Hydrogenative Ring-Rearrangement of Biobased Furanic Aldehydes to Cyclopentanone Compounds over Pd/Pyrochlore by Introducing Oxygen Vacancies

Article abstract of DOI:10.1021/acscatal.0c01666

Upgrading furanic aldehydes (such as furfural or 5-hydroxymethyl furfural) to cyclopentanone compounds (such as cyclopentanone or 3-hydroxymethyl cyclopentanone) is of great significance for the synthesis of high-value chemicals and biomass utilization. Developing an efficient reduced metal/acidic support with Lewis acidity is the key to facilitating the carbonyl hydrogenation and hydrolysis steps in the hydrogenative ring-rearrangement reaction. Herein, three pure Lewis acidic pyrochlore supports of the form A2B2O7 (La2Sn2O7, Y2Sn2O7, and Y2(Sn0.7Ce0.3)2O7-δ) with the same crystal structures and different metals are synthesized. The Lewis acidity and the surface properties of the pyrochlore can be tuned by inserting different kinds of A and B site metals. After impregnation, Pd nanoparticles with appropriate particle sizes are uniformly loaded on the surface of pyrochlore. For the reaction of the furanic aldehydes, all of these pyrochlore-based catalysts exhibit hydrogenation and hydrolysis rates that are both faster than those of traditional support-based catalysts due to the oxygen vacancy and pure Lewis acidity of the support. Among these pyrochlore-based catalysts, Pd/Y2Sn2O7 exhibits activity and selectivity that are higher than those of Pd/La2Sn2O7. Moreover, the Y2Sn2O7-based catalyst partially substituted by Ce3+ ions at the B site is more efficient, with the highest cyclopentanone yield and 3-hydroxymethyl cyclopentanone yield of 95.0percent and 92.5percent, respectively. Furthermore, the catalyst can still maintain an effective activity and stability after 4 runs. This study not only presents an efficient biobased route for the production of cyclopentanone compounds but also focuses on the acid catalytic performance of pyrochlore based on its pure Lewis acidity.

Full text of DOI:10.1021/acscatal.0c01666

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Article
Hydrogenative ring-rearrangement of bio-based
furanic aldehydes to cyclopentanone compounds
over Pd/pyrochlore by introducing oxygen vacancies
Qiang Deng, Rui Gao, Xiang Li, Jun Wang, Zheling Zeng, Ji-Jun Zou, and Shuguang Deng
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.0c01666 • Publication Date (Web): 10 Jun 2020
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ACS Catalysis
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Hydrogenative ring-rearrangement of bio-based furanic
aldehydes to cyclopentanone compounds over Pd/pyrochlore
by introducing oxygen vacancies
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a
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a
a
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Qiang Deng *, Rui Gao , Xiang Li , Jun Wang , Zheling Zeng , Ji-Jun Zou , Shuguang Deng *
a Key Laboratory of Poyang Lake Environment and Resource Utilization (Nanchang University) Ministry of Education,
School of Resource, Environmental and Chemical Engineering, Nanchang University, Nanchang 330031, PR China
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b Key Laboratory for Green Chemical Technology of the Ministry of education, School of Chemical Engineering and
Technology, Tianjin University; Collaborative Innovative Center of Chemical Science and Engineering (Tianjin), No.92
Weijin Road, Tianjin 300072, China
c School for Engineering of Matter, Transport and Energy, Arizona State University, 551 E. Tyler Mall, Tempe, AZ 85287,
USA
*
Corresponding Author. E-mail: dengqiang@ncu.edu.cn (Qiang Deng); Shuguang.Deng@asu.edu (Shuguang Deng).
KEYWORDS: hydrogenative ring-rearrangement; furanic aldehydes; Pd/pyrochlore; Lewis acidity; oxygen vacancy
ABSTRACT: Upgrading furanic aldehydes (such as furfural or 5-hydroxymethyl furfural) to cyclopentanone compounds (such as
cyclopentanone or 3-hydroxymethyl cyclopentanone) is of great significance for the synthesis of high-value chemicals and biomass
utilization. Developing an efficient reduced metal/acidic support with Lewis acidity is the key to facilitating the carbonyl
hydrogenation and hydrolysis steps in the hydrogenative ring-rearrangement reaction. Herein, three pure Lewis acidic pyrochlore
2 2 7 2 2 7 2 2 7 2 2
supports of the form A B O (La Sn O , Y Sn O , Y (Sn0.7Ce0.3) O7-) with the same crystal structures and different metals are
synthesized. The Lewis acidity and the surface properties of the pyrochlore can be tuned by inserting different kinds of A and B site
metals. After impregnation, Pd nanoparticles with appropriate particle sizes are uniformly loaded on the surface of pyrochlore. For
the reaction of the furanic aldehydes, all of these pyrochlore-based catalysts exhibit hydrogenation and hydrolysis rates that are both
faster than those of traditional support-based catalysts due to the oxygen vacancy and pure Lewis acidity of the support. Among
these pyrochlore-based catalysts, Pd/Y
2 2 7 2 2 7
Sn O exhibits activity and selectivity that are higher than those of Pd/La Sn O . Moreover,
3
+
the Y Sn -based catalyst partially substituted by Ce ions at the B site is more efficient, with the highest cyclopentanone yield
2
2 7
O
and 3-hydroxymethyl cyclopentanone yield of 95.0% and 92.5%, respectively. Furthermore, the catalyst can still maintain an
effective activity and stability after 4 runs. This study not only presents an efficient bio-based route for the production of
cyclopentanone compounds but also focuses on the acid catalytic performance of pyrochlore based on its pure Lewis acidity.
Introduction
pathway for fine chemicals and to efficiently utilize biomass
resources.
The synthesis of cyclopentanone compounds from furanic
aldehydes is occurred by continuous carbonyl group
hydrogenation, furan ring rearrangement, hydrogenation and
dehydration steps. Usually, the reaction is conducted in
Upgrading renewable biomass to high-valued fine
chemicals is a feasible pathway for achieving a sustainable
resource-based economy. Lignocellulose is the most abundant
bio-based organic matter, which can be continuously
hydrolyzed, dehydrated and generated furanic aldehydes (e.g.,
furfural (FFA) or 5-hydroxymethyl furfural (HMF)) [1,2].
These furanic aldehydes have been considered as bio-based
platform compounds for the preparation of various fine
chemicals, such as linear alcohols, 5-furancarboxylic acid,
tetrahydrofuran, 2,5-furandicarboxylic acid, 2-methylfuran,
aqueous solutions (140-190 °C, 2.0-8.0 MPa H
under a reduced metal-supported solid acid catalyst [14].
Currently, various acidic metal oxides (such as TiO and
Nb ), zeolites (such as Hβ, HZSM-5, and SBA-15), metal-
2
pressure)
2
2
O
5
organic frameworks (such as Cr-MIL-101 and Cu-MOF) and
carbon materials are used as supports for the reaction.[9,10,
15-22] Usually, catalysts with non-acidic support (such as
carbon) need a higher reaction temperature and hydrogen
pressure because of their weak catalytic ability in the
hydrolysis of the hydrogenated product of furfural aldehydes
2
,5-dimethylfuran,
2,5-dihydroxymethyltetrahydrofuran,
cyclopentanone (CPO), 3-hydroxymethyl cyclopentanone
(HCPN) [3-10]. Among these fine chemicals, cyclopentanone
compounds (e.g., CPO, HCPN) are important building blocks
for resins, lysine, vitamins, lubricating oils, and high-density
biofuels [11,12], because of the reactivity of hydroxyl and
carbonyl groups. At present, CPO is mainly prepared from
fossil-derived adipic acid [13]. However, HCPN has not been
(i.e., 2,5-bis(hydroxymethyl)furan and furfuryl alcohol). It is
widely accepted that the type of acidity has an important effect
on the reaction. A Lewis acid promotes the synthesis of the
target product by ring-opening and intramolecular aldol
reactions, and a Brønsted acid easily triggers the generation of
macromolecular humins via the intermolecular coupling
reaction of active intermediates [23]. These traditional
supports with Lewis and Brønsted acid character exhibit an
commercially synthesized yet. Hence, the route of
synthesizing cyclopentanone compounds from bio-based
furanic aldehydes is promising to provide a sustainable
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unsatisfactory catalytic effect on the reactions because of the
acidity is provided by the coordinated unsaturated metal
generation of low-value humins. Recently, we reported some
noble metals supported on a metal-organic framework
exhibiting pure Lewis acidity that produced a considerable
yield of the target product for the reaction [10, 24, 25]. The
type of noble metal (i.e., Pd, Pt, Ru, and Au) is optimized, and
the Pd nanoparticles exhibit an excellent catalytic performance
due to their excellent C=O hydrogenation ability. However,
the MOF support is usually unstable under the reaction
conditions.
cation. Meanwhile, the acidity and specific surface area of
these catalysts can be controlled by adjusting the kind of A
and B site cations. Compared with traditional supported
2 2 5
catalysts (Pd/Hβ, Pd/TiO , and Pd/Nb O ), the Pd/pyrochlore
exhibits a higher catalytic performance because of the strong
Lewis acidity, high Pd particle dispersion, and great
accessibility of the active sites. Among these Pd/pyrochlore
catalysts, Pd/Y (Sn Ce ) O possesses the best catalytic
2
0.7
0.3 2 7-
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performance, with the complete conversion of furanic
aldehydes, achieving selectivity of cyclopentanone compounds
of greater than 91%. Moreover, the catalyst exhibits a stable
recycled performance.
