Oxidation of a wood extractive betulin to biologically active oxo-derivatives using supported gold catalysts

Article abstract of DOI:10.1039/c9gc00949c

Betulin (90-94%) was extracted from birch with a non-polar solvent and recrystallized from 2-propanol. Liquid-phase oxidation of betulin aimed at obtaining its biologically active oxo-derivatives (betulone, betulonic and betulinic aldehydes), exhibiting e.g. antitumor, anti-inflammatory, antiparasitic, anticancer and anti-HIV properties, was demonstrated for the first time over gold-based catalysts. Gold was deposited on pristine TiO₂ and the same support modified with ceria and lanthana, followed by pretreatment with a H₂ or O₂ atmosphere. The catalysts were characterized by XRD, BET, ICP, TEM, XPS, DRIFT CO, TPD of NH₃ and CO₂ methods. The nature of the support, type of modification and the pretreatment atmosphere through the metal-support interactions significantly influenced the average particle size of gold, its distribution and the electronic state of gold, as well as the acid-base properties and, thereby, the catalytic performance (activity and selectivity) in betulin oxidation. Au/La₂O₃/TiO₂ pretreated in H₂ displayed the highest catalytic activity in betulin oxidation among the studied catalysts with selectivities to betulone, betulonic and betulinic aldehydes of 42, 32 and 27%, respectively, at 69% conversion. Side reactions resulting in oligomerization/polymerization products occurred on the catalyst surface with the participation of strong acid sites, diminishing the yield of the desired compounds. The latter was improved by adding hydrotalcite with the basic properties to the reaction mixture containing the catalyst. Kinetic modelling through numerical data fitting was performed to quantify the impact of such side reactions and determine the values of rate constants.

Full text of DOI:10.1039/c9gc00949c

View Article Online
View Journal
Green
Chemistry
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: E. Kolobova, E.
Pakrieva, S. A.C. Carabineiro, N. Bogdanchikova, A. Kharlanov, S. O. Kazantsev, J. Hemming, P. Mäki-
Arvela, A. Pestryakov and D. Murzin, Green Chem., 2019, DOI: 10.1039/C9GC00949C.
Volume 18 Number
7
7
April 2016 Pages 1821–2242
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Green
Chemistry
Cutting-edge research for a greener sustainable future
www.rsc.org/greenchem
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1463-9262
CRITICAL REVIEW
G. Chatel et al.
Heterogeneous catalytic oxidation for lignin valorization into valuable
chemicals: what results? What limitations? What trends?
rsc.li/green-chem

Page 1 of 14
Green Chemistry
Betulin can be transformed into its oxo-derivatives by liquid-phase oxidation over gold-based
View Article Online
DOI: 10.1039/C9GC00949C
catalysts under mild conditions.

Please Gd roe en no tC ha ed mj u iss tt r my argins
Page 2 of 14
View Article Online
DOI: 10.1039/C9GC00949C
ARTICLE
Oxidation of a wood extractive betulin to biologically active oxo-
derivatives using supported gold catalysts
a
a
b
c
Ekaterina N. Kolobova, Ekaterina G. Pakrieva, Sonia A.C. Carabineiro, Nina Bogdanchikova,
d
e
f
f
Andrey N. Kharlanov, Sergey O. Kazantsev, Jarl Hemming, Päivi Mäki-Arvela, Alexey N.
a
f
Pestryakov, Dmitry Yu. Murzin*
Betulin (90-94%) was extracted from birch with a non-polar solvent and recrystallized from 2-propanol. Liquid-phase
oxidation of betulin aiming to obtain its biologically active oxo-derivatives (betulone, betulonic and betulinic aldehydes),
exhibiting e.g. antitumor, anti-inflammatory, aniparasitic, anticancer and anti-HIV properties, was demonstrated for the first
time over gold-based catalysts. Gold was deposited on pristine TiO
followed by pretreatment with H or O atmosphere. The catalysts were characterized by XRD, BET, ICP, TEM, XPS, DRIFT
CO, TPD of NH and CO methods. The nature of the support, type of modification and the pretreatment atmosphere through
2
and the same support modified with ceria and lanthana,
2
2
3
2
the metal-support interactions significantly influenced the average particle size of gold, its distribution and the electronic
state of gold, as well as the acid-base properties and, thereby, the catalytic performance (activity and selectivity) in betulin
2 3 2 2
oxidation. Au/La O /TiO pretreated in H displayed the highest catalytic activity in betulin oxidation among the studied
catalysts with selectivities to betulone, betulonic and betulinic aldehydes of 42, 32 and 27%, respectively, at 69% conversion.
Side reactions resulting in oligomerization/polymerization products were occurring on the catalyst surface with the
participation of strong acid sites, diminishing the yield of the desired compounds. The latter was improved by adding
hydrotalcite with the basic properties to the reaction mixture containing the catalyst. Kinetic modelling through numerical
data fitting was performed to quantify the impact of such side reactions and determine the values of rate constants.
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
betulinic and betulonic acids) have valuable biologically active
properties, and are of exceptional interest for the pharmaceutical,
cosmetic and food industries. For example, betulinic acid and its
derivatives exhibit anti-cancer, anti-HIV, antiviral, anti-inflammatory,
Introduction
6
-9
Utilisation of natural compounds for chemical transformations to
obtain biologically active compounds has become one of the
promising and actively developing areas of fine organic synthesis and
pharmaceutical chemistry. Triterpenoids are a class of compounds
that combine accessibility, i.e., availability in nature and easiness of
isolation, with valuable biological activity. Betulin (lup-20 (29) -ene-
antiseptic,
antimicrobial,
anti-malarial,
anti-leishmaniasis,
anthelmintic and fungicidal activity. While betulonic acid has
pronounced anti-inflammatory, antimelanomas and antiviral effects.
Antiviral and anti-leukemic activity was also reported for betulonic
aldehyde, which is, moreover, active against diseases of the liver, the
digestive tract and disorders of reproductive function. The 3-oxo
derivative of betulin — betulone and its derivatives, exhibiting
antitumor, anti-inflammatory, aniparasitic, anti-HIV properties, also
demonstrate in vitro cytotoxic activity against different cancer cell
3
50 2
, 28-diol, C30H O , CAS: 473-98-3) – a pentacyclic triterpenoid of
the lupane series, is found in almost two dozen plants belonging to
different genera and families, wherein the main source of betulin is
birch bark with the content varying from 10 to 35%. The methods of
betulin extraction from birch bark are widely reported in the
literature including extraction of the bark outer layer by various
solvents, bark alkaline hydrolysis followed by ethanol extraction of
betulin, “explosive” autohydrolysis, etc.1 Betulin and especially its
oxo-derivatives (betulone, betulinic and betulonic aldehydes,
1
0-22
lines.
Recent studies indicate a clear demand for betulone as a
building block for creating effective anticancer agents with minimal
2
0-22
-6
side effects.
Currently, the main method of synthesis of betulin oxo-
2
3
derivatives is its oxidation. The work of Csuk et al. described
formation of betulinic acid via betulinic aldehyde by oxidation of
a. Research School of Chemistry & Applied Biomedical Sciences, Tomsk Polytechnic
University Lenin Avenue 30, 634050 Tomsk, Russia.
betulin with
tetramethylpiperidine-1-oxyl) - NaClO
a
mixture comprising TEMPO (2,2,6,6-
- NaOCl at 35⁰C with 92%
b.
2
Laboratory of Catalysis and Materials (LCM), Associate Laboratory LSRE-LCM,
Department of Chemical Engineering, Faculty of Engineering, University of Porto
yield. Synthesis of betulinic acid from betulin can be carried out in
one stage using butyl acetate with 4-acetamido-TEMPO and
Bu NBr·H O as oxidants in an aqueous solution of NaClO and NaOCl
4 2 2
Rua Dr Roberto Frias s/n, 4200-465 Porto, Portugal.
Centro de Nanociencias y Nanotecnología, UNAM Post box 14, 22860 Ensenada,
c.
México.
d.
Department of Chemistry, M.V. Lomonosov Moscow State University, Leninskie
at 50⁰C, regulating pH with phosphate buffer. Methods of obtaining
betulinic acid and betulinic aldehyde by betulin oxidation with
chromium oxide (VI), chlorochromate or pyridinium dichromate fixed
on a solid silica gel or alumina were also reported. Betulinic acid was
synthesized by oxidation of betulinic aldehyde with potassium
Gory, 119991 Moscow, Russia.
Institute of Strength Physics and Materials Science of Siberian Branch of Russian
e.
Academy of Sciences (ISPMS SB RAS) pr. Akademicheskii 2/4, 634055 Tomsk,
Russia.
Johan Gadolin Process Chemistry Centre, Abo Akademi University FI-20500 Turku,
f.
Finland. E-mail: dmurzin@abo.fi; Fax:+ 358 2 215 4479; Tel: +358 2 215 4985
2
4
†
Electronic Supplementary Information (ESI). See DOI: 10.1039/x0xx00000x
permanganate. A method for selective oxidation of betulin with
Please do not adjust margins

