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A generic cascade control for an exothermic catalytic hydrogenation reaction carried-out in a batch reactor has been studied using a lab-scale multi-phase reactor. The hydrogenation reaction is carried out in a three-phase slurry reactor, which is heated/cooled using oil circulating through an oil bath; additional coils are used for circulating refrigerating water. A series of tests was conducted to obtain the experimental physico-chemical parameters of the system which were then used on the modeling of the system, not only when using the controller from the oil bath but also for the study of the different control strategies. In the work we concluded that, although the system’s performance is limited by the heat exchange capacity, a gain-schedule control strategy is capable of improving the overall performance with an IAE error decrease of 40% and 20% of the overshooting temperature in relation to a single PID controller.

The demand for middle distillates (kerosene and diesel) in comparison to gasoline fractions is increasing constantly, particularly in the majority of European countries. Thus, maximizing the production of middle distillates in the refining process is of immediate interest to refiners. However, the production of liquid fuels, for instances using a catalytic cracker, always generates a significant amount of lighter fractions, in particular of olefinic nature. Thus, the use of oligomerization reactions to convert the lighter olefin cuts into middle distillates to incorporate in the diesel pool is a promising process for the production of clean diesel fractions. In this work, 1-butene oligomerization over H-ZSM-5 zeolite has been investigated in a differential reactor operating at ambient pressure. The effect of the reaction conditions, such as reaction temperature, contact time and partial pressure was studied on the activity, selectivity and stability of the catalyst. The results show that an increase in the reaction temperature and/or partial pressure and in the contact time produces an improved catalyst activity. The data also show that high partial pressure improves the selectivity to C 8 + . Moreover, when increasing the temperature from 150 °C to 200 °C the C 8 + hydrocarbons selectivity increases, whereas above this temperature it decreases as expected, due to the competition of cracking reactions. Furthermore, a decrease in contact time between the reaction mixture and the acid sites of the catalyst caused the C 8 + hydrocarbons fraction in the product to increase. The highest selectivity towards C 8 + hydrocarbons (∼86 wt.%) was obtained with H-ZSM-5, at 200 °C and 50 kPa of partial pressure and for the lowest value of contact time analyzed (12.5 × 10−3 h). In this way, the operating conditions must be tuned in order to achieve a significant conversion and selectivity in desired fraction ( C 8 + ).

In the present work, simultaneous thermogravimetric (TG) and differential scanning calorimetric (DSC) analyses were used to investigate the effect of the acidity of HZSM-5 zeolites on the catalytic degradation of high-density polyethylene (HDPE). The acidity of the zeolite was modified by ion exchange with sodium. The results obtained using HZSM-5 zeolites of varying acid strengths show the effect of increasing the acidity on the reduction of the degradation temperature. The addition of sodium to HZSM-5, by ion exchange, results in a decrease of the acid strength of the catalyst and an increase in the observed degradation temperature from 402 to 465 °C. The simultaneous use of the signals from the TG and DSC allowed the development of a kinetic model that is able to accurately describe all the runs performed, both the thermal and the catalytic degradation of the polymer. The kinetic parameters obtained clearly revealed the reduction in the activation energy due to the presence of the catalyst and its relation to the overall acidity of the samples. The gases evolved from the pyrolysis of polyethylene were also analysed using gas chromatography, and it was also found that volatile product selectivity changes with the catalyst acidity. The fact that the overall activity for the catalytic cracking of HDPE on these zeolites varies with internal acid strength of the zeolite indicates that the inner surface of these zeolites participates in this reaction despite the fact that the reactant molecules are extremely large.