Pyrochlore (format as A
metal oxides with a Fm3m space group and cubic unit cell. It
is a defective fluorite-type crystal structure (format as B ),
where the B cation is coordinated by eight oxygen ions (Figure
A). When half of the eight-coordinated B cation (a large
2 2 7 2 2 6
B O or A B O O’) is ternary
4
O
8
Experimental
Materials
1
radius, typically trivalent rare earth elements) is replaced by
six-coordinated A cation (a small radius, usually a tetravalent
transition metal elements), the topological structure is
transformed from fluorite to pyrochlore [26]. O’ and O anions
are sited at the 8b and 48f sites with mm and 43m site
symmetries, respectively. The A and B metal cations are sited
at the 16c and 16d sites respectively, both with 3m site
symmetry. The 48f oxygen anions are linked to two A and two
B cations, and the 8b oxygen anions are linked to four B
cations. In the pyrochlore structure, the 8a oxygen anions are
vacant (Figure 1B). Besides the natural oxygen vacancies, the
oxygen vacancies can be further generated when the B-site
cation is isomorphically substituted by another C metal cation
Furfural,
(Na SnO ·3H
(La(NO ·6H
(Y(NO ·6H O),
(Ce(NO ·6H
palladium chloride (PdCl
ammonia,
O), lanthanum
O), yttrium
2
cerium
sodium
stannate
nitrate
nitrate
nitrate
trihydrate
hexahydrate
hexahydrate
hexahydrate
2
3
2
3
)
3
2
3
)
3
3
)
3
2
O), sodium dihydrogen phosphate (NaH
), and sodium carbonate (Na
2
PO
CO
4
),
3
)
2
2
were supplied by Sinopharm Chemical Reagent Company.
Acetone was obtained from the Aladdin Reagent Company. 5-
Hydroxymethyl furfural (99%) and TiO
were purchased from Beijing Coupling Technology Company.
Nano Nb was supplied by Shanghai Chaoqin New Material
Technology Company. The Hβ (SiO /Al = 25) was obtained
2
(Degussa P25) power
2
O
5
2
2 3
O
from Tianjin Nankai Catalysts Company, and calcined in air
for 6 h at 550 °C. Other chemicals were directly used without
further treatment.
with
a
lower valence based on the principle of
electroneutrality (Figure 1C) [27-29]. In the field of
photocatalysis and electrocatalysis, these surface oxygen
defects can change the valence state of the metal cation and
build a hole in the band structure, leading to a rapid oxygen
generation rate for the oxygen evolution reaction [30-35] and
photocatalytic water splitting [36]. In contrast, in the field of
thermocatalysis, pyrochlore is rarely reported. Currently,
pyrochlore is mainly used in the dry reforming of methane
Preparation of the pyrochlore support
La
by a hydrothermal method. For La
of La(NO ·3H O (or 7.70 g of Y(NO
Na SnO ·3H O, and 80 mL of water were mixed and then
2
Sn
2
O
7
, Y
2
Sn
2
O
7
and Ce-doped Y
2
Sn
and Y
·6H
2
O
7
are synthesized
Sn , 8.70 g
O), 5.40 g of
2
Sn
2
O
7
2
2 7
O
3
)
3
2
3
)
3
2
2
3
2
adjusted the pH of 9.0 via ammonium hydroxide.
Subsequently, the mixture was added to a 100 mL Teflon-
lined autoclave and heated at 200 °C for 24 h. The resultant
solid was obtained by filtration, washed by water, dried
overnight at 150 °C, and then calcined at 800 °C for 6 h in an
[37], the oxidative coupling of methane [38], ethanol steam
reforming [39], the catalytic transformation of ethanol into
acetone [40], water gas shift reactions [41], and the catalytic
reforming of liquid fuels into synthesis gas [42]. These oxygen
vacancies are favorable for these reactions involving oxygen-
containing compounds. However, these reactions are
oxidation-reduction reactions. The pyrochlore has not been
reported in the field of acid reactions, nor has it been
mentioned in complicated biomass conversion reactions,
including acid catalysis and reduced metal catalysis.
air atmosphere. For Ce-doped
Ce(NO ·6H O, 7.70 g of Y(NO
Na SnO ·3H
pH of 9.0 via ammonium hydroxide, and heated at 200 °C for
24 h. The synthesized Y 7- was obtained by
filtration, washed, dried, and calcined using the same process
used to prepare La Sn and Y Sn . The element analysis
Y
2
Sn
2
O
7
,
2.17
g
of
3
)
2
2
3
)
3
·6H
2
O, 5.40 g of
2
3
2
O, and 70 mL of water were mixed, adjusted to a
2
2
(Sn0.7Ce0.3) O
2
2
O
7
2
2 7
O
shows that the molar ratio of Y:Sn:Ce is 1:0.7:0.3, which is
consistent with the molar ratio of the three metal precursors.
The Ce-doped
Y
2
Sn
2
O
7
compound is denoted as
2 2 7-
Y (Sn0.7Ce0.3) O .
Preparation of the Pd/Pyrochlore catalysts
A PdCl solution was impregnated onto the pyrochlore
supports via an incipient method. Typically, 1 g of pyrochlore,
a certain amount of PdCl , and 10 mL of water were
2
Figure 1. One-eighth of the unit cell of (A) fluorite (B
pyrochlore (A ) and (C) B-site substituted pyrochlore
(B 7-). The substitution of B with C cation of low
4 8
O ), (B)
2
2 7
B O
2
4
+
(A
2
x 1-x 2
C ) O
thoroughly mixed, and the mixture was heated at 80 °C, dried
overnight at 110 °C and calcined at 400 °C for 4 h in an air
valence states results in a lattice vacancy of oxygen.
atmosphere. If not mentioned, the PdCl
the Pd content on the support surface is 5.0wt%, which is
proved by the element analysis. As a comparison, the TiO -,
2
content is 0.88 g, and
Herein, a class of pyrochlore-supported Pd nanoparticle
bifunctional catalysts with pure Lewis acidity is prepared for
the production of cyclopentanone compounds. The pure Lewis
2
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Nb
process.
Catalyst characterizations
O
-, Hβ-supported catalysts are synthesized via the same
adsorbed furfural. In situ ATR-IR spectra of the solid-liquid
interface was recorded.
Results and discussion
2
5
The X-ray diffraction (XRD) was determined by a
Panalytical Empyrean diffractometer with a Cu target and Cu-
K radiation. The X-ray photoemission spectroscopy (XPS)
was obtained by an ESCALAB 250Xi with a monochromatic
Al anode X-ray gun. The morphology and particle size of the
samples were determined using a JEM-2100 transmission
electron microscope (TEM). The pore textural properties and
Structural characteristics of the Pd/pyrochlore catalyst
The XRD patterns of the pyrochlore and the corresponding
Pd-supported catalysts are displayed in Figure 2A. All of the
samples display the intense diffraction peaks typical of the
2 2 7
pure A Sn O (A = La, Y) crystalline phase (2θ = 28.7, 33.3,
4
7.8, and 56.8°), proving that the pyrochlore phase has been
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successfully synthesized, and the precipitation of a secondary
phase did not occur by the simple hydrothermal method. The
elemental analysis data exhibit that the A:B site metal molar
the specific surface areas were obtained by performing N
2
adsorption-desorption at -196 °C on an ASAP 2046 surface
analyzer. The elemental analysis was carried out on an
OPTIMA 5300DV inductively coupled plasma-atomic
emission spectrometer. The acid-base properties were
characterized by determining the temperature-programmed
desorption of ammonia (NH
TPD) on a HUASI DAS-7200 instrument. Temperature-
programmed reduction (H -TPR) were performed on a
ratios of La
:0.98, 1:0.97) are close to the expected stoichiometry of
2 7-
pyrochlore (i.e., 1) (Table 1). Meanwhile, Y (Sn0.7Ce0.3) O
2 2 7 2 2 7 2 2
Sn O , Y Sn O , Y (Sn0.7Ce0.3) O7- (i.e., 1:1.02,
1
2
4+
3+
with Sn : Ce molar ratio of approximately 0.7: 0.3 exhibits a
3
-TPD) and carbon dioxide (CO
2
-
4+
similar XRD pattern with Y
2
Sn
partially replaced by Ce , which will not change the crystal
structure of the Y Sn pyrochlore type. However, as the A-
2 7
O , indicating that Sn is
3+
2
2
2 7
O
Micromeritics AutoChem II 2920. The acid type was analyzed
by performing pyridine-adsorbed infrared spectroscopy using
a Bruker VERTEX 70 spectrometer. Catalyst was tabled to
3+
3+
4+
site cation La with replaced with Y or the B site Sn cation
is partially doped by Ce , the position of the diffraction peaks
3+
has shifted to a larger angle, indicating that the lattice
parameter of pyrochlore decreases. According to the literature,
2
wafer (10 mg/cm ), degassed and dewatered under vacuum at
2
6
00 °C for 1 h, and the pyridine adsorption was performed at
0 °C for 30 min. Then, the temperature gradually increased to
3+
3+
the ionic radius of La and Y is 0.106 and 0.09 nm,
respectively [43], and a smaller cation leads to smaller lattice
150 °C and 250 °C, and the spectra was recorded. The signal
detected at 150 °C and 250 °C was attributed to total acid sites
and strong acid sites, respectively.
