Catalytic Mo2C coatings for the water gas shift reaction: Electrosynthesis in molten salts

Electrosynthesis methods using molten salts are suggested for obtaining a new catalytic system based on the Mo2C/Mo composition for the water gas shift reaction. The coatings obtained by the discharge of the carbonate ion on a molybdenum substrate and by the simultaneous reduction of the electroactive species MoO42 and CO32- are catalytically more active than bulk Mo2C or the commercial catalyst Cu-ZnO-Al2O3 by one and three orders of magnitude, respectively.

Platinum and Palladium in Semiconductor Photocatalytic Systems FACTORS AFFECTING THE PURIFICATION OF WATER AND AIR

A wide range of organic pollutants can be destroyed by semiconductor photocatalysis using titania. The purification of water and air contaminated with organic pollutants has been investigated by semiconductor photocatalysis for many years and in attempts to improve the purification rate platinum and palladium have been deposited, usually as fine particles, on the titania surface. Such deposits are expected to improve the rate of reduction of oxygen and so reduce the probability of electron-hole recombination and increase the overall rate of the reaction. The effectiveness of the deposits is reviewed here and appears very variable with reported rate enhancement factors ranging from 8 to 0.1. Semiconductor photocatalysis can be used to purify air (at temperatures > 100 degrees C) and Pt deposits can markedly improve the overall rate of mineralisation. However, volatile organic compounds containing an heteroatom can deactivate the photocatalyst completely and irreversibly. Factors contributing to the success of the processes are considered. The use of chloro-Pt(IV)-titania and other chloro-platinum group metals-titania complexes as possible visible light sensitisers for water and air purification is briefly reviewed.

HETEROGENEOUS REDOX CATALYSIS - A NOVEL ROUTE FOR REMOVING BROMATE IONS FROM WATER

The oxidation of water to oxygen by bromate ions is mediated by the heterogeneous redox catalyst ruthenium-Adams, a high surface area and very stable form of ruthenium(IV) oxide. The initial kinetics of catalysis are investigated as a function of [BrO3-], [Ru-Adams], temperature and [anion], where ''anion'' = ClO4- Cl- or Br-. An electrochemical model of heterogeneous redox catalysis, in which the two participating redox couples are both electrochemically irreversible, is used to interpret most of the kinetic data. The observed inhibition of the initial rate of the redox reaction by Cl- and, especially, Br- ions is tentatively attributed to competitive adsorption. In the presence of organic species, such as methanol, ethanol and propan-1-ol, which are more easily oxidised than water by bromate ions, the rate of BrO3- ion reduction is significantly faster, i.e. ca 24-34 times.

OXIDATION OF WATER BY MNO4- MEDIATED BY THERMALLY ACTIVATED RUTHENIUM DIOXIDE HYDRATE

The kinetics of oxidation of water to oxygen by MnO4-, mediated by thermally activated ruthenium dioxide hydrate, has been studied. The rate of catalysis is 0.8 order with respect to the surface concentration of MnO4- (which in turn appears to fit a Langmuir adsorption isotherm) and proportional to the catalyst concentration, but is independent of the concentration of manganese(II) ions. The catalysed reaction appears to have an activation energy of 50 +/- 1 kJ mol-1. These observed kinetics are readily rationalised using an electrochemical model in which the catalyst particles act as microelectrodes providing a medium for electron transfer between the highly irreversible oxidation of water to O2 and the highly irreversible reduction of MnO4- to Mn2+.

Self-potential and spectral induced polarization signals associated with microbial sulphate reduction

Self-potential and spectral induced polarization responses associated with microbial processes involved in sulphate reduction have been monitored in a Perspex Winogradsky column filled with glass beads and growth medium. Salt-bridge is utilized as an electrolytic contact between experiment and control column. Equally spaced SP electrodes are used in combination of Ag-AgCl electrodes to compare electrodic and SP signals associated with the microbial processes involved in sulphate reduction. This study reveals that magnitude of SP varies from 5 to -2 mV and Electrodic potential 0 to -20 mV at the time of domination (day 39) of sulphate reducing bacteria which are very small in comparison to those measured by fixing both measuring and reference Ag-AgCl electrodes in experiment column. We observed that real and imaginary parts of complex conductivities increase with increase in production of H2S and CO in the experiment column. Both real and imaginary parts of surface complex conductivity vary at low frequencies similar to typical growth curve of bacterial population. Sodium lactate as a carbon source, dissolved in Lagan River water was flushed into the column for biostimulation on 144th day. The dissolved oxygen in flushed fluid might have killed the anaerobes in the column and decrease in complex conductivities similar to death phase of bacteria is observed for one week. The results obtained from this experiment should contribute to further understanding the biogeophysical responses involved in complex environments.


