Highly efficient catalytic transfer hydrogenation of furfural over defect-rich amphoteric ZrO2with abundant surface acid-base sites

Article abstract of DOI:10.1039/d0dt00055h

Currently, the catalytic transformation and utilization of biomass-derived compounds are of great importance to the alleviation of environmental problems and sustainable development. Among them, furfural alcohol derived from biomass resources has been found to be one of the most prospective biomass platforms for high-value chemicals and biofuels. Herein, high-surface-area ZrO2 with abundant oxygen defects and surface acid-base sites was synthesized and used as a heterogeneous catalyst for the catalytic transfer hydrogenation of furfural into furfural alcohol using alcohol as a hydrogen donor. The as-synthesized ZrO2 exhibited excellent catalytic performance with 98.2% FA conversion and 97.1% FOL selectivity, even comparable with that of a homogeneous Lewis acid catalyst. A series of characterization studies and experimental results revealed that acid sites on the surface of ZrO2 could adsorb and activate the CO bond in furfural and base sites could facilitate the formation of alkoxide species. The synergistic effect of surface acid-base sites affords a harmonious environment for the reaction, which is crucial for catalytic transfer hydrogenation of furfural with high efficiency. Furthermore, the as-prepared ZrO2 catalyst also exhibited a potential application for the efficient catalytic transfer hydrogenation of a series of biomass-derived carbonyl compounds. This journal is

Full text of DOI:10.1039/d0dt00055h

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Highly efficient catalytic transfer hydrogenation of
furfural over defect-rich amphoteric ZrO2 with
abundant surface acid–base sites†
Cite this: Dalton Trans., 2021, 50,
2616
Zekun Zhu,‡ Lingling Yang,‡ Changxuan Ke, Guoli Fan, * Lan Yang
Feng Li
and
*
Currently, the catalytic transformation and utilization of biomass-derived compounds are of great impor-
tance to the alleviation of environmental problems and sustainable development. Among them, furfural
alcohol derived from biomass resources has been found to be one of the most prospective biomass plat-
forms for high-value chemicals and biofuels. Herein, high-surface-area ZrO2 with abundant oxygen
defects and surface acid–base sites was synthesized and used as a heterogeneous catalyst for the cata-
lytic transfer hydrogenation of furfural into furfural alcohol using alcohol as a hydrogen donor. The as-
synthesized ZrO2 exhibited excellent catalytic performance with 98.2% FA conversion and 97.1% FOL
selectivity, even comparable with that of a homogeneous Lewis acid catalyst. A series of characterization
studies and experimental results revealed that acid sites on the surface of ZrO2 could adsorb and activate
the CvO bond in furfural and base sites could facilitate the formation of alkoxide species. The synergistic
effect of surface acid–base sites affords a harmonious environment for the reaction, which is crucial for
catalytic transfer hydrogenation of furfural with high efficiency. Furthermore, the as-prepared ZrO2 cata-
lyst also exhibited a potential application for the efficient catalytic transfer hydrogenation of a series of
biomass-derived carbonyl compounds.
Received 7th January 2020,
Accepted 19th January 2021
DOI: 10.1039/d0dt00055h
rsc.li/dalton
Among the above chemicals, FOL is one of the most inter-
esting and valuable intermediates since it can be used for the
1. Introduction
Presently, diminishing fossil fuel reserves and deteriorating production of thermostatic resins, synthetic fibers, foundry
environmental problems have encouraged the development of binders, farm chemicals, lubricants, lysine, vitamin C, etc.6,13
economically efficient and environmentally friendly techno- Commercial preparation of FOL using FA as a raw material has
logies for the preparation of renewable fuels and fine been performed over various copper–chromite (Cu–Cr) cata-
chemicals.1–5 Furfural (FA), one of the most important renew- lysts either in the liquid phase or in the vapor phase for
able platform molecules, has been produced by the acid hydro- decades.14,15 However, the main drawbacks of the copper–
lysis of five-carbon sugars contained in lignocellulosic chromite catalyst are the moderate activity for FA hydrogen-
biomass.6 Due to the presence of the CvO bond in the ation and the toxic nature of chromium oxides, thereby
branched chain and the CvC bond in the furan ring, FA can causing high energy consumption and serious environmental
be selectively transformed to produce various valuable chemi- pollution. To overcome the above problems, a variety of non-
cals and biofuels (Fig. 1), such as furfural alcohol (FOL), tetra- chromite based catalysts including precious metals (Pt, Pd, Ru,
hydrofurfuryl alcohol (THFOL), furfurylamine, 2-methylfuran and Ir),16–18 non-precious metals (Cu, Ni, and Fe),19–21 and bi-
(2-MF), tetrahydrofuran (THF), cyclopentanone (CPO), 1,5-pen- metallic alloys (Pt–M, Fe–M, Ni–M, and Cu–M) have been
tanediol (1,5-PDO), 1,4-butanediol (1,4-BDO), and so on.7–13
developed for the hydrogenation of FA to FOL.22–26 However,
poor selectivity of FOL originating from the unselective hydro-
genation of the CvC bonds and cracking of the C–C bonds in
FA, high cost of catalysts, and use of explosive molecular
hydrogen under stringent reaction conditions are prominent
barriers for large-scale applications.
During the past decade, for environmental, safety, and
economic considerations, formic acid or non-corrosive alco-
hols have been used as hydrogen sources to replace explosive
State Key Laboratory of Chemical Resources Engineering, Beijing Advanced
Innovation Center for Soft Matter Science and Engineering, Beijing University of
Chemical Technology, Beijing, 100029, China. E-mail: fangl@mail.buct.edu.cn,
lifeng@mail.buct.edu.cn; Fax: +861064425385; Tel: +861064451226
†Electronic supplementary information (ESI) available. See DOI: 10.1039/
d0dt00055h
‡These authors contributed equally to this work.
