Dramatic promotion of copper-alumina catalysts by sodium for acetone trimerisation

Article abstract of DOI:10.1039/c4cy00440j

Na-promoted Cu-Al materials are efficient multifunctional catalysts for the direct conversion of gas phase acetone to diisobutyl ketone (DIBK) with unprecedented yields (up to 31%). The Na content is a major parameter determining the stability and the catalytic performance of these materials.

Full text of DOI:10.1039/c4cy00440j

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Dramatic promotion of copper–alumina catalysts
by sodium for acetone trimerisation†
Cite this: Catal. Sci. Technol., 2014,
, 2480
4
a
b
c
a
Emanuelle Ligner, Frédéric Meunier, Arnaud Travert,* Sylvie Maury
a
and Nicolas Cadran
Received 8th April 2014,
Accepted 15th May 2014
DOI: 10.1039/c4cy00440j
www.rsc.org/catalysis
Na-promoted Cu–Al materials are efficient multifunctional
catalysts for the direct conversion of gas phase acetone to
diisobutyl ketone (DIBK) with unprecedented yields (up to 31%).
The Na content is a major parameter determining the stability and
the catalytic performance of these materials.
(2) described in Scheme 1, which can be varied by modifying
the acid–base and hydrogenation properties of the catalyst.
Aldol condensation of gas phase acetone into MIBK
has been extensively studied using various zeotypes and
metal oxides promoted by transition metals (Pd, Pt, Ni or Cu)
4
–6
such as ZSM-5, X, SAPO, ALPON, MgO, Al
2
O
3
or calcined
One-pot processes are interesting with regards to atom and
energy efficiency and have been widely investigated in an
attempt to develop further sustainable organic synthesis. The
aldol condensation of acetone in a single reactor leads to the
formation of many products including methyl isobutyl
ketone (MIBK) and diisobutyl ketone (DIBK), which are used
7–23
hydrotalcites.
In these studies, however, the selectivity
towards DIBK was usually low, the largest DIBK yield was
reported by Hetterley et al. being ca. 26% at 70% conversion
over a Ni and Al mixed oxide promoted by Pd. De Jesús
Martínez-Ortiz et al. reported a trimer yield of approximately
23
8
% obtained over different Pd and Cu impregnated mixed
1
as solvents in paints.
3
oxides of magnesium and aluminium. Kozhevnikova et al.
obtained a maximum yield of 14% using a Zn–Cr mixed oxide
promoted by Pd.
A common global reaction scheme is described in
2
,3
Scheme 1. Self-aldol condensation of acetone on acid–base
sites leads to diacetone alcohol (DAA). DAA undergoes dehy-
dration leading to mesityl oxide (MO). Selective hydrogena-
tion of the CC bond on metallic sites gives MIBK. DIBK is
obtained after further aldol condensation of acetone with
MIBK followed by dehydration and hydrogenation of different
intermediates. Concurrently, the hydrogenation of the carbonyl
group of acetone leads to the formation of isopropanol (IPA),
which can be dehydrated on the acidic sites of the catalyst,
leading to the formation of propene and propane after hydro-
genation on metallic sites. Therefore, the selectivity to MIBK
and DIBK depends on the relative rates of steps (1) and
22
We report here noble metal-free Cu–Al-based catalysts as
promising bifunctional catalysts for the one-pot conversion
of gas phase acetone to DIBK. Outstanding results on the
impact of sodium on the activity and stability of the Cu–Al
based materials are described in this communication.
Cu- and Al-based catalysts were prepared by coprecipitation
of Cu and Al nitrate precursors in a 30% NaOH solution
24
(
pH 8), using similar Cu/Al molar ratios (i.e. 0.53 ± 0.01).
After filtration and washing, the precipitate was dried at
20 °C for 24 h and calcined at 800 °C for 5 hours. The con-
1
tent of sodium in these samples was varied by varying the
intensity of the washing step during the synthesis of the dif-
ferent solids (catalysts A–C, Table 1) or by adding sodium
nitrate by incipient wetness impregnation of sample B followed
by drying and calcination steps (catalysts D and E, Table 1). All
catalysts showed the copper aluminate crystalline phase (CuAl O )
a
IFP Energies nouvelles, Rond-Point de l'échangeur de Solaize, BP3,
6
9360 Solaize, France. E-mail: nicolas.cadran@ifpen.fr; Tel: +33 4 37 70 20 00
b
Institut de Recherche sur la Catalyse et l'Environnement de Lyon (IRCELYON),
2 4
Université Lyon 1, CNRS, 2, Avenue Albert Einstein, 69626 Villeurbanne, France.
E-mail: fcm@ircelyon.univ-lyon1.fr; Fax: +33 4 72 44 53 65
and some also showed a CuO phase after calcination, which
led to a Cu metallic phase after reduction at 300 °C. Typical
in situ X-ray diffraction patterns recorded during temperature-
programmed reduction of catalyst C are shown in Fig. 1.
The catalytic activity of the different catalysts for the gas-
phase aldol condensation of acetone was assessed at 3 bars
c
Laboratoire Catalyse et Spectrochimie (LCS), ENSICAEN, Université de Caen,
CNRS, 6, Boulevard du Maréchal Juin, 14050 Caen, France.
E-mail: arnaud.travert@ensicaen.fr
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/
c4cy00440j
2480 | Catal. Sci. Technol., 2014, 4, 2480–2483
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Scheme 1 Main reaction pathways relating to acetone conversion.
Table 1 Catalyst composition and surface areaa
−1
2
−1
Catalyst
Cu/Al (mol mol
)
Na (ppm)
SBET (m g
)
Fig. 2 Acetone conversion as a function of time on stream. Operating