Read More: http://library.seg.org/doi/abs/10.1190/segj092009-001.57

Effect of organic matter amendment, arsenic amendment and water management regime on rice grain arsenic species

Arsenic accumulation in rice grain has been identified as a major problem in some regions of Asia. A study was conducted to investigate the effect of increased organic matter in the soil on the release of arsenic into soil pore water and accumulation of arsenic species within rice grain. It was observed that high concentrations of soil arsenic and organic matter caused a reduction in plant growth and delayed flowering time. Total grain arsenic accumulation was higher in the plants grown in high soil arsenic in combination with high organic matter, with an increase in the percentage of organic arsenic species observed. The results indicate that the application of organic matter should be done with caution in paddy soils which have high soil arsenic, as this may lead to an increase in accumulation of arsenic within rice grains. Results also confirm that flooding conditions substantially increase grain arsenic. (c) 2013 Elsevier Ltd. All rights reserved.

Water-mediated electrochemical nano-writing on thin ceria films

Bias dependent mechanisms of irreversible cathodic and anodic processes on a pure CeO2 film are studied using modified atomic force microscopy (AFM). For a moderate positive bias applied to the AFM tip an irreversible electrochemical reduction reaction is found, associated with significant local volume expansion. By changing the experimental conditions we are able to deduce the possible role of water in this process. Simultaneous detection of tip height and current allows the onset of conductivity and the electrochemical charge transfer process to be separated, further elucidating the reaction mechanism. The standard anodic/cathodic behavior is recovered in the high bias regime, where a sizable transport current flows between the tip and the film. These studies give insight into the mechanisms of the tip-induced electrochemical reactions as mediated by electronic currents, and into the role of water in these processes, as well as providing a different approach for electrochemical nano-writing.

Assessing the surface modifications following the mechanochemical preparation of a Ag/Al2O3 selective catalytic reduction catalyst

The surface modification of a mechanochemically prepared Ag/Al O catalyst compared with catalysts prepared by standard wet impregnated methods has been probed using two-dimensional T -T NMR correlations, HO temperature programmed desorption (TPD) and DRIFTS. The catalysts were examined for the selective catalytic reduction of NO using n-octane in the presence and absence of H. Higher activities were observed for the ball milled catalysts irrespective of whether H was added. This higher activity is thought to be related to the increased affinity of the catalyst surface towards the hydrocarbon relative to water, following mechanochemical preparation, resulting in higher concentrations of the hydrocarbon and lower concentrations of water at the surface. DRIFTS experiments demonstrated that surface isocyanate was formed significantly quicker and had a higher surface concentration in the case of the ball milled catalyst which has been correlated with the stronger interaction of the n-octane with the surface. This increased interaction may also be the cause of the reduced activation barrier measured for this catalyst compared with the wet impregnated system. The decreased interaction of water with the surface on ball milling is thought to reduce the effect of site blocking whilst still providing a sufficiently high surface concentration of water to enable effective hydrolysis of the isocyanate to form ammonia and, thereafter, N. This journal is © The Royal Society of Chemistry.

Physical and electrochemical evaluation of ATO supported IrO2 catalyst for proton exchange membrane water electrolyser

Antimony doped tin oxide (ATO) was studied as a support material for IrO₂ in proton exchange membrane water electrolyser (PEMWE). Adams fusion method was used to prepare the IrO₂-ATO catalysts. The physical and electrochemical characterisation of the catalysts were carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder conductivity, cyclic voltammetry (CV) and membrane electrode assembly (MEA) polarisation. The BET surface area and electronic conductivity of the supported catalysts were found to be predominantly arisen from the IrO₂. Supported catalyst showed higher active surface area than the pristine IrO₂ in CV analysis with 85% H₃PO₄ as electrolyte. The MEA performance using Nafion®−115 membrane at 80 °C and atmospheric pressure showed a better performance for IrO₂ loading ≥60 wt.% than the pristine IrO₂ with a normalised current density of 1625 mA cm⁻² @1.8 V for the 60% IrO₂-ATO compared to 1341 mA cm⁻² for the pristine IrO₂ under the same condition. The higher performance of the supported catalysts was mainly attributed to better dispersion of active IrO₂ on electrochemically inactive ATO support material, forming smaller IrO₂ crystallites. A 40 wt.% reduction in the IrO₂ was achieved by utilising the support material.

A microbiological survey of a constructed wetland system supplied by dairy 'dirty water' effluent

A constructed wetland at Greenmount College, Co. Antrim, N. Ireland was built in 2004 to study the treatment of ‘dirty water’ effluent from the Greenmount dairy unit. The effluent has a mean BOD5 of c.1000 mg/L and contains milking parlour wash-water and runoff from silage clamps and yard areas lightly contaminated with cattle manure. The nominal water retention time of this wetland is 100 days. The primary purposes of the wetland are to eliminate organic pollution and eutrophication risk from nitrogen and phosphorus compounds. However the wetland should also effectively remove any zoonotic pathogens present in manure and milk. Accordingly, a 12-month microbiological survey of water in the five ponds of the wetland commenced in August 2007. The aims of the survey are to determine changes, as effluent passes through the wetland system, in a broad range of indicator organisms (faecal coliforms, Escherichia coli, Enterococcus faecalis and Clostridium perfringens) and the occurrence of several pathogens - Salmonella, Campylobacter, Cryptosporidium and Mycobacterium avium subsp. paratuberculosis (Map). The highest indicator organism counts - E. coli and faecal coliforms, 103-104 CFU/ml - are observed in pond 1, and a significant reduction (1-3 log10) in all indicator organisms occurs as water passes through the wetland from pond 1 to pond 5. Hence the wetland is efficient at reducing levels of indicator organisms in the dairy effluent. Salmonella and Campylobacter spp. are being detected intermittently in all the ponds, whilst Cryptosporidium and Map have yet to be detected, and so the ability of the wetland to reduce/eliminate specific pathogens is less clear at present.

