G Model
CATTOD-8980; No. of Pages5
ARTICLE IN PRESS
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V.C. Corberán et al. / Catalysis Today xxx (2014) xxx–xxx
by the last turn of century [7]. Conventional oxidation processes
in industry are based upon the use of stoichiometric oxidants, and
are not environmentally friendly. Interest in green sustainable pro-
10-fold increase of papers on the subject from 1998 to 2012 [8], but
reports on selective oxidation of fatty alcohols with more than eight
carbon atoms (C8+) are really scarce: only 15 references since 1990;
noticeably, none on tetradecanol oxidation and none reporting the
use of nano gold catalysts [9].
Au
CeO2/Al2O3
Au/CeO2/Al2O3
This is probably due to their specific chemical and physical char-
acteristics. Being primary and aliphatic, reactivity of fatty alcohols
is the lowest among those of the different alcohol types (in fact, 1-
octanol oxidation is frequently tested as for comparative purposes
for this reason), and besides, it usually decreases with the increase
of carbon chain length. In addition, their hydrophobicity, viscos-
ity and melting and boiling points also increase with carbon chain
length, which imposes restrictions in the reaction conditions for
the higher alcohols oxidation.
CeO2/Al2O3
80
10
20
30
40
50
60
70
Fig. 1. X-ray diffractograms of the catalyst and the support.
In this paper, we investigate the oxidation of 1-tetradecanol
as a model molecule for the higher fatty alcohols. To our knowl-
reported only twice. The first one, in the liquid phase, using a
PtO2 catalyst pretreated in hydrogen; the main product was the
aldehyde or the acid depending on the amount of oxygen and the
reaction time [10]. The other, in the gas phase, catalyzed by gold
plated copper wire, that yields 59% aldehyde, with 85% selectivity,
at 312 ◦C [4]. In this work, we seek adherence to green chemistry
principles, by using a heterogeneous catalyst, a clean oxidant at a
pressure as low as possible, reaction temperatures as moderate as
possible, and no addition of base to the solvent.
We report here for the first time the selective oxidation of
1-tetradecanol over a nano sized Au catalyst, using oxygen at atmo-
spheric pressure as oxidant and base-free alkanes as solvents. The
catalyst, supported on ceria-alumina, was selected because of its
high efficiency for the oxidation of 1-octanol found in a paral-
lel study [11]. The effect of various reaction parameters (reaction
temperature, run time, solvent) on catalytic performance has been
investigated. Additionally, 1-octanol oxidation has been tested to
study the effect of the alcohol carbon chain on the oxidation of
fatty alcohols. The results of this preliminary study prove the fea-
sibility of the reaction under these moderate reaction conditions
and show the complexity of the dependence of selectivity on the
reaction parameters.
300 ◦C for 4 h. A detailed description of the synthesis procedure is
reported elsewhere [12].
2.3. Catalyst characterization
The catalyst chemical composition was determined by X-ray
microfluorescence spectrometry (XRMF) in an EDAX Eagle III
spectrophotometer with a rhodium source of radiation. X-ray
diffraction (XRD) analysis was performed on an X’Pert Pro PAN-
alytical instrument. Diffractograms were recorded using Cu K␣
radiation (40 mA, 45 kV) over a 2ꢀ-range of 10 to 80◦ with a
position-sensitive detector using a step size of 0.05◦ and a step time
of 240 s.
2.4. Catalytic oxidation tests
Tests were conducted under atmospheric pressure at 80–120 ◦C
in
a four-necked round bottom flask equipped with reflux
condenser, oxygen feed, thermometer and a septum cap. In
a typical test, catalyst was added (in a substrate/metal ratio
(A/M) = 100–500 mol/mol) to 20 mL of 1-tetradecanol solution
(0.1 M) in n-heptane or n-decane, with no base addition. The
suspension was stirred and heated to the selected reaction tem-
perature (TR). Once reached it, run time started when oxygen was
bubbled through it with a flow rate of 30 mL/min, under near atmo-
spheric pressure (P = 100 kPa), and the test was run for 6 h. Reaction
monitoring was done by analyzing small aliquots of the reaction
mixture taken at various intervals. Aliquots were syringe filtered
(pore 0.45 m), and were analyzed by GC in a Varian 450 GC, using
a capillary DB wax column (15 m × 0.548 mm), He as the carrier
gas and a FID detector. In all measurements the carbon balance
was within 100 3%. For comparative purposes, some similar tests
were conducted under the same conditions using 1-octanol instead
of 1-tetradecanol.
2. Experimental
2.1. Materials
Tetrachloroauric acid, HAuCl4 (Alfa Aesar) and a commercial
CeO2–Al2O3 support (Puralox® 20, Sasol) were used for cata-
lyst preparation. Oxygen (99,999%, Air Liquide), 1-tetradecanol
(97%, Sigma-Aldrich) and 1-octanol (Chromasolv® for HPLC, ≥99%,
Sigma-Aldrich) were used as reactants as received without any fur-
ther purification. Heptane (99% grade HPLC, Scharlau) and n-decane
(≥97%, Sigma-Aldrich) were used as solvents.
3. Results and discussion
The catalyst chemical composition, determined by XRMF, was:
2.0 wt.% Au, 77.7 wt.% Al2O3, 20.3 wt.% CeO2. Its BET specific surface
area was 165 m2/g. The XRD pattern (Fig. 1) shows only diffrac-
tion lines corresponding to the cubic CeO2 fluorite type structure
(JCPDS# 00-004-0593) and to the ␥-Al2O3 phase (JCPDS# 00-048-
0367). No diffraction corresponding to metallic gold was detected.
It should be mentioned, that the diffractions of the ␥-Al2O3 phase
overlaps the main diffraction peak of Au at 2ꢁ = 38◦; however,
there are no traces for gold diffractions at higher 2ꢁ angles where
no alumina contribution is found. The absence of Au diffraction
2.2. Catalyst preparation
Gold was deposited by the direct anionic exchange method,
assisted by NH3. An aqueous solution of HAuCl4 containing the
desired gold loading (2 wt.% nominal amount) was heated at 70 ◦C
and put into contact with the support for 20 min. Then the ammonia
solution was added and kept for another 20 min. The obtained solid
was filtered, dried in oven at 100 ◦C overnight and calcined in air at
Please cite this article in press as: V.C. Corberán, et al., Heterogeneous selective oxidation of fatty alcohols: Oxidation of 1-tetradecanol