Page 3 of 14
Please Gd roe en no tC ha ed mj u iss tt r my argins
ARTICLE
pyridinium dichromate (PDC), pyridinium chlorochromate (PCC) or of octanol37 which has, however, chemical and physiVcieawl pArrtoicpleeOrntliienes
Cr - 9M H SO
in the presence of tetrabutylammonium bromide different from those for betulin. No reports DonOIb:e10tu.1l0in39o/xCid9GatCio0n09o4v9eCr
TBAB) to betulinic aldehyde, or its mixture with betulonic aldehyde gold catalysts are available in the literature, thus it was interesting to
K
2
2
O
7
2
4
(
2
5
and ketol was developed by Komissarov et al. The yield of oxidation explore possibility of their utilization for a much more complex case
products did not exceed 75%. The method of obtaining betulonic acid than oxidation of octanol.
by oxidation of betulin, in the first step with the Jones reagent in
The aim of the present study is thus to evaluate applicability of
2
6,27
acetone, should also be mentioned.
Alternatives include gold-based catalysts in the liquid phase selective oxidation of betulin,
application of the pyridine dichromate complex and acetic anhydride to elucidate the influence of the support and nature of the additives,
2
8
in dimethylformamide, and chromium (VI) oxide in acetic acid, the impact of redox pretreatment on catalytic properties.
2
9
followed by reduction to betulinic acid. Two-stage methods for
Moreover, a comparative analysis of the catalytic properties of
synthesis of betulinic acid have significant shortcomings. Low ruthenium, silver and gold catalysts in betulin oxidation was
solubility of betulin in acetic acid, acetone and methylene chloride performed showing that the latter ones are more active and stable.
and of betulonic acid and its salts in alcohols, tetrahydrofuran and
water, imposes several limitations, preventing oxidation and
reduction and, thus, resulting in poor yields and purity. In the
Results and discussion
majority of the proposed oxidation methods, highly toxic Cr (VI) is
used. Moreover, separation of the products containing toxic Cr (III)
ions is very laborious and time consuming.
XRD was used to study the phase composition of the
investigated catalysts (ESI Fig. S1†). The XRD patterns showed
absence of the reflections characteristic for gold and modifiers,
indicating small sizes of gold and metal oxides particles (lower
than the sensitivity XRD threshold of 3–4 nm) or their X-ray
amorphous structure.
In addition to chemical modifications, attempts to transform
betulin using microorganisms were carried out, mainly for synthesis
1
0,30-33
of betulone.
However, such betulin biotransformation
processes using conditionally pathogenic yeasts, fungi, etc. have
significant drawbacks, requiring complex nutrient media, long
duration, low concentration levels of products as the biocatalyst
might not tolerate higher concentrations.
Table 1 shows the specific surface area of supports and
catalysts (SBET), Au content and gold particle size data. The
2
surface area of the pristine TiO was diminished by 13% after
2
modification (48 m /g) with both modifiers. Further gold
deposition did not significantly change the specific surface area
3
4,35
Recently,
some of the authors of this work demonstrated for
the first time the possibility to selectively oxidize betulin to betulinic
aldehyde using Ru/C as a catalyst mixed with the basic hydrotalcite
and SiO as a dehydrating agent at 108⁰C in toluene, with air as an
2
oxidant. Under these conditions, the conversion of betulin after 24
hours was 41% with 67% selectivity to betulinic aldehyde, whereas
2
without the addition of SiO , conversion and selectivity were 20%
and 66%, respectively. A higher conversion was achieved when the
reaction was carried out in an acidic medium, giving, however,
allobetulin as the main product. It was found that the presence of a
basic agent and elimination of water are crucial for selective
oxidation of betulin to betulinic aldehyde on Ru catalysts. Selective
oxidation of betulin to betulone was also reported using silver
supported on unmodified titania and modified with ceria under mild
conditions, e.g. atmospheric pressure, relatively low temperature
2 3 2
of the supports, except Au/La O /TiO , for which there was a
noticeable decrease by 10% (Table 1). ICP analysis showed that
Au contents were close to the nominal ones.
The average size of gold nanoparticles is lower than 3 nm for
2 2
most of the studied materials, except Au/TiO _pO (Table 1).
The largest size of gold nanoparticles and the broadest
distribution were observed in the case of gold supported on
unmodified titania (ESI Fig. S2†). On the contrary, for La-
modified materials, the size of Au particles and the range of
their distribution are the smallest. These values for Ce-modified
materials were in between other catalysts. In addition to the
2 2
support nature, the pretreatment atmosphere (H or O ) also
affects the uniformity of particles and their relative size. At the
same time, the impact of pretreatment depends also on the
support. For unmodified and lanthana-modified materials,
(
140⁰C), synthetic air as an oxidant, solvent – mesitylene. Conversion
of betulin over Ag/CeO /TiO catalyst reached 27% after 6 hours,
which was substantially larger than 11% obtained for Ag/TiO . In all
2
2
smaller particles were obtained after pretreatment in H
300⁰C), and for ceria-modified after O (300⁰C). These effects
2
2
(
2
cases the main product was betulone with selectivity exceeding 60%.
Based on the analysis of published studies on betulin oxidation,
it is obvious that currently there are no economically and ecologically
acceptable methods for producing oxo-betulin derivatives. Such
methods based on heterogeneous catalysis should replace existing
stoichiometric processes which lead to formation of large amounts
of toxic waste, being able to provide preferably a quantitative yield
of the desired product. In the present work, the possibility of
heterogeneous catalytic oxidation of betulin with synthetic air, using
catalysts based on gold nanoparticles supported on unmodified and
modified titania, will be demonstrated for the first time. Some of
these catalysts have been synthesized before and used for oxidation
can be attributed to the specificity of gold interactions with
different supports during catalyst preparation, as previously
confirmed, and to the different nature of the gold precursor
36
decomposition under reducing and oxidizing pretreatment,
37
previously revealed by TPR. It should also be taken into
account that a certain fraction of gold is in the form of highly
dispersed oxidized gold species, which are quite difficult to be
detected by electron microscopy because of the lower contrast
of oxidized species compared to the reduced ones. The
presence of such oxidized species was previously validated by
37
+
3+
TPR. Moreover, gold in the ionic state (Au or Au ) not
detected by TEM, could still be present, according to DRIFT CO
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 2
Please do not adjust margins

