Synergistic effects of MOF-76 on layered double hydroxides with superior activity for extractive catalytic oxidative desulfurization

Article abstract of DOI:10.1039/d0nj00612b

The combination of metal-organic frameworks (MOFs) with layered double hydroxides (LDHs) has been greatly limited by the agglomeration of pure MOFs and the height of the LDH gallery, so there are few reports on the combination of MOFs and LDHs. In this work, for the first time, the combination of MOF-76 with a layered double hydroxide (MOF-76?LDH) was used for desulfurization under room temperature and pressure conditions without the necessity of protecting with nitrogen. The structure of the heterogeneous catalyst was characterized using FT-IR, XRD, TG, BET, SEM, EDX, XPS, fluorescence and ICP-AES. The as-prepared catalyst exhibited superior activity in deep desulfurization of DBT (dibenzothiophene), BT (benzothiophene) and 4,6-DMDBT (4,6-dimethyldibenzothiophene). The above sulfides could be completely converted into their corresponding sulfones and sulfoxides at 60 °C in 25, 40 and 55 minutes, respectively. 49 wt% MOF-76?LDH exhibited a high desulfurization capacity (100%), much higher than that of LDH (16.3%), MOF-76 (48%) and MOF-76 + LDH (50.3%). Because MOF-76?LDH has a special one-dimensional channel on the surface of the material, it can efficiently promote the degradation of H₂O₂ into hydroxyl radicals (OH) and further improve the desulfurization effect. The catalyst is easy to recycle and can be reused at least 5 times, and the catalytic effect is not significantly reduced. This provides a completely new route for the synthesis of MOF-LDH advanced functional materials.

Full text of DOI:10.1039/d0nj00612b

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DOI: 10.1039/D0NJ00612B
Synergistic effects of MOF-76 on layered double hydroxides
with superior activity for extractive catalytic oxidative
desulfurization
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Siqi Liu , Xiaonan Li , Hong Zhang *
a
Institute of Polyoxometalate Chemistry, Department of Chemistry, Northeast Normal University,
Changchun, Jilin 130024, PR China
Abstract
Metal-organic frameworks(MOFs) combination with layered hydroxides(LDHs) has been greatly
limited by the agglomeration of pure MOF and the height of LDH gallery, So there are few reports on
the combination of MOF and LDHs. In this work, for the first time, the combination of MOF-76 with
layered double hydroxides (MOF-76@LDH) under room temperature and pressure conditions without
the necessity of protecting with nitrogen used for desulfurization. The structural analysis of the
heterogeneous catalyst were characterized using FT-IR, XRD, TG, BET, SEM, EDX, XPS,
Fluorescence and ICP-AES. The as-prepared catalyst exhibited superior activity in deep desulfurization
of DBT(dibenzothiophene), BT(benzothiophene) and 4,6-DMDBT(4,6-dimethyldibenzothiophene).
The above sulfides could be completely converted into their corresponding sulfones and sulfoxides at
60°C in 25, 40 and 55minutes, respectively. 49wt.% MOF-76@LDH ability to exhibits high
desulfurization capacity (100%), much higher than LDH (16.3%), MOF-76 (48%) and
MOF76+LDH(50.3%). Because MOF-76@LDH a special one-dimensional channel pair on the surface
of the material can efficiently promote H O degrade into hydroxyl radicals(•OH) and further improve
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the desulfurization effect. The catalyst can be easy to recycled and reused at least 5 times and the
catalytic effect is not significantly reduced. This provides a completely new route for the synthesis of
MOF-LDH advanced functional materials.
1
. Introduction
There are huge amount of organic/inorganic species such as SO , NO , CO , unreacted hydrocarbons
x
x
x
including polycyclic aromatic hydrocarbons pollute our environment resulting from the needs of social
development such as industry, daily life and water pollution. For the environment protection and
healthcare concerns, a maximum sulfur content of 10ppm in fuels has been stringently implemented in
America and Europe . Currently, the most widely used diesel desulfurization method is
hydrodesulfurization(HDS) . However, high requirements and the harsh operating conditions for the
instrument restrict its application greatly. In addition, it is difficult to completely remove DBT and its
derivatives. Under these circumstances, oxidative desulfurization(ODS) is an effective way to
supplement HDS, owing to the ODS method's operating conditions is relatively mild. As the most
promising in ODS processes, extractive catalytic oxidative desulfurization(ECODS) , which is the
combination of oxidative desulfurization and extractive desulfurization . As a result, ECODS is
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considered to be a very promising way to produce little or no sulfur content clean fuels, in which H O2
2
is the oxidant and ionic liquids(ILs) are the extractants. ILs can serve as one of the most environmental
benign solvents in desulfurization systems because of their unique physical and chemical properties
such as negligible vapor pressure, high chemical and thermal stabilities and ability to dissolve a wide
range of organic and inorganic compounds. It has been demonstrated that ILs can extract different
aromatic sulfur compounds from diesel and gasoline fuel, with a desulfurization efficiency roughly in
the range 10-30% . In addition, Our group has previously proposed that the IL emulsion catalytic
oxidation process for ultra-deep desulfurization and it is worth clarifying that a deep desulfurization
was achieved with the optimized H O /DBT/MgAlLDH-Mo molar ratio at 60°C using H O as oxidant
and IL as extractant in the ECODS system according to our group and the optimized H O /DBT/
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Mg Al- IL-EuW molar ratio according to Song and coworkers .
