One-Pot Myrtenol Amination over Au, Au–Pd and Pd Nanoparticles Supported on Alumina

Article abstract of DOI:10.1007/s10562-019-02958-6

Abstract: One-pot bio-based myrtenol amination was studied in the presence of alumina supported Au, Au–Pd and Pd nanoparticles subjected to the thermal treatment under oxidizing or reducing atmosphere. Myrtenol amination with aniline was carried out under nitrogen atmosphere (9?bar) at 453?K using toluene as a solvent. The effect of the active metal along with the influence of redox pre-treatment on the catalytic behavior in the hydrogen borrowing reaction was explored. The catalyst characterization was done by transmission electron microscopy, X-ray photoelectron spectroscopy, inductively coupled plasma optical emission spectroscopy, nitrogen adsorption. The active metal and the catalysts redox pretreatment affected more noticeably selectivity to the reaction products rather than myrtenol conversion. Monometallic Au/Al₂O₃ catalyst promoted predominantly formation of the target secondary amine and the corresponding imine without a significant impact of the side reaction of C=C bond hydrogenation in myrtenol, whereas monometallic Pd catalyst activated C=C bond resulting in its hydrogenation. At the same time in the presence of Au–Pd simultaneous hydrogenation of both C=C and C=N bond occurred. Au–Pd catalysts activated in oxygen and hydrogen showed different catalytic activity determined by the composition of surface active sites. Monometallic gold catalyst was more effective in the hydrogen transfer in the case of substrates with competitive unsaturated functional groups. Graphic Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-019-02958-6

Catalysis Letters
https://doi.org/10.1007/s10562-019-02958-6
One‑Pot Myrtenol Amination over Au, Au–Pd and Pd Nanoparticles
Supported on Alumina
Yu. S. Demidova1,2 · I. L. Simakova1,2 · M. Estrada3 · S. Beloshapkin4 · E. V. Suslov5 · K. P. Volcho2,5
N. F. Salakhutdinov2,5 · A. Simakov3 · D. Yu. Murzin6
·
Received: 5 June 2019 / Accepted: 12 September 2019
© Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
One-pot bio-based myrtenol amination was studied in the presence of alumina supported Au, Au–Pd and Pd nanoparticles
subjected to the thermal treatment under oxidizing or reducing atmosphere. Myrtenol amination with aniline was carried
out under nitrogen atmosphere (9 bar) at 453 K using toluene as a solvent. The efect of the active metal along with the
infuence of redox pre-treatment on the catalytic behavior in the hydrogen borrowing reaction was explored. The catalyst
characterization was done by transmission electron microscopy, X-ray photoelectron spectroscopy, inductively coupled
plasma optical emission spectroscopy, nitrogen adsorption. The active metal and the catalysts redox pretreatment afected
more noticeably selectivity to the reaction products rather than myrtenol conversion. Monometallic Au/Al2O3 catalyst pro-
moted predominantly formation of the target secondary amine and the corresponding imine without a signifcant impact of
the side reaction of C=C bond hydrogenation in myrtenol, whereas monometallic Pd catalyst activated C=C bond resulting
in its hydrogenation. At the same time in the presence of Au–Pd simultaneous hydrogenation of both C=C and C=N bond
occurred. Au–Pd catalysts activated in oxygen and hydrogen showed diferent catalytic activity determined by the composi-
tion of surface active sites. Monometallic gold catalyst was more efective in the hydrogen transfer in the case of substrates
with competitive unsaturated functional groups.
* I. L. Simakova
simakova@catalysis.ru
1
Boreskov Institute of Catalysis, pr. Lavrentieva, 5,
Novosibirsk, Russia 630090
2
Novosibirsk State University, Pirogova, 2, Novosibirsk,
Russia 630090
3
Centro de Nanociencias y Nanotecnología, Universidad
Nacional Autónoma de México, km. 107 carretera Tijuana a
Ensenada, C.P. 22860 Ensenada, Baja California, Mexico
4
Bernal Institute, University of Limerick,
Limerick V94 T9PX, Ireland
5
Novosibirsk Institute of Organic Chemistry, pr. Lavrentieva,
9, Novosibirsk, Russia 630090
6
Process Chemistry Centre, Åbo Akademi University,
20500 Turku/Åbo, Finland
Vol.:(0123456789)
1 3

Y. S. Demidova et al.
Graphic Abstract
Keywords Alcohol amination · One-pot · Hydrogen borrowing · Redox treatment efect · Gold · Palladium · Bimetallic
catalyst · Myrtenol · Terpenoids · Biomass
Synthesis of terpene amines is of great interest for
the development of new pharmaceuticals [6–9]. Terpe-
noinds are the largest group of natural compounds that
1 Introduction
Catalytic one-pot alcohol amination proceeding through
the hydrogen borrowing process (Fig. 1) is an efective
approach in producing valuable amines for fne chemi-
cal synthesis and chemical industry. However, a one-pot
process involving multiple catalytic reactions allows an
increase of the process efciency only when the catalytic
properties in the complex catalytic system are optimized.