Please Gd roe en no tC ha ed mj u iss tt r my argins
Page 4 of 14
ARTICLE
Au/CeO2/TiO
2
_pO
2
83
11
19
6
and XPS (Fig. 1 and Table 2). The amount of these gold species
ionic and oxidized gold species) depends on the support and
pretreatment.
View Article Online
Au/La
2
O
3
/TiO
2
_pH
DOI: 10.1039/C9GC00949C
(
8
8
1
3
0
*
2
Au/La
2
O
3
/TiO
2
_pO
17
0
*
2
*
Data from.37
Table 1 Textural properties of supports and catalysts, analytical
contents of Au, dispersion and average particle size of gold
For a more detailed study of the electronic state of gold in the
investigated catalysts, and also as for the evaluation of the strength
and stability of the adsorption centers, DRIFT spectroscopy of
adsorbed CO was applied. CO adsorption was carried out at different
pressures: 5, 20, and 50 Torr, making it possible to evaluate the
strength of the centers. Pure supports did not exhibit bands of
adsorbed CO in this region of the spectrum under the studied
conditions. From Fig. 1, it can be concluded that for all catalysts,
regardless of the pretreatment, one absorption band with the
Au
conten
t wt.%
by ICP*
S
BET
2
,
Au average
nanoparticl
e size, nm
Dispersion
, %
Sample
m /g
*
TiO
La
CeO
Hydrotalcite
2
55
48
48
43
50
50
-
-
-
-
-
-
-
-
2
O
3
/TiO
/TiO
2
2
2
-1
Au/TiO
Au/TiO
2
_pH
_pO
/TiO
2
4.0
4.0
2.9
3.3
34
30
36
maximum in the range of 2100 - 2120 cm , attributed to the surface
0
38
2
2
carbonyls of gold atoms Au -CO, was observed. The intensity of this
band increased with increasing CO pressure. Differences in the signal
position are caused by CO adsorption on the metal clusters of
different size, bands with low-frequency associated with larger
nanoparticles. CO starts to adsorb on larger gold clusters as the
pressure increases. Moreover, carbon monoxide is very weakly
adsorbed on metallic gold because of some features of σ-π binding
Au/CeO
2
2
_pH
4
6
4.1
4.1
3.3
2.8
2.4
2.6
2
Au/CeO2/TiO
2
_pO
2
46
42
38
2
Au/La O
3
/TiO
2
_pH
4
4
3
3
2
2
Au/La O
3
/TiO
2
_pO
37
3.3
2.7
2
0
Data from.37
in M –CO for Au, in comparison to other noble metals (Pt, Pd, Ru, Rh,
*
Cu).39 Only highly dispersed gold clusters or atoms can be sites for CO
adsorption. This explains different intensities of the absorption
0
bands corresponding to Au -CO at CO pressure of 50 Torr.
Table 2 shows the relative atomic concentrations of
Subsequently, it can be assumed that there are larger particles in
various electronic states of gold, calculated according to
XPS. As can be seen, the relative values of different gold
states depend strongly on the support and pretreatment
conditions. On the surface of all studied catalysts, most of
Au/TiO
Au/La
2
_pH
/TiO
2
, Au/CeO
2 2 2 2 2 2
/TiO _pH , Au/CeO /TiO _pO , and especially
_pO catalysts, which were not taken into account
2
O
3
2
2
when analyzing TEM images because of their relatively low
abundance. In our previous study,40 there was a similar discrepancy
between the average particle size obtained by TEM and SR-XRD. The
average particle size of gold obtained from SR-XRD was in good
agreement with the catalytic results, and for some catalysts it was
larger than the values determined by TEM. Another absorption band
the gold (68 – 89%) is in a metallic state with BE(Au4f7/2
)
in the range of 84.2 – 84.3 eV, but also a part of gold (11
+
–
20%) is in the form of single charged ions (Au ) with
BE(Au4f7/2) in the range of 85.2 – 85.5 eV. In the case of
unmodified and Ce-modified samples pretreated in H
2
,
3
+
another state related to three-charged gold (Au ) with
BE(Au4f7/2) equal to 86.5 and 86.3 eV appears in the XPS
spectrum (11 and 12%, respectively). These data confirm
that the formation of the active surface on different
supports, under the action of various pretreatments,
occurs differently, and are in good agreement with TEM
-1
with the maximum in the range of 2140 – 2185 cm , related to the
+
41,42
complexes of ions Au -CO
was observed in almost all cases,
except Au/TiO _pH . However, the intensity of this absorption band,
as well as its change with pressure variation, are different. This
absorption band is less intense than the attributed to Au -CO, and
also strongly depends on CO pressure. The intensity increases with
2
2
0
(
Table 1).
the pressure increase. It is interesting to note that, for
+
2
Au/La O
3
/TiO
2
_pO
2
(Fig. 1f), reduction of Au sites is observed in the
CO atmosphere, which indicates their very low stability. Absence of
this absorption band for Au/TiO
2
_pH
2
can be due to the presence of
Table 2 Electron states of Au calculated according to XPS for the
studied catalysts
+
only weak Au sites, and even a CO pressure of 50 Torr is not enough
for their identification by DRIFT CO, while according to XPS (Table 2),
Au(0, +1 or +3) content in the samples, %
Sample
+
Au0
Au+
Au3+
Au is 15% of the total amount of gold. It should also be noted that
*
the XPS method determines the ionic states of gold in the near-
surface layer, some of which may not be accessible for adsorbed
molecules. At the same time, the method of DRIFT adsorbed CO
Au/TiO
Au/TiO
Au/CeO
2
_pH
2
74
89
68
15
11
20
11
0
12
*
2
_pO
/TiO
2
2
2
_pH
2
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Page 5 of 14
Please Gd roe en no tC ha ed mj u iss tt r my argins
ARTICLE
allows identification of the active sites on the surface available for
the reactions.
TPD of NH was used to determine acidity of supports and respective
gold catalysts, namely the concentration and strength of acid sites
Table 3 and ESI Fig. S†) . Physical adsorption can take place in the
View Article Online
DOI: 10.1039/C9GC00949C
3
(
case of ammonia TPD, being, however, typical for low temperatures.
Therefore, to avoid contribution of physical adsorption, the analysis
started from 100 ⁰C.
Fig. 1 DRIFT spectra of CO adsorbed on catalysts pretreated at 300⁰C for 1 h in
2 2
H or O atmospheres. The spectra of adsorbed CO were recorded at different
CO pressures — 5, 20, 50 Torr.
Three types of acid sites are detected for the initial supports, but
their concentration and strength are different (Table 3). The pristine
titania showed the highest acidity among the used supports with the
majority of acidic sites being of weak strength, while the
concentration of the medium and strong acidic sites is 2.6 and 6.9
folds lower than the previous one. Therewith, they are all Brønsted
acid sites (acidic OH groups).43-45 However, it is possible that the
strong acid sites are of aprotic nature and are Lewis acid sites (e.g.
4
+ 46
tetrahedral coordinated Ti ).
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 4
Please do not adjust margins

