Green synthesis of dihydroxybenzene from phenol with hydrogen peroxide catalyzed by iron modified FSM-16

Article abstract of DOI:10.1007/s11164-018-3428-7

Catechol and hydroquinone are very important fine chemical intermediate products, which have a wide range of applications. The hydroxylation of phenol with hydrogen peroxide to produce dihydroxybenzene is a mild and environmental friendly route. In this work, FSM-16 modified by iron (Fe/FSM-16) is used as a catalyst. With Fe content of 5% (wt), phenol to H₂O₂ ratio of 3:1, reaction temperature of 60?°C, catalyst amount of 0.1?g and reaction time of 6?h, phenol conversion of 29.1% and dihydroxybenzene selectivity (catechol/hydroquinone = 1.6) of 93.5% are achieved. The results are close to that of TS-1 which is used in industry production and shows good prospects for industrial applications. The characterizations revealed that the Fe/FSM-16 could be reusable and stable.

Full text of DOI:10.1007/s11164-018-3428-7

Res Chem Intermed
https://doi.org/10.1007/s11164-018-3428-7
Green synthesis of dihydroxybenzene from phenol
with hydrogen peroxide catalyzed by iron modified
FSM-16
Guanhua Luo1 Yujuan Jiao1 Xuechuan Lv1 Xiaofan Zhang1
Xiaohan Gao1
•
•
•
•
Received: 3 January 2018 / Accepted: 2 April 2018
Ó Springer Science+Business Media B.V., part of Springer Nature 2018
Abstract Catechol and hydroquinone are very important fine chemical intermediate
products, which have a wide range of applications. The hydroxylation of phenol
with hydrogen peroxide to produce dihydroxybenzene is a mild and environmental
friendly route. In this work, FSM-16 modified by iron (Fe/FSM-16) is used as a
catalyst. With Fe content of 5% (wt), phenol to H2O2 ratio of 3:1, reaction tem-
perature of 60 °C, catalyst amount of 0.1 g and reaction time of 6 h, phenol con-
version of 29.1% and dihydroxybenzene selectivity (catechol/hydroquinone = 1.6)
of 93.5% are achieved. The results are close to that of TS-1 which is used in
industry production and shows good prospects for industrial applications. The
characterizations revealed that the Fe/FSM-16 could be reusable and stable.
Keywords Catalysis Á Hydroxylation Á Zeolites Á Iron
Introduction
The hydroxylation of phenol to dihydroxybenzene is a very important industrial
process. The products, catechol and hydroquinone, are important fine manufactures
used in many diverse fields. Catechol is widely used as a starting material for
pharmaceutical, pesticide, perfume, dope and many fine chemicals. Hydroquinone is
mainly used in photographic chemicals, antioxidants, flavoring agents, polymer-
ization and inhibitors. Hydrogen peroxide has been regarded as a clean oxidant
which afforded water as by-product [1]. Phenol oxidation with hydrogen peroxide to
&
Xiaohan Gao
gaoxhan@163.com
1
School of Chemistry and Material Science, College of Chemistry, Chemical Engineering and
Environmental Engineering, Liaoning Shihua University, Fushun 113001, Liaoning, China
123

