(351d) 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.