Optimizing the carburization conditions of supported rhenium carbide for guaiacol conversion

Article abstract of DOI:10.1016/j.apcata.2021.118267

The present work evaluates the effect of ethylene content of a carburization mixture on the formation of carburized rhenium supported on activated carbon. The resulting catalysts were characterized by N₂ physisorption, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and temperature-programmed reduction, and the results show a strong effect on the final phase obtained. A high amount of ethylene inhibited the carburization process, resulting in carbon formation, while a lower amount (≤ 35 %) of ethylene was favorable to the formation of the carbide phase. The catalysts were evaluated for the hydrodeoxygenation (HDO) of guaiacol, a bio-oil model compound, and a high yield of benzene (50 %), a desirable aromatic compound, was obtained at complete conversion over the catalysts containing the carbide phase.

Full text of DOI:10.1016/j.apcata.2021.118267

Applied Catalysis A, General 623 (2021) 118267
Contents lists available at ScienceDirect
Applied Catalysis A, General
journal homepage: www.elsevier.com/locate/apcata
Optimizing the carburization conditions of supported rhenium carbide for
guaiacol conversion
,
b
,
c
d
c
Elodie Blancoa *, Ana Belen Dongil , I. Tyrone Ghampson , Jose Luis García-Fierro ,
´
a,b,e,f,
´
Nestor Escalona
*
a
´
Departamento de Ingeniería Química y Bioprocesos, Pontificia Universidad Catolica de Chile, Santiago, Chile
b ANID – Millennium Science Initiative Program- Millennium Nuclei on Catalytic Process Towards Sustainable Chemistry (CSC), Chile
c
´
Instituto de Catalisis y Petroleoquímica, CSIC, Cantoblanco, 28049, Madrid, Spain
d Department of Applied Chemistry for Environment, Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji,
Tokyo, 192-0397, Japan
e
´
Departamento de Química Física, Facultad de Química y de Farmacia, Pontificia Universidad Catolica de Chile, Santiago, Chile
f
´
´
Centro de Investigacion en Nanotecnología y Materiales CIEN-UC, Pontificia Universidad Catolica de Chile, Santiago, Chile
A R T I C L E I N F O
A B S T R A C T
Keywords:
The present work evaluates the effect of ethylene content of a carburization mixture on the formation of
carburized rhenium supported on activated carbon. The resulting catalysts were characterized by N2 phys-
isorption, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and temperature-
programmed reduction, and the results show a strong effect on the final phase obtained. A high amount of
ethylene inhibited the carburization process, resulting in carbon formation, while a lower amount (≤ 35 %) of
ethylene was favorable to the formation of the carbide phase. The catalysts were evaluated for the hydro-
deoxygenation (HDO) of guaiacol, a bio-oil model compound, and a high yield of benzene (50 %), a desirable
aromatic compound, was obtained at complete conversion over the catalysts containing the carbide phase.
Rhenium carbide
Guaiacol conversion
Carburization
1. Introduction
Several catalysts have been studied for this purpose [8–10].
Recently, carbides have emerged as promising catalysts for several re-
Biomass is an attractive renewable carbon source composed mainly
of three different fractions, namely, cellulose, hemicelluloses, and
lignin. Currently, biomass can be obtained from wastes generated, for
example, by agriculture or forestry industries. In the past decades, many
efforts have been employed towards upgrading biomass to chemicals to
progressively reduce dependency on non-renewable feedstock [1–3].
The production of such bio-based commodities involves an initial
thermochemical and/or biological conversion of biomass to bio-oil
containing "platform chemicals" that can further be upgraded [4–7].
Among the possible targeted products, phenolics or aromatics, such as
benzene, toluene, or xylene can be obtained by hydrodeoxygenation
(HDO) of the bio-oil. One of the main challenges is to selectively remove
oxygen without affecting the aromaticity of the compounds, which re-
quires the use of effective heterogeneous catalysts. Many researchers
have focused on using model compound studies to assess the viability of
these catalysts, of which guaiacol is a common choice as a lignin-derived
model compound.
actions such as hydrogenation, isomerization, reforming, and hydro-
treatment (including HDO) [11–16]. The carbides of molybdenum and
tungsten were widely employed for these studies. Carbides have been
shown to be versatile systems, and their catalytic properties can be
modulated during preparation. Indeed, in this respect, several parame-
ters have been investigated, such as carburization temperature [17–21],
heating rate [17,19], carburization time [19,22], carburization atmo-
sphere [19,23,24], and composition [19]. The heating rate, tempera-
ture, and carburization time have been shown to influence the degree of
carburization, while the atmosphere and the composition of the carbu-
rization mixture have been found to affect the final structure obtained.
In the case of Mo carbides, Bhan and coworkers found that the oxygen
content at the surface is an essential parameter for HDO [25–30].
Recently, the same group showed that this parameter played a key role
in the conversion of anisole to either benzene or phenol [31]. For W
carbides, a correlation between the surface carbon/tungsten atomic
ratio of the catalysts and the phenol yield during the conversion of
´
* Corresponding authors at: Departamento de Ingeniería Química y Bioprocesos, Pontificia Universidad Catolica de Chile, Santiago, Chile.
E-mail addresses: elblanco@uc.cl (E. Blanco), neescalona@ing.puc.cl (N. Escalona).
https://doi.org/10.1016/j.apcata.2021.118267
Received 8 April 2021; Received in revised form 10 June 2021; Accepted 14 June 2021
Available online 17 June 2021
0926-860X/© 2021 Elsevier B.V. All rights reserved.

E. Blanco et al.
Applied Catalysis A, General 623 (2021) 118267
guaiacol has been reported [32]. Other aspects, such as the structure of
the carbide, have been shown to affect their activity in different re-
actions [33,34].
during reduction. The effluent stream was monitored by MS and the
masses 15 (CH4), 18 (H2O), 28 (CO), and 44 (CO2) were recorded.
CO chemisorption was carried out using the 3Flex apparatus
(Micromeritics). Prior to the measurement, about 40ꢀ 50 mg of catalyst
were evacuated for 30 min under vacuum at 110 ◦C and reduced under
However, most of the studies on carbides have mainly been on those
of Mo and W. In previous works, Re carbide was shown to be able to
produce high yields of benzene from guaiacol [35]. The carbide was
obtained by using C2H4 as a carbureting agent [36], and it was also
found that the use of different carburization temperatures led to
different carbides, which impacted the reaction [35]: the catalyst pre-
pared at 650 ◦C was the most active and productive for the formation of
benzene. A synthesis mechanism was proposed for the Re carbide which
involved an initial formation of metallic Re together with carbon, and
the progressive dissolution of the carbon over the metal particle to form
the carbide as temperature increases. The present study builds on the
previous findings and is aimed at optimizing the composition of the
carburizing atmosphere, which is intrinsically linked to the formation of
the carbon phase (mainly graphitic).