Please Gd roe en no tC ha ed mj u iss tt r my argins
Page 6 of 14
ARTICLE
2
Modification of titania with ceria and lanthana led to a decrease temperature range in which CO desorption occurs, the basic sites
View Article Online
in the concentration of weak and medium acid sites. This is most are divided into three types: weak, mediuDmOaI:n1d0.1s0t3ro9/nCg9,GrCef0l0e9ct4i9nCg
likely a consequence of surface dehydration after calcination at their nature. The weak basic sites (25 - 200⁰C) are usually attributed
5
50⁰С during preparation. Alongside with that, the amount of strong to surface hydroxyl groups, medium ones (200 - 400⁰C) to metal
acid sites increased for Ce-modified, but decreased for La-modified oxide pairs, and strong sites (400 - 600⁰C) to low-coordinated oxygen
titania. In the case of ceria-modified TiO , this can be explained by anions. All types of basic sites mentioned above were observed for
2
4
+
3+
the appearance of new Lewis sites, due to the presence of Ce /Ce , the supports studied in this work (Table 4 and ESI Fig. S4†). Pristine
which existence was indirectly confirmed by TPR.37 For lanthana- titania exhibited the average total basicity among the studied
modified material, no hydrogen consumption was observed in TPR supports, with the dominance of basic sites of medium strength and
profiles. Thus, it can be assumed that lanthana blocked the acid sites almost absent strong sites. A similar distribution of the basic sites
on the pristine titania surface leading to a decrease in acidity. After was also observed for Ce-modified titania, while the amount of these
gold deposition, in all cases, there was a redistribution of acid sites. sites was lower. After modification of titania by lanthana, there was
Regardless of pretreatment for unmodified and Ce-modified an increase in the concentration of weak and strong basic sites, while
materials, an increase in the concentration of weak acid sites and a the amount of medium sites remained almost unchanged. Table 4
significant decrease of strong acid sites were observed. The amount also presents the results for hydrotalcite, basicity of which is 2-3 folds
2 2
of medium sites in the case of Au/CeO /TiO was increased, while for higher than of the used supports. The gold deposition on the support
Au/TiO it remained almost unchanged. The distribution of acid sites surface led to a redistribution of the basic sites similar to the acidic
2
is noticeably different for the La-modified catalyst, compared with ones (Table 3). For almost all studied catalysts, there was an increase
the other materials. This is most clearly seen for strong acid sites, in the amount of basic sites while, in all cases, the strong basic sites
which concentration significantly increased. Moreover, there was a increased. The reasons for the changes in basicity after gold
decrease of weak acid sites in comparison with unmodified and Ce- deposition are apparently the same as for acidity in a sense that they
modified materials. Such changes in acidity after metal deposition originate from exposure of the support to the metal precursor during
may originate from several reasons. One of the options can be preparation, mutual influence of the support and the precursor, and
associated with a change in the support properties during catalyst base site blocking.
preparation resulting the mutual influence of the support and the
In addition, as shown in,54,55 CO
2
is also capable of being
metal precursor, as previously discussed.36,47-49 Another possibility is adsorbed on small gold nanoparticles, with abstraction of oxygen by
0
+O2- species, which cannot be considered as
-TPD (Table 4) and TEM (Table
blocking the acid sites, previously existing on the surface by newly Au , giving CO and Au
2
formed metal nanoparticles. It should be noted that, in the case of the basic sites. When comparing CO
2
-4
2
La-modified catalyst, a part of the strong acid sites (90·10 mol/m ) 1), it can be concluded that the highest increase in the amount of
+
may be associated with the Lewis acid sites, namely Au . This is basic sites was observed for samples with the smallest particle sizes.
confirmed by comparing XPS (Table 2), DRIFT CO (Fig. 1) and NH
3
-TPD Subsequently, a part of the strong basic sites can be associated with
adsorption on small gold nanoparticles.
(Table 3) data. Considering that lanthana is a non-reducible oxide, it CO
2
can be suggested that another part of the strong acid sites is
associated with Brønsted acidity and belongs to the support or the
modifier.
Table 4 Basic properties of supports and catalysts
Concentration of basic sites, mol·10 /m
-4
2
Sample
weak
53
medium
93
strong total
Table 3 Acidic properties of supports and catalysts.
-
4
2
TiO
CeO
La
Hydrotalcite
2
9
155
145
248
555
149
168
334
162
372
213
Concentration of acid sites, mol·10 /m
Sample
2
/TiO
/TiO
2
56
83
96
230
85
58
137
67
107
88
6
weak
378
304
302
528
520
496
421
146
276
medium strong
total
577
509
400
706
670
932
677
713
732
2
O
3
2
117
284
30
68
130
43
35
37
34
42
67
52
177
74
TiO
CeO
La
2
144
90
90
55
115
8
16
18
80
69
239
170
2
/TiO
/TiO
2
Au/TiO
Au/TiO
2
_pH
_pO
2
2
O
3
2
2
2
Au/TiO
Au/TiO
Au/CeO
Au/CeO
2
_pH
2
162
132
356
187
135
286
Au/CeO
Au/CeO
2
/TiO
/TiO
2
_pH
_pO
2
2
_pO
2
2
2
2
2
/TiO
/TiO
2
_pH
_pO
2
Au/La
Au/La
2
O
3
/TiO
/TiO
2
_pH
_pO
2
88
51
2
2
2
2
O
3
2
2
Au/La
Au/La
2
O
3
/TiO
/TiO
2
_pH
_pO
2
193
2
O
3
2
2
Catalytic behavior of Au supported catalysts in the betulin liquid
phase oxidation (Figure 2) was studied at 140⁰C and a synthetic air
pressure of 1 bar in mesitylene. To assess the influence of the
support nature and pretreatment atmosphere, gold was deposited
In order to assess the basic properties of the studied materials
TPD of CO
was used. Based on the literature,50-53 depending on the
2
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Page 7 of 14
Please Gd roe en no tC ha ed mj u iss tt r my argins
ARTICLE
2
on pristine titania and TiO modified with ceria and lanthana. The determined by the catalyst properties. In this particVuielawrArctaicsleeO, ntlhinee
obtained materials were pretreated in H
2
or O
2
.
GCLPA was 90%. Betulin conversion and DseOleI:c1t0iv.1i0ty39f/oCr9GthCe00s9a4m9Ce
material (Au/TiO ), but pretreated in O , were almost the same
Table 5, entry 2). However, due to a better GCLPA - 96%, the total
yield of products for this catalyst turned out to be 1.7 fold higher than
for the one pretreated in H
In contrast to the unmodified material, betulin conversion for Ce-
modified catalyst was higher after the pretreatment in H (betulin
2
2
(
2
.
2
conversion - 45%, Table 5, entry 3). However, the mass balance
closure in this case was the worst – 77 %, ultimately giving only 22%
total yield of the main products. For the same catalyst, but
pretreated in oxygen, a lower conversion - 33%, was achieved (Table
5
, entry 4). The best 95% GCLPA was, however, reached for this case,
with the total yield of products being 1.2 fold higher than after
pretreatment in H . The pretreatment atmosphere even affected
Fig. 2 Reaction scheme for betulin oxidation.
2
selectivity for the primary products, such as betulone (B) and
betulinic aldehyde (C), which should be less sensitive to conversion
levels. For Au/CeO /TiO _pO in particular, the main product was
2 2 2
It was found that both the nature of the support and the
pretreatment atmosphere have a significant influence on the
catalytic behavior of the studied catalysts (Table 5). Among the
betulinic aldehyde (C), while for Au/CeO
mainly obtained.
2 2 2
/TiO _pH betulone (B) was
2 2
studied gold containing materials, Au/TiO pretreated in H (Table 5,
entry 1) had the lowest activity. Betulin (A) conversion was 25%, with
selectivity to betulone (B) and betulinic aldehyde (C) of 40 and 53%,
at this conversion level, respectively. Herewith, the total yield of
products was only 15%, which is 1.7 fold lower than the observed
conversion (Table 5 - entry 1, Fig. 3a,d). This difference is due to
incomplete mass balance (the sum of the masses of the reactant and
products visible in GC, GCLPA). This is most likely caused by strong
adsorption of reactants or products on the catalyst surface. The mass
balance closure was different for the various catalysts, being
2 3 2
Au/La O /TiO pretreated in hydrogen had the highest activity
among the studied catalysts. Betulin conversion was 69% and the
main products were betulone (B), betulonic (D) and betulinic (C)
aldehydes, with selectivities of 42, 32 and 27%, respectively (Table 5
entry 5, Figure 3b,d). It should be noted that due to GCLPA of 80%,
the total yield of the main products turned out to be 1.4 fold lower
than the observed conversion, being 48%. Betulin conversion for the
-
same material (Au/La
lower than after treatment in H
2
O
3
/TiO
2
), but pretreated in O
(Table 5, entry 6).
2
was 2.8 fold
2
Table 5 Catalytic behaviour of Au, Ru and Ag supported catalysts in betulin oxidation
Selectivity, %
Entry
Catalyst
X (%)
GCLPA (%)
∑Yproduct (%)
S
B
S
D
S
F
S
C
S
E
S
allobetulin
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
TiO
CeO
La
Au/TiO
Au/TiO
2
13
17
4
25
27
45
33
69
25
70
71
48
93
91
97
90
96
77
95
80
97
85
87
87
88
-
65
69
53
40
38
48
34
42
44
54
52
57
64
0
3
9
47
6
5
0
0
tr.
1
tr.
1
tr.
1
0
0
0
tr.
1
5
49
4
15
0
0
2
22
0
1
tr.
1
0
0
0
0
0
0
tr.
2
0
0
4
3
7
0
0
0
0
0
0
0
0
0
0
0
0
0
72
2
1
4
0
0
6
8
3
2
/TiO
/TiO
2
2
O
3
2
2
_pH
2
53
51
40
54
27
48
21
21
19
17
16
77
37
67
21
6
15
25
22
27
48
22
55
58
35
46
-
2
_pO
2
10
11
11
32
7
25
27
24
19
2
9
13
8
8
4
Au/CeO
Au/CeO
2
/TiO
/TiO
2
_pH
_pO
2
2
2
2
Au/La
Au/La
Au/La
Au/La
Au/La
Au/La
Ru/C, Degussad
Ru/C, Degussad,e
Ru/C, Degussaf
Ru/C, Degussad,g
2
2
2
2
2
2
O
3
/TiO
3
/TiO
3
/TiO
3
/TiO
3
/TiO
3
/TiO
2
2
2
2
2
2
_pH
_pO
2
O
O
O
O
O
2
a
0
1
2
3
4
5
6
7
8
9
_pH
_pH
_pH
_pH
2
2
2
2
b
c
d
58
54*
16*
12*
41**
11
-
-
-
-
0
0
0
59
60
-
-
-
-
Ag/ TiO
Ag/CeO
2
3
1
2
/TiO
2
27
-
-
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 6
Please do not adjust margins

