Preparation of nanosize Pt clusters using ion exchange of Pt(NH3) 4 2+ inside mesoporous channel of MCM-41

Mesoporous molecular sieve MCM-41 with a Si/Al ratio of 35 was obtained by hydrothermal synthesis using a gel mixture with a molar composition of 6 SiO₂0.1 Al₂O₃1 hexadecyltrimethylammonium chloride 0.25 dodecyltrimethylammonium bromide 0.25 tetrapropylammonium bromide0.15 (NH₄)₂O1.5 Na₂O300 H₂O. The MCM-41 sample was calcined in O₂ flow at 813 K and subsequently ion exchanged with Ca²⁺. A small Pt cluster has been supported on the MCM-41 sample following a procedure using ion exchange of Pt(NH₃) ₄ ²⁺ . The Pt(NH₃) ₄ ²⁺ ion supported on MCM-41 has been activated in O₂ flow at 593 K and subsequently reduced with Fh flow at 573 K, in the same way used for the preparation of a Pt cluster entrapped inside the supercage of zeolite NaY. The resulting Pt cluster supported on the MCM-41 shows hydrogen chemisorption oftotal two H atoms per Pt at 296 K (based on the total amount of Pt) and high catalytic activity for hydrogenolysis of ethane. The chemical shift in¹²⁹Xe NMR spectroscopy of adsorbed xenon indicates that the Pt cluster is located inside the mesoporous molecular sieve.     

Selective vapor phase hydroformylation of ethylene over cluster-derived cobalt catalyst

Vapor phase hydroformylation of ethylene was studied with silica-supported metal catalysts. A cobalt metal catalyst derived from Co₂(CO)₈ gave propanal and its derivatives in as high selectivity of about 36% as Rh/SiO₂ catalyst under the reaction conditions of 1.1 MPa of a gas-mixture of ArCOC₂H₄H₂ = 1333 at 423–503 K. On the other hand, conventional cobalt catalysts derived from cobalt nitrate, chloride, or acetate, and other noble metal catalysts (Pd/SiO₂ and Ir/SiO₂) produced mainly ethane.     

Shape-Selective Alkylation of Biphenyl over H-[Al]-SSZ-31 with Propylene

Isopropylation of biphenyl (BP) over [Al]-SSZ-31, a large-pore, one-dimensional zeolite has been studied. Effects of temperature, pressure and SiO₂/Al₂O₃ ratio were examined. SSZ-31 was found to be an active catalyst in the isopropylation of biphenyl with propylene. The selectivity for 4-isopropylbiphenyl (4-IPBP) and 4,4-diisopropylbiphenyl (4,4-DIPB) was high among isopropylbiphenyl (IPBP) and diisopropylbiphenyl (DIPB) isomers, respectively, indicating SSZ-31 shows shape-selective catalysis. The selectivity for 4,4-DIPB decreased with temperature increase; correspondingly the selectivity for thermodynamically more stable isomers (3,3- and 3,4 DIPB) increased with temperature. The yield of IPBP isomers decreased while that of DIPB isomers increased with temperature increase. Pressure showed less effect on conversion; however, increase in pressure suppresses the isomerization of 4,4-DIPB to 3,3- and 3,4-DIPB. Conversion decreased with increase in SiO₂/Al₂O₃ ratio. At low SiO₂/Al₂O₃ ratio of 136, relatively high triisopropylbiphenyl (TriIPB) isomers were formed in bulk products and their amount decreased with increase in SiO₂/Al₂O₃ ratio.     

Partial oxidation of methane to synthesis gas

Partial oxidation of methane to synthesis gas has been carried out over a number of transition metal catalysts under a range of conditions. It is found that the metals Ni, Ru, Rh, Pd, Ir and Pt, either supported on alumina or present in mixed metal oxide precursors, will bring the system to equilibrium. The yield of CO and H2 improves with increasing temperature in the range 650–1050 K, and decreases with increasing pressure between 1 and 20 atm. An excellent yield (92%) is obtained with a 421 N₂CH₄O₂ ratio at 1050 K and atmospheric pressure, with a space velocity of 4×10⁴ hour^–1.     

