Ammonia synthesis over Ru/C catalysts with different carbon supports promoted by barium and potassium compounds

Ammonia synthesis over ruthenium catalysts supported on different carbon materials using Ba or K compounds as promoters has been investigated. Ba(NO3)(2), KOH, and KNO3 are used as the promoter or promoter precursor, and activated carbon (AC), activated carbon fiber (ACF). and carbon molecular sieve (CMS) are used as the support. The activity measurement for ammonia synthesis was carried out in a flow micro-reactor under mild conditions: 350-450 degreesC and 3.0 MPa. Results show that KOH promoter was more effective than KNO3. and that Ba(NO3)(2) was the most effective promoter among the three. The roles of promoters can be divided into the electronic modification of ruthenium, the neutralization of surface functional groups on the carbon support and the ruthenium precursor. The catalyst with AC as the support gave the highest ammonia concentration in the effluent among the supports used, while the catalyst with ACF as the support showed the highest turnover-frequency (TOF) value. It seems that the larger particles of Ru on the carbon supports are more active for ammonia synthesis in terms of TOF value. (C) 2001 Elsevier Science B.V. All rights reserved.

Coadsorption of nitric oxide and oxygen on the Ag(110) surface

The coadsorption of NO and O-2 on Ag(110) surface has been studied by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and in situ Raman spectroscopy. The existence of oxygen enhances the adsorption of NO by forming the NOx species, that is, NO2 and NO3, and the NO in turn as a promotor facilitates the cleavage of the dioxygen bond, forming the surface atomic oxygen species having the same spectral characteristics as those produced using oxygen at high pressure. The oxygen species generated by the interaction is composed of two parts. One is produced directly by the decomposition of surface NO-O-2 complex at ca 625 K, which raised an O 1s feature at 530.5 eV and is absent at ca 800 K, while the another with an O 1s binding energy of 529.2 eV emerges at higher temperatures and shows similar properties as the reported gamma-state oxygen which bound tightly on restructured silver surface. The exposure to NO and O-2 causes noticeable changes in the morphology of the Ag(110) surface and the flat terraces superseded by small (ca 0.1 mu m) pits, and particles with typical diameters of a few micrometres were formed at elevated temperatures. (C) 1999 Elsevier Science B.V. All rights reserved.

Highly ordered periodic mesoporous ethanesilica synthesized under neutral conditions

Highly ordered mesoporous ethanesilica (MES) with 2D hexagonal structure was synthesized from 1,2-bis(trimethoxysilyl) ethane under neutral conditions for the first time. Divalent salts, such as NiCl2, MgCl2, ZnCl2, ZnSO4 and Zn(NO3)(2), were used to help the formation of the ordered mesostructure. The MES samples were characterized by powder X-ray diffraction, nitrogen sorption, transmission electron microscopy, FT-IR, C-13 and Si-29 solid-state NMR and thermal gravimetric analysis. A phase transition from a disordered wormhole-like structure to an ordered P6mm structure was observed upon the addition of inorganic salts. The pore size of the MES decreases from 4.7 to 3.9 nm with increasing content of the inorganic salts. Fluoride was also found to be important for the formation of ordered MES under neutral conditions.

Preparation of supported PtRu/C electrocatalyst for direct methanol fuel cells

In this work, high-surface supported PtRu/C were prepared with Ru(NO)(NO3)(3) and [Pt(H2NCH2CH2NH2)(2)]Cl-2 as the precursors and hydrogen as a reducing agent. XRD and TEM analyses showed that the PtRu/C catalysts with different loadings possessed small and homogeneous metal particles. Even at high metal loading (40 wt.% Pt, 20 wt.% Ru) the mean metal particle size is less than 4 nm. Meanwhile, the calculated Pt crystalline lattice parameter and Pt (220) peak position indicated that the geometric structure of Pt was modified by Ru atoms. Among the prepared catalysts, the lattice parameter of 40-20 wt.% PtRu/C contract most. Cyclic voltammetry (CV), chronoamperometry (CA), CO stripping and single direct methanol fuel cell tests jointly suggested that the 40-20 wt.% PtRu/C catalyst has the highest electrochemical activity for methanol oxidation. (c) 2004 Elsevier Ltd. All rights reserved.

Hydrothermal synthesis of alumina nanotubes templated by anionic surfactant

The alumina nanotubes were prepared by using the anionic surfactant, sodium dodecyl sulfonate (SDS), as structure-directing template for the first time with Al(NO3)(3)center dot 9H(2)O as precursor via a hydrothermal method. Structure and morphology of the nanotubes were characterized by XRD, TEM, FT-IR, TG and N-2 adsorption-desorption. The obtained nanotubes were found having outer diameters from 6 to 8 nm with length up to 200 nm. (C) 2005 Elsevier B.V. All rights reserved.

