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A.M.R. Galletti et al. / Applied Catalysis A: General 386 (2010) 124–131
Table 3
Selective hydrogenation of cinnamaldehyde (CAL) to hydrocinnamaldehyde (HCAL) in the presence of commercial (1% and 5% Pd/Al2O3 Aldrich) and synthesized 2–7 catalysts
and of colloidal Pd-nanoparticles (Sample 1)a.
Run
Catalyst sample
CAL conv. (mol%)
Selectivity to HCAL (mol%)b
0.5 h
1 h
3 h
99.3
98.1
20.5
98.8
33.3
100
100
100
6 h
7 h
0.5 h
1 h
92.5
3 h
6 h
7 h
1
2
1%
5%
84.0
60.2
6.1
93.1
85.0
9.1
93.8
93.1
98.4
94.0
95.5
97.1
97.1
96.9
92.7
93.1
100
92.0
90.3
96.5
93.8
94.6
96.9
96.8
96.4
91.8
91.1
93.2
91.3
98.0
93.9
95.3
97.0
96.9
96.5
92.1
92.2
3
4
5
2
3
4
5
74.7
59.7
87.0
77.0
93.3
93.5
93.0
92.1
78.8
11.1
79.8
78.6
78.9
18.1
15.9
4.4
93.8
16.0
97.9
96.3
97.7
25.4
23.1
9.0
6
7c
8
5 recycled from run 6
5-bis
9
10
11
6
7
1
47.7
39.0
11.8
69.2
61.1
18.3
80.8
75.0
21.0
91.6
90.9
84.9
91.4
90.7
83.2
100
a
Reaction conditions: Pd: 2.50 mg; solvent: decalin (100 ml); cinnamaldehyde: 3.8 ml; temperature: 100 ◦C; PH2 :2 MPa.
Solid catalyst recovered from run 6 was recycled.
b
c
ducible results in terms of both activity and selectivity (compare
inexpensive and safe procedure has been employed for the
reproducible preparation of a family of supported palladium
nanoparticles characterized by small diameters and narrow particle
size distributions using a low-boiling alcohol as solvent/reducing
agent in the absence of any additional polymeric stabilizer. This
approach is of particular interest because represents a valuable
route involving low energy and time consumptions.
These new supported palladium nanocatalysts have shown
interesting catalytic performances in terms of both activity and
selectivity when employed in preliminary runs of heteroge-
neous hydrogenation of cinnamaldehyde to hydrocinnamaldehyde,
reaching from high to complete substrate conversions and selec-
tivities up to 97% in hydrocinnamaldehyde at complete substrate
conversion.
run 7 with run 6, Table 3), and two further successive recycle runs
gave quite analogous results, thus confirming the stability of this
heterogeneous system under recycling. On the other hand, when
the duplicate Sample 5-bis was tested (run 8, Table 3), almost iden-
tical results to those obtained with Sample 5 were ascertained.
The best catalytic performances of Sample 5 could be reasonably
ascribed to different concomitant factors: (a) the almost complete
reduction of palladium(II) to palladium(0), (b) the low palladium
loading and (c) the small average diameter and the relatively nar-
terized by much higher metal loading (4.8 wt%) and larger particle
diameter and size distribution as well as by not complete reduction
extent, were significantly lower in terms of both activity and selec-
terms of activity and selectivity, were observed for Sample 7, pre-
pared in ethylene glycol and characterized by a morphology and an
10, Table 3).
Acknowledgments
This work was financially supported by University of Pisa. G.G.
thanks FIRENZE HYDROLAB for financial supports.
The catalytic activity is favoured by the reduction extent and,
on the other hand, the particle size effect resulted determinant
for the C C bond hydrogenation ability, as observed by Gallezot
et al. [50,52] and very recently by Chizari et al. for Pd/CNTs cata-
lysts [53]. The small particles, with narrow size distribution, result
more selective towards the formation of HCAL than big ones, whose
surface is seen as a flat surface which leads to an enhanced repul-
sion between the phenyl ring of the rigid molecule of CAL and the
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In this paper a simple and environmentally friendly microwave-
assisted protocol for the synthesis of Pd nanocolloids and supported
Pd/␥-Al2O3 nanocatalysts has been developed. This very rapid,