176
C. Pirovano et al. / Catalysis Today 197 (2012) 170–177
Table 5
Catalytic performance of Ti-containing catalysts in TMP oxidation.
b
Catalyst
Ti content (wt.%)
Ti surface concentrationa (Ti atom nm−2
)
TMP conversion (%)
TMBQ selectivity (%)
TOFTMP (min−1
)
Ti4/SiO2-D-1
Ti4/SiO2-D-2
Ti4/SiO2-N-1
Ti/SiO2-N
Ti/MCM-41
Ti/MCM-41
1.26
2.18
1.19
2.09
2.00
0.95
0.30
0.52
0.22
0.38
0.26
0.12
99
97
96
97
98
97
96
100
99
91
77
2.0
2.2
1.6
1.4
2.7
2.7
47
Reaction conditions: 0.1 M TMP, 0.35 H2O2, 0.006 mmol Ti catalyst, 1 mL acetonitrile solvent, 80 ◦C, 30 min.
a
Estimation based on BET surface area of the support and Ti content.
(moles of TMP consumed)/(moles of Ti × time), determined from the initial rates of TMP consumption.
b
Ti4/SiO2 catalysts were easily recovered by filtration, washed,
calcined and reused, at least, in a second catalytic run. The calcina-
tion step at 500 ◦C was necessary to remove the organic by-products
(ca. 2–5 wt.%, as shown by TGA analysis) that lead to deactivation
of the Ti centres and to regenerate the chemical environment of the
catalytic sites. The recycled catalysts kept their oxidation ability. In
particular, reused Ti4/SiO2 systems showed a small loss (ca. 8–10%)
of activity for limonene and trans-stilbene with respect to fresh
catalyst. For cyclohexene epoxidation, fully comparable or even
slightly better activity with respect to the first run was recorded.
For TMP oxidation, the catalysts were reused in several consecutive
catalytic runs and solids with a higher Ti concentration showed to
be more stable to deactivation than the catalysts with a lower Ti
loading.
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Acknowledgements
C.P., M.G., V.D.S. and R.P. acknowledge financial support from EC
7th Framework Programme through the Marie Curie Initial Training
Network NANO-HOST (Grant Agreement No. 215193) and of the
Italian Ministry of Education, University and Research through the
Project “ItalNanoNet” (Rete Nazionale di Ricerca sulle Nanoscienze;
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