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Metal-organic frameworks(MOFs) are a class of crystalline porous materials constructed by metal
ions or clusters and bridging organic ligands . The integration of high surface areas, structured
diversities and tunable pore surface functionalities endows them with the capability of applications in
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gas storage and separation, sensors, catalysis, luminescence and so on
. The metal organic

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DOI: 10.1039/D0NJ00612B
. This because organic chain stabilize the inorganic metals and subsequent
framework which accompany organic and inorganic characteristics are highly promising catalyst for
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the desulfurization
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enhance the overall catalysis stability and activity . However, compared with MOF-derived materials,
unmodified MOF showing relatively low desulfurization capacity due to the agglomeration of pure
MOF. As a result, several MOF-derived materials have also been applied as heterogeneous catalysts to
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activate H O and generate free radicals for the catalytic ODS process
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Layered double hydroxides(LDHs), which contain host-guest layer solids and exchangeable
interlayer anions, their formula representation are [M 1-xM (OH) ] (A ) ·mH O ,where M and
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M
are the divalent and trivalent metal cations , respectively, which are mainly located on the layer
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boards; x represents the molar ratio of M /(M +M ). A is a counter anion, which is intercalated into
the interlayer. LDHs can provide a flexible limited space by adjusting the arrangement and the size of
guest molecules. The flexible limited interlayer space can not only fit small-sized molecules but also
provide bulky catalytic sites that are difficult for not even possible to enter the rigid pores with fixed
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dimension . Therefore, LDHs are ideal supports for bulky MOF catalysts. It is worth noting that the
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trivalent cation of MOF can also constitute the component of material LDHs , which can provide
theoretical support for the synthesis of MOF@LDH composites. As far as we know, there have not
been any reports of catalytic oxidation extraction desulfurization using MOF@LDH composites as
catalysts.
Herein, we designed and prepared of a heterogeneous catalyst, MOF-76@LDH, which was prepared
by the combination of MOF76 with rod LDH. The extractive catalytic oxidative desulfurization
experiments show that 100% desulfurization efficiency in DBT, BT and 4,6-DMDBT can be obtained
using MOF76@LDH as the catalyst , H O as the oxidant and IL as extraction at 60℃ in 25,40 and 55
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min, respectively.
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. Experimental
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.1 Materials
Tb(NO )3·6H O (99%), Benzenetricarboxylic acid(99%), urea(99%), Ca(NO )2·4H O(99%),
Mg(NO )2·6H O(99%), Al(NO )3·9H O(99%), DBT (dibenzothiophene), BT(benzothiophene),
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,6-DMDBT(4,6-dimethyldibenzothiophene), hydrogen peroxide(30 wt% H O ), n-octane(99%).
2 2
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.2 Preparation of the rod LDH and MOF76@LDH heterogeneous catalyst
Rod LDHs were prepared according to references only with slight modifications . Urea(0.160mol,
.6g), Ca(NO )2·4H O(4.023mmol, 0.95g), Mg(NO )2·6H O(7.995mmol, 2.05g),
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Al(NO )3·9H O(5.998mmol, 2.25g) was dissolved in 20ml deionized water and stir vigorously for
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another 2h. The mixture subsequently was poured into a Teflon-lined stainless-steel autoclave and
heated with a rate of 20°C /min and heated at 80°C for 36h. The precipitation collection by vacuum
filtration, subsequently washed with deionized water and ethanol for several times. Then, the
precipitation was dried in a vacuum oven at 80°C overnight. Then, the rod LDH was obtained.
Synthesis of MOF76@LDH: in a typical synthesis, Tb(NO ) ·6H O(0.508mmol, 0.23g),
,3,5-benzenetricarboxylic acid(H BTC)(0.252mmol, 0.053g) were dissolved in 10ml volume ratio(1:1)
3
of N,N′-dimethylformamide(DMF) and deionized water in the beaker and stir vigorously for another 2h.
Then various amounts of rod LDH (0.047, 0.070, 0.100, 0.117 and 0.141g, corresponding to 0.5, 0.75,
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.0, 1.25 and 1.5mmol) were separately placed in the aforementioned beaker and stir vigorously for
another 2h.The mixture was poured into a Teflon-lined stainless-steel autoclave and heated with a rate
of 20°C /min and heated at 80°C for 16h. The precipitation collection by vacuum filtration,
subsequently washed with deionized water and ethanol for several times. Then, the precipitation was
dried in a vacuum oven at 80°C overnight. Then, the obtained composites are denoted x
wt.%MOF76@LDH, where wt.% is the MOF76 Mass percentage in the final product heterogeneous
catalysts, which was calculated according to the inductively coupled plasma atomic emission
spectrometer(ICP-AES) data. The added amount of the MOF76 precursor and the MOF76 final loaded
amount in the MOF76@LDH complex are shown in Table S1†.Therefore, the optimal catalyst
described below was chosen as 49wt.% MOF76@LDH.