Please Gd roe en no tC ha ed mj u iss tt r my argins
Page 8 of 14
ARTICLE
View Article Online
DOI: 10.1039/C9GC00949C
Conditions: 140⁰C, synthetic air (50 ml/min) as oxidant, solvent - mesitylene, entries 1-12, 18 and 19; X – conversion of betulin after 6 h (%); GCLPA - the sum
of reactant and product masses in GC analysis (%); S – selectivity to betulone (%); S – selectivity to betulonic aldehyde (%); S – selectivity to betulonic acid
B
D
F
(
%); S
C
– selectivity to betulinic aldehyde (%); S
E
– selectivity to betulinic acid (%); Sallobetulin - selectivity to allobetulin (%); ∑Yproduct - total product yield after 6 h
a
b
; csecond run; conditions: 108⁰C, synthetic air (50 ml/min) as oxidant,
d
(%); tr. – traces; with 0.2 g of hydrotalcite; with 0.2 g of hydrotalcite and 0.2 g SiO
2
e
f
g
solvent – toluene, entries 13 - 17; with 0.5 g of hydrotalcite; conditions are the same as for entries 1-12; with 0.5 g of hydrotalcite + 0.5 g SiO
of betulin after 5 h (%); **conversion of betulin after 24 h (%); data of 14 - 17 entries from34; data of 18 and 19 entries from 35
2
; *conversion
.
Fig. 3 Kinetics of betulin oxidation on a) Au/TiO
2
_pH
2 2 3 2 2
, b) Au/La O /TiO _pH
and c) Au/La /TiO _pH with 0.2 g of hydrotalcite, data are presented taking
2
O
3
2
2
into account the mass balance; d) Selectivity towards betulone and betulonic
aldehyde as a function of betulin conversion. Conditions: 140⁰C, synthetic air
(50 ml/min) as oxidant, initial betulin concentration – 4.5 mmol/l, solvent -
mesitylene, 0.2 g catalyst.
For this catalyst, the products distribution was also different. It can
be also related to the conversion as betulinic aldehyde (C) can be
transformed to betulonic aldehyde (D). In this case, betulonic
aldehyde (D) was practically not formed and the main products were
betulone (B) and betulinic aldehyde (C), with higher GCLPA (97%).
Table 5 also presents the results of the previous studies on
betulin oxidation over Ru and Ag catalysts.34,35 As can be seen from
the data (Table 5, entries 4–9, 15, 17, 18), under the same
experimental conditions, activity of supported gold catalysts
significantly exceeds activity of Ru and Ag counterparts. Selectivity of
Ru is significantly different from that for Au and Ag catalysts. Over
2
the majority of Au(Ag)/(modifier)/TiO catalysts the main reaction
products were betulone (B) and betulinic aldehyde (C), while
betulonic acid (F) and betulinic aldehyde (C) were obtained for Ru/C.
It is also worth noting that allobetulin was not observed in the
2
reaction products for Au(Ag)/(modifier)/TiO in comparison with Ru.
Moreover in the previous work the mass balance closure was not
explicitly accounted for, making a direct comparison of the yields not
straightforward .
In the work,34 it was also shown that the catalytic behavior
(activity and selectivity) of Ru catalysts depends strongly on the
reaction conditions. In toluene as a solvent at 108 ⁰C, betulin
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Page 9 of 14
Please Gd roe en no tC ha ed mj u iss tt r my argins
ARTICLE
conversion over Ru/C (entry 14) was 54% after 5 hours with strong acid sites. The lower is this concentration, the hiVgiehweArrttihclee Omnalinses
allobetulin (77%), a structural isomer of betulin, as the main product. balance closure (Figure 4), which can be expDlaOiIn: e10d.1b0y39si/dCe9GreCa0c0t9io4n9sC,
To evaluate how the reaction conditions affect the catalytic behavior promoted on stronger sites leading to lower GCLPA. This is also
of gold materials, a similar experiment was carried out using confirmed by comparing the catalytic and ammonia TPD data for the
Au/La
entry 8, betulin conversion decreased 1.2 fold, however, the main modified TiO
reaction products were still betulone (B), betulonic (D) and betulinic was the highest among supports, and the GCPLA was the lowest. For
C) aldehydes. It is worth noting that in this case, the mass balance La-modified TiO , the opposite situation was observed. From this
closure was higher (88%) compared with entry 8 (80%), therefore, point of view, hydrotalcite indirectly affected the catalyst properties,
the difference in ∑Yproduct between 8 and 13 entries was only 2%. in particular the strong acid sites, preventing the side reactions and
2
O
3
/TiO
2
_pH
2
in toluene at 108 ⁰C (entry 13). Compared with supports applied in this work (Table 3, Table 5 – entries 1-3). For Ce-
2
, the concentration of medium and strong acid sites
(
2
Selectivity to a more desired product (betulinic aldehyde as increasing the product yield.
opposed to allobetulin) was increased34 by adding basic hydrotalcite
Along with the acidity of the materials, their basicity also plays
to the reaction mixture, even if there was a negative influence on an important role (Table 4). Betulin conversion was higher for
activity decreasing betulin conversion from 54% to 16%, Table 5, catalysts with more pronounced basic properties. Herewith, H2-
entry 15. The betulin conversion reached 41% with selectivity to pretreated materials were more basic, but at the same time, they
2
betulinic aldehyde 67% (Table 5, entry 17) with increasing reaction also demonstrated higher acidity. The exception was Au/TiO , for
time up to 24 hours, adding hydrotalcite and silica as a dehydrating which conversion or the product distribution was almost
agent. In the present work, a similar experiment was carried out, and independent of the pretreatment atmosphere. This can be explained
hydrotalcite was added to the reaction mixture containing that the acid-base properties of this material vary only slightly upon
Au/La
2
O
3
/TiO
2
_pH
2
(Table 5, entry 10, Fig. 3c,d). However, there different pretreatment.
It should be noted that while a certain correlation between the
were no significant changes in betulin conversion or in the product
distribution. Betulin conversion increased by only 1% after adding acid-base properties and catalytic performance was seen, the role of
hydrotalcite. Despite a slight increase in betulin conversion, TOF gold in betulin oxidation is decisive. Moreover, correlations between
-1
2
increased 1.4 fold and was 0.010 s , compared to the experiment TPD of ammonia and CO made in the gas-phase with catalytic
-1
without hydrotalcite, for which it was 0.007 s . Moreover, due to the properties should be taken with caution when the catalysts are
better GCLPA – 85%, the total yield of the main products increased employed in the liquid-phase processes. Nevertheless, TPD methods
to 55% compared with entry 5, being 48% (Table 5). Addition of silica provide general information on the nature of solid surfaces and the
to the reaction mixture, along with Au/La
hydrotalcite, additionally increased betulin conversion by 1% and properties of solid catalysts even for the liquid phase reactions.
products yield by 3%, as well as GCPLA to 87% (Table 5, entry 11). In order to find out the reason for a decrease in GCPLA, namely,
2 3 2 2
O /TiO _pH and types of sites and are often applied for characterizing the acid-base
Thus, it can be assumed that addition of hydrotalcite, giving what was adsorbed on the catalyst surface, size exclusion
apparently local changes in concentrations of proton and hydroxyls chromatography (SEC) was used.
in the vicinity of the catalyst surface, can thereby affect the
After carrying out the extraction and SEC analysis, it was found
properties of the catalyst surface. In turn, silica prevents the that polymers and oligomers with a molecular weight of 5000 and
inhibitory action of water. However, in the case of betulin oxidation 1000 Da, respectively, were formed on the catalyst surface (ESI Fig.
over gold catalysts, inhibition by water is much less pronounced than S5†). The weight of oligomers/polymers on the catalyst was not
for Ru catalysts.34 In general, gold materials were less sensitive to quantified, being, however, related to the mass imbalance between
changes in the reaction conditions than ruthenium ones. When the theoretical GCLPA (100%) and the corresponding values of GCLPA
2 3 2 2
Au/La O /TiO _pH was recycled (Table 5, entry 12), a 30% drop in reported in Table 5.
activity compared to entry 8 was observed, indicating some catalyst
deactivation. However, the gold catalyst was still more stable than
ruthenium, for which the activity decreased by 44% in the second run
(
from 41% to 23%).34 As mentioned above in Introduction betulone
is equally important as betulinic aldehyde or betulinic acid.
Selectivity to betulone can be increased by adding to the reaction
mixture besides the catalyst also hydrotalcite and silica or by
replacing the solvent and lowering the reaction temperature.
When comparing GCLPA for the same catalyst, but pretreated in
different
Au/La
Table 3 and 4), it can be assumed that GCLPA is determined by the
atmospheres
(e.g.
Au/La
2
O
3
/TiO
2
_pH
2
and
2
O
3
/TiO
2
_pO , Table 5, entries 4 – 8) with acid-base properties
2
(
acidity of the materials, namely the concentration of medium and
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 8
Please do not adjust margins

Please Gd roe en no tC ha ed mj u iss tt r my argins
Page 10 of 14
ARTICLE
Fig. 4 Dependence of GCLPA on concentration of medium and strong acid
View Article Online
DOI: 10.1039/C9GC00949C
sites.
Thus, it can be concluded that a decrease in GCPLA is associated with
side
reactions
of
betulin
or
its
derivatives
oligomerization/polymerization on the catalyst surface, with the
participation of strong acid sites. Formation of oligomers/polymers
on the catalyst surface is also likely to cause partial deactivation of
the recycled catalyst (Table 5, entry 12). Despite washing the catalyst
after the first run in hot acetone, a part of the oligomers/polymers
could remain on the surface thereby blocking partially active sites.
This is also confirmed by an increase in GCPLA after the second run
(Table 5, entry 12).
In order to quantify the kinetic significance of various steps
comprising the reaction network and a contribution of side reactions
leading to oligomers/polymers, kinetic modelling was performed for
Fig. 5 Modified reaction scheme for betulin oxidation, which includes
formation of oligomers (O) and polymers (P).
2 3 2 2
betulin oxidation in the presence of Au/La O /TiO _pH and
hydrotalcite (Fig. 3c). The reaction scheme given in Fig. 2 was
somewhat modified (Fig. 5) to incorporate formation of oligomers
In the preliminary development of the kinetic model (eq. 1),
adsorption of all reactants was considered. However, the initial
parameter estimation showed that the calculated terms in the
denominator involving adsorption coefficients, for all substances and
their concentrations apart from betulonic aldehyde, are very low.
This allows assuming that coverage of these species is rather low. The
constants in eq. (1) are lumped ones comprising implicitly also
dependence on oxygen pressure.
(
O) and finally polymers (P) and account for a clear lack of mass
balance closure in Fig. 3c. The reaction scheme was simplified as the
concentration of acids was negligible for Au/La /TiO _pH . In
2
O
3
2
2
general, oligomers can originate not only from the reactant as in Fig.5
but also from the products, as mentioned above. However, a lack of
mass balance closure in some cases was seen already at the
beginning of experiments justifying that the main contribution for
formation of oligomers comes from the reactants. To keep a more
general character of the model, formation of oligomers was
considered to be reversible, while generation of polymers as
terminal species was supposed to be irreversible.
The reactor mass balances for each component in the reaction
system are as follows:
'
'
'
'
푑퐶퐴
― 푑푡 = 휌
(푘1 + 푘2 + 푘5)퐶퐴 ― 푘 ―5퐶0
1 + 퐾퐷퐶퐷
(
푟1 + 푟2 + 푟5
)
= 휌
(2)
'
'
푑퐶퐵
푘2퐶퐴 ― 푘4퐶퐵
=
=
=
=
휌
(
푟2 ― 푟4
)
= 휌 1 + 퐾퐷퐶퐷
(3)
The equations for the reaction rates presented in Fig. 5 can be
easily written:
푑푡
'
'
푑퐶퐶
푑푡
푘1퐶퐴 ― 푘3퐶퐶
휌
(
푟1 ― 푟3
)
= 휌 1 + 퐾퐷퐶퐷
(4)
(5)
(6)
푘1퐾퐴퐶퐴
푘2퐾퐴퐶퐴
푘3퐾퐶퐶퐶
푘4퐾퐵퐶퐵
푟1 = (1 + ∑퐾푖퐶푖); 푟2 = (1 + ∑퐾푖퐶푖); 푟3 = (1 + ∑퐾푖퐶푖); 푟4 = (1 + ∑퐾푖퐶푖)
;
'
'
푑퐶퐷
푑푡
푘3퐶퐶 ― 푘4퐶퐵
휌
(
푟3 + 푟4
)
= 휌 1 + 퐾퐷퐶퐷
푘5퐾퐴퐶퐴 ― 푘 ―5퐾0퐶0
푘6퐾0퐶0
; 푟6 = (1 + ∑퐾푖퐶푖)
푟5 =
(1)
(
1 + ∑퐾푖퐶푖)
'
'
'
푑퐶0
푘5퐶퐴 ― (푘 ―5 + 푘6)퐶0
휌 푟5 ― 푟6 = 휌
( )
1 + 퐾퐷퐶퐷
푑푡
These equations correspond to adsorption of all organic compounds
and subsequent oxidation with noncompetitively adsorbed oxygen.
Dependence of the oxygen concentration is thus implicitly
i
In eq. (1)-(6) C denotes concentration of respective compounds,
mol/L, ρ is catalyst bulk density given in g/L. Modified constants, etc.
contain also the respective adsorption coefficients.
incorporated in the rate constants k
i
.
The differential equations (2-6) were solved using the backward
difference method and the parameter estimation was performed
with the simplex and Levenberg-Marquardt methods. The numerical
tools are inbuilt the optimization software ModEst,56 in which the
objective function Q is defined through experimental 푦푖 and
calculated 푦푖 concentrations of the components in the reacting
system:
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
Please do not adjust margins

