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Titanium silicalite (TS-1) (Taramasso et
al., 1983) is one of the most important active
and selective heterogeneous catalysts which can be synthesized by isomorphous
substitution of Si4+ with
Ti4+ of silicalite zeolite. Ti-containing siliceous nanoporous and
mesoporous materials have been found to exhibit excellent performance in low-temperature
oxidation reactions in the presence of aqueous solutions of
H2O2 (Notari, 1996). Typical
reactions catalyzed by TS-1 include phenol hydroxylation (Notari, 1996), olefin epoxidation
(Clerici et al., 1991; Clerici and Ingallina, 1993; Mantegazza et al., 1994; Notari, 1996; and Lane and Burgess, 2003), alkane oxidation (Clerici, 1991; Notari, 1996; and Clerici,
2001), oxidation of ammonia to hydroxylamine (Mantegazza et al., 1994; Notari, 1996; and Mantegazza et al., 1999), cyclohexanone ammoximation (Roffia et al., 1990; Notari, 1996; LeBars et
al., 1996; and Mantegazza et al., 1999), ammoximation of
ortho and
para-hydroxyacetophenones (LeBars et al., 1996), conversion of secondary amines
to dialkylhydroxylamines (Roffia et al., 1990; and Notari, 1996) and conversion of
secondary alcohols to ketones (Notari, 1996). Several experimental (Roffia et al., 1990; Clerici et al., 1991; Clerici, 1991; Milliani et al., 1992; Clerici and Ingallina, 1993; Mantegazza et al., 1994; Le Bars et al., 1996; Notari, 1996; Vayssilov, 1997; Lamberti et al., 1998; Lamberti et al., 1999; Mantegazza et al., 1999; Gleeson et al., 2000;Clerici,
2001; Lane and Burgess, 2003; and Antcliff et
al., 2003) and theoretical studies (de Man andSauer, 1996; Njo et al., 1997; Vayssilov and van, 1998; Ricchiaridi et al., 2000; Munakata et al., 2001; Damin et al., 2002; Atoguchi and Yao, 2003; and Deka et al., 2005) reveal that the substitution of
Si by Ti is isomorphous in well-prepared samples. It is also believed that the distribution of
Ti over the available framework sites is partially disordered. The factors responsible
for remarkable and unusual catalytic activities of TS-1 are believed to be high
coordination ability of Ti (IV) sites associated with the hydrophobicity of silicalite structure,
spatial selectivity and random distribution of Ti (IV) sites.
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