G. Luo et al.
dihydroxybenzene is considered as a promising and valuable chemical industrial
process. The typical industrial processes to synthesize dihydroxybenzenes from
phenol and hydrogen peroxide were catalyzed by inorganic acid or a molecular
sieve, such as the Rhone-Poulenc process [2], using sulfuric acid as catalyst. The
Enichem process [3] is now industrialized with high hydroquinone selectivity
(hydroquinone/catechol ratio = 1) and high hydrogen peroxide efficiency, using TS-
1 (titanium silicalite-1) as catalyst. Phenol conversion is 25%, and 90% of
dihydroxybenzene selectivity is obtained. However, this process has many problems
with separation, catalyst reclamation and expensive spending.
The catalysts with cheaper price, better performance, higher conversion and
selectivity, easy recycle and simple preparation are the main direction of research.
Many papers and monographs [4–6] concerning the process of hydroxylation of
phenol to dihydroxybenzene, and the investigations concerning the catalyst for the
process have been reported. The reported catalysts include complex metals oxide
[7–9], modified molecular sieves [10–12], or heteropoly acid [13].
The family of silica-based mesoporous silica materials designated as M41S [14]
has received considerable interest over the last years. They have some attractive
characteristics, such as very high surface areas, regular mesopores and hydropho-
bicity. One of them, FSM-16 [15] (Folded-Sheet Mesoporous Material) is easily
synthesized from a layered sodium silicate by using cetyltrimethyammonium
cations as a template, and the raw material is cheaper and convenient to obtain.
In this work, the FSM-16 was selected as the carrier and modified by iron. Effects
of the Fe capacity, the ratio of phenol to hydrogen peroxide, temperature and
catalyst dosage on the catalytic performances for hydroxylation of phenol to
catechol and hydroquinone were investigated. Catalysts were characterized with
X-ray diffraction (XRD), NH3-TPD and N2 adsorption–desorption experiment.
Experimental
Materials and reagents
All the above reagents were of analytical grade and obtained from the Sinopharm
Chemical Reagent Co. Ltd.
Catalyst preparation
FSM-16 was typically prepared by the following procedure as in the literature
[16, 17], kanemite crystals (10.0 g) obtained by calcinations of a water glass (SiO2/
Na2O = 2) at 500 °C for 5 h were dispersed in 100 mL water and stirred for 3 h at
room temperature. After filtration, the wet kanemite was dispersed in cetyltrimath-
ylammomium bromine aqueous solution (200 mL 0.1 mol/L) with stirring for 3 h at
70 °C. The pH of the suspension was adjusted to 8–9 by addition of 2 mol/L HCl
solution again and the suspension was left at 70 °C for a further 3 h. After filtration,
the sample was dried at 120 °C and calcined at 500 °C for 5 h to remove the
surfactant to obtain FSM-16.
123

Green synthesis of dihydroxybenzene from phenol with…
FSM-16 modified by iron was typically prepared by the following procedure,
Iron(III) nitrate nonahydrate was dissolved in 20 mL of water and then FSM-16
(5.0 g) was added in the solution. The above slurry was stirred and dried at room
temperature. Finally, the product was calcined at 500 °C for 5 h and Fe/FSM-16
was obtained.
Hydroxylation reaction and products analysis
The hydroxylation of phenol with hydrogen peroxide was carried out in a 100 mL
flask with thermometer and condensator. In the typical run, 0.1 g of catalyst,
0.02 mol of phenol and 20 mL of water were placed in the reactor and heated.
Hydrogen peroxide (30%) was added dropwise through a dropping funnel. The
addition rate was controlled at 0.1 mL per min. After the complete addition of
hydrogen peroxide, the mixture was further stirred at a certain temperature for 6 h
and then cooled down to room temperature. The GC analyses (GC-7900, Shanghai
Techcomp Instrumengts Ltd) of products were performed with an OV-1 capillary
column (35 m 9 0.32 mm 9 0.8 lm) using benzyl alcohol as an internal standard.
Characterization of catalysts
Powder X-ray diffraction (XRD) patterns were recorded using Rigaku D/Max 3400
X (Rigaku Corporation Jan) with Cu Ka radiation at 0.02 steps per second in angle
range 2h = 5°–90°.
Low-temperature N2 adsorption–desorption experiments were carried out using a
Quantachrome Autosorb-1 system (Quantachrome Instruments U.S.). The modal
pore diameter was calculated using the BJH method based on the desorption
isotherm, and the surface area was calculated using the BET method based on the
adsorption isotherm.
NH3-TPD (temperature-programmed desorption) experiments were performed
using AutoChem II 2920(Micromeritics Instrument Corporation U.S.). Before the
adsorption of NH3, the sample (* 0.1 g) was pretreated at 350 °C in He (30 mL/
min) for 30 min. Then the sample was cooled down to 100 °C and adsorbed NH3 for
0.5 min. Subsequently, the catalyst was flushed with He until the baseline was
steady. The desorption process was monitored with a thermal conductivity detector
at a temperature ramp from 100 to 500 °C, with a heating rate of 15 °C/min.
Results and discussion
Effect of the Fe content
The results of hydroxylation of phenol over mesoporous silica materials FSM-16
modified by different Fe content are shown in Table 1. Phenol conversion of 2.8% is
obtained over the unmodified FSM-16. The product is only benzoquinone. As
Fe(NO3)3Á9H2O was used as catalyst alone, the conversion of phenol is 23.5%, and
123