The acid-catalysed transformation of hydrocarbons constitutes a very important set of reactions for industrial applications of zeolites. These transformations have a high degree of complexity due both to the variability of the loads that are used, usually an intricate mixture of different hydrocarbons with various reactivities, and to the fact that zeolites possess acid sites with a wide range of acid strength distribution. In this paper we intend to give a contribution to the analysis of the transformation of hydrocarbons over zeolites taking into account this latter effect. An example on the conversion of propene over ZSM-5 catalysts, with Si/Al = 15 and 24, 30 and 32% H + exchanged by Na cations is described; in this example we show that it is possible to correlate the catalytic activity of a series of catalysts with their acid strength distribution, as measured using ammonia TPD, using Polanyi-type relationships. The use of these acidity–activity relationships allows the description of the behaviour of a set of catalysts using a single set of kinetic parameters that includes the sensitivity of the reaction to the acidity of the site and opens the way to the prediction of the activity of a catalyst based solely on the characterization of its acid site distribution.

A novel biocomposite electrode containing horseradish peroxidase (HRP) and zeolite co-immobilized on gelatin particles mixed with graphite was described. Comparing the composite (zeolite/graphite) and the biocomposite (gelatin/HRP/zeolite/graphite) electrodes showed that the latter presented an enhancement on the electrodes diffusion properties and, apparently, the enzyme co-immobilized with zeolite on gelatin was electro-active and functioned as mediator in the electro-oxidation of phenol. Various HRP/zeolite ratios were tested and the best result was obtained with the 1:100 m HRP / m zeo biocomposite electrode. These results confirm the existence of HRP–zeolite interactions, as previously observed in pseudo-homogeneous oxidation of phenol.

The acid-catalysed transformation of light olefins was studied at various temperatures and partial pressures over ZSM-5 of varying acidic contents. It was observed that, as the temperature increased, the rate of consumption of ethene and propene decreased, whereas the rate of consumption of butene increased. Despite the fact that this reaction proceeds by a rather complex network mechanism, a single kinetic model describing the rate of consumption of the three reactants was developed, with the explicit inclusion of the step corresponding to the adsorption of the reactant molecules.

This review paper presents the significant advances which were made in the last decade in the understanding of the transformation over acid and bifunctional zeolite catalysts of the cheap and readily available C2–C4 alkanes into more valuable products: mechanism of activation, reaction scheme, nature of the active sites. Both the transformations of pure alkanes: n-butane isomerization, C2–C4 alkane aromatization and of alkanes in mixture with alkenes: isobutane–butene alkylation or with aromatic hydrocarbons: benzene alkylation with ethane or propane are considered.

On previous papers it was shown that composite electrodes, incorporating Y zeolite, in its sodium form, were able to induce the electro-oxidation of phenol; it was also established that exchanging sodium by protons seriously deteriorated the electrode's ability to oxidise phenol, indicating that cation composition of the zeolite was very important in the electrode's performance. In this work the influence of the nature and content of cations in the zeolite and in the supporting electrolyte were studied for this electro-oxidation. Cations such as lithium, sodium, potassium, calcium and praseodymium were used. The presence of these cations, as compensating cations in the zeolite, bears a direct influence the electrode's performance, but the cation content of the electrolyte also has a bearing on this performance. Although ion exchange processes probably occur during measurements, it was not significant in comparison with the phenol diffusion into the electrode. The influence of having different cations in the electrolyte, such as sodium, potassium, cesium or ammonium (NH4+) was also inspected and it was observed that they also have a bearing on the electro-oxidation of phenol, probably due to their influence in the mass transfer of phenol into the composite zeolite/graphite electrode and probably to molecular traffic effects originated in the ion-exchange processes that occur simultaneously with the electro-oxidation, in which the last one has less influence. Among all conditions and zeolites that were tested, the electrode using a sodium Y zeolite with a Si/Al ratio of 2.5, composited with graphite, in the combination with a sodium phosphate buffer, gave the best results for the electro-oxidation of phenol.