H2 flow (60 mL minꢀ 1) for 30 min at 350 C (10 C minꢀ 1). CO was
chemisorb at 35 ◦C and the CO uptake was calculated from the sub-
traction of two isotherms recorded with 60 min evacuation between
them in order to remove the contribution of physisorbed CO.
◦
◦
2.3. Catalytic testing
Catalytic properties were evaluated using a 100 mL stirred-batch
reactor from Parr instrument. A quantity of the catalyst (200 mg) was
placed in the reactor and mixed with a liquid mixture consisting of
guaiacol (1.7 g), dodecane (32 g) as the solvent, and hexadecane (700
μL) as the internal standard. All the liquid compounds are reagent grade
and were purchased from Merck. The reactor was then purged for 10
min under N2 flow (50 mL minꢀ 1) and heated under autogenous pres-
sure to 350 ◦C with continuous stirring (645 rpm). Once the final tem-
perature was reached, a first liquid sample was collected corresponding
to the time 0. Then the final pressure was adjusted at 5.0 MPa with
hydrogen, and the reaction was conducted for 4 h. Periodic aliquots
were collected and analyzed off-line by gas chromatography using a
Nexis GC-2030 instrument (Shimadzu) equipped with an Elite-1 column
2. Experimental
2.1. Synthesis
Catalysts were prepared by incipient wetness impregnation of acti-
vated carbon (Type CO-850, Petrochil S.A). Typically, the support was
◦
grounded, sieved (<150
μ
m), and dried at 110 C for 2 h, and subse-
quently impregnated with a solution of NH4ReO4 (99 %, Aldrich) to
obtain a Re nominal loading of 10 wt%. The mixture was left for
maturation for 6 h at ambient temperature, and dried overnight at 80 ◦C.
Finally, the sample was heated from ambient temperature to 650 ◦C at a
rate of 5 ◦C minꢀ 1 in a fixed bed reactor, and held at 650 ◦C for 1.5 h,
under a mixture of C2H4 and H2. The total flow rate was kept constant at
100 mL minꢀ 1, whereas the volumetric ratio between C2H4 and H2 was
varied; accordingly, the prepared catalysts are denoted here based on
the volumetric composition of C2H4 (C2H4 = 0 %, 10 %, 25 %, 35 %, 50
%, 75 %, and 100 %). After carburization, the samples were passivated
for 1 h at ambient temperature under flowing 5% O2/N2 (50 mL minꢀ 1).
(Perkin Elmer, 30 m ×0.32 mm, film thickness of 0.25 μm) and a FID
detector. The products obtained were identified by injecting external
standards as well as with GC–MS, and they were quantified from cali-
brated chromatographs.
Conversion, selectivity, and initial rate (r0, mol. gꢀ 1.sꢀ 1) were
defined as already described with the following formulae:
n0GUA ꢀ nGUA
Conversion (%) =
Conversion (%) =
(1)
(2)
(3)
n0GUA
nproducts
nreagent remaining + nproducts
× 100
2.2. Characterization
nproduct i
× 100
nproducts
∑
Selectivity (%) =
Textural properties were obtained by N2-sorption at ꢀ 196 ◦C using a
3flex instrument (Micromeritics). Before the analysis, the sample was
first degassed under vacuum at 350 ◦C for 4 h in a SmartVacPrep device
(Micromeritics).
b × n0GUA
r0 =
(4)
m
In these equations, n◦
is the quantity (mol) of guaiacol at the
beginning of the reaction,GnUGAUA is the quantity at a time t, nproducts cor-
responds to the sum of all the products detected (mol), nproduct i is the
amount (mol) of a product i, m is the weight (g) of the catalyst, and b
corresponds to the initial slope obtained by plotting conversion vs. time
Structural properties were determined from X-ray diffraction (XRD)
measurements. The diffractograms were obtained on a Polycrystal
X’Pert ProPANalytical instrument using Ni-filtered Cu Kα radiation (λ
=0.15406 nm) and a graphite monochromator. For each sample, Bragg’s
angles between 4◦ and 100◦ were scanned at a rate of 0.04◦.
(s). In addition, nreagent
represents the difference between the
remaining
Surface species were analyzed by X-ray photoelectron spectroscopy
(XPS) using an Escalab 200 R spectrometer equipped with a hemi-
quantity (mol) of guaiacol at the beginning of the reaction (n◦GUA) and at
a time t. For the calculation of the initial rates (4), only the data at the
low conversion region (≤ 30 %) were considered.
spherical analyzer. The spectra were measured with
a
non-
monochromatic Mg K X-ray radiation (h
ν =1253.6 eV). The passivated
Carbon balance was defined as the ratio between the conversion
equations (eqn. 1/eqn. 2). Turnover frequency (TOF, sꢀ 1) was calculated
◦
catalysts were reduced in situ at 350 C before analysis to mimic the
working catalyst. The binding energy (BE) was measured by reference to
the C 1s peak at 284.6 eV, with an equipment error of less than 0.01 eV
in the energy determinations. The surface atomic ratios were estimated
from the integrated intensities of Re 4f, C 1s, and O 1s lines after
background subtraction and correction by the atomic sensitivity factors.
The spectra were fitted to a combination of Gaussian–Lorentzian lines of
variable proportions.
based on sites counted by CO uptake (
μ
mol gꢀ 1) measurements:
r0
TOF =
(5)
CO uptake
3. Results and discussion
Temperature programmed reduction (H2-TPR) measurements were
conducted using the 3Flex apparatus (Micromeritics) equipped with a
thermal conductivity detector (TCD) and a mass spectrometer (Cirrus 2,
MKS Spectra product). Typically, the catalysts were heated until 1050 ◦C
3.1. Catalyst characterization
The textural properties of the support and catalysts were obtained
from N2-sorption isotherms (Fig. 1) and are summarized in Table 1.
