Preparation and catalytic performance of active metal sintered membrane reactor anchored with Pt atoms

Article abstract of DOI:10.1039/d0ra10175c

In the chemical industry, reactors are typically designed and filled with supported catalyst particles. However, the intrinsic problems associated with the internal/external diffusion effect and catalyst separation/loss in these traditional reactors can be very challenging to mitigate. To address these issues, herein, an active metal sintered membrane reactor anchored with Pt atoms was successfully developed, and applied into continuous, liquid-phase, hydrogenation processes. The catalyzing reactions transpired on the active sites that were fastened onto the surface of the reactor's microchannels. As a result, the mass transfer at the gas-liquid-solid three-phase was greatly enhanced, and an incredibly high reaction efficiency was obtained. The novel, active reactor demonstrated a superior catalytic performance and stability to nitrobenzene (NB) hydrogenation at 120 °C and 0.5 MPa H2, which enabled an aniline (ANI) yield of 19.28 molANI h-1 L-1. This work opens a new window for the design of high-performance gas-liquid-solid reactor toward multiphase catalytic reactions. This journal is

Full text of DOI:10.1039/d0ra10175c

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Preparation and catalytic performance of active
metal sintered membrane reactor anchored with Pt
atoms
Cite this: RSC Adv., 2021, 11, 2848
*
*
Xiaoshu Ding, Dongsheng Zhang
Xiaoliang Ren, Shufang Wang,
*
and Yanji Wang
In the chemical industry, reactors are typically designed and filled with supported catalyst particles.
However, the intrinsic problems associated with the internal/external diffusion effect and catalyst
separation/loss in these traditional reactors can be very challenging to mitigate. To address these issues,
herein, an active metal sintered membrane reactor anchored with Pt atoms was successfully developed,
and applied into continuous, liquid-phase, hydrogenation processes. The catalyzing reactions transpired
on the active sites that were fastened onto the surface of the reactor's microchannels. As a result, the
mass transfer at the gas–liquid–solid three-phase was greatly enhanced, and an incredibly high reaction
efficiency was obtained. The novel, active reactor demonstrated a superior catalytic performance and
stability to nitrobenzene (NB) hydrogenation at 120 ꢀC and 0.5 MPa H2, which enabled an aniline (ANI)
Received 2nd December 2020
Accepted 2nd January 2021
DOI: 10.1039/d0ra10175c
yield of 19.28 molANI hꢁ1
L
ꢁ1. This work opens a new window for the design of high-performance gas–
rsc.li/rsc-advances
liquid–solid reactor toward multiphase catalytic reactions.
catalytic active components were fastened onto the surface of
metal internals (e.g. inner walls, stirring impeller, etc.) in
a kettle reactor, resulting in an active kettle reactor with supe-
rior hydrogenation performance. Thus, the challenges of
limited internal diffusion, poor catalyst separation and loss,
were mitigated. It was found that the hydrogenation activity of
the aforementioned reactor predominantly depends on the
surface area of metal internals. Unfortunately, it is rather
difficult to further improve the effective surface area of kettle
reactor. If the reactor vessel was enlarged, the active surface area
per unit reactor volume would signicantly decrease, which
lead to a diminished production efficiency. Furthermore, the
reaction process was greatly affected by the mass transfer
(external diffusion) of gas–liquid–solid three-phase in kettle
reactor. In order to obtain a good mass transfer effect, vigor-
ously stirring speed was required. But it is very difficult to
achieve in large-scale industrial reactor.