2
.3 Characterization
Fourier transform infrared(FT-IR) spectroscopy analysis was carried on a Mattson Alpha-Centauri
infrared spectrometer in the range 4000-400cm . Powder X-ray diffraction(PXRD) analysis was
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carried on a Rigaku D/Max-RA X-ray diffractometer with graphite mono-chromatized Cu/Kɑ radiationV.iew Article Online
Thermogravimetric(TG) patterns were recorded on a PerkinElmer Thermal Analyzer under a nitrogen
atmosphere from 25 to 600°C at a heating rate of 10°C /min. Fluorescence spectra were obtained using
a FLSP920 fluorescence spectrometer(Fluorescence). N2 adsorption-desorption isotherms were
recorded on a Micromeritics V-Sorb 2800p. The Brunauer-Emmett-Teller(BET) and pore width
measurements were carried out at 373.15K on a Micromeritics V-Sorb 2800p analyzer. The
morphology of the catalyst were obtained by a Hitachi SU8010 field emission scanning electron
DOI: 10.1039/D0NJ00612B
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microscope(FE-SEM) and energy dispersive X-ray(EDX) analysis was performed on
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Gatanmul-tipole CCD camera and working voltage of 200kv. X-ray photoelectron spectroscopy(XPS)
analytical data were collected using Thermo Fisher ESCALAB 250 X-ray photoelectron
spectrometer(powered at 150W) with Al κɑ radiation. The MOF76@LDH heterogeneous catalyst was
collected by
a
Leeman Prodigy Spec inductively coupled plasma atomic emission
spectrometer(ICP-AES). GC was analyzed on an Agilent 7820A-GC System equipped with a flame
ionization detector a 25m×0.32mm×0.5μm phenylmethyl silicone capillary column.
2
.4 Extractive catalytic and oxidative desulfurization procedure
In a typical ECODS process, a model oil was prepared according to references that dissolved
DBT(BT or 4,6-DMDBT) in n-octane and mixed in biphenyl as the internal standard , total sulfur
content is 500 ppm. 5mL of simulated oil was added to a 25mL round-bottle flask with water bath
heating and vigorous stirring at 60°C for 10min to activated oil sample. A mixture consisting of the
catalyst (0.01g MOF76@LDH), 15μL of H O (O/S molar ratio =3) and 1mL [Bmim]PF ( prepared as
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mentioned in the references) were mixed into the oil sample, the remaining liquid in the upper oil
sample was taken out periodically. 0.1μL upper layer of the oil sample was injected into a gas
chromatograph to measuring the effect of the desulfurization.
3
. Results and discussion
3
.1 structural analysis
The entire preparation process of MOF76@LDH is illustrated in Fig. S1†, the morphology and
structure of the as-synthesized sample were characterized using the scanning electron
microscope(SEM), we can see that pure LDH with smooth and relatively regular rod morphology, with
an average length of 3μm and MOF76 shows the typical brick-like hole stacking structure.
MOF76@LDH surface displays rougher and exhibits non-uniform rod structure(Fig.3).
Fig.1 (A) FT-IR spectra of MOF76, LDH and MOF76@LDH; (B) XRD patterns of MOF76, LDH
and MOF76@LDH; (C) TG characterization of MOF76@LDH and (D) N adsorption-desorption of
2
MOF76@LDH
The FT-IR spectra of LDH, MOF76 and MOF76@LDH are shown in Fig.1(A). The peaks of LDH
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located at about 3477cm suggests the H-bonds and the -OH group stretching vibration in the
-1
hydroxide layer, the shoulder band at approximately 3185cm can be assigned to the presence of water
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molecules and hydrogen bonding with inner layer carbonate ions, the peak located at about 1376cm
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corresponds to the CO3 adsorption vibrations and peak located at approximately 1099,974,843 and

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32cm can be attributed to the bending vibrations of M-O-H(M is Ca ,Al or Mg , here in) in the
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octahedral layers
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M-O-H red shift by approximately 70cm , showing strong interaction between LDH and the MOF76
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framework . The characteristic IR peaks of MOF76 at about 1619,1355 and 1099cm can be assigned
to the N-H, C-N and C-H bending vibration of aliphatic amines and alkanes, respectively. The
characteristic IR peaks of both LDH and MOF76 can be also obviously found in the IR spectra of
MOF76@LDH complex, for MOF76@LDH, a new adsorption peak at about 1045cm can be
attributed to the M-O lattice vibration. further indicating the successful combination of the MOF76
with LDH.
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The XRD patterns of MOF76, LDH and MOF76@LDH are shown in Fig.1(B), which show lattice
structure and crystal image of the catalyst. The characteristic diffraction peaks of the as-synthesized
MOF76 are highly matched with the simulated spectrum, indicates that MOF76 is successfully
synthesized and has a high degree of crystallinity. For pure LDH, the sharp, symmetric and strong
peaks located at approximately 14.96º, 26.8º and 30.8º can be assigned to the (003), (006) and (009)
planes of LDH , respectively. Based on Bragg equation , the height of LDH gallery is
.97Ǻ(2θ=14.96º, λ=0.15406nm), which is similar to the previously reported literature. The
characteristic XRD peaks of both LDH and MOF76 can be obviously found in the XRD pattern of
MOF76@LDH composites but peak width slightly increased, peaks shift to a smaller angles. This
probably indicates that synergistic effects between MOF76 active metal component and LDH carriers.