Surface area (SBET) was obtained using the Brunauer-Emmett-Teller
(BET) theory, the total pore volume (VTOT) was obtained from the
ꢀ 1
◦
at 10 C min under flowing 5 % H2/Ar. A cold trap was placed be-
tween the outlet of the reactor and the TCD to remove water produced
2

E. Blanco et al.
Applied Catalysis A, General 623 (2021) 118267
observed, which could either be associated with well-dispersed particles
(in the case of Re-100, Re-75 and Re-50 samples) or poor crystallinity (in
the case of the Re-35 sample). For the Re-25 catalyst, three peaks at 18◦,
27◦, and 42◦ are discernible. In the case of the Re-10 and Re-0 catalysts,
additional and more intense diffraction peaks than those obtained for
the Re-25 sample are observed, indicating a higher degree of crystal-
linity in the Re-10 and Re-0 samples, which is probably related to larger
particle sizes. To ascertain any structural differences between Re-0 and
Re-10, the diffraction pattern of the samples at an expanded scale is
presented in Fig. 2, along with the reference patterns for ReOꢀ4 (00ꢀ 010-
252), ReO3 (00ꢀ 040-1155), and metallic Re (01ꢀ 087-0599). Fig. 2a
shows that the patterns for ReO4ꢀ and ReO3 are largely indistinguishable
and that they are both present in the samples. Nevertheless, there is a
noticeable shift in diffraction positions, which suggests a distortion of
the ReOx phase. Such modification in the cell parameters may be asso-
ciated with the introduction of carbon into the matrix, leading to the
formation of an oxycarbide phase, ReOxCy. Fig. 2b presents the super-
position of the XRD patterns of Re-0 and Re-10 with that of a reference
Re◦ pattern. In the case of the Re-0 catalyst, the diffraction planes match
quite well with the Re◦ phase, except for a slight shift of the (101) plane
(at around 43◦). Such a shift could be representative of some carbon in
the metallic Re matrix (ReCx). For the Re-10 catalyst, all the diffraction
planes appear shifted, suggesting a higher degree of carburization
(ReCx+) compared to the Re-0 sample. In summary, the XRD results
suggest the possible coexistence of ReCx, and ReOxCy on the Re-0 sample
and the presence of ReCx+ and ReOxCy on the Re-10 sample.
Fig. 1. N2-sorption isotherm obtained for the support and catalysts.
single-point adsorption volume at p/p0 = 0.99, and micropore volume
(VMICRO) was calculated from the t-plot equation.
Fig. 1 shows that the support displayed a type I isotherm with an H4-
hysteresis loop, characteristic of microporous material with a slit-like
pore shape. It appears, however, that the carburization mixture
strongly affected the textural properties of the final catalysts. Treatment
with pure H2 (for Re-0) resulted in a decrease of the quantity of N2
adsorbed and a corresponding decrease in the textural parameters
(compared to that of the bare support). On the other hand, carburization
with a 10 % C2H4/90 % H2 mixture (for Re-10) did not affect the textural
properties, whereas carburization with a mixture containing a higher
volumetric ratio of C2H4 (up to 35 %) led to a continuous decrease of the
parameters. It should be noted, however, that despite the decrease in the
textural properties the materials remained mainly microporous. Inter-
estingly, carburization with a 50 % C2H4/H2 mixture (Re-50) drastically
decreased the textural parameters and created mesopores, as evidenced
by the presence of an H4-hysteresis loop. Finally, carburization with a
C2H4-rich mixture (Re-75 and Re-100) led to the formation of macro-
porous or nonporous materials, as deduced from the presence of a type II
isotherm. Therefore, the composition of the carburization mixture had a
substantial effect on the resulting materials. Indeed, it is known that
ethylene can be converted into several products depending on the re-
action condition. Under non-oxidative conditions, it has been reported
that ethylene can be decomposed to graphite/graphene [37,38], but can
also form oligomers like butadiene or aromatics [39]. It has also been
reported that Re-based catalysts are active for ethylene conversion
[40–42]. Thus, it is suggested that the likely formation of graphite and
aromatics during the carburization step resulted in pore blocking,
leading to the loss of microporosity of the material.
Raman spectra were recorded to evaluate possible changes in the
relative intensity of the D and G bands, which are related to defective
and graphitic carbon of the support, respectively. Surface modifications
through oxidative and thermal treatments have been shown to affect the
relative intensity of these bands and provide a useful comparison of the
prepared materials [43,44]. A comparative result of the effect of treat-
ment with different carburization mixtures on the modification of the
parent carbon material species are presented in Fig. S2. The results show
that upon carburization with mixtures containing a higher amount of
C2H4, a decrease of defective carbon relative to graphitic carbon can be
observed indicating that under such conditions, some graphitic carbon
was formed. Such result is somehow consistent with the textural anal-
ysis, where a significant loss of surface areas was obtained upon
increasing the C2H4 amount in the gas phase.
To further investigate the catalytic system, the surface composition,
obtained by XPS, of the Re-50 catalyst was compared to that of the Re-25
sample. Prior to the analyses, the catalyst was reduced in situ at 350 ◦C to
remove the passivation layer. The Re and C signals were deconvoluted
and fitted, and the results are presented in Fig. S3 while the fitting pa-
rameters are summarized in Table 2.
Fig. S3 shows that changing the composition of the carburization
mixture changed the resulting surface species formed. Three different
species could be observed at 40.4–40.8 eV, 42.5 eV, and 45.7 eV, when
the catalyst was carburized with mixtures containing 25 and 50 % of
C2H4. Previously, the band at around 40.4 and 40.8 eV was assigned to
Re2+ in RexC and ReC carbide, respectively [35], the band at 42.5 eV to
Re4+ in ReO2, and the band at 45.7 eV to Re6ꢀ 7+ species in ReOx [45].
The results in the present study can be assigned to these species as well.
Nevertheless, the contributions of ReOxCy cannot be ruled out.
Structural properties were investigated by XRD, and the diffracto-
grams obtained for all the catalysts and the support are shown in Fig. S1.
All the XRD patterns present two broad bands centered around 25◦ and
42◦, corresponding to the (002) and (100)/(101) diffraction planes,
characteristic of amorphous carbon materials. For the Re-100, Re-75,
Re-50, and Re-35 catalysts, no additional diffraction planes can be
On the other hand, as observed in the textural analysis, the support
was also affected by the composition of the carburization mixture. The C
1s band was fitted to four components for both catalysts; however, some
Table 1
Textural properties of the support and the resulting catalysts.
Support
Re-100
Re-75
Re-50
Re-35
Re-25
Re-10
Re-0
S
BET (m2 gꢀ 1
)
882
2
6
51
440
811
878
642
V
V
TOT (cm3 gꢀ 1
)
0.51
0.38
0.01
0
0.023
0
0.063
0.017
0.25
0.18
0.39
0.33
0.44
0.37
0.38
0.29
MICRO (cm3 gꢀ 1
)
3

E. Blanco et al.
Applied Catalysis A, General 623 (2021) 118267
Fig. 2. Comparison of the diffractograms obtained for the Re-10 and Re-0 catalysts: a) an expanded region of diffraction positions showing ReOx patterns, and b) an
expanded region of diffraction position showing Re◦ patterns.
Table 2
XPS data obtained for the catalyst after in situ reduction at 350 ◦C.
Binding Energies, eV (%)
Cat.