Recently, metal sintered membrane was applied in the eld
of ltration and mixing.26–28 It retains the superior characteris-
tics of metal substrates, while possessing abundant micro-
channel architectures, large surface areas for gas–liquid
contact, and great mass-transfer rates.29,30 Considering the
advantage of the metal sintered membrane, active Pt compo-
nent was loaded into the microchannels of the metal sintered
membrane, and the gas–liquid–solid catalytic reaction could
transpire within the microchannels. It is anticipated that
incorporation of active metal sintered membrane into the
reactor will not only provide a large active surface area, but also
enhance the mass transfer process, both of which could
Introduction
Multi-phase catalytic reactions, such as oxidation, hydrogena-
tion, carbonylation, etc., are industrially crucial to many
processes in the chemical eld.1–6 The chemical processes
typically involve gas and liquid reactants in the presence of
a solid catalyst.7–11 For instance, xed bed reactors (e.g. trickle-
bed reactor, bubble column reactor) and stirred tank slurry
reactors are usually employed for gas–liquid–solid, three-phase
reaction systems.12–16 However, these traditional reactors
possess a few intrinsic problems: (i) the diffusion of reactants
and/or products is hindered by limited diffusion channels
within the catalytic zone, which result in decreased reaction
rates and poor product selectivity.17–20 (ii) poor thermal
conductivity and mechanical strength in catalyst supports can
lead to catalyst sintering and structural degradation during
these reactions.21–23 (iii) the post-reaction, separation of the
catalyst from the products increases the operational cost.24
To address these issues, in our preliminary work,25 Pt-metal
catalysts were successfully prepared by creating single-atom
active sites on the surface of metallic catalyst supports. Due to
the smooth metal surface and lack of micropores, the diffusion
and mass-transfer limitations of the reactants on the catalyst
surface were effectively reduced. By the foregoing method,
Hebei Provincial Key Lab of Green Chemical Technology and High Efficient Energy
Saving, School of Chemical Engineering and Technology, Hebei University of
Technology, Tianjin 300130, China. E-mail: wangshufang@hebut.edu.cn; zds1301@
hebut.edu.cn; yjwang@hebut.edu.cn
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promote the multi-phase catalytic reaction. As far as we con- spectroscopy (EDS, Ametek Octane Plus). The XPS measurement
cerned, few works have been reported on loading Pt into metal was performed on Escalab 250Xi (Thermo Fisher Scientic,
sintered membranes for continuous gas–liquid–solid catalytic USA) using Al Ka radiation as the X-ray source. The C 1s peak at
reaction.
284.8 eV, representing carbon contamination, was used as the
Herein, a novel, active metal sintered membrane reactor reference for the spectra. Inductively coupled plasma atomic
anchored with Pt atoms was prepared. The performance of the emission spectrometry (ICP-AES) analysis was performed on
active membrane reactor was assessed by continuous hydroge- a PerkinElmer Optima 7300 V instrument.
nation of nitro-compounds to anilines reaction. Various oper-
ating parameters were also investigated in the active membrane
reactor.
Performance evaluation
The reaction performance of the as-prepared membrane reactor
was evaluated via the continuous, liquid-phase hydrogenation
of nitroaromatic compounds into their corresponding anilines
as the chosen model-reaction. Initially, both the gas and liquid
enter the reactor through the inner cylinder of the tubular
membrane, then radially proceed out through the micro-
channels of the membrane and along the exterior of the
membrane (between the concurrent cylinders) until the prod-
ucts leave the reactor. Meanwhile, the heat generated in the
reaction process was dissipated into the thermal oil owing in
the jacket.
For comparison, an active trickle-bed reactor lled with
metal q-ring packing was prepared by the same method as active
membrane reactor, enabling the hydrogenation of nitrobenzene
(NB) to aniline (ANI). The inner tube diameter of the trickle-bed
reactor is 18 mm, and 60 cm in length. The size of 316 L
stainless steel q-ring packing is 2 ꢂ 2 mm, with specic surface
area of 3.7 m2 Lꢁ1. The loading capacity of q-ring packing is 75
mL. During the hydrogenation process, the liquid phase was fed
from the top of the reactor, while the gas was introduced at the
bottom of the reactor, allowing the gas and liquid phases to ow
concurrently in the trickle-bed reactor.
Experimental methods
Materials
In this study, all chemicals were of analytical grade and used
without further purication. Chloroplatinic acid hexahydrate
and 2,4-dinitrotoluene were supplied from Sinopharm Chem-
ical Reagent Co., Ltd. Nitrobenzene was purchased from Tianjin
Fuchen Chemical Reagent Co., Ltd. o-Nitrotoluene, m-nitro-
toluene and p-nitrotoluene were purchased from Shanghai
Aladdin Reagent Co., Ltd. 4-Nitroanisole was supplied by TCI
(Shanghai) Chemical Industry Development Co., Ltd. Ethanol
was supplied by Tianjin Chemical Reagent Third Factory. The
water used was distilled water obtained from an Ulupure UPR-II
system.
