Carlo Resini

Technologies for the removal of phenol from fluid streams: A short review of recent developments

The available technologies for the abatement of phenol from water and gaseous streams are briefly reviewed, and the recent advancements summarized. Separation technologies such as distillation, liquid-liquid extraction with different solvents, adsorption over activated carbons and polymeric and inorganic adsorbents, membrane pervaporation and membrane-solvent extraction, have been discussed. Destruction technologies such as non-catalytic, supercritical and catalytic wet air oxidation, ozonation, non-catalytic, catalytic and enzymatic peroxide wet oxidation, electrochemical and photocatalytic oxidation, supercritical wet gasification, destruction with electron discharges as well as biochemical treatments have been considered. As for the abatement of phenol from gases, condensation, absorption in liquids, adsorption on solids, membrane separation, thermal, catalytic, photocatalytic and biological oxidation have also been considered. The experimental conditions and the performances of the different techniques have been compared.

An FTIR study of the accessibility of the protonic sites of H-mordenites

The interaction of different probes with two H-MOR samples has been studied by IR. In the case of the sample with Si/Al = 10 acetonitrile perturbs all the hydroxy groups while 2,2-dimethylpropionitrile (pivalonitrile) perturbs only very few. Pyridine also perturbs all the hydroxy groups but only some of them protonate the pyridine, the others only H-bond to it. n-Hexane and 2,2-dimethylbutane give the same result, perturbing only some of the bridging hydroxy groups. The results are interpreted by assuming that no OHs are located in the 8-ring channels, and that the hydrocarbons cannot interact (due to the steric hindrance of the methyl group) with the OHs located in the side pockets. On the contrary, the flat molecule pyridine can enter slightly into the side pockets and H-bond with the OHs there. Pivalonitrile interacts only with the OHs which are well exposed in the main channels. It is concluded that the active sites for alkane isomerization are likely exclusively those that are well exposed in the main channels of H-MOR and that Al substitution in the T3 sites probably does not occur. The sample with Si/Al 45, taken as an example of a dealuminated sample, presents many less bridging OHs which are entirely available for interaction with even pivalonitrile.

Spectroscopic characterization of cobalt-containing solid catalysts

Abstract The nature of the cobalt centers in oxidized and reduced CoO x /Al 2 O 3 catalysts and in oxidized Co-H-mordenite (Co-H-MOR) have been characterized by UV-Vis spectroscopy and by IR spectroscopy. The UV-Vis spectroscopy of CoO x /Al 2 O 3 catalysts is dominated by the features of divalent cobalt in tetrahedral coordination. These sites can be reduced by hydrogen to cobalt metal centers that have been characterized by IR spectroscopy of adsorbed carbon monoxide. The surface of CoO x /Al 2 O 3 when it is in contact with CO/H 2 mixtures and works as the catalyst for hydrocarbon synthesis has also been characterized by IR. Surface formate species were detected that could act as reaction intermediates. The active sites of Co-H-MOR are also constituted by tetrahedrally coordinated Co 2+ that act as medium strong Lewis sites. The presence of Co species seems to cause a slight increase of the average Bronsted acidity of the residual hydroxy groups in Co-H-MOR samples.

A Study of the Oxidative Dehydrogenation of Cyclohexane Over Oxide Catalysts

The vapor-phase cyclohexane oxidative dehydrogenation has been investigated over several catalysts. A typical catalyst for total oxidation, as Mn2O3, materials applied in the field of oxide hydrogenation reactions, as silica-supported vanadia- and niobia-based catalysts, V-, Fe-, and Ce-phosphates used for partial oxidation reactions and ZSM5 zeolite, protonic and Co exchanged, have been tested. Over almost all the catalysts, benzene is the main product obtained, although cyclohexene is obtained with high selectivity at low conversion on phosphate catalysts.

Structural and morphological characterization of Mn–Zr mixed oxides prepared by a sol–gel method

Abstract Mn–Zr mixed oxide materials have been prepared by a sol–gel method from a Mn (III) precursor salt and a solution of zirconium acetate in acetic acid, being characterized from a structural and morphological point of view. Conventional solid state techniques show that as obtained powders are formed by mixtures of manganese and zirconium acetates and (hydro) oxides, which evolve to bixbyite, hausmannite, as well as tetragonal and monoclinic zirconia above 873 K. Zirconium enhances the formation of the non-thermodynamically stable manganese compounds instead of the thermodynamically stable ones. This effect was not observed in other samples previously prepared by coprecipitation. In general, mixed systems are thermally stable up to 1073 K due to the formation of a solid solution phase of 10% Mn into zirconia, and display higher specific surface areas than those prepared by the coprecipitation method. Their activities in the combustion of heavy aromatic molecules are higher than those of the pure manganese oxides, very likely due to a synergic effect of zirconium. Moreover, the catalytic properties of hausmannite and bixbyite phases for burning this type of hydrocarbons seem to be very similar.

Oxidation of ethane over vanadia-alumina-based catalysts: co-feed and redox experiments

Abstract The conversion of ethane in mixture with oxygen and helium (or air) over a V2O5/Al2O3 12:88 (w/w) and a V2O5-K2O/Al2O3 12:6:82 (w/w) catalysts has been studied. Results of co-feed experiments (with ethane–oxygen–He and with ethane–air feeds) and redox experiments, performed feeding pure ethane over fully oxidized catalysts, have been compared. Data concerning propane conversion over the same catalysts have also been considered. Over the heavily K-doped sample a direct combustion way to CO2 parallel to the oxydehydrogenation way to ethylene is likely to exist. On the contrary, over undoped vanadia-alumina the main combustion way is successive and mainly gives CO. Similar yields have been obtained but at lower temperatures for co-feed than for redox experiments. However, in similar conditions the productivities can be definitely higher in redox than in co-feed experiments. Nevertheless the conversion of ethane in the empty reactor gives rise to definitely higher selectivities and yields, although at very high temperatures, than the catalyzed reactions.

A study of some bivalent metal divanadates and their catalytic activity in the oxidation of propane

The divanadates M2V2O7 of a virtually unreducible and unoxidizable cation, Mg2+, of a reducible cation, Cu2+, and of an oxidizable cation, Mn2+, have been prepared and characterized by X-ray diffraction, surface area measurements, skeletal IR and UV-vis-NIR spectroscopies, and DTA-TG analyses. These materials have also been tested as catalysts for propane oxidative dehydrogenation at two different contact times. Mg divanadate is more active and more selective than Mn divanadate, while Cu divanadate is a little bit more selective than the Mg compound. The activity is likely mainly associated to the redox behavior of V cations which could be improved by reducible centers. Gas phase phenomena predominate at relatively low contact times and higher temperatures while true catalytic phenomena are observed at higher contact times and lower temperatures.