Selectivity control in oxidation of 1-tetradecanol on supported nano Au catalysts

Article abstract of DOI:10.1016/j.cattod.2016.06.019

Selective oxidation of tetradecanol, a model higher fatty alcohol, on Au/CeO₂-Al₂O₃ catalyst has been investigated to assess the factors that control selectivity. The analysis of the effect of operation conditions (temperature, run time and alcohol/metal (A/M) ratio) on catalytic performance revealed a quite complex reaction network, in which acid formation starts only after a certain level of conversion is reached. This level depends linearly on the total support surface available, indicating that it must be saturated by species generated by the reaction itself to allow acid formation to start. Addition of water to reaction medium did not modify this level, indicating that such species is not adsorbed water, as previously hypothesized, but probably spilled over hydrogen species. The resulting drastic change in the selectivity trends makes the ratio A/M a critical factor to control selectivity to aldehyde and to acid. Selectivity to ester is less sensible to operation parameters. It is noteworthy that aldehyde yields up to 27% with 90% selectivity, and acid yields up to 40% with 81% selectivity can be reached by proper selection of operation parameters.

Full text of DOI:10.1016/j.cattod.2016.06.019

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Selectivity control in oxidation of 1-tetradecanol on supported nano
Au catalysts
S. Martínez-Gonzáleza, Svetlana Ivanovab, María I. Domínguezb, V. Cortés Corberána,∗
a Institute of Catalysis and Petroleumchemistry (ICP), Spanish Council for Scientific Research (CSIC), Marie Curie 2, 28049 Madrid, Spain
b Institute of Materials Science of Seville (ICMS), University of Seville - CSIC, Av. Américo Vespucio 49, 41092 Seville, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Selective oxidation of tetradecanol, a model higher fatty alcohol, on Au/CeO2-Al2O3 catalyst has been
investigated to assess the factors that control selectivity. The analysis of the effect of operation conditions
(temperature, run time and alcohol/metal (A/M) ratio) on catalytic performance revealed a quite complex
reaction network, in which acid formation starts only after a certain level of conversion is reached. This
level depends linearly on the total support surface available, indicating that it must be saturated by species
generated by the reaction itself to allow acid formation to start. Addition of water to reaction medium did
not modify this level, indicating that such species is not adsorbed water, as previously hypothesized, but
probably spilled over hydrogen species. The resulting drastic change in the selectivity trends makes the
ratio A/M a critical factor to control selectivity to aldehyde and to acid. Selectivity to ester is less sensible
to operation parameters. It is noteworthy that aldehyde yields up to 27% with 90% selectivity, and acid
yields up to 40% with 81% selectivity can be reached by proper selection of operation parameters.
© 2016 Elsevier B.V. All rights reserved.
Received 8 March 2016
Received in revised form 27 May 2016
Accepted 8 June 2016
Available online xxx
Keywords:
Tetradecanol
Alcohol selective oxidation
Gold nanocatalysts
Fatty alcohols
Green oxidation
Selectivity control
1. Introduction
feedstock increased from 35% to 70% between 2005 and 2010 [5].
Selective oxidation of alcohols is one of the key transformations
Long-carbon chain aldehydes, acids and esters are fine chem-
icals of wide use as pharmaceuticals, agrochemicals, fragrances,
lubricants, emulsifiers and cosmetics [1]. For instance, aliphatic
linear C10–C18 aldehydes are potent odoriferous components in
perfumes [2]. However, in many cases they are not easily available.
Some of them, such as wax esters (esters of long-chain fatty acids
with long-chain fatty alcohols) are widespread in nature, as com-
mon components of the waxy cuticle on aerial surfaces of higher
plants [3] but usually found in low concentrations. Also, fatty acids
are abundant in nature, but with even numbers of carbon atoms
due to its biological synthesis route, most of them unsaturated [4],
and those with C20+ are very rare; thus, new synthesis methods are
needed to prepare those acids not available in nature (aliphatic, odd
carbon atoms number or very long carbon chain).