Re 4f7/2
Re2+
C 1 s
Re/C at/at. 10ꢀ 3
Re4+
Re6ꢀ 7+
–
C
C
C
π-π*
–
C
–
–
O
–
C
–
C C
Re-50
Re-25
40.8 (6)
42.5 (27)
45.7 (67)
284.5 (39)
284.5 (18)
284.8 (48)
284.9 (68)
286.9 (6)
289.2 (4)
289.2 (2)
291.0 (3)
290.6 (2)
5.9
9.0
40.4 (100)
–
–
286.8 (10)
variation in the BE and relative intensity could be observed. The com-
ponents were detected at 284.5, 284.8, 286.9, and 290.6 eV, which
partial pressure. The latter could be due to an increase of aromatic
species at the surface of the catalyst (evidenced by an increase of the
–
–
–
– –
could be associated with C C, C C, C O, C O, and
π
-
π* species,
proportion of C C species), which inhibited carburization of Re. It was
–
–
–
respectively [46–49].
previously proposed that during the carburization process, C2H4 is first
transformed over Re species to graphite, which then subsequently dis-
solves over Re, leading to the formation of carbide phase [35]. The work
of Xu et al., where Co was exposed to a cycle of C2H4, showed that low
exposure of C2H4 allowed it to be chemisorbed and decomposed to
As discussed previously, Re-based catalysts can catalyze the con-
version of ethylene to butadiene and aromatics. From the XPS results, it
can be observed that Re is fully carburized with the use of a low C2H4
partial pressure but is only partially carburized under a higher C2H4
Fig. 3. Evolution of the TCD signal and the MS signals of CH4, CO, and CO2 during the H2-TPR.
4

E. Blanco et al.
Applied Catalysis A, General 623 (2021) 118267
◦
graphite on vacant sites. In contrast, a higher exposure led to higher
coverage and limited the vacant sites, and, as a consequence, hampered
the formation of graphite [37]. Consistent with these findings, it is
suggested here that carburization of Re could be inhibited under high
C2H4 partial pressure.
the case of CO, a feature observed around 650 C can be ascribed to
phenolic groups, while another feature observed around 900 ◦C can be
attributed to quinone groups, according to a report in the literature [57].
For CO2, a broad band centered at 300 ◦C can be associated with car-
boxylic and/ or lactonic groups. Since the catalysts were carburized at
650 ◦C, it is reasonable to assume that only the quinone groups are ex-
pected to be linked to the support and that the presence of a new
CO/CO2 signal is associated with new functional groups which origi-
nated from the carburization process, or to the presence of oxycarbide
species. For the CO MS signal, the contribution of quinone groups was
indeed observed for catalysts carburized with high amount of C2H4 (e.g.
≥ 50 %); however, a shift to lower temperature is observed upon
increasing the H2 fraction. Such a shift could be related to a new
contribution originating from the carburized metal, as explained pre-
viously. This contribution is more prominent in the Re-35 catalyst but
decreases as the concentration of H2 increases during carburization.
In the case of the CO2 MS signal, for the Re-100 catalyst, two features
can be observed around 332 ◦C and 436 ◦C. These features become more
intense for the samples prepared with carburization mixtures with
increasing H2 fraction, reaching a maximum for the Re-35 sample. A
new feature was observed at lower temperatures (around 100 ◦C) as the
H2 concentration of the carburization mixture increased. These features
could be associated with carboxylic and lactonic groups that may have
been formed during the passivation step, as they are not as thermally
stable as the other species. On the other hand, CO2 could also be ob-
tained by reaction of water with defective carbon (6), followed by the
water-gas shift (WGS) reaction (7). Such a reaction also leads to the co-
production of H2 and could explain the lack of reduction bands around
300 ◦C for the Re-35, Re-50, Re-75, and Re-100 catalysts.
Finally, the surface distribution of Re species was calculated from the
ratio of the Re 4f7/2 band to the C 1s band, normalized using the
sensitivity factors of each component. This value represents the surface
distribution of Re species on the catalyst. The results showed that the
Re/C atomic ratio is higher on Re-25 than on Re-50, indicating a higher
concentration of Re on the surface. This can be related to the presence of
aromatics, rendering some Re species on Re-50 inaccessible. The for-
mation of smaller particles on Re-25 compared to Re-50 could also be
the reason for the different Re/C atomic ratio, since treatment under
hydrogen atmosphere normally results in smaller particle sizes.
Temperature-programmed reduction measurements of the different
catalysts were carried out and the gases formed were monitored by mass
spectroscopy. The results, presented in Fig. 3, show a strong effect of the
carburization mixture on the reduction behaviors of the samples.
Fig. 3 shows the TCD signals and the H2-TPR traces of masses 15
(CH4), 28 (CO), and 44 (CO2). The TCD signals represent the H2
consumed by oxide species during the H2-TPR. The figure shows that
only one reduction peak can be observed at around 300 ◦C for Re-0, Re-
10, and Re-25, corresponding typically to the reduction of ReOx species
[45,50,51]. However, no reduction peak can be observed for the other
samples which were prepared under mixtures containing higher C2H4
volumetric ratios.
The production of CH4 during H2-TPR has already been reported on
carbon-based materials and is usually associated with gasification of the
support catalyzed by metal or carbide phases [52–54]. For Mo2C cata-
lysts, it was reported that the CH4 formed could be related to different C
species, such as adsorptive carbon, carbidic carbon, and free carbon [55,
56]. Among the free carbons, two types can be distinguished, namely,
reactive pyrolitic carbon and unreactive graphitic carbon. Indeed, these
species can be identified according to the temperature at which they
were observed [55,56]. Based on this, the CH4 produced at around
200ꢀ 300 ◦C, 460ꢀ 490 ◦C, 600ꢀ 690 ◦C, and 700ꢀ 800 ◦C can be
assigned to adsorptive, carbidic, pyrolytic, and graphitic carbon,
respectively. The results show that the H2-TPR traces of CH4 was
featureless for the catalysts prepared by carburization under a high
amount of C2H4 (e.g., ≥ 50 %), indicating that gasification of the support
did not occur. This is evidence that the rhenium species present on these
catalysts are neither in a carbide nor metallic state. Furthermore, the
lack of CH4 formation also evidence that the carbon formed during
carburization under such conditions is stable enough to withstand
thermal gasification in this temperature range. On the other hand, the
CH4 traces for the catalysts prepared under C2H4-deficient atmospheres
(from 35 % C2H4/H2) show peaks at high temperatures (> 600 ◦C). The
peak shifted to a lower temperature for the Re-25 catalyst (ca. 500 ◦C),
which could be indicative of lower extent of graphitic carbon formed
weakening the interactions with the support or some changes in the
pyrolitic and graphitic carbon formed during the carburization process.