G. Luo et al.
Table 1 Effect of Fe contents in catalysts
Content of Fe/
wt%
Phenol
conversion/%
Products distrobution/%
Catechol/
hydroquinone/mol
Catechol Hydroquinone Benzoquinone
FSM-16
2.8
0
0
0
100
–
–
Fe/FSM-16
(0.5)
18.9
30.2
69.8
Fe/FSM-16
(1.5)
18.1
22.1
27.5
26.3
27.4
50.3
50.9
55.5
52.9
53.1
54.1
24.3
29.9
31.9
32.8
33.6
27.8
25.4
19.2
12.6
14.3
13.3
18.1
2.1
1.7
1.7
1.6
1.6
1.9
Fe/FSM-16
(2.5)
Fe/FSM-16
(5.0)
Fe/FSM-16
(7.5)
Fe/FSM-16
(10.0)
Fe(NO3)3Á9H2O 23.5
Reaction condition: n(phenol):n(H2O2) = 3:1, catalyst 0.1 g, temperature 50 °C, time 6 h
the selectivity of dihydroxybenzene is 81.9%. However, it is homogeneous catalytic
reaction and Fe(NO3)3Á9H2O is impossible to be reused.
Phenol conversion and dihydroxybenzene selectivity increased obviously at the
presence of the FSM-16 modified by iron (Fe/FSM-16) in the reaction that
illuminates Fe is the active center of the Fe/FSM-16. The formation of
benzoquinone is restrained over Fe/FSM-16. It can be seen from the performances
of catalysts with different Fe content that the conversion of phenol increased as the
Fe content increased. The catalyst with Fe content of 5.0% (wt) displays the highest
phenol conversion of 27.5% and dihydroxybenzene selectivity of 87.4%. The ratio
of catechol to hydroquinone is 1.6 that is in accord with the industrial desirability.
When Fe content is more than 5.0% (wt), the conversion of phenol has little change.
The low Fe content causes the less active center, which is not a benefit to the
activation of H2O2. Then the conversion of phenol is low. Small amounts of
generated hydroquinone are easily oxidized to benzoquinone that result in the low
hydroquinone selectivity. The active center increased as the Fe content increased.
Then phenol conversion increased, the amount of generated hydroquinone increased
and hydroquinone selectivity increased. However, the catalyst activity center
increased slightly when Fe content is more than 5.0% (wt). Phenol conversion and
dihydroxybenzene selectivity remained. Therefore, the optimum Fe content was
5.0% (wt).
Effect of the ratio of phenol to hydrogen peroxide
Effect of the ratio of phenol to hydrogen peroxide in the reaction is shown in
Table 2. Conversion of phenol increased a little as the hydrogen peroxide dosage
123

Green synthesis of dihydroxybenzene from phenol with…
Table 2 Effect of the ratio of phenol to hydrogen peroxide
Phenol/
H2O2/mol
Phenol conversion/ H2O2 utilization/ Products distribution/%
%
%
Catechol Hydroquinone Benzoquinone
3:1
3:2
3:3
27.5
30.4
39.1
82.5
44.5
39.1
55.5
49.8
48.0
31.9
26.5
25.9
12.6
23.7
26.1
Reaction condition: Fe content 5.0% (wt), catalyst 0.1 g, temperature 50 °C, time 6 h
increased. However, the utilization of hydrogen peroxide and the selectivity of
dihydroxybenzene decreased sharply. The decomposition rate of hydrogen peroxide
to O2 and OHÁ increased as the concentration of hydrogen peroxide increased [18].
The higher decomposition rate of hydrogen peroxide lead to the higher concen-
tration of OHÁ that easily oxidized hydroquinone to benzoquinone. As a result, the
utilization of hydrogen peroxide and the selectivity of dihydroxybenzene decreased.
It is found that the quick addition speed of hydrogen peroxide results in the decrease
of the dihydroxybenzene selectivity during the experiments. From the point of the
economic efficiency, the optimum ratio of phenol to hydrogen peroxide is 3:1, and
the addition speed of hydrogen peroxide must be slow.
Effect of the reaction temperature
Table 3 is the influence of reaction temperature on the catalytic performance in the
reaction. Fe/FSM-16 exhibits high catalytic activity for hydroxylation of phenol
with hydrogen peroxide to produce dihydroxybenzene at low temperature.
Conversion of phenol increased firstly and then decreased with increasing the
reaction temperature. Excellent phenol conversion of 29.1% with dihydroxybenzene
selectivity of 93.5% was obtained at 60 °C. Catalyst had lower efficiency to activate
hydrogen peroxide which accounts for the lower phenol conversion at low
temperature. The decomposition rate of hydrogen peroxide to O2 and OHÁ increased
Table 3 Effect of reaction temperature
Temperature/°C
Phenol conversion/%
Products distribution/%
Catechol
Hydroquinone
Benzoquinone
30
40
50
60
70
80
18.2
21.1
27.5
29.1
26.9
20.9
55.5
50.1
55.5
55.6
50.2
46.3
26.4
23.5
31.9
37.9
28.3
32.3
18.1
24.3
12.6
6.5
21.5
21.4
Reaction condition: n(phenol):n(H2O2) = 3:1, catalyst 0.1 g, Fe content 5.0% (wt), time 6 h
123