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The thermogravimetric(TG) curve of MOF76@LDH is shown in Fig.1(C), three stages of
weight-loss can be noticed as the increase of temperature from 27 to 600°C . The first weight-loss of 5%
occur from 27 to 101°C , which can be assigned to the elimination of small molecular solvents(H O,
DMF) from the surface and interior of the heterogeneous catalyst. The second weight loss of 15%
occur from 101 to 416°C owing to the dehydroxylation of brucite-like layer and the collapse of the
LDH layer structure into the oxide. The third weight-loss of 1.21% occur between 416 and 500°C is
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owing to the resolution of the MOF76 from the catalyst into the oxide form .
The fluorescence performance of MOF76, LDH and MOF76@LDH is shown in Fig S2†, the
normalized room temperature PL emission spectra of MOF76, LDH and MOF76@LDH at an
excitation wave-length of 544nm, pristine MOF76 displays emission bands between 350 and 800nm
with maxima centered at about 488nm, 545nm, 584nm and 620nm is a combination of blue, green,
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yellow and orange lights respectively
. Such a significant luminescence of MOF76 is caused by the
numerous surface defects on it, interestingly, the PL emission bands intensity of MOF76@LDH is
higher than LDH and lower than MOF76, further indicating the successful combination of the MOF76
with LDH.
The nitrogen adsorption-desorption isotherm of MOF76@LDH is shown in Fig.1(D), which shows
the typical IV isotherm pattern occur in mesopores with capillary condensation, and a H3-type
hysteresis loop at ralative pressure(p/p >0.5) associated with the pores are produced by the aggregation
of slit-shaped pores with some microporosity, demonstrating the presence of both interlayer micropores
and interparticle mesopores, which is similar to the conventional Mg AlCO -LDH . According to the
above analysis, the catalyst contains mesoporous and microporous construction. In addition, the BET
of the MOF76@LDH(72.019m g ) are smaller than that of LDH(150.632m g ) and larger than that of
MOF76(55.2624m g )(Table S2†), this indicates that MOF76@LDH can be successfully synthesized
and can effectively reduce the agglomeration of MOF76, further provide more surface active sites for
catalytic desulfurization. According to the Horvath-Kawazoe Report, the pore width for MOF76@LDH
are 0.673nm and 0.814nm, which was consistent with the pore width of the one-dimensional channels
for MOF76 (Fig S3†), this is because MOF76 are on the surface of LDH and LDH can effectively
reduce the agglomeration of MOF76. it is worth noting that the channels are very close to that of the
model oil sample (Table S3†), this indicates that the catalysts can largely prevent the mass transfer of
model oil sample and its oxidative products in the skeleton. The catalyst can adequately touch with
model oil sample thereby promote H O decomposition .
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Fig.2 (A) Survey spectrum for MOF76@LDH; (B) High-resolution Tb 4d XPS spectrum of
MOF76@LDH; (C) High-resolution Al 2p XPS spectrum of MOF76@LDH and (D) High-resolution
O 1s XPS spectrum of MOF76@LDH
The chemical states and surface composition of the catalyst MOF76@LDH were investigated by
X-ray photoelectron spectroscopy(XPS) spectrum. The research spectrum is shown in Fig.2(A)
indicated that the MOF76@LDH is composed of Ca, Al, Mg, Tb, C and O elements. Tb is originated
from MOF76, in Fig.2(B) , the peaks at 153.53, 156.22 and 158.73eV originate from Tb 4d3/2 and the
peaks at 147.80 and 151.00eV originate from Tb 4d . Indicated that the main valence of Tb element is
4 and there may be a small amount of +3 valence . According to the previous literature reports, that
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the binding energy of Tb and Tb species for MOF76@LDH are higher than pure TbO and Tb O ,
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and are derived from synergistic effects between active metal component(MOF76) and carriers(LDH)
instead of a simple physical mixture. The high-resolution Al 2p spectrum is show in Fig.2(C), the peak
at 74.20eV proves the presence of Al in LDH gallery. The high-resolution Mg 2p spectrum and Ca 2p
spectrum are shown in Fig. S4†, these are also proved the presence of Mg and Ca in the LDH
gallery of the catalyst. The high-resolution O 1s spectrum is shown in Fig.2(D), the O 1s spectrum can
be divided into three peaks at 531, 532 and 533.5eV, which is attributed to C=O on the catalyst surface,
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+
2+
2+
O-H(surface hydroxyl groups) and absorbed H O.Through the peaks of oxygen in XPS, which
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indicates that the loss of lattice oxygen and the increase of hydroxyl oxygen .
The Ca, Mg and Al atomic ratio of the MOF76@LDH composite catalyst is about 0.03:0.36:0.51 by
ICP measuring[Ca=0.53wt%, Mg=6.43wt%, Al=9.13wt%, Tb=2.06wt%, C=48.85wt%, N=0.05wt%]
The result is consistent with the theoretical prediction. According to the element measurements and TG,
the catalyst molecular formula can be written as [Ca0.03Mg0.35Al0.50Tb0.12(OH)1.72
C H O ] [NO ] 1.83H O.