in organic synthesis and industrial practice, with a world-wide
annual production of carbonyl compounds of 10,000 million t/a at
the turn of the last century [6]. However, conventional industrial
oxidation processes are based upon the use of stoichiometric oxi-
dants, and are not environmentally friendly. This has motivated the
search of more sustainable processes, causing an almost twenty-
fold increase of publications on catalytic alternatives for these
reactions from 1995 to 2015 [7]. On the contrary, selective oxida-
tion of fatty alcohols with more than eight carbon atoms (C8+) has
been scarcely investigated to date, with just fifteen reports between
1990 and 2013 [1]. This is probably due to their chemical and phys-
ical characteristics: reactivity of unsubstituted, aliphatic, primary
alcohols is the lowest among those of the different alcohol types,
and the hydrophobicity, viscosity and melting and boiling points
of fatty alcohols increase with carbon chain length, which imposes
restrictions in the operation conditions for their oxidation via green
chemistry processes [8]. In addition, most literature on fatty alco-
hols oxidation reports activity data after a certain reaction time,
but not their evolution with run time.
All these valuable products (rare aldehydes and fatty acids, wax
esters) could be produced from their corresponding fatty alco-
hols by selective oxidation. In 2010, world production capacity of
fatty alcohols was estimated to be 3.35 × 106 t/a, based on natu-
ral and petrochemical feedstocks, and the contribution of natural
It was noteworthy that, among those scarce reports on fatty
C8+ alcohols oxidation, none reported the use of nano gold cata-
lysts, and no paper on tetradecanol oxidation was found [1]. This
reaction may produce the industrially important myristaldehyde
∗
Corresponding author.
E-mail address: vcortes@icp.csic.es (V. Cortés Corberán).
http://dx.doi.org/10.1016/j.cattod.2016.06.019
0920-5861/© 2016 Elsevier B.V. All rights reserved.
Please cite this article in press as: S. Martínez-González, et al., Selectivity control in oxidation of 1-tetradecanol on supported nano Au
catalysts, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.06.019

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Fig. 1. Selected TEM images of the catalyst.
(tetradecanal), used as flavor additive for human food, and myristyl
myristate (tetradecyl tetradecanate), broadly used in cosmetics as
skin conditioning agent and emulsifier. All this led us to investigate
the heterogeneous selective oxidation of 1-tetradecanol as a rep-
resentative model of these reactions, and to study the evolution of
the reaction with run time to get insight into the kinetic aspects.
For this purpose we chose to use nano gold based catalysts, because
supported gold catalysts were found active for oxidizing different
types of functionalized alcohols and polyols in the presence of O2
[9–11], and showed higher resistance to poisoning than those based
on Pt or Pd [9].
Thus, in our previous work [12] we reported for the first time
that the selective oxidation of 1-tetradecanol is feasible in the liq-
uid phase in accordance with green chemistry principles [8], say,
using a heterogeneous nano sized gold catalyst, air as oxidant at
near atmospheric pressure, and an alkane solvent without base
addition. Under the conditions tested, conversion reached 22 mol%
at 80 ◦C and the only products were the aldehyde (tetradecanal)
with quite high selectivity (76.5–79 mol%) and the ester (tetrade-
cyl tetradecanoate), but no acid formation was detected. At higher
temperatures a sharp selectivity trend change (increase of acid for-
mation) was observed when alcohol conversion reached a critical
value, around 30%, regardless the temperature. It was hypothesized
that the observed change was due to a change in the reaction mech-
anism caused by the water produced by the reaction itself, when it
becomes available to react once it saturates the hydrophilic support
surface. A deeper understanding of this phenomenon was needed
in order to properly direct the reaction to the most desired product,
be it the aldehyde, the ester or the acid.
1-tetradecanol (97%, Sigma-Aldrich) was used as received, without
any further purification, as substrate, and n-decane (≥97%, Sigma-
Aldrich) was used as solvent.
2.2. Catalyst preparation
Gold was deposited by the direct anionic exchange method
(DAE), assisted by NH3, as detailed elsewhere [13]. Briefly, an aque-
ous solution of HAuCl4 containing the desired gold loading 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 300 ◦C for 4 h.