The development of internal water cooling techniques for the rotational moulding process

This paper reports the findings from internal mould cooling trials using a water spray configuration applied at various internal mould air temperatures from 120°C to 180°C for an aluminium mould. To achieve maximum benefit in terms of cycle time reduction, internal mould water cooling was used in conjunction with a combination of external forced air and water cooling. Savings in cooling times of up to 30% were achieved compared to conventional external only forced air cooling.

Origin of double dinitrogen release feature during fast switching between lean and rich cycles for NOx storage reduction catalysts

The performance of NOx storage and reduction over 1.5 wt% Pt/20 wt% KNO3/K2Ti8O17 and 1.5 wt% Pt/K2Ti8O17 catalysts has been investigated using combined fast transient kinetic switching and isotopically labelled (NO)-N-15 at 350 degrees C. The evolution of product N-2 has revealed two significant peaks during 60 s lean/1.3 s rich switches. It also found that the presence of CO2 in the feed affects the release of N-2 in the second peak. Regardless of the presence/absence of water in the feed, only one peak of N-2 was observed in the absence of CO2. Gas-phase NH3 was not observed in any of the experiments. However, in the presence of CO2 the results obtained from in situ DRIFTS-MS analysis showed that isocyanate species are formed and stored during the rich cycles, probably from the reaction between NOx and CO, in which CO was formed via the reverse water-gas shift reaction. 

Ethanol-induced water stress and fungal growth

Fungal growth inhibition by ethanol was compared with that caused by five other agents of water stress (at 25, 40 and 42.5°C), using Aspergillus oryzae. Ethanol, KCl, glycerol, glucose, sorbitol, and polyethylene glycol 400 were incorporated into media at concentrations corresponding to water activity (a(w)) values in the range 1 to 0.75. Generally, as temperature increased there was a decrease in the a(w) value at which optimum growth occurred. The a(w) limit for growth on KCl, glycerol, glucose, sorbitol, or polyethylene glycol 400 media was about 0.85, regardless of temperature. However, the a(w) limit for growth on ethanol media varied between 0.97 and 0.99 a(w) and was temperature-dependent. Water stress accounted for up to 31, 18 and 6% of growth inhibition by ethanol at 25, 40, and 42.5°C, respectively. For media containing ethanol, the decrease in growth rate per unit of a(w) reduction was greater as temperature increased. However, ethanol-induced water stress remained constant regardless of temperature, suggesting that other inhibitory effects of ethanol are closely temperature- dependent. Water stress may account for considerably more than 30% of growth inhibition by ethanol in cells that remain metabolically active at higher ethanol concentrations.

Ethanol-induced water stress in yeast

This review considers the effect of ethanol-induced water stress on yeast metabolism and integrity. Ethanol causes water stress by lowering water activity (a(w)) and thereby interferes with hydrogen bonding within and between hydrated cell components, ultimately disrupting enzyme and membrane strut and function. The impact of ethanol on the energetic status of water is considered in relation to cell metabolism. Even moderate ethanol concentrations (5 to 10%, w/v) cause a sufficient reduction of a(w) to have metabolic consequences. When exposed to ethanol, cells synthesize compatible solutes such as glycerol and trehalose that protect against water stress and hydrogen-bond disruption. Ethanol affects the control of gene expression by the mechanism that is normally associated with (so-called) osmotic control. Furthermore, ethanol-induced water stress has ecological implications.

Reduction of the temperature sensitivity of Halomonas hydrothermalis by iron starvation combined with microaerobic conditions

The limits to biological processes on Earth are determined by physicochemical parameters, such as extremes of temperature and low water availability. Research into microbial extremophiles has enhanced our understanding of the biophysical boundaries which define the biosphere. However, there remains a paucity of information on the degree to which rates of microbial multiplication within extreme environments are determined by the availability of specific chemical elements. Here, we show that iron availability and composition of the gaseous phase (aerobic vs. microaerobic) determine susceptibility of a marine bacterium, Halomonas hydrothermalis, to sub-optimal and elevated temperature and salinity by impacting rates of cell division (but not viability). In particular, iron starvation combined with microaerobic conditions (5 % v/v of O2, 10 % v/v of CO2, reduced pH) reduced sensitivity to temperature across the 13 °C range tested. These data demonstrate that nutrient limitation interacts with physicochemical parameters to determine biological permissiveness for extreme environments. The interplay between resource availability and stress tolerance, therefore, may shape the distribution and ecology of microorganisms within Earth's biosphere.