Vincenzo Solinas

The atypical lipase B from Candida antarctica is better adapted for organic media than the typical lipase from Thermomyces lanuginosa

Candida antarctica lipase B (CALB) and Thermomyces lanuginosa lipase (TLL) were evaluated as catalysts in different reaction media using hydrolysis of tributyrin as model reaction. In o/w emulsions, the enzymes were used in the free form and for use in monophasic organic media, the lipases were adsorbed on porous polypropylene (Accurel EP-100). In monophasic organic media, the highest specific activity of both lipases was obtained in pure tributyrin at a water activity of >0.5 and at an enzyme loading of 10 mg/g support. With tributyrin emulsified in water, the specific activities were 2780 micromol min(-1) mg(-1) for TLL and 535 micromol min(-1) mg(-1) for CALB. Under optimal conditions in pure tributyrin, CALB expressed 49% of the activity in emulsion (264 micromol min(-1) mg(-1)) while TLL expressed only 9.2% (256 micromol min(-1) mg(-1)) of its activity in emulsion. This large decrease is probably due to the structure of TLL, which is a typical lipase with a large lid domain. Conversion between open and closed conformers of TLL involves large internal movements and catalysis probably requires more protein mobility in TLL than in CALB, which does not have a typical lid region. Furthermore, TLL lost more activity than CALB when the water activity was reduced below 0.5, which could be due to further reduction in protein mobility.

Activity and deactivation of Fe-MFI catalysts for benzene hydroxylation to phenol by N2O

Abstract Isomorphously substituted Fe-MFI zeolite catalysts with various Si/Al and/or Si/Fe ratios were synthesized and characterized by many different techniques, such as ICP, XRD, SEM, TPR, microcalorimetry, FTIR, and EPR. Under standard reaction conditions the best catalyst gave 20% benzene conversion and over 90% selectivity to phenol. For Fe-ZSM5 catalysts, addition of steam to the feed improved catalyst activity, selectivity, and durability. Phenol formed onto Fe-based sites only. Active sites could very likely be composed of oxygen-bridged, extraframework binuclear Fe redox species, charge-compensating the framework Fe 3+ or Al 3+ ions. Surface acidity was not responsible for activity in the main reaction, but it was heavily involved in catalyst deactivation by coking. Catalyst deactivation derived mainly from the decomposition-condensation of phenol onto acid sites; the stronger the latter, the quicker was the coking rate.

Microcalorimetric characterisation of acid–basic catalysts

Abstract Fundamentals of microcalorimetry are briefly reviewed. A heat-flow microcalorimeter of the Tian–Calvet type has been used to obtain information on the differential molar enthalpy of adsorption. Ammonia, pyridine, n-butylamine or CO2 and SO2 have been used to characterize the acid–base properties of several catalysts such as zeolites and oxides.

Oxidative dehydrogenation of propane over V2O5/TiO2/SiO2 catalysts obtained by grafting titanium and vanadium alkoxides on silica

The oxidative dehydrogenation (ODH) of propane have been studied on three different vanadium oxide catalysts, containing comparable amounts of vanadium. All the proven catalysts have been prepared by grafting but following different procedures. One has been prepared by grafting vanadyl tri-isopropoxide, dissolved in n-hexane on a support of silica coated with a multi-layer of TiO2. The support has been prepared by grafting in three different steps titanium alkoxide on silica. Another catalyst has been prepared by partially hydrolysing vanadyl tri-isopropoxide, dissolved in isopropanol, before grafting the obtained product on the same support. The third catalyst has been prepared by reacting partially hydrolysed vanadyl tri-isopropoxide with titanium alkoxide in isopropanol and anchoring then the reaction product, a vanadium–titanium bimetallic alkoxide, directly on silica. The first and second catalysts have similar activities and selectivities, while the third catalyst is less active but more selective than the other two ones. A kinetic approach has been made and a pseudo-first order kinetic law has been used to interpret the results. All the observed catalytic phenomena have been interpreted also with the aid of the several used characterisation techniques.