Complexity of the one-pot alcohol amination determines
a variety of parameters that can afect the catalytic perfor-
mance [1–5]. In the case of complex substrates the control
on the side reactions should be performed as well.
Fig. 1 General scheme of the one-pot alcohols amination
1 3

One-Pot Myrtenol Amination over Au, Au–Pd and Pd Nanoparticles Supported on Alumina
Fig. 2 Scheme of myrtenol
amination with aniline over Au
H
N
N
O
catalysts
OH
NH2
2
1
Myrtenal
2H
+
Aniline
Myrtenol
2H
H
N
OH
N
O
3
4
Myrtanol
Myrtanal
are extensively applied in the food and perfumery industry
as favors, fragrances and spices. At the same time high
reactivity of terpenoids can lead to insufcient selectivity
in various transformations of terpenoids over heterogene-
ous catalysts [3, 10–20]. Thus in the case of complex ter-
penoids it is important to control impact of side reactions
in their transformations to achieve reasonable selectivity
to the desired product.
hydrogenation of imine. Note that it was clearly demon-
strated that alcohol dehydrogenation to carbonyl compound
can occur both in the presence and absence of gold nano-
particles, while hydrogen formation was observed only in
the presence of gold [3, 28, 29]. Alcohol dehydrogenation
proceeding only on the support active sites led to inability to
produce hydrogen species for further hydrogenation.
A series of alumina supported Au, Au–Pd and Pd cat-
alysts subjected to activation in oxygen or hydrogen was
studied in one-pot myrtenol amination. Based on our previ-
ous results alumina was selected as a support providing an
adequate catalytic performance in terms of activity, allowing
also comprehensive characterization by a range of physi-
cal–chemical techniques [3]. Note that while zirconia was
shown to be an optimal catalyst for myrtenol amination the
catalyst characterization faced certain difculties particu-
larly in the case of bimetallic systems [3].
In our previous work it was shown that gold catalysts
exhibited good catalytic activity in one-pot bio-based myrte-
nol amination (Fig. 2) along with a low impact of side reac-
tions such as hydrogenation of the reactive C=C group of
myrtenol by hydrogen formed in the frst step [3, 16].
The infuence of the support nature and gold catalysts
redox pre-treatment on the catalytic activity and selectivity
in myrtenol amination was explored in detail [3, 4], reveal-
ing the key parameters determining catalytic performance in
this reaction. A certain balance between acid and base sites
was shown to be required for the efcient one-pot alcohol
amination that can be tuned by the support nature or/and pre-
liminary catalyst activation [3, 4]. According to the plausible
reaction mechanism the basic sites on metal oxide surfaces
are required for the initial alcohol activation, while the avail-
ability of protonic groups was suggested to be important for
hydrogen transfer and therefore for the target amine forma-
tion [3, 21–24].
2 Experimental/Methodology
2.1 Preparation of Catalysts
The catalysts tested in the current paper were synthesized
similar to the procedure described in [30]. Briefy, gold (2.8
wt% according to ICP analysis) was deposited on alumina
(Sigma Aldrich) by deposition–precipitation technique using
HAuCl4 (Alfa-Aesar) as a gold precursor and urea (Sigma
Aldrich) as a precipitating agent. 4 g of alumina were sus-
pended in 400 ml of HAuCl4 (1.6 × 10−3 M) and of urea
(0.42 M). The initial pH of the formed aqueous suspension
was ca. 2. Then the mixture was kept at 80 °C under vigor-
ous stirring for 4 h. In order to remove the excess of chloride
In this study to enhance fundamental understanding
of one-pot alcohol amination in terms of the role of cata-
lyst active sites as well as to optimize hydrogen transfer,
the doped gold catalysts with Pd were studied [25–27].
