Efficient Conversion of Glucose to Methyl Lactate with Sn-USY: Retro-aldol Activity Promotion by Controlled Ion Exchange.

Sn-USY materials have been prepared through an optimized post-synthetic catalytic metalation procedure. These zeolites displayed, upon ion exchange with alkaline metals, an outstanding activity in the direct transformation of glucose into methyl lactate, yielding more than 70% of the starting glucose as the target product, and an overall combined retro-aldol condensation product yield above 95% in a short reaction time (<4 h). This outstanding catalytic performance is ascribed to the neutralization of Brønsted acid sites, the consequent depression of side reactions, and a higher population of tin open sites in the ion-exchanged Sn-USY zeolites. Reusability tests evidenced some loss of catalytic activity, partially caused by the closing of tin sites, although the use of small amounts of water in the reaction media demonstrated that this deactivation mechanism can be, at least, partially alleviated.

3D GIS for surface modelling of magnetic fields generated by overhead power lines and their validation in a complex urban area.

Residential exposure to magnetic fields generated by overhead high-voltage power lines, continues to be a matter of social concern and, for the scientific community, a challenge to model this exposure accurately enough to reliably detect even small effects in large populations complexes. In any expression of the magnetic field intensity, the source-receiver distance is a determining variable, especially in an environment closer to the electrical installation and critical with the existence of significant unevenness in the terrain. However, MF exposure studies adopt, due to their complexity, simplifications of reality where even sometimes the terrain relief and the buckling of the line are not considered. The application of 3D techniques with Geographic Information Systems (GIS) allows us to address this problem. This article presents a model for generating magnetic field intensity surfaces from high-precision terrain elevation data. The series expansion of the Biot-Savart law to an infinite rectilinear conductor with variable height according to the catenary described by the cables using ArcGIS software is applied to calculate the magnetic field. For the validation, 69 control points (1035 field measurements) were used in a free urban area and another 28 points (420 field measurements) in a built-up urban area with complex relief. Good estimates were obtained, although with differences in both areas. With MAPE 9.65% and 19.51%, R2 = 0.922 and 0.949, RMSE = 0.154 and 0.094 µT, respectively. Furthermore, 86% of the points were correctly classified according to usual exposure percentiles. However, the use of a 5 m resolution digital terrain model to obtain high-precision elevation data was an indispensable condition for the good performance of our model. The result as a continuous surface of magnetic field values at the real elevation of the ground can contribute significantly to the development of new environmental and public health studies.

Dehydration of xylose to furfural over MCM-41-supported niobium-oxide catalysts.

A series of silica-based MCM-41-supported niobium-oxide catalysts are prepared, characterized by using XRD, N2 adsorption-desorption, X-ray photoelectron spectroscopy, Raman spectroscopy, and pyridine adsorption coupled to FTIR spectroscopy, and tested for the dehydration of D-xylose to furfural. Under the operating conditions used all materials are active in the dehydration of xylose to furfural (excluding the MCM-41 silica support). The xylose conversion increases with increasing Nb2 O5 content. At a loading of 16 wt % Nb2 O5 , 74.5 % conversion and a furfural yield of 36.5 % is achieved at 170 °C, after 180 min reaction time. Moreover, xylose conversion and furfural yield increase with the reaction time and temperature, attaining 82.8 and 46.2 %, respectively, at 190 °C and after 100 min reaction time. Notably, the presence of NaCl in the reaction medium further increases the furfural yield (59.9 % at 170 °C after 180 min reaction time). Moreover, catalyst reutilization is demonstrated by performing at least three runs with no loss of catalytic activity and without the requirement for an intermediate regeneration step. No significant niobium leaching is observed, and a relationship between the structure of the catalyst and the activity is proposed.

Preparation and characterization of Mg-Zr mixed oxide aerogels and their application as aldol condensation catalysts.

A series of Mg-Zr mixed oxides with different nominal Mg/(Mg+Zr) atomic ratios, namely 0, 0.1, 0.2, 0.4, 0.85, and 1, is prepared by alcogel methodology and fundamental insights into the phases obtained and resulting active sites are studied. Characterization is performed by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, N(2) adsorption-desorption isotherms, and thermal and chemical analysis. Cubic Mg(x)Zr(1-x)O(2-x) solid solution, which results from the dissolution of Mg(2+) cations within the cubic ZrO(2) structure, is the main phase detected for the solids with theoretical Mg/(Mg+Zr) atomic ratio ≤0.4. In contrast, the cubic periclase (c-MgO) phase derived from hydroxynitrates or hydroxy precursors predominates in the solid with Mg/(Mg+Zr)=0.85. c-MgO is also incipiently detected in samples with Mg/(Mg+Zr)=0.2 and 0.4, but in these solids the c-MgO phase mostly arises from the segregation of Mg atoms out of the alcogel-derived c-Mg(x)Zr(1-x)O(2-x) phase during the calcination process, and therefore the species c-MgO and c-Mg(x)Zr(1-x)O(2-x) are in close contact. Regarding the intrinsic activity in furfural-acetone aldol condensation in the aqueous phase, these Mg-O-Zr sites located at the interface between c-Mg(x)Zr(1-x)O(2-x) and segregated c-MgO display a much larger intrinsic activity than the other noninterface sites that are present in these catalysts: Mg-O-Mg sites on c-MgO and Mg-O-Zr sites on c-Mg(x)Zr(1-x)O(2-x). The very active Mg-O-Zr sites rapidly deactivate in the furfural-acetone condensation due to the leaching of active phases, deposition of heavy hydrocarbonaceous compounds, and hydration of the c-MgO phase. Nonetheless, these Mg-Zr materials with very high specific surface areas would be suitable solid catalysts for other relevant reactions catalyzed by strong basic sites in nonaqueous environments.