3+
parameters. Meanwhile, the Ce ion has a larger ionic radius
4+
than Sn (0.103 vs 0.07 nm). To maintain electrical neutrality,
the partial substitution leads to the formation of oxygen
vacancies, which also decrease the lattice parameters.
Although the Pd content is approximately 5wt% after
impregnation, the Cl content is not detected due to the thermal
Catalytic reactions
Typically, 10.4 mmol of furanic aldehydes, 40 mL of water,
and 0.1 g of catalyst were added into a 100 mL stainless-steel
autoclave from Anhui Kemi Machinery Technology Co., Ltd..
The hydrogen was purged to replace the air for 4 times, and
kept at a 4.0 MPa hydrogen pressure. Subsequently, the
mixture was stirred at a rate of 600 rpm, and heated to 150 °C,
and sampled periodically. 1 mL of the resultant product
mixtures was removed from the reactor, extracted by 2 mL
ethyl acetate, and 20 µL of internal standard substance (N,N-
dimethyl formamide) was added. The concentrations of
products were analyzed by a Trace 1300 gas chromatograph
equipped with a TG-WAXMS capillary column (30 m × 0.32
mm) and a flame ionization detector (FID). The carbon loss
was defined as humins.
decomposition of PdCl
2
during the preparation conditions (400
°
C, 4 h)[44]. The XRD patterns of the catalyst are almost the
same as those of the corresponding supports, confirming that
Pd nanoparticles are well dispersed on the surface. Moreover,
the XRD of Pd/TiO
characteristic peak of anatase TiO
Nb crystals, without the characteristic peak of Pd
nanoparticles (Figure S1) [45,46].
The N adsorption-desorption isotherms in Figure 2B show
that all of the catalysts exhibit IV type isotherms and H3 type
hysteresis rings, which indicated the existence of
mesoporous pore structure generated by particle accumulation.
Compared with Pd/La Sn , the Y-contained Pd/Y Sn has
2
and Pd/Nb
2
O
5
only show the
2
and pseudohexagonal
2
O
5
2
a
In situ Attenuated total reflection infrared (ATR-IR)
measurements
The ATR-IR spectroscopy was acquired with a Nicolet iS
2
2
O
7
2
2 7
O
2
a larger specific surface area of 66.7 m /g and a larger pore
volume of 0.258 cm /g (Table 2). After Ce modification, the
3
5
0 spectrometer installed with a highly sensitive MCT detector
2 2
specific surface area of Pd/Y (Sn0.7Ce0.3) O7- increases to 89.5
and a heating chamber equipped with CaF windows. The
ethanol suspension of the catalyst was dropwise added onto
the surface of the diamond probe equipped on the instrument
and dried at 100 °C. ATR-IR spectra were recorded with
averaging 32 scans at the resolution of 2 cm . To simulate
catalytic reaction conditions, the catalyst was firstly reduced at
2
3
m /g, while the pore volume decreases to 0.131 cm /g. These
results indicate that replacing the A and B site metal changes
the particle size of pyrochlore. The Pd/TiO
2 2 5
and Pd/Nb O
2
-1
possess low specific surface areas of 44.6 and 10.6 m ·g ,
-1
3
-1
pore volumes of 0.321 and 0.028 cm ·g , respectively.
1
2
50 °C for 1 h in a 5% H /Ar flow, and the background
spectrum was recorded before adding of the substrate.
Subsequently, the liquid furfural was introduced into the
surface of the catalyst by bubbling with an Ar gas stream
(flow rate of 40 mL/min). The adsorption of furfural was
conducted at 150 °C for 30 min, and the Ar gas stream (flow
rate of 40 mL/min) was used to remove the physically
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Table 1. Element analysis of Pd/pyrochlore.
Pd content
(wt %)
4.98
Cl content
La content
Y content
(wt %)
-
Sn content
(wt %)
25.88
Ce content
Molar ratio of
A:B
Molar ratio of
Samples
(wt %)
(wt %)
(wt %)
Sn:Ce
Pd/La
Pd/Y
Pd/Y
2
Sn
2
O
7
-
-
-
29.44
-
-
1: 1.02
-
-
2
Sn
2
O
7
4.95
-
-
21.16
26.51
27.67
1: 0.98
2
(Sn0.7Ce0.3
)
2
O
7-
5.01
24.39
11.88
1:0.97
0.7:0.3
2
-1
Pd/Hβ shows a specific surface area of 510.2 m ·g and pore
To investigate the influence of the acid-base properties of
the catalyst, NH and CO -TPD tests were carried out, as
shown in Figure 3, Figure S5 and Figure S6. Obviously, the
NH -TPD result shows that all the pyrochlore-based catalysts
exhibit a much higher acid amount than that of the TiO - and
Nb -based catalysts. For the pyrochlore-based sample, two
desorption peaks appear at 200 and 400 °C, which was
attributed to the acidity of the coordinated unsaturated B-site
metal sites, respectively. The acid strength is described by the
NH
Pd/Y
than that of Pd/La
277 °C). Furthermore, CO
2
these Pd/pyrochlore possess a large amount of basic site
because of the rare earth metals.[38] Subsequently, IR spectra
of the in-situ adsorbed pyridine were used to detect the acid
types. The acid density of Lewis and Brønsted acidic sites was
calculated using the Emeis equation (Table 2, Figure S7) [48].
The pyridine-adsorbed FTIR spectra of the pyrochlore-, TiO2-
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
3
-1
volume of 0.503 cm ·g due to their microporous structure
Figure S2). As shown by TEM, the pyrochlore crystal size of
Pd/La Sn is obviously larger than that of Pd/Y Sn and
Pd/Y 7- (Figure 2 C, D, E). The Pd clusters are
uniformly and randomly dispersed on the surfaces of all
pyrochlore and other supports (i.e., TiO , Nb , Hβ) in the
range of 3-5 nm (Figure S3). The distribution of Pd
nanoparticles was further evaluated by H -TPR (Figure S4).
3
2
(
2
2
O
7
2
2
O
7
3
2
(Sn0.7Ce0.3
)
2
O
2
2
O
5
2
2
O
5
2
All Pd supported catalysts have an obvious peak below 100 °C,
which has an approximate peak area. These results indicate
that Pd is easily reduced and the dispersion degree of Pd is
3
-desorbed temperature. Among the Pd/pyrochlore,
7- (210, 308 °C) shows a stronger acidity
Sn (182, 261 °C) and Pd/Y Sn (179,
-TPD result in Figure S6 indicates
2
2
(Sn0.7Ce0.3) O
2
2
O
7
2
2 7
O
similar in these catalysts. According to the result of H
2
-TPR, a
peak that appeared above 500 °C is attributed to the reduction
4
+
of Sn of pyrochlore supports[47].
180
150
120
90
B
Pd/La2Sn2O7
Pd/Y2Sn2O7
A
0.012
0.006
0.000
Pd/Y2(Sn0.7Ce0.3)2O7-
La Sn
O
7
2
2
Pd/La Sn
O
7
2
2
7
Y
Sn
O
5
10
15
20
25
30
2 5
and Nb O -based samples treated at 150 °C exhibit peaks at
1450 cm and very weak peaks at 1540 cm . This confirms
the pure Lewis acidity of the pyrochlore, TiO , and Nb
2
2
Pore size (nm)
-1
-1
60
Pd/Y Sn
O
2
2
7
2
2 5
O
Y
(Sn0.7Ce0.3)
O
2
2
7-
30
0
supports. On the contrary, in addition to exhibiting Lewis
acidity, zeolite Hβ exhibits a considerable Brønsted acidity.