Genetic aspects of interpopulational differences in pheromone blend of cabbage looper moth,Trichoplusia ni

The genetic basis of interpopulational differences in the pheromone blend emitted by the cabbage looper moth,Trichoplusia ni (Hübner), was examined by crossing individuals from a field-derived population (P₁) with individuals from a long-maintained laboratory colony (P₂). These colonies differed in the emission rate and relative proportions of four of the five known minor pheromone components, but not in the emission rate of the major component, (Z)-7-dodecenyl acetate (Z7-12Ac). These differences in pheromone blend were quantitatively small but biologically significant, because in the field, males responded preferentially to traps baited with a pheromone blend that is similar to that emitted by P₁ females relative to a blend similar to that emitted by P₂ females. In initial crosses, variation in the quantity and quality of pheromone blends among families of P₁, P₂, and F₁ hybrid females was examined. In F₁ females the relative proportions (quantity relative to the major component) of (Z)-5-dodecenyl acetate (Z5-12Ac) and (Z)-7-tetradecenyl acetate (Z7-14Ac) were intermediate to parental lines. In a second more extensive set of crosses, analyses included P₁, P₂, F₁, F₂, and selected backcrosses. The relative proportion of Z5-12Ac, Z7-14Ac, and Z9-14Ac emitted by F₁ females were intermediate to parental lines. The frequency distributions of relative proportions of these components emitted by females were not consistent with those expected under a single autosomal or sex-linked gene hypothesis, suggesting that more than one gene is involved in the quantitative differences in the pheromone blend.     

Catalytic conversion of methane to synthesis gas over europium iridate,Eu2Ir2O7: Anin situ study by x-ray diffraction and mass spectrometry

The selective partial oxidation of methane over the europium iridium pyrochlore, Eu₂Ir₂O₇, has been studiedin situ by using powder X-ray diffraction and mass spectrometry. At a temperature of 873 K and 1 atmosphere pressure, with a CH₄O₂ ratio of 21 under argon dilution, high yields of synthesis gas are obtained. The pyrochlore structure of the iridate is modified during the initiation of the catalyst, giving an active solid that is shown to comprise particles of iridium metal, 30 Å in diameter, supported on europium oxide, Eu₂O₃. The modification of the pyrochlore structure was monitored by X-ray diffraction, and the product gases were continuously analysed by mass spectrometry.     

31P and119Sn high resolution solid state CP/MAS NMR study of Al2O3-SnO2 systems

A series of Al₂O₃-SnO₂ catalysts with the mole ratio of Al₂O₃ to SnO₂ equal to 1:1, 1 0.5, 1 0.1, 1 0.05 and 1 0.01 were characterized by³¹P NMR of adsorbed trimethyl phosphine (TMP) and¹¹⁹Sn MAS NMR spectroscopy. It was found from³¹P NMR that no Brønsted acid sites exist in these samples. Pure SnO₂ shows two different types of Lewis acid sites; in the mixed oxide samples a Lewis peak characteristic of pure Al₂O₃ is always seen, together with either one or two other Lewis peaks, depending on the Sn concentration.¹¹⁹Sn CP/MAS NMR spectra of the highest Sn-content sample show one narrow line at –603 ppm superimposed on a very broad line, indicating a strong interaction between Al and Sn oxides.     

Chromium-titanium-antimony oxide composite anodes: Electro-organic oxidations

An activated titanium electrode with an oxide layer, composed of a mixture of Cr₂O₃, TiO₂ and Sb₂O₃ (optimal mole ratio chromium:titanium:antimony about 211) has been fabricated by thermal decomposition of the chlorides on a titanium substrate at 650°C. The black-green layer adheres well and has a thickness in the order of micrometres. Its structure is explained using a pore model, based on SEM, AES and electrochemical results. Service life time of electrodes in 1 M H₂SO₄ for oxidation of isopropanol in terms of the turn over factor of Cr₂O₃ is between 100 and 400.Preparative electro-organic oxidation of isopropanol, tetrahydrofuran and ethylbenzene have been performed with current densities of 0.5 to 5 mA cm^–2. The current efficiencies for the main products, acetone, -butyrolactone and acetophenone are 100, 53 and 20%, respectively. These results parallel those of the homogeneous oxidation with chromic acid in solution.     