Page 11 of 14
Please Gd roe en no tC ha ed mj u iss tt r my argins
ARTICLE
2
size, the electronic state of gold and acid-base propeVrtieiwesAratinclde,Oanslinae
consequence, the catalytic behavior (activiDtyOaI:n1d0.1s0e3le9c/Cti9vGityC)00o9f4t9hCe
푄 = ∑(푦푖 ― 푦푖)
(7)
studied materials in betulin oxidation. The smallest gold
nanoparticles with their narrow distribution and the strongest and
The results (Fig. 6) show that this model can describe the
experimental data rather well.
0
+
most stable adsorption sites (Au and Au ) were formed on La-
modified TiO surface after H pretreatment. Additionally, this
For 24 data there were initially 8 adjustable parameters, namely 7
'
'
'
rate constants (푘1to 푘6 and 푘 ―5) and one adsorption constant (퐾퐷).
2
2
material exhibited the highest basicity and the highest concentration
of medium and strong acid sites among the studied catalysts, and as
a consequence the best catalytic results. Betulin conversion was 69%
for 6 h at 140⁰C, and the main products were betulone, betulonic and
betulinic aldehydes, with selectivities of 42, 32 and 27%, respectively.
However, the total yield of products was 1.4 fold lower than the
observed conversion, which was due to an incomplete mass balance
and was caused by side reactions of oligomerization/polymerization
on the catalyst surface, promoted on stronger acid sites. The product
yield was increased by adding basic hydrotalcite to the reaction
medium along with the catalyst. Such results can be explained by an
indirect influence of hydrotalcite on the surface properties of the
catalyst, in particular strong acid sites which, in turn prevents the
side reactions and increases the product yield. Kinetic modelling was
performed to quantify the significance of such side reactions.
During the parameter estimation it turned out some of these
'
'
constants, namely 푘3and 푘6, are negligible. Thus the final model
comprised 6 parameters. Their values are given in Table S1. Even is the
number of data points is much larger than the number of parameters
they were somewhat correlating with each other, preventing a
detailed analysis of their physicochemical significance. Apparently, a
separate kinetic study accounting for catalyst deactivation and more
rigorous chemical analysis of oligomers/polymers is required, being,
however, outside of the scope of the current work.
The degree of explanation R2:
(
(
푦푖 ― 푦푖)2
∑
푅2 = 1 ―
푦 ― 푦푖)2
(8)
∑
푖
was 99.3% reflecting applicability of the model.
Experimental
Catalyst preparation
Betulin
2
TiO P25 (nonporous, 70% anatase and 30% rutile, particle size 21
5
nm, purity 99.5%, Evonik Degussa GmbH) were used as starting
support. For comparative studies, titania was modified with ceria and
lanthana by impregnation with solutions of the corresponding
nitrates (molar ratio Ti/M = 40, where M – Ce or La). After
impregnation, the samples were dried at room temperature for 48 h,
then at 110⁰C for 4 h, followed by calcination at 550⁰C for 4 h.
Gold catalysts (Au/TiO , Au/CeO /TiO and Au/La O /TiO ) were
prepared by deposition-precipitation with urea, according to the
procedure previously described.36,57-59 The nominal gold content in
4 2
all catalysts was 4 wt.%. The gold precursor (HAuCl ·3H O, Merck)
4
3
2
1
0
.5
4
.5
3
.5
2
.5
1
2
2
2
2
3
2
.5
0
0
50
100
150
200
250
300
350
400
time (min)
and urea (Merck) were dissolved in distilled water, thereafter the
support was added to the solution. The resulting mixture was heated
to 80⁰C and kept at constant temperature for 16 h, with stirring.
Fig. 6 Comparison between experimental (points) and calculated (lines)
concentration profiles in betulin oxidation on Au/La
and notation of components are given in Fig. 3.
2 3 2 2
O /TiO _H . Conditions
Thereafter, the catalysts were pretreated at 300⁰C for 1 hour in H
2
or
O
2
atmosphere.
x y 2
The catalysts are denoted hereinafter as Au/(M O )/TiO
_P,
x y 2 2 3
where M O is CeO or La O and P indicates the pretreatment
Conclusions
atmosphere (O or H ).
2
2
Catalyst characterization
The current work is the first study dealing with the liquid-phase
oxidation of betulin over gold-based catalysts. As a support, titania
The specific surface area (SBET) of supports and catalysts was
measured by nitrogen adsorption with a "TriStar 3000" analyzer
per se, or modified with CeO
support and pretreatment atmosphere (H
affected the uniformity of gold particles distribution and their mean
2
or La
2
O
3
, were used. The nature of the
or O ) significantly
2
2
(Micromeritics, USA). Prior to measurements, the samples were
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 10
Please do not adjust margins