Due to the similar topology of three pyrochlore, the acid
amount of Pd/pyrochlore is positively correlated with the BET
area. Because of the larger specific surface area, more active
coordinated metal sites are exposed. In particular,
Pd/Y2(Sn0.7Ce0.3)2
O
7-
0.0
0.2
0.4
0.6
0.8
1.0
10
20
30
40
50
60
70
80
90
2 
P/P
0
2 2
Pd/Y (Sn0.7Ce0.3) O7- exhibits the highest Lewis acid amount
of 0.046 mmol/g, as shown in Table 2. Meanwhile, the acid
density of strong Lewis acidic sites was calculated based on
the signal detected 250 °C. Agreed with the result of NH
the Pd/Y (Sn0.7Ce0.3) O7- shows the highest strong Lewis acid
3
-TPD,
Figure 2. (A) X-ray diffraction patterns of pyrochlore, (B) N
adsorption-desorption isotherms and pore diameter distribution of
pyrochlore-based catalysts and TEM micrographs of (C)
2
2 2
amounts of 0.032 mmol/g (Figure 3B).
B0.05
Total Lewis
Strong Lewis
2 2 7 2 2 7 2 2 7-
Pd/La Sn O , (D) Pd/Y Sn O , (E) Pd/Y (Sn0.7Ce0.3) O .
0.04
Table 2. Physicochemical properties of catalysts.
0.03
0.02
0.01
Total
Lewis
Acid
Amount
(mmol/g)
Strong
Lewis
Acid
Amount
(mmol/g)
Pore
Brønsted
Acid
Amount
Alkali
Amount
S
BET
2
Samples
Volume
(m /g)
3
(
cm /g)
(mmol/g)
0.00
(mmol/g)
b 2O 5
/N
O 7
Sn 2
S
Pd/
Y 2
O 7
-
O 7
iO 2
Pd/T
n 2
) 2
Pd
/
L
a 2
Ce 0
.3
P
d
n 0.7
Pd/TiO
Pd/Nb
Pd/Hβ
Pd/La Sn
Sn
2
44.6
10.6
510.2
20.9
66.7
0.321
0.028
0.503
0.054
0.258
0.006
0.006
0.044
0.018
0.041
0.003
0.004
0.032
0.009
0.023
0.001
0.001
0.151
0.001
0.001
0.008
0.009
/
(S
Pd/
Y 2
2
O
5
3
Figure 3. (A) NH -TPD profile and (B) Lewis acid amount
detected by pyridine-adsorbed FTIR spectra of catalysts.
2
2
O
7
0.029
0.033
The surface properties were further investigated by XPS for
the catalysts (Figure 4). The Pd 3d XPS spectra of the
supported catalyst shows that peaks appear at 335.1 and 340.8
eV (attributed to the 3d5/2 and 3d3/2 peaks of Pd(0)) as well as
Pd/Y
2
2 7
O
Pd/Y
2
(Sn0.7
Ce0.3) O
2 7-
8
9.5
0.131
0.046
0.032
0.001
0.037
3
37.8 and 343.2 eV (ascribed to the 3d5/2 and 3d3/2 peaks of
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Pd(II)) [49]. Agreed with the result of H
-TPR, Pd(II) can be
three obvious advantages. First, the conversion of FFA is
increased from 51.0% to 91.1% within 6 h by the acceleration
of the C=O hydrogenation reaction. Secondly, the selectivity
of THFA is decreased from 11.0% to 2.0%, and the furan ring
hydrogenation reaction is completely inhibited. Thirdly, the
selectivity of FA decreased from 8.1% to 5.1% and the
selectivity of humins decreased from 14.8% to 1.9%.
2
in-situ reduced to Pd(0) under the reaction conditions, which is
confirmed by the XPS spectrum of the used catalysts (Figure
S8) [50]. The weak peak around 200 eV may be ascribed to
the trace residue Cl on the catalyst surface. Meanwhile, the
XPS peaks of O1s has two peaks (O
I
and OII) at 530.0 and
is
5
31.7 eV for all pyrochlore-based catalysts [51]. The O
I
attributed to the lattice oxygen, and the OII is attributed to the
surface-adsorbed oxygen species on oxygen vacancies. After
O
B100
O
OH
Hydration
Dehydration
O
Hydrogenation
O
FFA
FA
CPO
A
THFA
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
4+
3+
O
O
80
Humin
partial substitution of Sn by Ce , the OII/O
of Pd/Y 7- is obviously higher than Pd/Y
0.91 vs 0.71). Combined with the result of NH -TPD, the
I
peak area ratio
FA
FFA
PED
Aldol
Hydrogenation
2
(Sn0.7Ce0.3
)
2
O
2
Sn
2
O
7
60
OH
O
(
3
4
0
0
0
oxygen vacancies are further created and then the B-site cation
is isomorphically substituted by another metal cation with a
lower valence based on the principle of electroneutrality.
HO HCPEO
Hydrogenation
THFA
O
O
2
Dehydration
Hydrogenation
Combined with the result of NH
3
-TPD and Py-FTIR, the
0
1
2
3
4
5
6
CPO
HO
HCPO
Reaction time (h)
3
+
incorporation of Ce in the pyrochlore leads to the formation
of oxygen vacancies and further exposure of the coordinative-
C100
80
D 100
80
FFA
FA
CPO
FFA
THFA
CPO
Humin
FA
THFA
4
+
unsaturated Sn .
Humin
60
Pd(II)
Pd(0)
Pd/La Sn
2
O
60
2
7
Pd(0)
OII/O =0.67
I
OI
40
Pd(II)
O1s
40
20
OII
Pd3d
20
0
yst
t c Ce 0.3
-
O 7
d/H b 2
O 7
al
Pd
/C
O 5
iO 2
/T
O 7
n 2 Sn 2
S
-
O 7
) 2
at
)
2
P
Pd
/N
P
d
a 2 /Y 2
d/L
Pd
ou
Ce 0
.3
0
With
(Sn 0.7
P
Sn 0.7
0
1
2
3
4
5
6
(
Y 2
Pd/
Y 2
Pd/Y Sn
O
Reaction time (h)
2
2 7
OII/O =0.71
I
Figure 5. (A) The reaction pathway of FFA reaction; (B), (C)
product concentration over Pd/TiO and Pd/Y Sn ; (D) catalytic
performance of FFA reaction over various catalysts. Reaction
conditions: H O (40 mL), catalyst (0.1 g), FFA (10.4 mmol),
temperature 150 °C, time 6 h, 4.0 MPa H pressure.
2
2
2 7
O
2
2
Pd/La (Sn Ce ) O
2
0.7 0.3 2 7-
OII/O =0.91
I
Figure 5D further evaluates the catalytic performance of
other catalysts. The reaction without catalyst or with only
pyrochlore show no FFA conversion and CPO yield, because
the hydrogen cannot be activated. Pd/C exhibits a high
hydrogenation activity, whereas basically no CPO is generated
due to the lack of acid sites. All of the conventional metal
1
000
800
600
400
200
0346 344 342 340 338 336 334 332 330
536
534
532
530
528
526
Binding Energy (eV)
2 2 5
oxide-supported Pd catalysts (Pd/TiO , Pd/Nb O , Pd/Hβ)
Figure 4. XPS spectra of Pd/pyrochlore.
show a mass generation of humins by the Brønsted acidity
catalysis. Pd/Nb O and Pd/TiO possess a relatively high CPO
Hydrogenative ring-rearrangement of furfural
2
5
2
As shown in Figure 5A, the hydrogenative ring-
rearrangement of furfural (FFA) to cyclopentanone (CPO)
involves a hydrogenation reaction to form furfuryl alcohol
selectivity, whereas their catalytic activities are low, and a
large amount of THFA is generated because of the furan ring
hydrogenation reaction. These results indicate that the
promotion of C=O hydrogenation and furan ring hydrolysis
and inhibition of furan ring hydrogenation are extremely
challenging for the selective synthesis of cyclopentanone. All
the pyrochlore-based catalysts exhibit a better activity and
selectivity than the traditional metal-oxide-based catalysts
because the pyrochlore-based catalysts have a large number of
oxygen vacancies and a Lewis acidity. Interestingly, among
these pyrochlore-based catalysts, the order of the FFA
conversion agreed with the amount of oxygen vacancies:
Pd/Y (Sn Ce ) O (99.9%, 0.91) > Pd/Y Sn O (91.1%,
(
FA), hydrolysis ring-opening reaction to form 2-pentene-1,4-
dione (PED), intramolecular aldol reaction to form 4-hydroxy-
-cyclopentenone (HCPEO), then hydrogenation, dehydration
2
reactions to form CPO. A trace amount of PED, HCPEO, and
HCPO is detected by GC-MS, indicating that the reactivity of
intramolecular aldol and dehydration are fast. Figure 5B, 5C
2 2 2 7
shows the catalytic kinetics under Pd/TiO and Pd/Y Sn O
catalysis. A large amount of FFA and FA exhibits that the
carbonyl group hydrogenation and hydrolysis reactions are the
rate-limiting steps. With increasing reaction time, FA is
gradually transformed, and CPO is gradually generated. The
concentration of FA intermediate first increased and then
decreased. The active carbonyl, furan ring, and hydroxyl
groups in FA, intermediates and CPO can easily result in a
carbon loss by some intermolecular coupling reactions.
