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D. Wang et al. / Catalysis Communications 28 (2012) 159–162
Table 2
Catalytic performance of the samples.a
Entry
Catalyst
Conversion (%)
Urea
Yield (%)b
Phenol
Salicylamide
4-hydroxy-benzamide
Xanthone
2,4,6-tris
(2-hydroxyphenyl)-1,
3,5-s-triazine
1
2
3
4
5
6
7
None
Al2O3
MgO
ZnO
MgAlO-2
MgAlO-3
MgAlO-4
3.7
5.9
0.3
0.4
2.3
3.2
3.7
3.1
2.1
3.7
5.9
0
0
0
0
0
1.9
0
0
0
34.0
45.5
53.7
45.7
31.3
28.6
32.4
43.2
37.8
26.6
0.6
1.3
2.1
1.6
0.5
1.6
3.3
2.8
2.1
1.4
0
0
a
Reaction conditions: reaction temperature, 230 °C; reaction time, 12 h; catalyst amount, 0.15 g; urea, 0.017 mol; phenol, 0.25 mol.
The product yields were calculated based on urea.
b
important role in the reaction. The yield of salicylamide was closely
related to the amounts of moderate basic sites.
In addition, a further study on the catalytic re-usability of MgAlO-2
was carried out. After the first run, the used MgAlO-2 sample was sep-
arated by filtrating, and washed with methanol several times, dried
and reused in four other catalytic cycles. Fig. 5 presents that it still
showed high catalytic performance after the fourth catalytic run. Addi-
tionally, the recovered catalyst after being reused four times was ana-
lyzed using XRD technique (see Fig. 1(b) MgAlO-2 after reaction).
Both diffraction peak number and intensity did not show any significant
changes. This demonstrated that a heterogeneous catalyst with high
catalytic performance and stability for this reaction was successfully
developed.
The effect of reaction time on the reaction is illustrated in Fig. 4
over MgAlO-2 as catalyst. The conversions of urea and phenol as
well as 4-hydroxybenzamide yield were consistently enhanced by in-
creasing the reaction time. However, the salicylamide yield reached
its peak at 12 h and then decreased. This might be due to the fact
that the consumption of salicylamide in the dehydration reaction to
produce 2,4,6-tris (2-hydroxyphenyl)-1,3,5-s-triazine surpasses its
formation from urea and phenol.
4. Conclusion
Mesoporous Mg/Al mixed oxides were prepared from hydrotalcite
precursors. These catalysts showed higher base-catalytic performance
than the corresponding pure MgO and Al2O3 for the synthesis of
salicylamide from urea and phenol, owing to their improved moder-
ate basic sites. When the reaction was carried out at 230 °C for
12 h, salicylamide yield could reach 43.2% over MgAlO-2. In addition,
it could be used for several runs without any obvious changes in the
catalytic performance.
Acknowledgment
This work was financially supported from the Special Fund of the
Chinese Academic of Science for Pilot Strategy of Science and Tech-
nology (XDA05010108) and the State Key Laboratory of Coal Conver-
sion Open Foundation (J12-13-609).
Fig. 4. Effect of reaction time on the reactant conversions and product yields over MgAlO-2.
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Fig. 5. Catalytic reusability of MgAlO-2.