Alkylaromatic carbene ions on H-TsVK zeolites

Conclusions The adsorption of styrene (298 K), triphenylcarbinol (298 K), and of propylene with toluene (473 K) on H-TsVK zeolite leads to the formation of alkylaromatic carbocations which are stable up to 473–573 K and are characterized by bands in DRS at 320–330 and 400–440 nm and in IR by vC=C of the aromatic ring in the regions 1500 and 1610–1620 cm^–1. In the adsorption of benzene, toluene, isopropylbenzene, and 1,3-dimethylnaphthalene at 298 K, only weakly bonded surface complexes are formed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1486–1490, July, 1989.     

Adsorption of acetone and hydrogen on aluminum oxide

It was established that the adsorption of acetone at 333–365°K on the surface of aluminum oxide proceeds irreversibly and is accompanied by chemical interaction of chemisorbed molecules. A probable mechanism of the surface condensation of acetone is proposed.Translated from Teoreticheskaya i Éksperlmental'naya Khimiya, Vol. 21, No. 3, pp. 329–333, May–June, 1985.The authors would like to express gratitude to V. K. Pogorelov for his useful discussion of the results of the work.     

Kinetics of nitric oxide reduction with pure and potassium-doped carbon

Summary The kinetics of the reduction of nitric oxide with pure and potassium-doped carbon, NO+C=1/2 N₂+CO, were investigated. For the reaction of NO with pure carbon, measurements were made in the temperature range from 1750 K to 2130 K and at initial NO pressures between 5×10^–3 Pa and 7×10^–2 Pa. The reaction was first order with respect to nitric oxide at NO pressures below 3×10^–2 Pa. The activation energy was 54 kJ/mol for temperatures below 2000 K, while at higher temperatures a second (parallel) reaction became noticeable with a definitely higher activation energy. Potassium-doped carbon was prepared by a molecular beam technique. AES studies verified that potassium was intercalated into the graphite surface and that the potassium-to-carbon ratio changed continuously with sample temperature. The reduction of NO with K-doped carbon was investigated in the temperature range from 710 K to 1080 K and at initial NO pressures between 7×10^–5 Pa and 6×10^–4 Pa while monitoring, in-situ using AES the K/C-ratio of the surface. The NO reduction rate rose linearly with K/C. Compared to pure carbon, the reaction rate for the NO reduction with K-doped carbon increased by a factor in the range of 10⁴. The activation energy for the NO reduction with K-doped carbon was found to be 82 kJ/mol.     

Photophysics of pyrene adsorbed on aerosil

The spectral luminescence properties of pyrene adsorbed on the surface of aerosil have been investigated at different thermal activation temperatures (453, 773, and 1073°K) and different degrees of surface coverage (0.01–10% of monolayer). The differences from the properties of pyrene adsorbed on silica gel are dictated by the high polarity of the aerosil surface, the less significant rearrangement of its hydroxyl coverage in thermal treatment, and its pronounced energetic discrete homogeneity at low degrees of coverage.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 1, pp. 121–125, January–February, 1987.     

Surface Properties of Polyacid–Poly(N-Vinyl Pyrrolidone) Complexes

The effect of the complexation of polyacrylic (PAA) and polymethacrylic (PMAA) acids with poly(N-vinyl pyrrolidone) (PVP) on their surface properties was studied by measuring surface tension, conductivity, and the viscosity of aqueous mixed polymer solutions, as well as by the potentiometric titration at 293.15 K. The values of relaxation times and the surface activity of polycomplexes were calculated from kinetic data and the surface tension isotherms of the solutions. The complexation was found to increase the surface layer relaxation time, surface activity, and the ability of the macromolecules to reduce the surface tension of solvent. The values of adsorption free energy were calculated for PVP and polycomplexes. They were equal to –22.0, –23.0, and –24.8 kJ/base-mole (per one mole of PVP monomer unit) for PVP and PMAA–PVP and PAA–PVP polycomplexes, respectively.     

Effect of preparation pH on pore structure of silica gels

Surface characterization of silica gels prepared at different gelation pH from water glass and sulphuric acid were made by argon adsorption at 77 K using continuous volumetric method. While microporous silica gels prepared in the pH range of 1–3 had BET surface areas of 504–571 m² g^–1, total pore volumes of 0.26–0.31 cm³ g^–1 and micropore volumes of 0.16–0.23 cm³ g^–1, mesoporous silica gels prepared in the pH range of 3.36–0.65 had BET surface areas of 374–530 m² g^–1 and pore volumes of 0.61–0.79 cm³ g^–1.     

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.     