Please Gd roe en no tC ha ed mj u iss tt r my argins
Page 12 of 14
ARTICLE
subjected to thermal vacuum treatment at 300⁰C for 5 hours. To accuracy of 5%. The obtained spectra were recaVliecwulAarttieclde Oinnlitnoe
calculate the SBET, a multipoint BET method with linearization of the Kubelka-Munk units (KMU). The backDgrOoIu: 1n0d.103s9p/eCc9tGruCm009w49aCs
adsorption isotherm for the relative pressure between 0.005 to 0.25 subtracted from the spectrum of the sample with adsorbed CO and
was used.
the baseline was corrected. All calculations were performed using
The phase composition of supports and catalysts was studied by OPUS 6.0 software (Bruker).
the step-scanning procedure (step size 0.02⁰; 0.5 s) with Philips XPert
Acidic and basic properties of the catalysts and corresponding
PRO diffractometer, using CuKα radiation (λ = 0.15406 nm) and Ni- supports were studied by temperature-programmable desorption
filter. The measured diffractograms were analyzed with the ICDD- (TPD) of ammonia («Chemosorb» chemical adsorption instrument)
2
013 powder diffraction database.
The morphology of catalysts and the size of gold particles were both cases was almost the same apart from the starting desorption
investigated by transmission electron microscopy (TEM) and STEM- temperature, which was 100⁰C for ammonia TPD and 25⁰C in the
HAADF (scanning transmission electron microscopy-High Angle case of CO and the carrier gas, in the former case being helium, and
2
and CO (Autochem 2900 apparatus), respectively. The procedure in
2
Annular Dark Field) using a JEOL JEM-2100F. The samples were the latter argon. Prior to the analysis, the samples were treated at
grounded to a fine powder and sonicated in hexane at room 300⁰C in the inert atmosphere (helium or argon) for 1 h to remove
temperature. Then a part of the suspension was placed on a lacey the impurities adsorbed on the surface. Thereafter, the temperature
carbon-coated Cu grid. In order to obtain micrographs that most fully was decreased to 100⁰C (25⁰C) followed by saturation with NH
reflect the real structure of the samples, a thorough examination of for 60 min and flushing with He (Ar) for 1 h to remove physisorbed
the samples was carried out, after which the selected area was NH (CO ). The temperature was increased to 600⁰C with 10⁰C/min
scanned at various resolutions. For each sample, at least 150 ramp in helium (argon) atmosphere.
particles were registered. For comparative analysis, NH and CO
The metal loading of the catalysts was determined by inductively supports and corresponding catalysts are demarcated into
coupled plasma optical emission spectrometry (ICP-OES) Perkin temperature ranges: 100 – 200⁰C (for TPD CO starting temperature
3 2
(CO )
3
2
3
2
desorption profiles of the
2
Elmer ICP-OES Optima 3300 DV spectrometer. The solids were 25⁰C), 200 – 400⁰C and 400 – 600⁰C and are designated as weak,
dissolved by acid dissolution, digested in a microwave oven, diluted medium and strong acid or basic sites, respectively.
to 100 mL and analyzed in the spectrometer.
The catalysts were characterized by X-ray photoelectron Catalytic testing
spectroscopy (XPS) with a SPECS GmbH custom made system using a
PHOIBOS 150 WAL hemispherical analyzer and
a
non-
Betulin (90-94%) was extracted from birch with a non-polar
monochromated X-ray source. All the data were acquired using Al Kα solvent and recrystallized from 2-propanol in Åbo Akademi
2
X-rays (1486.6 eV, 200 W). A pass-energy of 50 eV, a step size of 0.1 University. Betulin oxidation was performed over supported Au
eV/step and a high-intensity lens mode were selected. The diameter catalysts under atmospheric pressure with synthetic air (AGA, 20%
of the analysed area was 3 mm. Charging shifts were referenced oxygen, 80% nitrogen) as an oxidant in mesitylene at 140⁰C or in
2
against the Ti 2p3/2 peak of TiO at 458.8 eV. The pressure in the toluene at 108 ⁰C (Sigma Aldrich, > 99%). Synthetic air was bubbled
−8
analysis chamber was kept lower than 1 x 10 mbar. The accuracy of through the liquid with the inlet for the gas (flow rate 50 ml/min)
the binding energy (BE) values was about ±0.1 eV. Peak areas were located at the bottom of the reactor to enhance the gas-liquid mass
estimated by calculating the integral of each peak after subtracting a transfer. Moreover, a metallic sinter was applied to diminish the size
Shirley type background, fitting the experimental peak to a of air bubbles. Typically oxidation of betulin was carried out using
combination of Lorentzian/Gaussian lines with a 30/70 proportion 200 mg of the reagent in 100 ml of the solvent (the initial betulin
and keeping the same width on all lines. Deconvolution of spectra concentration was 4.5 mmol/l) using 200 mg of the catalyst. The
was performed with the program CasaXPS.
reaction started when the desired temperature was reached, via
Diffuse Reflectance Fourier Transform Infrared (DRIFT) spectra of turning on the stirring (450 rpm). Small catalyst particles (< 63 µm)
CO adsorbed on the catalysts were recorded by using a Bruker and high stirring rate of 450 rpm were used to suppress the internal
-
EQUINOX 55/S FTIR spectrometer with homemade accessory at 4 cm and external mass transfer limitations. In some experiments,
1
resolution at room temperature. The powdery fraction of an oxide hydrotalcite (Merck) was used together with the catalyst as a base-
was placed in a quartz ampoule with a window of CaF
were preliminarily calcined at 100⁰C in vacuum not less than 10 Torr
in 1 h. For each catalyst three samples were investigated: as- regular intervals. Prior to GC-analyses, the samples (150 µL) were
prepared, and after pretreatments either in H or in O (100 Torr) at silylated by adding 150 µL of a mixture of pyridine (VWR
00⁰C for 1 h and then cooled down for room temperature. Then, H International, Fontenay-sous-Bois, France), N,O-
was evacuated and CO adsorption (>99%) was carried out. The bis(trimethylsilyl)trifluoroacetamide (BSTFA, Supelco Analytical,
2
. The samples additive. Hydrotalcite was calcined for 3 h at 500⁰C prior to its use.
–4
The samples for analysis were withdrawn from the reactor at
2
2
3
2
or O
2
spectra of adsorbed CO were recorded at several pressures — 5, 20, Bellefonte, PA, USA), and trimethylsilyl chloride (TMCS, Merck KGaA,
0 Torr, at room temperature, with the pressure measurement Darmstadt, Germany) in a 1:4:1 volume ratio, and the mixture was
5
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 11
Please do not adjust margins

Page 13 of 14
Please Gd roe en no tC ha ed mj u iss tt r my argins
ARTICLE
heated in an oven at 70⁰C for 45 min. GC analysis was performed on
a PerkinElmer AutosystemXL gas chromatograph using an Agilent HP-
capillary column, 25 m (L) × 0.2 mm (ID), film thickness 0.11 mm.
Hydrogen was used as a carrier gas, with a flow of 0.8 ml/min.
Betulinic aldehyde and betulinic acid (90% purity), used as standards,
were purchased from MedChem Express and Merck, respectively.
The products were confirmed by GC-MS. The conditions of betulin
oxidation and the analytical procedure were previously
published.34,35
References
View Article Online
DOI: 10.1039/C9GC00949C
[
1]
E. W. H. Hayek, U. Jordis, W. Moche, F. Sauter, Phytochem.
1
1
989, 28, 2229.
[
[
2]
3]
C. Eckerman, R. Ekman, Paperi ja Puu 1985, 67, 100.
H. Pakdel, M. Murwanashyuka, C. Roy, J. Wood Chem.
Technol. 2002, 22, 147.
[
[
[
[
[
[
[
[
[
4]
S. Ohara, Y. Hayashi, M. Yatagai, Henkan Keikaku Kenkyu
Hokoku 1990, 24, 12. [C. A. 120 (1994) 301339f].
B.N. Kuznetsov, V.A. Levdansky, N.I. Polezhaeva, Chem. Plant
Raw Mater. 2004, 2, 21 - 24.
G. A. Tolstikov, O. B. Flekhter, E. E. Shultz, L. A. Baltina, A. G.
Tolstikov, Chem. Sus. Dev. 2005, 13, 1–29.
5]
Size exclusion chromatography was performed to investigate
oligomers and polymers formation on the spent catalysts surface.60
6]
2
2
0 mg of the spent catalysts was added to a round flask together with
0 ml of the solvent heptane and a condenser. The flask was placed
7]
S. Alakurtti, T. Mäkelä, S. Koskimies, Eur. J. Pharm. Sci. 2006,
in an oil bath and heated to 98⁰C. Thereafter, extraction occurred for
four hours with a stirring rate of 400 rpm. The flowrate of the inert
gas, consisting of 5 % Ar in 95 % N , was set to 100 ml/min. The
2
solution obtained after the 4 h extraction was then kept at 40⁰C, until
complete evaporation of heptane. The resulting residue was then
dissolved in 10 ml of tetrahydrofuran, being thereafter filtered for
analysis. The resulting concentration of the residue was 2 mg/ml. The
analysis was carried out using a SEC-HPLC equipped with two
columns, a Guard column with the dimensions of 50 mm × 7.8 mm
and a Jordi Gel DVB 500A column with the dimensions of 300 mm ×
2
9, 1–13.
R.C. Santos, J.A.R. Salvador, S. Marín, Bioorg&Med. Chem.
009, 17, 6241-6250.
8]
2
9]
S.C. Jonnalagadda, P. Suman, D.C. Morgan, J.N. Seay, Stud.
Nat. Prod. Chem. 2004, 53, 45-84.
V. V. Grishko, E. V. Tarasova, I. B. Ivshina, Proc. Biochem.
10]
11]
12]
2
013, 48, 164-1644.
S. Alakurtti, P. Bergström, N. Sacerdoti-Sierra, C.L. Jaffe, J. Yli-
Kauhaluoma, J. Antibiot. 2010, 63, 123-126.
M.S Gachet, O. Kunert, M. Kaiser, R. Brun, M. Zehl, W. Keller,
R.A. Munoz, R. Bauer, W. Schuehly, J. Nat. Prod. 2011, 74,
7
.8 mm.
The TOF values were calculated as the number of converted
5
59-566.
moles of betulin per mole of exposed catalytic site per unit time,
during the first 15 min, taking into account the metal dispersion:
[
13]
C.P. Reyes, M.J. Núnez, I.A. Jiménez, J. Busserolles, M.J.
Alcaraz, L. BazzocchiI, Bioorg. Med. Chem. 2006, 14, 1573-
1
579.
푛퐵푒푡푢푙푖푛
푇푂퐹 = 푛푀푒푡푎푙퐷푡
(9)
[14]
15]
K. Hata, K. Hori, S. Takahashi, J. Nat. Prod. 2002, 65, 645-648.
A. Koohang, N.D. Majewski, E.L. Szotek, A.A. Mar, D.A.
Eiznhamer, M.T. Flavin, Z.Q. Xu, Bioorg. Med. Chem. Lett.
2009, 19, 2168-2171.
[
where nBetulin is number of converted moles of betulin, nMetal is the
number of moles of the metal, D is dispersion and t is time. The
number of surface metal atoms was calculated knowing the average [16]
gold particle size measured by transmission electron microscopy
M. Liu, S. Yang, L. Jin, D. Hu, Z. Wu, S. Yang, Molecules 2012,
17, 6156–6169.
(TEM).
[17]
A.A. Mar, A. Koohang, N.D. Majewski, E.L. Szotek, D.A.
Eiznhamer, M.T. Flavin, Z.Q. Xu, Chin. Chem. Lett. 2009, 20,
1
141-1141.
Conflicts of interest
There are no conflicts to declare.
[
[
18]
19]
I.C. Sun, J.K. Shen, H.K. Wang, L.M. Cosentino, K.H. Lee,
Bioorg. Med. Chem. Lett. 1998, 8, 1267-1272.
I.C. Sun, H.K. Wang, Y. Kashiwada, J.K. Shen, L.M. Cosentino,
C.H. Chen, L.M. Yang, K.H. Lee, J. Med. Chem. 1998, 41, 4648-
4657.
Acknowledgements
[
[
20]
21]
E. Bębenek, M. Kadela-Tomanek, E. Chrobak, J. Wietrzyk, J.
Sadowska, S. Boryczka, Med. Chem. Res. 2016, 26, 1–8.
E. Bębenek, M. Kadela-Tomanek, E. Chrobak, M. Latocha, S.
Boryczka1, Med. Chem. Res. 2018, 27, 2051-2061.
The research is funded from the Russian Science Foundation
project № 18-73-00019 and Tomsk Polytechnic University
Competitiveness Enhancement Program, project VIU-ISHBMT-
6
e
5/2019 (Russia). SACC acknowledges Fundação para a Ciência
a
Tecnologia (FCT) for Investigador FCT program [22] V.V. Grishko, I. A. Tolmacheva, V.O. Nebogatikov, N.V.
(IF/01381/2013/CP1160/CT0007). This work was also financially
Galaiko, A.V. Nazarov, M.V. Dmitriev, I.B. Ivshina, Eur. J. Med.
supported by Associate Laboratory LSRE-LCM
-
Chem. 2017, 125, 629-639.
UID/EQU/50020/2019 - funded by national (Portuguese) funds [23] R. Csuk, K. Schmuck, R. Schafer, Tetrahedron Lett. 2006, 47,
through FCT/MCTES (PIDDAC).
8
769-8770.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 12
Please do not adjust margins