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 10–80◦ with a position-
sensitive detector using a step size of 0.05◦ and a step time of
240 s. Gold dispersion was estimated by using Philips CM200 trans-
mission electron microscope with a structural resolution of 2.3 Å,
equipped with a X-ray Energy Dispersive Analyser (EDX) and an
Electron Energy Loss Spectrometer (PEELS) (Gatan, model 766-
2 keV). Before use, the powder samples were dispersed in ethanol
and deposited on a copper grid covered by amorphous carbon thin
film.
This work is aimed to investigate the operation parameters that
allow to control the selectivity of this reaction to the desired prod-
uct, as well as to verify that hypothesis on the role of the support
surface in such a control. To reach these goals we studied the effect
of reaction temperature, A/M ratio and run time on the product dis-
tribution and its evolution with conversion. The obtained results led
us to modify our hypothesis and showed that high yields to either
aldehyde or acid can be reached with high selectivity by proper
selection of operation parameters.
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 con-
denser, oxygen feed, thermometer and a septum cap. In a typical
test, catalyst was added in a substrate/metal molar ratio (A/M) = 50-
200 to 20 mL of 1-tetradecanol solution (0.1 M) in n-decane. No
base was added. The suspension was stirred and heated to the
selected reaction temperature (TR). Once reached it, run time
started when oxygen was bubbled through it with a flow rate of
30 mL/min, under near atmospheric 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 analyzed by
gas chromatography in a Varian 450 GC, using a capillary DB
wax column (15 m × 0.548 mm), He as the carrier gas and a flame
2. Experimental
2.1. Materials
Tetrachloroauric acid, HAuCl4 (Alfa Aesar) and a commercial
CeO2-Al2O3 support (Puralox® 20, Sasol) were used for catalyst
preparation. Oxygen (99.999%, Air Liquide) was used as oxidant,
Please cite this article in press as: S. Martínez-González, et al., Selectivity control in oxidation of 1-tetradecanol on supported nano Au
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Fig. 2. Effect of A/M ratio on tetradecanol oxidation at 80 ◦C: conversion as function of run time (A) and selectivity to aldehyde (B), ester (C) and acid (D) as a function of
conversion. Symbols: A/M = 50 (diamonds), 100 (triangles) and 200 (squares).
ionization detector. In all measurements the carbon balance was
within 100 3%.
It is noteworthy that ester formation was detected in all analyses,
even when acid was not detected. No other products were detected.
In our previous work [12] no acid formation was detected at
80 ◦C, but the highest conversion reached (22%) was below the con-
version value (near 30%) for which acid formation was observed
at higher temperatures with the only A/M ratio explored. So, we
first investigated the effect of A/M ratio at this temperature to
check if the absence of selectivity trend change was due to the
lower temperature used or to the lower conversion level reached.
As expected, the reaction initial rate and the conversion at equal
run time increased with the decrease of A/M, i.e., with the increase
of catalyst mass (Fig. 2). In fact, the final conversions after 6 h were
roughly proportional to the reciprocal of A/M, i.e., to the catalyst
mass. The highest tetradecanal selectivity (86–89%) was observed
up to 12% conversion with the lower catalyst amount (A/M = 200).
Increasing the catalyst amount increased the selectivity to ester to
20–25% at the cost of aldehyde. Interestingly, acid formation was
detected only just at the higher conversions, above around 30%, as
previously observed at the higher temperatures. This agrees with
our interpretation that the shift in selectivity trend was related to
catalyst amount and not to reaction temperature [12].
3. Results and discussion
3.1. Catalyst characterization
The main catalyst characteristics were reported in our previ-
ous work [12]. Its chemical composition was: 2.0 wt.% Au, 77.7 wt.%
Al2O3, 20.3 wt.% CeO2. Its BET specific surface area was 165 m2/g.
Its XRD pattern showed only broad diffraction lines corresponding
to the fluorite type cubic CeO2 and ␥-Al2O3 phases; those of metal-
lic Au were absent, indicating that gold particles size are typically
under the XRD detection limit of around 5 nm. Fig. 1 shows rep-
resentative TEM images of the catalyst. The low contrast between
Au and CeO2 made difficult their recognition, but as both showed
similar sizes around 4 nm, the gold particles size below 5 nm was
confirmed. The DAE synthesis method used here results in metal-
lic gold state, as validated in a previous XPS study on a similar
Au/CeO2-Al2O3 catalyst that also showed a gold average size of
3.8 0.5 nm [14].
