Heterogeneous Catalysis by Flame-Made Nanoparticles

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Abstract
In search of highly active nanoparticles for catalytic applications, flame aerosol technology turns out to be a promising method for its capacity to consistently produce highly pure nanoparticles. Starting with the production of simple oxides such as silica and titania in the forties, flame aerosol technology now facilitates production of nanoparticles in megaton quantities. Fundamental research on particle formation in the gas phase and the influence of process parameters and reactor design on final product properties have advanced the field to a stage where multicomponent materials can be produced. Flame production of vanadia/titania catalysts for NOx removal from exhaust gases by selective reduction by ammonia affords enhanced activity at low temperature when compared to corresponding materials prepared by wet-chemical methods. Furthermore, flame synthesis of titania/silica yields catalysts for the epoxidation of olefins with high accessibility of the active titanium sites and improved selectivity. Spectroscopic studies revealed that the same active sites as in the wet-phase derived catalysts are produced by flame synthesis but at a higher content. The high temperature during the preparation favors the formation of well-defined species on a hydrophobic surface. The flame synthesis of heterogeneous catalysts is brought from laboratory scale to pilot scale production at up to 500 g/h to make the novel materials suitable for industrial performance tests.