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Fig. 1 Catalytic conversion of furfural to fuel components and chemicals.
molecular hydrogen for the catalytic transfer hydrogenation the CTH of biomass-derived molecules is limited so far,
(CTH) of biomass to fine chemicals over several metal catalysts especially for the CTH of FA to FOL. From the perspective of
under mild conditions.27–30 Meanwhile, carbonyl-selective catalytic applications, the catalytic performance of ZrO2 is
hydrogenation of biomass, even in the presence of other active closely associated with the specific surface area and the
groups (alkoxyl groups, unsaturated carbon moieties, nitriles, surface properties. However, ZrO2 obtained by conventional
etc.), has been achieved via the Meerwein–Ponndorf–Verley precipitation of zirconyl salts with ammonia or sodium
(MPV) reduction over several low-cost metal oxides. The per- hydroxide usually possesses a low surface area (70–150 m2
formance of MPV catalysts is mainly affected by the Lewis g−1) and scarce surface acid–base sites after post-calcination
acidity in the catalyst, which is responsible for the polarization treatment.44 Hence, the practical application of the ZrO2 cata-
of the carbonyl group in biomass materials.31–35 To date, the lyst for the CTH of FA to FOL has been limited. Previously, we
CTH of FA to FOL over metal catalysts has been investigated reported the successful synthesis of porous ZrO2 with large
and has achieved acceptable catalytic performance; further- surface areas and controlled morphologies via a two-step
more, a few kinds of acid zeolites and basic metal oxides or solution-phase strategy.45 The synthesized ZrO2 was used as a
hydroxides were also reported to be used as efficient catalysts support for the fabrication of highly dispersed zirconium-
for the CTH of FA to FOL.36–38 For instance, Zhang et al. based supported catalysts, which exhibited excellent catalytic
reported that a hydroxyapatite-encapsulated magnetic γ-Fe2O3 performance for the hydrogenations of cinnamaldehyde and
(γ-Fe2O3@HAP) catalyst yielded 95.3% selectivity to FOL at γ-valerolactone.46,47
about 96.2% FA conversion.39 They found that base sites play a
In this work, we synthesized ZrO2 nanocrystals with large
positive role in the CTH of FA to FOL. Compared with the con- surface areas, porous structures, and abundant surface acid–
ventional hydrogenation of FA by H2, CTH processes seem to base sites and oxygen defects by a two-step solution-phase
be more economical, safer, and more eco-friendly, but they are strategy that we developed previously, and systematically inves-
still far from being satisfactory due to the low reaction activity tigated the influence of the surface acid–base sites of ZrO2 on
toward hydrogen donors, high catalyst dosages, and low FOL the catalytic behavior of CTH of FA to FOL with alcohol as a
selectivity. Hence, designing and developing environmentally mild hydrogen source. The results indicated that acid sites on
friendly and high-performing heterogeneous catalysts is the surface of ZrO2 are beneficial for the adsorption and acti-
crucial for the CTH of FA to FOL from the perspective of the vation of the CvO bond in FA, base sites are good for the for-
utilization of biomass resources and fuel economy.
mation of alkoxide species, and the synergistic effect of
Zirconium-based materials such as zirconium-beta zeolite, surface acid–base sites affords a harmonious environment for
zirconium oxide or hydroxide, and Zr-doped metal oxides the CTH of FA, and thus the as-prepared ZrO2 catalyst exhibi-
possess acidic and basic functionalities, as well as high ted excellent catalytic performance with a high 95.4% yield of
thermal and chemical stability, which have been investigated FOL under mild conditions. To the best of our knowledge,
as catalytic materials (i.e., catalysts, supports, or promoters) there is no report about the application of such defect-rich
for the transformation of biomass-derived molecules into amphoteric ZrO2 catalysts for the CTH of FA to produce FOL.
valuable chemicals.40–43 Steven V. Ley et al. prepared a par-
tially hydrated ZrO2 catalyst from a zirconium hydroxide pre-
cursor, used it as a catalyst for the transfer hydrogenation of
ketones and aldehydes via a mild and efficient flow pro-
2. Experimental section
2.1 Materials
cedure, and investigated the effect of flow conditions on cata-
lytic performance systematically.42 However, investigation on
Zr(NO3)4·5H2O (99.9%) and NaBH4 (99.7%) were purchased
the synthesis and application of pure ZrO2 as a catalyst for
from Sigma-Aldrich, and FA (98.0%) and FOL (98.0%) were
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purchased from J&K Scientific Ltd. 2-Propanol (2-PrOH) and fural or 2-PrOH adsorption, the ZrO2 sample was exposed to
other analytical grade reagents were purchased from Beijing saturated vapour at room temperature firstly, and the phys-
Chemical Co. and used directly without further purification.
ically adsorbed molecules were removed by evacuation. All the
FT-IR spectra were recorded at 30 °C and normalized based on
the sample weight. NH3 temperature-programmed desorption
2.2 Preparation of catalysts
The ZrO2 sample was prepared via a two-step solution-phase (NH3-TPD) and CO2 temperature-programmed desorption
method.45 Typically, two solutions were prepared prior to the (CO2-TPD) were carried out on a Micromeritics Chemi-Sorb
synthesis. Zr(NO3)4·5H2O (0.01 mol) was ultrasonically dis- 2720 instrument. 100 mg ZrO2 sample was loaded into a
persed in 40 mL of deionized water to form a clear salt solu- quartz tube and degassed by heating under He at 200 °C for
tion A. NaBH4 (0.15 mol) was dissolved in 40 mL of deionized 1 h to remove physically adsorbed species. NH3 adsorption was
water to form solution B. Solutions A and B were synchro- performed at 100 °C in an NH3–He gas mixture (5 : 95, v/v) for
nously added to a colloid mill with the rotor rotating at a 1.5 h; the residual NH3 was removed by purging with He. Then
speed of 6000 rpm; a white slurry was formed after being the sample was heated to 700 °C at a heating rate of 10 °C
mixed for 2 min, and the obtained slurry was sealed in a min−1, and the desorbed NH3 was monitored using a mass
100 mL autoclave and aged at 150 °C for 12 h. After cooling, spectrometer. CO2-TPD was carried out by using a similar pro-
the resulting precipitate was washed with deionized water and cedure. 31P NMR spectra were acquired on a Bruker Avance III
ethanol, dried at 70 °C for 12 h, and denoted as ZrO2. 400 WB solid-state spectrometer with a response frequency of
Furthermore, the as-prepared ZrO2 was then calcined at 200, 161.904 mHz using a 4 mm rotor at a spinning rate of 8 kHz.
400, and 600 °C for 8 h and marked as ZrO2-200, ZrO2-400, All samples were pre-treated under vacuum with the pressure
and ZrO2-600, respectively. For comparison, ZrO2-S was also below 10−3 Pa for 10 h, and the preparation of TMPO adsorbed
prepared under similar experimental conditions using NaOH ZrO2 samples was carried out according to the method
as a precipitant.
reported by Zheng’s group.48 The chemical shift of 31P reso-
nance was referenced to adenosine triphosphate.
2.3 Characterization
2.4 Catalytic test
Powder X-ray diffraction (XRD) data were recorded at room
temperature on a Bruker D8 Advance system with a graphite-
filtered Cu-Kα radiation source (λ = 0.15418 nm). The mor-
phology and microstructure of the samples were observed
using a Zeiss Supra 55 field-emission scanning electron micro-
scope (FESEM) operating at an accelerating voltage of 20 kV
and a JEOL 2100 high-resolution transmission electron micro-
scope (HRTEM) operating at an accelerating voltage of 200 kV.