Interestingly, some by-products of tetrahydrofurfuryl alcohol
2
0.7
0.3 2 7-
2
2
7
0.71) > Pd/La Sn O (83.4%, 0.67). According to previous
2
2
7
work, the strong Lewis acidity is favorable for the hydrolysis
of FA[10,24]. Meanwhile, the order of the CPO selectivity
agreed with the amount of strong Lewis acid sites:
Pd/Y
Pd/Y
2
(Sn0.7Ce0.3
)
2
O
7-
(95.1%, 0.032 mmol/g)
>
2 7
2
Sn
O
2 7
(91.0%, 0.023 mmol/g) > Pd/La Sn O
2
(
(
THFA) are created via the furan ring hydrogenation of FA
Figure 5A). Compared with Pd/TiO , Pd/Y Sn possesses
2 2
(87.6%, 0.009 mmol/g). The Pd/Y (Sn0.7Ce0.3) O7- catalyst
2
2
2 7
O
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with the largest amount of oxygen vacancies and strong Lewis
selectivity of HCPN also agreed with the order of the strong
Lewis acid amount: Pd/Y (Sn Ce ) O (92.6%, 0.032
acid sites exhibits a satisfactory catalytic performance, with a
FFA conversion of 99.9%, CPO selectivity of 95.1% and CPO
yield of 95.0%. To further promote the catalytic effect of
Pd/pyrochlore, the Pd loading content was optimized, and 5
wt% Pd/pyrochlore produces the highest yield of CPO (Figure
S9). The initial reaction solution before and after adding
catalyst was neutral with a pH of 7.0. Then, as pH value was
2
0.7
0.3 2 7-
mmol/g) > Pd/Y Sn O (76.4%, 0.023 mmol/g) > Pd/La Sn O
7
2
2
7
2
2
(60.0%, 0.009 mmol/g). Finally, after 12 h, the conversion
over Pd/ Y (Sn Ce ) O is 99.9%, the selectivity is 92.6%,
2
0.7
0.3 2 7-
and the yield is 92.5%. Besides, compared with the result of
our previous study catalyzed by a MOF-based catalyst, the
stronger acidity of the pyrochlore-based catalyst more easily
catalyzes the intramolecular aldol reaction and produces a high
yield of HCPN (92.5% vs 82.0%) [10].
adjusted from 7.0 to 5.8 and 4.5 by the weak acidic NaH
2 4
PO
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(Figure S10), the presence of Brønsted acid in the acidic
solution causes carbon loss rather than the generation of CPO
[52,53]. Meanwhile, as pH was increased from 7.0 to 10.5 by
AHO
O
HO
Hydrogenation
OH
Hydration
O
B100
O
O
HMF
HHD
HCPN
OH
Dehydration
THBHF
the basic Na
2
CO
3
, the ring-opening reaction is completely
O
HHED
O
80
Humin
HMF
BHF
Hydrogenation
Hydrogenation
suppressed and approximately 90% yield of FA and THFA is
obtained.
OH
60
HO
O
OH
O
HHD
Aldol
40
Hydrogenative
ring-rearrangement
of
5-
THBHF
O
hydroxymethylfurfural
O
20
Dehydration
Hydrogenation
These catalysts are also used with 5-hydroxymethyl furfural.
5-hydroxymethyl furfural (HMF) can be converted to 1-
hydroxy-3-hexene-2,5-dione (HHED) through carbonyl
hydrogenation and hydrolysis ring-opening steps similar to
those of the furfural reaction (Figure 6A). These intermediates
HO
0
HO
0
3
6
9
12
HO
HCPN
HHCPN
Reaction time (h)
C 100
80
D
100
HMF
THBHF
HCPN
Humin
HHD
HMF
HHD
HCPN
THBHF
8
6
0
0
Humin
(
e.g., 2,5-bis(hydroxymethyl)furan (BHF), HHED) are verified
by GC-MS. In contrast to the FA reaction, the large amount of
-hydroxyl-2,5-hexanedione (HHD) that existed in the
60
40
20
0
1
4
0
reaction mixture shows that 4-hydroxy-4-hydroxymethyl-2-
cyclopentanone (HHCPN) has been synthesized from the
hydrolyzed intermediate HHED, which occurs during the first
hydrogenation step; then, the intramolecular aldol reaction
proceeds rather than the first intramolecular aldol reaction, and
then hydrogenation occurs in the furfural reaction. In contrast
to the results of our previous study catalyzed by MOF, the
BHF concentration is very low catalyzed the metal oxide-
based catalyst because the hydrolysis reaction is very fast
because of the strong Lewis acidity of pyrochlore[10]. The
result indicates that the rate-limiting steps in the HMF reaction
are the carbonyl hydrogenation and intramolecular aldol
reactions. Compared with the intramolecular aldol of PED to
HCPEO in the CPO synthesis, the hydroxymethyl group in
HHD transfers electrons to the carbonyl group, thus reducing
the aldol reactivity [54]. Moreover, the steric hindrance of
hydroxymethyl group further makes the synthesis of 3-
hydroxymethyl cyclopentanone (HCPN) more difficult. To
synthesize HCPN with a high yield, the reaction time was
extended to 12 h. Similarly, the excessive hydrogenation and
intermolecular C-C coupling reactions produce the THFA and
humin by-products. Likewise, the time-dependent product
curve indicates that Pd/pyrochlore exhibits a better activity
20
0
yst 3) 2O 7-Pd/C /H

O 7
O
7
-
tal
d/Nb 2 Pd
O 5
/T 2Sn
iO 2
2
O
7
2Sn
2
)
2
ca .7Ce 0.
(
P
d
/Y 0.7Ce 0.3
ut
P
/L
a
d
itho
Sn
0
Pd
P
d
n
0
3
6
9
12
2(S
w
Y
2
/Y
Reaction time (h)
P
Figure 6. (A) The reaction pathway of HMF reaction; (B), (C)
product concentration over Pd/TiO and Pd/Y Sn ; (D) catalytic
performance of HMF reaction over various catalysts. Reaction
conditions: H O (40 mL), catalyst (0.1 g), HMF (10.4 mmol),
2
2
2 7
O
2
2
temperature 150 °C, time 12 h, 4.0 MPa H pressure.
Reaction mechanism
To more clearly explain the excellent performance of
Pd/pyrochlore, kinetic studies of the FFA hydrogenation step
and the FA hydrolysis step are performed. For the
0
hydrogenation step, plotting the ln(C/C ) of FFA with respect
to time results in a linear relationship, which suggests that the
FFA hydrogenation reaction is pseudo-first-order reaction
(Figure S11). The hydrogenation kinetics constant is strongly
dependent on the amount of oxygen vacancies:
-
1
-1
Pd/Y (Sn Ce ) O (1.29 h , 0.91) > Pd/Y Sn O (0.41 h ,
2
0.7
0.3 2 7-
2
2
7
-1
0.71) > Pd/La Sn O (0.30 h , 0.67 ) (Figure 7C). According
2
2
7
to previous work, the oxygen vacancy easily selectively fixes
and promotes the C=O hydrogenation [51,55]. To understand
the mechanism of oxygen vacancy, in-situ attenuated total
reflection infrared spectra (ATR-IR) were employed to gain
some molecular insight into the adsorption and surface species
present on the catalysts under the reaction conditions (Figure
7A). The spectra of the pristine furfural clearly show peaks at
2
and selectivity than Pd/TiO due to the higher catalytic activity
of the carbonyl hydrogenation, hydrolysis, and intramolecular
aldol reactions (Figure 6B, C).