]
[
9
3
6 0..30
3 0.05•
2
Fig.3 SEM images of (A) Rod LDH; (B) MOF76; (C) MOF76@LDH and (D) EDX spectra of
MOF76@LDH
Scanning electron microscopy(SEM) images were recorded to illustrate the structure and
morphology of the catalyst. The SEM presentation in Fig.3(A) shows pure LDH with smooth and

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relatively regular rod morphology, with an average length of 3μm. In Fig.3(B) MOF76 shows thVeiew Article Online
typical brick-like hole stacking structure. From Fig.3(C), MOF76@LDH surface displays rougher and
exhibits non-uniform rod structure. This is because the MOF76 is uniform and well-dispersed on the
surface of LDH, MOF76 successfully wrapped on the surface of LDH helps to reduce the
agglomeration of MOF76. So compared to pure MOF76, the heterogeneous catalyst provide more
surface active sites for catalytic desulfurization. Moreover, the catalyst all elements were analyzed by
EDX in Fig.3(D), the amounts of all elements are close to the data obtained by ICP.
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.2 catalytic performance of desulfurization
Fig.4 Sulfur removal efficiencies of DBT for (A) x wt.% MOF76@LDH (x=40, 45 and 49) at
different time;(B) Different temperatures; (C) Different O/S molar ratios and (D) Different amounts of
MOF76@LDH; Reaction conditions: model oil=5ml, [Bmim]PF =1ml, T=60°C , n(O/S)=3 and
6
m =0.01g.
cat
To define the optimal reaction for the MOF76@LDH catalyst, the influences of the MOF76-loaded
27
amount, O/S molar ratio, catalyst dosage and reaction temperature on DBT conversion were studied .
The effects of the MOF76-loaded amount was first examined, as shown in Fig.4(A), 49wt.%
MOF76@LDH catalyst show the outstanding DBT desulfurization efficiency. As far as we known,
MOF76 on MOF76@LDH catalyst provides the activity site, that probably promoted hydrogen
peroxide to generate hydroxyl radicals(•OH), and subsequently DBT was oxidized to DBTO and
2
DBTO via •OH. Therefore, the quantity of MOF76 loaded in LDH rods greatly influenced the
desulfurization effect. The desulfurization effect of MOF76@LDH enormous increased with increasing
MOF76 density and reached 100% in 25min when the MOF76 density reached 49wt.%, below 49wt.%
loading quantity, the catalysis desulfurization effect was decreased because the activity sites of MOF
catalysts were sufficient catalyzed oxidative DBT completely. the smaller surface areas lead to
providing less active sites are in touch with DBT. Thence, the optimum loading quantity of MOF76
was 49 wt.% for MOF76@LDH desulfurization and used for the subsequent experiments.
The DBT conversion was implemented at different temperatures ranging from 40 to 70°C shown in
Fig.4(B), When the temperature further enhance from 40 to 60°C , that can improve self-decomposition
ability of H O self-decomposition and improve the rate of oxidation. When the temperature further
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rise higher than 60°C , the velocity of H O self-decomposition is faster than that of H O oxidation .
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Thence, in this ECODS system 60°C was selected as the optimal reaction temperature.
The O/S molar ratio is one of the most important influencing factors that affects the economy and
efficiency value of the reaction system. Because of some secondary reactions including H O2
2
decomposition easily occur during the ECODS procedure, great majority of ECODS processes need a
high O/S molar ratio, particularly when they are executed at high temperature. As shown in Fig.4(C),
when O/S molar ratio is 3, the desulfurization effect can achieve 100%, compared with other
desulfurization systems in Table 1, which is the lowest dose of H O in this work, this probability as a
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result of the active sites of the MOF76, which can fully accessible the substrates, promoting the
utilization of H O . Therefore, n(O/S)=3 was chosen as the optimum reaction molar ratio in this
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ECODS.
The effect of different amounts of MOF76@LDH for sulfur removal on DBT was shown in Fig.4(D),
the low amounts of catalysts were inadequate to catalysis sulfur compound totally and the excess

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MOF76@LDH may result in the aggregation of catalysts, which covered on the surface of the catalysVtiew Article Online
and reduced the quantities of active sites available. Hence, 0.01g catalyst is the appropriate amount for
removing sulfur.