G. Luo et al.
at higher temperature that lead to the utilization of hydrogen peroxide decreasing.
More amounts of generated OHÁ oxidized hydroquinone to benzoquinone that
decreased the selectivity of dihydroxybenzene. From the energy saving and yield of
dihydroxybenzene point of view, the optimum temperature for the reaction is
between 50 and 60 °C.
Performance of recycling Fe/FSM-16 (5.0 wt%)
The used Fe/FSM-16 (5.0 wt%) catalyst was separated by filtration, washed with
copious amounts of water and calcined at 500 °C for 5 h. Table 4 is the reusability
test results of the Fe/FSM-16 (5.0 wt%) catalyst. The activity of Fe/FSM-16
(5.0 wt%) catalyst changed a little so that phenol conversion is about 29.0% from
first run to third run. In the fourth run, the conversion of phenol dropped to 26.1%.
The selectivity of dihydroxybenzene decreased at the second run and remained
stable from the second run to fourth run. The reason may be that some of the active
centers of the catalyst may be leached out or become inactive. The recycling test
confirms that the catalyst is reusable.
XRD analysis of FSM-16 and Fe/FSM-16 (5.0 wt%)
A powder low angle XRD pattern of FSM-16 is shown in Fig. 1. The curve of FSM-
16 showed the typical diffraction patterns of silica-based mesoporous molecular
sieves in the low-angle region [19]. Three peaks of (100) (110) and (210) appear at
2.45°, 4.19° and 4.75°. The corresponding d values of FSM-16 are 3.55, 1.90 and
1.67 nm calculated by the formula 2dsinh = k.
Figure 2 is the powder low angle XRD patterns of fresh Fe/FSM-16 (5.0 wt%)
and used Fe/FSM-16 (5.0 wt%). A widened peak of d100 is observed in the curve of
Fe/FSM-16. However, the d100 peak location does not shift (2h = 2.45°). The peaks
of d110 and d210 disappear in the curve of Fe/FSM-16. Because of the support action
of iron oxide and the interaction between iron oxide and the framework of FSM-16,
some of the {100} planes were covered and regularity of the {100} planes was
disturbed. Therefore, the diffraction intensity of the {100} planes weakened. The
peaks of d110 and d210 are too weak to appear.
Table 4 Performance of recycling Fe/FSM-16 (5.0 wt%)
Recycle time
Phenol conversion/%
Products distrobution/%
Catechol
Hydroquinone
Benzoquinone
1
2
3
4
5
29.1
28.5
28.7
26.1
25.8
55.6
52.1
54.5
53.6
52.3
37.9
33.5
32.9
32.3
38.3
6.5
14.4
12.6
13.1
12.4
Reaction condition: n(phenol):n(H2O2) = 3:1, catalyst 0.1 g, Fe content 5.0% (wt), time 6 h
123

