G. Zhang et al. / Journal of Catalysis 379 (2019) 100–111
101
interlayer space, constructing a host-guest supramolecular struc-
ture. Such structural flexibility and versatility of LDHs make them
promising catalyst precursors. Correspondingly, a variety of readily
available, highly active, and stable supported metal catalyst
systems can be fabricated through structural transformation
reduced according to the identical procedure to that for Ni-
MoO /Al -500. The calcined NiAl-CO -LDH was denoted as
NiAl-MMO, while the reduced NiAl-MMO was denoted as Ni/
Al -500. In addition, commercial Al and MoO (99%, Alfa
Aesar) supported Ni catalysts (im-Ni/Al and im-Ni/MoO ) with
x
2
O
3
3
2
O
3
2
O
3
3
2
O
3
3
[
26–30]. Recently, we have reported highly dispersive Ni-based
the Ni loading of about 35% were prepared by an incipient wetness
impregnation method.
catalysts derived from Ni-containing LDH precursors for efficiently
catalyzing the selective hydrogenation of LA to GVL using molecu-
lar hydrogen [3].
2.2. Characterization
x
In this work, we developed a new MoO -decorated Ni-based
catalyst system for liquid-phase selective hydrogenolysis of GVL
to produce 1,4-PDO and 2-MTHF, which was derivable from a
X-ray diffraction (XRD) patterns were obtained on a Shimadzu
XRD-6000 diffractometer with Cu Ka radiation. The metal content
was analyzed on Shimadzu ICPS-75000 inductively coupled plasma
emission spectrometer (ICP–AES). Raman spectra of samples were
collected from a microscopic confocal Raman spectrometer (Jobin
Yyon Horiba HR800) using Ar laser of 514 nm wavelength as the
excitation source. Fourier transform infrared (FTIR) spectra were
recorded on a Bruker Vector-22 spectrometer. Low temperature
6
-
molybdate (Mo
the reduction temperature of catalyst precursors, the generation of
surface defective MoO species (i.e. low-coordinated molybdenum-
7
O24) intercalated NiAl-LDH precursor. By adjusting
x
+
oxygen vacancy pairs) was governed. It was demonstrated that
efficiently controlling the adsorption and activation of carbonyl
group in GVL by surface defective MoO species could significantly
x
promote the selective cleavage of C@O bond and its adjacent C-O
bond of ester group in GVL to generate 1,4-PDO and 2-MTHF. The
present work provides a representative example for efficiently
modulating the surface defective structure of Ni-based catalysts,
thus rationally governing the activation of reactant molecules
and enhancing the selectivity of desired products in the upgrading
of biomass-derived oxygenates.
N
2
adsorption-desorption experiments were conducted on
Micromeritics ASAP 2020 absorptometer. X-ray photoelectron
spectra (XPS) were recorded from a Thermo VG ESCALAB 250 X-
ray photoelectron spectrometer using Al Ka X-ray of 1486.6 eV.
The microstructure of samples was determined using transmission
electron microscopy (HRTEM, JEOL2100). Positron annihilation
spectroscopy (PAS) was carried out on a fast/slow coincidence
22
ORTEC system in the transmission mode using
Na as the
radioactive positron source at Beijing Synchrotron Radiation
2
. Experimental
Facility. Temperature programmed decomposition (TPDE),
temperature-programmed reduction (H -TPR) and
temperature-programmed desorption (H
were conducted on Micromeritics ChemiSorb 2920 using a thermal
conductivity detector (TCD). For H -TPR, the sample (100 mg) was
degassed under Ar flow at 200 °C for 2 h to remove adsorbed water
on the surface. During H -TPR process, a cold trap was applied to
H
H
2
2
2
2.1. Catalyst preparation
2
-TPD) of the samples
Nitrate-type NiAl-LDH was prepared by a traditional coprecipi-
2
tation method. First, Ni(NO
3
)
2
ꢁ6H
2
O (0.04 mol) and Al(NO
3
)
3 2
ꢁ9H O
(
0.02 mol) were dissolved in 100 ml of decarbonated deionized
2
water. Subsequently, the above salt solution was titrated by NaOH
solution (1.2 M) under vigorous agitation under nitrogen atmo-
sphere at room temperature, until the pH value reaches 8.0. The
resulting suspension was aged at 70 °C for 24 h under nitrogen
atmosphere, centrifuged and washed with decarbonated deionized
remove the formed water due to the reduction, and the tempera-
ture of cold trap was set below ꢀ88.5 °C by mixing liquid nitrogen
with isopropanol. Afterwards, TPR measurement was performed in
ꢀ1
a
flow of 10%
H
2
/Ar (30 ml min
) with a heating rate of
ꢀ1
10 °C min from 50 to 900 °C. For TPDE, NiMoAl-MMO (100 mg)
was reduced in a flow of H /Ar gas of 10% H /Ar (50 ml min ) at
2 2
ꢀ1
water for several times to obtain NiAl-NO
Molybdate intercalated NiAl-LDH precursor (NiAl-Mo
was prepared by an ion-exchange method. First, NiAl-NO
was dispersed into 100 ml of decarbonated deionized water. Sub-
sequently, (NH Mo (0.04 mol) was dissolved in
24ꢁ4H
00 ml of decarbonated deionized water. Then the salt solution
3
-LDH sample.