Low-temperature N2 adsorption–desorption measurements
were performed using a Micromeritics ASAP 2020 instrument,
and the surface area and pore size distribution were deter-
mined by using Brunauer–Emmett–Teller (BET) and nonlocal
density functional theory (NL-DFT) models. X-ray photo-
electron spectra (XPS) were collected using a Thermo VG
ESCALAB250 X-ray photoelectron spectrometer with Al Kα
X-ray (1486.6 eV) as the excitation source. The oxygen storage
capacity (OSC) of ZrO2 samples was investigated by the oxygen
pulse injection method. 100 mg of ZrO2 sample was purged
with He at 150 °C firstly, and the flow rate was set at 40 mL
min−1. Then, the O2/He gas mixture (1 : 9, V/V) at a rate of
40 mL min−1 was injected periodically into the sample until
the signal area was constant. The number of surface oxygen
vacancies (Nv) was calculated based on the consumption of
oxygen. In situ Fourier transform infrared (FT-IR) spectra of
The liquid phase catalytic transfer hydrogenation of FA was
carried out in a 100 mL autoclave equipped with a timing
heating system and a magnetic stirrer. Typically, 0.01 mol fur-
fural, 0.2 g catalyst, and 0.1 mol 2-PrOH were added into the
reactor, and air was purged out of the reactor with 2 MPa N2
ten times. The reaction was initiated by stirring at a rate of
1000 rpm at a predefined temperature. After the reaction, the
reactor was cooled in an ice-water bath and depressurized care-
fully. Qualitative and quantitative analyses of the obtained pro-
ducts were performed on an Agilent GC-7890B gas chromato-
graph equipped with a DB-WAX capillary column (30.0 m ×
250 μm × 0.25 μm). The products were identified by compari-
son with known standards, and dodecane was used as an
internal standard. In each case, the calculated carbon balance
was above 96%. After the reaction, the catalyst was centrifuged,
washed, dried at 70 °C overnight, and employed to investigate
its reusability by adding a fresh substrate under similar reac-
tion conditions.
3. Results and discussion
3.1 Structural analysis of catalysts
pyridine, furfural, and 2-PrOH adsorbed on catalysts were Fig. 2a shows the XRD pattern of the as-prepared ZrO2 sample.
recorded on a Thermo Nicolet 380 spectrometer. 50 mg of All the intensive and broad diffraction peaks in the range of
ZrO2 sample was pressed into a self-supporting wafer, which 10–80° can be well indexed to the tetragonal ZrO2 (t-ZrO2)
was placed in an evacuable IR cell with CaF2 windows, evacu- phase (JCPDS no. 42-1164), indicative of the highly pure and
ated at 200 °C for 2 h, and then cooled to room temperature. well-crystallized nature of the ZrO2 sample. Fig. 2b shows the
For pyridine adsorption, pyridine was introduced at room N2 adsorption–desorption isotherms and pore size distribution
temperature after acquisition of the background spectrum; the of ZrO2. The isotherm is of complex type including types I and
sample was heated gradually to 200 °C under vacuum. For fur- IV, indicating that the as-prepared ZrO2 sample possesses
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Fig. 2 XRD pattern (a), low-temperature nitrogen adsorption–desorption isotherm and pore size distribution (b), HRTEM image (c), and O 1s XPS
spectra (d) of ZrO2.
microporous and mesoporous structure. The surface area is 1 : 1.92, very close to the ideal stoichiometric value of the ZrO2
high up to 278 cm2 g−1, and the total pore volume is about phase. In line with the SEM result, the TEM image shows that
0.289 cm3 g−1. The pore size distribution reveals that ZrO2 has the as-prepared ZrO2 is composed of interconnected spherical
abundant mesopores accompanied by a small amount of particles of about 3 2 nm in size (Fig. 2c), and sponge-like
micropores. As presented in Table 1, the BET surface areas, pores can be formed among the compactly arranged ZrO2
the total pore volumes, and the average pore sizes of calcined nanoparticles. The clear lattice fringe with a d-spacing of
ZrO2 samples decrease slightly with the increase of the calcina- 0.296 nm can be ascribed to the (101) plane of the t-ZrO2
tion temperature (Fig. S1†), demonstrating the good structural phase, further confirming the tetragonal phase of the as-pre-
stability of the as-prepared ZrO2. The SEM image shows that pared ZrO2 sample.49
ZrO2 exhibits a compact configuration of homogeneous nano-
The surface/near-surface chemical states of Zr and O
particles (Fig. S2†), which is quite different from those of ZrO2- species on the ZrO2 samples were investigated by XPS. The
S and commercial ZrO2-C samples (Fig. S3†). Elemental map- core levels of Zr 3d and O 1s can be identified, and no con-
pings in Fig. S2† indicate the homogeneous distributions of Zr taminant species corresponding to the boron element can be
and O species in ZrO2 with a Zr/O atomic ratio of about detected. In the fine Zr 3d spectrum (Fig. S4†), two peaks at
Table 1 The structural and textural data of the samples
b
c
d
Crystal
SBET
Vtotal
Vmicro
Smicro
SBET
/
Total acid sitesi Total basic sitesk
(mmol g−1 (mmol g−1
sizea (nm) (m2 g−1
)
(cm3 g−1
)
(cm3 g−1
)
Df (nm) OII/OI
Nv h (μmol g−1
)
)
)
e
g
Sample
ZrO2
3.5
4.0
4.6
278
245
225
173
44
12
258
0.289
0.261
0.232
0.222
0.228
0.022
0.272
0.054
0.036
0.022
0.008
—
—
0.048
22.6
18.1
14.2
6.5
0
0
19.5
4.1
4.2
4.2
5.4
16.8
7.3
0.70
0.62
0.59
0.51
0.42
0.24
0.66
238.5
198.7
168.4
145.2
118.7
38.2
0.524 (0.461)j
0.498 (0.356)
0.211 (0.126)
0.108 (0.078)
n.d.
1.702 (1.187)l
1.528 (1.104)
0.722 (0.432)
0.409 (0.298)
0.312 (0.159)
n.d.
ZrO2-200
ZrO2-400
ZrO2-600
ZrO2-S
5.1
19.5
40.5
3.5
ZrO2-C
n.d.
0.513 (0.425)
ZrO2-Rm
4.1
215.3
1.680 (1.098)
a Crystal size based on XRD and TEM results. b Specific surface area calculated by the BET method. c Single-point total pore volume calculated
from nitrogen adsorption at P/P0 = 0.994. d Micropore volume calculated by the NL-DFT method. e Micropore surface area calculated by the
NL-DFT method. f Average pore diameter. g Determined by XPS of the O 1s region. h Determined by the oxygen pulse injection method. i The
amount of total acid sites determined by NH3-TPD analysis. j The amount of medium and strong acid sites in the total amount of acid sites.
k The amount of total base sites determined by CO2-TPD analysis. l The amount of medium and strong base sites determined by CO2-TPD ana-
lysis. m ZrO2 catalyst reused 4 times.
