Heterogeneous products and tests for an appropriate aggregation level considering different qualities: evidence from fresh hake at Barcelona’s wholesale market

[cat] Aquest estudi destaca la importància de considerar un nivell d’agregació adequat en els anàlisis de demanda, ja que treballar utilitzant un nivell d’agregació inadequat pot donar lloc a estimacions esbiaixades. Aquest fet es mostra a través de l’anàlisi de diferents productes de lluç fresc comercialitzats a Mercabarna, el mercat majorista de Barcelona. La literatura sobre la demanda de peix tracta al lluç com un únic producte i espècie. No obstant això, en el mercat espanyol, es comercialitzen molts peixos com a lluç, els quals mostren comportaments molt diferents (des de béns inferiors fins a béns de luxe). Els resultats obtinguts, en concordança amb les observacions empíriques, demostren que l’anàlisi s’ha de realitzar amb un major grau de detall que a nivell d’espècie. Això qüestiona els resultats d’anteriors estudis de demanda i la majoria de les bases de dades, on l’observació del nivell d’agregació adequat dels productes no es té en compte.

Unambiguous assessments of reaction paths for selected pericyclic reactions

Four commonplace concerted reactions are examined using (i) correlation diagrams, (ii) frontier molecular orbital analyses for transition states, (iii) Zimmerman-Dewar analyses for transition states and (iv) modified Zimmerman-Dewar analyses for transition states. Only the latter approach is consistently satisfactory.

Química organometálica de superfície aplicada à preparação de catalisadores heterogêneos bem definidos

The study of the reactions of organometallic complexes with the surfaces of inorganic oxides, zeolites and metals constitutes the basis of Surface Organometallic Chemistry (SOMC). The basic rules of organometallic chemistry are often valid when applied to surfaces and well-defined surface organometallic complexes can be obtained. These complexes can be used as heterogeneous catalysts or, by controlled reactions, can be transformed in other species useful for a given catalytic reaction. In some cases, these catalysts exhibit higher activity and/or selectivity than their analogous molecular complexes.

Produção de etilenoglicóis e derivados por reações catalíticas do óxido de eteno

Products resulting from the ethoxylation of hydroxylated compounds, especially water and ethanol, are of great commercial importance. This work presents several aspects concerning the catalytic reactions of ethylene oxide, a chemical substance used in the production of a wide variety of products. Mechanisms of ethoxylation, distribution of products, formation of undesired by-products and perspectives for new processes using heterogeneous catalysis are also reviewed and discussed.

Construção e estudos de perfomance de um reator fotoquímico tipo CPC ("Compound Parabolic Concentrator")

A CPC (Compound Parabolic Concentrator) reactor was projected and constructed aiming to promote the degradation of the organic matter present in considerable volumes of aqueous effluents, under the action of solar radiation. The essays were done using a model effluent which consists of a mixture of fragments of a sodium salt of lignosulphonic acid possessing a mean molecular weigth of 52,000 Daltons, and a real effluent, from a chip board industry. The volume of effluent in each test was about 50 L. The tests involved heterogeneous (TiO2 P25 Degussa and formulations made from the association of TiO2 with a photosensitiser), and homogeneous (thermal and photochemical Fenton reactions) catalysis of the effluents. The results demonstrate the viability of application of this kind of reactor even when the load of organic pollutants is high.

Adaptação de forno de microondas doméstico para realização de reações de transesterificação sob refluxo e catálise por argilas

The microwave oven became an important source of heating for many laboratory procedures including accelerating organic reactions. Reactions that require long reflux times can sometimes be carried out in a few hours or minutes in a conventional microwave oven. However, longer reflux times can be troublesome since domestic microwave ovens are not prepared for these harsh conditions. This technical note presents our finding on heterogeneous catalysis transesterification reactions between b-keto-esters and carbohydrate derivatives under heating or microwave irradiation using an adapted domestic microwave oven.

Reactions of Chlorambucil and its main metabolite, Phenylacetic Acid Mustard, with 2’-deoxyribonucleosides and Calf Thymus DNA

Chlorambucil is an anticancer agent used in the treatment of a variety of cancers, especially in chronic lymphocytic leukemia, and autoimmune diseases. Nevertheless, chlorambucil is potentially mutagenic, teratogenic and carcinogenic. The high antitumor activity and high toxicity of chlorambucil and its main metabolite, phenylacetic acid mustard, to normal tissues have been known for a long time. Despite this, no detailed chemical data on their reactions with biomolecules in aqueous media have been available. The aim of the work described in this thesis was to analyze reactions of chlorambucil with 2’-deoxyribonucleosides and calf thymus DNA in aqueous buffered solution, at physiological pH, and to identify and characterize all adducts by using modern analyzing methods. Our research was also focused on the reactions of phenylacetic acid mustard with 2’-deoxynucleosides under similar conditions. A review of the literature consisting of general background of nucleic acids, alkylating agents and ultraviolet spectroscopy used to identify the purine and pyrimidine nucleosides, as well as the results from experimental work are presented and discussed in this doctoral thesis.