Optimization of the hydrogen transfer is related to alcohol
dehydrogenation involving metal nanoparticles and result-
ing in hydrogen formation followed by selective C=N bond
1 3

Y. S. Demidova et al.
after gold deposition, the sample was washed with a 25 M
solution of NH4OH (pH ca. 10), as in [31]. Thereafter the
sample was washed with deionized water, fltered and dried
at room temperature for 24 h. Au(OH)3/Al2O3 prepared in
this way was used for subsequent synthesis of both Au/Al2O3
and Au–Pd/Al2O3 catalysts. Palladium containing catalysts,
Pd/Al2O3 and Au–Pd/Al2O3, (0.2 wt. Pd% according to ICP
analysis) were obtained by deposition of Pd species on alu-
mina or on alumina with previously deposited gold hydrox-
ide using PdCl2 (Alfa-Aesar) in an aqueous solution slightly
acidifed with HCl. Obtained suspensions were stirred for
12 h at room temperature followed by fltration and washing
with ammonium hydroxide to remove chloride ions similar
to the catalyst containing only gold on alumina. Subsequent
treatment included washing with water until pH 7, fltering
and drying at room temperature for 24 h. Before catalytic
tests, the samples were reduced in hydrogen or oxidized in
air fow under a temperature increase to 350 °C with a ramp
rate of 20 °C/min. The samples treated in oxygen have TPO
in their code, while in hydrogen treated one were coded as
sample-TPR.
carried out with the background estimated via the Shirley
method.
2.3 Catalytic Experiments
Liquid-phase myrtenol amination was performed in a
stainless steel reactor (150 ml), equipped with an electro-
magnetic stirrer (1100 rpm) and the sampling system. In a
typical experiment, a mixture of myrtenol (1 mmol), ani-
line (1 mmol) and the powdered catalyst (92 mg) in toluene
(10 ml) was intensively stirred at 180 °C under N2 atmos-
phere (9 bar). During the course of the reaction the samples
aliquots were withdrawn periodically from the reactor and
analyzed by gas chromatography. Maximally fve samples
were taken with the volume ca. 0.1–0.2 ml each being thus
in total 0.5–1 ml or 5–10 vol% from the initial volume of the
substrate solution. The reaction mixture was taken together
with the catalyst under stirring and then fltered. In this way
there was a negligibly infuence of sampling on the catalyst
bulk density.
The measurements of catalytic activity were performed
in the kinetic regime. The impact of internal difusion was
determined through estimation of the Weisz–Prater criterion.
The impacts of external difusion and mass transfer limita-
tions through the liquid–solid interface were evaluated by
the corresponding criterion calculation [16].
2.2 Characterization of Supports and Catalysts
The gold and palladium content in the synthesized catalysts
was analyzed with an inductively coupled plasma atomic
emission spectroscopy (ICP-AES) using a Varian Liberty
110 ICP Emission Spectrometer.
2.4 Product Analysis
The porous structure of the catalysts was evaluated by
nitrogen adsorption in a Micromeritics TriStar II-3020
device. Prior the analysis, the samples were degassed in
vacuum at 300 °C for 4 h using a Micromeritics VacPrep
061-Sample degas system. The value of specifc surface area
was estimated by the BET model, while the pore size distri-
bution was determined by the BJH model.
Aliquots were withdrawn from the reactor at appropriate
time intervals and analyzed by gas chromatography using
SLB-5 ms column (length 30 m, inner diameter 0.25 mm
and flm thickness 0.25 μm) and a fame ionization detector
operating at 300 °C. Additionally the chemical nature of
the products was confrmed by gas chromatography mass
spectrometery (Agilent Technologies 7000 GC/MS Tri-
ple Quad, HP-5MS column) as well as 1H- and 13C-NMR
(Bruker DRX-500 spectrometer). NMR and GC/MS data of
the products are presented in our previous work [1].
Elemental composition of the reaction products was
determined by mass spectra data recorded on a DFS Thermo
Scientifc spectrometer in a full scanning mode in the range
0–500 m/z, ionization by electron impact 70 eV with a direct
sample insertion.
The mean size, morphology and elements distribution for
supported nanoparticles were determined by STEM using a
JEOLJEM-2100F microscope with an XMAX OXFORD
detector. EDX analysis for Au and Pd was performed using
the INCA software. Prior to analysis, the samples were ultra-
sonically deposited from a suspension in propan-2-ol on a
copper grid coated with carbon flm. The mean diameter was
evaluated via measuring more than 150 particles. The mean
diameter (dm) of∑particles was calculated using the following
(x d ), where xi is the number of particles
i
i
i
equation: dm =
∑
Selectivity was calculated based on the following equa-
tion: selectivity = (yield of the product)/(total yield of all
products). The initial reaction rate was calculated within the
linear part of the kinetic curves.
xi
i
with diameter di.
XPS was performed using a Kratos AXIS 165 spectrome-
ter with a monochromatic AlKα radiation (hv=1486.58 eV)
and a fxed analyzer pass energy of 20 eV. All measured
binding energies (BE) were referred to the C1 s line of
adventitious carbon at 284.8 eV. Spectra deconvolution was
1 3

One-Pot Myrtenol Amination over Au, Au–Pd and Pd Nanoparticles Supported on Alumina
Table 1 TEM and ICP data for Au, Au–Pd and Pd catalysts
3 Results and Discussion
Catalyst
Metal content, wt%
Mean particle diameter,
nm
3.1 Catalysts Characterization
Au
Pd
TPOa
TPRa
Prior to the catalytic tests a series of Au, Au–Pd and Pd
catalysts subjected to activation in oxygen or hydrogen was
characterized by nitrogen adsorption, STEM, XPS and ICP.