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about 181.8 and 184.1 eV can be assigned to Zr 3d5/2 and Zr the absorption bands at 1442 and 1592 cm−1 can be associated
3d3/2, respectively.50,51 It is noteworthy that the binding energy with H-bonding (HA) pyridine, and the absorption band at
of Zr 3d5/2 is smaller than those of ZrO2-S and commercial 1584 cm−1 can be ascribed to the physically adsorbed (PA) pyri-
ZrO2-C samples, reflecting the formation of more surface dine.29 Furthermore, the intensity of peaks corresponding to
oxygen vacancies to some extent.43 The O 1s fine spectrum was LA, BA, and HA decreases with the increase of the calcination
analyzed and is shown in Fig. 2d; the fitted peak at about temperature, reflecting a decreased amount of acid sites on
530.4 eV (referred to as I) is assigned to the lattice oxygen ZrO2 with the increase of the calcination temperature. In con-
species in the structure of ZrO2, while two other peaks at trast, as for ZrO2-S, only weak peaks associated with LA and
around 531.7 eV (referred to as II) and 533.2 eV (referred to as HA sites can be observed, and even no apparent peak is
III) correspond to both defect oxides or hydroxyl species in the observed in the profile of the ZrO2-C sample. The Py-IR results
subsurface and surface adsorbed CO2, respectively.52,53 The reveal that the as-prepared ZrO2 possesses more acid sites with
amount of surface defects (e.g. oxygen vacancies) was esti- a higher acid strength in comparison with those of ZrO2-S and
mated based on the OII/OI intensity ratio. As presented in ZrO2-C samples.
Table 1, the OII/OI intensity ratio is much higher than those of
Solid-state 31P NMR of adsorbed TMPO was also used to
contrastive ZrO2 samples, mirroring the existence of abundant distinguish the Brønsted acid and Lewis acid on the as-pre-
defects on the surface of ZrO2. Furthermore, quantitative ana- pared ZrO2 samples.48,57,58 As shown in Fig. 4, the 31P spec-
lysis of the concentration of surface oxygen vacancies was trum of ZrO2 can be fitted into four peaks with chemical shifts
determined by oxygen storage capacity (OSC) measurements. It of 68, 62, 52, and 34 ppm, respectively. The peaks at about
is noted from Table 1 that the concentration of oxygen 68 ppm can be ascribed to the TMPO adsorbed on Brønsted
vacancies of the ZrO2 sample is high up to 238.5 μmol g−1
;
acid sites, the two peaks at 62 and 52 ppm can be assigned to
meanwhile, the OII/OI ratio and the oxygen vacancies present a the TMPO adsorbed on two types of Lewis acid sites with
declining trend with the increase of the calcination tempera- different acid strengths (a larger chemical shift means a
ture, which may result from the slightly increased particle size higher acid strength), and the peak at 34 ppm is attributed to
and improved crystallinity at high calcination temperatures.
physiosorbed or mobile TMPO.48,57 Notably, with increasing
As we know, surface acid–base sites play important roles in calcination temperature, the peak intensity at around 62 ppm
the catalytic behaviour of many heterogeneous catalysts. As for decreases, while the peak intensity at around 52 ppm increases
amphoteric ZrO2, surface acid–base sites are usually ascribed at first and then decreases. In addition, after calcination treat-
to the abundant surface Zr-OH species, unsaturated Zr4+ ment, the Brønsted acid signal (chemical shift at 68 ppm)
cations, and oxygen vacancy. Fig. 3 shows the FT-IR spectra of cannot be detected anymore, reflecting the decrease of the
different pyridine-adsorbed ZrO2 samples. As for ZrO2, the acid strength and the amount of acid sites over the calcined
absorption bands at 1457, 1491, and 1612 cm−1 reveal the pres- ZrO2 samples. In contrast, ZrO2-S presents a weak peak at
ence of Lewis acid (LA) sites, while the absorption bands at about 60 ppm, and only a weak peak corresponding to physi-
1542 and 1638 cm−1 demonstrate the presence of Brønsted sorbed TMPO can be observed for the ZrO2-C sample, indicat-
acid (BA) sites.54–56 We speculated that surface coordinatively ing their poor acidic nature. The 31P NMR results are well con-
unsaturated Zr4+ cations and abundant surface defects are sistent with the FT-IR analysis.
responsible for the generation of LA sites, and the presence of
BA sites is related to the surface Zr-OH species. In addition,
Fig. 3 FT-IR spectra of pyridine adsorbed onto ZrO2 (a), ZrO2-200 (b),
Fig. 4 31P MAS NMR spectra of TMPO adsorbed onto ZrO2 (a), ZrO2-
ZrO2-400 (c), ZrO2-600 (d), ZrO2-S (e), and ZrO2-C (f).
200 (b), ZrO2-400 (c), ZrO2-600 (d), ZrO2-S (e), and ZrO2-C (f).
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Fig. 6 CO2-TPD profiles of different ZrO2 samples: ZrO2 (a), ZrO2-200
(b), ZrO2-400 (c), ZrO2-600 (d), ZrO2-S (e), and ZrO2-C (f).
Fig. 5 NH3-TPD profiles of different ZrO2 samples: ZrO2 (a), ZrO2-200
(b), ZrO2-400 (c), ZrO2-600 (d), ZrO2-S (e), and ZrO2-C (f).
ponding catalytic performance. In order to obtain more infor-
mation on the surface-bonding state for reactants adsorbed on
catalysts, in situ FT-IR studies of FA and isopropanol molecules
adsorbed on typical ZrO2 samples were conducted, respect-
ively. Fig. 7 shows the FT-IR spectra of FA-adsorbed ZrO2
samples. In all cases, the FT-IR spectra in the range of
1600–1750 cm−1 present three absorption peaks at 1673, 1691,
Fig. 5 shows the NH3-TPD of different ZrO2 samples. For
the ZrO2 sample, the broad desorption peak of NH3 in the
temperature region of 50–700 °C can be fitted into four peaks.