HPLC-ESI-MS/MS analysis of oxidized di-caffeoylquinic acids generated by metalloporphyrin-catalyzed reactions

This paper reports an HPLC-ESI-MS/MS investigation on the oxidation of 3,5- and 4,5- dicaffeoylquinic acid using iron(III) tetraphenylporphyrin chloride as catalyst. Two major mono-oxidised products of the quinic acid moiety have been identified for both compounds. However, only the 4,5-derivative afforded two different tri-oxo products. Thus, it seems that the oxidation pattern depends on the number and positions of the caffeic acid moieties present in caffeoylquinic acid molecules.

Materiais à base de óxido de ferro para oxidação de compostos presentes no efluente da despolpa do café

Materials based on pure iron oxide and impregnated with niobia (Nb2O5) were prepared. Their catalytic activities were tested on the oxidation of compounds present in the wastewater from the processing of coffee berries. Particularly caffeine and catechol were tested. The oxidation reactions were carried out with the following systems (i) UV/H2O2, (ii) photo-Fenton and (iii) heterogeneous Fenton. All materials were characterized with X-ray diffraction, Mössbauer and infrared spectroscopy. Iron was mainly in the forms of goethite and maghemite. The oxidation kinetics were monitored by UV-vis and the oxidation products were monitored by mass spectrometry. The photo-Fenton reaction presented highest oxidation efficiency, removing 98% of all caffeine and catechol contents.

Estudio cinético de la descomposición catalizada de peróxido de hidrógeno sobre carbón activado

The kinetic study of decomposition of hydrogen peroxide catalyzed by activated carbon was carried out. The effect of concentrations of reactants and temperature were experimentally studied. Kinetic data were evaluated using differential method of initial rates of reaction. When a typical kinetic law for reactions in homogeneous phase is used, first order of reaction is obtained for hydrogen peroxide and activated carbon, and activation energy of 27 kJ mol-1 for the reaction was estimated. Experimentally was observed that surface of activated carbon is chemically modified during decomposition of hydrogen peroxide, based on this result a scheme of reaction was proposed and evaluated. Experimental data fits very well to a Langmuir- Hinshelwood kinetic model and activation energy of 40 kJ mol-1 was estimated for reaction in heterogeneous phase.

Gas-phase solvolysis type reactions of SiCl3+ cations

Gas-phase SiCl3+ ions undergo sequential solvolysis type reactions with water, methanol, ammonia, methylamine and propylene. Studies carried out in a Fourier Transform mass spectrometer reveal that these reactions are facile at 10-8 Torr and give rise to substituted chlorosilyl cations. Ab initio and DFT calculations reveal that these reactions proceed by addition of the silyl cation to the oxygen or nitrogen lone pair followed by a 1,3-H migration in the transition state. These transition states are calculated to lie below the energy of the reactants. By comparison, hydrolysis of gaseous CCl3+ is calculated to involve a substantial positive energy barrier.

Retrieval of kinetic rates in reactions with semi batch liquid phase using ill-posed inverse problem theory

A neural network procedure to solve inverse chemical kinetic problems is discussed in this work. Rate constants are calculated from the product concentration of an irreversible consecutive reaction: the hydrogenation of Citral molecule, a process with industrial interest. Simulated and experimental data are considered. Errors in the simulated data, up to 7% in the concentrations, were assumed to investigate the robustness of the inverse procedure. Also, the proposed method is compared with two common methods in nonlinear analysis; the Simplex and Levenberg-Marquardt approaches. In all situations investigated, the neural network approach was numerically stable and robust with respect to deviations in the initial conditions or experimental noises.

Catalisadores heterogêneos para a produção de monoésteres graxos (biodiesel)

The recent increase in the world biodiesel demand, along with the need to reduce costs while improving the environmental sustainability of the entire biodiesel production chain, have led to the search for heterogeneous catalysts that would be efficient and highly amenable to recycling. Many classes of materials have been tested for these purposes. Among these are zeolites, ion-exchange resins, inorganic oxides, guanidines, metal complexes, layered compounds and ionic liquids. This review article describes the structure, properties, synthesis and performance of compounds that are catalytic active in both esterification and transesterification reactions.

H3PW12O40 (HPA), an efficient and reusable catalyst for biodiesel production related reactions: esterification of oleic acid and etherification of glycerol

In esterification of oleic acid with methanol at 25 °C HPA displayed the highest activity. Moreover the HPA could be reused after being transformed into its cesium salt. In the reaction of etherification of glycerol HPA and Amberlyst 35W showed similar initial activity levels. The results of acid properties demonstrate that HPA is a strong protonic acid and that both surface and bulk protons contribute to the acidity. Because of its strong affinity for polar compounds, HPA is also seemingly dissolved in both oleic acid and methanol. The reaction in this case proceeds with the catalyst in the homogenous phase.

Modification of the performance of WO3-ZrO2 catalysts by metal addition in hydrocarbon reactions

A study of the different hydrocarbon reactions over Ni doped WO3-ZrO2 catalysts was performed. Ni was found as NiO at low Ni concentration while at high Ni concentrations a small fraction was present as a metal. For both cases, Ni strongly modified total acidity and concentration of strong acid sites. In the cyclohexane dehydrogenation reaction, Ni addition promotes both benzene and methyl cyclopentane production. The hydroconversion activity (n-butane and n-octane) increases with the augment of total acidity produced by Ni. The selectivity to reaction products is modified according to the acid strength distribution changes produced by Ni addition.