Diurnal variation in uptake and xylem contents of inorganic and assimilated N under continuous and interrupted N supply to Phleum pratense and Festuca pratensis

J. H. Macduff and A. K. Bakken. (2003). Diurnal variation in uptake and xylem contents of inorganic and assimilated N under continuous and interrupted N supply to Phleum pratense and Festuca pratensis. Journal of Experimental Botany, 54 (381) pp.431-444 Sponsorship: BBSRC / Norwegian Crop Research Institute RAE2008

Effects of a stay-green mutation on plant nitrogen relations in Lolium perenne during N starvation and after defoliation

Macduff, J. H., Humphreys, M. O., Thomas, Howard (2002). Effects of a stay-green mutation on plant nitrogen relations in Lolium perenne during N starvation and after defoliation. Annals of Botany, 89 (1), 11-21. Sponsorship: BBSRC RAE2008

Differences in growth and nitrogen productivity between a stay-green genotype and a wild-type of Lolium perenne under limiting relative addition rates of nitrate supply

James Macduff, Neil Raistrick and Mervyn Humphreys (2002). Differences in growth and nitrogen productivity between a stay-green genotype and a wild-type of Lolium perenne under limiting relative addition rates of nitrate supply. Physiologia Plantarum, 116 (1), 52-61. Sponsorship: BBSRC RAE2008

Direct and Indirect Effects of Dissolved Organic Matter Source and Concentration on Denitrification in Northern Florida Rivers

Using a natural gradient of dissolved organic carbon (DOC) source and concentration in rivers of northern Florida, we investigated how terrestrially-derived DOC affects denitrification rates in river sediments. Specifically, we examined if the higher concentrations of DOC in blackwater rivers stimulate denitrification, or whether such terrestrially-derived DOC supports lower denitrification rates because (1) it is less labile than DOC from aquatic primary production; whether (2) terrestrial DOC directly inhibits denitrification via biochemical mechanisms; and/or whether (3) terrestrial DOC indirectly inhibits denitrification via reduced light availability to-and thus DOC exudation by-aquatic primary producers. We differentiated among these mechanisms using laboratory denitrification assays that subjected river sediments to factorial amendments of NO3- and dextrose, humic acid dosing, and cross-incubations of sediments and water from different river sources. DOC from terrestrial sources neither depressed nor stimulated denitrification rates, indicating low lability of this DOC but no direct inhibition; humic acid additions similarly did not affect denitrification rates. However, responses to addition of labile C increased with long-term average DOC concentration, which supports the hypothesis that terrestrial DOC indirectly inhibits denitrification via decreased autochthonous production. Observed and future changes in DOC concentration may therefore reduce the ability of inland waterways to remove reactive nitrogen. © 2013 Springer Science+Business Media New York.

Denitrification and inference of nitrogen sources in the karstic Floridan Aquifer

Aquifer denitrification is among the most poorly constrained fluxes in global and regional nitrogen budgets. The few direct measurements of denitrification in groundwaters provide limited information about its spatial and temporal variability, particularly at the scale of whole aquifers. Uncertainty in estimates of denitrification may also lead to underestimates of its effect on isotopic signatures of inorganic N, and thereby confound the inference of N source from these data. In this study, our objectives are to quantify the magnitude and variability of denitrification in the Upper Floridan Aquifer (UFA) and evaluate its effect on N isotopic signatures at the regional scale. Using dual noble gas tracers (Ne, Ar) to generate physical predictions of N2 gas concentrations for 112 observations from 61 UFA springs, we show that excess (i.e. denitrification-derived) N2 is highly variable in space and inversely correlated with dissolved oxygen (O2). Negative relationships between O2 and δ15N NO3 across a larger dataset of 113 springs, well-constrained isotopic fractionation coefficients, and strong 15N:18O covariation further support inferences of denitrification in this uniquely organic-matter-poor system. Despite relatively low average rates, denitrification accounted for 32 % of estimated aquifer N inputs across all sampled UFA springs. Back-calculations of source δ15N NO3 based on denitrification progression suggest that isotopically-enriched nitrate (NO3-) in many springs of the UFA reflects groundwater denitrification rather than urban- or animal-derived inputs. © Author(s) 2012.

Anoctamin 1 (Ano1) is required for glucose-induced membrane potential oscillations and insulin secretion by murine β-cells.