Preparation and properties of new acid catalysts obtained by grafting alkoxides and derivatives on the most common supports note I — grafting aluminium and zirconium alkoxides and related sulphates on silica

Abstract In this paper we will show that it is possible to modify the acid properties of a surface, rich of hydroxyl groups by grafting in suitable conditions metal alkoxides, such as aluminium and zirconium alkoxide. Depending on the amount of metal alkoxide it is possible to obtain, after steaming of the surface and calcination, different coverage degree up to the monolayer. Iteration of the grafting technique gives a multilayer, completely modifying the orginal surface. Grafting aluminium and zirconium alkoxides pre-treated in homogeneous phase with pure sulphuric acid leads to catalysts with very strong acid sites on the surface. The acidic properties of the catalysts obtained by grafting aluminium and zirconium alkoxides and their sulphate derivatives on silica have been characterized by different techniques such as: potentiometric titrations, Temperature Programmed Desorption of organic bases and differential calorimetry to evaluate the density of the active sites and their strength. Prepared catalysts were proven in test reactions such as methanol dehydration and hydrocarbon isomerization and cracking. We have shown that sulphated catalysts have very strong acid sites of both the Bronsted and Lewis type, able to promote hydrocarbon isomerization and cracking at the relatively low temperature of 250°C.

Thermodynamic properties of aqueous non-electrolyte mixtures. Alkanols + + water systems.

Abstract The molar excess enthalpies, H E , at 298.15 K, and the liquid-liquid equilibrium, LLE, of aqueous mixtures of alkanols have been measured. The results are interpreted qualitatively in terms of intercomponent molecular interactions and hydrophobic stabilization of the water structure by the alkanol molecules. The results obtained indicate that the geometry, the number of alkyl groups in the aliphatic chain and the relative position of the functional group -OH have an important action on these two effects.

Physical and Chemical Lipase Adsorption on SBA‐15: Effect of Different Interactions on Enzyme Loading and Catalytic Performance

Immobilization of Pseudomonas fluorescens lipase (Pfl) on the chemically modified, or unmodified, surface of SBA‐15 mesoporous silica has been achieved. X‐ray diffraction (XRD), transmission electron microscopy (TEM), and N2 physisorption are used to monitor the effect of surface functionalization on the structural and textural features of the SBA‐15 silica support. The enzyme loading strongly depends on the type of enzyme–support interaction, the maximal loading of the chemisorbed lipase being about twice that of the physisorbed (502 and 256 mgprotein 

Temperature-programmed desorption study of ammonia desorption-diffusion in molecular sieves: II. Application to partially decationated Y-zeolites

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Thermodynamic properties of binary mixtures containing aldehydes. I. Excess enthalpies of some n-alkanal + n-alkane mixtures: Measurement and analysis in terms of a quasi-chemical group-contribution model and estimation of excess Gibbs Energies

respectively). The resulting biocatalysts, regardless of the different loading, are tested with a hydrolytic catalytic assay. Despite the lower loading, the physically immobilized Pfl is more active than that which is chemically immobilized. Both biocatalysts are also active in a green process for biodiesel production, leading to almost full conversion of sunflower oil and ethanol into the corresponding ethyl esters after about 7 h at 30 °C, atmospheric pressure, and in solvent‐free conditions. Recycling experiments showed that the chemically immobilized Pfl was still active after twenty reaction cycles whereas the physically immobilized Pfl lost its activity after the tenth cycle.

Thermodynamics of binary mixtures containing tertiary amines. I. Excess enthalpies of some N,N-dialkylmethylamine+normal alkane mixtures. Measurement and analysis in terms of group contributions. Estimation of excess gibbs energies

Abstract An analysis of TPD data relating to the desorption of ammonia from two different samples of partially decationated Y-zeolite is reported, assuming various chemical or physical steps to be rate-determining. The process is shown to be controlled by intracrystalline surface diffusion, with values of the apparent activation energy E a = 30.8 and 27.1 kcal/mol, respectively, for the two zeolite samples. These values include the retardation effect associated with the hindering interaction of the diffusing ammonia molecules with the acid sites of the zeolite. Values of the apparent effective diffusion coefficient ranging from ca. 3 10 −18 to ca. 4 10 −14 cm 2 /s have been calculated for the 423–573 K temperature range.