DOI: 10.1039/D0NJ00612B
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Fig.5 (A)Effect of different substrates on sulfur removal in the desulfurization system;(B) Effect of
different catalysts on sulfur removal of DBT ; (C) Effect of different fuel composition on sulfur
removal of DBT and (D) Sulfur removal of DBT (black) and ln(C /C ) as a function of reaction time at
t
0
6
0°C (red);Reaction conditions: model oil=5ml, [Bmim]PF =1ml, T=60°C , n(O/S)=3 and m =0.01g
6 cat
We all known that thiophenes quantity for more than 80% of the total sulfur content in diesel and
gasoline fuel, simultaneously DBT,BT and 4,6-DMDBT occupy 70% of it. Hence, the removal of
2
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thiophehes is a top priorty . The effect of different substrates for desulfurization effect in the
desulfurization system was shown in Fig.5(A), The composite catalyst appeared superior activity in
deep desulfurization of DBT, BT and 4,6-DMDBT.The above sulfides could be completely converted
to their corresponding sulfones and sulfoxides at 60°C in 25, 40 and 55minutes, respectively. The
sulfides conversions abided by the order: DBT > BT > 4,6-DMDBT. Based on the above conclusions, it
probability owing to the electron density of sulfur atom on BT(5.739) was lower than that on
DBT(5.758), high charge density on sulfur atoms are beneficial to its oxidation. Though 4,6-DMDBT
28
possesses the highest electron density(5.760) , the desulfurization effect of 4,6-DMDBT was the
lowest than that of BT and DBT. This is possibility as a result of the steric hindrance of methyl groups
of the 4,6-DMDBT, resulting in the active sites difficult to approach the sulfur atom. Which was
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consistent with the results of reference .
To further understanding the mechanism of oxidation over MOF76@LDH, performed a control
experiment. As shown in Fig.5(B), no significant DBT conversion (11%) were observed without
catalyst, this can be primary thanked to the result of ILs and demonstrated the indispensability of
catalyst to promote the DBT conversion and MOF-76@LDH catalyst ability to exhibits high
desulfurization capacity(100%) much higher than LDH (16.3%) with MOF-76 (48%), obviously, the
desulfurization capacity of MOF76@LDH composite is not only higher than that of LDH or MOF76
but also higher than the sum of pure LDH and MOF76(50.3%). Such a high desulfurization capacity
can be primary owing to the uniform dispersion of MOF76 molecules on the LDH carrier, which can
provide more active sites and thus improve the desulfurization capacity. the promotion of the catalytic
activity of the MOF76@LDH may originated from the synergistic effect of the host LDH carrier and
the loaded MOF76 molecules instead of physical mixing. Moreover, the removal of MOF76@LDH
catalyst from the reaction mixture after 10min and the reaction was allowed to execute without catalyst.
The result manifested that the heterogeneous essence of MOF76@LDH catalyst and no revelation of
MOF76 molecules into the reaction solution. In order to reduce the agglomeration of MOF76 using
physical methods, preparation of MOF76 solution, the obtained solution was further ultrasonic
dispersion for 20min and then transferred to a Teflon-lined stainless-steel autoclave according to the
above preparation method. The desulfurization capacity of ultrasonic MOF76 slightly higher than
MOF76 without any treatment. Therefore, the ultrasonic effect can not effectively solve the
agglomeration problem of MOF76. So as to make a thorough inquiry the reaction mechanism of
ECODS and the main active ingredient over the MOF76@LDH catalyst, we researched the inhibiting
effect of DMSO on ECODS activity with the hydroxyl radical(•OH) scavenger, the ECODS efficiency
30
drops completely in the appearance of DMSO (quencher of •OH). This result shows that •OH is the

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most important reaction intermediate in the ECODS procedure. we researched the inhibiting effect oVfiew Article Online
tert-butanol on ECODS activity with the hydroxyl radical(•OH) scavenger, the ECODS efficiency
drops completely in the appearance of tert-butanol(quencher of •OH). This result shows that •OH is the
most important reaction intermediate in the ECODS procedure. It is worth stress that the presence of
DOI: 10.1039/D0NJ00612B
•
OH during the ECODS reaction system has been reported in previous literature through the EPR test
3
on the MOF catalyst .
Under the oxidizing environment , the coexistence of other components in the model oil sample, it
includes a lot of aromatics. Therefore , it is need to investigate the influences of the different aromatics
on DBT desulfurization. In this aspect, toluene, mesitylene and naphthalene were selected as
representative substances and mixed in the model oil so as to investigate the influences of these
additives on the desulfurization procedure. As shown in Fig.5(C), showed that the existence of toluene
or mesitylene has no obvious impact on the desulfurization effect. In the situation of naphthalene, we
observed a reduce in the desulfurization effect from 100% to 98%, furthermore, Fig.5(C) revealed that
the three model oil sample mixed have no obvious impact on the desulfurization effect, which indicates
that this ECODS reaction system could be applied to actual diesel desulfurization.
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catalyst
time(min-1) temperature(°C) O/S conversion(%) reference
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42%PTA@MOF-808A
40wt%PW /TiO
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10%HPW/MgAl-LDH
49%MOF76@LDH
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99.81
100
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This work
Table1 Comparision of the optimal reaction conditions and corresponding DBT conversions among
various catalysts.