The metal content based on ICP data is presented in Table 1.
According to nitrogen adsorption the specifc surface area
and average pore diameter for alumina were found to be
136 m2/g and 5.2 nm, respectively. The deposition of gold
or gold–palladium nanoparticles did not afect signifcantly
Au/Al2O3
AuPd/Al2O3
Pd/Al2O3
2.3
2.8
–
0
0.2
0.2
2.6 0.8
2.5 0.5
–
2.4 0.7
2.7 0.7
–
aPreliminary catalysts activation
Fig. 3 Particle size distribution
according to TEM analysis for
Au/Al2O3 (frst column), AuPd/
Al2O3 (second column) after
TPO (a, b) and TPR (c, d).
Typical TEM micrograph for
Au/Al2O3 sample after TPR (e)
and profles of Au (blue) and Pd
(red) across an Au–Pd nanopar-
ticle according to STEM-EDS
line scanning technique for Au–
Pd/Al2O3 sample after TPR (f)
1 3

Y. S. Demidova et al.
the value of specifc surface area, being 125 and 130 m2/g,
respectively.
Note that earlier comparable series of Au, Au–Pd and
Pd catalysts subjected to activation in oxygen and hydrogen
were characterized in detail in [30]. Some additional data
obtained by TEM, XPS and UV–Vis for these samples can
be found there [30].
According to TEM data the gold and gold–palladium nan-
oparticles are characterized with almost semispherical shape
practically without well detectable crystallographic planes
(Fig. 3). A uniform and narrow distribution of gold metal
particles both for monometallic and bimetallic catalysts was
observed, being practically independent on the type of the
sample pre-treatment (Table 1, Fig. 3). The gold particles
size was 2.6 and 2.4 nm for monometallic Au/Al2O3 cata-
lyst pre-treated under oxidizing or reducing atmospheres,
respectively. Deposition of palladium onto gold nanoparti-
cles practically did not afect the size of bimetallic nanopar-
ticles because of a low palladium loading. The bimetallic
AuPd/Al2O3 catalyst exhibited gold particles sizes of 2.5 and
2.7 nm for pre-oxidized and pre-reduced samples, respec-
tively. The exclusive presence of palladium on the surface
of gold nanoparticles in case of AuPd/Al2O3 was confrmed
by STEM-EDS technique (Fig. 3f). The profle for palladium
coincides well with that for gold across Au–Pd nanoparticles
(Fig. 3f). Exact location of Pd on the Au nanoparticle sur-
face or subsurface layer cannot be revealed based on EDS
analysis due to low intensity of Pd profle. Nevertheless, a
stepwise strategy of Pd deposition on the catalyst already
bearing Au and a relatively mild thermal treatment proce-
dure allow to propose that Pd species are efciently localized
in the subsurface layer on the Au nanoparticles. Note that
the Pd clusters with the size lower than 0.3-0.4 nm are not
detectable at the conditions used for TEM imaging. Pres-
ence of palladium particles with the sizes larger than 0.3 nm
(resolution of the measurements) has not been observed in
TEM micrographs for Pd/Al2O3 catalysts as it was reported
also in [30].
In the current study, the synthesized catalysts were
also characterized by XPS to explore the chemical state
of Au and Pd. The XPS spectra for Au 4f, Au 4d and
Pd 3d are shown in Figs. 4 and 5. The spectra for Pd 3d
are characterized with a low intensity while the spectra
for Au 4f and Au 4d manifest high intensity due to the
diference in the Au and Pd loading. The Au 4f spectra,
characterized by the two spin–orbit components, Au 4f7/2
and Au 4f5/2 separated by 3.67 eV, exhibit two doublets
attributed to Auo and Au+ species (according to [32]) only
for samples after the oxidative thermal pre-treatment.
Spectra deconvolution revealed that the relative content
of positively charged gold was equal ca. 6.6% and 24.9%
for pre-oxidized Au/Al2O3 and AuPd/Al2O3, respectively.
