Experiments and ab initio calculations have been performed to study the catalytic activity of calcium oxide and magnesium oxide toward N 2 O decomposition. The experiments were carried out in a fixed-bed quartz reactor in the temperature range 773-1223 K. The decomposition of N 2 O appeared to be a first-order reaction with activation energies of 26 kcal/mol for CaO and 36 kcal/mol for MgO, respectively. The decomposition rate did not change when excess oxygen was introduced to the inlet gas. The ab initio energy barriers of the dissociative reaction:-, in which the oxygen anion is seated in a CaO(100) or MgO(100) model surface, are 22 and 33 kcal/mol. High-temperature preexponential factors and activation energies are estimated from transition-state theory and collision theory expressions. The values agree well with those obtained experimentally. This indicates that most of the surface anions of both CaO and MgO are active in decomposing N 2 O in the temperature range investigated. A model of a plug-flow reactor is used to demonstrate that the temperature dependence of the overall reaction rate obtained at high N 2 O concentrations reflects the regenerating process of the surface and not the molecular dissociation of N 2 O.

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This paper is a continuation of the discussion of N2O formation during char combustion started in a previous paper (Energy Fuels 1995, 9, 10−19). The effect of different NO and CO concentrations in the inlet gas, as well as the effect of changing gas residence time within the fixed bed and after the fixed bed on the emission of N2O from char particles burning at single particle conditions, is reported. In order to distinguish between char nitrogen and NO from the inlet gas a 15N-isotope-marked NO was used in the inlet gas. The experiments were carried out in a fixed bed reactor containing quartz sand (SiO2) to support the coal particles. The bituminous coal particles were devolatilized in situ prior to the actual combustion in an argon flow. The inlet gas mixture contained 15NO, CO, O2, and Ar or just 15NO, O2, and Ar. The 15NO concentration was varied between 500 and 1950 ppm, and the CO concentration was varied between 0 and 2500 ppm. The inlet gas flow was varied between 297 and 1200 mL/min NTP (273 K, 1 atm). The bed temperature was 1073 K. The off-gases were analyzed for N2O. The addition of 15NO to the inlet gas led to the formation of 15N14NO and 15N2O, and the formation of these species increased with increasing concentration of 15NO in the inlet gas, especially the formation of 15N2O. The formation of 15N14NO was greater than the formation of 15N2O under all circumstances examined, but with increasing 15NO concentration in the inlet gas the 15N2O formation increased, and was almost as great as the formation of 15N14NO. The influence of gas residence time within the fixed bed and after the fixed bed was confirmed, and the N2O formation and formation of 15N14NO and 15N2O increased substantially with increasing gas residence time. The addition of CO to the inlet gas had almost no effect on the N2O formation.

A water content of about 10% in the horny layer is necessary for softness and pliability of this part of the epidermis. In conditions with dry skin, emollients of different types are used. It is important that solid data are collected about the effect of the ingredients of emollients and moisturizers. Urea has since long been used in the treatment of dry skin. In the present report, the mixture of urea and sodium chloride has been analyzed with respect to its effect on the water vapor pressure in concentrated solutions. The depression of the water vapor pressure by NaCl and urea was found to be additive. Thus, the decrease in water vapor pressure in aqueous solution of urea-NaCl mixtures can be estimated by adding the decrease of water vapor pressure caused by dissolving the pure compounds. The results indicate that urea and NaCl in aqueous solution do not interact strongly and are, therefore, compatible in moisturizing preparations. They can, therefore, both be expected to be effective in mixtures giving a better than one of them alone.

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