Figure 6D also evaluates the catalytic performance of other
catalysts. Blank experiment, pure pyrochlore, Pd/C, Pd/TiO
2
,
-1
Pd/Nb and Pd/Hβ show unsatisfactory catalytic conversion
2
O
5
756, 933, 1020 (related to the furan ring ) and 1675 cm
or selectivity. The pyrochlore-based catalysts exhibit a higher
activity of HMF and selectivity toward HCPN than traditional
support-based catalysts. Likewise, the order of the HMF
conversion agreed with the amount of oxygen vacancies:
(related to the carbonyl structure) [56]. For Pd/TiO , peaks
2
correlated to the furan ring and carbonyl groups have been
-1
redshifted about 20 and 30 cm . The strong interaction of both
furan and carbonyl groups with catalyst suggests flat
Pd/Y
.71) > Pd/La
aldol condensation reactions are also catalyzed by acids, the
2
(Sn0.7Ce0.3
)
2
O
7- (99.9%, 0.91) > Pd/Y
2
Sn
2
O
7
(96.8%,
adsorption of furfural on the Pd/TiO
contrast, the spectra of adsorbed furfural on Pd/Y
a remarkable red shifted of the carbonyl band (by 20 cm ),
2
surface [57,58]. In
0
2
Sn
2
O
7
(95.0%, 0.67). Because the rate-limiting
2
Sn shows
2 7
O
−1
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3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
whereas the furan ring bands remain unchanged compared
with the pristine furfural, indicating that Pd/Y Sn only
absorb carbonyl of furfural via a vertical configuration. This
adsorption configuration ensures highly selective carbonyl
hydrogenation, and the low yield of THFA by-product over all
Pd/pyrochlore catalysts. Meanwhile, the adsorption kinetic of
hydrolysis steps, which are based on Pd/pyrochlore possessing
the most oxygen vacancies and Lewis acid amounts, and alkali
amounts. To verify whether the conversion of HCPEO from
2
2
O
7
FA proceeds through
a two-step of hydrolysis and
intramolecular aldol reaction mechanism or a one-step of
Piancatteli reaction mechanism, FA is used as the reactant and
a certain amount of acetone is added to the reaction system. It
is worth mentioning that HCPEO is unstable in water phase,
which is easy to aggregate to form humins unless a rapid
hydrogenation conversion. PED and HCPEO can be detected
by GC-MS when no acetone is added (Figure S14A, Figure
S15). After addition of acetone, since the intermolecular aldol
reaction rate of PED is faster than that of intramolecular aldol,
the aldol product of PED and acetone can be detected instead
of HCPEO (Figure S14B, Figure S15). The result
demonstrates the two-step mechanism of the ring-
rearrangement catalyzed by pyrochlore.
furfural from H
Figure 7B, Figure S12). Figure 7B shows the adsorption
quality of Y Sn is obviously higher than TiO . The result
clearly elucidate the positive influence of the oxygen vacancy.
2 2 2 7 2
O over Y Sn O and TiO support is studied
(
2
2
O
7
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
B 50
A
FFA+Pd/Y Sn
2
FFA+Pd/TiO
2
O
TiO
2
2
7
C=O
Y
Sn O
2 2 7
furan ring
FFA
40
30
2
0
0
0
1
Catalyst stability and reusability
The reusability of the catalyst was determined by the FFA
reaction. The spent catalyst was centrifuged, washed by water,
2
500
2000
1500
1000
0
5
10
15
20
25
30
-1
Wavenumber (cm
)
Time (min)
C 1.5
D 1.2
dried before the use for next runs. After
Pd/Y 7- shows a high FFA conversion rate of
9.6%, and the CPO selectivity of 91.2% (Figure 8). The XRD
4 runs,
2
2
(Sn0.7Ce0.3) O
1.0
0
0
0
.8
9
and XPS data of the reused catalysts exhibits that the
pyrochlore crystals and oxygen vacancy have been retained
0.5
.4
2
(Figure 8B, Figure S8, Table S1). The N adsorption-
0
.0
0
desorption results indicate the stability of the physical
structure (Figure S16, Table S1). This result exhibits that
these Pd/pyrochlore catalysts are efficient and stable.
.0
0.00
.6
0.7
0.8
/O
0.9
1.0
0.02
0.04
O
Ⅰ
Ⅰ
Lewis acid amount (mmol/g)
Figure 7. (A) ATR-IR spectra of FFA adsorbed on different
catalysts, (B) adsorption kinetics of FFA under Y Sn , and
TiO (C) Relationship between oxygen vacancies and
2
2 7
O
1
00
80
60
B
,
A
FFA
CPO
2
hydrogenation rate of FFA; (D) Relationship between acid
amount and FA hydrolysis rate. Adsorption conditions: 0.0015 g
FFA, 0.05 g catalyst, 30 mL H O, temperature 30 °C.
2
Before reaction
After reaction
4
0
For the FA hydrolysis step, to remove the effect of the FA
hydrogenation, the reaction is carried out under nitrogen
atmosphere. Likewise, the hydrolysis step of FA has also
followed pseudo-first-order kinetics (Figure S13). According
20
0
1
2
3
4
10
20
30
40
50
60
70
80
90
Recycle times
2 
to the result of Py-FTIR and NH
3
-TPD, the result is that the
Figure 8. (A) Recycling performance of the Pd/Y
in FFA reaction. Reaction conditions:
Pd/Y 7- (0.1 g), FFA (10.4 mmol), reaction time 6
h, 4.0 MPa H pressure, temperature 150 °C; (B) XRD diffraction
2 2 7-
(Sn0.7Ce0.3) O
hydrolysis kinetics constant is dependent on the strong Lewis

2
H O (40 mL),
-1
acid amount of the catalyst: (1.07 h , 0.032 mmol/g) >
2
2
(Sn0.7Ce0.3) O
-1
-1
Pd/Y
2 2 7 2 2 7
Sn O (0.93 h , 0.023 mmol/g) > Pd/La Sn O (0.84 h ,
2
0
.009 mmol/g) (Figure 7D). More acidic sites are beneficial to
patterns of Pd/pyrochlore before and after four catalytic runs.
the hydrolysis of FA because the Lewis acid sites are more
easily accessible to the reactant. Exceptionally, Hβ with a high
acid amount exhibits a relatively weak ability to hydrolyze due
to their small pore size. Interestingly, in the absence of a
catalyst, FA can undergo a slow transformation catalyzed by
the hydrogen proton formed by auto-dissociation of water
under the reaction temperature (150°C) (Figure S13) [59].
According to the results of the reaction solution with different
pH, homogeneous Brønsted acid in the solution is not
conducive to ring-rearrangement reaction, but the
intermolecular C-C coupling for the formation of humins. The
low amount of humins over pyrochlore-based catalysts can be
attributed to a large amount of basic site, which can neutralize
the in-situ generated hydrogen proton, and guarantee the real
pure Lewis acid catalysis. These results show that the great
catalytic performance of pyrochlore-based catalysts is
ascribable to the high efficiency of the hydrogenation and
Conclusion
A series of highly tunable pyrochlore-supported Pd catalysts
were developed for the bio-based preparation of
cyclopentanone compounds. The oxygen vacancies and Lewis
acid amount have a great influence on the hydrogenation and
hydrolysis steps, respectively. Various pure Lewis acidities
and oxygen vacancies can be tuned by the substitution or
partial substitution of the A and B site metal ions in the
A B O pyrochlore structure. Compared with the traditionally
2
2
7
supported catalysts Pd/Nb O and Pd/TiO , the pyrochlore
2
5
2
catalyst with abundant oxygen vacancies and a strong Lewis
acidity exhibits a much higher activity and selectivity. Among
3
+
2
0.7
0.3 2 7-
the pyrochlore catalysts, the Ce -doped Y (Sn Ce ) O
catalyst exhibits the best performance, with cyclopentanone
compound yields above 92%, due to the largest specific
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surface area, highest oxygen vacancies and highest strong
furanic aldehydes to cyclopentanone compounds. J. Catal. 2019, 378,
01-208.
11] Deng, Q.; Nie, G.; Pan, L.; Zou, J.; Zhang, X.; Wang, L. Highly
selective selfcondensation of cyclic ketones using MOF-encapsulating
phosphotungstic acid for renewable high-density fuel. Green Chem.
2015, 17, 4473-4481.
2
[
Lewis acid amount. In addition, the pyrochlore catalyst
exhibits good stability in the recycling experiment, without
any significant pyrochlore structure degradation and Pd
leaching. This research provides a highly efficient reaction
system for the preparation of cyclopentanone compounds and
extends the application prospects of an adjustable pyrochlore
catalyst.
[12] Li, H.; Deng, Q.; Chen, H.; Cao, X.; Zheng, J.; Zhong, Y.;
Zhang, P.; Wang, J.; Zeng Z.; Deng, S. Benzenesulfonic acid
functionalized hydrophobic mesoporous biochar as an efficient
catalyst for the production of biofuel. Appl. Catal. A:Gen. 2019, 580,
178-185.
[13] Renz, M.; Ketonization of carboxylic acids by decarboxylation:
mechanism and scope. Eur. J. Org. Chem. 2005, 6, 979-988.
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Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acscatal.xxxxxx.
Some catalyst physicochemical properties and catalytic reaction
results, namely, XRD, TEM micrographs, Pyridine-adsorbed
[14] Hronec, M.; Fulajtarová, K.; Soták, T. Highly selective
rearrangement of furfuryl alcohol to cyclopentanone. Appl. Catal. B:
Environ. 2014, 154, 294-300.