The liquid–gas interface of oxygen–nitrogen solutions 2: Description in the Framework of the van der Waals gradient theory

The van der Waals gradient theory (vdW GT) is used to calculate surface tension, density profiles, adsorption, the Tolman length and to determine the position of dividing surfaces in the liquid–gas interface of an oxygen–nitrogen solution. The Helmholtz energy density (HED) is determined via an equation of state (EOS), unified for a liquid and gas, which describes stable, metastable and two-phase states of solutions. The influence parameters are calculated from data on the surface tension of pure components with the use of the mixing rule. At temperatures T > 100 K the vdW GT describes experimental data on the surface tension of oxygen–nitrogen solutions [V.G. Baidakov, A.M. Kaverin, V.N. Andbaeva, The liquid–gas interface of oxygen–nitrogen solutions: 1. Surface tension, Fluid Phase Equilib. 270 (2008) 116–120] within the experimental error. It is shown that the Tolman length, which determines the dependence of surface tension on the curvature of the dividing surface, depends considerably on the solution concentration.     

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.     

Volume diffusion of I− anions in near surface region of silver

Volume diffusion coefficients of I^– anions in the near surface region of silver have been determined using¹³¹I. The distribution of the labelled ions with depth is determined by acid etching and counting the residual activity. The coefficient of diffusion is determined for surface layers of three different thicknesses over the temperature range 373–823 K. The mechanism proposed assumes the dissociation of Ag⁺I^– in surface layer and the diffusion of I^– into the interstitial free space immediately beneath the surface. This process is found to be accompanied by a small negative entropy change.     

Reaction of oxygen with adsorbed hydrogen species of a reduced Pt/TiO2 catalyst

Reaction of oxygen with the adsorbed hydrogen species of Pt/TiO₂ catalysts reduced in the temperature range of RT-773 K has been studied by temperature-programmed oxidation (TPO). It is obtained that the Pt-assisted reaction of oxygen with both the surface hydroxy groups and titanium hydride species occurs in the temperature range of 320–450 K; direct oxidation of the surface hydrogen species takes place on the surface of TiO₂ in the temperature range of 500–600 K; and oxygen reacts with the stored hydrogen species in the sublayer and bulk of the TiO₂ support when the temperature was increased to above 600 K.     

MFTIR spectra of polyethylene synthesized on germanium surfaces

MFTIR spectra of thin layers of polyethylene synthesized on the surfaces of germanium monocrystals in the 700–3000 cm^–1 range have been investigated. The optical constants of the polymer n() and () have been calculated in the range of natural absorption corresponding to the C-H valence vibration bands. Dichroism of the 2848 and 2912 cm^–1 bands disclosed is caused by the orienting influence of the monocrystal surface and in value is comparable with values obtained for monoaxially oriented massive specimens of polyethylene having a high degree of crystallinity. There have been established reversible changes of the relative orientation function of the macromolecule surface layer during heating and cooling of the specimens in the temperature range 293–355 K. This is explained by the nematic state of the polymer in the thin layer, the macromolecules of which are chemically bonded to the surface of the germanium monocrystal.Deceased.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 3, pp. 380–383, May–June, 1988.The authors express their gratitude to K. K. Kalnin'sh for valuable discussion of material in the article and to M. E. Yudovich for his assistance in the calculations.     

Numerical modeling of polymolecular adsorption of argon on a model amorphous oxide

Using the Monte Carlo method for the grand canonical ensemble, we have calculated the Ar adsorption isotherms in the range 77–107 K on an inhomogeneous surface with random close packing of spheres (the Bemal model), representing oxygen ions in a model oxide. The isotherm at 77 K is very close to the standard Ar adsorption isotherm on nonporous silica. The difference involves the weak step character of the calculated isotherm. The adsorbate on the model oxide at 77 K has a layered structure, reminiscent of the structure of Ar on the basal face of graphite, but significantly more extended. The atomic area of Ar depends on the method for determination of the capacity of the monolayer and lies within the range 0.1–0.13 nm².Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2007–2011, September, 1990.     

Photonics of perylene on the surface of SiO2

Stationary and kinetic spectrofluorometry and diffuse reflection spectroscopy have been used to study the photophysics and photochemistry of perylene, adsorbed on the surface of porous (silica gel) and nonporous (aerosil) silica after thermal activation in air (at 453, 773, and 1073 K) as function of the degree of surface coverage.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 2, pp. 231–235, March–April, 1988.     

Silica Matrix with anhydride groups for immobilization of enzymes

We have studied the process of preparing a silica support with anhydride groups. The process includes introducing vinyl groups onto the surface with subsequent radiative copolymerization of maleic anhydride with them. The maximum degree of grafting of the functional groups of the matrix occurs for -irradiation doses of 20–30 Mrad. The carboxyl groups grafted to the aerosil surface, formed upon hydrolysis of the support, can be converted to anhydride by calcination at 403 K for 3 h.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 6, pp. 750–753, November–December, 1989.     

