Fundamental studies of hydrocarbon conversions over supported bimetallic catalysts

The reactions of ethane and ethylene over selected silica-supported group VIII metal catalysts have been investigated using reaction studies and nuclear magnetic resonance (NMR) spectroscopy. The activity of the ruthenium-group IB bimetallic system for the ethane hydrogenolysis reaction was investigated as a function of group IB metal content and ethane and hydrogen partial pressures, while the reactions of ethylene over silica-supported platinum catalysts were studied using NMR;The turnover frequency of the silica-supported ruthenium catalysts for ethane hydrogenolysis as either copper or silver was added tended to change as the group IB metal was first added until a critical point was reached. After this point, increasing the proportion of group IB metal had no significant effect on the specific activity of the catalyst. As was expected, copper, the more strongly segregating element, reached this critical point before silver. The critical point is believed to correspond to the point at which all the edge and corner sites in the supported bimetallic crystallite are occupied by the group IB metal;The apparent orders of reaction for ethane hydrogenolysis over the ruthenium-group IB catalysts was measured as a function of temperature. It appears from these measurements that the principal role of the edge and corner sites of a ruthenium catalyst for this reaction is the desorption and adsorption of hydrogen. At the higher temperatures studied, it appears that copper occupying the low coordination sites of a bimetallic crystallites is also active for the desorption/adsorption of hydrogen;The reactions of ethylene over silica-supported platinum catalysts has been investigated using NMR. The ethylene to surface platinum atom ratio used in this work was in the 10 to 20 range, far higher than that used for typical single crystal studies. No significant activity was observed at room temperature. At temperatures in the 400 K to 550 K region a number of products were identified, including ethane, methane, and cis- and trans-but-2-ene. At still higher temperatures coke was formed on the surface of the catalyst. This coke was characterized as being predominantly aromatic in nature

Resilience of New Zealand indigenous forest fragments to impacts of livestock and pest mammals

A number of factors have combined to diminish ecosystem integrity in New Zealand indigenous lowland forest fragments surrounded by intensively grazed pasture. Livestock grazing, mammalian pests, adventive weeds and altered nutrient input regimes are important drivers compounding the changes in fragment structure and function due to historical deforestation and fragmentation. We used qualitative systems modelling and empirical data from Beilschmiedia tawa dominated lowland forest fragments in the Waikato Region to explore the relevance of two common resilience paradigms – engineering resilience and ecological resilience – for addressing the conservation management of forest fragments into the future. Grazing by livestock and foraging/predation by introduced mammalian pests both have direct detrimental impacts on key structural and functional attributes of forest fragments. Release from these perturbations through fencing and pest control leads to partial or full recovery of some key indicators (i.e. increased indigenous plant regeneration and cover, increased invertebrate populations and litter mass, decreased soil fertility and increased nesting success) relative to levels seen in larger forest systems over a range of timescales. These changes indicate that forest fragments do show resilience consistent with adopting an engineering resilience paradigm for conservation management, in the landscape context studied. The relevance of the ecological resilience paradigm in these ecosystems is obscured by limited data. We characterise forest fragment dynamics in terms of changes in indigenous species occupancy and functional dominance, and present a conceptual model for the management of forest fragment ecosystems

Stable manifolds under very weak hyperbolicity conditions

We present an argument for proving the existence of local stable and unstable manifolds in a general abstract setting and under very weak hyperbolicity conditions.Comment: 20 page

Biocompatibility of CaO-Na2O-SiO2/TiO2 Glass Ceramic Scaffolds for Orthopaedic Applications

This work aims to determine the effect of substituting TiO2 for SiO2 in a 0.62SiO2-Na2O-0.24CaO based glass-ceramic scaffold. High temperature X-ray Diffraction (HT-XRD) was used to determine the sintering temperature (700oC). Both optical microscopy and x-ray micotomography was used to determine the average pore size (540-680ìm) of each scaffold. Cytocompatibility of each scaffold was conducted using murine mesenchymal stem cells. © 2013 IEEE

Fabrication of CaO-NaO-SiO2/TiO2 Scaffolds for Surgical Applications

A series of titanium (Ti) based glasses were formulated (0.62 SiO2-0.14 Na2O-0.24 CaO, with 0.05 mol% TiO2 substitutions for SiO2) to develop glass/ceramic scaffolds for bone augmentation. Glasses were initially characterised using X-ray diffraction (XRD) and particle size analysis, where the starting materials were amorphous with 4.5 μm particles. Hot stage microscopy and high temperature XRD were used to determine the sintering temperature (̃700 °C) and any crystalline phases present in this region (Na2Ca3Si6O16, combeite and quartz). Hardness testing revealed that the Ti-free control (ScC- 2.4 GPa) had a significantly lower hardness than the Ti-containing materials (Sc1 and Sc2 ̃6.6 GPa). Optical microscopy determined pore sizes ranging from 544 to 955 lm. X-ray microtomography calculated porosity from 87 to 93 % and surface area measurements ranging from 2.5 to 3.3 SA/mm3. Cytotoxicity testing (using mesenchymal stem cells) revealed that all materials encouraged cell proliferation, particularly the higher Ti-containing scaffolds over 24-72 h. © Springer Science+Business Media, LLC 2012