This was further confirmed by the results at 110 ◦C (Fig. 3).
While ester selectivity was not affected by the A/M ratio, slightly
increasing with conversion in the whole conversion range, a very
drastic increase of acid selectivity at the cost of that of aldehyde
was observed for all A/M ratios, but, noticeably, this drastic change
occurred after reaching a different conversion level in each case.
This effect has two important practical implications. From the
3.2. Catalytic tetradecanol oxidation
Under all the conditions tested, the main reaction product was
the aldehyde, tetradecanal, with smaller amounts of the ester,
tetradecyl tetradecanoate, while the acid, tetradecanoic acid, was
formed in some tests and at high conversions as described below.
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Fig. 3. Effect of A/M ratio on tetradecanol oxidation at 110 ◦C: conversion as function of run time (A) and selectivity to aldehyde (B), ester (C) and acid (D) as a function of
conversion. Symbols A/M = 100 (triangles), 150 (circles), and 200 (squares).
research point of view, it evidenced that reporting just final con-
version and product distributions has little relevance and hides
important information on the reaction mechanism and network.
From the point of view of application, it involves that, using the
same catalyst, one may obtain high yields with high selectivity (i.e.,
at high conversions) either to the aldehyde (near 90% selectivity up
to 30–32% conversion) or to the acid (75-72% selectivity at 40–50%
conversion).
in literature for the ester formation in the oxidation of alcohols. On
supported Pd catalysts, Baker’s group [15] proposed that, via hydra-
tion to a germinal diol, the initially formed aldehyde was oxidized
to the acid, which in turn was esterified with the reactant alco-
hol (Fig. 5, upper path), which involves that ester is a secondary
product. Choudhary et al. [16] studied the solventless oxidation
of benzyl alcohol on several gold supported catalysts with high
Au contents (4–8 wt.%) and attributed the absence of benzoic acid
among the final products (after 5 h test) to the very fast reaction of
the formed acid with the alcohol to give the ester. However, if one
considers that tetradecanol, a non-functionalized primary alkanol,
is much less reactive than benzyl alcohol; that benzoic acid is much
stronger than tetradecanoic acid (pKa = 4.2 and 8.2, respectively);
and that alcohol concentration in our tests is much lower (0.1 M),
that hypothesis seems little probable in our case. Even more rele-
vant is that it cannot explain the sudden rise of acid formation after
a certain run time and why this change has practically no effect
on the ester selectivity, nor the formation of the ester as primary
product; thus, one may discard that hypothesis in this case.
More recently, Ishida et al. [17] proposed, in their study of
1-octanol oxidation on supported nano gold catalysts, that the
initially formed aldehyde may undergo an acetalization with the
alcohol to form an hemiacetal, which, in turn, is further oxidized to
form the ester (Fig. 5, lower path). They found that this route was
the favored one in the oxidation of 1-octanol on Au/CeO2 catalyst
while the previous one was favored for Au/NiO catalyst, both using
water as the solvent. From our results one may infer that at the
initial stages of the tetradecanol oxidation only this second route is
Similar effects were observed at 120 ◦C, though at this tem-
perature the increase of conversion and rate with the decrease of
A/M was less marked (Fig. 4). Again here the conversion at which
acid formation starts depended on the A/M ratio, but acid selectiv-
ity seems to level off at the high conversions. Comparison of the
selectivity trends at 110 and 120 ◦C for tests conducted with the
same A/M ratio revealed that the acid formation starts at the same
conversion for a given A/M ratio at both temperatures, and that
acid selectivity at isoconversion slightly decreased when increas-
ing temperature. Nevertheless, the highest acid selectivity and yield
in this study, say, 80.8% selectivity at 49.4% conversion (39.9% yield)
was observed at this temperature.
3.3. General discussion: reaction network and mechanism
It is noteworthy that ester formation was detected in all analy-
ses for all catalytic tests, even when acid was not detected. In fact,
the trends observed in the isothermal selectivity to ester vs. con-
version plots (graphs C in Figs. 2, 3 and 4) are typical for a primary
and secondary, stable product. Formation of the ester as a primary
product is noteworthy. Two different routes have been proposed
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Fig. 4. Effect of A/M ratio on tetradecanol oxidation at 120 ◦C: conversion as function of run time (A) and selectivity to aldehyde (B), ester (C) and acid (D) as a function of
conversion. Symbols A/M = 100 (triangles), 150 (circles), and 200 (squares).
