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- Author or Editor: D. Viorel x
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Abstract
The radiation stability of methionine-35S and selenomethionine75Se was investigated using the methods of thin-layer chromatography, gas chromatography and ESR. Radiation decomposition of methionine-35S mainly consists in an oxidation process and in the release of volatile products. The ESR-spectra of irradiated DL-methionine indicated a strong localization of the unpaired electrons on sulfur atoms. Radiation damage to selenomethionine-75Se as a function of radiation dose proved an increased stability of this compound, and its radiation decomposition consists in the formation of oxidized products and by direct rupture of the selenium bonds accompanied by the formation of volatile compounds like CH3SeH and SeH2. The self-radiolysis of the aqueous solution of selenomethionine-75Se during its storage in air leads, however, to a lower decomposition rate which consists in the release of inorganic selenium and in an oxidation process.
Abstract
The effect of Ag (1 wt%) and Au (1 wt%) on the catalytic properties of Ni/Al2O3 (7 wt% Ni) for methane steam reforming (MSR) was studied in parallel with the effect of CeO2 (6 wt%) and La2O3 (6 wt%) addition. The addition of 1 wt% Ag to the alumina supported nickel catalyst drastically decreased its catalytic properties at temperatures lower than 600 °C, due to the blockage of metal catalytic centers by silver deposition. The addition of Au and CeO2 (La2O3) to the nickel catalyst improved the methane conversion, CO2 selectivity and hydrogen production at low reaction temperatures (t < 600 °C). At 700 °C under our working conditions, the additives have no important effect in hydrogen production by MSR. The best hydrogen production at low temperatures was obtained for Ni–Au/Al2O3, due to the higher CO2 selectivity, cumulated with slightly higher methane conversion in comparison with Ni/CeO2–Al2O3. At high temperature, Ni/CeO2–Al2O3 is stable for 48 h on stream. Ni–Au/Al2O3 and Ni–Ag/Al2O3 are mainly deactivated due to the temperature effect on Au and Ag nanoparticles and less through coke formation. On Ni/Al2O3 and Ni/La2O3–Al2O3, crystalline, graphitic carbon was deposited after 48 h of reaction leading to catalyst partial deactivation. On the Ni/CeO2–Al2O3 surface, a porous amorphous form of deposited carbon was found, which does not decrease its catalytic activity after 48 h of reaction.