A further decrease in the C2H4 ratio led to the appearance of a new CH4
C* + H2O ↔ CO + H2
H2O + CO ↔ H2 +CO2
(6)
(7)
To summarize, as illustrated in Fig. 4, carburization of Re requires a
low amount of C2H4 in the gas phase as high amount of C2H4 promotes
polymerization reactions of C2H4 to graphitic carbon (based on Raman
spectra and XPS analysis). These reactions are responsible for the drastic
loss of surface areas due to pore blocking (based on N2 physisorption
results), which consequently decreased the dispersion of Re on the cat-
alysts (based on XPS analysis). From the H2-TPR results, the formation of
CH4 could be related to the formation of the carbide phase, which was
only obtained with a low amount of C2H4 in the carburization mixture
(ca. ≤ 35 %). Catalysts carburized by 10 % and 0 % of C2H4 in H2 pre-
sented the highest content of the carbide phase.
3.2. Catalytic properties
The prepared catalysts were evaluated for guaiacol conversion at 350
◦C and under 5 MPa of H2 in a batch reactor. The activity is expressed as
initial reaction rate, calculated from the initial slope of the plot of
conversion versus time, and is based on the weight of the catalyst
(Table 3).
As expected, the initial rate of conversion depends strongly on the
C2H4/H2 ratio, in line with the changes observed from the character-
ization results. Catalysts prepared with lower concentration of C2H4 (Re-
35, Re-25, Re-10, and Re-0) exhibited an order of magnitude higher
initial rates than those prepared under C2H4-rich conditions (Re-100,
Re-75, and Re-50). The results show clearly that the least active catalysts
were those with the lowest surface areas, which was a direct effect of the
carburization conditions. Recall that the loss of surface area was
ascribed to pore blockage by carbon formed by the conversion of
ethylene on ReOx phase during the carburization process. Similarly,
these carbon layer can also block active sites, as evidence from the low
CO uptake values (Table 3). On the other hand, the main species
detected at the surface were associated with ReOx and ReOxCy phases,
which have been reported to be active in guaiacol conversion [45,50,60,
◦
band at around 300 C, ascribed to surface carbidic carbon. Deconvo-
lution and fitting of the CH4 signals are presented in Fig. S4 and the
fitting parameters are summarized in Table S1. The figure shows that the
band corresponding to carbidic carbon increased as the concentration of
C2H4 in the carburization mixture decreased. Interestingly, for the Re-0
catalyst two carbide species could be distinguished, whereas for the
Re-10 and Re-25 catalysts, some adsorptive C species could be observed.
The appearance of CO and CO2 during the H2-TPR analyses results
from thermal decomposition of the surface functional groups [57]. It has
been widely reported that CO is formed during the carburization of
metals [54,58,59]. Therefore, analysis of the contribution of the support
to the observed signals is first required prior to the study of the catalysts.
The H2-TPR traces for CO and CO2 obtained are presented in Fig. S5. In
5

E. Blanco et al.
Applied Catalysis A, General 623 (2021) 118267
Fig. 4. Schematic representation of the effect of the composition mixture during carburization.
The comparison of the product selectivities calculated at similar
conversion (around 25 %) is displayed in Fig. 5. The result shows that
the product distribution differed depending on the composition of the
carburization mixture used to prepare the catalysts. This suggests the
existence of different active phases on the catalysts, in agreement with
the characterization results: ReOx species were mainly obtained under a
C2H4-rich carburization mixture, while carbides were formed with a H2-
rich mixture.
Table 3
Evolution of the initial rate of guaiacol conversion.
Re-
Re-
75
Re-
50
Re-
35
Re-
25
Re-
10
Re-
0
100
CO uptake (
μmol.
1.1
2.2
6.7
10.7
14.0
1.3
95
90
106
gꢀ 1
)
r0 (10ꢀ 6 mol. g-1.s-
3.87
3.5
2.45
1.1
2.39
0.35
19.6
0.21
21.0
0.23
22.7
0.21
1
)
TOF (sꢀ 1
a
)
a
When the catalyst was treated under C2H4 with volumetric ratio
between 35 and 100 %, the main product observed was catechol, fol-
lowed by toluene, and then phenol. It should be noted that the carbon
balance hovered around 60 %. This low carbon balance may be due to
the formation of catechol which has been reported to form oligomers on
Re2O7 phase [65]. In the specific case of the Re-35 catalyst, a higher
amount of phenol was obtained at the expense of toluene and catechol,
and the carbon balance was improved: this may be a direct result of the
presence of carbides on this catalyst, consistent with deductions from
the H2-TPR traces for CH4 presented previously. For the catalysts pre-
pared with a lower amount of C2H4, the main product obtained was
phenol, in agreement with already reported studies on carbide materials
[17,32,66–74]. Nevertheless, some variation can be noticed, especially
in the case of the catalyst carburized under H2 only (Re-0). Indeed,
Turnover frequency calculated by considering sites counted by CO
chemisorption.
61]. Hence, there is a direct correlation between the reactivity and the
surface characteristics of the catalysts induced by the carburization
process.
To probe the aforementioned effect of site blockage on reactivity, the
activity is also expressed as turnover frequency (TOF), based on sites
titrated by CO chemisorption (Table 3). However, no clear correlation
could be obtained for the catalysts carburized by 100ꢀ 35 % of C2H4.
This behavior could be due to differences in the nature of the sites
counted by CO chemisorption, in agreement with the XPS. It is possible
that these sites possess different activities toward guaiacol conversion.
Another explanation could be that the sites probed by CO chemisorption
were not uniquely responsible for guaiacol conversion. Indeed, the ReOx
phase, which does not chemisorb CO effectively, is active for guaiacol
conversion [45,50], and Re◦ and RexC species, which chemisorb CO, are
also active [35,61]. On the other hand, when the catalysts were prepared
with a lower amount of C2H4 (25 % to 0 %), the difference in the initial
rate can be explained by the different CO uptake values as the calculated
TOF is the same, indicating that the reaction was catalyzed by a similar
active phase. Finally, the difference in CO uptake in Re-25 vs. Re-10 can
be ascribed to different particle sizes as evidenced by XRD. On the
contrary, Re-0 shows a higher uptake that could not be the consequence
of different particle sizes. Rather, it may be due to greater accesibility of
Re species since it was previously shown that this catalyst, which was
carburized using only H2, presented less graphitic carbon at the surface
(and confirmed in Table S1) than the catalysts prepared when C2H4 was
employed, generally leading to higher CO uptake [14,62–64].
Another important insight from activity and characterization results
relates to the evolved gases during H2-TPR (Fig. 3). The most active
catalysts also evolved CH4 during H2-TPR, a behavior that could be
related in some manner to carbide species formed.
Fig. 5. Comparison of the product selectivities obtained for 25 % of guaiacol
conversion and the respective C balance. Reaction conditions: 200 mg catalyst,
350 ◦C, 5.0 MPa H2.