Fig. 5. Possible reaction pathways for acid and ester formation (R = n-C13H27). Adapted from [12].
operating on Au/CeO2-Al2O3 catalyst, which agrees well with the
results of Ishida et al. with Au/CeO2 catalyst.
desorbed as aldehyde or transformed into the hemiacetal precur-
sor by interaction with a second alcohol molecule. Desorption of
the ester produced by oxidation of this hemiacetal will make ester
to appear also as a primary product.
However, the ester formation by this route leads to a secondary
product, which contradicts the observation that the ester is mainly
a primary product. To interpret this fact one may hypothesize as
follows. Periodic density functional theory (DFT) calculations of
selective alcohol oxidation to aldehyde on a series of gold cat-
alyst models [18] have shown that its mechanism proceeds by
two elementary steps, namely, dehydrogenation of the hydroxyl
group of adsorbed alcohol to give an alcoxy species and a hydro-
gen atom adsorbed on the metal surface, followed by transfer of a
second hydrogen atom from the C atom bonded to O in the alcoxy
intermediate to the Au surface, yielding a carbonyl adsorbed inter-
mediate, which may desorb as aldehyde, and a second hydrogen
atom adsorbed on the gold surface [18]. Then, one may assume
that depending on the relative rates of aldehyde precursor desorp-
tion and the adsorption of the alcohol, the former may be either
Nevertheless, the ester selectivity curves at 110 and 120 ◦C show
a positive slope, revealing that a part of the ester is also a secondary
product, which involves that the aldehyde, once formed, also reacts
to give the ester as proposed by Ishida et al. In a previous study of
1-octanol oxidation on a similar Au/CeO2-Al2O3 catalyst [19] we
found that though the bare support surface is inactive by itself, it
plays a role in the product distribution. The addition of bare support
to the reaction medium had no effect on the alcohol conversion but
increased a 30% the selectivity to ester at isoconversion, at the cost
of aldehyde. So, the support was unable to activate the alcohol but
catalyzed the aldehyde transformation to ester. By analogy, one
may assume that in tetradecanol oxidation a small part of ester
could be formed on the uncovered portion of the support surface.
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Another interesting feature is that at 120 ◦C selectivity to acid
levels off at the higher conversions (Fig. 4D). It should be noted
that this effect is parallel to the change in the slope of the ester
selectivity curve (Fig. 4C), which indicates the formation of ester
by one additional secondary route. Thus, it can be interpreted as
due to the esterification of the acid, and evidences that ester may be
formed by three different ways: as primary product on gold centers,
and as secondary product either by aldehyde interaction with the
support surface or by esterification of the acid at the higher reaction
temperatures and conversion levels.
What causes formation of acid to start after the reaction has
reached some conversion level? A key to understand what sparks
the formation of the acid comes from the fact that it starts at dif-
ferent conversion levels depending on the A/M ratio. Fig. 6 shows
that there is a linear dependence of these conversion levels and
the reciprocal of the A/M ratio and, hence, of the total amount
of catalyst and the total bare support surface present in the test.
So, the observed effect must be related to the support surface sat-
uration by a product or species generated by the very reaction.
The stoichiometry of the alcohol oxidation involves the forma-
tion of one water molecule per molecule of aldehyde and two
per molecule of ester. Hence, as conversion increases, water will
be increasingly available as an additional reactant in the reaction
medium. This lead us hypothesize that initially formed water is
retained by irreversible absorption on the support surface, due to
the hydrophobicity of the solvent and the hydrophylic nature of
the surface of the ceria-alumina support [9]; then, once the sup-
port surface becomes saturated of absorbed water, the additional
Fig. 6. Effect of A/M ratio on the conversion for which the acid formation start to be
detected (selectivity drastic change). Reaction temperature: 110 ◦C.
water starts the hydration route to acid formation (Fig. 4, upper
path). To verify this hypothesis, we conducted a test in which we
added to the liquid reaction medium the amount of water enough
to fully saturate the total surface of the catalyst sample used, as
estimated from the alcohol conversion for which the change in
selectivity trend was observed. Within experimental dispersion,
Fig. 7. Effect of water addition to reaction medium on tetradecanol oxidation on Au/CeO2-Al2O3 at 120 ◦C with A/M = 100: conversion as function of run time (A) and selectivity
to aldehyde (B), ester (C) and acid (D) as a function of conversion. Symbols: without (triangles) or with (diamonds) added water.