Phenol is an industrial pollutant and its removal from industrial wastewaters is of great importance. In order to design optimised phenol removal procedures by using horseradish peroxidase-based systems, there are some points that have to be dealt with. One of the most important issues is the need for reliable kinetics as this is one of the difficulties found during process scale-up. Although simplified kinetics can be used for limited ranges of operating conditions, they are not usually reliable for the description of varying process conditions. The present work describes the implementation of a kinetic model, based on a mechanism, for the co-oxidation of phenol and 4-aminoantipyrine (Am-NH2), which is used as a chromogen agent, with hydrogen peroxide as the oxidant. The model covers not only the variation of the concentrations of all the species involved, but also the effect of temperature in the reaction. The estimation of kinetic rate constants and activation energies for the various steps in the mechanism is performed with a single optimisation procedure, and all the experimental results are described using a unique set of parameters, which, thus, is valid over an extended range of operating conditions. The mechanism allowed the determination of a reliable kinetic model which is appropriate for the range of experimental conditions used. The computational model was also tested with an independent set of experiments with different conditions from the ones for which the parameters were estimated.

The acidities (number and strength of the Bronsted acidic sites) of two zeolite samples, H-MFI and H-BEA, were measured by ammonia temperature-programmed desorption (ATPD) and proton nuclear magnetic resonance (1H MAS NMR). Deconvolutions of the ATPD and 1H MAS NMR spectra lead to acid sites distributions (number and strength) that are nearly similar. Acid sites of increasing acid strength are characterized by higher desorption temperatures and higher 1H NMR chemical shifts. A linear relationship was found between the activation energy for ammonia desorption and the 1H NMR chemical shift. The acid strength distributions determined by ATPD and 1H MAS NMR have been quantitatively correlated.

The acidity and the catalytic activity for n-hexane cracking of three related HZSM-5 catalysts have been determined. A method is described for obtaining the distribution of acid strength by deconvoluting ammonia TPD spectra and it is shown that a linear relationship exists between the enthalpy of the reaction and the activation energy for the desorption of ammonia. Both the Polanyi and the Marcus models were used to derive relationships between the reaction activation energy and the ammonia desorption activation energy. As expected, the former decreases when the latter increases; the reaction activation energy is lower on acidic sites of greater strength. Similarly, equations were derived relating the catalytic activity to the acid strength of the catalytic sites expressed by the activation energy for the desorption of ammonia. Observed activities for the cracking of n-hexane were correlated satisfactorily to theoretical ones evaluated using the Polanyi and the Marcus models, considering the distribution of acid site strength. For the cracking of n-hexane and the range of experimental conditions used, the Marcus model does not present a significant improvement relative to the Polanyi model. The strategy described in this work indicates that it is possible to predict the activity of a zeolite for a given reaction, provided the acid sites strength distribution is known; one simple method for obtaining the latter being ammonia TPD.

The nickel complexes {bis[ N , N ′-di(2- t -butylphenyl)imino]acenaphthene} dibromonickel ( 1 -NiBr 2 ) and {bis[ N , N ′-di(2-phenylphenyl)imino]acenaphthene} dibromonickel ( 2 -NiBr 2 ) were studied in homo-, co- and terpolymerization of ethylene and propylene with polar monomers and the results compared to those previously obtained with another catalyst precursor [bis( N , N ′-dimesitylimino)acenaphthene] dibromonickel ( 3 -NiBr 2 ). In order to understand the effect of the ligand in the activity and rate of comonomer incorporation some theoretical studies, using both a semi-empirical molecular orbital method and a density-functional theory model, were performed. Good agreement was found between the computed parameters and the experimental results for the order of homo-polymerization, the differences in polymer molecular weight distribution, and, in some cases, the incorporation of functionalized copolymers in the case of copolymerization, and also on the inhibition effects caused by these copolymers.

In this paper, a new parameterised microkinetic model for the catalytic cracking of paraffins is described. This model allows us to simulate the complex network of reactions involved in the catalytic cracking of paraffins over an acidic solid; the model includes six different elementary steps (adsorption, desorption, protolytic scission, β-scission, chain growth and hydride transfer). The reaction scheme is detailed to the carbon atom number of the species and explicitly distinguishes between carbenium ions, paraffins and olefins. The number reaction rate constants required to describe all the individual reactions that are possible within the network is well over one hundred and, by using a system of equations which describes the dependency of the rate constants with the nature of the reaction and the species involved, the number of parameters that are fitted in the model is reduced to fourteen. This microkinetic model was fitted, using a genetic algorithm, to the experimental data for the catalytic cracking of n -hexane over a protonic ZSM-5 catalyst at 450 °C with very satisfactory results. The model parameters obtained from n -hexane data, were then used to simulate the catalytic cracking of n -heptane under similar conditions; this simulation compared very well with actual experimental results on n -heptane cracking. This ability to predict the catalytic behaviour for one reaction based on data obtained for other reactions is a significant step in the goal of obtaining models that are able to describe the transformation of a wide range of compounds using a limited number of parameters.

