Молекулярный дизайн катализаторов и катализ в Ð¿Ñ€Ð¾Ñ†ÐµÑÑÐ°Ñ ...

most abundant form of tin is Sn-Pt alloy (85-100 %, depending on the Sn/Pt s
ratio). The Sn/Pt s ratio was increased up to 2.5 resulting in at least two types of
supported bimetallic nanoclusters: the Pt-rich and Sn-rich alloy phases.
The novelty is ascribed to the formation of different Lewis-acid type active sites
at the top of the supported platinum nanoclusters. In the new approach the
decomposition of tin organometallic species was carried out in the presence of
oxygen by using Temperature Programmed Oxidation and can be written as
follows:
M–{SnR (3-x) –(SnR (4-y) ) m } + a O 2 M–(SnO z ) n + b CO 2 + g H 2 O (2)
Upon changing conditions of CSRs used for tin anchoring variety of tin
containing entities, such as (i) tin enriched platinum, (ii) Sn-Pt alloy phases, (iii)
SnO x species anchored directly to the Pt surface, (iv) SnO x species at the Ptsupport
interface, (v) SnO x species at the support, can be formed. Different
spectroscopic techniques, such as FTIR, XPS, Mossbauer and methods of
computational chemistry were applied to study the formation of “metal ion-metal
nanocluster” type ensemble sites and the activation of different carbonyl
compounds and CO molecule.
In these supported Sn-Pt catalysts the Lewis-acid type active sites, i.e., SnO x
species, or electron deficient Sn ? δ+
entities formed in the atomic closeness of
supported platinum nanoclusters were involved in the creation of "metal ion-metal
nano-cluster" ensemble sites. The formation of the above species has been
evidenced by chemisorption, Mossbauer and FTIR spectroscopy. The atomic
closeness of ionic and metallic species provides unusual activity and selectivity to
these catalysts in variety of reactions. Sn-Pt/SiO 2 catalysts showed high, "reactant
induced" activity and unprecedented selectivity in the gas and liquid phase
hydrogenation of unsaturated aldehydes into unsaturated alcohols. The in situ
formation of Sn +4 species in the presence of crotonaldehyde and hydrogen has
been verified by in situ Mossbauer and FTIR spectroscopy.
In this way new type of Sn-Pt/Al 2 O 3 and Sn-Pt-Re/Al 2 O 3 naphtha reforming
catalysts with decreased aromatization and increased isomerization selectivity were
also prepared. Sn-Pt/SiO 2 catalysts containing SnO x moieties anchored to
platinum showed high activity in low temperature oxidation of CO by molecular
oxygen.
In this lecture details on the (i) design, (ii) preparation, (iii) characterization
and (iv) testing of new catalytic compositions containing highly active “metal ionmetal
nanocluster” type active site ensembles will be demonstrated and discussed.
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