Effect of Calcination and Reduction Temperatures on the Reduction and Activity of Boron-modified Co/TiO2 Fischer-Tropsch Catalys

The effect of calcination and reduction temperatures on the reducibility, dispersion and Fischer-Tropsch activity of 10 wt% cobalt supported on titania catalyst modified by 0.1 wt% boron has been studied. The percentage reduction and percentage dispersion were found to decrease with increasing calcination temperature. The higher calcination temperatures decreased the total CO hydrogenation activity, but did not affect the turnover frequency. The decrease in CO hydrogenation rate with increasing calcination temperature is attributed to a decrease in the number of surface active sites. The higher reduction temperature also decreased the total activity. This may be due to the loss of the surface active sites, caused by blocking of the TiOc phases produced at higher reduction temperatures. The higher calcination temperature shifted the F-T product spectrum to the lower weight hydrocarbons. The reduction temperature did not affect the product selectivity. South African Journal of Chemistry Vol.57 2004: 49-5

Effect of Cobalt Source on the Catalyst Reducibility and Activity of Boron-modified Co / TiO2 Fischer-Tropsch Catalysts

The effect of cobalt precursor (nitrate, acetate and chloride salts) on the catalyst reducibility and dispersion, as well as the catalytic activity of the Fischer-Tropsch (FT) synthesis, of boron-modified titania-supported cobalt catalysts (0.1%B/10%Co/TiO2) has been investigated. FT studies were performed on both calcined and uncalcined catalysts prepared from the three cobalt sources. The uncalcined nitrate catalyst showed a higher activity for FT synthesis compared to the uncalcined acetate and chloride catalysts. For the calcined catalysts, the acetate and nitrate catalysts exhibited higher FT activity. The low activity associated with the chloride catalyst related to poisoning by residual chloride ions. Calcination was found to enhance the extent of cobalt bulk reduction and FT activity for all three of the catalysts. The FT reaction rate increased with increasing percentage cobalt dispersion while the turnover frequency (TOF) was found be near independent of cobalt source. South African Journal of Chemistry Vol.56 2003: 1-

IN SITU AND POST REACTION COBALT-INCORPORATION INTO AMINOPROPYL-MODIFIED PERIODIC MESOPOROUS ORGANOSILICA MATERIALS

Bifunctional periodic mesoporous organosilica materials with and without cobalt ion incorporation were synthesized by co-condensation of 1,2-bistrimethoxysilylethane (BTME) with 3-aminopropyltriethoxysilane (APTS) in the presence of cetyltrimethylammonium bromide. Cobalt was incorporated onto APTS-modified ethylene-bridged silica materials by in situ and by incipient wetness addition methods. The periodicity of the new materials is indicated by the presence of low angle diffraction peaks found in the XRD profiles (pore size ca. 40 nm). The surface area, pore volume and pore diameter of the new ethylene-bridged silica materials decreased with increasing loading of APTS as well as after cobalt incorporation. Thermogravimetric analysis and Raman spectroscopy show that the surfactant is removed by solvent extraction. Cobalt ion incorporation is confirmed by Raman spectroscopy and UV-vis diffuse reflectance spectroscopy. KEY WORDS: Bifunctional periodic mesoporous organosilica, 1,2-bistrimethoxysilylethane, 3-aminopropyltriethoxysilane, Sol-gel, Cobalt Bull. Chem. Soc. Ethiop. 2005, 19(2), 197-212

Optimising reactive disease management using spatially explicit models at the landscape scale

Increasing rates of global trade and travel, as well as changing climatic patterns, have led to more frequent outbreaks of plant disease epidemics worldwide. Mathematical modelling is a key tool in predicting where and how these new threats will spread, as well as in assessing how damaging they might be. Models can also be used to inform disease management, providing a rational methodology for comparing the performance of possible control strategies against one another. For emerging epidemics, in which new pathogens or pathogen strains are actively spreading into new regions, the spatial component of spread becomes particularly important, both to make predictions and to optimise disease control. In this chapter we illustrate how the spatial spread of emerging plant diseases can be modelled at the landscape scale via spatially explicit compartmental models. Our particular focus is on the crucial role of the dispersal kernel-which parameterises the probability of pathogen spread from an infected host to susceptible hosts at any given distance-in determining outcomes of epidemics. We add disease management to our model by testing performance of a simple "one off" form of reactive disease control, in which sites within a particular distance of locations detected to contain infection are removed in a single round of disease management. We use this simplified model to show how ostensibly arcane decisions made by the modeller-most notably whether or not the underpinning disease model allows for stochasticity (i.e. randomness)-can greatly impact on disease management recommendations. Our chapter is accompanied by example code in the programming language R available via an online repository, allowing the reader to run the models we present for him/herself

A nonlocal inhomogeneous dispersal process

AbstractThis article in devoted to the study of the nonlocal dispersal equationut(x,t)=∫RJ(x−yg(y))u(y,t)g(y)dy−u(x,t)in R×[0,∞), and its stationary counterpart. We prove global existence for the initial value problem, and under suitable hypothesis on g and J, we prove that positive bounded stationary solutions exist. We also analyze the asymptotic behavior of the finite mass solutions as t→∞, showing that they converge locally to zero