The peaks at about 200, 320–450, and 600 °C are ascribed to
the NH3 desorption from weak, medium, and strong acidic
sites, respectively.43,59,60 It should be noted that the acidity of
ZrO2 is mostly medium strength, and the total acidic sites
show a downward trend with increasing calcination tempera-
ture. In contrast, the ZrO2-S sample shows only a weak desorp-
tion peak at around 520 °C, and no apparent desorption peak
is observed for the commercial ZrO2-C sample, indicating the
scarce nature of acidic sites on the surface of ZrO2-S and com-
mercial ZrO2-C samples. Furthermore, the relative proportions
of different basic sites are obtained based on the integrated
areas of these desorption peaks (Table 1), well consistent with
those of Py-IR and 31P MAS NMR results.
and 1721 cm−1
, respectively. The adsorption peak at
1721 cm−1 is ascribed to the trans-stretch vibration of the
CvO bond in physisorbed FA based on the NIST database,63
while the adsorption peaks at 1673 and 1691 cm−1 should be
assigned to the weak cis-stretch and trans-stretch vibrations of
the CvO bond in FA due to the interaction of the carbonyl
group with the surface Lewis acid sites.29,64 Notably, the
vibration intensity of the CvO band at 1673 and 1691 cm−1
Fig. 6 shows the CO2-TPD of different ZrO2 samples. The
CO2-TPD profile of ZrO2 can be fitted into seven peaks. The
peak centered at about 98 °C can be attributed to the phys-
ically adsorbed CO2, whereas the peak centered at 150 °C can
be associated with the CO2 desorption from weak basic sites
(bicarbonate carbonate), three peaks centered at 260, 330, and
420 °C are ascribed to the CO2 desorption from medium-
strength basic sites (bidentate carbonate), and two peaks at
490 and 560 °C are related to the CO2 desorption from strong
basic sites (unidentate carbonate).41,61,62 In contrast, the CO2
desorption peaks of ZrO2-C and ZrO2-S samples are not appar-
ent, indicating that these two samples possess fewer basic
sites than that of ZrO2. Similarly, the basicity of ZrO2 is mostly
medium strength, and the total basic sites decrease gradually
with the increase of the calcination temperature (Table 1).
As we know, the adsorption behaviour of the reactants over
Fig. 7 FT-IR spectra of FA adsorbed onto ZrO2 (a), ZrO2-S (b), and
the catalyst directly affects the extent of influence of the corres- ZrO2-C (c).
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the tested samples, three absorption peaks corresponding to
the CH stretching modes (υ(CH), υas(CH3), υs(CH3)) can be
observed after 2-PrOH adsorption on the tested samples, and
the vibration intensity of CH groups increases in the order
ZrO2-C < ZrO2-S < ZrO2, reflecting that the as-prepared ZrO2
possesses superior adsorption capacity for 2-PrOH to those of
ZrO2-S and ZrO2-C samples. Furthermore, compared with
those of contrastive ZrO2 samples, the υ(CH) and υas(CH3)
bands in the spectrum of the as-prepared ZrO2 were red-
shifted clearly, resulting from the interaction of basic sites in
ZrO2 and the acidic methyl hydrogen atoms in 2-PrOH, which
is beneficial for the deprotonation of 2-PrOH during the hydro-
genation process.65
3.2 Catalytic performance of different ZrO2 catalysts
Fig. 8 FT-IR spectra of 2-PrOH adsorbed onto ZrO2 (a), ZrO2-S (b), and
ZrO2-C (c).
All the above characterization results indicate that the as-pre-
pared defect-rich ZrO2 with abundant surface acid–base sites
may be a superior catalyst for the CTH of FA to FOL. The cata-
increases in the order ZrO2-C < ZrO2-S < ZrO2, reflecting that lytic performance of the ZrO2 catalyst was first investigated
ZrO2 possesses superior adsorption capacity for FA to those of using 2-PrOH as the hydrogen donor. As shown in Fig. 9a, the
ZrO2-S and ZrO2-C samples. This phenomenon may originate conversion of FA increases almost linearly from 57.8% to
from the existence of abundant surface defects on the as-pre- 91.6% with relatively high FOL selectivity (>98.1%) in the
pared ZrO2, which is beneficial for the chemisorption of FA.
initial 3 h at 170 °C; ∼0.68% difurfuryl ether (DFE) and
FT-IR spectra of 2-PrOH-adsorbed samples were also ∼1.02% 4-(2-furyl)-3-buten-2-one (FAT) are detected as the
measured and are shown in Fig. 8. Due to the interaction main by-products. The formation of DEF is caused by the
between the acidic CH groups in 2-PrOH and the basic sites of intermolecular dehydration of the formed FOL, while the for-
Fig. 9 Effects of the reaction time (a) and reaction temperature (b) on the CTH of FA over the ZrO2 catalyst. CTH of FA over ZrO2 calcinated at
different temperatures (c) and with different ZrO2 contrastive samples (d). Reaction conditions: substrate, 0.01 mol; solvent, 0.1 mol; catalyst, 0.2 g;
2 MPa N2 atmosphere; stirring speed, 1000 rpm.
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mation of FAT is caused by the intramolecular dehydration of calcined ZrO2 samples. Furthermore, the catalytic performance
4-(2-furyl)-4-hydroxy-butan-2-one, which is generated from the of contrastive ZrO2 catalysts was also investigated (Fig. 9d). The
condensation between FA and acetone.66–70 The possible reac- conversions of FA over ZrO2-S and commercial ZrO2-C catalysts
tion pathways and the corresponding products over the as-pre- under the optimized reaction conditions are 69.5% and 6.8%,
pared ZrO2 catalyst are shown in Fig. S5.† As we further and the selectivities towards FOL are 88.2% and 72.8%,
increase the reaction time to 5 h, the conversion of FA remains respectively, which are much lower than those of the as-pre-
almost unchanged, but the selectivity towards FOL decreases pared ZrO2 catalyst.
to 97.1%. Notably, the conversion of FA increases from 41.2%
To deeply understand how surface acid sites and base sites
to 98.2% as the reaction temperature increases from 120 °C to affect the CTH of FA to FOL, H2SO4 and N(CH2CH3)3 were used
170 °C, and the FOL selectivity remains above 97% (Fig. 9b). as homogeneous catalysts under the optimized reaction con-
However, further increasing the reaction temperature to 180 °C ditions. As presented in Table 3, H2SO4, a typical Brønsted
is not only unfavourable for the conversion of FA but also acid, gives 10.1% FA conversion, 37.7% FOL selectivity, and
causes a decline of FOL selectivity (96.1%) because of the for- 62.3% DFE selectivity (entry 1), indicating that Brønsted acid
mation of more DFE by-products (2.2%), reflecting that high can catalyse the CTH of FA to FOL. N(CH2CH3)3, a homo-
temperature may be beneficial for the etherification of the geneous base, affords poor catalytic performance (entry 2).
newly formed FOL.66,67
However, when Sc(OTf)3 was used as a homogeneous Lewis
The influence of different hydrogen donors on the CTH of acid catalyst (entry 3), the FA conversion reaches up to 99.2%,
FA to FOL over the as-prepared ZrO2 catalyst was studied and the selectivity towards FOL is 98.9%. Based on the above
(Table 2). In contrast to using secondary alcohols (2-PrOH, results, we deduced that both Lewis and Brønsted acid sites
2-butanol) as hydrogen donors, lower FA conversion was could act as active sites for the CTH of FA, the catalytic activity
obtained when using primary alcohols (1-propanol, 1-butanol) is mainly affected by Lewis acid sites, and the surface base
or cyclohexanol as hydrogen donors, which may result from sites play a promotional role in the CTH of FA.