Preparation of active membrane reactor
A tubular 316 L stainless steel sintered membrane (9 mm inner
diameter, 11 mm outer diameter, 32 cm length, 30% porosity
and 50 mm average pore size) was selected to prepare active
membrane reactor. The metal sintered membrane was contin-
uously treated with chloroplatinic acid aqueous solution of
Lastly, the reaction products were quantitatively analyzed
with a GC-2010plus (Shimadzu) gas chromatograph tted with
an FID detector.
ꢀ
0.80 ppm Pt concentration for 4 h under 155 C and 0.45 Mpa
H2. Aer that, the metal membrane was cleaned with deionized
water, and naturally dried at room temperature. Then, an active
metal sintered membrane anchored with Pt atoms was ob-
tained, and used for fabricating the active membrane reactor.
The conguration of the active metal sintered membrane
reactor is depicted in Fig. 1.
Results and discussion
The SEM image of the active metal sintered membrane was
displayed in Fig. 2. Abundant microchannel architectures could
be clearly observed, the pore size was around 50 mm, such
vigorously microchannel structure was able to induce the
perturbation to the uid ow.31 Moreover, the energy-dispersive
X-ray spectroscopy (EDS) analysis of active metal sintered
membrane (Fig. 3) conrmed the uniformly distribution of Pt
Characterizations
Scanning Electron Microscopic (SEM) image was recorded on
a FEI Nano SEM450 microscope. The distribution of Pt active
component was analyzed using energy-dispersive X-ray
Fig. 1 The schematic configuration of the active metal sintered
membrane reactor.
Fig. 2 SEM image of the active metal sintered membrane.
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active component on the metal membrane support. Addition-
ally, our previous characterization result (HAADF-STEM)
showed that Pt interacted on metal support was dispersed as
single atoms.25 Therefore, it can be inferred that similar single
atom was formed, when Pt was anchored on the metal sintered
membrane support with the same way.
The chemical state of Pt on the active metal sintered
membrane was investigated by high-resolution XPS. The Pt 4f
spectrum showed that Pt 4f7/2 located at 71.6 eV (Fig. 4). As
compared to Pt0 of 71.1 eV,32 a positive shi in Pt binding
energies of the active metal sintered membrane was observed.
This result is consistent with our previous characterization
result of Pt-metal catalyst prepared by the same method.25 Part
of electrons of Pt was transferred to the carrier because of the
strong interaction between Pt atoms and substrate. Thus posi-
tively charged Pt atoms were formed, and a positive shi in Pt
binding energies was observed. Similar phenomena have been
reported in literatures.33–36
Fig.
membrane.
4
The XPS analysis of Pt 4f of the active metal sintered
Table 1, when changing the gas feed rates from 1200 mL minꢁ1
to 2200 mL minꢁ1, the ANI yield was changed from 18.80 molANI
hꢁ1 Lꢁ1 to 19.52 molANI hꢁ1 Lꢁ1, which is a 3.83% yield increase.
With increasing the liquid feed rates from 4 mL minꢁ1 to 6
mL minꢁ1, the yield of ANI was increased from 19.28 molANI hꢁ1
Lꢁ1 to 19.95 molANI hꢁ1 Lꢁ1. There is an increase of 3.48% ANI
yield. These variations were not signicant. The results indi-
cated that the active membrane reactor possessed a superior
multi-phase mixing and dispersion capacity. And interphase
mass transfer was less inuenced by the gas and liquid feed
rates.