Selective conversion of furfural to maleic anhydride and furan with VO(x)/Al(2)O(3) catalysts.

Furfural can be converted into maleic anhydride (73 % yield) through selective gas phase oxidation at 593 K with O(2) by using VO(x)/Al(2)O(3) (10 at(V) nm(-2)) as solid catalysts. The use of lower temperatures and/or O(2) pressures result in the additional formation of furan (maximum 9 % yield). Mechanistically, furfural (C(5)H(4)O(2)) is oxidized stepwise to furan (C(4)H(4)O), 2-furanone (C(4)H(4)O(2)), and finally, maleic anhydride (C(4)H(2)O(3)). The specific structure of the supported vanadium oxides and reaction conditions (temperature and reactants pressures) all influence furfural oxidation catalysis. We have found that Al(2)O(3)-supported polyvanadates are intrinsically more active (2.70 mmol h(-1) g-at V(-1)) than monovanadates (VO(4)) and V(2)O(5) crystals (0.89 and 0.70 mmol h(-1) g-at V(-1), respectively) in maleic anhydride and furan formation rates (553 K, 1.6 kPa furfural, 2.5 kPa O(2)). Our alternative approach enables the use of biomass instead of petroleum to synthesize maleic anhydride and furan from furfural. The potential variety of industrial applications is of enormous interest for the development of future biorefineries.

Catalytic dehydration of xylose to furfural: vanadyl pyrophosphate as source of active soluble species.

The acid-catalysed, aqueous phase dehydration of xylose (a monosaccharide obtainable from hemicelluloses, e.g., xylan) to furfural was investigated using vanadium phosphates (VPO) as catalysts: the precursors, VOPO(4)·2H(2)O, VOHPO(4)·0.5H(2)O and VO(H(2)PO(4))(2), and the materials prepared by calcination of these precursors, that is, γ-VOPO(4), (VO)(2)P(2)O(7) and VO(PO(3))(2), respectively. The VPO precursors were completely soluble in the reaction medium. In contrast, the orthorhombic vanadyl pyrophosphate (VO)(2)P(2)O(7), prepared by calcination of VOHPO(4)·0.5H(2)O at 550°C/2 h, could be recycled by simply separating the solid acid from the reaction mixture by centrifugation, and no drop in catalytic activity and furfural yields was observed in consecutive 4 h-batch runs (ca. 53% furfural yield, at 170°C). However, detailed catalytic/characterisation studies revealed that the vanadyl pyrophosphate acts as a source of active water-soluble species in this reaction. For a concentration of (VO)(2)P(2)O(7) as low as 5 mM, the catalytic reaction of xylose (ca. 0.67 M xylose in water, and toluene as solvent for the in situ extraction of furfural) gave ca. 56% furfural yield, at 170°C/6 h reaction.

Silylation of a Co/SiO2 catalyst. Characterization and exploitation of the CO hydrogenation reaction.

Several silylated- and nonsilylated Co/SiO2 catalysts have been prepared by reaction of the surface silanol groups with hexamethyldisilazane (HMDS). These samples have been characterized by means of N2 adsorption isotherms, solid-state nuclear magnetic resonance (29Si and 1H), X-ray photoelectron spectroscopy, thermogravimetric analysis, and diffuse reflectance IR spectroscopy. We have focused on the study of the silylated surface stability at high temperatures and in different atmospheres. The characterization techniques have shown that silica silylation after cobalt impregnation leads to a silylated SiO2 surface composed of hydrophobic Si-(CH3)3 species highly stable up to 600-650 K in both oxidizing and reducing atmospheres. However, X-ray diffraction and temperature-programmed reduction have shown that the hydrophobic nature of the silica surface does not affect the metal dispersion and its reducibility. The materials prepared in this way have been tested as catalysts for the Fischer-Tropsch synthesis reaction. The CO conversion reaction rate increased over the silylated catalyst, probably as a consequence of the higher number of available active sites because water adsorption over the catalyst surface is impeded. However, catalyst deactivation was not affected by the hydrophobic nature of the support, suggesting that carbon deposition is the more probable mechanism of cobalt-based catalyst deactivation during the Fischer-Tropsch synthesis.

Reactivation of a commercial diesel oxidation catalyst by acid washing.

