Acidez Hidrotalcitas

Applied Catalysis A: General 178 (1999) 145±157

In¯uence of the acid±base properties of solid catalysts
derived from hydrotalcite-like compounds on the
condensation of formaldehyde and acetaldehyde
Emil Dumitriua,*, Vasile Huleaa, Carmen Chelarua, Cezar Catrinescua,
Didier Tichitb, Robert Durandb
b

a
Laboratory of Catalysis, Technical University of Iasi, 71 D. Mangeron Ave.,6600-Iasi, Romania
Laboratoire de Materiaux Catalytiques et Catalyse en Chimie Organique, UMR 5618 ENSCM-CNRS, Montpellier, France

Received 11 March 1998; received in revised form 24 July 1998; accepted 30 July 1998

Abstract
The vapor-phase aldol condensation of formaldehyde with acetaldehyde was studied using various oxide mixtures obtained
in situ from hydrotalcite-like materials as catalysts.All samples exhibited catalytic activity, but the selectivity to both the aldol
condensation and the acrolein formation is governed by the balance of acidic and basic properties. The oxides containing Mg
and Al or Co and Al showed a high selectivity to aldol condensation (90% at 3008C) as well as to cross-condensation (80% at
3008C). The effects of both the reaction variables (temperature,mole ratio of reagents) and the catalyst variables (nature of
cations, nature of anions) were studied. # 1999 Elsevier Science B.V. All rights reserved.
Keywords: Hydrotalcite-like materials; Acid±base properties; Aldol condensation; Acrolein; Formaldehyde; Acetaldehyde

1. Introduction
The condensation reactions of aldehydes, as well as
of ketones, are widely used in organic synthesis,mainly because they lead to C±C bond formation:

These reactions are typically catalyzed by bases, but
can also proceed over acid catalysts. Of course, the
aldehydes (ketones) can be the same or different.
*Corresponding author.

In the case of the aldol condensation of aldehydes,
when the aldehydes are different, two pathways may
be involved, namely the self- and cross-condensationreactions. We can note that besides the aldol condensation products, depending on the nature of active
sites, the aldehydes can be involved into Cannizzaro,
Tischenko and other reactions, which enlarge the
range of the ®rst generation of products. In the second
stage various condensation, polymerization and other
reactions can take place.
Obviously, the two aldehydes have a close reactivity, andthus an interesting problem appears: if the
reaction can be selectively carried out towards self- or
cross-condensation, in other words, if the acid±base

0926-860X/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S0926-860X(98)00282-8

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E. Dumitriu et al. / Applied Catalysis A: General 178 (1999) 145±157

Scheme 1.

properties of the solid catalystscan signi®cantly
in¯uence the ratio between self- and cross-condensation. In order to investigate this problem we have
chosen the gas phase condensation of acetaldehyde
with formaldehyde (Scheme 1) which introduces certain simpli®cations, especially due to the fact that in
the gas phase formaldehyde does not self-condense.
Also, the formaldehyde acts only as carbonyl component, whileacetaldehyde acts both as carbonyl and
methylene component.
The aldol condensation of acetaldehyde with formaldehyde in gaseous phase was carried out over
various catalysts: single, binary or ternary oxides
[1±4], small pore zeolites [5±7], HZSM-5 and boralites [8,9], pillared clays [10], etc. Referring to the
oxide catalysts, Ai [1,2] showed that the activity and
selectivity of catalysts for thealdol condensation of
formaldehyde and acetaldehyde may be governed by
the balance of acidic and basic properties. He suggests
that the aldol condensation is catalyzed by basic sites,
but the sites required to promote the cross-condensation consist of very weakly basic centers. Also, Ai
found that the catalyst loses from its activity when the
basic property is suppressed too much by the...