Only metallic gold species were found for the pre-reduced
samples (see Table 2). The Pd 3d spectra characterized
by two spin–orbit components, Pd 3d5/2 and Pd 3d3/2
separated by 5.26 eV, exhibit only one doublet attributed
to Pdo species according to [32] (Table 3). No traces of
positively charged Pd species were found even for pre-
oxidized AuPd/Al2O3 catalyst. Interactions between Au
and Pd seem to be efcient enough resulting in the forma-
tion Au–Pd solid alloy. It is well known that Pd metallic
species well mixed with gold in such alloys are resistant to
re-oxidation [30, 33, 34]. Indeed, a slight noticeable shift
of the Au4f7/2 peak maximum for Auo species to lower
energy for a bimetallic catalyst (Table 3), characteristic
for Au–Pd alloys was observed [34]. Such a shift of Au
Fig. 4 XPS Au 4f spectra of Au/Al2O3 TPO (left) and TPR (right) catalysts (symbols—experimental data, curves—ftting)
1 3

One-Pot Myrtenol Amination over Au, Au–Pd and Pd Nanoparticles Supported on Alumina
Fig. 5 XPS Au 4f (frst row) and Au 4d, Pd 3d (second row) spectra for AuPd/Al2O3 TPO (left) and TPR (right) catalysts (symbols—experimen-
tal data, curves—ftting)
Table 2 Relative content of Pd and Au species in samples after difer-
4f7/2 peak to low energy is usually attributed to formation
of highly dispersed gold species. However, according to
TEM data Pd–Au/Al2O3 is characterized with almost the
same (TPO) or larger (TPR) gold particles than Au/Al2O3.
Therefore, this efect similar to the one observed earlier
in [35, 36] could be interpreted by electronic interactions
between Pd and Au due to formation of the Au–Pd alloy.
The latter may explain the presence of only metallic Pd
species even for the sample treated in oxygen. A very low
Pd content (ca. 0.039 atom.%) did not allow acquisition
ent treatments according to XPS analysis
Sample
Type of treatment
TPO
TPR
Au 4f5/2
Pd 3d5/2
Au 4f5/2
Pd 3d5/2
Au/Al2O3
Au0 (93.4)
Au+(6.6)
Au0 (100)
Pd-Au/Al2O3
Au0 (75.1)
Au+ (24.9)
Pd0 (100)
Au0 (100)
Pd0 (100)
1 3

Y. S. Demidova et al.
Table 3 XPS data of Au 4f, Pd
3d binding energies values, eV
referred to as C 1 s (284.8 eV)
for studied samples
Sample
Type of sample pretreatment
TPO
TPR
Au4f7/2
Pd3d5/2
Au4f7/2
Pd3d5/2
–
Au/Al2O3
Auo(83.9; 1.2)
–
Auo(83.9;1.2)
Au+(85.3;1. 4)
AuPd/Al2O3
Auo(83.7; 1.4)
Au+(84.8; 1.7)
Pdo(334.9; 1.3)
Auo(83.5; 1.4)
Pdo(334.8; 1.2)
In parentheses the peak position of Pd and Au species and the full width at half maximum (FWHM) are
shown
of a reliable Pd XPS spectrum for Pd/Al2O3 catalyst and
to perform a fair comparison of the state of Pd state in
Au–Pd/Al2O3 and Pd/Al2O3 catalysts.
3.2 Catalytic Results
In order to explore the infuence of bimetallic interactions
on the catalytic performance, gold, gold–palladium, and pal-
ladium catalysts activated in oxygen or hydrogen were tested
in one-pot myrtenol amination with aniline.
Based on our previous results gold-catalyzed myrtenol
amination with aniline led to the predominant formation of
myrtenal and its imine (1) and amine (2) (Fig. 2). At the
same time depending on the catalysts the hydrogenation of
C=C bond as a side process occurred. As a result myrtanol,
myrtanal and the corresponding imine (3) and amine (4)
were formed in small amounts in the presence of gold cata-
lysts [3]. Additionally no myrtenol isomerization products
were observed in the presence of Au catalysts. Alumina per
se resulted in the formation of the corresponding imine (1)
with selectivity of 94% at myrtenol conversion ca. 40% after
7 h independent on the support redox activation. To enhance
mainly the hydrogen transfer to C=N bond, low amounts
of Pd (0.2 wt%) were introduced to the gold catalyst in the
present work. At the same alumina supported Au, Au–Pd
and Pd catalysts showed diferent catalytic behavior in the
reaction. The results are presented in Fig. 6 and Table 4.