7
O
24-LDH)
-LDH
400 °C and was degassed under Ar flow at 200 °C for 2 h. After-
ward, the temperature was raised from 50 to 900 °C under Ar flow
3
ꢀ
1
at a ramping rate of 10 °C min . For H
2
-TPD, the sample (100 mg)
ꢀ1
4
)
6
7
O
2
O
was reduced in a flow of H /Ar gas of 10% H /Ar (50 ml min ) at a
2
2
1
certain reduction temperature and was degassed under Ar flow at
was titrated by LDH dispersion solution under vigorous agitation
and nitrogen atmosphere at room temperature. Meanwhile, the
pH value of the solution was controlled at 5.0 ± 0.2 by dilute nitric
acid (0.2 M). After titration, the resulting suspension was aged at
200 °C for 2 h. After that, the reduced sample was treated in a flow
of H
was desorbed in a flow of Ar at a ramping rate of 10 °C min . In
addition, H -TPD experiments using mass spectrometer detector
(UK HIDEN QIC-20) also were carried out under the identical pro-
cedure to that for H
-TPD experiments using TCD detectorꢁNH
2
/Ar gas mixture and held for 2 h at 25 °C. Finally, chemisorbed
ꢀ1
H
2
2
7
0 °C for 18 h and centrifuged. The precipitate was washed with
decarbonated deionized water for several times and dried at
0 °C overnight under vacuum to obtain NiAl-Mo 24-LDH. Then
NiAl-Mo 24-LDH was calcined in static air at 500 °C for 4 h to
2
3
-
7
7
O
TPD experiments were performed using a chemical adsorption
instrument (Thermo Fisher TPDRO-1100). In situ FTIR spectra of
GVL adsorbed on samples were obtained on a Nicolet 380 type
spectrophotometer. First, the pressed thin slice sample was placed
into an IR cell and heated to 200 °C and held for 1 h under nitrogen
atmosphere. After cooling to 25 °C, GVL was introduced and bal-
anced for 2 h. Finally, FTIR spectra were recorded under vacuum.
7
O
obtain Ni-Mo-Al mixed metal oxide (denoted as NiMoAl-MMO).
Finally, NiMoAl-MMO put into the quartz tube was reduced in a
1
2
0% (v/v) H
°C/min and held for 4 h to obtain reduced Ni-MoO
/Al -500 and Ni-MoO /Al -600 samples. After cooling
2
/Ar flow at 400, 500 and 600 °C at a ramping rate of
x 2 3
/Al O -400,
Ni-MoO
x
2
O
3
x
2 3
O
to room temperature, the quartz tube was filled with nitrogen and
the obtained reduced Ni-based catalyst was placed in a glove box
2
H pulse chemisorption was conducted using a Micrometric Che-
miSorb 2920 chemisorption instrument Oxygen consumption
amount (OC, mol/g) of Ni-based samples was obtained via oxygen
pulse injection method. First, the reduced sample was purged in a
He flow (40 ml/min) and heated to 200 °C for 0.5 h. After cooling to
25 °C, a mixed O /He flow (1:9, v/v) was injected periodically until
2
the oxygen signal kept unchanged. Considering that an oxygen
and sealed in a sample tube filled with N
ples from being exposed to air before characterization and reac-
tions. For comparison, carbonate-type NiAl-LDH (NiAl-CO -LDH)
was prepared according to the identical procedure to that for
NiAl-NO -LDH in the presence of a mixed base solution of NaOH
1.2 M) and Na CO (0.6 M). NiAl-CO -LDH was calcined and
2
to prevent reduced sam-
3
3
(
2
3
3
atom to metallic Ni atom stoichiometric factor is 1:1, the amount