Prior to the evaluation of the active membrane reactor, the
blank test was conducted to check the activity of the bare metal
sintered membrane (without loading Pt). It was found that no
ANI was produced on the bare metal membrane. While in the
active metal membrane reactor (loading Pt), the yield of ANI per
ꢁ1
unit membrane volume reached 19.28 mol
h
Lꢁ1 (see Table
ANI
1). This is consistent with characterization results (EDS and
XPS) that active Pt component has been anchored on the metal
sintered membrane aer treated with chloroplatinic acꢁid1
aqueous solution. Compared with the result of 1.04 molANI h
Lꢁ1 in conventional trickle-bed reactor with commercial 0.3%
Pd/Al2O3 catalyst at similar reaction conditions,37 such high
production efficiency of the membrane reactor brings great
competitive advantage to the reactor in industrial application.
The effects of reaction temperature and H2 partial pressure
on the catalytic activity of the membrane reactor were studied.
Table 1 shows the reaction results of NB hydrogenation on
Another effective method to increase the active surface area
per unit volume, is to attach the active Pt component to high
surface-area metallic packing, then ll the active packing into
reaction tube to prepare active trickle-bed reactor. The reaction
performance of the trickle-bed reactor in NB hydrogenation was
investigated, compared with that of membrane reactor at
similar conditions. As can be seen from Table 1, when the liquid
feed rates was changed from 4 mL minꢁ1 to 6 mL minꢁ1, the
yield of ANI was increased from 0.74 molANI hꢁ1 Lꢁ1 to 1.01
molANI hꢁ1 Lꢁ1, which is a 36.5% yield increase. As the
increasing of gas feed rates from 1200 mL minꢁ1 to 2200
mL minꢁ1, the ANI yield was varied from 0.63 molANI hꢁ1 Lꢁ1 to
0.81 molANI hꢁ1 Lꢁ1 (28.6% yield increase). These results
showed that the reaction performance of the trickle-bed reactor
was greatly affected by feed rates. The highest ANI yield pꢁe1r unit
the membrane reactor at the H2 partial pressure of 0.3–0.6 MPa,
ꢁ1
the yield of ANI was ranged from 13.23 mol
h
Lꢁ1 to 21.99
ANI
ꢁ1
mol
h
Lꢁ1. When increasing the reaction temperature from
ANI
100 ꢀC to 130 ꢀC, the ANI yield for the reactor was increased
from 11.64 molANI hꢁ1 Lꢁ1 to 23.41 molANI hꢁ1 Lꢁ1. These
results demonstrated that the reaction performance of the
membrane reactor could be signicantly improved by
increasing reaction temperature and H2 pressure.
volume in the trickle-bed reactor was only 1.01 molANI h Lꢁ1
.
Moreover, the feed rates of the liquid and gas streams in the
active membrane reactor were also investigated. As shown in
The reaction performance of the membrane reactor (19.95
ꢁ1
mol
h
Lꢁ1) was about 20 times as high as that of trickle-bed
ANI
reactor. Hence the membrane reactor exhibited much higher
production efficiency.
Furthermore, the reaction results per unit active surface area
of the two reactors were given to compare the gas–liquid–solid
mass transfer in the two reactors. It can be seen from Table 1
that the ANI yield per unit active surface area of membrane
reactor was more than 3 times greater than that of the trickle-
bed reactor under the same reaction conditions. And the
inuence of feed rates on the results of membrane reactor was
obviously smaller than that of trickle-bed reactor, which
demonstrated
a superior mass transfer capacity of the
Fig. 3 EDS analysis of Pt on the active metal sintered membrane.