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the presence of water in the liquid did not modify the conversion
evolution with run time (Fig. 7A), but, in contrast to what would be
expected according to the hypothesis, it neither modified the con-
version level at which acid formation started (Fig. 7B and D). Only
a slight increase of acid selectivity at the cost of that of ester was
observed at the higher conversion levels. All this points to a differ-
ent species, and not water adsorbed from the reaction medium, to
cause the observed selectivity drastic change effect linked to the
support surface “saturation”. As said above, the formation of the
aldehyde involves the formation of two adsorbed hydrogen atoms
on the gold surface. Formation of water requires to oxidize these
species; however, gold catalysts are often used as catalysts for pref-
erential CO oxidation in a hydrogen stream (PROX) because of their
relatively low activity for hydrogen oxidation at low temperatures
(as compared with CO oxidation), and the concentration of oxygen
available in the organic medium is quite low, limited by its solubil-
ity in it. Then, one may assume that the adsorbed hydrogen species
may, instead of being oxidized to water on gold surface, spill over
the support oxidic surface, creating surface hydroxyls. Thus, only
when the surface may not further accept hydrogen, because all sur-
face oxygens have been hydroxylated, water becomes available as
reactant and the hydration route to acid formation may start, most
probably on these surface hydroxyl centers. Both, water in the reac-
tion medium and totally modified support surface centers, seem to
be needed to proceed with the acid formation reaction. Additional
characterization studies are needed to ascertain the nature of the
“saturated” surface and the species involved.
modification of the support surface during the reaction and the
selectivity drastic change caused by the surface “saturation” play
a key role for it. Selectivity to aldehyde can be very high before
the said support surface “saturation”, which makes the alcohol-to-
metal ratio the critical factor to keep it high at high conversions. On
the other hand, as this “saturation” depends on the time on stream,
this could be a limitation for a continuous process. High selectivity
to acid can be obtained after the selectivity drastic change, which
evidences the role of run time on selectivity control. This role also
implies that comparison of catalytic performances based on data
obtained at different reaction times may be misleading. The various
routes to ester formation may be the reason why its selectivity is
much less sensible to reaction conditions.
It should be noted, nevertheless, that aldehyde yields up to 27%
with 90% selectivity, and acid yields up to 40% with 81% selec-
tivity can be reached by proper selection of combination of A/M,
temperature and run time conditions.
Acknowledgements
Funding of this work by CSIC (project 201480E070) and MINECO
(project CTQ2013-41507-R) is greatfully acknowledged.
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Despite of its apparent simplicity due to stoichiometry and the
reduced number of products, tetradecanol oxidation on Au/CeO2-
Al2O3 catalyst involves a quite complex reaction network. The
intermediate formed by alcohol adsorption on the gold centers
may be further dehydrogenated to be desorbed as aldehyde (main
route), or interact with a second alcohol molecule to generate the
ester via hemiacetal formation (minor route). Part of the desorbed
acetaldehyde may also react with alcohol on the support bare sur-
face to form the ester. In parallel, the adsorbed hydrogen species
produced by the alcohol dehydrogenation spill over the support
surface, modifying its properties to make it able to catalyze the
acid formation. As this reaction requires the availability of free
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retained by the bare support surface (in other words, when those
species ‘saturate’ the surface). In addition, at the higher tempera-
tures and conversion levels, ester can be formed by esterification
of the formed acid.
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As a consequence, the selectivity to each main product depends
on a complex set of factors which makes difficult its control. The
Please cite this article in press as: S. Martínez-González, et al., Selectivity control in oxidation of 1-tetradecanol on supported nano Au
catalysts, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.06.019