Synthesis, Structure and Catalytic Activity of ... - Jacobs University

Ch.1 Introduction
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Fig. 1.19 Polyhedral representations of: a) the [α-1,2-PW10Ti2O39]2 dimer and b) the monomer
[PW10Ti2O40] 7-
Other results were published in 2005 66 concerning the influence of structures
around titanium centers in dimeric mono-, di-, and tri-titanium substituted
Keggin polyoxotungstates (Fig. 1.20) on the catalytic efficiency in alkenes
epoxidation. Later in 2007 67 , the three structures were compared to the novel
1host-2guest POM mentioned earlier (Fig. 1.11). In summary, there was a
non-linear increase in activity with the increase in titanium atoms. The tri-Ti
containing [(α-1,2,3-PTi3W9O37)2O3] 12- exhibited the fastest rate of formation
of the active hydroperoxo species facilitated by the intramolecular transfer of
protons bound to the surface edge sharing oxygens. And thus it also showed
the highest turnover frequency of the epoxidation of alkenes. In comparison,
the 1host-2guest was considerably more active than the three dimers showing
that it is more about structure rather than titanium content where the µ2-O
Ti-O-Ti site had obviously the significant influence.
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