The catalysts demonstrated nearly close catalytic activ-
ity within one type of the catalysts activation in terms of
myrtenol conversion versus time decreasing in the following
range Au>Au–Pd>Pd and Au–Pd>Au>Pd for pre-oxi-
dized and pre-reduced catalysts, respectively (Fig. 6). Taking
into account the active metal content in the samples deter-
mined by ICP and the metal dispersion (D) estimated from
TEM images (Table 1) for metal nanoparticles using formula
D = 8 ⋅ rMe∕dMe, Where rMe is radius of metal atom (nm)
and dMe is particle mean diameter (nm), the initial reaction
rates normalized by amount of accessible active metal atoms
were calculated (Table 4). As it has been mentioned above
deposition of palladium onto gold nanoparticles practically
Fig. 6 The efect of catalyst active metal and redox treatment on
myrtenol conversion in the presence of Au, Au–Pd, Pd supported
on Al2O3 pre-treated in oxygen (TPO, a) or hydrogen (TPR, b). The
reaction conditions: T=180 °C, myrtenol 1 mmol, aniline 1 mmol,
toluene 10 ml, catalyst 92 mg
did not afect the size of bimetallic nanoparticles because of
a low palladium loading. For AuPd catalysts the TOF value
was calculated using TEM data. In the case of monometallic
Pd catalyst it was proposed that all Pd atoms are accessible
for the reactants. Assuming each surface atom constitutes an
active centre, the TOF can then be given as,
1 3

One-Pot Myrtenol Amination over Au, Au–Pd and Pd Nanoparticles Supported on Alumina
Table 4 Initial normalized
reaction rate and selectivity to
the products at the same value
of myrtenol conversion (85%)
for myrtenol amination in the
presence of Au, Au–Pd, Pd
supported on Al2O3 pre-treated
in oxygen (TPO) or hydrogen
(TPR)
Catalyst
TOFb, h−1
Selectivity, %c
Myrtenal
Myrtanol
Myrtanal
1
2
3
4
TPOa
Au/Al2O3
AuPd/Al2O3
Pd/Al2O3
TPRa
67
38
129
6
50
26
12
25
31
6
7
2
40
8
32
31
2
1
3
3
3
4
2
2
Au/Al2O3
AuPd/Al2O3
Pd/Al2O3
137
143
294
26
8
21
12
9
46
5
20
1
35
36
27
19
7
2
1
8
1
1
10
1
The reaction conditions: T=180 °C, myrtenol 1 mmol, aniline 1 mmol, toluene 10 ml, catalyst 92 mg
aPreliminary catalysts activation
bTurnover-frequency was calculated after 1 h
cSelectivity to the reaction products presented in Fig. 2
be mainly related to a diferent degree of the support basic
properties modifcation by residual ammonia [4].
n0myrtenol − nmyrtenol
TOF =
More noticeable diferences in the catalytic behavior for
the studied catalysts were seen in selectivity towards the
products profoundly afected by the nature of nanoparticles.
Selectivity to diferent groups of the reaction products is
presented in Table 4.
nMe ⋅ D ⋅ t
where n0myrtenol and nmyrtenol are the initial amount of myrtenol
in moles and the molar amount of myrtenol after 1 h,
n Me(mol) the amount of active metal in the catalyst, D is the
dispersion of particles, t is the reaction time (h).
Au/Al2O3 catalyst was active in the formation of the tar-
get amine (2) and the corresponding imine (1) without a
signifcant impact of the side reaction of C=C bond hydro-
genation. Au/Al2O3 catalyst treated under an oxidizing
atmosphere was more efective in terms of the target sec-
ondary amine (1) yield. An increase in selectivity to myrte-
nal for the pre-reduced catalysts was also related to catalyst
activation. Myrtenal accumulation in the reaction mixture in
the presence of pre-reduced catalysts was caused by a lack
of aniline adsorption on the catalysts due to modifcation of
their basic properties afecting eventually selectivity to the
target amine. This efect was described in detail in [4]. Thus,
the gold catalyst was efective for the hydrogen transfer.
Opposite, in the case of monometallic Pd catalyst the
formation of imine (1) was observed, whereas the products
of hydrogen borrowing reaction to C=N bond were almost
not detected and hydrogen produced in the frst step was
consumed for C=C bond hydrogenation in the initial myrte-
nol to form myrtanol (Table 4). Selectivity to myrtanol was
even higher over the pre-reduced sample compared to the
pre-oxidized one most likely due to formation of the trace
amounts of non-active palladium oxide flm over Pd nano-
particles under pre-treatment in oxygen. Indeed, the forma-
tion of palladium oxide flm over Pd nanoparticles exposed
to oxygen was found in [30].
In this case, for the pre-oxidized bimetallic catalyst intro-
duction of Pd did not improve the catalytic activity. Mono-
metallic Pd catalyst was rather active in myrtenol dehydro-
genation compared Au-containing catalysts with the initial
reaction rate being ca. 3.4 fold higher for Pd/Al2O3 catalyst.
The TOF value for pre-reduced AuPd/Al2O3 catalyst was
close to the monometallic Au catalyst. Within one active
metal composition the pre-reduced samples promoted sig-
nifcantly faster myrtenol dehydrogenation being caused by
the efect of the catalyst redox activation (Table 4). Such
efect of redox activation on catalytic performance was
studied in detail in our previous work [4]. Note that accord-
ing to the plausible reaction mechanism the basic sites on
the metal oxide surfaces are required for the initial alco-
hol activation, while availability of protonic groups was
suggested to be important for the desired amine formation
and accumulation of the primary amine on the surface [3].