the difficulty in deprotonation of primary alcohols and the
Poisoning tests were performed to investigate the influence
strong steric effect of the cyclol structure.68 Meanwhile, more of acid sites on the CTH of FA over the ZrO2 catalyst. 2,6-
side reactions such as self-condensation of the aldehyde Dimethylpyridine (diPy) was added to block the surface
formed after dehydrogenation of the hydrogen donor, as well Brønsted acid sites, while pyridine (Py) was used as a blocker
as etherification of alcohol occurred when using a primary for both surface Lewis and Brønsted acid sites.56 As presented
alcohol as the hydrogen donor, leading to an unsatisfactory in Table 3, the conversion of FA decreases to 84.8% with
FOL selectivity. Hence, the optimized reaction conditions (5 h, almost unchanged FOL selectivity after the surface Brønsted
170 °C, 2-PrOH as a hydrogen donor) were chosen and used in acid sites of ZrO2 were poisoned by diPy (entry 5). However,
the comparison study.
after being poisoned by Py, the FA conversion over Py poisoned
The CTH of FA to FOL over ZrO2 calcinated at different ZrO2 (ZrO2-py) further decreases to 66.9% with slightly
temperatures was investigated (Fig. 9c). With the increase of decreasing FOL selectivity. Meanwhile, the selectivity towards
the calcination temperature, the FA conversion and FOL DFE is on the rise, while the selectivity towards FAT shows a
selectivity decreased significantly; meanwhile, the selectivity downward trend (entry 6). The slightly enhanced selectivity
towards DFE increased from 1.5% to 3.9% and 10.3%, and the towards DEF is probably caused by the inhibition of aldol con-
selectivity towards 4-(2-furyl)-3-buten-2-one (FAT) decreased densation between FA and acetone.
from 7.8% to 7.3% and 4.2%, respectively. As we know, Lewis
The reusability of the as-prepared ZrO2 catalyst was studied
acid sites can interact with methyl hydrogen atoms in acetone representatively. It is noteworthy that the reused catalyst ZrO2-
molecules to form the electronegative intermediate, which can R exhibits a slightly decreased catalytic performance (95.3% FA
attack the electropositive C atom of CvO in FA and form the conversion and 96.2% FOL selectivity) in the fourth cycle
final FAT by-product.69,70 The decreased selectivity towards
FAT may be originated from the decrease of acid sites in the
Table 3 Transformation of FA to FOL over various catalystsa
Sel. (%)
Table 2 CTH of FA using different hydrogen donorsa
Entry
Catalysts
Con. (%)
FOL
DFE
FAT
1b
2c
3
4
5
H2SO4
10.1
6.6
99.2
98.2
84.8
66.9
37.7
86.1
98.9
97.1
97.3
95.6
62.3
—
0.4
1.8
1.5
2.9
0
—
0.7
1.1
1.2
1.1
Hydrogen donor
Con. (%)
Sel. (%)
N(CH2CH3)3
Sc(OTf)3
ZrO2
ZrO2-dipy
ZrO2-py
1-Propanol
Cyclohexanol
1-Butanol
2-Butanol
2-PrOH
60.4
80.2
62.4
89.5
98.2
84.2
54.5
61.8
83.8
97.1
6
a Reaction conditions: Furfural, 0.01 mol; 2-PrOH, 0.1 mol; catalyst,
a Reaction conditions: Substrate, 0.01 mol; solvent, 0.1 mol; catalyst, 0.2 g; reaction temperature, 170 °C; reaction time, 5 h; 2 MPa N2 atmo-
0.2 g; reaction temperature, 170 °C; reaction time, 5 h; 2 MPa N2 atmo- sphere; stirring speed, 1200 rpm. b Catalyst amount, 5 μmol. c Catalyst
sphere; stirring speed, 1000 rpm.
amount, 10 μmol.
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Fig. 10 Recyclability of ZrO2 in the CTH of FA (a). TEM image (b) of ZrO2 reused after four consecutive runs.
(Fig. 10a). Systematic characterization studies of the reused FA. Subsequently, the hydride ion transferred from the surface-
catalyst were carried out, and the relevant results are presented adsorbed isopropoxide attacks the aldehyde group of FA to yield
in Table 1. Compared with the fresh ZrO2 catalyst, the struc- FOL, and 2-PrOH is converted to acetone consequently
ture, surface area, and particle size of the reused catalyst (Scheme 1(I)). In the case of the α-H elimination route, the
remain almost unchanged (Table 1 and Fig. 10b). The XPS proton from Brønsted acid sites can interact with FA via coordi-
result shows that the ratio of surface OII to OI species decreases nating with the O atom in the aldehyde group to weaken the
slightly from 0.70 to 0.66, and the total surface acid sites and CvO bond, resulting in the formation of protonated FA.
base sites show a slight decrease, which probably might be the Meanwhile, base sites can adsorb 2-PrOH and abstract a hydro-
reason for the decreased catalytic performance over the reused gen atom from the alcoholic group to form isopropoxide.
ZrO2-R catalyst.
Subsequently, the α-H atom is removed to form the corres-
ponding acetone, and the generated active hydrogen attacks the
protonated FA to generate FOL (Scheme 1(II)). In both cases, the
synergistic effect of surface acid–base sites affords a harmo-
nious environment for the hydrogenation of FA to FOL.
The CTH of a series of biomass-derived compounds con-
taining carbonyl groups was also investigated to verify the
applicability and feasibility of the ZrO2 catalyst. As shown in
Table 4, in all cases, conversions above 90% are achieved
over the ZrO2 catalyst, and the selectivities towards the target
products are more than 85%. The results further indicate
that the defect-rich ZrO2 with abundant surface acid–base
sites can work as an ideal catalyst for the CTH of carbonyl
compounds, reflecting its potential applications in the
efficient exploitation and utilization of biomass-derived
compounds.
3.3 Reaction mechanisn for the CHT of FA
The above-mentioned facts revealed that the excellent catalytic
performance over the as-prepared ZrO2 is not only affected by
the surface acid properties but is also influenced by the syner-
gistic effect of acid and base sites. Based on our experimental
results, the CTH of FA to FOL with 2-PrOH over the as-prepared
ZrO2 may proceed through two reaction routes: one follows the
MPV reduction pathway related to surface Lewis acid sites, and
the other follows a pathway related to surface Brønsted acid
sites (Scheme 1). For the MPV reaction route, base sites can
adsorb 2-PrOH and assist the formation of isopropoxide, and
FA was also adsorbed on Lewis acid sites simultaneously. Then,
transfer of hydrogen, a coordinated process, proceeds via a six-
membered ring transition state formed between 2-PrOH and
Scheme 1 Proposed Lewis acid (I) and Brønsted acid (II) involved reaction mechanisms for the CTH of FA with 2-PrOH over the ZrO2 catalyst.