The catalytic activity of samples taken from an oxidation catalyst mounted on diesel-driven automobiles and aged under road conditions was recovered to a significant extent by washing with a dilute solution of citric acid. The characterization of samples arising from a fresh, a vehicle-aged, and a regenerated catalyst was carried out by scanning electron microscopy (SEM-EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Relatively high levels of S and P, in the form of aluminum sulfate and phosphate, respectively, together with contaminant Si were detected in the used catalyst. Washing of the vehicle-aged catalytic oxidation converter revealed high efficiency in the extraction of the main contaminants detected (S and P) by this nondestructive methodology. The results of the experiments reported here should encourage the development of a technology based on this reactivation procedure for the rejuvenation of the catalytic device mounted on diesel exhaust pipes.

Sensibilidad a aeroalergenos en pacientes asmáticos de la ciudad de Salta / Sensitivity to aeroallergens in asthmatic patients in Salta city

Objetivos: discriminar la frecuencia de sensibilidad a aeroalergenos y patologías alérgicas simultáneas en asmáticos de esta ciudad. Material y métodos: pacientes (pac.) con diagnóstico funcional y/o clínico de asma, registrándose edad, sexo, evolución de asma, patología alérgica concomitante, IgE total y sensibilidad por skin prick test. Se testificaron con: ácaros mix, cucarachas mix, pool hongos (Alternaria, Cladosporium, Penicillum, Aspergillus; epitelios perro y gato, pool Gramíneas, Amarantaceae, Ambrosía, Chenopodiacea, pool árboles (plátano, abedul, álamo, pino, eucalipto); control (+) fosfato histamina y (-) solución glicerinada; lancetas prick lanceter. Se consideró (+) a toda pápula > 3 mm con relación al control (-). Resultados: se analizaron 35 pac.; edad media 22,1 años (4-70), 11 masculinos y 24 femeninos, 6,9 años de evolución de asma (1-30) y nivel de IgE total de 402,6 kU/L (13-2000). Se encontró sensibilidad a ácaros en 83 por ciento, cucarachas 8,5 por ciento, hongos 20 por ciento, perro 20 por ciento, gato 26 por ciento, gramíneas 31,5 por ciento, chenopodeacea 8,5 por ciento, árboles 6 por ciento, Ambrosía y Amaranthaceae 3 por ciento cada una. Las patologías asociadas fueron rinitis en 60 por ciento, rinosinusitis en 17 por ciento, dermatitis de contacto en 6 por ciento, adenoiditis en 6 por ciento, dermatitis atópica en 3 por ciento, displasia broncopulmonar en 3 por ciento y ex tuberculosis 3 por ciento, sin otra patología 8,5 por ciento. Conclusiones: los ácaros son los alergenos más sensibilizantes en asmáticos de esta región; gramíneas, epitelio de gato, perro y hongos le siguen en forma decreciente. La coexistencia de rinitis más rinosinusitis (77 por ciento) como patologías asociadas frecuentes apoyan la conexión nariz-pulmón

Sensibilidad a aeroalergenos en pacientes asmáticos de la ciudad de Salta / Sensitivity to aeroallergens in asthmatic patients in Salta city

Objetivos: discriminar la frecuencia de sensibilidad a aeroalergenos y patologías alérgicas simultáneas en asmáticos de esta ciudad. Material y métodos: pacientes (pac.) con diagnóstico funcional y/o clínico de asma, registrándose edad, sexo, evolución de asma, patología alérgica concomitante, IgE total y sensibilidad por skin prick test. Se testificaron con: ácaros mix, cucarachas mix, pool hongos (Alternaria, Cladosporium, Penicillum, Aspergillus; epitelios perro y gato, pool Gramíneas, Amarantaceae, Ambrosía, Chenopodiacea, pool árboles (plátano, abedul, álamo, pino, eucalipto); control (+) fosfato histamina y (-) solución glicerinada; lancetas prick lanceter. Se consideró (+) a toda pápula > 3 mm con relación al control (-). Resultados: se analizaron 35 pac.; edad media 22,1 años (4-70), 11 masculinos y 24 femeninos, 6,9 años de evolución de asma (1-30) y nivel de IgE total de 402,6 kU/L (13-2000). Se encontró sensibilidad a ácaros en 83 por ciento, cucarachas 8,5 por ciento, hongos 20 por ciento, perro 20 por ciento, gato 26 por ciento, gramíneas 31,5 por ciento, chenopodeacea 8,5 por ciento, árboles 6 por ciento, Ambrosía y Amaranthaceae 3 por ciento cada una. Las patologías asociadas fueron rinitis en 60 por ciento, rinosinusitis en 17 por ciento, dermatitis de contacto en 6 por ciento, adenoiditis en 6 por ciento, dermatitis atópica en 3 por ciento, displasia broncopulmonar en 3 por ciento y ex tuberculosis 3 por ciento, sin otra patología 8,5 por ciento. Conclusiones: los ácaros son los alergenos más sensibilizantes en asmáticos de esta región; gramíneas, epitelio de gato, perro y hongos le siguen en forma decreciente. La coexistencia de rinitis más rinosinusitis (77 por ciento) como patologías asociadas frecuentes apoyan la conexión nariz-pulmón (AU)