This is the first of a series of papers concerning the transformation of propane over a H-ZSM5 catalyst comprising experimental data, a kinetic model, and molecular dynamics calculations. The aim of this work is to provide a more fundamental insight on the catalytic processes involving light alkanes activation over solid acid catalysts. Experimental data for propane cracking was collected in the temperature range 623–773 K and low propane feed partial pressures varying from 3.0 to 9.1 kPa. The results show the existence of two parallel reaction pathways: (1) two monomolecular initiation steps (protolytic cracking or dehydrogenation), characterized by a relatively high activation energy, which becomes predominant at low conversions and high temperatures. Bond rupture may occur on either a CC or CH position leading to stoichiometric amounts of methane and ethene, or hydrogen and propene, respectively, when extrapolated at zero conversion; (2) a bimolecular route (classical cracking mechanism) with lower activation energy which involves carbenium ions chain carriers, and whose relative importance grows with increasing conversion and decreasing temperature, as secondary products, mainly olefins, become important. It is also clear that dehydrogenation reactions are favored at low temperatures, while at higher temperatures cracking is the dominant reaction pathway.

Kinetic models for ethylene polymerization based on a general coordination–insertion mechanism, in which either a monocoordinated species or a bicoordinated species could lead to migratory insertion, were constructed. These models were implemented through the solution of a set of differential equations resulting from the material balances for all the species involved. The application of these kinetic models to monomer consumption for different supported catalysts produced very good fittings and allowed the estimation of the kinetic rate constants of each elementary step. Although the same kinetic scheme was used to describe all the observations, the results of the fitting showed that the supported chromium species behaved very differently according to the support. Only in the case of the silica-supported catalysts was mechanical fragmentation of the particles observed during the course of the reaction, and this implied the inclusion of a new term in the model. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3464–3472, 2004

Cr catalysts supported on silica, zeolite NaY, and charcoal were prepared with two different methods. They were characterized and examined in the polymeriza- tion of ethene. Cyclic voltammetry, electron spin resonance, X-ray photoelectron spec- troscopy and silicon-29 magic-angle spinning nuclear magnetic resonance spectroscopy were used to characterize them, demonstrating that Cr is not in a single oxidation state, that the distribution among the various oxidation states depends on the history of the sample, and that even for a single oxidation state a variety of different environments can occur. In the polymerization of ethene, the supported Cr catalysts exhibited activity values varying from 10 3 to 10 5 gPE molCr 1 (M) 1 h 1 , depending on the choice of the support and on the method by which the Cr is placed on it. Silica seemed to be the most efficient support for Cr for this reaction. However, the zeolite-supported catalysts also showed reasonable activity values (Ap 10 4 units) and presented the advantage of having a strong interaction between the Cr and the support, which may prevent leaching of the cation into the surrounding environment. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3768 -3780, 2003

In this study, we described the modelling of the expansion/maintenance of human hematopoietic stem/progenitor cells from adult human bone marrow. CD 34(+)-enriched cell populations from bone marrow were cultured in the presence and absence of human stroma in serum-free media containing bFGF, SCF, LIF and Flt-3 ligand for several days. The cells in the culture were analysed for expansion and phenotype by flow cytometry. Although significant expansion of bone marrow cultures occurred in the presence and absence of human stroma, the results of expansion were effectively better in the presence of a stromal layer. In both situations the phenotypic analysis demonstrated a great expansion of CD 34(+)38(-) cells. The differentiative potential of bone marrow CD 34(+) cells co-cultured with human stroma was primarily shifted towards the myeloid lineage with the presence of CD 15 and CD 33.