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Table 1 Yield of the continuous liquid-phase hydrogenation of NB in the active membrane and trickle-bed reactorsa
Liquid feed Gas feed
rate rate
(mL minꢁ1) (mL minꢁ1) (ꢀC)
Reaction
ANI yield per unit
ANI yield per unit active
surface area (molANI hꢁ1 Standard
Type of
reactors
temperature H2 pressure membrane (packing)
Standard
(MPa)
volume (molANI hꢁ1 Lꢁ1) deviation mꢁ2
)
deviation
Active
membrane
reactor
4
5
6
4
4
4
4
4
4
4
4
4
5
6
4
4
1700
1700
1700
2200
1200
1700
1700
1700
1700
1700
1700
1700
1700
1700
2200
1200
120
120
120
120
120
130
110
100
120
120
120
120
120
120
120
120
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.6
0.4
0.3
0.5
0.5
0.5
0.5
0.5
19.28
19.77
19.95
19.52
18.80
23.41
14.29
11.64
21.99
16.13
13.23
0.74
0.460
0.484
0.357
0.240
0.331
0.318
0.434
0.305
0.350
0.285
0.405
0.016
0.028
0.030
0.034
0.018
0.80
0.82
0.83
0.81
0.78
0.98
0.60
0.49
0.92
0.67
0.55
0.20
0.24
0.27
0.22
0.17
0.019
0.020
0.015
0.010
0.014
0.013
0.018
0.013
0.015
0.012
0.017
0.004
0.008
0.008
0.009
0.005
Active trickle-
bed reactor
0.89
1.01
0.81
0.63
a
Reaction conditions: 1.05 mol Lꢁ1 NB, ethanol as solvent.
membrane reactor. In fact, metal sintered membrane reactor catalyst surface can be signicantly shortened within the
possesses the characteristic of abundant microchannel archi- microscale range.38,39 Furthermore, microchannel structure is
tecture. And the mass transfer of gas–liquid–solid three-phase able to induce the perturbation to the uid ow and enhance
can transpire within the microchannels during the reaction. the mixing process.31,40 During the process, each individual
As a result, the diffusion distance from the reactants to the microchannel can operate as a microreactor for carrying out the
Table 2 The hydrogenation results of alternative substituted nitroaromatic compounds in the active membrane reactora
Product yield per
Product yield per unit
Concentration unit membrane volume
Standard
deviation
active surface area (mol Standard
Substrate
(mol Lꢁ1
)
(mol hꢁ1 Lꢁ1
)
hꢁ1 mꢁ2
)
deviation
Product
0.22
4.98
0.100
0.090
0.21
0.004
0.22
4.34
0.18
0.004
0.39
0.77
8.33
0.206
0.409
0.35
0.68
0.009
0.017
16.25
0.77
0.77
15.34
14.06
0.289
0.316
0.64
0.59
0.012
0.013
a
Reaction conditions: liquid ow rate: 4 mL minꢁ1, gas ow rate: 1700 mL minꢁ1, T ¼ 120 ꢀC, P ¼ 0.50 MPa H2, ethanol as solvent.
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Fig. 7 EDS analysis of Pt on the active metal sintered membrane after
25 h of hydrogenation.
ꢁ1
to 4.34 mol
h
Lꢁ1, and the reaction efficiency of the active
2,4-TDA
Fig. 5 The long-term reaction performance of the active membrane
reactor. Reaction conditions: liquid flow rate: 4 mL minꢁ1, gas flow
rate: 1700 mL minꢁ1, 1.05 mol Lꢁ1 NB, ethanol as solvent, T ¼ 120 ꢀC, P
¼ 0.50 MPa H2.
membrane reactor was superior to that found in literature, which
utilizes the traditional trickle-bed reactor equipped with 5% Pd/
Al2O3 catalyst.44
The stability of the metal sintered membrane was further
evaluated in NB hydrogenation. Fig. 5 depiꢀcts the yield of ANI
with respect to the operational time at 120 C and 0.5 MPa H2.
The yield of ANI consistently remained at about 19.28 molANI
hꢁ1 Lꢁ1 with minor variations during the 25 h operational
period. Compared the micromorphology of the membrane
before (Fig. 2) and aer (Fig. 6) the long-term tests, it was found
that no obvious change of the metal sintered membrane was
observed, which indicated the good structure stability of the
membrane reactor. The EDS analysis (Fig. 7) of active metal
sintered membrane aer 25 h of hydrogenation showed that the
Pt atoms were still evenly distributed on the metal membrane
support. Moreover, ICP-AES analysis of the reaction solution
aer the hydrogenation was performed, and no Pt species were
detected in the solution. These results conrmed the excellent
stability of the catalytic membrane reactor under normal
operating conditions.
gas–liquid–solid catalytic reaction. It has been proved that
continuous ow microreactor is benecial for accelerating the
reaction rate with enhanced mass transfer, as comparing to
conventional reactors.31,41–43 Therefore, it was concluded that
the active membrane reactor has a remarkable effect on
enhancing gas–liquid–solid mass transfer and promoting the
multi-phase catalytic reaction process. It was also a key factor
for high production efficiency of the active membrane reactor.