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Table 4 Catalytic transfer hydrogenation of different carbonyl com-
pounds over the as-prepared ZrO2 catalysta
Notes and references
1 Z. R. Zhang, J. L. Song and B. X. Han, Chem. Rev., 2017,
117, 6834–6880.
Entry
1
Substrates
Products
Con. (%)
98.6
Sel. (%)
96.1
2 D. L. Sun, S. Sato, W. Ueda, A. Primo, H. Garcia and
A. Corma, Green Chem., 2016, 18, 2579–2597.
3 T. Ennaert, J. V. Aelst, J. Dijkmans, R. D. Clercq,
W. Schutyser, M. Dusselier, D. Verboekend and B. F. Sels,
Chem. Soc. Rev., 2016, 45, 584–611.
2
3
99.2
92.1
98.1
87.4
4 M. Besson, P. Gallezot and C. Pinel, Chem. Rev., 2014, 114,
1827–1870.
5 F. J. Liu, L. Wang, Q. Sun, L. F. Zhu, X. J. Meng and
F. S. Xiao, J. Am. Chem. Soc., 2012, 134, 16948–16950.
6 X. D. Li, P. Jia and T. F. Wang, ACS Catal., 2016, 6, 7621–
7640.
4
5
87.9
95.3
98.3
97.5
7 M. J. Taylor, L. Jiang, J. Reichert, A. C. Papageorgiou,
S. K. Beaumont, K. Wilson, A. F. Lee, J. V. Barth and
G. Kyriakou, J. Phys. Chem. C, 2017, 121, 8490–8497.
8 C. Li, G. Y. Xu, X. H. Liu, Y. Fu and Y. Zhang, Ind. Eng.
Chem. Res., 2017, 56, 8843–8849.
a Reaction conditions: Substrate, 0.01 mol; 2-PrOH, 0.1 mol; catalyst,
0.2 g; reaction temperature, 170 °C; reaction time, 8 h; 2 MPa N2 atmo-
sphere; stirring speed, 1000 rpm.
9 M. Chatterjee, T. Ishizaka and H. Kawanami, Green Chem.,
2016, 18, 487–496.
10 S. H. Zhu, Y. F. Xue, J. Guo, Y. L. Cen, J. G. Wang and
W. B. Fan, ACS Catal., 2016, 6, 2035–2042.
11 Y. L. Yang, Z. T. Du, Y. Z. Huang, F. Lu, F. Wang, J. Gao and
J. Xu, Green Chem., 2013, 15, 1932–1940.
12 F. B. Li, T. Lu, B. F. Chen, Z. J. Huang and G. Q. Yuan, Appl.
Catal., A, 2014, 478, 252–258.
4. Conclusions
In this work, defect-rich ZrO2 with abundant surface acid–base
sites was prepared via a two-step solution-phase strategy and
employed as a heterogeneous acid–base catalyst for the catalytic
transfer hydrogenation of FA to FOL using alcohol as a hydrogen
donor. The as-prepared ZrO2 catalyst exhibited excellent catalytic
performance with 98.2% FA conversion and 97.1% FOL selectivity
in 5 h at 170 °C under a nitrogen atmosphere, even comparable
to that of a homogeneous Lewis acid catalyst. A series of charac-
terization studies and experiments revealed that abundant surface
acid–base sites are of crucial importance for the efficient CTH of
FA; acid sites on ZrO2 can adsorb FA and activate the CvO bond
in FA, while base sites are good for the formation of alkoxide
species. The synergistic effect of surface acid–base sites affords a
harmonious environment for the hydrogenation reaction. The as-
formed defect-rich ZrO2 catalyst was also efficient for the hydro-
genation of a series of carbonyl compounds. Such a highly
efficient and cost-effective amphoteric acid–base ZrO2 catalyst pro-
vides potential applications for the efficient transformation and
utilization of biomass resources, which is of great significance in
terms of sustainable economic and ecological development.
13 O. F. Aldosari, J. Saudi Chem. Soc., 2019, 23, 938–
946.
14 W. B. Gong, C. Chen, Y. Zhang, H. J. Zhou, H. M. Wang,
H. M. Zhang, Y. X. Zhang, G. Z. Wang and H. J. Zhao, ACS
Sustainable Chem. Eng., 2017, 5, 2172–2180.
15 C. P. Jiménez-Gómez, J. A. Cecilia, D. Durán-Martín,
R. Moreno-Tost, J. Santamaría-González, J. Mérida-Robles,
R. Mariscal and P. Maireles-Torres, J. Catal., 2016, 336,
107–115.
16 S. Bhogeswararao and D. Srinivas, J. Catal., 2015, 327, 65–
77.
17 P. Panagiotopoulou and D. G. Vlachos, Appl. Catal., A,
2014, 480, 17–24.
18 Y. Nakagawa, K. Takada, M. Tamura and K. Tomishige, ACS
Catal., 2014, 4, 2718–2726.
19 M. Manikandan, A. K. Venugopal, A. S. Nagpure,
S. Chilukuri and T. Raja, RSC Adv., 2016, 6, 3888–3898.
20 J. Zhang and J. Z. Chen, ACS Sustainable Chem. Eng., 2017,
5, 5982–5993.
Conflicts of interest
There are no conflicts to declare.
21 M. Manikanddan, A. K. Venugopal, K. Prabu and R. K. Jha,
J. Mol. Catal. A: Chem., 2016, 417, 153–162.
22 M. Sankar, N. Dimitratos, P. J. Miedziak, P. P. Wells,
C. J. Kiely and G. J. Hutchings, Chem. Soc. Rev., 2012, 41,
8099–8139.
Acknowledgements
We greatly acknowledge the financial support from the National
Natural Science Foundation of China (21991102, 21776017, 23 S. T. Thompson and H. H. Lamb, ACS Catal., 2016, 6, 7438–
21521005, 21627813), the Joint Funds of the National Natural 7447.
Science Foundation of China (U19B6002) and the Fundamental 24 K. Fulajtárova, T. Soták, M. Hronec, I. Vávra, E. Dobročka
Research Funds for the Central Universities (XK1802-6).
and M. Omastová, Appl. Catal., A, 2015, 502, 78–85.
This journal is © The Royal Society of Chemistry 2021
Dalton Trans., 2021, 50, 2616–2626 | 2625

View Article Online
Paper
Dalton Transactions
25 N. Pino, S. Sitthisa, Q. H. Tan, T. Souza, D. López and 47 S. S. Liu, G. L. Fan, L. Yang and F. Li, Appl. Catal., A, 2017,
D. E. Resasco, J. Catal., 2017, 350, 30–40. 543, 180–188.
26 S. De, J. G. Zhang, R. Luque and N. Yan, Energy Environ. 48 A. M. Zheng, S. J. Huang, S. B. Liu and F. Deng, Phys.
Sci., 2016, 9, 3314–3347. Chem. Chem. Phys., 2011, 13, 14889–14901.