3.3 Kinetic studies
To further comprehend the DBT removal effect over MOF76@LDH, the catalytic kinetic of the
catalytic oxidation of DBT was fixed at 40,50,60 and 70°C . The result are shown in Fig.5(D) and Fig
2
S5(A)†, which are interpreted by a pseudo-first-order kinetic model(R >0.99902), as predicted, the
-1
kinetic constant (k) increase as the increasing temperature and the k value reached 0.11min at 60°C .
this value is relatively large among the excellent heterogeneous catalysts for previously reported
literature for DBT oxidation and then confirmed that MOF76@LDH is an excellent catalyst for
31
ECODS . The half-life of the reaction(t ) calculated by the pseudo-first-order kinetic equation is
1/2
merely 5.7min under the optimum conditions, which is relatively small among the excellent
heterogeneous catalysts for previously reported literature, confirming the high efficient of the
MOF76@LDH composite in catalytic oxidation DBT. According to the k values at different
temperatures, the apparent activation energy(E ) for the DBT oxidation over MOF76@LDH was
a
-1
19, 32, 33
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0.81kJ mol , which was evaluated with the Arrhenius equation
Fig S5(B)†. This value is
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relatively small among the excellent heterogeneous catalysts for previously reported literature (Table
S4†), which further demonstrates the high efficiency of the catalyst.
3.4 Recyclability of the composite material

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DOI: 10.1039/D0NJ00612B
.
Fig.6 (A) The recyclability performance of the catalytic system at 60°C , Reaction conditions: model
oil=5ml, [Bmim]PF =1ml, n(O/S)=3 and m =0.01g; (B)FT-IR spectra; (C) XRD patterns and (D)SEM
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image of the pristine MOF76@LDH and its recycled sample after five successive catalytic runs.
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The recycling capacity of the heterogeneous catalyst is most imperative for its industrial applications.
After each desulfurization process carried out , the upper layer solution was poured out, then the
catalyst was collected by centrifugation from the resultant mixture, washed with acetonitrile(3×5ml)
and dried at 60°C in a vacuum oven overnight . As shown in Fig.6(A), no obvious reduce in catalytic
activity was investigated and the DBT conversion efficiency still could reach 98% after five constantly
catalytic times under the optimum reaction conditions, which could be owing to the high stability of the
supports of carrier and the heterogeneous essence of the catalyst. FT-IR, XRD patterns, SEM image etc.
35
(
Fig.6) prove that the catalyst maintained its structural and composition integrity during recycled runs.
The investigated structural stability of MOF76@LDH is maybe owing to the two-dimensional effect of
LDHS and the diverse interactions (hydrogen bonding and electrostatic interaction forces) between
guest MOF76 and the host layers.
3.5 Mechanism of reaction
Fig.7 Proposed mechanism of the desulfurization of an oil mixture by MOF76@LDH.
The put forward reaction mechanism for MOF76@LDH of effective desulfurization is illustrated in
Fig.7, the substrate is extracted from the oil phase to the interface in which the ionic liquid and the
LDH layers. Lately, rare earth-MOF have unique peroxidase-like activity and were capable of catalyze
ECODS when IL as extractant and H O as oxidant for model gasoline desulfurization, which can
catalytic decomposition of hydrogen peroxide into active •OH radicals, then, sulfide can access the
active radicals(•OH) and are oxidation effective to the corresponding sulfones and sulfoxides, finally,
sulfones and sulfoxides was retained in the ILs owing to higher polarity, which made the upper layer
solution as an environment friendly oil samples.
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4. Conclusions
In summary, the combination of MOF-76 with layered double hydroxides (MOF-76@LDH) under
room temperature and pressure conditions without the necessity of protecting with nitrogen used for
desulfurization for the first time. The MOF76@LDH heterogeneous catalyst(100%) displays excellent
desulfurization performance in comparison with pure MOF76(48%) and rod LDH(16.3%). The
increased catalytic activity is owing to the active sites of the •OH radicals, which can adequately
contact with the substrates, greatly upgrade the efficiency of desulfurization. The resultant catalyst
shows 100% desulfurization effect of DBT, BT and 4,6-DMDBT at 60°C in 25, 40 and 55min in the

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DOI: 10.1039/D0NJ00612B
presence of H O and in the case of the O/S=3;1, respectively. In addition, the heterogeneous catalyst is
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easy to separate by simple centrifugation and recycled five times with no obvious reduce in its catalytic
activity and it is worth emphasizing that this ECODS reaction system could be applied to actual diesel.
This work demonstrates the preparation of MOF combination with LDHs the first time for deep
desulfurization procedure and offers a potentially universal new design strategy that MOF can grafted
on the LDHs. The recent work extends information in the design of MOFs-LDHs heterogeneous
catalysts with effective desulfurization effect for solving environmental problems in actual.
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Conflicts of interest
There are no conflicts to declare.
Acknowledgements
We gratefully acknowledge the financial support from the NSF of China (21571032 21271038), the
China High-Tech Development 863 program (2007AA03Z218) as well as the analysis and testing
platform of Northeast Normal University.
Notes and references
1.
2.
3.
J. Fu, Y. Guo, W. Ma, C. Fu, L. Li, H. Wang and H. Zhang, Journal of Materials Science, 2018, 53,
5418-15429.
1
W. Zhou, Q. Wei, Y. Zhou, M. Liu, S. Ding and Q. Yang, Applied Catalysis B: Environmental,
2018, 238, 212-224.
H.-Q. Zheng, Y.-N. Zeng, J. Chen, R.-G. Lin, W.-E. Zhuang, R. Cao and Z.-J. Lin, Inorganic
Chemistry, 2019, 58, 6983-6992.