A series of substituted nitroarenes were also assessed in the
active membrane reactor to verify its substrate tolerance. As can
be seen from Table 2, the membrane reactor exhibited a superior
catalytic performance in reducing substituted nitrobenzenes (in
para, meta and ortho positions) to their corresponding amines,
demonstrating that the reactor's surface active sites possess good
space-steric hindrance tolerance. In addition, the active
membrane reactor was successfully applied to the hydrogenation
of 2,4-dinitrotoluene (2,4-DNT) to 2,4-toluenediamine (2,4-TDA).
Besides main product of 2,4-TDA, a small amount of by-products
such as 2-nitro-4-aminotoluene and 2-amino-4-nitrotoluene, were
also detected in reaction solution. The reason may be as follows.
The 2,4-DNT contains two –NO2 groups, one of the –NO2 was rst
converted to –NH2 during the hydrogenation.44,45 The electron-
donating effect of the formed –NH2 reduced the hydrogenation
rate of the other –NO2 group.46,47 Thus, some by-products of
mono-nitro group reduction were formed. At 0.5 MPa H2 and
120 ꢀC, the 2,4-TDA yield per unit membrane volume reached up
Conclusions
In this study, an active metal sintered membrane reactor
anchored with Pt atoms was successfully developed, and
applied to continuous liquid-phase catalytic hydrogenation
processes. More specically, the hydrogenation was carried out
in the reactor's microchannels that loaded with active Pt
component. Such design could not only provide large active
surface area, but also enhance mass transfer process, thus
improving the production efficiency. The active membrane
reactor exhibited an excellent catalytic performance in the
hydrogenation of NB to ANI. For instance, at 120 ꢀC and
a hydrogen pressure of 0.5 MPa, the yield of ANI per unit
membrane volume reached 19.28 molANI hꢁ1 Lꢁ1 while main-
taining an impressive catalytic stability. Alternatively, hydroge-
nation of 2,4-DNT to 2,4-TDA can also be performed ꢁin1 the
active membrane reactor, yielding up to 4.34 mol2,4-TDA h Lꢁ1
.
This successful development of the novel active metal sintered
membrane reactor is of great importance towards enhancing
the mass transfer effect, simplifying production processes and
improving production efficiency for gas–liquid–solid, three-
phase reactors.
Fig. 6 SEM image of the active metal sintered membrane after the
long-term tests.
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20 J. Aumo, J. Warna, T. Salmi and D. Y. Murzin, Chem. Eng. Sci.,
2006, 61, 814–822.
Conflicts of interest
21 P. Forzatti and L. Lietti, Catal. Today, 1999, 52, 165–181.
22 C. H. Bartholomew, Appl. Catal., A, 2001, 212, 17–60.
23 R. Zhao, J. G. Goodwin and R. Oukaci, Appl. Catal., A, 1999,
189, 99–116.
There are no conicts to declare.
Acknowledgements
24 H. Q. Yang, T. Zhou and W. J. Zhang, Angew. Chem., Int. Ed.,
2013, 52, 7455–7459.
25 X. L. Ren, J. D. Li, S. F. Wang, D. S. Zhang and Y. J. Wang,
Catal. Commun., 2019, 128, 105709.
26 B. Zhu, M. Duke, L. F. Dumee, A. Merenda, E. des Ligneris,
L. X. Kong, P. D. Hodgson and S. Gray, Membranes, 2018,
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27 Z. Xu and J. Yu, Chem. Eng. Sci., 2008, 63, 1941–1949.
28 H. Singh, P. Saxena and Y. M. Puri, Mater. Lett., 2020, 269,
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This work was nancially supported by the National Natural
Science Foundation of China (No. 21576069, 21236001,
21606070 and 21878069) and Hebei Science and Technology
Project (17214203D).
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