Effect of cobalt loading on the solid state properties and ethyl acetate oxidation performance of cobalt-cerium mixed oxides.

Cobalt-cerium mixed oxides were prepared by the wet impregnation method and evaluated for volatile organic compounds (VOCs) abatement, using ethyl acetate (EtAc) as model molecule. The impact of Co content on the physicochemical characteristics of catalysts and EtAc conversion was investigated. The materials were characterized by various techniques, including N2 adsorption at -196°C, scanning electron microscopy (SEM), X-ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS) to reveal the structure-activity relationship. The obtained results showed the superiority of mixed oxides compared to bare CeO2 and Co3O4, demonstrating a synergistic effect. The optimum oxidation performance was achieved with the sample containing 20wt.% Co (Co/Ce atomic ratio of ca. 0.75), in which complete conversion of EtAc was attained at 260°C. In contrast, temperatures above 300°C were required to achieve 100% conversion over the single oxides. Notably, a strong relationship between both the: (i) relative population, and (ii) facile reduction of lattice oxygen with the ethyl acetate oxidation activity was found, highlighting the key role of loosely bound oxygen species on VOCs oxidation. A synergistic Co-Ce interaction can be accounted for the enhanced reducibility of mixed oxides, linked with the increased mobility of lattice oxygen.

Surface and catalytic elucidation of Rh/gamma-Al2O3 catalysts during NO reduction by C3H8 in the presence of excess O2, H2O, and SO2.

The present study aims at exploring the surface and catalytic behavior of Rh/gamma-Al(2)O(3) catalysts during the selective reduction of NO by C(3)H(8) in the presence of excess oxygen, H(2)O, and SO(2) with particular emphasis on identifying the elementary steps that describe the reaction mechanism. To this end, detailed activity and stability tests were employed and a precise kinetic analysis was carried out at differential conditions to elucidate the effect of each reactant, including H(2)O and SO(2), on the total reaction rate. At the same time, temperature programmed desorption (TPD) studies in combination with in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy were carried out under various reaction conditions to correlate the catalytic performance of Rh/gamma-Al(2)O(3) catalyst with its corresponding surface chemistry. The results reveal that in the absence of H(2)O and SO(2), the reaction follows a typical "reduction" type mechanism, where the active intermediates (NO(X), carboxylates, isocyanates) are interacting to yield the final products. In this reaction sequence the formation of carboxylate (C(x)H(y)O(z)) species is considered as the rate determining step. Water affects in a different way the NO and C(3)H(8) conversion performance of Rh/gamma-Al(2)O(3) catalyst; its effect is totally reversible in the case of C(3)H(8) oxidation, while the NO reduction was permanently affected mainly due to the oxidation of Rh active sites. In contrast, SO(2) poisons both reactions irreversibly via the formation of strongly adsorbed sulfate compounds, which hinder the adsorption and consequently the activation of reactants.

Delta-Notch lateral inhibitory patterning in the emergence of ciliated cells in Xenopus: experimental observations and a gene network model.

In diverse vertebrate and invertebrate systems, lateral inhibition through the Delta-Notch signaling pathway can lead to cells in initially uniform epithelial tissues differentiating in "salt-and-pepper", regular spacing patterns. In this paper we examine lateral inhibition during the emergence of ciliated cells in Xenopus embryonic skin, using experimental manipulations of the Delta-Notch pathway and a connectionist gene-network model of the process. The results of our model are in agreement with previous models of regular patterning through lateral inhibition and reproduce the observations of our experimental assays. Moreover, the model provides an account for the variability of embryonic responses to the experimental assays, points to a component of lateral inhibition that may be the chief source of this variability, and suggests ways to control it. Our model could thus serve as a tool to generate predictions about this and other regular patterning systems governed by lateral inhibition.

Ammonia synthesis at atmospheric pressure

Ammonia was synthesized from its elements at atmospheric pressure in a solid state proton (H+)-conducting cell-reactor. Hydrogen was flowing over the anode and was converted into protons that were transported through the solid electrolyte and reached the cathode (palladium) over which nitrogen was passing. At 570 degreesC and atmospheric pressure, greater than 78 percent of the electrochemically supplied hydrogen was converted into ammonia. The thermodynamic requirement for a high-pressure process is eliminated.

A gene network approach to modeling early neurogenesis in Drosophila.

We have produced a model of genetic regulation to simulate how neuroblasts and sensory organ precursor (SOP) cells differentiate from proneural clusters of equivalent cells. Parameters of the model (mainly gene interaction strengths) are optimized in order to fit schematic patterns of expression, drawn from the literature, of genes that are involved in this process of cell fate specification. The model provides suggestions about the role of lateral signalling in neurogenesis and yields specific and testable predictions about the timing and position of appearance of neuroblasts and SOPs within proneural clusters, and about the dynamics of gene expression in individual cells. Experimental testing of these predictions and fits to more accurate quantitative data will help determine which set of model parameters can best describe early neurogenesis.

The role of F-cadherin in localizing cells during neural tube formation in Xenopus embryos.

The cell adhesion molecule F-cadherin is expressed in Xenopus embryos at boundaries that subdivide the neural tube into different regions, including one, the sulcus limitans, which partitions the caudal neural tube into a dorsal and ventral half (alar and basal plate, respectively). Here we examine the role of F-cadherin in positioning cells along the caudal neuraxis during neurulation. First, we show that ectopic expression of F-cadherin restricts passive cell mixing within the ectodermal epithelium. Second, we show that F-cadherin is first expressed at the sulcus limitans prior to the extensive cell movements that accompany neural tube formation, suggesting that it might serve to position cells at the sulcus limitans by counteracting their tendency to disperse during neurulation. We test this idea using an assay that measures changes in cell movements during neurulation in response to differential cell adhesion. Using this assay, we show that cells expressing F-cadherin localize preferentially to the sulcus limitans, but still disperse when located away from the sulcus limitans. In addition, inhibiting cadherin function prevents cells from localizing precisely at the sulcus limitans. These results indicate that positioning of cells at the sulcus limitans is mediated in part by the differential expression of F-cadherin.