Pre-reduced catalysts were shown to be more efective in
alcohol dehydrogenation due to enhancing of the support
basic properties required for the initial alcohol activation
[4]. Thermal activation of catalysts in oxygen resulted in a
higher efciency of ammonia removal, formed as a result
of decomposition/transformation of compounds used during
catalyst preparation (i.e. NH4OH and urea), compared to
treatment in hydrogen. Diferences in activity and selectivity
for pre-reduced and pre-oxidized catalysts were proposed to
Bimetallic Au–Pd catalyst despite high activity demon-
strated lower selectivity to the target amine (2) independently
on the type of the catalyst activation. Note, that pre-oxidized
1 3

Y. S. Demidova et al.
Au–Pd catalyst did not promote imines formation and only
a small amount of N-containing products was detected in
the reaction mixture. Myrtenal accumulation occurred along
with C=C bond hydrogenation in myrtenol. A low amount
of N-containing products can be explained by a lack of ani-
line on the catalyst surface as discussed above. Contrary to
that, Au–Pd catalyst pre-treatment in hydrogen did not result
in any limitations regarding imine (1) formation, while the
target amine (2) was formed only in a small amount. Both
myrtanol and myrtanal were detected in the reaction mix-
ture. Moreover, formation of imine (3) and amine (4) with
the saturated C–C bond was more noticeable compared to
monometalic Au and Pd catalysts. Therefore, Au–Pd nano-
particles activate C=C bond rather than C=N one and did
not promote hydrogen transfer because of hydrogen con-
sumption for the side C=C bond hydrogenation. Note that
formation of imine observed over Pd-containing catalysts
can be also of interest. Imines are important intermediates in
the synthesis of biologically active N-containing compounds
and in industrial synthetic processes [37–40].
palladium catalysts independent on the type of the catalyst
pre-treatment.
Nevertheless comparison between Au and Pd catalysts
revealed that Au catalyst was more active and selective in
one-pot alcohol amination for the initial substrates with a
reactive unsaturated C=C bond and even promoted hydrogen
transfer more efectively. Pd presence resulted in C=C bond
activation and its further hydrogenation by hydrogen formed
in the frst step of alcohol dehydrogenation. At the same
time the catalytic activity of palladium catalyst with a low
active metal content (0.2 wt%) is higher than Au-containing
catalyst. In this case Pd catalysts seems to be efective for the
substrates with a less complicated structure when there is no
need to avoid side reactions, in particular C=C bond hydro-
genation. A similar result was observed for Pd/MgO catalyst
by Corma et al. [41], who showed that Pd catalysts were
active for benzyl alcohol amination with aniline catalyzing
on the other hand the fnal step of C=N bond hydrogenation
with a signifcantly lower chemoselectivity for the substrates
containing a nonconjugated C=C bond. These palladium
catalysts [27] even did not promote hydrogen transfer for
the imine bond in the presence of a conjugated C=C bond. In
the current work introduction of Pd to Au nanoparticles even
in a small amount resulted in simultaneous hydrogenation of
both C=C and C=N bonds.
Thus, the frst step of one-pot alcohol amination, alcohol
dehydrogenation, is promoted on the support basic sites and
strongly depends of the support basic properties [3], while
hydrogen is further stabilized on active metal and reacting
directly with the unsaturated bond activated on the active
metal. However, the active metal composition and the sup-
port treatment during the catalyst synthesis can afect the
surface active sites of the support resulting as well in cata-
lytic activity modifcation.
4 Conclusions
Overall, the pre-reduced monometallic Pd catalyst com-
pared to bimetallic Au–Pd was more active in direct myrte-
nol hydrogenation to myrtanol, while for Au–Pd formation
of myrtanal was mainly detected among saturated products
containing oxygen. In fact, previously Pd catalysts were
shown to be highly efective for C=C bond hydrogena-
tion in α-pinene with a similar structure [11]. On the other
hand, pre-oxidized Au–Pd catalyst resulted in myrtenal
and myrtanol formation among O-containing products giv-
ing limited amounts of imines. A noticeable diference in
activity of pre-oxidized and pre-reduced Au–Pd catalysts
is proposed to be related to the active phase composition.
