The state of metals in the supported bimetallic Pt−Pd/SO4/ZrO2 system

The behavior of the metals in the Pt−Pd/ZrO₂ and Pt−Pd/SO₄/ZrO₂ systems was studied by DRIFT spectroscopy. After reduction of Pt−Pd/ZrO₂ at 100 °C, the states of the metals are mainly Pt⁰ and Pd⁰ with a minor admixture of positively charged forms of Pt⁺ or Pd²⁺. An increase in the temperature of reduction leads to the formation of a bimetallic alloy. In the Pt−Pd/SO₄/ZrO₂ system, the effects of alloy formation and the interaction of the surface SO₄ groups superimpose. At low reduction temperatures, the surface SO₄ groups interact mainly with palladium. The influence of the surface sites on both supported metals increases with increasing reduction temperature. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1265–1270, July, 1999.     

Synthesis and characterization of the ZnxCd1−xIn2S4 pseudoternary solid solution

We have synthesized several compounds of the Zn_xCd_1−xIn₂S₄ family by solid phase reactions and chemical transport reactions using iodine. The reaction products have been characterized as to composition, structure, and lattice dynamics. Here we discuss and compare the different results obtained by the two synthesis methods.     

Characterization of fine particles of the α-Fe2O3-SnO2 system with residual SO2−4 ions on the surface

The α-Fe₂O₃-SnO₂ system in fine powder form prepared by thermal decomposition at 873 K of precursory oxide hydroxides and containing a few weight percent of residual SO²⁻₄ ions on the surface has been characterized by X-ray diffraction, by the⁵⁷Fe and¹¹⁹Sn Mo¨ssbauer effects, and by other techniques. A certain α-Fe₂O₃-rich composition of this system has been used practically as an excellent but cheap CH₄ sensor as a city gas-leak alarm. Fine particles of generally ≲10³ nm³ with intermediate compositions remain far from the equilibrium state in the aspect that the solubility is drastically widened for both α-Fe₂O₃ and SnO₂, especially for the latter: solid solutions (Fe₂O₃)_1−x(SnO₂)_x withx ≲ 0.2 crystallizing in the corundum-type structure and withx ≳ 0.7 crystallizing in the rutile-type structure seem to be formed. The SO²⁻₄ ions may be considered to form microscopic cages around fine particles which, although being thermodynamically unstable, are nevertheless practically stable for more than a few years at the operating temperature of 673 K as demonstrated by the practical use as a sensor. A rapid separation into and a rapid particle growth of α-Fe₂O₃ and SnO₂ are brought about by thermal release of the SO²⁻₄ ions at 1073 K.     

Reactions of Au+ and Au− with benzene and fluorine-substituted benzenes

Reactions of gold anions and cations generated by laser desorption/ionization were studied in the FTICR spectrometer. Au⁻ associated with C₆F₆ to give the novel Au⁻(C₆F₆) complex, whose binding energy was estimated to be 24 ± 4 kcal mol⁻¹ from analysis of the radiative association (RA) kinetics. Au⁺ associated with C₆F₅H to give Au⁺(C₆F₅H), with binding energy estimated to be 31 kcal mol⁻¹. Au⁺ reacted with C₆H₆ to form the well known Au⁺(C₆H₆) and Au⁺(C₆H₆)₂ complexes. The observation of rapid charge transfer from Au⁺(C₆H₆) to C₆H₆ was interpreted as showing that benzene binds more strongly to neutral Au than to Au⁺. The neutral Au–C₆H₆ bond is accordingly concluded to be stronger than about 70 kcal mol⁻¹.     

The pre-resonance raman effect of the species I−·SO2 and SCN−·SO2

The Raman spectra of the solvated ions I⁻·SO₂ and SCN⁻·SO₂ were obtained using several exciting wavelengths. The excitation profiles show a pre-resonance enhancement of the SO₂ symmetric stretching mode in the solvates as the exciting frequency approaches the corresponding electronic transition frequency in the near UV. Such behavior and the presence of the overtone of the enhanced mode strongly indicate the charge transfer nature of the interaction between the ions and sulfur dioxide in the solvates.     

Secondary environment effects on the first step of the protonation of SO 4 2− in saline aqueous solutions

The solubility of strontium sulfate in the mixtures of isomolar LiClO₄(NaClO₄) and HClO₄ aqueous solutions was determined at 25°C and ionic strengths of I = 0.5, 1.0, 2.0, 3.0, and 4.0. At I>-2, the solubility of SrSO₄ as a function of the hydrogen ion (HClO₄) concentration passes through a maximum, clearly showing a substantial contribution from environment effects (H⁺ substitution for Li⁺ or Na⁺), which counteract complexation (i.e., HSO ₄ ^? formation). A correct method for separating these two effects was proposed, and the parameters of the environment effect and the standard values of pSP° and logβ° were evaluated.     

