E. Santacesaria

Catalytic alkylation of phenol with methanol: factors influencing activities and selectivities: I. Effect of different acid sites evaluated by studying the behaviour of the catalysts: γ-alumina, nafion-H, silica-alumina and phosphoric acid

Abstract Activities and selectivities obtained in the catalytic alkylation of phenol with methanol, performed on four different catalysts, are compared. The tested catalysts have different but well defined acidic characteristics such as: γ-alumina containing strong Lewis acid sites, Nafion-H containing strong Bronsted acid sites, silica-alumina containing both Bronsted and Lewis sites, and Kieselguhr-supported phosphoric acid containing Bronsted acid sites of medium and weak strength. On the basis of the behaviour obtained in the cases mentioned, information about the reaction path models, mechanisms and kinetics is provided.

Lactose hydrolysis by immobilized β-galactosidase: the effect of the supports and the kinetics

Abstract The kinetic behaviour of β-galactosidase from Kluyveromices marxianus (Saccharomyces) lactis, immobilized on different oxides supports, such as alumina, silica, and silicated alumina has been studied. We observed a strong dependence of the immobilized enzyme activities on the chemical nature and physical structure of the supports. In particular, when the particle sizes of the supports are increased, the enzymatic activity strongly decreases. The hydrolysis of lactose, promoted by the mentioned enzyme immobilized on small commercial silica spheres, has been studied in different operative conditions, by changing: feed rate, reagent and products concentration and temperature, while pH has been kept constant (7.0). A depressing effect originated by both the reaction products, has been observed. Therefore, a kinetic model based on the Michaelis–Menten mechanism, in which the depressing effects of both the hydrolysis products (galactose and glucose) are also considered, have been developed and the related parameters determined.

Kinetic and catalytic aspects in the hydrogen peroxide production via anthraquinone

The kinetic and catalytic aspects involved in the hydrogen peroxide production via anthraquinone (method all-tetra) have been examined considering three of the four main production steps, i.e., hydrogenation of 2-ethyltetrahydroanthraquinone catalyzed by palladium-supported catalysts, oxidation of the product obtained in the first step, and reconversion of the deteriorated molecules for the regeneration of active quinones. For each reaction considered, a mechanism and a kinetic law are suggested with the numerical values of the related parameters.

Catalytic alkylation of phenol with methanol: factors influencing activities and selectivities: II. Effect of intracrystalline diffusion and shape selectivity on H-ZSM5 zeolite

Abstract Six samples of H-ZSM5 zeolites, differing in the size of crystallites and acidity, have been tested as catalysts in the alkylation of phenol with methanol. We observed that the size of crystallites strongly influences activity, even for very small crystallites (220–280A), by the intervention of intracrystalline diffusion. Kinetic runs have been performed on the most active catalyst. A moderate shape selectivity has been observed only in the formation of p-methylanisole and xylenols. Catalyst deactivation occurs through two mechanisms which are independent of the contact time, the first evolving exponentially and the second linearly. The interpretation of this behaviour and of related consequences on the reaction is discussed in the paper together with the reaction path model, the mechanism and the kinetics.

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.

Double bond oxidative cleavage of monoenic fatty chains

Abstract A two steps process for the production of azelaic acid and pelargonic acid or alternatively of ω-hydroxynonanoic and pelargonic acid, starting from respectively oleic acid and oleyl alcohol has been studied. In the first step, the monoenic reagent reacts with hydrogen peroxide, in the presence of pertungstic acid, as catalyst, to give the corresponding diol (hydroxylation of the double bond). In the second step, the reaction mixture obtained in the first step containing the formed diol and the exhausted catalyst, was additioned of cobalt acetate and reacted with molecular oxygen (oxidative cleavage of vicinal diols). As the first step has largely been studied in the literature, the study of the nature of the catalytic site and of the catalytic mechanism of the second step of the process is the main subject of this work with the objective of identifying, for this step, an independent and reusable catalyst. In particular, we focused our attention on the diol deriving from oleyl alcohol, because reagents and products are more easily separated and analyzed. The study of the mentioned reactions is complicated by the presence of respectively two or three phases in the reactor. The “in-situ” formed catalyst, active in the second reaction step, seems to be a lacunary poly-oxometalate in which cobalt, sequestered by the tungstate anion groups and accessible to the reagent, is the active component. This has been shown by polarographic analyses of the catalyst solution before and after the reaction, and is also confirmed by the observation that cobalt, sequestered by EDTA, in the absence of tungstic acid is active, too.

