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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.

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Abstract: In recent years, noble metals atomically dispersed on solid oxide supports have become a frontier of heterogeneous catalysis. In pursuit of an ultimate atom efficiency, the stability of single-atom catalysts is pivotal. Here we compare two Pd/CeO2 single-atom catalysts that are active in low-temperature CO oxidation and display drastically different structural dynamics under the reaction conditions. These catalysts were obtained by conventional impregnation on hydrothermally synthesized CeO2 and one-step flame spray pyrolysis. The oxidized Pd atoms in the impregnated catalyst were prone to reduction and sintering during CO oxidation, whereas they remained intact on the surface of the Pd-doped CeO2 derived by flame spray pyrolysis. A detailed in situ characterization linked the stability of the Pd single atoms to the reducibility of the Pd–CeO2 interface and the extent of reverse oxygen spillover. To understand the chemical phenomena that underlie the metal–support interactions is crucial to the rational design of stable single-atom catalysts.

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Abstract: Platinum functions exceptionally well as a nanoparticulate catalyst in many important fields, such as in the removal of atmospheric pollutants, but it is scarce, expensive and not always sufficiently durable. Here, we report a perovskite system in which 0.5 wt% Pt is integrated into the support and its subsequent conversion through exsolution to achieve a resilient catalyst. Owing to the instability of most Pt oxides at high temperatures, a thermally stable platinum oxide precursor, barium platinate, was used to preserve the platinum as an oxide during the solid-state synthesis in an approach akin to the Trojan horse legend. By tailoring the procedure, it is possible to produce a uniform equilibrated structure with active emergent Pt nanoparticles strongly embedded in the perovskite surface that display better CO oxidation activity and stability than those of conventionally prepared Pt catalysts. This catalyst was further evaluated for a variety of reactions under realistic test environments—CO and NO oxidation, diesel oxidation catalysis and ammonia slip reactions were investigated.

Open Access

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Abstract: Hybrid metal extrusion & bonding (HYB) is a joining method that enables solid-state bonding by combining addition of aluminium filler material through continuous extrusion with pressure exerted by a rotating steel tool. This work presents mechanical and microstructural characterisation of a second generation HYB butt joint of aluminium alloy 6082 and structural steel S355. The ultimate tensile strength was measured to be in the range of 184–220 MPa, which corresponds to 60–72% joint efficiency. Digital image correlation analysis of the strain development during tensile testing revealed that root cracks formed, before the final fracture ran close to the aluminium-steel interface. A significant amount of residual aluminium was found on the steel fracture surface, especially in regions that experienced higher pressure during joining. Scanning and transmission electron microscopy revealed that the bond strength could be attributed to a combination of microscale mechanical interlocking and a discontinuous nanoscale interfacial Al-Fe-Si intermetallic phase layer. Analysis of scanning electron diffraction data acquired in a tilt series, indicated that the polycrystalline intermetallic phase layer contained the cubic αc phase. The results give insight into the bonding mechanisms of aluminium-steel joints and into the performance of HYB joints, which may be used to better understand and further develop aluminium-steel joining processes.

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Abstract: Several concepts for platinum-based catalysts for the oxygen reduction reaction (ORR) are presented that exceed the US Department of Energy targets for Pt-related ORR mass activity. Most concepts achieve their high ORR activity by increasing the Pt specific activity at the expense of a lower electrochemically active surface area (ECSA). In the potential region controlled by kinetics, such a lower ECSA is counterbalanced by the high specific activity. At higher overpotentials, however, which are often applied in real systems, a low ECSA leads to limitations in the reaction rate not by kinetics, but by mass transport. Here we report on self-supported platinum–cobalt oxide networks that combine a high specific activity with a high ECSA. The high ECSA is achieved by a platinum–cobalt oxide bone nanostructure that exhibits unprecedentedly high mass activity for self-supported ORR catalysts. This concept promises a stable fuel-cell operation at high temperature, high current density and low humidification.