[15] Hronec, M.; Fulajtarová, K. Selective transformation of furfural
to cyclopentanone. Catal. Commun. 2012, 24, 100-104.
2 2 3
FTIR spectra, N adsorption-desorption isotherms, H -TPR, NH -
TPD, CO -TPD, XPS spectra, catalytic effect of Pd loading and
2
pH, catalytic kinetics, GC-MS patterns, and UV-vis absorption
spectrum (PDF).
[16] Zhang, G.; Zhu, M.; Zhang, Q.; Liu, Y.; He, H.; Cao, Y. Towards
quantitative and scalable transformation of furfural to cyclopentanone
with supported gold catalysts. Green Chem. 2016, 18, 2155-2164.
[17] Guo, J.; Xu, G.; Han, Z.; Zhang, Y.; Fu, Y.; Guo, Q. Selective
conversion of furfural to cyclopentanone with CuZnAl catalysts. ACS
Sustain. Chem. Eng. 2014, 2, 2259–2266.
Acknowledgments
The authors appreciate the support from the National Natural
Science Foundation of China (21878138, 21706112), Postdoctoral
Science Foundation of China (2018T110660, 2017M622104) and
the start-up funds provided by Nanchang University and Arizona
State University.
[18] Li, X.; Deng, J.; Shi, J.; Pan, T.; Yu, C.; Xu, H.; Fu, Y. Selective
conversion of furfural to cyclopentanone or cyclopentanol using
different preparation methods of Cu-Co catalysts. Green Chem. 2015,
17, 1038-1046.
[19] Wang, Y.; Sang, S.; Zhu, W.; Gao, L.; Xiao, G. CuNi@C
References
catalysts with high activity derived from metal-organic frameworks
precursor for conversion of furfural to cyclopentanone. Chem. Eng. J.
2016, 299, 104-111.
[20] Liu, C.; Wei, R.; Geng, G.; Zhou, M.; Gao, L.; Xiao, G. Aqueous
phase catalytic hydrogenation of furfural over Ni-bearing hierarchical
Y zeolite catalysts synthesized by a facile route. Fuel Process.
Technol. 2015, 134, 168–174.
[21] Ohyama, J.; Kanao, R.; Ohira, Y.; Satsuma, A.; The effect of
heterogeneous acid-base catalysis on conversion of 5-
hydroxymethylfurfural into a cyclopentanone derivative. Green
[1] Sudarsanam, P.; Zhong, R.; Van den Bosch, S.; Coman, S. M.;
Parvulescu, V. I.; Sels, B. F. Functionalised heterogeneous catalysts
for sustainable biomass valorisation. Chem. Soc. Rev. 2018, 47, 8349-
8402.
[2] Huber, G. W.; Chheda, J. N.; Barrett, C. J.; Dumesic, J.
A. Production of liquid alkanes by aqueous-phase processing of
biomass-derived carbohydrates. Science. 2005, 308, 1446.
[3] Hayashi, E.; Yamaguchi, Y.; Kamata, K.; Tsunoda, N.; Kumagai,
Y.; Oba, F.; Hara, M. Effect of MnO crystal structure on aerobic
2
oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid. J.
Am. Chem. Soc. 2019, 141, 890-900.
Chem. 2016, 18, 676-680.
[22] Ohyama, J.; Kanao, R.; Esaki, A.; Satsuma, A. Conversion of 5-
hydroxymethylfurfural to cyclopentanone derivative by ring
[4] Motagamwala, A. H.; Won, W.; Sener, C.; Alonso, D. M.;
a
Maravelias, C. T.; Dumesic, J. A. Toward biomass-derived renewable
plastics: Production of 2,5-furandicarboxylic acid from fructose. Sci.
Adv. 2018, 4, 9722.
rearrangement over supported Au nanoparticles. Chem. Commun.
2014, 50, 5633-5636.
[23] Swift, T. D.; Nguyen, H.; Erdman, Z.; Kruger, J. S.; Nikolakis,
V.; Vlachos, D. G. Tandem Lewis acid/Brønsted acid-catalyzed
conversion of carbohydrates to 5-hydroxymethylfurfural using zeolite
beta. J. Catal. 2016, 333, 149-161.
[24] Li, X.; Deng, Q.; Zhang, L.; Wang, J.; Wang, R. Zeng, Z.; Deng,
S. Highly efficient hydrogenative ring-rearrangement of furanic
aldehydes to cyclopentanone compounds catalyzed by noble
metals/MIL-MOFs. Appl. Catal. A: Gen. 2019, 575, 152-158.
[25] Deng, Q.; Wen, X.; Zhang, P. Pd/Cu-MOF as a highly efficient
catalyst for synthesis of cyclopentanone compounds from biomass-
derived furanic aldehydes. Catal. Commun. 2019, 126, 5-9.
[26] Shimakawa, Y.; Kubo Y.; Manako, T. Giant magnetoresistance
[5] Tan, J.; Cui, J.; Zhu, Y.; Cui, X.; Shi, Y.; Yan, W.; Zhao, Y.
Complete aqueous hydrogenation of 5-hydroxymethylfurfural at room
temperature over bimetallic RuPd/graphene catalyst. ACS Sustainable
Chem. Eng. 2019, 7, 10670-10678.
[6] Kumalaputri, A. J.; Bottari, G.; Erne, P. M.; Heeres, H. J.;
Barta, K. Tunable and selective conversion of 5-HMF to 2,5-
furandimethanol and 2,5-dimethylfuran over copper-doped porous
metal oxides. ChemSusChem. 2014, 7, 2266.
[7] Artz, J.; Mallmann, S.; Palkovits, R. Selective aerobic oxidation of
HMF to 2,5-diformylfuran on covalent triazine frameworks-supported
Ru catalysts. ChemsusChem. 2015, 8, 672-679.
[
8] Xiao, B.; Zheng, M.; Li, X.; Pang, J.; Sun, R.; Wang,
H.; Pang, X.; Wang, A.; Wang, X.; Zhang, T. Synthesis of 1,6-
hexanediol from HMF over double-layered catalysts of Pd/SiO + Ir-
ReOx/SiO in a fixed-bed reactor. Green Chem. 2016, 18, 2175-2184.
2 2 7
in Tl Mn O with the pyr ochlore structure. Nature. 1996, 379, 53-55.
[27] Blundred, G. D.; Bridges, C. A.; Rosseinsky, M. J. New
oxidation states and defect chemistry in the pyrochlore structure.
Angew. Chem. Int. Ed. 2004, 43, 3562-3565.
[28] Hess, N. J.; Begg, B. D.; Conradson, S. D.; McCready, D. E.;
Gassman, P. L.; Weber, W. J. Spectroscopic investigations of the
structural phase transition in Gd (Ti1-yZr ) O Pyrochlores. J.ꢀPhys.
2 y 2 7
Chem.ꢀB. 2002, 106, 4663-4677.
[29] Pakhare, D.; Shaw, C.; Haynes, D.; Shekhawat, D.; Spivey, J.
Effect of reaction temperature on activity of Pt- and Ru-substituted
2
2
[9] Ramos, R.; Grigoropoulos, A.; Perret, N.; Zanella, M.;
Katsoulidis, A. P.; Manning, T. D.; Claridge, J. B.; Rosseinsky, M. J.
Selective conversion of 5-hydroxymethylfurfural to cyclopentanone
derivatives over Cu-Al
Chem. 2017, 19, 1701-1713.
10] Li, X.; Deng, Q.; Zhou, S.；Zou, J.; Wang, J.; Wang, R.; Zeng,
2
O
3
and Co-Al
2
O
3
catalysts in water. Green
[
2 2 7 2
lanthanum zirconate pyrochlores (La Zr O ) for dry (CO ) reforming
Z.; Deng, S. Double-metal cyanide-supported Pd catalysts for highly
efficient hydrogenative ring-rearrangement of biomass-derived
of methane (DRM). J. CO Util. 2013, 1, 37.
2
ACS Paragon Plus Environment

Page 9 of 10
1
ACS Catalysis
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
[30] Shih, P. C.; Kim, J.; Sun, C. J.; Yang, H. Single-Phase
Pyrochlore Y Ir Electrocatalyst on the activity of oxygen evolution
reaction. ACS Appl. Energy Mater. 2018, 1, 3992-3998.
31] Lebedev, D.; Povia, M.; Waltar, K.; Abdala, P. M.; Castelli, I. E.;
[48] Emeis, C. A. Determination of integrated molar extinction
coefficients for infrared absorption bands of pyridine adsorbed on
solid acid catalysts. J. Catal. 1993, 141, 347-354.
[49] Yang, X.; Chen, D.; Liao, S.; Song, H.; Li, Y.; Fu, Z.; Su, Y.
High-performance Pd-Au bimetallic catalyst with mesoporous silica
nanoparticles as support and its catalysis of cinnamaldehyde
hydrogenation. J. Catal. 2012, 291, 36-43.
