Catalytic combustion in environmental protection and energy production

Sammanfattning: Catalytic combustion is an important area of catalysis and is used in energy production as well as in the abatement of harmful emissions of various types. This thesis is focused on three different areas of catalytic combustion: - Catalytic combustion of diesel soot - Development of catalytically active wire meshes through thermal spraying - Stabilisation and activation of g-alumina for methane combustion The first part of the thesis gives an introductory description of different aspects of catalytic combustion. This part also includes a review of different catalytic burners which have been studied during the course of the research work. Emissions of diesel soot may be trapped and combusted in a particulate trap coated with catalytically active materials. The soot particles must be combusted at temperatures prevailing in diesel exhausts, generally between 150 and 400°C. To facilitate effective combustion at these temperatures, the particulate trap should be coated with an oxide catalyst consisting of V2O5/CuO (V:Cu=0.9 on molar basis). Catalytically active wire meshes offer a number of advantages over pellets and monolith catalysts. They combine geometric flexibility with excellent mass- and heat- transfer characteristics and a low pressure drop. By using a modified thermal spray technique, it is possible to produce porous adhesive ceramic coatings on metal surfaces. The specific surface area can be increased through deposition of a high-surface-area material into the macro-porosity of the as-sprayed layer. The ceramic layer is finally activated through a conventional impregnation technique. Palladium dispersed onto a Si-stabilised g-alumina is an appropriate combustion catalyst at temperatures below 1000°C. Adding small amounts of rhodium or platinum to the palladium increases the catalyst activity but decreases the catalyst's stability to thermal deactivation. The addition of rare-earth-metal oxides will lead to increased thermal stability but to a decreased activity. Long-term deactivation tests show that the activity for combustion of methane decreases to the same extent as the value of the specific surface area, thus indicating that the alumina surface may play an important role during the activation of adsorbed methane molecules.