As it was earlier demonstrated in [30] external surface of
bimetalic Au–Pd nanoparticles activated in hydrogen exhib-
its predominantly well mixed metallic Au–Pd species with
a possible formation Au–Pd alloy, while the catalyst pre-
oxidation leads to formation of both Au–Pd alloy and PdO
species, with the later present most likely as a thin layer over
Au–Pd alloy. Availability of metallic gold species in the case
of pre-reduced Au–Pd catalyst seems to result in a more
efective hydrogen transfer compared to the pre-oxidized
sample. At the same time, formation of myrtanol observed
in the presence of pre-oxidized AuPd/Al2O3 was typical for
The regularities of one-pot terpene alcohol amination were
studied in the presence of Au, Au–Pd and Pd nanoparti-
cles supported on alumina and subjected to activation in
oxygen or hydrogen. The efect of the active metal com-
position on catalytic performance was investigated with
biomass derived terpene alcohol (myrtenol), containing
diferent functional groups. Selectivity to the target prod-
uct (amine) as well as the products of side reactions could
serve a descriptor of catalytic behavior in addition to activ-
ity evaluation. The synthesized catalysts were studied in
detail by TEM, XPS, ICP and nitrogen adsorption.
A noticeable efect of the active metal on selectivity
was observed. Monometallic Au/Al2O3 catalyst promoted
predominantly formation of the target secondary amine
and the corresponding imine without a signifcant impact
of the side reaction of C=C bond hydrogenation in myrte-
nol. Bimetallic Au–Pd catalyst despite its high activity
demonstrated lower selectivity to the target amine due
to occurrence of the side C=C bond hydrogenation mak-
ing the products formation non-selective. Au–Pd nano-
particles activate C=C bond rather than C=N one and
did not promote hydrogen transfer because of hydrogen
consumption for the side C=C bond hydrogenation. For
1 3

One-Pot Myrtenol Amination over Au, Au–Pd and Pd Nanoparticles Supported on Alumina
15. Demidova YuS, Suslov EV, Simakova OA, Simakova IL, Vol-
Pd catalyst hydrogenation of the C=C bond in myrtenol
occurred selectively without hydrogen transfer to C=N
bond. Monometallic Pd catalyst was mainly characterized
by formation of myrtanol and imine. The active metal thus
determines selectivity of hydrogen transfer. Hydrogen pro-
duced in the frst step of alcohol dehydrogenation reacts
directly with the unsaturated bond activated on the active
metal. Pd presence resulted in C=C bond activation and
its further hydrogenation, while Au promoted C=N bond
hydrogenation. Nevertheless, utilization of Pd-containing
catalyst can be justifed for the substrates with a less com-
plicated structure without competitive unsaturated groups
due to noticeably higher activity.
cho KP, Salakhutdinov NF, Murzin DYu (2015) Catal Today
241:189–194
16. Demidova YuS, Simakova IL, Wärnå J, Simakov AV, Murzin DYu
(2014) Chem Eng J 238:164–171
17. Semikolenov VA, Ilyna II, Simakova IL (2001) Appl Catal A
211:91–107
18. Ancel JE, Maksimchuk NV, Simakova IL, Semikolenov VA
(2004) Appl Catal A 272:109–114
19. Semikolenov VA, Ilyna II, Simakova IL (2002) J Mol Catal A
182–183:383–393
20. Demidova YuS, Suslov EV, Simakova IL, Mozhajcev ES, Kor-
chagina DV, Volcho KP, Salakhutdinov NF, Simakov AV, Murzin
DYu (2018) J Catal 360:127–134
21. Ishida T, Takamura R, Takei T, Akita T, Haruta M (2012) Appl
Catal A 413–414:261–266
22. Ishida T, Kawakita N, Akita T, Haruta M (2009) Gold Bull
42:267–274
Acknowledgements The authors acknowledge the technical assis-
tance of E. Smolentseva, E. Flores, P. Casillas, F. Ruiz, E. Apa-
ricio and J. Peralta. This work was supported by Ministry of Sci-
ence and Higher Education of the Russian Federation (Project
AAAA-A17-117041710075-0).
23. Zaytseva YuA, Panchenko VN, Simonov MN, Shutilov AA,
Zenkovets GN, Simakova IL, Parmon VN (2013) Top Catal
56:846–855
24. Shimizu K, Nishimura M, Satsuma A (2009) ChemCatChem
1:497–503
25. Mäki-Arvela P, Kuusisto J, Sevilla ME, Simakova IL, Mikkola
J-P, Myllyoja J, Salmi T, Murzin DYu (2008) Appl Catal A
345:201–212
Compliance with Ethical Standards
26. Mäki-Arvela P, Martin G, Simakova IL, Tokarev A, Wärnå J,
Hemming J, Holmbom B, Salmi T, Murzin DYu (2009) Chem
Eng J 154:45–51
Conflict of interest All authors claim no confict of interest.
27. Simakova OA, Simonov PA, Romanenko AV, Simakova IL (2008)
React Kinet Catal Lett 95:3–12
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