27 M. Villaverde, T. F. Garetto and A. J. Marchi, Catal. 49 D. Ávila-Brande, R. Perezzan, E. Urones-Garrote and
Commun., 2015, 58, 6–10. L. C. Otero-Díaz, Inorg. Chem., 2011, 50, 4640–4646.
28 F. J. Liu, W. P. Kong, L. Wang, X. F. Yi, I. Noshadi, 50 M. K. Dongare, A. M. Dongare, V. B. Tare and E. Kemnitz,
A. M. Zheng and C. Z. Qi, Green Chem., 2015, 17, 480–489. Solid State Ionics, 2002, 152–153, 455–462.
29 Z. Gao, L. Yang, G. L. Fan and F. Li, ChemCatChem, 2016, 8, 51 S. Ram and A. Mondal, Appl. Surf. Sci., 2004, 221, 237–247.
3769–3779.
52 Z. Y. Wang, Y. Lu, S. Yuan, L. Y. Shi, Y. Zhao, M. H. Zhang
and W. Deng, J. Colloid Interface Sci., 2013, 396, 9–15.
53 M. A. Rahman, S. Rout, J. P. Thomas, D. McGillivray and
K. T. Leung, J. Am. Chem. Soc., 2016, 138, 11896–11906.
54 Z. M. Ma, X. Meng, C. Yang, N. W. Liu, Y. T. Zhang and
L. Shi, Ind. Eng. Chem. Res., 2017, 56, 5598–5606.
55 Y. Matsunaga, H. Yamazaki, T. Yokoi, T. Tatsumi and
J. N. Kondo, J. Phys. Chem. C, 2013, 117, 14043–14050.
56 W. Li, Y. Z. Li, G. L. Fan, L. Yang and F. Li, ACS Sustainable
Chem. Eng., 2017, 5, 2282–2291.
30 Q. Wu, F. J. Liu, X. F. Yi, Y. C. Zou and L. L. Jiang, Green
Chem., 2018, 20, 1020–1030.
31 W. L. Li, S. Z. Liu, H. Y. Wang, B. Gao, C. Y. Tu and
Y. B. Luo, Catal. Commun., 2020, 133, 105845.
32 R. Cohen, C. R. Graves, S. T. Nguyen, J. M. L. Martin and
M. A. Ratner, J. Am. Chem. Soc., 2004, 126, 14796–14803.
33 L. Bui, H. Luo, W. R. Gunther and Y. Román-Leshkov,
Angew. Chem., Int. Ed., 2013, 52, 8022–8025.
34 R. S. Assary, L. A. Curtiss and J. A. Dumesic, ACS Catal.,
2013, 3, 2694–2704.
35 J. L. Song, L. Q. Wu, B. W. Zhou, H. C. Zhou, H. L. Fan,
57 K. Shimizu, T. N. Venkatraman and W. G. Song, Appl.
Catal., A, 2002, 224, 77–87.
Y. Y. Yang, Q. L. Meng and B. X. Han, Green Chem., 2015, 58 H. G. Yu, H. J. Fang, H. L. Zhang, B. J. Li and F. Deng,
17, 1626–1632. Catal. Commun., 2009, 10, 920–924.
36 H. Li, S. Yang, A. Riisager, A. Pandey, R. S. Sangwan, 59 H. Chen, H. H. Ruan, X. L. Lu, J. Fu, T. Langrish and
S. Saravanamurugan and R. Luque, Green Chem., 2016, 18,
5701–5735.
37 C. T. Wang, Z. Q. Liu, L. Wang, X. Dong, J. Zhang,
X. Y. Lu, Mol. Catal., 2018, 445, 94–101.
60 W. Li, G. L. Fan, L. Yang and F. Li, ChemCatChem, 2016, 8,
2724–2733.
G. X. Wang, S. C. Han, X. J. Meng, A. M. Zheng and 61 M. A. Aramendía, V. Borau, C. Jiménez, J. M. Marinas,
F. S. Xiao, ACS Catal., 2018, 8, 474–481.
38 M. Koehle and R. F. Lobo, Catal. Sci. Technol., 2016, 6,
3018–3026.
39 F. Wang and Z. H. Zhang, ACS Sustainable Chem. Eng.,
2017, 5, 942–947.
J. R. Ruiz and F. J. Urbano, Appl. Catal., A, 2003, 244, 207–
215.
62 Q. Hu, L. Yang, G. L. Fan and F. Li, ChemNanoMat, 2016, 2,
888–896.
63 From http://webbook.nist.gov/.
40 E. Hernández-Ramírez, J. A. Wang, L. F. Chen, M. A. Valenzuela 64 G. Allen and H. J. Bernstein, Can. J. Chem., 1955, 33, 1055–
and A. K. Dalai, Appl. Surf. Sci., 2017, 399, 77–85. 1061.
41 X. Tang, L. Hu, Y. Sun, G. Zhao, W. W. Hao and L. Lin, RSC 65 V. K. Díez, C. R. Apesteguía and J. I. D. Cosimo, Catal.
Adv., 2013, 3, 10277–10284. Today, 2000, 63, 53–62.
42 C. Battilocchio, J. M. Hawkins and S. V. Ley, Org. Lett., 66 G. M. González Maldonado, R. S. Assary, J. Dumesic and
2013, 15, 2278–2281. L. A. Curtiss, Energy Environ. Sci., 2012, 5, 6981–6989.
43 J. Wang, S. Jaenicke and G. K. Chuah, RSC Adv., 2014, 4, 67 R. González, R. Martínez and P. Ortiz, Macromol. Chem.
13481–13489. Phys., 1992, 193, 1–9.
44 V. G. Deshmane and Y. G. Adewuyi, Microporous 68 M. Boronat, A. Corma and M. Renz, J. Phys. Chem. B, 2006,
Mesoporous Mater., 2012, 148, 88–100. 110, 21168–21174.
45 W. P. Cao, J. Kang, G. L. Fan, L. Yang and F. Li, Ind. Eng. 69 V. A. Ivanov, J. Bachelier, F. Audry and J. C. Lavalley, J. Mol.
Chem. Res., 2015, 54, 12795–12804. Catal., 1994, 91, 45–59.
46 S. P. Wei, Y. T. Zhao, G. L. Fan, L. Yang and F. Li, Chem. 70 M. X. Su, W. Z. Li, T. W. Zhang, H. S. Xin, S. Li, W. Fan and
Eng. J., 2017, 322, 234–245.
L. L. Ma, Catal. Sci. Technol., 2017, 7, 3555–3561.
2626 | Dalton Trans., 2021, 50, 2616–2626
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