6

E. Blanco et al.
Applied Catalysis A, General 623 (2021) 118267
higher selectivity to secondary products such as aromatic hydrocarbons
(benzene and toluene) and methyl-transfer products (cresol and meth-
ylanisole) were obtained at the expense of primary products (phenol and
anisole) on the Re-0 catalyst. This suggests that the additional presence
of metallic Re (confirmed by XRD) enhanced selectivities to secondary
products.
Table 4
Comparison of the textural properties of fresh and spent catalysts.
Re-25
Fresh
Re-10
Fresh
Re-0
Textural properties
Spent
Spent
Fresh
Spent
SBET (m2 gꢀ 1
)
811
462
878
680
642
384
VTOT (cm3 gꢀ 1
)
0.39
0.33
0.25
0.17
0.44
0.37
0.33
0.27
0.38
0.29
0.20
0.15
To better evaluate differences in the secondary products, product
selectivities obtained at higher conversion (90 %) were compared and is
shown in Fig. S6. Interestingly, at high conversion Re-25 and Re-10
displayed a higher selectivity to benzene than Re-0, which is opposite
to the trend observed at lower conversion (25 %). On the other hand, the
trend for the selectivity to cresol and methylanisole was the same at both
low and high conversions.
V
MICRO (cm3 gꢀ 1
)
The Re-0 catalyst was prepared by carburization by CH4 (generated
upon support gasification), while Re-10 and Re-25 were carburized by
C2H4-deficient mixtures. Previous reports on Mo carbides have shown a
strong effect of the carburizing agent on the textural and structural
properties of the resulting carbide [19,23]. For example, the use of CH4
led to the formation of hexagonal closed packed (hcp) carbide, the use of
butane led to mainly face-centered cubic (fcc) carbide, and the use of
ethane led to a mixture of hcp and fcc phases [23]. These phases have
been reported to exhibit different activities for ethane hydrogenolysis
[33], and CH4 aromatization [34]. In relation to the present study,
although XRD results did not show different crystalline phases, it
showed clear evidence of distortion of the cell. This was ascribed to
penetration of carbon in the lattice. As explained in the XRD part, the
Re-0 catalyst contained a lower amount of C (ReCx) as its diffraction
pattern was similar to Re◦ while the Re-25 and Re-10 catalysts contained
higher amount of carbon in the matrix (ReCx+). Therefore, the changes
observed in the secondary products between these two groups could be
associated with the different Re active phases. The presence of ReCx
appeared to promote methylanisole and cresol formation, whereas the
existence of ReCx+ appeared to favor further conversion of phenol to
benzene.
The evolution of the conversion of guaiacol and yields of the prod-
ucts are presented in Fig. S7. Since the reaction over the Re-100, Re-75,
Re-50, and Re-35 catalysts gave a poor C balance, only the results for Re-
25, Re-10, and Re-0 catalysts will be discussed. The figure shows that the
benzene yield increased slowly initially and then more sharply when the
phenol yield plateaued, suggesting that benzene was obtained mainly
from phenol hydrogenolysis as previously reported [35].
Fig. 6. XRD patterns of fresh and spent Re-0, Re-10, and Re-25 catalysts.
10, a slight shift to a higher angle of the (101) plan at around 42◦ is
discernible. Such a shift suggests that the ReCx phase has lost some
carbon, leading to a ‘’lower carburization degree’’ that could explain the
decrease of the conversion rate of guaiacol with time if the Re◦ sites are
less active in HDO than ReCx. To summarize, base on these results Re-25
underwent some sintering that may have enhanced the rate of conver-
sion during the reaction. Such behavior has been previously reported in
HDO of stearic acid over Mo2C/CNF, where higher activity was reported
for catalyst with particle size around 10ꢀ 12 nm compared to the same
catalyst with smaller particle size (2 nm) [75]. On the other hand, the
lower activity over the Re-10 catalyst could be due to the occurrence of
partial reduction, as noted previously, while the lower activity over the
Re-0 catalyst could be due to partial pore-blocking probably because of
coke deposition.
Another notable point is that despite a lower initial reaction rate, the
Re-25 catalyst appears to reach higher conversion earlier than the other
two catalysts. The data show that an induction period seemed to have
occurred at the beginning of the reaction over the Re-25 catalyst (0ꢀ 20
min). This could be explained by the H2-TPR results, which showed the
presence of adsorptive carbon on this catalyst. Therefore, the decom-
position of these carbon species at the beginning of the reaction could
have liberated and/or created some active sites. In the case of both the
Re-0 and Re-10 catalysts, no induction period was observed; neverthe-
less, the conversion rate of guaiacol decreased with time, suggesting
either some modification of the active sites or a change in the order of
reaction occurred.
To evaluate the potential modification of the active sites, post-
reaction catalysts were characterized by N2-sorption and XRD. The re-
sults obtained are displayed, respectively, in Table 4 and Fig. 6. Table 3
shows a loss of surface area of around 50 % for the Re-25 and Re-
0 catalysts during the reaction, leading to partial pore blocking by
coke deposition. The surface area of the Re-10 catalyst also decreased
during the reaction, although in a less-pronounced manner.
4. Conclusion
The present workevaluated the effect of the carbureting atmosphere
on the formation of rhenium carbide catalysts using a mixture of C2H4
and H2. Results showed that a high amount of C2H4 favored polymeri-
zation of C2H4 on the catalyst, while a lower amount (≤ 25 %) led to the
formation of the carbide phase. Results from H2-TPR analysis indicated
that observation of CH4 traces can be related to the carburization of Re,
and that the absence of C2H4 in the carburization mixture led to a lower
degree of carburization of Re. The resulting catalysts were tested for the
On the other hand, Fig. 6 shows that there were also structural
changes, especially in the case of the Re-25 catalyst: a higher crystal-
linity of the phases was obtained after the reaction, which may be
indicative of some particle sintering which would explain the partial
pore-blocking discussed above. For the Re-0 and Re-10 catalysta, such
structural modification was not observed; nevertheless, in the case of Re-
7

E. Blanco et al.
Applied Catalysis A, General 623 (2021) 118267
[19] T. Mo, J. Xu, Y. Yang, Y. Li, Catal. Today 261 (2016) 101–115.
HDO of guaiacol, and it was observed that the initial rate of conversion
followed the same trend as the formation of CH4 during H2-TPR,
implying a direct link between activity and the nature of species formed
during carburization. The results show that multiple reactions occurred
with different reactivities, typical of the upgrading of a complex model
compound such as guaiacol. Some of the most dominant reactions which
occurred on the catalysts containing carbides were demethoxylation and
hydrogenolysis. For example, the best yield of benzene was obtained on
the Re-25 catalyst (50 %), which was shown to contain only Re carbide
species, clearly indicating that these active phases are effective for the
upgrading of guaiacol to hydrocarbon products. Finally, among the
three catalysts where carbides were predominantly obtained, slight
differences in the secondary product formation were observed and were
related to different degrees of carburization.