The electrochemical intramolecular cyclisation of allyl 2-bromophenyl ethers in N,N'dimethylformamide at constant current in a diaphragmless cell has been developed using Ni(II) and Co(II) complexes as electron-transfer mediators. Cyclic compounds are obtained in good yields under appropriate experimental conditions.

Core-binding domains of fungal cellulases from Trichoderma reesei were purified using a new and simple technique. Cellulases were hydrolysed with papain and the binding domains were then separated from the digested mixture by ultrafiltration. The enzymatic digestion process was monitored using capillary electrophoresis. This methodology produced a yield of 85% of binding domains.

Treatment of trans-[FeH(Cl)(dppe)2] 1 (dppe = Ph2PCH2CH2PPh2) in thf with PCBut, in the presence of Tl[BF4], gave the η1-co-ordinated phosphaalkyne complex trans-[FeH(η1-PCBut)(dppe)2][BF4] 2a which forms trans-[FeH(η1-PCBut)(dppe)2][BPh4] 2b on reaction with Na[BPh4] or, upon reaction with HBF4 in CH2Cl2, converts into the η1-fluorophosphaalkene and the difluorophosphine complexes trans-[FeH(η1-PFCHBut)(dppe)2]A (A = BF4 3a or FeCl2F2 3b) and trans-[FeH(PF2CH2But)(dppe)2][BF4] 4, respectively. The phosphine complex trans-[FeH(PH3)(dppe)2][BF4] 5a was also formed in a reaction of 1 with PCBut in the presence of Tl[BF4] and [NH4][BF4] and converts into trans-[FeH(PH3)(dppe)2][BPh4] 5b upon treatment with Na[BPh4]. A single crystal structural study of 2b showed that a shortening of the PC triple bond from 1.542(2) to 1.512(5) A results upon η1 co-ordination of the phosphaalkyne, which represents the shortest P–C bond so far reported. The electrochemical PL ligand parameter has been estimated for η1-PCBut and its net electron donor/acceptor ability is compared with those of related unsaturated ligands.

In this article, we considered all aspects of acidity (nature of acid sites, strength, density, etc.) in solid catalysts and in zeolites in particular. After reminding the definition of acidity in liquid and solid acids, we emphasized acidity characterization by the most used physical techniques, such as Hammett's indicator titration, microcalorimetry of adsorbed probe molecules (ammonia, pyridine or other amines for acidity characterization and CO2 or SO2 for basicity characterization), ammonia or any amine thermodesorption, IR spectroscopy of hydroxyl groups and of several probe molecules adsorbed (ammonia, pyridine, piperidine, amines, CO, H2, etc.), MAS-NMR of 27Al, 29Si, 1H elements and of 1H, 13C, 31P, etc. of adsorbed probe molecules, and model catalytic reactions. Modeling the way the acid features of zeolites influence the catalytic activity of these catalysts toward acid-catalyzed reactions (relation between ammonia desorption activation energy values and catalytic activities, reaction mechanism...

In this article, we considered all aspects of acidity (nature of acid sites, strength, density, etc.) in solid catalysts and in zeolites in particular. After reminding the definition of acidity in liquid and solid acids, we emphasized acidity characterization by the most used physical techniques, such as Hammett's indicator titration, microcalorimetry of adsorbed probe molecules (ammonia, pyridine or other amines for acidity characterization and CO2 or SO2 for basicity characterization), ammonia or any amine thermodesorption, IR spectroscopy of hydroxyl groups and of several probe molecules adsorbed (ammonia, pyridine, piperidine, amines, CO, H2, etc.), MAS-NMR of 27Al, 29Si, 1H elements and of 1H, 13C, 31P, etc. of adsorbed probe molecules, and model catalytic reactions. Modeling the way the acid features of zeolites influence the catalytic activity of these catalysts toward acid-catalyzed reactions (relation between ammonia desorption activation energy values and catalytic activities, reaction mechanism...

