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В научном совете по катализу

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Фонд им. К.И. Замараева




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Convenient route to oxovanadocene

Chemists at the University of California, Irvine, have devised a convenient synthesis of oxo(pentamethylcyclopentadienyl)vanadium dichloride [Organometallics, 16, 1994 (1997)]. Such transition metallocenes with "super" cyclopentadienes find use in experiments to increase solubilities and define or limit access to reactive sites for catalysis. But few such compounds containing vanadium are known. Chemistry professor Nancy M.Doherty, graduate student Arnis Aistars, and postdoctoral fellows Claire Newton and T hilo Rubenstahl have developed a "straightforward synthesis ... that is on a very easy to handle vanadium reagent". They add vanadium trichloride to a solution of pentamethylcyclopentadienyl(tributyl)tin to get pentamethylcyclopentadienylvanadium dichloride. Bubbling oxygen through a solution of the dichloride yields the oxo compound.

Advanced materials

B-Cyclodextrin-modified diphosphanes as ligands in "supramolecular" rhodium catalysts have unusually high substrate selectivity and activity in two-phase hydroformylations of olefins (M.T.Reetz and S.R.Waldvogel, ibid, 1997, 36, 870). The phosphanes are obtained in three steps from the easily accessible monotosylated cyclodextrin. Treatment with [Rh(cod)]BF4 yields a highly active catalyst which accumulates at the interface in two-phase water/olefin systems (the cyclodextrin macrocycle with its seven glucos e units is linked by 1,4-a-glycosidic bonds). Hydroformylation of, for example, 1-octene at 80 oC and 100 bar H2/CO takes 18 h and favours the n-aldehyde (nonanal) in 76 % yield over the iso-product (2-methyloctanal). Turnover numbers reach 3172, and the necessary catalyst amount can be as low as 0.03 mol %. The formation of an intermediate host-guest complex explains why olefin substrates with high association constants are preferred, why the new catalysts are over 150 times more active than conventional Rh catalysts based on P(C6H4SO3Na)3, and why often unreactive olefins such as E-3-hexene can also be hydroformylated.

Optimisation is in progress which should help to increase further regioselectivity and catalyst recovery.

Electrochemical capacitors or supercapacitors are attractive temporary storage devices for electrical energy. Carbon electrodes are widely used because they have the highly porous structure necessary for ion uptake. However, large parts of the micropores are not accessible for ion storage in activated carbon or carbon fibres. Better performance is found with electrochemical capacitors based on catalytically grown carbon nanotubes (C.Niu et al, Appl. Phys. Lett., 1997, 70, 1480). Carbon nanotubes not only have remarkably uniform diameters - 80 Е on average - they can also be obtained uncontaminated by other forms of carbon and free of catalyst residues. Treatment with nitric acid introduces -CO2H, -OH and C=O groups on the surface. Such functionalised carbon nanotubes are self-adhesive and stick to electrode surfaces without the need for binding materials. The resulting electrode consists of randomly entangled carbon nanotubes with a defined pore structure, highly accessible surface area, good thermal and chemical stability, and power densities exceeding 8 kW/kg.

New zeolite like structures

Chemists at the University of California at Santa Barbara have synthesized cobalt rich zeolite type crystals. The new materials may be useful for use in catalysis and gas separations. The cagelike frames of zeolites enclose molecular sized cavities and the porous materials belong to the aluminosilicate family both in natural and synthetic forms. The wide range of oxidation states and other chemical properties available to transition metals which have replaced the aluminum) is expected to be beneficial for promoting catalytic reactions. More details are found in Nature 388 (1997) 735.