Anions such as Cl(-) and HCO3 (-) are well known to play an important role in glucose-stimulated insulin secretion (GSIS). In this study, we demonstrate that glucose-induced Cl(-) efflux from β-cells is mediated by the Ca(2+)-activated Cl(-) channel anoctamin 1 (Ano1). Ano1 expression in rat β-cells is demonstrated by reverse transcriptase-polymerase chain reaction, western blotting, and immunohistochemistry. Typical Ano1 currents are observed in whole-cell and inside-out patches in the presence of intracellular Ca(++): at 1 μM, the Cl(-) current is outwardly rectifying, and at 2 μM, it becomes almost linear. The relative permeabilities of monovalent anions are NO3 (-) (1.83 ± 0.10) > Br(-) (1.42 ± 0.07) > Cl(-) (1.0). A linear single-channel current-voltage relationship shows a conductance of 8.37 pS. These currents are nearly abolished by blocking Ano1 antibodies or by the inhibitors 2-(5-ethyl-4-hydroxy-6-methylpyrimidin-2-ylthio)-N-(4-(4-methoxyphenyl)thiazol-2-yl)acetamide (T-AO1) and tannic acid (TA). These inhibitors induce a strong decrease of 16.7-mM glucose-stimulated action potential rate (at least 87 % on dispersed cells) and a partial membrane repolarization with T-AO1. They abolish or strongly inhibit the GSIS increment at 8.3 mM and at 16.7 mM glucose. Blocking Ano1 antibodies also abolish the 16.7-mM GSIS increment. Combined treatment with bumetanide and acetazolamide in low Cl(-) and HCO3 (-) media provokes a 65 % reduction in action potential (AP) amplitude and a 15-mV AP peak repolarization. Although the mechanism triggering Ano1 opening remains to be established, the present data demonstrate that Ano1 is required to sustain glucose-stimulated membrane potential oscillations and insulin secretion.

Fertilización nitrogenada en cultivos de invierno en base a nitrógeno disponible en suelo y condiciones climáticas pre - siembra (temperatura y precipitaciones)

El correcto manejo del N resulta muy importante en los cultivos de trigo y cebada. Esto se explica por la importancia que tiene este nutriente en el crecimiento de los cultivos, por la movilidad que presenta en el suelo, por la diversidad de factores (bióticos como abióticos) que lo afectan y por el peso económico que tiene el correcto uso de este nutriente. Por lo expresado hemos estudiado con datos de 164 chacras para diferentes años (1999-2000-2001-2002) el efecto de la Temperatura, Precipitación, Fecha de Siembra y Antecesores sobre la disponibilidad de N-NO3 - a la siembra de cultivos de invierno. Bajas precipitaciones durante los 40 días previos a la siembra, alta temperatura del período y fecha de siembra temprana se asociaron a los mayores niveles de N-NO3 - disponibles en el suelo a la siembra. En función de esta información, cuando las lluvias durante los 40 días previos a la siembra son menos de 20 mm y se logran siembras tempranas, es esperable que no haya déficit inicial de N para los cultivos. En siembras inmediatas a períodos de precipitaciones excesivas (135 mm) es esperable muy baja disponibilidad de N-NO3 -, por lo que, si no se dispone del valor de análisis, sería necesario corregir con la dosis máxima propuesta. Para las situaciones intermedias, la única herramienta válida sería el análisis de suelo correspondiente

Transferencia de nitrógeno de ecosistemas agrícolas recientemente intensificados a acuíferos: efecto de la variación en las precipitaciones

A partir del monitoreo a campo de cultivos, suelo y agua subterránea, modelos de simulación y un experimento en lisímetros se estudió el intercambio de nitrógeno (N) inorgánico entre cultivos y el agua subterránea en sistemas agrícolas recientemente intensificados con suelos ricos en materia orgánica (MO). El monitoreo (1998-2010) en tres posiciones del paisaje de la Pampa Ondulada permitió captar períodos plurianuales húmedos y secos (1506-444 mm año-1) disparadores de cambios intensos en las profundidades freáticas (mayor 1 a menor a 6 m) que afectaron la función del agua subterránea y de los cultivos como moduladores de los flujos de agua y N. Con niveles freáticos superficiales, se redujo la capacidad de almacenaje del agua drenada hacia la zona no saturada, produciéndose un flujo lateral subsuperficial que redistribuyó el N lixiviado desde posiciones altas hacia los bajos y contribuyó a la recarga del acuífero aguas abajo. Este flujo, favorecido por fuertes gradientes hidráulicos, y la concentración local de solutos disparada por el consumo de agua subterránea por los cultivos en la posición de pie de loma, produjeron picos de concentración de cloruro (menor a 500 mg Cl. l-1) y nitrato (menor a 45 mg N-NO3. l-1) en el agua freática superficial. Durante períodos normales a secos los drenajes de diferentes eventos de lluvia se alojan en la zona no saturada, disipando y retrasando la respuesta del nivel freático a eventos individuales. El agua de lluvia fluye verticalmente arrastrando N del suelo hacia una superficie freática profunda (con mayor desfasaje temporal entre la concentración de nitrato del drenaje y la del agua freática a medida que el nivel se profundiza) y luego descarga en el arroyo. La aplicación de un fertilizante enriquecido con 15N a un cultivo de maíz en lisímetros permitió demostrar que la fertilización representa un aporte insignificante (1 por ciento) al flujo de N lixiviado y que el N derivado de la mineralización de la MO del suelo constituye una fuente importante de N lixiviable durante períodos con balance hídrico positivo y/o baja demanda de los cultivos. A partir de los resultados obtenidos se propone un modelo conceptual de los flujos hidrológicos y de N en paisajes ondulados de uso agrícola para situaciones climáticas contrastantes