Mass transfer and kinetics in ehtoxylation spray tower loop reactors

A mathematical model has been developed for describing the behaviour of the spray tower loop reactors. Th reactors are characterised by the fact that mass transfer and reaction occurs independently in two distinct zone of the reactor. The model has been used for simulating the performance of a pilot plant both by assuming liquid drops internally stagnant and turbulent. The last assumption gives the better results.

Role of mass transfer and kinetics in the hydrogenation of rapeseed oil on a supported palladium catalyst

Abstract The partial hydrogenation of a rapeseed oil in the presence of a supported palladium catalyst was studied. In the temperature range 60–120°C, at which kinetic data were collected, we observed that diffusion limitations are always operative, in particular intraparticle diffusion limitations. The contribution of the mass transfer to the reaction rates was carefully evaluated by determining the mass transfer parameters according to independent routes. In spite of the masking effect of diffusion, kinetic laws suitable to describe the hydrogenation of trienic, dienic and monoenic compounds were identified. A Langmuir-Hinshelwood kinetic equation describes well the behaviour of the unsaturated molecules in the reaction, while the hydrogen reaction order was indirectly shown to be zero. A 3/2/1 ratio between the adsorption constants of trienic, dienic and monoenic compounds was assumed, corresponding to the different probability of a double bond interaction with the palladium surface. The kinetic constants obtained by fitting experimental data gave quite similar results for the polyunsaturated fatty acids and very different for the monounsaturated ones, revealing an intervention of two distinct reaction mechanisms. In the case of polyunsaturated fatty acids, double bond migration with the formation of conjugated dienes would occur before hydrogenation. Conjugated dienes are more quickly hydrogenated than isolated or single double bonds. In a second part of the paper, a more general kinetic model is developed based on a complex scheme of simultaneous and consecutive reactions where hydrogenation reactions occur together withcis-trans isomerizations. A kinetic equation with the corresponding parameters for thecis-trans isomerization of the C18 monoenic species was determined from experimental data. Subsequently, this equation was used with the same parameters in the general kinetic model to describe the behaviour of all the othercis-trans isomerization reactions. This assumption has turned out to be reasonable. The reliability of the more general kinetic model, of the mass transfer and kinetic equations for hydrogenation processes, of the kinetic equation forcis-trans isomerizations, and of the parameters appearing in the model was verified on the basis of all the experimental data collected. A brief discussion on the factors influencing the catalyst selectivity concludes the paper.

Performances of V2O5-based catalysts obtained by grafting vanadyl tri-isopropoxide on TiO2-SiO2 in SCR

Abstract A V2O5-based catalyst obtained by grafting vanadyl tri-isopropoxide on a TiO2-SiO2 support obtained by grafting titanium alkoxide on silica has been studied as to the selective catalytic reduction (SCR) of NO with ammonia. The performances obtained have been compared with those of other catalysts in which V2O5 was supported, respectively, on the same support by impregnating it with ammonium vanadate and on TiO2 both by grafting vanadyl tri-isopropoxide and by impregnating it with ammonium vanadate. The first mentioned catalyst turned out to be the best as to activities and selectivities. All the used catalysts and supports have been characterised using many techniques in order to explain the different performances observed. As it will be seen, activities and selectivities, in the mentioned reaction, are mainly affected by three factors that are: (i) V2O5 dispersion largely favoured by the grafting technique; (ii) the morphological properties of TiO2 surfaces that cannot be foreseen but only investigated when TiO2 is obtained by grafting titanium alkoxide on the surface of another oxide and (iii) the type of surface acidity, retaining ammonia reagent.

Oxidative dehydrogenation of ethanol to acetaldehyde on V2O5/TiO2-SiO2 catalysts obtained by grafting vanadium and titanium alkoxides on silica

Abstract Oxidative dehydrogenation of ethanol to acetaldehyde has been performed on vanadium based catalysts prepared by grafting on titania–silica supports with different procedures. A comparison of the performances of the prepared catalysts in terms of activity and selectivity has been made. Grafting technique gives place to well dispersed catalysts that resulted more selective than catalysts prepared by impregnation. In particular, very selective catalysts have been obtained by grafting vanadium–titanium bimetallic alkoxides directly on silica support. The effect of both the preparation methods and the used supports on the catalytic performances have been studied and an attempt to correlate the observed properties with the obtained results has been made.