Source: C@EN September1,1997, page11

Dioxin removed on a TiO2 V2O5 honeycomb

Greater than 99% of dioxins in incinerator flue gas can be destroyed by a new titanium-vanadium catalyst from Nippon Shokubai Co. New Japanese dioxin standards will go into effect in 1998 which specify dioxin levels of 0.2 ng/Nm3 for new furnaces and 0.5 ng/Nm3 for existing ones. The catalyst is in the form of a honeycomb and comprises mainly TiO2 and V2O5 and is installed in the exhaust duct of the incinerator. Dioxins are decomposed to CO2, HCI and H2O at ambient pressure and between 200 and 350°C. Destruction at levels above 99% were reported in a 10-m-t/day semicommercial facility with a gas stream that contained 5-10 ng of dioxin TEQ/Nm.

Source: Chemical Engineering September 1997

VOC removal by condensation

BOG Gases has developed a control and recovery system for volatile organic compounds produced by chemical plants. BOC's Kryoclean system works with a range of solvents including methylene chloride, toluene and methonal. Emissions from the plant are fed to a condenser, which is held at - 160°C. The condensed VOCs can be reused. Kryoclean use gaseous nitrogen as coolant and the required temperature is achieved by mixing liquid and gaseous nitrogen. A fraction of the vapourised nitrogen is siphoned off for use in other processes in the plant and this allows fresh liquid nitrogen to be added to the coolant circuit.

Source: Chemistry and Industry October 1997

Ammoxidation of ethane to acetonitrile over Co-Beta catalyst

Juejin Li and John N. Armor report in JCS, Chem. Commun. p. 2013, 1997, significantly improved yields of acetonitrile from ethane ammoxidation. They observed yields of 26% over a catalysts comprised of Co exchanged into beta zeolite. Previously the best oxide catalysts for this reaction only achieved a yield of 2.6 %. In addition the productivity of the catalyst as measured by the molar rate of acetonitrile production per gram of catalyst was also greater by a factor of 20 than the best complex oxide catalysts. The authors point out that metal cations exchanged into zeolites provide unique catalytic centres, as Lewis acid sites, with a higher site density than can be achieved with conventional oxides.

Source: JCS, Chem. Commun. p. 2103,1997

Oxidation decomposition of nitrogen-containing compounds over Pt/HM, Pd/HM and CuO/HM catalysts

An article with the above title has been reported by Yijun Zhong et ai. (Chin. J. Environ. Chem., 16 (1997) 204). The catalysts Pt/HM, Pd/HM and Cu/HM used were prepared by impregnation of 0.005 mol Pt(NH3)4CI2, 0,005 mol Pd (NH2)2Cl2 and 0.2 mol CuO, respectively on 100 g of a HCl treated natural mordenite. The oxidative decomposition of acetonitrile, nitromethane and ethylenediamine was studied. It was found that in the temperature range 250 to 600°C, three N-containing products (N2, N2O and NO2) were for med. N2 selectivity of the catalyst for nitromethane oxidation decreased with increasing temperature, but with those for acetonitrile and ethylenediamine oxidation a minimum was observed. Catalytic activity for acetonitrile and ethylenediamine decomposition was Pt>Pd>CuO, and that for nitromethane is Pt>CuO>Pd. N2 selectivity of the catalyst was CuO>Pd>Pt. The authors have claimed that if using CuO/HM as catalyst, a high N2 selectivity can be obtained at a proper temperature, and that the decomposition products can directly be released without a further treatment for removal of NOx from the products.

Ding-Zhu Wang

Nippon Shokubai: devise removes over 99% of dioxins from burning waste

More than 99% of dioxins produced when industrial waste is incinerated can be decomposed using a new catalytic device developed in Germany and licensed by Nippon Shokubai co. in Summer 1997, new Air Pollution Control legislation comes into effect in Japan, and this device enables companies to meet the dioxin emission standart set.

Sourse: Japan Chemical Week, 24 Jul. 1997, 38 (1935), 1

Focus on Catalusts is puplished monthly by the Royal Society of Chemistry, Cambrige, UK. Editor: Alan T. Comuns. Tel. (+44-1223) 423429 for sample issues/enquiries.


Фонд им. К.И. Замараева

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