´
[20] E. Blanco, D.A. Aguirre-Abarca, J.N. Díaz de Leon, N. Escalona, New J. Chem. 44
(2020) 12027–12035.
[21] H. Wang, S. Liu, B. Liu, V. Montes, J.M. Hill, K.J. Smith, J. Solid State Chem. 258
(2018) 818–824.
[22] E. Ochoa, D. Torres, J.L. Pinilla, I. Suelves, Catal. Today (2019).
[23] T. Xiao, A.P.E. York, K.S. Coleman, J.B. Claridge, J. Sloan, J. Charnock, M.L.
H. Green, J. Mater. Chem. 11 (2001) 3094–3098.
[24] L. Souza Macedo, R.R. Oliveira, T. van Haasterecht, V. Teixeira da Silva, H. Bitter,
Appl. Catal. B 241 (2019) 81–88.
[25] C.J. Chen, A. Bhan, ACS Catal. 7 (2017) 1113–1122.
[26] C.-J. Chen, W.-S. Lee, A. Bhan, Appl. Catal., A 510 (2016) 42–48.
[27] M.M. Sullivan, A. Bhan, J. Catal. 344 (2016) 53–58.
[28] M.M. Sullivan, A. Bhan, ACS Catal. 6 (2016) 1145–1152.
[29] M.M. Sullivan, A. Bhan, J. Catal. 357 (2018) 195–205.
[30] M.M. Sullivan, J.T. Held, A. Bhan, J. Catal. 326 (2015) 82–91.
[31] A. Kumar, A. Bhan, Chem. Eng. Sci. 197 (2019) 371–378.
[32] H. Fang, A. Roldan, C. Tian, Y. Zheng, X. Duan, K. Chen, L. Ye, S. Leoni, Y. Yuan,
J. Catal. 369 (2019) 283–295.
[33] K.-Z. Qi, G.-C. Wang, W.-J. Zheng, Appl. Surf. Sci. 276 (2013) 369–376.
[34] C. Bouchy, I. Schmidt, J.R. Anderson, C.J.H. Jacobsen, E.G. Derouane, S.
B. Derouane-Abd Hamid, J. Mol. Catal. A Chem. 163 (2000) 283–296.
[35] E. Blanco, A.B. Dongil, J.L. García-Fierro, N. Escalona, Appl. Catal., A 599 (2020),
117600.
CRediT authorship contribution statement
Elodie Blanco: Conceptualization, Investigation, Methodology,
´
Visualization, Writing - original draft, Funding acquisition. Ana Belen
[36] E. Blanco, C. Sepulveda, K. Cruces, J.L. García-Fierro, I.T. Ghampson, N. Escalona,
Catal. Today 356 (2020) 376–383.
Dongil: Resources, Writing - review & editing. I. Tyrone Ghampson:
Resources, Writing - review & editing. Jose Luis García-Fierro: Re-
[37] L. Xu, Y. Ma, Y. Zhang, B. Chen, Z. Wu, Z. Jiang, W. Huang, J. Phys. Chem. C 115
(2011) 3416–3424.
´
sources. Nestor Escalona: Conceptualization, Supervision, Project
[38] Y. Qi, C. Meng, X. Xu, B. Deng, N. Han, M. Liu, M. Hong, Y. Ning, K. Liu, J. Zhao,
Q. Fu, Y. Li, Y. Zhang, Z. Liu, J. Am. Chem. Soc. 139 (2017) 17574–17581.
[39] V. Hulea, ACS Catal. 8 (2018) 3263–3279.
administration, Writing - review & editing, Funding acquisition.
[40] S. Lwin, I.E. Wachs, ACS Catal. 4 (2014) 2505–2520.
[41] E. Buluchevskii, M. Mikhailova, A. Lavrenov, Chem. Sustainable Dev 21 (2013)
47–51.
Declaration of Competing Interest
[42] L. Ma, X. Zou, Appl. Catal. B 243 (2019) 703–710.
[43] A.Y. Lee, K. Yang, N.D. Anh, C. Park, S.M. Lee, T.G. Lee, M.S. Jeong, Appl. Surf. Sci.
536 (2021), 147990.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
[44] Y. Wang, D.C. Alsmeyer, R.L. McCreery, Chem. Mater. 2 (1990) 557–563.
[45] I.T. Ghampson, C. Sepulveda, R. Garcia, J.L.G. Fierro, N. Escalona, Catal. Sci.
Technol. 6 (2016) 4356–4369.
Acknowledgment
¨
[46] R. Blume, D. Rosenthal, J.-P. Tessonnier, H. Li, A. Knop-Gericke, R. Schlogl,
ChemCatChem 7 (2015) 2871–2881.
[47] M. Enterría, J.L. Figueiredo, Carbon 108 (2016) 79–102.
[48] J.L. Figueiredo, M.F.R. Pereira, Catal. Today 150 (2010) 2–7.
[49] A.B. Dongil, B. Bachiller-Baeza, A. Guerrero-Ruiz, I. Rodríguez-Ramos,
EB and NE gratefully acknowledge funding from ANID Chile for the
following projects: Fondecyt N◦ 3170072, Fondequip N◦ EQM160070
and the Millennium Science Initiative Program – NCN17_040.
´
A. Martínez-Alonso, J.M.D. Tascon, J. Colloid Interface Sci. 355 (2011) 179–189.
[50] K. Leiva, R. Garcia, C. Sepulveda, D. Laurenti, C. Geantet, M. Vrinat, J.L. Garcia-
Fierro, N. Escalona, Catal. Today 296 (2017) 228–238.
Appendix A. Supplementary data
[51] F. Toledo, I.T. Ghampson, C. Sepúlveda, R. García, J.L.G. Fierro, A. Videla,
R. Serpell, N. Escalona, Fuel 242 (2019) 532–544.
´
[52] A.B. Dongil, L. Pastor-Perez, N. Escalona, A. Sepúlveda-Escribano, Carbon 101
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.apcata.2021.118267.
(2016) 296–304.
[53] C. Liang, P. Ying, C. Li, Chem. Mater. 14 (2002) 3148–3151.
´
[54] D. Mordenti, D. Brodzki, G. Djega-Mariadassou, J. Solid State Chem. 141 (1998)
114–120.
References
[55] J.S. Lee, S.T. Oyama, M. Boudart, J. Catal. 106 (1987) 125–133.
[56] T. Miyao, I. Shishikura, M. Matsuoka, M. Nagai, S.T. Oyama, Appl. Catal., A 165
(1997) 419–428.