Hydrothermal processing and characterization of Ce1−xPbxO2−δ solid solutions

Nanocrystals of Ce_1?xPb_xO_2?δ (x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, and 0.35) were prepared by a hydrothermal reaction route. During the formation reaction, buffer solutions were explored as an effective additive to retain the initial molar ratio. With increasing the Pb²⁺ content, the average crystallite size was slightly retarded. Morphologies observed by transmission electron microscope indicated that the particles were spherical-like and highly uniformed. Pb²⁺ ions are homogenously distributed in the solid solutions. Analyses using X-ray diffraction, Raman and UV spectroscopies showed that the solid solubility limit of Pb²⁺ in CeO₂ was about x = 0.20. For x < 0.20, with increasing the Pb²⁺ content, the bulk conductivity increased, and the oxygen storage capacity was enhanced as followed by a decrease in reduction temperature.     

Lack of salt effect on the kinetics of the reaction SO2−4 + H3O+ → HSO−4 + H2O

It is found that the broadening of the 1100-cm⁻¹ line of SO⁻²₄, caused by increasing [H₃O⁺], is unaffected by addition of 4 M LiCl, NaBr, KCl and NH₄Cl. This finding is in line with the lack of influence of NaCl reported earlier. The significance of these findings, in terms of the reaction mechanism, is discussed.     

Formation of SO−2, SO2·O− and SO2·SO− by electron attachment to van der waals SO2 clusters

SO⁻₂, SO₂·O⁻ and SO₂·SO⁻ are produced by electron attachment to SO₂ clusters under single collision conditions. SO⁻₂, which is not produced at all in low-pressure ion sources, is more abundant than SO₂·O⁻ and SO₂ ·SO⁻. Measured relative attachment cross sections for these ions show significant differences when compared to O⁻ and SO⁻ produced by attachment to SO₂, i.e. the first resonance is very efficiently quenched in favor of SO⁻₂ production. This is in contrast to previous findings in O₂, CO₂ and N₂O.     

Thermochemical investigations of the systems KCl−KBr−H2O,K2SO4−(NH4)2SO4−H2O and KNO3−NH4NO3−H2O at 298.15 K

For the equilibrium solid phases occurring in the systems: KCl?KBr?H₂O, K₂SO₄?(NH₄)₂SO₄?H₂O and KNO₃?NH₄NO₃?H₂O, the concentration dependencies of differential solution enthalpies, Δ_sol H ₂ for several crystallization paths, were measured. The limiting differential solution enthalpies, Δ_sol H ₂ ⁰ , were determined by extrapolation of the above dependencies to the ionic strength,I _m ⁰ , corresponding to the appropriate binary solutions. For KCl?KBr?H₂O system only, the clear dependence between Δ_sol H ₂ ⁰ andI _m ⁰ values was found and discussed.     

Hydrolysis of Methylphenyldiethoxysilane with Rare Earth Superacid Catalysts SO2− 4/TiO2/Ln3+

Abstract

An environmentally benign hydrolysis of methylphenyldiethoxysilane (MePhSi(OEt)₂) catalyzed by a rare earth superacid catalyst SO ^2? ₄ /TiO₂/Ln³⁺ has been investigated. The hydrolysis rates decrease in the order SO ^2? ₄ /TiO₂/Nd³⁺ > SO ^2? ₄ /TiO₂/Y³⁺ > SO ^2? ₄ /TiO₂/Sm³⁺ > SO ^2? ₄ /TiO₂. The hydrolysis of MePhSi(OEt)₂ is a first-order reaction with respect to the concentration of MePhSi(OEt)₂, and the hydrolysis rate constant increases with increasing temperature. The activation energy E _a and the pre-exponential factor for this hydrolysis catalyzed by SO ^2? ₄ /TiO₂/Nd³⁺ have been determined as 322.50 kJ mol^?1 and 7.12 × 10⁴¹ s^?1, respectively. The products of the hydrolysis are oligomers of polymethylphenylsiloxane. The mechanism of MePhSi(OEt)₂ hydrolysis is also discussed.     

Study on the alkylation reaction of guanine and N-acetylguanine and the synthesis of 1''''-C alkylated carba-DHPG analogues

The alkylation reaction of guanine and N-acetylguanine with model compounds such as isopropyl bromide or 4-heptyl tosylate were studied. The reaction conditions such as temperature, solvent, base, and catalyst were examined for their effects on the reaction rate, and the yield and regioselectivity of the coupling reaction. The highest yield was obtained by using DMSO as the solvent. The reaction proceeded in a homogenous manner to give higher yield of 9-N and 7-N substituted product in a mole ratio of 1:1. The ratio could be raised to 2:1 if dibenzo-18-crown-6 was used as a catalyst. Using the above procedure, three carba-DHPG analogues bearing different 1'-C alkyl side chains were synthesized.     