Oxidation of limonene catalyzed by MnIII(Salen)Cl-H2O

The cationic Mn^III(Salen) complex was proved to be an effective catalyst for the oxidation of limonene with iodosobenzene as terminal oxidant. For reactions conducted in CH₂Cl₂ at rt, with molar ratio of 1 0.05 1 (limonene: catalyst: iodosobenzene) limonene oxidation does occur with an optimal conversion of 60%. The major products according to HRGC-MS and HRGC-IR analyses were cis- and trans-l,2-epoxylimonene (30% and 16.7%, selectivity, respectively), the two diastereoisomers of 1p-menthen-9-al (20% selectivity), and carvone (10% selectivity). A turnover of 60 was observed at 1 0.01 1 ratio. The higher selectivity toward epoxide formation supports the rebound oxygen mechanism.     

Combined catalytic partial oxidation and CO2 reforming of methane over supported cobalt catalysts

The combined partial oxidation and CO₂ reforming of methane to synthesis gas was investigated over the reduced Co/MgO, Co/CaO, and Co/SiO₂ catalysts. Only Co/MgO has proved to be a highly efficient and stable catalyst. It provided about 94–95% yields to H₂ and CO at the high space velocity of 105000 mlg^–1h^–1 and for feed ratios CH₄/CO₂/O₂=4/2/1, without any deactivation for a period of study of 110 h. In contrast, the reduced Co/CaO and Co/SiO₂ provided no activity for the formation of H₂ and CO. The structure and reducibility of the calcined catalysts were examined using X-ray diffraction and temperature-programmed reduction, respectively. A solid solution of CoO and MgO, which was difficult to reduce, was identified in the 800°C calcined MgO-supported catalyst. The strong interactions induced by the formation of the solid solution are responsible for its superior activity in the combined reaction. The effects of reaction temperature, space velocity, and O₂/CO₂ ratio in the feed gases (while keeping the C/O ratio constant at 1/1) were investigated over the Co/MgO catalyst. The H₂/CO ratio in the product of the combined reaction increased with increasing O₂/CO₂ ratio in the feed.     

Reduction of Zr (IV) in (KCl/NaCl) eutectic (50/50 mol%) containing KF/ZrCl4 in molar ratios of 6/1 or 4/1 at 750° C. Characterization of the dissolved species by IR spectroscopy

Infrared analysis of baths which are mixtures of (KCl/NaCl) (50/50) with KF and ZrCl₄ in the molar ratio 4 or 6, indicates that the species present at 750° C are ZrF₄ and K₃ZrF₇. Voltammetric study of these melts containing 1 wt % Zr shows that ZrF₄ reduces in three steps: ZrF₄ ZrF₂, ZrF₄ Zr, ZrF₂ Zr, whilst K₃ZrF₇ is reduced via: K₃ZrF₇ Zr or K₃ZrF₇ ZrF₂, ZrF₂ Zr. It appears that ZrF₄ vanishes completely by increasing the KF/ZrCl₄ ratio until the KF concentration is able to stabilize K₃ZrF₇ in the melt.     

Combustion and the transition to detonation in a gas mixture in a closed space

The possibility of going from deflagration to detonation in mixtures of CH₄+2(O₂+N₂) and 2H₂+O₂ ±N₂ (03.76) was investigated experimentally in a space enclosed by various combinations of three thin-walled metal concentric turbulator-sphere (diameters in a ratio 124) with large numbers of openings (permeability 0.1–0.4). Transition from deflagration to detonation was observed for 1 in the first mixture and for 3.2 in the second.Balashikha. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 3, pp. 171–174, May–June, 1993.     

