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N. Carrara et al. / Catalysis Communications 61 (2015) 72–77
Table 2
Supports mechanical properties.
Support
SDa
SLa
Attrition loss (%)
1800 turns
Attrition loss (%)
1800 turns
(kg/cm2)
(kg/cm2)
Carbon RX3
γ-Al2O3
α-Al2O3
UTAl
b100
b100
282 43
392 57
348 41
217 101
703 199
2053 398
4708 690
3741 900
1.659
0.167
1.124
0.028
0.046
6.859
3.103
6.002
0.136
0.189
BTAl
a
From Badano et al. 2010 [11].
At the reaction conditions used, irrespective of the chemical nature
of the organic phase of the composite support, global selectivities to
the desired products in excess of 98% were obtained. The desired reac-
tions were the hydrogenation of styrene to ethylbenzene and the hydro-
genation of 2,3-butanedione to 3-hydroxy-2-propanone (Fig. 5(a) and
(b)). The hydrogenation reaction of styrene to ethylbenzene is used as
a reference for the performance of the catalysts for the stabilization of
pyrolysis gasoline. Many of them are based on supported Pd due to
the good properties of this metal [12]. Pd is also the best noble metal
in terms of selectivity for the partial hydrogenation of diketones [13].
Besides the reaction of hydrogenation of 1-heptyne, as seen in
Fig. 5(c) and (d), behaved as a consecutive reaction of the type
A → B → C, where the main product of the first step is 1-heptene.
Once the main reactant is depleted, in a second step the hydrogenation
of 1-heptene to n-heptane occurs. In both catalysts the selectivity to 1-
heptene remained at values of 90–93% until the maximum concentra-
tion of the alkene was achieved. The values of initial activity were in-
cluded in Table 1.
The PdBTAl catalysts have a higher activity than the PdUTAl ones, the
effect being more evident in the catalysts with a lower noble metal
charge. The difference can be related to the presence of electrodeficient
Pdδ+ species with δ ≈ 0. In other types of reactions a promoting effect
has been attributed to the presence of Pdn+ species [20].
Additional experiments regarding the reusability were made with
the 0.3PdBTAl and 0.3PdUTAl catalysts in a series of three consecutive
reactions of styrene hydrogenation. The results showed negligible dif-
ferences in the initial and final conversion, and ICP analysis demonstrat-
ed that there was no leaching of the Pd active phase. This points to the
high reusability of this kind of novel catalysts.
4. Conclusions
Two composite supports of mixed organic–inorganic nature were
synthesized. The inorganic phase is provided by γ-Al2O3 particles and
the organic phase by polymers obtained by the combination of two
monomers of acrylic base with functionality 4. These new materials
proved to have good mechanical properties both to diametral and
axial compression as well as attrition resistance, displaying values supe-
rior to common commercial supports.
The pelletized egg-shell catalysts were active and highly selective to
the desired products in the reactions tested, that were of the A → B → C
consecutive type. A high concentration to the B intermediate (ethylben-
zene, 3-hydroxy-2-butanone or 1-heptene) was obtained in all cases.
This pattern was attributed to the low contact time of the reactants
and products with the metal phase and to the better heat dissipation
from the catalyst surface. The latter would prevent the overheating
over the active sites and the formation of undesired by-products.
These properties would be related to the small thickness of the metal
layer on the outer surface of the catalysts, as indicated by the OM,
SEM, EPMA and XPS characterization data.
Fig. 5. Catalytic evaluation results: a) styrene hydrogenation [toluene solvent, C0
=
styrene
0.445 M, 2.0 MPa, 353 K, WCat = 0.3 g (1 wt.% Pd) or 2 g (0.3 wt.% Pd)]; b) 2,3-butanedione
hydrogenation [isopropyl alcohol solvent, C0
= 0.057 M, 4.0 MPa, 368 K,
2,3-butanodione
WCat = 2 g]; and c) 0.3PdBTAl and d) 0.3PdUTAl 1-heptyne hydrogenation [toluene sol-
vent, C01-heptyne = 0.350 M, 0.15 MPa, 303 K, WCat = 0.75 g].
The results of mechanical resistance and catalytic activity show that
these inorganic–organic composites show promise as supports of noble
metals for selective hydrogenation reactions. Particularly they enable
the synthesis of egg-shell catalysts in a simple way due to the preferen-
tial deposition of the metal on the outer layer during impregnation.
These catalysts could be advantageously used in slurry reactors and
The highest activity is obtained with the BTAl based catalysts. This
could be due to the different electronic state of the metal on these sup-
ports. According to the XPS results over BTAl the metal was mainly pres-
ent as Pdδ+ while on UTAl it was found as Pd0.