A
B
C
D
E
0.52
0.54
0.52
0.54
0.54
<10
175
1640
4110
48 000
73
59
73
60
28
−1
conditions: T = 200 °C, P = 3 bar, WHSV = 1 h (1 g of catalyst,
−1
−1
−1
acetone = 1 g h ), N
2
= 9 L h , H
2
= 1 L h . Conversion based on
carbon weight.
a
Na content was determined by ICP-AES.
the stability of the catalysts were noted. Samples A, B and E
to a lesser extent exhibited significant deactivation with time
on stream. In contrast, the conversion measured over samples
C and D remained stable at ca. 70% and 60%, respectively.
These data clearly indicate that there is an optimal range of
Na loading in which the catalytic activity is stable under our
experimental conditions.
The yields of the main classes of products obtained over
the various samples after 10 and 120 min are shown in
Fig. 3. A fuller product distribution is given in the ESI.†
Samples A and B, which had the lowest Na content, exhibited
1 4
the highest yields of light products (C –C ), particularly
Fig. 1 XRD patterns of catalyst C after reduction for 30 min at
propene/propane and some cracking products of acetone
dimers (such as methane and isobutene). This can be rationalised
by the fact that, at low sodium content, the sample acidity is
sufficient to catalyze the dehydration of IPA in propene or the
cracking of, e.g., DAA in isobutene. Catalysts A and B were
also those that displayed the fastest decrease in the yield of
linear trimers with time on stream (Fig. 3).
In contrast, catalysts C and D exhibited lower yields
of light products and essentially stable yields of dimers and
trimers between 10 and 120 min. Dimers and trimers were by
far the main reaction products over samples C and D. The
yields of linear trimers obtained over catalyst C, ca. 33%,
were actually the highest ever reported, to the best of our
knowledge, including over noble metal-based catalysts.
Finally, catalyst E, with the largest Na content, showed
a moderate initial activity and some deactivation despite
low dehydration and cracking activities, indicating that larger
Na contents have a detrimental impact on the catalyst
performance.
different temperatures. Phases: CuO (ICDD PDF No. 04-005-4712);
0
CuAl
Al
2
O
4
(ICDD PDF No. 04-015-0578); Cu (ICDD PDF No. 04-003-1450);
2
O
3
(ICDD PDF No. 10-0425).
2
6
absolute pressure and 200 °C in a fixed bed reactor (stainless
−
1
steel; 1 g of catalyst; WHSV = 1 h ; [H ]/[acetone] = 2.56;
2
[
N ]/[H ] = 9) by on-line GC analysis. Prior to the reaction, the
2 2
catalysts were pre-treated with hydrogen at 300 °C for 2 h
and then overnight at 200 °C. Conversions are based on car-
bon weight.
2 4
The interest of using CuAl O as catalyst consists of the
well-known decomposition of these oxides under a reducing
atmosphere, which leads to the formation of metallic copper
and alumina. The presence of a large concentration of well-
dispersed copper metal should suffice to provide a significant
hydrogenation activity to the sample and make unnecessary
2
5
the use of noble metals.
The conversion of acetone with time on stream for our five
catalysts is shown in Fig. 2. Distinct behaviours concerning
It is likely that the presence of Na influences in many
different ways the structure of the catalyst, which in turn
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Fig. 3 Yields of the main reaction products of acetone conversion after 10 and 120 min under time on stream for the various catalysts. Light
products = propene, propane, cracking products; IPA = isopropanol; dimers = MIBK, MIBA (4-methylpentan-2-ol), 2-MP (2-methylpentane); linear
trimers = DIBK, DIBA (2,6-dimethylheptan-4-ol); others = TMB (1,3,5-trimethylbenzene), C12, unknown products. Operating conditions: T = 200 °C,
−
1
−1
−1
−1
2 2
P = 3 bar, WHSV = 1 h (1 g of catalyst, acetone = 1 g h ), N = 9 L h , H = 1 L h . Conversion based on carbon weight. Yields are based on
carbon weight%.
determines the catalytic activity and stability. A few hypothe-
ses, supported by the present catalytic tests, can be consid-
ered to explain the stabilization of the acetone conversion. In
particular, addition of sodium decreases surface acidity and IPA
dehydration/cracking reactions, as indicated by the decrease
of light gas yields (C –C ), hence limiting coke precursors
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1
4
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Another effect of Na could be the modification of the
structure of the Cu metallic particles. More work would be
needed to assess the structural effects induced by the promo-
tion with Na and then attempt to relate those to the improved
catalytic properties. This surely will be a difficult task, since
the reaction network is highly complex, involving many inter-
mediates and catalytic steps (Scheme 1).
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In conclusion, noble metal-free Na–Cu–Al-based for-
mulations are outstanding catalysts for the production of
DIBK from the direct aldol condensation of acetone in the
presence of hydrogen. The presence of sodium dramatically
modifies the catalytic properties of Cu–Al-based catalysts for
this reaction. Intermediate doping of sodium (corresponding
−
2
to a level of ca. 1 μmol m ) leads to highly selective and
stable catalysts for acetone conversion to linear dimers and
trimers.
1
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