Crystal structure and size distribution of Pt-Cu-Fe alloy clusters supported on carbon black

Carbon supported alloy electrocatalysts based on Pt, Cu and Fe (atomic ratios PtCuFe=211 and 611) are prepared at various alloying temperatures and are characterized by XRD and TEM techniques. Powder XRD analyses show that Pt₆CuFe clusters form a face-centered cubic structure (AuCu₃ type), while Pt₂CuFe clusters form an ordered alloy with a facecentered tetragonal structure (AuCu type) at higher temperature than 700C. Transmission electron micrographs reveal that the size of metal clusters increases gradually and size distribution becomes broader, as alloying temperature increases from 500 to 1100C.     

Mass spectrometric investigations on the release of inorganic species during gasification and combustion of Rhenish lignite

To reduce problems such as fouling, slagging and corrosion, which can occur during thermal utilisation of lignite, an enhanced understanding of the underlying release mechanisms for the involved Na-, K-, Cl-, and S-species is needed. Therefore basic investigations have been performed in an atmospheric tube furnace at 1400 °C under gasification and combustion like conditions in lab-scale experiments. Molecular beam mass spectrometry has been used for on-line qualitative and semi-quantitative analysis of the hot product gas. ³⁴H₂S⁺ has been formed during gasification experiments, while has been formed during combustion experiments. ³⁶HCl⁺, ⁵⁸NaCl⁺, ³⁹K⁺ (assumed to be partly a fragment of KCl) have been the main alkali and chlorine species and have been released mainly during pyrolysis phase. Linear correlation analysis has been undertaken to investigate the dependence of coal composition on the release of Na-, K-, Cl, and S-species. The correlations have been found to be similar for both gasification and combustion experiments. The release of ³⁴H₂S⁺ and is in high negative correlation with the Ca/S ratio and in high positive correlation with the S-content of the coals. The release of ³⁶HCl⁺ shows a negative correlation with the Na/S ratio and the Na/Si ratio of the lignite under investigation. The release of ⁵⁸NaCl⁺ depends with negative correlation on the S/Cl ratio and the content of Al + Si of the investigated lignite. The experimental results have been compared with thermodynamic equilibrium calculations. The release of H₂S, SO₂, and NaCl could be predicted with sufficient accuracy, though the release of HCl and K-species could not satisfactorily be predicted.     

Electrochemical investigation on prostaglandin F2α derivatives. II. Cathodic reduction of the iodinated prostaglandin F2α and its methyl ester

Based on voltammetric studies, preparative controlled potential reduction on an Hg cathode of iodinated PGF₂ (IPG) resulted in the production of either PGF₂ (nearly quantitatively) or PGF₂ and the biologically active PGI₁ (in a 2:3 ratio at maximum), depending on the medium and the potential used. The 5-Z isomer percentage in the PGF₂ thus formed varied between 50 and 60, while originally, before the anodic iodination and the subsequent reduction of IPG, this ratio was 98%. The electrochemically formed PGI₁ contained 95% 6-S and 5% 6-R isomer. In any selected medium the first voltammetric wave can be ordered to PGF₂ formation, and that of the second wave (in aqueous and non-aqueous media) to PGI₁ formation. On the basis of the experimental results a mechanism is proposed for the electroreduction process in aqueous media.     

Zirconium tetra-n-butylate modified with different organic acids: Hydrolysis and polymerization of the products

In this work; (a) complexation reaction of zirconium tetra-n-butylate, Zr(OBu ⁿ )₄, with MAc and different organic acids. (b) the hydrolysis reaction of modified Zr species, and (c) the polymerization reaction of complex products are studied. Zr(OBu ⁿ )₄ was reacted with different mole ratios of methacrylic acid (MAc) at room temperature and the maximum combination ratio was found to be 12 [Zr(OBu ⁿ )₄MAc] by FT IR. The modification of zirconium tetra-n-butylate with the acid mixtures [methacrylic acid-acetic acid (MeCOOH), methacrylic acid-propionic acid (EtCOOH), methacrylic acidbutyric acid (PrCOOH)] was made for a combination ratio of 111 [MAcRCOOHZr(OBu ⁿ )₄RMe. Et, Pr] and the products were characterized by¹H-NMR, FT-IR, and UV-spectroscopies. Following their synthesis, hydrolysis of the complexes with various amounts of water and polymerization with benzoyl peroxide were realized. The hydrolysis and polymerization products of the complexes were studied by Karl-Fischer Coulometric titration and thermal analysis respectively. Methyl-ethyl-ketone (MEK) and chloroform were chosen as solvents.     

