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Премии правительства РФ РФ:
Конкурсы на соискание золотых медалей и
премий имени выдающихся ученых,
проводимые Российской академией наук
в 2002 - 2003 гг.

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Catalyst system for CO2 fixation

A new catalyst system gives high yields of cyclic carbonates from the coupling of epoxides and carbon dioxide under mild conditions. Northwestern University chemists SonBinh T. Nguyen and Robert L. Paddock report efficient CO2 fixation using a chromium (III) bis(salicylaldimine) complex as catalyst and 4-dimethyl-aminopyridine as cocatalyst [J. Am. Chem. Soc., 123, 11498 (2001)]. They find that a variety of terminal epoxides - including aliphatic and aromatic epoxides and epichlorohydrin - give the corresponding cyclic carbonates in near quantitative yield and 100 % selectivity. The catalyst system is air stable, doesn't require any solvent, and maintains its activity over long periods of time. In contrast to other catalytic processes where CO2 is used as a reagent, high activity is attained at a pressure of only 50 psig."This is a truly green reaction," Nguyen tells C&EN:"No side product and no waste".

Nanoparticles pass aquifer test

Palladium-coated iron nanoparticles 100 to 200 nm in diameter have been demonstrated in a field trial to be potentially useful for reducing chlorinated hydrocarbons to nontoxic hydrocarbons in contaminated groundwater plumes [Environ. Sci. technol., 35, 4922(2001)]. Generally, colloidal or particulate additives, such as microscale iron particles, have low mobility in aquifers and so don't perform optimally. To reduce the mobility problem, graduate student Daniel W. Elliott and environmental engineering professor Wei-xian Zhang at Lehigh University determined the optimum particle size. The Fe-Pd couple creates numerous galvanic cells that allow iron to become oxidized more rapidly, they find. The palladium remains unchanged, but it may promote dechlorination by catalytic hydrogenation. Lab tests confirm that the nanoparticles are effective for reducing an array of chlorinated hydrocarbons. In a field test, a nanoparticle suspension was fed into a small test area lying within a larger area contaminated with trichloroethene (TCE). Samples from monitoring wells show that up to 96 % of TCE in the migrating groundwater - about 500 μg per L - can be reduced, mostly to ethane. The ability to use the nanoparticles in contaminant"hot spots," slurry reactors, or anchored to activated carbon makes them amenable to many applications, the researchers note.

A step toward clean catalytic processes

Using a microporous membrane to immobilize catalysts, researchers in the Netherlands have demonstrated a technique for carrying out reactions in supercritical CO2. The method may lead to advances in clean industrial catalytic processes. Supercritical CO2 is attractive for catalytic reactions because it is more environmentally friendly than conventional solvents and because, in general, homogeneous catalysis offers higher activity and better product selectivity than heterogeneous catalysis. But taking advantage of these benefits requires a suitable procedure for separating catalyst from product and finding catalysts that are soluble in CO2. A solution to this problem has been found by professors Jos T.F. Keurentjes and Leo J.P. van den Broeke in the department of chemical engineering and chemistry at Eindhoven University of Technology, chemistry professor Gerard van Koten at Utrecht University, and their coworkers. They devised a reactor in which an ultrathin silica membrane with 0.6-nm pores immobilizes a derivative of Wilkinson' s catalyst that's been modified with perfluoroalkyl side chains for enhanced solubility [Angew. Chem. Int. Ed., 40, 4473 (2001)]. Tests run on a model system - hydrogenation of 1-butene - show good catalytic performance and no transport of the catalyst through the membrane.

Zeolites expand under pressure

Zeolites are known for their unusual behavior: they have been observed to contract when heated and to expand under high pressure. Although temperature-dependent studies have been carried out, the porous framework of zeolites and experimental complexities have hampered efforts to observe pressure-induced changes. An international research team, including lead author Yongjae Lee, a postdoc at Brookhaven National Lab, has now overcome those challenges [J. Am. Chem. Soc., 123, 12732 (2001)]. The team focused on natrolite, Na16Al16Si24O80.nH2O, placing samples in a diamond anvil cell filled with a water-alcohol mixture. Lee and coworkers passed a synchrotron X-ray beam through the diamond cell while incrementally increasing the pressure. The diffraction patterns obtained show that the pressure initially compresses the zeolite as expected. But as the pressure climbs between 0.8 and 1.5 gigapascals, structural changes allow the hydration number, n, to increase from 16 to 32, causing the zeolite to swell. Above 1.5 GPa, the material contracts again. The results have implications for tuning the catalytic properties of zeolites. The phenomenon also could be used to trap chemical pollutants or radioactive wastes.

Water dissociates on metal surface

Despite its importance for catalysis, weathering, and other processes, the structure of water adsorbed on metal surfaces is not well understood. Scientists have thought that, on many metals, the first water molecules to adsorb arrange themselves intact in a surface bilayer similar to that is found in ice, with half the oxygen atoms in a plane about 1 Å above the rest of the oxygen atoms. But experimental studies of the geometry of D2O on Ru (0001) indicate that the oxygen atoms in the first water layer on this metal surface are almost coplanar. Now, calculations by Sandia National Laboratories Senior Scientist Peter J. Feibelman suggest an alternative that appears to resolve the discrepancy: Half of the water molecules on the surface are dissociated [Science, 295, 99 (2002)]. Using density functional theory, Feibelman finds that a hydrogen atom is removed from every other water molecule and that these hydrogens bind directly to the metal.

Benzene to phenol in one of catalytic step

Converting benzene into industrially useful phenol usually requires several chemical steps that produce a lot of unwanted side products. Scientists are working to streamline the process - for example, by using nitrous oxide to directly oxidize benzene to phenol. But these methods can be expensive. Now, materials chemist Fujio Mizukami and colleagues at the National Institute of Advanced Industrial Science & Technology in Tsukuba, Japan, and other institutions have come up with a one-step process using a palladium catalyst [Science, 295,105 (2002)]. Although the phenol yields are low - 2 to 16 % - they are on par with those of other one-step processes. And phenol comprises 80 to 97 % of the products formed. The researchers load a gaseous mixture of benzene and oxygen into a porous alumina tube coated with a thin palladium membrane. H2 is then dissociated into hydrogen atoms as it is forced through the palladium membrane and into the tube with the oxygen and benzene. The hydrogen atoms react with O2, producing species such as HOO· and HO· that hydroxylate the benzene to produce phenol. Because the oxygen and hydrogen aren't directly mixed, the scientists say, the chance of an explosion is reduced.

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Science & Technology 2, 2002


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