SULFOXIDES OF HIGH ENANTIOPURITY FROM BACTERIAL DIOXYGENASE-CATALYZED OXIDATION

Selected strains of the bacterium Pseudomonas putida (previously shown to effect dioxygenase-catalysed asymmetric cis-dihydroxylation of alkenes) have been found to yield chiral sulfoxides from the corresponding sulfides with a strong preference for the (R)- or (S)-configurations but without evidence of sulfone formation; similar results obtained using an Escherichia coli clone (pKST11, containing the Tod C1 C2 B and A genes encoding toluene dioxygenase from P. putida NCIMB 11767) are again consistent with a stereoselective dioxygenase-catalysed sulfoxidation.

Preferential CO oxidation over a copper-cerium oxide catalyst in a microchannel reactor

The activity of a 5-wt% Cu/CeO2-x catalyst during preferential CO oxidation in hydrogen-rich gas mixtures was studied in a microchannel reactor. The CO concentration dropped from 1 vol.% to 10 ppm at a selectivity of 60%, at a temperature of 190 degrees C, and a weight hour space velocity (WHSV) of 55,000 cm(3) g(-1) h(-1). Both the CO concentration and the temperature increased when the WHSV was increased from 50,000 to 500,000 cm(3) g(-1) h(-1). An increase of the O-2 concentration from a 1.2 to 3 fold excess reduced the CO concentration to 10 ppm in a broad temperature interval of 50 degrees C at WHSVs up to 275,000 cm(3) g(-1) h(-1). The preferential CO oxidation could be carried out at higher flow rates and at higher selectivities in the microchannel reactor compared to a fixed-bed flow reactor. (C) 2008 Elsevier B.V. All rights reserved.

Synthesis of protective Mo-Si-B coatings in molten salts and their oxidation behavior in an air-water mixture

The formation of various phases during boronizing of silicided molybdenum substrates (MoSi2/Mo) was investigated. Boronizing treatments were conducted in molten salts under an inert gas atmosphere in the 700-1000 degrees C temperature range for 3-7 h. Depending on the process type (non-current or electrochemical) and molten salt temperature, the formation of different boride phases (MoB, Mo2B5, MoB2, MoB4) was observed. At the same time, substantial oxidation of the bulk molybdenum disilicide phase (MoSi2) to the Mo5Si3 phase was observed in non-current boronizing. The oxidation resistance of the coatings was investigated by the weight change in an air-water (2.3 vol.%) mixture at a temperature of 500 degrees C for a period up to 700 h. Results indicated that a two-phase microstructure consisting of the MoSi2, matrix phase with 12-15 wt.% of the MoB4 phase greatly improved the oxidation resistance of the molybdenum substrates. The weight gain rate observed was 6.5 center dot 10(-4) mg/cm(2) h. (c) 2006 Elsevier B.V. All rights reserved.