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Abstract: Ceria (cerium oxide) based materials have been widely used for catalytic applications including; fluid catalytic cracking, water gas shift reactions, solid oxide fuel cells and automotive catalytic after-treatment. It has often been the material of choice for supporting precious metals in many of the applications previously mentioned, as it can provide a high surface area and has excellent redox properties. This enables ceria to absorb oxygen into its structure and release it again, to facilitate oxidation reactions. Cerium is also one of the most abundant rare earth metals, making it a relatively cost effective material to use in industrial applications. For these reasons, cerium oxide remains to be a material of high interest for the development of cost-effective industrial catalysts and is, therefore, the focal material for this work. Modern internal combustion engine technology is being directed towards lean burn operation, involving higher air-fuel ratios in order to improve thermal efficiency. In turn, the operating temperature of modern engines is being reduced, providing less of the heat energy required to activate the catalysts in the after-treatment system. Therefore, in order to mitigate the emission from efficient lean burn engines and comply with emission regulations, the requirement for low temperature automotive catalysts is apparent. The objective of this work is to develop effective ceria based materials for the application of modern automotive after-treatment catalysis. The first approach is the use of a novel method for the preparation of a mixed oxide catalysts, which show high activity for CO and HC oxidation at low temperature. The preparation of ceria/manganese mixed oxide catalysts using a novel synthesis method has been studied and the materials were characterised to gain insights of their structure and morphology. Temperature programmed reactions using a complex mixture of reactants, before and after hydrothermal aging, were carried out to investigate their application for automotive emission control. The results from these studies were compared with more conventional ceria based materials that are often used for automotive after-treatment. A second approach used in this work is a post synthesis technique for the surface modification of ceria catalysts using ion bombardment. This technique was carried out on a commercially sourced, model catalyst. A Pt-CeO2/ZrO2 was treated with nitrogen ion irradiation and the effects of the adjustable parameters of the ion beam were investigated by carrying out temperature programmed reactions. The samples were also extensively characterised using XAFS and XPS techniques to understand the effects of the ion beam treatment on the structure, morphology and Pt dispersion of the materials.

Open Access

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Abstract: CYP505A30 is a fungal, self-sufficient cytochrome P450 monooxygenase that can selectively oxyfunctionalise n-alkanes, fatty alcohols, and fatty acids. From alkanes, it produces a mixture of non-vicinal diols by two sequential hydroxylation reactions. Here we report the structure of the haem domain of CYP505A30, the first structure for a member of the CYP505 family, with dodecanoic acid bound within the active site. Overall, a high structural similarity to the related bacterial CYP102A1 was observed, despite low sequence identity (<40 %). Comparison of the active sites, however, showed a high degree of conservation with only two amino acid differences close to the haem. Stabilisation of the acid substrate in CYP505A30 also occurs, as in CYP102A1, via an arginine residue. However, compared to R47, which is situated in the β1 region of CYP102A1, R358 is located in the β3 region of CYP505A30. We furthermore created mutants to test if it is possible to rationally transfer the knowledge on active site mutations in CYP102A1 to change the regioselectivity of CYP505A30. The introduction of F93V, I334F mutations resulted in increased ω-1 (C2) regioselectivity, similar to CYP102A1 328-87, of more than 80 % for n-octane and 90 % for n-decane. Changing residues to resemble the 102A1 wildtype increased the regioselectivity towards ω-2 (C3) to over 60 % for both substrates. The knowledge gained from this study unlocks a more selective production of symmetrical non-vicinal diols from n-alkanes.

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Abstract: Despite self-supporting ultrathin Si membranes are already being widely applied, its thickness control in micron scale still remains a big challenge for delicate systems such as micro-opto-electro-mechanical systems and silicon-based X-ray diffractive optics. Instead of using the conventional wet etch rate of Si to monitor the membrane thickness, this work has developed a reliable approach to control the membrane thickness in the precision of micrometer order by using an optical detection hole with high precision depth, which decides the membrane thickness in the Si thinning process. The wet etch rate is first optimized to ensure the fundamental condition for such a thickness control. Furthermore, the membrane surface roughness is greatly reduced by optimizing the additive ethanol concentration in the KOH etchant, based on the investigation results for the origin of the membrane surface roughness. Using the proposed etching and thickness-monitoring method, self-supporting micron thick Si (100) membranes with the surface roughness of <15 nm have been successfully fabricated.

Open Access

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Abstract: Isobutene is a high value gaseous alkene used as fuel additive and a chemical building block. As an alternative to fossil fuel derived isobutene, we here develop a modified mevalonate pathway for the production of isobutene from glucose in vivo. The final step in the pathway consists of the decarboxylation of 3-methylcrotonic acid, catalysed by an evolved ferulic acid decarboxylase (Fdc) enzyme. Fdc belongs to the prFMN-dependent UbiD enzyme family that catalyses reversible decarboxylation of (hetero)aromatic acids or acrylic acids with extended conjugation. Following a screen of an Fdc library for inherent 3-methylcrotonic acid decarboxylase activity, directed evolution yields variants with up to an 80-fold increase in activity. Crystal structures of the evolved variants reveal that changes in the substrate binding pocket are responsible for increased selectivity. Solution and computational studies suggest that isobutene cycloelimination is rate limiting and strictly dependent on presence of the 3-methyl group.

Open Access

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Abstract: Herein we report unprecedented location-dependent, size-selective binding to designed lanthanide (Ln 3+ ) sites within miniature protein coiled coil scaffolds. Not only do these engineered sites display unusual Ln 3+ selectivity for moderately large Ln 3+ ions (Nd to Tb), for the first time we demonstrate that selectivity can be location-dependent and can be programmed into the sequence. A 1 nm linear translation of the binding site towards the N-terminus can convert a selective site into a highly promiscuous one. An X-ray crystal structure, the first of a lanthanide binding site within a coiled coil to be reported, coupled with CD studies, reveal the existence of an optimal radius that likely stems from the structural constraints of the coiled coil scaffold. To the best of our knowledge this is the first report of location-dependent metal selectivity within a coiled coil scaffold, as well as the first report of location-dependent Ln 3+ selectivity within a protein.