The Synthesis of Carbon Nanomaterials using Chlorinated Hydrocarbons over a Fe-Co/CaCO3 Catalyst

The effect of chlorine on the morphology of carbon nanotubes (CNTs) prepared from a Fe-Co/CaCO3 catalyst was investigated using chlorobenzene (CB), dichlorobenzene (DCB), trichlorobenzene (TCB), dichloroethane (DCE), trichloroethane (TCE) and tetrachloroethane (TTCE) as chlorine sources using a catalytic chemical vapour deposition (CCVD) method. Toluene was used as a chlorine-free carbon source for comparison. Multi-walled carbon nanotubes (MWCNTs) were successfully synthesized. The physicochemical properties of the CNTs were studied using transmission electron microscopy (TEM), Raman spectroscopy, thermal gravimetric analysis (TGA), energy-dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (PXRD) spectroscopy, and X-ray photoelectron spectroscopy (XPS) techniques. The inner and outer diameters of the MWCNTs increased with an increase in the number of chlorine atoms contained in the reactant. Chlorine incorporation into the MWCNTs was observed by EDS analysis for all reactants. Formation of ‘bamboo-like’ structures for the MWCNTs generated from TCE and TTCE was also observed, facilitated by the presence of the high percentage of chlorine in these reactants. Numerous MWCNTs revealed the presence of small carbon nanostructures that grew on top of the dominant CNTs, suggesting an unexpected secondary carbon growth mechanism.KEYWORDS Multi-walled carbon nanotubes, CVD, synthesis, chlorine, benzenes, ethanes

A review of shaped carbon nanomaterials

Materials made of carbon that can be synthesised and characterised at the nano level have become a mainstay in the nanotechnology arena. These carbon materials can have a remarkable range of morphologies. They can have structures that are either hollow or filled and can take many shapes, as evidenced by the well-documented families of fullerenes and carbon nanotubes. However, these are but two of the shapes that carbon can form at the nano level. In this review we outline the types of shaped carbons that can be produced by simple synthetic procedures, focusing on spheres, tubes or fibres, and helices. Their mechanisms of formation and uses are also described

Origin of conductivity cross over in entangled multi-walled carbon nanotube network filled by iron

A realistic transport model showing the interplay of the hopping transport between the outer shells of iron filled entangled multi-walled carbon nanotubes (MWNT) and the diffusive transport through the inner part of the tubes, as a function of the filling percentage, is developed. This model is based on low-temperature electrical resistivity and magneto-resistance (MR) measurements. The conductivity at low temperatures showed a crossover from Efros-Shklovski (E-S) variable range hopping (VRH) to Mott VRH in 3 dimensions (3D) between the neighboring tubes as the iron weight percentage is increased from 11% to 19% in the MWNTs. The MR in the hopping regime is strongly dependent on temperature as well as magnetic field and shows both positive and negative signs, which are discussed in terms of wave function shrinkage and quantum interference effects, respectively. A further increase of the iron percentage from 19% to 31% gives a conductivity crossover from Mott VRH to 3D weak localization (WL). This change is ascribed to the formation of long iron nanowires at the core of the nanotubes, which yields a long dephasing length (e.g. 30 nm) at the lowest measured temperature. Although the overall transport in this network is described by a 3D WL model, the weak temperature dependence of inelastic scattering length expressed as L_phi ~T^-0.3 suggests the possibility for the presence of one-dimensional channels in the network due to the formation of long Fe nanowires inside the tubes, which might introduce an alignment in the random structure.Comment: 29 pages,10 figures, 2 tables, submitted to Phys. Rev.

The lavender plumage colour in Japanese quail is associated with a complex mutation in the region of MLPH that is related to differences in growth, feed consumption and body temperature

Background The lavender phenotype in quail is a dilution of both eumelanin and phaeomelanin in feathers that produces a blue-grey colour on a wild-type feather pattern background. It has been previously demonstrated by intergeneric hybridization that the lavender mutation in quail is homologous to the same phenotype in chicken, which is caused by a single base-pair change in exon 1 of MLPH. Results In this study, we have shown that a mutation of MLPH is also associated with feather colour dilution in quail, but that the mutational event is extremely different. In this species, the lavender phenotype is associated with a non-lethal complex mutation involving three consecutive overlapping chromosomal changes (two inversions and one deletion) that have consequences on the genomic organization of four genes (MLPH and the neighbouring PRLH, RAB17 and LRRFIP1). The deletion of PRLH has no effect on the level of circulating prolactin. Lavender birds have lighter body weight, lower body temperature and increased feed consumption and residual feed intake than wild-type plumage quail, indicating that this complex mutation is affecting the metabolism and the regulation of homeothermy. Conclusions An extensive overlapping chromosome rearrangement was associated with a non-pathological Mendelian trait and minor, non deleterious effects in the lavender Japanese quail which is a natural knockout for PRLH