Green synthesis of dihydroxybenzene from phenol with…
10000
8000
6000
4000
2000
0
Fig. 1 XRD pattern of FSM-16
(5.0 wt%)
100
2.45
4.19
110
4.75
210
1
3
5
2
4
2θ/degree
3000
2500
2000
1500
1000
500
2.44
2.45
100
100
fresh Fe/FSM-16
used Fe/FSM-16
0
1
2
3
4
5
6
2θ/degree
Fig. 2 XRD patterns of fresh Fe/FSM-16 (5.0 wt%) and used Fe/FSM-16 (5.0 wt%)
The powder low angle XRD pattern of the used Fe/FSM-16 (5.0 wt%) is similar
to that of the fresh Fe/FSM-16 (5.0 wt%). It shows that the used Fe/FSM-16 had no
obvious change compared with the fresh Fe/FSM-16 and the catalyst structure and
crystallinity were stable.
NH3-TPD of catalysts
It is known that the acid sites of molecular sieves are related to their catalytic
oxidation activity. Therefore, it is essential to analyze the acidity of the catalyst in
detail. The acid strength of the zeolites was analyzed by NH3-TPD (Fig. 3). The
strength distribution of the acid sites is estimated from the deconvolution of the TPD
plots with Gaussian curves [20]. The results are listed in Table 5. Fe content of
FSM-16 is connected with the surface acidity and hydrophobicity of catalyst [21]
123

G. Luo et al.
0.012
0.010
0.008
0.006
0.004
0.002
0.000
-0.002
Used Fe/FSM-16(5%)
Fe/FSM-16(7.5%)
Fe/FSM-16(5%)
Fe/FSM-16(2.5%)
FSM-16
0
100
200
300
400
500
600
Temperature/
Fig. 3 NH3-TPD profiles of catalysts
Table 5 Acidity of catalysts
Catalysts
Total acid sitesa
(mmol/g)
Weak acid sitesb
(mmol/g)
Strong acid
sites (mmol/g)
FSM-16
0.295
0.401
0.533
0.438
0.565
0.242
0.401
0.533
0.438
0.565
0.053
Fe/FSM-16 (2.5%)
Fe/FSM-16 (5.0%)
Fe/FSM-16 (7.5%)
Fe/FSM-16 (5%)
–
–
–
–
aDetermined by NH3-TPD
bThe peak centered below 280 °C was defined as NH3 desorbed from weak acid sites
that is related to the catalytic performance. Two desorption peaks that appeared at
107 and 294 °C in the curve of FSM-16 are assigned to the weak and medium acid
sites, respectively. The peak assigned to the weak acid sites still appeared at 107 °C
in the curve of Fe/FSM-16, and the weak acid sites increased obviously as the Fe
content increased (0, 2.5, 5.0%). It illuminating that the amount of weak acid sites
great increased, and acid strength had no change. Then, the catalyst activity
increased. The weak acid sites of the Fe/FSM-16 (7.5 wt%) are less than that of the
Fe/FSM-16 (5.0 wt%) (Table 5) whereas the catalyst activity of the Fe/FSM-16
(7.5 wt%) is close to that of the Fe/FSM-16 (5.0 wt%) (Table 1). It indicates that
the effect of the amount of weak acid sites on catalyst activity is not significant
when the weak acid sites amount exceeds a certain level.
The weak acid sites of the used Fe/FSM-16 (5.0 wt%) are more than that of the
fresh Fe/FSM-16 (5.0 wt%). It can be seen from Fig. 3 that the acid strength had a
little addition which caused the increase of benzoquinone selectivity (Table 4).
However, the peak at 294 °C assigned to the medium acid disappeared in the curve
123