Catalysis of SO_4~(2-)-ZrO_2/TiO_2 nanometer solid superacid

Superacid catalyst SO4 -ZrO2/TiO2 was applied in esterification of Acetic Acid and 2- Butanol. The particle size of ZrO2 in the catalyst was about 12.5 nm. In catalyst preparation conditions, the effect factor order on catalytic activity is H2SO4 concentration > calcination temperature > ZrO2 supported content. The optimum preparation condition is as follows: ZrO2 content 3.5g/g; calcination temperature 600℃, and H2SO4 concentration 0.5mol/L. The catalytic activity is 96.5 vol%. S…     

SO4−2/SnO2–catalyzed cyclocondensation for the synthesis of fully functionalized pyridines

An efficient and promising synthetic approach to assemble skeletons of multifunctionalized pyridine derivatives in presence of recyclable heterogeneous sulfated tin oxide (STO) catalyst has been evolved. The STO catalyst was used as a promoter for the cyclocondensation process in ethanol at 70°C. Overall performance of this catalyst was attributed to the cooperative contribution of its Lewis and Brønsted-Lowry acidic sites. Nanosized STO catalyst was synthesized by using sol-gel process and characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), ¹H-NMR, and scanning electron microscopy (SEM). This catalyst tolerates most of the substrates, and protocol shows precious capabilities consist of high yields, operational simplicity, less reaction time, and eco-friendly conditions. The newly synthesized heterogeneous catalyst was easily separated and reused. All the reactions are carried out for subsequent cycles without significant loss of catalytic activity and with good proficiency.     

The promotional effect of SO42− on N2 selectivity for selective catalytic oxidation of ammonia over RuO2/ZrO2 catalyst

Research on Chemical Intermediates - The promoting effects of SO42? on N2 selectivity for selective catalytic oxidation (SCO) of ammonia to nitrogen over RuO2/ZrO2 catalyst were...     

Reactivity of O2 − radical anions on hydrated ZrO2 surface

The concentration of O₂ ^? radical anions generated on the surface of hydrated ZrO₂ in an H₂O₂ solution was found to depend on H₂O₂ concentration. It was shown that this method can be used for detecting H₂O₂ in solutions at concentration as low as 0.01 wt%. The radical anions were found to react with organic molecules, even at room temperature. The decomposition kinetics of O₂ ^? radical anions was double-exponential with two reaction rate constants. The existence of two distinct rate constants suggests that two types of O₂ ^? radical anions with similar spectroscopic properties but different reactivity are present on the surface of hydrated ZrO₂. It is highly likely that different arrangements of hydroxyl groups near the radical anions account for the presence of the two types of O₂ ^? with different reactivity. The rate constants obtained in the presence of the organic compounds studied were found to conform with the expected order of reactivity: toluene > benzene ? hexane.     

Adsorption of chlorobenzene and benzene on γ-Al2O3/atl>

Adsorption of chlorobenzene and benzene on -Al₂O₃ was investigated in the 413--572 K temperature region at an adsorbate partial pressure ranging from 2 to 1000 Pa. The adsorption isotherms were measured and the isosteric heats and the entropy characteristics of adsorption were determined. The experimentally found and theoretically calculated entropy changes upon adsorption were compared. The mobility of the molecules of both adsorbates in the adsorption layer was limited with respect to that predicted by the ideal two-dimensional gas model. The mechanism of adsorption of benzene and chlorobenzene is discussed.     

Synthesis and studies of new organic conductors based on ET and EDT-TTF with the [ZnBr4]2− anions

New layer organic conductors based on bis(ethylenedithio)tetrathiafulvalene (ET)₄ZnBr₄Solv (Solv stands for solvent) were synthesized in various halobenzenes as solvents (C₆H₅X, X = Cl, Br, F and C₆H₄Y₂, Y = Cl, Br), as well as based on ethylenedithiotetrathiafulvalene (EDT-TTF)₄MBr₄(1,1,2-C₂H₃Cl₃) (M = Zn, Mn) and (EDT-TTF)₉(ZnBr₄)₂. The crystal structure of (ET)₄ZnBr₄(C₆H₄Cl₂) at room temperature was established. It was found to be composed of alternating conducting layers with various structure of stacks formed of the ET radical cations. Their conductivity and ESR spectra were measured. The ET compounds obtained are organic metals up to the temperatures of 4.2, 72, 80, or 183 K (depending on the solvent: C₆H₄Cl₂, C₆H₅Cl, C₆H₅Br, or C₆H₅F, respectively); the replacement of the solvent with more bulky 1,2-dibromobenzene led to the formation of a semiconductor. The compounds (EDT-TTF)₄MBr₄(C₂H₃Cl₃) with M = Zn, Mn and (EDT-TTF)₉(ZnBr₄)₂ retain metallic character of conductivity up to the temperatures of 260, 280, and 210 K.     

Modeling of esterification of acetic acid with n-butanol in the presence of Zr(SO4)2·4H2O coupled pervaporation

Modeling of esterification of acetic acid with n-butanol in the presence of Zr(SO₄)₂·4H₂O coupled pervaporation was studied in this paper. The influence of several process variables, such as process temperature, initial mole ratio of acetic acid over n-butanol, the ratio of the effective membrane area over the volume of reacting mixture and catalyst content, on the esterification was discussed. The calculated results for the conversion of n-butanol to water and permeation flux were consistence with the experimental data. The permselectivity and water content can be roughly estimated by the model equations.