Applied Catalysis A: General 262 (2004) 43–51
On the catalytic properties of mixed oxides obtained from
the Cu-Mg-Al LDH precursors in the process of
hydrogenation of the cinnamaldehyde
J. Barrault
a,∗
, A. Derouault
a
, G. Courtois
a
, J.M. Maissant
a
, J.C. Dupin
b
,
C. Guimon
b
, H. Martinez
b
, E. Dumitriu
c
a
Laboratoire de Catalyse en Chimie Organique (LACCO), UMR CNRS 6503, ESIP,
40 Avenue du Recteur Pineau, 86022 Poitiers Cedex, France
b
LPCM, UMR 5624, 2 Avenue P. Angot, 64053 Pau Cedex9, France
c
Laboratory of Catalysis, Technical University of Iasi, Iasi, Romania
Received in revised form 3 November 2003; accepted 12 November 2003
Abstract
Catalytic hydrogenation of cinnamaldehyde (CNA) was investigated over oxidic materials obtained by the calcination of Cu-Mg-Al
layered double hydroxide (LDH) precursors. A series of precursors with different Cu/Mg ratios (with a constant M
2+
/Al
3+
ratio) were
prepared by coprecipitation (under low supersaturation) and heated under reductive atmosphere until 623K in order to avoid the formation
of Cu-based spinels and to reduce the copper cations. The presence of Mg noticeably enhanced the selectivity of Cu-based catalysts with
respect to the hydrogenation of the carbonyl group relative to the favoured hydrogenation of the C=C bond. Moreover, the self-condensation
of hydrocinnamaldehyde (HCNA) and the cross-condensation of hydrocinnamaldehyde with cinnamaldehyde were also observed especially
when the basic sites of LDH structures are preponderant over hydrogenation species. Finally, all that reaction from CNA are of great interest
for getting information about: (i) basic sites involved in condensation of CNA and HCNA; and (ii) active species for selective hydrogenation
of CNA to cinnamyl alcohol (CNOL) which seem in strong interaction with the first ones.
© 2003 Elsevier B.V. All rights reserved.
Keywords: Hydrogenation; Cinnamaldehyde; Layered double hydroxides; Mixed oxides; Aldol condensation
1. Introduction
The chemio- and regioselective catalytic hydrogenation
of ,-unsaturated aldehydes, such as cinnamaldehyde, is
of great importance in the synthesis of valuable fine chem-
icals. Both the cinnamaldehyde and the cinnamyl alcohol
(CNOL), the last being obtained by the selective reduction
of the cinnamaldehyde, are widely used in perfumes and
flavouring industries. In addition, cinnamyl alcohol is an im-
portant building block in organic synthesis. Normally, dur-
ing the hydrogenation of cinnamaldehyde (CNA), both the
carbonyl C=O group and the C=C double bond are hydro-
genated to hydrocinnamaldehyde (HCNA) and CNOL via
two parallel processes (1) and (2) in Scheme 1, and finally
to hydrocinnamyl alcohol (HCNOL).
∗
Corresponding author. Tel.: +33-549-453999; fax: +33-549-453349.
E-mail address: joel.barrault@univ-poitiers.fr (J. Barrault).
Although hydrogenation of the C=C bond is thermody-
namically more favourable, numerous studies were done to
enhance the selective hydrogenation of the C=O bond. The
most successful attempts were carried out in the presence
of heterogeneous catalysts prepared from metals belonging
to group VIII, such as Pt, Ir, Os, etc. It was observed that
the reaction selectivity is influenced by several parameters
such as the metal particle size, the precursor, the method of
preparation, the support (Al
2
O
3
[1], SiO
2
[2], zeolite [3,4],
clays [5], carbon nanofibres [6,7], etc.), the nature of the
solvent [8] or the application of the ultrasonic irradiation
[9]. Often, the selectivity to the unsaturated alcohol required
catalyst modification and promotion, such as the addition of
transition metal salts, promoters (e.g. Ge, Sn, Pb [10,11])
or alloying the base metal of the catalyst with another one
[12].
Besides the noble metal-based catalysts, other catalytic
materials, such as those containing Cu, were investigated for
0926-860X/$ – see front matter © 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2003.11.020