The liquid–gas interface of oxygen–nitrogen solutions: 1. Surface tension

The capillary method of surface tension measurement has been used to measure the surface tension of oxygen–nitrogen solutions in the temperature range from 80 to 132 K. At temperatures below the nitrogen critical temperature (T_c = 126.2 K) the capillary constant and the surface tension of solutions are smaller than their additive values and vary linearly with the temperature. Experimental data are compared with the results of calculating the surface tension by the theories of Pinnes and Rowlinson.     

Solubility of Solid 2,3-Dimethylbutane and Cyclopentane in Liquid Argon and Nitrogen at the Standard Boiling Points of the Solvents

The solubilities of solid 2,3-dimethylbutane and cyclopentene in liquid argon at a temperature of 87.3 K and in liquid nitrogen at 77.4 K have been measured by the filtration method. The hydrocarbon contents in solutions were determined using gas chromatography. GC–MS was used to identify impurities in solutes. The experimental value of the mole fraction solubility of solid 2,3-dimethyl-butane in liquid argon at 87.3 K is (8.26 ± 1.60) × 10^–6 and (2.77 ± 0.94) × 10^–8 in liquid nitrogen at 77.4 K. The experimental value of the mole fraction solubility of solid cyclopentene in liquid argon at 87.3 K is (5.11 ± 0.44) × 10^–6 and (4.60 ± 0.76) × 10^–8 in liquid nitrogen at 77.4 K. The Preston–Prausnitz method was used for calculation of the solubilities of solid hydrocarbons in liquid argon in the temperature range 84.0–110.0 K and in liquid nitrogen from 64.0 to 90.0 K. The solvent–solute interaction parameters l ₁₂ were also calculated. At 90.0 K liquid argon is a better solvent for investigated solid hydrocarbons than is liquid nitrogen.     

Mechanism of heterogeneous catalytic oxidation of acetone vapor on vanadium pentoxide

We have used an extensive set of kinetic data to consider the probable reaction mechanism for the oxidation of acetone on vanadium pentoxide at 433–473 K. It is concluded that a significant part is played by the stage of the reoxidation of the catalyst surface, coupled with the transfer of oxygen during the formation of the reaction products. Computer calculations have been used to determine the best values of the rate constants of the separate stages of the proposed mechanism.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 1, pp. 115–120, January–February, 1990.     

Desorption of catalytic oxidation products of o-xylene from the surface of carbon catalysts

In a study of the oxidation of o-xylene on carbons (in the range of 523–573°K) under nonstationary conditions, it was found that considerable amounts of the reaction products (phthalic anhydride and CO₂) are adsorbed on the surface of the catalysts (phthalic anhydride more strongly than CO₂). The adsorption of the products is chemical in nature, like the adsorption of initial o-xylene. The bond between the adsorbates and the surface weakens with increase in the number of acidic groups on the surface. Since the active carbons are characterized by a higher basicity than the oxidized ones, in the first case the oxidation products of o-xylene are adsorbed more strongly and desorbed more slowly.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 4, pp. 499–503, July–August, 1986.     

Adsorption of Freon 113

Summary The adsorption of Freon 113 (1,1,2 trichloro-1,2,2 trifluoroethane) at 260–310 K on Graphon was measured and compared with the adsorption of krypton at 104–120 K on the same surface. The adsorption isotherms, and resulting thermodynamics, for both adsorbates were similar over the entire pressure range studied. Surface area analysis of the data suggests that the Freon molecule occupies approximately 2.5 times the area of the krypton molecule on Graphon. Further, the Freon molecules are hindered in their rotational freedom on this surface at these temperatures, with their dipole axes aligning perpendicular to the surface of the Graphon.

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Zusammenfassung Es wurde die Adsorption von Freon 113 (1,1,2 Trichlor-1,2,2 Trifluoräthan) an Graphon bei 260–310 °K gemessen und mit der Adsorption von Krypton bei 104–120 °K auf der gleichen Grenzfläche gemessen. Die Adsorptionsisothermen und die daraus resultierenden thermodynamischen Daten waren für beide Adsorbate im gesamten untersuchten Druckbereich ähnlich. Eine Analyse der Daten legt nahe, daß ein Freonmolekiil annähernd das 2,5fache der Fläche eines Kryptonmoleküls auf Graphon beansprucht. Es ist anzunehmen, daß die Freonmoleküle auf dieser Oberfläche und bei diesen Temperaturen in ihren Rotationsfreiheitsgraden gehindert sind und ihre Dipolachsen senkrecht zur Oberfläche liegen.

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With 9 figures and 2 tables