Supported and sulfided Pb-Mo oxides: Active and stable hydrotreatment catalysts

A newly developed PbMo/Al₂O₃ HDS catalyst shows activity and stability that are comparable to or better than the traditional CoMo/Al₂O₃. Activity is optimum when the atomic ratio PbMo is 16. At that ratio, the generated surface phase(s) display maximum degree of Mo coordinative unsaturation, as measured by low temperature oxygen chemisorption.     

Synthesis of HFC-134a over CrF3/AlF3 catalysts

The effect of the structure of AlF₃ supports in CrF₃/AlF₃ catalysts and their activity were studied, and a selection of suitable reaction conditions for fluorination of trichloroethylene and HCFC-133a was made. We found that neither AlF₃ (- and -modifications) nor CrF₃/-AlF₃ exhibits significant activity for the reaction of HF with CCl₂=CHC1 or CF₃CH₂Cl. However, CrF₃/-AlF₃ exhibits high activity, which increases with increasing surface area and decreasing crystallite size of the -AlF₃ support, and that dramatically affects the fiuorination of CF₃CH₂Cl. Investigation of a series of CrF₃/-AlF₃ catalysts shows that the turnover rates per unit of the total surface area and of the free CrF₃ surface area significantly increase with increasing content of Cr³⁺ loading. Optimum temperature for the reaction of HF with CCl₂=CHCl is 260°C, while with CF₃CH₂Cl it is 350°C, with flow ratios HFTCE = 61 andHFHCFC-133a = 101.     

Phase inversions and properties of refractories in the system MgO-Al2O3-ZrO2

Conclusions In the compositions for the system MgOAl₂O₃ZrO₂=111 fired at 1750°, with the use of original components of different chemical activity, conditions are created for partial stabilization of the monoclinic zirconium dioxide on account of the magnesia which has not succeeded in reacting with the alumina, resulting in the formation of spinel.The presence in the fired products (together with monoclinic zirconia) of its cubic modification makes it actually possible to obtain thermal shock resistance and strong refractories on the basis of this system.The maximum quantity of stabilizing zirconium dioxide is present in the sinters in which we use chemically active ZrO₂ as the initial material obtained by the thermal decomposition of zirconium nitrate, and high-temperature fired magnesium oxides. The quantity of stabilized ZrO₂ in these sinters is about 70%.The quantity of stabilized zirconium dioxide in the compositions MgO-Al₂O₃-ZrO₂ depends on the activity of the alumina employed, as with the magnesium oxide, which is connected with the rate and temperature of formation of the magnesia spinel. The maximum quantity of cubic solid solutions is formed with the use of less active alumina.The technical properties of the products from firing these compositions are determined not only by their phase composition but also the distribution of the phases in the volume of the specimen.Translated from Ogneupory, No. 8, pp. 46–50, August, 1972.     

Electrochemical impedance and solid-state electrical characterization of silicon (1 1 1) modified with ω-functionalized alkyl monolayers

In order to reveal the relationship between the dipole moment and electric properties of organically modified semiconductor, a series of ω-functionalized alkyl monolayers on oxide-free silicon (Si-(CH₂)₁₀COOH, Si-(CH₂)₁₁CH₃, Si-(CH₂)₁₀COOC₂H₅, and Si-(CH₂)₁₁OH) was prepared and characterized. Electrochemical impedance measurements showed excellent insulating effects of these monolayers. It has been demonstrated that the dielectric constants of these organic monolayers are affected by the dipole moments introduced by the different terminal-groups. Solid-state electrical measurements showed that mercury | ω-functionalized alkyl monolayer | silicon junctions exhibit molecular tunability and a clear correlation between ideality factor and the film thickness/dielectric constant ratio. The barrier height is approximately proportional to the dipole moment of the monolayer. These results augment the possibility of fine-tuning the electrical properties of silicon-based microelectronic devices using functionalized organic monolayers.