becomes more exothermic as the dioxane content increases; a qualitative interpretation. The temperature coefficient of the integral heat is zero at 2–25°C for 45. 95 % by wt dioxane. The initial heats of solution of NaI at 25° in water and the mixtures are –1. 81, –4. 99, –5. 39, –6. 63 kcal/mole and bear a linear relation to the composition and dielectric constant of the solvent.     

Discrete site model for methane adsorption on microporous adsorbents

A statistical thermodynamic treatment of adsorption on zeolites assuming quasiindependent sites has been applied to methane adsorption on the zeolite NaX and the carbon adsorbent PAU-10 from polyvinylidenechloride in the pressure range 0.1–10⁷ Pa and 120–410 K. The relation between the isosteric adsorption heats and the magnitude of adsorption at different temperatures was calculated for both adsorption systems. A sharp decrease in these heats was observed at high adsorption values up to and in the supercritical temperature range.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 974–978, May, 1990.The authors would like to thank V. A. Bakaev for discussions about this work.     

Gas chromatographic investigation of adsorption equilibria on graphitized thermal carbon black

Summary Retention volumes and heats of adsorption at low surface coverages of graphitized thermal carbon black (GTCB) for C₆–C₁₄ aromatic hydrocarbons have been determined. The dependence of heats of adsorption of these molecules on their structure and the number of carbon atoms in the molecule have been investigated. Substitution in the ring in methylbenzenes is not equivalent to the lengthening of the side-chain in the isomers of n-alkylbenzenes and gives rise to a much greater increase in the retention volumes and heats of adsorption.     

New thermochemical reference system expressing the relative energy of organic compounds

To facilitate the comparison of the energies of nonisomeric organic compounds, we introduce a new thermochemical reference system. The reference substances, instead of elements, are series of compounds: unbranched alkanes and their selected derivatives (halogenides, ethers, sulfides, and tertiary amines). The relative enthalpies calculated from the heats of formation directly reflect the relative energy of both isomeric and nonisomeric compounds, and they can be used in the calculation of the heats of reaction. The relative enthalpies of the elements (in kJ/mol) are C, –22.846; H₂, 43.426; O₂, 251.66; N₂, –178.62; S, –41.62; F₂, 396.12; C1₂, 94.22; Br₂, 8.16; and I₂, –107.64.     

Mechanism of cationic polymerization of glycidic esters

The kinetics of cationic polymerization of glycidyl esters (glycidyl acetate, glycidyl benzoate, glycidyl naphthoate) were studied. The kinetic parameters of this process were determined. It was shown that the rate of polymerization is anomalously dependent on the polarity of the medium. The existence of an internal complexation and an equilibrium between two types of active centers, determining the rate of the process, has been suggested.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 6, pp. 722–726, November–December, 1985.     

Study of the reaction of water vapors with carbon fibers by an adsorption-calorimetric method

The isotherms and differential heats of adsorption of water vapor on two samples of activated carbon fiber material (CFM) have been measured. The adsorption of water vapor on CFM has been found to take place virtually over the entire range of surface occupation with thermal effects lower than the heat of condensation. The appearance of endothermic thermal effects on the thermograms made it possible to establish the hitherto unknown submicroscopic swelling of carbon fibers caused by water vapors.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 30, No. 2, pp. 85–88, March–April, 1994.The authors are grateful to the State Commitee of the Ukraine for Problems of Science and Technology for financial support of this study.     

Forms of adsorption of methanol on anatase and directions of their transformation

The adsorption of methanol on titanium(IV) oxide in the anatase crystalline modification was investigated by IR spectroscopy and thermal desorption. It was established that coordinationally bonded alcohol and two types of methoxides are formed on the surface of the titanium dioxide (anatase). The adsorption centers of the methanol were found. The thermal stability and the degree of particípation in oxidation were determined for the surface structures of the adsorbed alcohol. The possibility of the conversion of the coordinationally bonded alcohol and the weakly bonded methoxyl into partial oxidation products and the strongly bonded methoxyl into total oxidation products was demonstrated. In the investigated system formate complexes at concentrations sufficient for detection by IR spectroscopy were only formed with the participation of the oxygen of the gas phase through further oxidation of the strongly bonded methoxyls.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 6, pp. 707–712, November–December, 1988.The authors thank V. A. Gerasimova and S. K. Anan'in for assistance in the production of the experimental results.     

IR spectroscopic study of adsorption of ammmonia on Brønsted acid centers of a fluorinated surface of silica

The adsorption of aqueous ammonia solution vapor on a fluorinated surface of aerosil was studied by IR spectroscopy. The adsorption of NH₃ is accompanied by the appearance of absorption bands at 740, 1450, and 3330 cm^–1 in the IR spectra. The surface compounds were identified from the results of a study on the thermal degradation of adsorbed complexes and an analysis of literature data. The IR absorption bands at 1450 and 3330 cm^–1 correspond to deformational and stretching vibrations of the N-H bonds of the ammonium cation, The 740 cm^–1 band was assigned to the vibrations of the Si-F bonds in the complex anion, containing a fragment of SiO₂ surface, a fluorine atom, a hydroxyl group and a molecule of water. In this surface-coordinated compound, the silicon atom has a coordination number of six.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 6, pp. 747–751, November–December, 1986.