The synthesis of some intermediates of furofuran lignans was accomplished by a chemical cyclisation reaction using N-ethylpiperidine hypophosphite and azobisisobutyronitrile. This reaction afforded the 5-exo-dig cyclic compound as the major product along with another isomeric cyclic compound which possess an endocyclic double bond. A brief discussion is presented to explain the formation of these isomeric cyclic compounds by a base-catalysed tautomerism mechanism. Some structural aspects are discussed based on nuclear magnetic resonance data., FEDER. Fundação para a Ciência e Tecnologia - POCTI/QUI/37808/2001.

51-6 FIELD Section Title:Fossil Fuels, Derivatives, and Related Products 22, 67 IBB - Institute for Biotechnology and Bioengineering, Centre for Biological and Chemical Engineering, Instituto Superior Tecnico/UTL, Lisbon, Port. FIELD URL: written in English; The authors analyzed the influence of the acidity of a ZSM-5 catalyst on the catalytic transformation of various short-chain olefins (ethylene, propylene and 1-butene). Four ZMS-5 catalysts with different acid strength distributions were studied at different temps. and partial pressures. The results were fitted using a kinetic model based on a network mechanism, which details the products by type (olefins, paraffins and aroms.) and no. of C atoms. Polanyi-type equations, supported on quantum chem. calcns., were used to derive quant. relations between the NH3 adsorption energy, used as a measure of the acidity of a given acid site, and the energetics of the various steps involved in the reaction. Although the qual. aspects of the reactivity differs from olefin to olefin and according to the catalyst's acidity, the model is able to describe both activity and product distribution for all catalysts, reactants and conditions using a single reaction scheme and a single set of kinetic parameters. [on SciFinder(R)]

High-density polyethylene (HDPE) was cracked over HZSM-5 and HY zeolites and the reaction was followed using simultaneous thermogravimetry (TG) and differential scanning calorimetry (DSC) and was compared with the degradation of the same material in the absence of an added catalyst. The products obtained in the degradation reaction were analyzed by gas chromatography. The simultaneous use of the signals from the TG and DSC allowed an accurate description of the thermal and catalytic degradation of the polymer by application of a novel kinetic model that correlates the two signals that are measured. The kinetic parameters were estimated by fitting this model to the experimental data obtained by TG and DSC. For both zeolites, the polymer degradation takes place at lower temperatures when compared with pure thermal degradation. It was also observed that the two zeolites have a distinct influence on the product distribution.

An H-ZSM5 zeolite has been characterized by TPD of ammonia and its performance was tested with several olefins (ethylene and propylene) and n-hexane. The catalytic tests were performed at a wide range of temperatures (300 – 450°C) and molar fractions of reagent in the feed. The results from the TPD have been deconvoluted in order to obtain a distribution of the strength of the acidity of the active sites. A micro-kinetic model and a simplified kinetic equation have been developed and fitted to results for the conversion of n-hexane and the olefins, respectively.

The total cell expansion of human umbilical cord blood (CB) and adult bone marrow (BM) CD34+-enriched cells cultured in supplemented serum-free media, either over irradiated human feeder layers or in stroma-free systems, were characterized by a simple kinetic model using only two parameters: the specific cell expansion rate, μ, and the death rate constant, k k . Both CB and BM cells can expand at approximately the same rate (0.21 day−1) in this culture system however, cell death depends on the presence of stroma and the environment in which the cells are cultured.