Green synthesis of dihydroxybenzene from phenol with…
of Fe/FSM-16. It is concluded from the result of NH3-TPD and effects of the Fe
content on the catalytic performance (Table 1) that weak acid sites were at the
catalyst active center which is responsible for the hydroxylation of phenol with
hydrogen peroxide to produce catechol and hydroquinone. The conversion of phenol
increased and reached the best result as the Fe content increased that is accordant
with the variation trend of weak acid sites with the Fe content addition.
N2 absorption–desorption isotherms of FSM-16, fresh and used Fe/FSM-16
(5.0 wt%)
N2 adsorption–desorption isotherms and pore distribution profiles of FSM-16, fresh
Fe/FSM-16 (5.0 wt%) and used Fe/FSM-16 (5.0 wt%) are given in Fig. 4. The
FSM-16 sample (Fig. 4a) exhibited type IV isotherms (defined by IUPAC) with a
small hysteresis loop [22], which is characteristic for the capillary condensation in
the mesopores. The initial part of the isotherm (until p/p° & 0.2) can be attributed
to monolayer-multilayer adsorption because it follows the same path of desorption,
which demonstrates weak adsorbate-adsorbent interactions. The hysteresis loop is of
type H3, which is usually indicative of aggregates of platelet particles or adsorbents
containing slit pores. Figure 4b, c clearly shows that less nitrogen was adsorbed on
fresh Fe/FSM-16 (5.0 wt%) and used Fe/FSM-16 (5.0 wt%) than on FSM-16. This
finding can be attributed to the pore blocking by iron oxide particles which is
dispersed on the inner wall of pore. The IUPAC classifies the adsorption curves as
type IV and the hysteresis loop types as H3, which is similar to the FSM-16 case.
The nitrogen sorption study showed that the BET surface area of FSM-16 is
1318 m2 g-1 and the mesopore volume is 1.59 cm3 g-1. The average pore diameter
is calculated to be 2.94 nm using the BJH method. For Fe/FSM-16 (5.0 wt%), the
BET surface area is 993 m2 g-1 and the mesopore volume is 0.88 cm3 g-1. The
average pore diameter is 2.69 nm. The change is due to that the iron oxide particles
blocking the macropores and some larger mesopores, leaving the smaller mesopores
for the reactants. The pore size distribution of Fe/FSM-16 (5.0 wt%) shrinks
compared to that of FSM-16. It indicates that the iron oxide particles were dispersed
on the inner wall of pores. In the case of used Fe/FSM-16 (5.0 wt%), the BET
surface area is 996 m2 g-1 and the mesopore volume is 0.94 cm3 g-1. The average
pore diameter is 2.60 nm. The results were similar to that of the fresh Fe/FSM-16
(5.0 wt%).
Conclusions
In summary, Fe/FSM-16 is shown to be an efficient catalyst for the hydroxylation of
phenol to catechol and hydroquinone. Phenol conversion and dihydroxybenzene
selectivity increased greatly after the FSM-16 was modified by iron. The optimized
reaction conditions are that the dosage of catalyst is 0.1 g, Fe content is 5.0% (wt),
temperature is 60 °C, reaction time is 6 h and n(phenol):n(H2O2) = 3:1. Phenol
conversion of 29.1% and dihydroxybenzene selectivity (catechol/hydro-
quinone = 1.6) of 93.5% were achieved. The catalytic performance of Fe/FSM-16
123

G. Luo et al.
a
1000
800
600
400
200
0
FSM-16
Desorption
Absorption
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
2
4
6
8
10
12
14
Pore diameter/nm
0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure /P/P0
b
600
500
400
300
200
100
0
fresh Fe/FSM-16
Desorption
Absorption
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
2
4
6
8
10
12
14
Pore diameter/nm
0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure /P/P0
c
600
500
400
300
200
100
0
used Fe/FSM-16
Desorption
Absorption
0.04
0.03
0.02
0.01
0.00
0
2
4
6
8
10
12
14
Pore diameter/nm
0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure /P/P0
123

Green synthesis of dihydroxybenzene from phenol with…
bFig. 4 N2 absorption–desorption isotherms and pore distribution profiles for FSM-16 (a), fresh (b) and
used (c) Fe/FSM-16 (5.0 wt%)
is close to that of TS-1 used in industry production. Moreover, Fe/FSM-16 is
characterized with simple short-period preparation, abundant availability for the raw
material and relatively cheap cost. All of these show excellent prospects for
industrial applications. The results of NH3-TPD show that the weak acid sites are an
active center and responsible for the catalytic activity. The amount of weak acid
sites increased as the Fe content increased. The catalytic activity reached the
maximum. The research of the catalyst N2 absorption–desorption isotherms
illustrates that the iron oxide particles were dispersed on the inner wall of pores
and blocked the macropores and some larger mesopores, leaving the smaller
mesopores to benefit from the reaction. The used catalyst structure, crystallinity,
acid density, surface area, mesopore volume and pore diameter changed a little. It
showed that the Fe/FSM-16 is stable and reusable.
Acknowledgements The work was financially supported by the National Nature Science Foundation of
China under the grant NSFC. Nos. 21103078, 21003069.
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