2
2
O
7
[
Fabbri, E.; Blanco, M. V.; Fedorov, A.; Copéret, C.; Marzari, N.;
Schmidt, T. J. Highly active and stable Iridium pyrochlores for
oxygen evolution reaction. Chem. Mater. 2017, 29, 5182-5191.
[
32] Sun, W.; Liu, J.; Gong, X.; Zaman, W. Q.; Cao, L.; Yang, J.
[50] Hronec, M.; Fulajtárová, K.; Vávra, I.; Soták, T.; Dobročka, E.;
Mičušík, M. Carbon supported Pd-Cu catalysts for highly selective
rearrangement of furfural to cyclopentanone. Appl.ꢀCatal. B-Environ.
2016, 181, 210-219.
[51] Hu, Q.; Yang, L.; Fan, G.; Li, F. Hydrogenation of biomass-
derived compounds containing a carbonyl group over a copper-based
nanocatalyst: Insight into the origin and influence of surface oxygen
vacancies. J. Catal. 2016, 340,184-195.
[52] Yang, Y.; Du, Z.; Huang, Y.; Lu, F.; Wang, F.; Gao, J.; Xu, J.
Conversion of furfural into cyclopentanone over Ni-Cu bimetallic
catalysts. Green Chem. 2013, 15, 1932-1940.
[53] Ohyama, J.; Ohira, Y.; Satsuma, A. Hydrogenative ring-
rearrangement of biomass derived 5-(hydroxymethyl)furfural to 3-
(hydroxymethyl)cyclopentanol using combination catalyst systems of
OER activity manipulated by IrO coordination geometry: an insight
from pyrochlore iridates. Sci. Rep. 2016, 6, 38429.
[33] Parrondo, J.; George, M.; Capuano, C.; Ayers, K. E.; Ramani, V.
Pyrochlore electrocatalysts for efficient alkaline water electrolysis. J.
Mater. Chem. A. 2015, 3, 10819-10828.
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2 2 7
[34] Kim, M.; Ju, H.; Kim, J. Single crystalline Bi Ru O pyrochlore
oxide nanoparticles as efficient bifunctional oxygen electrocatalyst for
hybrid Na-air batteries. Chem.ꢀEng.ꢀJ. 2019,358, 11-19.
[35] Kim, J.; Shih, P. C.; Tsao, K. C.; Pan, Y. T.; Yin, X.; Sun, C. J.;
Yang, H. High-performance pyrochlore-type Yttrium ruthenate
electrocatalyst for oxygen evolution reaction in acidic media. J. Am.
Chem. Soc. 2017, 139, 12076-12083.
[36] Kiss, B.; Didier, C.; Johnson, T.; Manning, T. D.; Dyer, M. S.;
Cowan, A. J.; Claridge, J. B.; Darwent, J. R.; Rosseinsky, M. J.
Photocatalytic water oxidation by a pyrochlore oxide upon irradiation
with visible light: rhodium substitution into yttrium titanate. Angew.
Chem. Int. Ed. 2014, 53, 14480-14484.
Pt/SiO
2953.
2
and lanthanoid oxides. Catal. Sci. Technol. 2017, 7, 2947-
[54] Deng, Q.; Xu, J.; Han, P.; Pan, L.; Wang, L.; Zhang, X.; Zou, J.
Efficient synthesis of high-density aviation biofuel via solvent-free
aldol condensation of cyclic ketones and furanic aldehydes. Fuelꢀ
Process.ꢀTechnol.ꢀ2016, 148, 361-366.
[55] Zhang, S.; Chang, C. R.; Huang, Z. Q.; Li, J.; Wu, Z.; Ma, Y.;
Zhang, Z.; Wang, Yong.; Qu, Y. High catalytic activity and
chemoselectivity of sub-nanometric Pd clusters on porous nanorods of
[
37] Pakhare, D.; Schwartz, V.; Abdelsayed, V.; Haynes, D.;
Shekhawat, D.; Poston, J.; Spivey, J. Kinetic and mechanistic study of
dry (CO ) reforming of methane over Rh-substituted La Zr
pyrochlores. J. Catal. 2014, 316, 78-92.
38] Xu, J.; Zhang, Y.; Xu, X.; Fang, X.; Xi, R.; Liu, Y. Zheng, R.
Wang, X. Constructing La (B = Ti, Zr, Ce) compounds with
2
2
2
O
7
[
2
B
2
O
7
2
CeO for hydrogenation of nitroarenes. J. Am. Chem. Soc. 2016, 138,
2629-2637.
three typical crystalline phases for the oxidative coupling of methane:
the effect of phase structures, superoxide anions, and alkalinity on the
reactivity. ACS Catal. 2019, 9, 4030-4045.
[56] Rogojerov, M.; Keresztury, G.; Jordanov. B. Vibrational spectra
of partially oriented molecules having two conformers in nematic and
isotropic solutions: furfural and 2-chlorobenzaldehyde. Spectrochimꢀ
Acta,ꢀPartꢀA. 2005, 61, 1661-1670.
[57] Ma, M.; Hou, P.; Cao, J.; Liu, H.; Yan, X.; Xu, X.; Yue, H.;
Tian, G.; Feng, S. Simple basic zirconium carbonate: low temperature
catalysis for hydrogen transfer of biomass-derived carboxides. Green
Chem. 2019, 21, 5969-5979.
[58] Gao, R.; Pan, L.; Wang, H.; Yao, Y.; Zhang, X.; Wang, L.; Zou,
J. J. Breaking trade-off between selectivity and activity of Nickel-
based hydrogenation catalysts by tuning both steric effect and d-Band
center. Adv. Sci. 2019, 6, 1900054.
[59] Li, G.; Li, N.; Zheng, M.; Li, S.; Wang, A.; Cong, Y.; Wang X.;
Zhang, T. Industrially scalable and cost-effective synthesis of 1,3-
cyclopentanediol with furfuryl alcohol from lignocellulose. Green
Chem. 2016, 18, 3607-3613.
[39] Musso, M.; Romero, M.; Faccio, R.; Bussi, J. Catalytic
assessment of a Ni-La-Sn ternary metallic system in ethanol steam
reforming and the influence of the Sn/La atomic ratio in the catalytic
performance. Catal. Today. 2019, DOI: 10.1016/j.cattod.2019.05.043.
[40] Bussi, J.; Parodi, S.; Irigaray, B.; Kieffer, R. Catalytic
transformation of ethanol into acetone using copper-pyrochlore
catalysts. Appl. Catal. A:Gen. 1998, 172, 117-129.
[41] Playford, H. Y.; Modeshia, D. R.; Barney, E. R.; Hannon, A. C.;
Wright, C. S.; Fisher, J. M.; Amieiro-Fonseca, A.; Thompsett, D.;
O’Dell, L. A.; Rees, G. J.; Smith, M. E.; Hanna, J. V.; Walton, R. I.
Structural characterization and redox catalytic properties of
Cerium(IV) pyrochlore oxides. Chem. Mater. 2011, 23, 5464-5473.
[42] Haynes, D. J.; Berry, D. A.; Shekhawat, D.; Spivey, J. J.
Catalytic partial oxidation of n-tetradecane using pyrochlores: Effect
of Rh and Sr substitution. Catal. Today 2008, 136, 206-213.
[
43] Xu, X.; Zhang, R.; Zeng, X.; Han, X.; Li, Y.; Liu, Y.; Wang, X.
Effects of La, Ce, and Y oxides on SnO catalysts for CO and CH
oxidation. ChemcatChem 2013, 5, 2025-2036.
44] Wang, H.-F.; Ariga, H.; Dowler, R.; Sterrer, M.; Freund, H.-J.
Surface science approach to catalyst preparation-Pd deposition onto
thin Fe (111) films from PdCl precursor. J. Catal. 2012, 286, 1-5.
45] Yildizhan, M. M.; Sturm S.; Gulgun M. A. Structural and
electronic modifications on TiO anatase by Li, K or Nb doping below
and above the solubility limit. J. Mater. Sci. 2016, 51, 5912-5923.
46] Chai, S.-H.; Wang, H.-P.; Liang, Y.; Xu, B.-Q. Sustainable
2
4
[
3
O
4
2
[
2
[
2 5
production of acrolein: gas-phase dehydration of glycerol over Nb O
catalyst. J. Catal. 2007, 250, 342-349.
[
47] Ma, Y.; Wang, X.; You, X.; Liu, J.; Tian, J.; Xu, X.; Peng, H.;
Liu, W.; Li C.; Zhou, W.; Yuan, P.; Chen, X. Nickel-supported on
La Sn and La Zr pyrochlores for methane steam reforming:
2
2
O
7
2
2 7
O
insight into the difference between Tin and Zirconium in the Bsite of
the compound. ChemcatChem 2014, 6, 3366-3376.
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