Cyclic voltammetry and controlled-potential electrolysis have been employed to investigate and characterize the reductive intramolecular cyclization of ethyl 2-bromo-3-(3′,4′-dimethoxyphenyl)-3-propargyloxy-propanoate (1) promoted by (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane)nickel(I), [Ni(tmc)]+, electrogenerated at glassy carbon cathodes in dimethylformamide containing tetraalkylammonium salts. Cyclic voltammograms for reduction of [Ni(tmc)]2+ in the presence of 1 reveal that [Ni(tmc)]+ catalytically reduces 1 at potentials more positive than those required for direct reduction of 1. During controlled-potential electrolyses of solutions containing [Ni(tmc)]2+ and 1, catalytic reduction of the latter proceeds via one-electron cleavage of the carbon–bromine bond to form a radical intermediate that undergoes cyclization to afford 2-(3′,4′-dimethoxyphenyl-3-ethoxycarbonyl-4-methylene-tetrahydrofuran (2). In the presence of a base (either electrogenerated or deliberately added as potassium tert-butoxide), 2 rearranges to give 2-(3′,4′-dimethoxyphenyl-3-ethoxycarbonyl-4-methyl-2,5-dihydrofuran (3). A mechanistic scheme is proposed to explain the results obtained by means of cyclic voltammetry and controlled-potential electrolysis., Fundação Calouste Gulbenkian.

The effect of isolated cellulose binding domains (CBDs) on the hydrolysis of filter paper and microcrystalline cellulose by both cellobiohydrolase I and endoglucanase, was studied. CBDs were obtained by proteolysis from cellulases using a scaled-up variant of our previous method. Experiments were performed for different enzyme/substrate ratios in both the absence and presence of CBDs. Hydrolysis of filter paper by intact cellobiohydrolase I in the presence of additional CBDs was found to have a synergistic effect, leading to an increase of the sugar production of up to 30%. The effect was less pronounced using microcrystalline cellulose, where an increase up to 16% was observed. Similar trends were found during the hydrolysis of both substrates by endoglucanase., Fundação para a Ciência e a Tecnologia (FCT) – PRAXIS XXI.

Acid catalysis plays a major role in industrial applications of catalytic processes. In particular, the use of microporous solid acid catalysts has an enormous impact in the petroleum refining industry, where large-scale processes, such as the catalytic cracking of heavy oil fractions, are carried out over very active zeolite catalysts. In this paper we will try to give an overview of the way one can characterise the acidity of a solid catalyst and used this information to predict the activity of the catalyst for a given acid catalysed reaction.

The use of enzymes in secondary fiber (old paperboard containers) upgrading was investigated. The following aspects were analyzed: (i) the effect of several enzymes and (non-hydrolytic) cellulose-binding domains on the pulp and paper properties; (ii) factors influencing enzymatic treatment of secondary fiber: enzyme dosage and reaction time; and (iii) enzyme action on fractions with different fiber-length. In general, all the tested enzymatic preparations were able to improve the pulp drainability. In most cases this improvement was obtained at the expense of paper strength. The use of cellulose-binding domains allowed for the simultaneous increase in drainability and strength properties.

Publisher Summary This chapter discusses a clear relation between the catalytic activity and the acidity for acid catalysis using Y zeolites and that this relationship has theoretical support through quantum chemical calculations on model acid sites. The study is centered on the transformation of ethene and propene over acidic Y and USY zeolites.

The stereoregulation in α-olefins polymerization is one of the most important capabilities of Ziegler-Natta catalysts. Homogeneous ansa-metallocene complexes of group 4 metals have been shown to produce isotactic [1–5], syndiotactic [6] and crystalline-amorphous stereoblock polypropylene [1, 7, 8]. Molecular mechanics and ab initio methods have been used to model the catalytic sites [1, 9–13]. The results of these calculations have been used not only to confirm experimental results but also to predict the tacticity obtained with certain catalyst precursors [12]. The design of stereochemical control based on these calculations can help the experimentalists to save time and efforts.

In the present study we have applied digital simulation techniques to the investigation of the electrochemical behaviour of a metal cation, cobalt, inside the porous structure of an Y zeolite. The CoNaY zeolite was prepared by ion-exchange and the electrochemical behaviour was studied by cyclic voltammetry using a CoNaY/graphite composite electrode in a specially designed apparatus.

The electrochemical intramolecular cyclization of propargyl derivatives containing a carbon­halogen bond in N,N'-dimethylformamide at constant current in a diaphragmless cell has been developed using Ni(II) complexes as electron-transfer mediators.