Tailoring the Properties of Flame-Made Mixed Metal-Oxide Catalysts

Mixed metal-oxide based catalysts constitute a large fraction of today's heterogeneous catalysts. Especially supported transition metal oxides like V₂O₅, have proven to be very attractive for many catalytic applications including selective catalytic reduction (SCR), selective partial oxidations, total oxidations and oxidative dehydrogenation. Another important class of catalysts constitutes supported noble metal catalysts (e.g. Pt/Al₂O₃) often used in the synthesis of fine chemicals. For such catalyst systems surface properties like support ionicity can have substantial influence on the catalytic performance.

Here the application of flame spray pyrolysis (FSP) as powerful tool for the single-step synthesis of mixed metal-oxide catalysts (V₂O₅/TiO₂, V₂O₅/SiO₂) with high purity and reproducibility was explored. Special focus was placed but not limited on vanadia-based supported catalysts and the characterization of the material properties like specific surface area, cristallinity, reducibility and the VO_x species structure which constitute the active sites. Furthermore the influence of said structure on the catalytic behavior (activity and selectivity) in different catalytic applications (selective oxidation, total oxidation oxidative dehydrogenation) was analyzed and compared to classic wet-impregnated materials. In case of mixed-metal supported noble metal catalysts (Si- or Cs-doped Pt/Al₂O₃) emphasis was put on tuning the surface ionicity of the support and analyzing the influence on the noble metal particle size and the catalytic performance in hydrogenation reactions.

Such flame-made catalysts showed unique structural properties of the active site and distinct different catalytic behavior, often with superior activity and selectivity, compared to conventional catalytic materials derived by wet-chemistry methods.