4.
H.-T. Lv, Y. Cui, G.-D. Zou, N. Li, P. Yang and Y. Fan, Dalton transactions, 2019, 48,
14044-14048.
5.
6.
7.
8.
W. Ma, Y. Xu, K. Ma and H. Zhang, Applied Catalysis A: General, 2016, 526, 147-154.
Y. Xu, W.-W. Ma, A. Dolo and H. Zhang, RSC Advances, 2016, 6, 66841-66846.
S. Cheon, K. Kim, H. C. Yoon and J.-I. Han, Chemical Engineering Journal, 2019, 375, 122008.
Z. Zuhra, C. Mu, F. Tang, Y. Zhou, L. Zhang, Z. Zhao and L. Qin, Dalton transactions, 2019, 48,
14792-14800.
9.
Y. Muhammad, H. U. Rashid, S. Subhan, A. U. Rahman, M. Sahibzada and Z. Tong, Chemical
Engineering Journal, 2019, 375, 121957.
10.
Y. Guo, J. Fu, L. Li, X. Li, H. Wang, W. Ma and H. Zhang, Inorganic Chemistry Frontiers, 2018, 5,
2205-2210.
11.
Y. Xu, W. Xuan, M. Zhang, H. N. Miras and Y. F. Song, Dalton transactions, 2016, 45,
19511-19518.
12.
13.
14.
15.
X. Lian and B. Yan, RSC Advances, 2016, 6, 11570-11576.
H.-L. Jiang, N. Tsumori and Q. Xu, Inorganic Chemistry, 2010, 49, 10001-10006.
N. A. Khan and S. H. Jhung, Inorganic Chemistry, 2015, 54, 11498-11504.
Z.-J. Lin, H.-Q. Zheng, J. Chen, W.-E. Zhuang, Y.-X. Lin, J.-W. Su, Y.-B. Huang and R. Cao,
Inorganic Chemistry, 2018, 57, 13009-13019.
1
6.
7.
W. Xie and F. Wan, Catalysis Letters, 2019, 149, 2916-2929.
1
Z. Zuhra, C. Mu, F. Tang, Y. Zhou, L. Zhang, Z. Zhao and L. Qin, Dalton transactions, 2019, 48,

Page 11 of 12
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/D0NJ00612B
1
4792-14800.
1
1
2
8.
9.
0.
H. Li, F. Liu, S. Wang, F. Wang, X. Qian, C. Zhang, Y. Ma and L. Wang, Fuel Processing
Technology, 2019, 194, 106125.
S. Omwoma, W. Chen, R. Tsunashima and Y.-F. Song, Coordination Chemistry Reviews, 2014,
2
58-259, 58-71.
A. Chakraborty and H. Acharya, Colloid and Interface Science Communications, 2018, 24,
5-39.
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
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
2
1.
2.
S. Yang, L. Wang, S. Yue, X. Guo, Y. Song and J. He, RSC Advances, 2013, 3, 16990.
K. Liu, Z. Yao and Y.-F. Song, Industrial & Engineering Chemistry Research, 2015, 54,
9133-9141.
2
23.
W. Yang, Z.-Q. Bai, W.-Q. Shi, L.-Y. Yuan, T. Tian, Z.-F. Chai, H. Wang and Z.-M. Sun, Chemical
Communications, 2013, 49, 10415.
24.
Y. Chen, D. Yan and Y. F. Song, Dalton transactions, 2014, 43, 14570-14576.
P. Huang, A. Liu, L. Kang, M. Zhu and B. Dai, New Journal of Chemistry, 2018, 42,
25.
1
2830-12837.
Z. Han, Y. Guo, R. Tsunashima and Y.-F. Song, European Journal of Inorganic Chemistry, 2013,
013, 1475-1480.
26.
2
2
7.
8.
I. Ahmed, N. A. Khan and S. H. Jhung, Inorganic Chemistry, 2013, 52, 14155-14161.
Y. Cai, H. Song, Z. An, X. Xiang, X. Shu and J. He, Green Chemistry, 2018, 20, 5509-5519.
Y. Chen, C. Shen, J. Wang, G. Xiao and G. Luo, ACS Sustainable Chemistry & Engineering, 2018,
2
29.
6, 13276-13286.
30.
X. Wang, W. Chen and Y.-F. Song, European Journal of Inorganic Chemistry, 2014, 2014,
2779-2786.
31.
32.
33.
34.
35.
Y. Chen and Y.-F. Song, ChemPlusChem, 2014, 79, 304-309.
J. C. Liu, B. Qi and Y. F. Song, Dalton transactions, 2019.
F. Zhang, H. Guo, Y. Liu, F. Liu and R. Hu, Fuel, 2019, 257, 116028.
F. Wu, X. Li, H. Zhang, S. Zuo and C. Yao, Frontiers in Chemistry, 2018, 6.
S. Zhao, J. Xu, M. Wei and Y.-F. Song, Green Chemistry, 2011, 13, 384.

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View Article Online
DOI: 10.1039/D0NJ00612B
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Combination of MOF76 with LDH provides a completely new route for
the synthesis of MOF-LDH advanced functional materials.