A. Di Michele

Ultrasound and microwave assisted synthesis of high loading Fe-supported Fischer–Tropsch catalysts

Supported iron-based Fischer-Tropsch (FT) catalysts with high loading of active metal have been prepared using both traditional and innovative methods. In these latter the impregnation of silica support has been performed by adding a step involving an ultrasound (US) or a microwave (MW) treatment to improve the metal deposition and to increase the catalyst activity. FT results have indicated the catalysts prepared by US as the most efficient, particularly when sonication is performed in argon atmosphere. MW prepared samples have given results very similar to those obtained with the traditional method. In order to explain the different catalytic activity, all the samples have been characterized by BET, TPR, SEM, TEM, XRD and micro-Raman analyses.

Effects of temperature on micellar-assisted bimolecular reaction of methylnaphtalene-2-sulphonate with bromide and chloride ions

Reactivity of methyl naphthalene-2-sulphonate, MeONs, with H2O, Br(-) and Cl(-) in water and in cationic micelles of cetyltrialkylammonium surfactants, n-C16H33N(+)R3X(-), R=Me (CTA(+)), n-Pr (CTPA(+)), X=Br, Cl, CH3SO3, has been investigated in the temperature range 25-45°C. Micellar rate effects were analysed by using the pseudophase treatment, and the second-order rate constants in the micellar pseudophase were evaluated at the various temperatures. Values of these rate constants increase with temperature, and the effect is less important in micelles than in water and more important for chloride than for bromide ions. Micelles lead to an ion behaviour discrimination, whose extent depends on surfactant type and on temperature, with maximum effect in CTPA(+) at 25°C and with bromide being always more reactive than chloride. Quantitative analysis of the temperature effect by the Eyring equation showed that micelles speed up reaction of MeONs with halide ions by decreasing the activation enthalpies, which is partially offset by decreases in the activation entropies. The rate acceleration by increase in surfactant head group size has only enthalpic origin for bromide and only entropic origin for chloride: this different behaviour was rationalised taking into account both solvation of anions and the hydrophobic effect.

Mercury acetate produced by metallic mercury subjected to acoustic cavitation in a solution of acetic acid in water

Mercury acetate (MA) can be obtained by metallic mercury immersed in a mixture of deionised, bidistillated water (dbw) and acetic acid. We show that MA crystallization time is drastically reduced if the previous mixtures are subjected to acoustic cavitation. The largest quantity of crystals is obtained by a concentration of acetic acid of about 7% in volume. NMR analysis of identical mixtures in the presence of mercury, performed as soon as possible after cavitation, showed the largest quantity of mercury acetate molecules, for the same concentration of acetic acid of 7% in volume.