[1] W.C. Wang, A.C. Lee, Renew. Energy 133 (2019) 1–10.
[2] A.J. Ragauskas, G.T. Beckham, M.J. Biddy, R. Chandra, F. Chen, M.F. Davis, B.
H. Davison, R.A. Dixon, P. Gilna, M. Keller, P. Langan, A.K. Naskar, J.N. Saddler, T.
J. Tschaplinski, G.A. Tuskan, C.E. Wyman, Science 344 (2014), 1246843.
´
˜
[57] J.L. Figueiredo, M.F.R. Pereira, M.M.A. Freitas, J.J.M. Orfao, Carbon 37 (1999)
1379–1389.
[58] A. Hanif, T. Xiao, A.P.E. York, J. Sloan, M.L.H. Green, Chem. Mater. 14 (2002)
´
´
[3] C.O. Tuck, E. Perez, I.T. Horvath, R.A. Sheldon, M. Poliakoff, Science 337 (2012)
1009–1015.
695.
´
[59] J.-S. Choi, G. Bugli, G. Djega-Mariadassou, J. Catal. 193 (2000) 238–247.
[4] A. Corma, S. Iborra, A. Velty, Chem. Rev. 107 (2007) 2411–2502.
[5] G.W. Huber, S. Iborra, A. Corma, Chem. Rev. 106 (2006) 4044–4098.
[6] C. Li, X. Zhao, A. Wang, G.W. Huber, T. Zhang, Chem. Rev. 115 (2015)
11559–11624.
[60] C. Alvarez, K. Cruces, R. Garcia, C. Sepulveda, J.L.G. Fierro, I.T. Ghampson,
N. Escalona, Appl. Catal., A 547 (2017) 256–264.
´
[61] K. Leiva, N. Martinez, C. Sepulveda, R. García, C.A. Jimenez, D. Laurenti,
M. Vrinat, C. Geantet, J.L.G. Fierro, I.T. Ghampson, N. Escalona, Appl. Catal., A
[7] M. Ventura, A. Marinas, M.E. Domine, Top. Catal. 63 (2020) 846–865.
[8] M. Saidi, F. Samimi, D. Karimipourfard, T. Nimmanwudipong, B.C. Gates, M.
R. Rahimpour, Energy Environ. Sci. 7 (2014) 103–129.
[9] J. Zhang, J. Sun, Y. Wang, Green Chem. 22 (2020) 1072–1098.
[10] E. Furimsky, Appl. Catal., A 199 (2000) 147–190.
[11] Y. Aoki, H. Tominaga, M. Nagai, Catal. Today 215 (2013) 169–175.
[12] S. Boullosa-Eiras, R. Lødeng, H. Bergem, M. Stocker, L. Hannevold, E.A. Blekkan,
Catalysis 26 (2014) 29–71.
490 (2015) 71–79.
[62] E. Iglesia, F.H. Ribeiro, M. Boudart, J.E. Baumgartner, Catal. Today 15 (1992)
307–337.
[63] E. Iglesia, F.H. Ribeiro, M. Boudart, J.E. Baumgartner, Catal. Today 15 (1992)
455–458.
[64] F.H. Ribeiro, M. Boudart, R.A. Dalla Betta, E. Iglesia, J. Catal. 130 (1991) 498–513.
[65] F. Yan, Y. Sang, Y. Bai, K. Wu, K. Cui, Z. Wen, F. Mai, Z. Ma, L. Yu, H. Chen, Y. Li,
Catal. Today (2019).
[13] C.E. Chan-Thaw, A. Villa, Appl. Sci. 8 (2018) 259.
[14] E. Iglesia, J.E. Baumgartner, F.H. Ribeiro, M. Boudart, J. Catal. 131 (1991)
523–544.
´
[66] E. Blanco, J.N. Díaz de Leon, J.L. García-Fierro, N. Escalona, Catal. Today 367
(2021) 290–296.
[67] J. Chang, T. Danuthai, S. Dewiyanti, C. Wang, A. Borgna, ChemCatChem 5 (2013)
3041–3049.
´
[15] A.B. Dongil, Q. Zhang, L. Pastor-Perez, T. Ramírez-Reina, A. Guerrero-Ruiz,
I. Rodríguez-Ramos, Catalysts 10 (2020) 1213.
[68] A.L. Jongerius, R.W. Gosselink, J. Dijkstra, J.H. Bitter, P.C.A. Bruijnincx, B.
M. Weckhuysen, ChemCatChem 5 (2013) 2964–2972.
[69] R. Ma, K. Cui, L. Yang, X. Ma, Y. Li, Chem. Commun. 51 (2015) 10299–10301.
[70] E. Santillan-Jimenez, M. Perdu, R. Pace, T. Morgan, M. Crocker, Catalysts 5
(2073–4344) (2015) 424–S424.
´
´
[16] D.H. Carrales-Alvarado, A.B. Dongil, J.M. Fernandez-Morales, M. Fernandez-
García, A. Guerrero-Ruiz, I. Rodríguez-Ramos, Catal. Sci. Technol. 10 (2020)
6790–6799.
[17] E. Ochoa, D. Torres, R. Moreira, J.L. Pinilla, I. Suelves, Appl. Catal. B 239 (2018)
463–474.
[71] A.V. Vasilevich, O.N. Baklanova, A.V. Lavrenov, ChemistrySelect 5 (2020)
4575–4579.
´
[18] R. Guil-Lopez, E. Nieto, J.A. Botas, J.L.G. Fierro, J. Solid State Chem. 190 (2012)
285–295.
8

E. Blanco et al.
Applied Catalysis A, General 623 (2021) 118267
ˇ
´
ˇ
´
´
[72] U. Akhmetzyanova, Z. Tisler, N. Sharkov, L. Skuhrovcova, L. Pelískova,
[74] E. Blanco, A. Rosenkranz, R. Espinoza-Gonzalez, V.M. Fuenzalida, Z. Zhang,
¨
´
O. Kikhtyanin, P. Maki-Arvela, M. Opanasenko, M. Peurla, D.Y. Murzin,
S. Suarez, N. Escalona, Catal. Commun. 133 (2020) 105833.
ChemistrySelect 4 (2019) 8453–8459.
[75] D.R. Stellwagen, J.H. Bitter, Green Chem. 17 (2015) 582–593.
¨
[73] A. Sulman, P. Maki-Arvela, L. Bomont, M. Alda-Onggar, V. Fedorov, V. Russo,
¨
´
ˇ
´
K. Eranen, M. Peurla, U. Akhmetzyanova, L. Skuhrovcova, Z. Tisler, H. Grenman,
¨
J. Warnå, D.Y. Murzin, Catal. Lett. 149 (2019) 2453–2467.
9