Please Gd roe en no tC ha ed mj u iss tt r my argins
Page 14 of 14
ARTICLE
[
[
24]
25]
A. Pichette, H. Liu, С Roy, S. Tanguay, F. Simard, S. Lavoie, [45]
Synth.Commun. 2004, 34, 3925-3937.
N. G. Komissarova, N. G. Belenkova, O.V. Shitikova, L. V. [46]
Spirikhin, M. S. Yunusov, Chem. Nat. Compd. 2006, 338(1),
L. Zhu, Y. Zeng, Sh. Zhang, J. Deng, Q. Zhong, J.VEienwv.ASrtcicil.e2O0n1lin7e,
54, 277-287.
P.N. Amaniampong, K. Li, X. Jia, B. Wang, A. Borgna, Y. Yang,
ChemCatChem. 2014, 6, 2105 – 2114.
DOI: 10.1039/C9GC00949C
5
8-61.
[47]
D. Kubicka, N. Kumar, P. Mäki-Arvela, M. Tiitta, V. Niemi, H.
Karhu, T. Salmi, D.Yu. Murzin, J. Catal. 2004, 227, 313–327.
D. Kubicka, N. Kumar, T. Venäläinen, H. Karhu, I. Kubickova,
H. Österholm, D.Yu. Murzin, J. Phys. Chem. B 2006, 110,
4937-4946.
[
26]
S. D. Kim, Z. Chen, T. V. Nguyen, J. M. Pezzuto, S. Qui, Z. Z. Lu,
Synth. Commun. 1997, 27, 1607-1612.
J. M. Pezzuto, S. H. L. Darrick Kim, Pat US 5804575, 1998.
V. I. Roshchin, N. Yu. Shabanova., D. N. Vedernikov, Pat RU
[48]
[
[
27]
28]
2
190622, 2002 [MGG C07J053/00, C07J063/00].
V. A. Levdansky, N. I. Polezhaeva, B. N. Kuznetsov, Pat RU
269541 2004 [IPC C07J53/00, C07J63/00].
[49]
J. I. Villegas, D. Kubicka, H. Karhu, H. Österholm, N. Kumar, T.
Salmi, D. Yu. Murzin, J. Mol. Catal. A. Chem. 2007, 264, 192–
201.
[
[
29]
30]
2
K. Muffler, D. Leipold, M. Schellera, C. Haas, J. Steingroewer, [50]
T. Bley, H. E. Neuhaus, M. A. Mirata, J. Schrader, R. Ulber,
D. N. Thanh, O. Kikhtyanin, R. Ramos, M. Kothari, P. Ulbrich,
T. Munshi, D. Kubicka, Catal. Today 2016, 277, 97–107.
J. I. Di Cosimo, V. K. Dıez, M. Xu, E. Iglesia, C. R. Apesteguıa, J.
Cat.1998, 178, 499–510.
M. Di Serio, M. Ledda, M. Cozzolino, G. Minutillo, R. Tesser,
E. Santacesaria, Ind. Eng. Chem. Res. 2006, 45, 3009–3014.
C. O. Veloso, C. N. Pérez, B. M. de Souza, E. C. Lima, A. G. Dias,
J. L. F. Monteiro, C. A. Henriques, Micr. Mes. Mater. 2008,
107, 23–30.
M. Mihaylov, E. Ivanova, Y. Hao, K. Hadjiivanov, B. C. Gates,
H. Knozinger, Chem. Commun. 2008, 175-177.
M. Mihaylov, E. Ivanova,Y. Hao, K. Hadjiivanov, H. Knozinger,
B. C. Gates, J. Phys. Chem. C 2008, 112, 18973–189.
H. Haario, ModEst, Modelling and optimization software,
Helsinki (Finland), 2011.
Proc. Biochem. 2011, 46, 1-15.
D.B. Mao, Y.Q. Feng, Y.H. Bai, C.P. Xu, J. Taiwan Inst. Chem.
Eng. 2012, 43, 825-829.
[51]
[52]
[53]
[
[
[
[
31]
32]
33]
34]
H. Liu, X.L. Lei, N. Li, M.H. Zong, J. Mol. Catal. B: Enzym. 2013,
8
8, 32-35.
E. V. Tarasova, V.V. Grishko, I. B. Ivshina, Proc. Biochem.
017, 52, 1-9.
2
P. Mäki-Arvela, M. Barsukova, I. Winberg, A. Smeds, J. [54]
Hemming, K. Eränen, A. Torozova, A. Aho, K. Volcho, D. Yu.
Murzin, Chem. Select. 2016, 1, 3866-73869.
[55]
[
35]
E. Kolobova, Y. Kotolevich, E. Pakrieva, G. Mamontov, M.H.
Farias, V. Cortés Corberán, N. Bogdanchikova, J. Hemming, A. [56]
Smeds, P. Mäki-Arvela, D. Yu. Murzin, A. Pestryakov, Fuel
2
018, 234, 110-119.
R. Zanella, L. Delannoy, C. Louis, Appl. Catal. A: Gen. 2005, 29,
2–72.
[57]
[58]
R. Zanella, S. Giorgio, C. R. Henry, C. Louis, J. Phys. Chem. B
2002, 106, 7634–7642.
M. Hinojosa-Reyes, R. Camposeco-Solis, R. Zanella, V.
Rodríguez-González, F. Ruiz, Catal. Lett. 2018, 148(1), 383-
396.
[
[
36]
37]
6
E. Pakrieva, E. Kolobova, G. Mamontov, N. Bogdanchikova,
M. H. Farias, L. Pascual, V. Cortés Corberán, S. Martinez
Gonzalez, S. A. C. Carabineiro, A. Pestryakov, ChemCatChem [59]
019, 11, 1-11. [60]
A. Penkova, K. Chakarova, O. H. Laguna, K. Hadjiivanov, F.
R. Zanella, C. Louis, Catal. Today 2005, 107–108, 768–777.
A. H. Abdullah, A. Hauser, F. A. Ali, A. Al-Adwani, Energy Fuels
2006, 20(1), 320–323.
2
[
38]
Romero Saria, M. A. Centeno, J. A. Odriozola, Catal. Commun.
2
009, 10, 1196–1202.
A. N. Pestryakov, A. A. Davydov, Appl. Catal. A 1994, 120, 7-
5.
[
[
39]
40]
1
Y. Kotolevich, E. Kolobova, E. Khramov, M.H.Farías, Ya.
Zubavichus, H. Tiznado, S. Martínez-González, V.Cortés
Corberán,
J.D.
Mota-Moralez,
A.Pestryakov,
N.
Bogdanchikova, J. Mol. Cat. A: Chem. 2017, 427,1–10.
[
[
41]
42]
A. Simakov, I. Tuzovskaya, A. Pestryakov, N. Bogdanchikova,
V. Gurin, M. Avalos, M.H. Farıas., App. Catal. A: Gen. 2007,
3
31, 121–128.
N. Bogdanchikova, A. Pestryakov, I. Tuzovskaya, T.A. Zepeda,
M. H. Farias, H. Tiznado, O. Martynyuk, Fuel 2013, 110, 40–
4
7.
[
[
43]
44]
S. V. Nayak, R. V. Chodhary, J Catal. 1983, 81(1), 26–45.
H. D. Olson, T. G. Kokotailo, L. S. Lawton, M. W. Meier, J. Phis.
Shem. 1981, 85(15), 2238–43.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 13
Please do not adjust margins