Highly dispersed Co-based Fischer-Tropsch synthesis catalysts from metal-organic frameworks

Article abstract of DOI:10.1039/c7ta02128c

The influence of pore texture and nitrogen species of the carbon support for the Fischer-Tropsch synthesis was investigated using well-defined catalysts derived from metal-organic frameworks (MOFs). Two typical MOFs were employed in the carbonization process to prepare the target catalysts, i.e. nitrogen-rich ZIF-67 and nitrogen-free Co-MOF-74. The Co-MOF-74-derived nanocomposite (Co@C) showed a carbon monoxide (CO) conversion of 30%, whereas the ZIF-67-derived nanocomposite (Co@NC) exhibited a CO conversion of 10%. The nitrogen-free Co@C composite showed 65% selectivity for long-chain hydrocarbons (C₅⁺) and 10% selectivity for short-chain hydrocarbons (C₂-C₄) after 100 h on stream; on the other hand, the Co@NC composite showed 31% selectivity for C₅⁺ products and 37% selectivity for short-chain hydrocarbons (C₂-C₄) after 100 h on stream. The excellent CO conversion was attributed to the large pore size of the carbon support, which facilitates the diffusion of the hydrocarbons. The high C₂-C₄ selectivity originates from the influence of nitrogen species in the carbon support. This study is expected to open a new avenue for the design of new catalysts for the Fischer-Tropsch synthesis with high activity and superior selectivity via choosing suitable MOFs precursors.

Full text of DOI:10.1039/c7ta02128c

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ISSN 2050-7488
PAPER
Kun Chang, Zhaorong Chang et al.
Bubble-template-assisted synthesis of hollow fullerene-like
MoS nanocages as a lithium ion battery anode material
2
rsc.li/materials-a

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ARTICLE
Highly Dispersed Coꢀbased FischerꢀTropsch Synthesis Catalysts
from MetalꢀOrganic Frameworks
Received 00th January 20xx,
Accepted 00th January 20xx
a,†
b,†,ǂ
a
b
a
b,*
a,*
Bin Qiu , Ce Yang , Wenhan Guo , Yao Xu , Zibin Liang , Ding Ma and Ruqiang Zou
DOI: 10.1039/x0xx00000x
www.rsc.org/
The influence of pore texture and nitrogen species of the carbon support for FischerꢀTropsch synthesis had
been investigated by using wellꢀdefined catalysts derived from metal organic frameworks (MOFs). Two
typical MOFs were employed for carbonization to prepare target catalysts, i.e. the nitrogenꢀrich ZIFꢀ67 and
nitrogenꢀfree CoꢀMOFꢀ74. CoꢀMOFꢀ74 derived nanocomposites (Co@C) showed carbon monoxide (CO)
conversion of 30% while ZIFꢀ67 derived nanocomposites (Co@NC) exhibited CO conversion of 10%. The
+
nitrogenꢀfree Co@C composites showed selectivity for longꢀchain hydrocarbons (C
5
) of 65% and the
selectivity for shortꢀchain hydrocarbons (C
2
ꢀC
4
) of 10% for 100 h on stream. On the other hand, Co@NC
ꢀC
+
5
composites showed selectivity of C
products of 31% and the selectivity for shortꢀchain hydrocarbons (C
2
4
)
of 37% for 100 h on stream. The excellent CO conversion was attributed to large pore size of the carbon
support which facilitated the diffusion of hydrocarbons. High C ꢀC selectivity came from the influence of
2
4
nitrogen species in the carbon support. This work would open a new avenue to design new catalysts for
FischerꢀTropsch synthesis with high activity and superior selectivity by choosing the suitable MOFs
precursors.
2
ꢀ4
Introduction
Ru. Although Ru shows high activity and selectivity for FTS, it is
5
aꢀ5c
With the rapid consumption of oil, FischerꢀTropsch synthesis (FTS) not suitable for commercial usage due to its scarcity.
And Feꢀ
from syngas (CO and H derived from natural gas, coal and biomass) based catalysts endure the comparatively low stability and poor
2
6
ꢀ7
has become an efficient alternative strategy to meet the demand of selectivity towards longꢀchain hydrocarbons.
Meanwhile, Coꢀ
1
oil fuel. The most widely used catalysts for FTS are Co, Fe and based catalysts have characteristics of reasonable cost, high activity,
superior selectivity and low CO emission, which make the Coꢀbased
2
a.
Beijing Key Laboratory for Theory and Technology of Advanced Battery catalysts the most widely used catalysts for commercial FTS process,
Materials, Department of Materials Science and Engineering, College of
Engineering, Peking University, Beijing 100871, China. Eꢀmail:
rzou@pku.edu.cn.
8
such as Pearl GTL, the world’s largest FTS plant in Qartar.
b.
Beijing National Laboratory for Molecular Sciences, College of Chemistry and
Molecular Engineering, Peking University, Beijing 100871, China. Email: Metal organic frameworks (MOFs) is a kind of microporous
dma@pku.edu.cn.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
crystalline polymers constructed by metal and organic ligand with
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high surface area and porosity, which can be widely used in gas Synthesis of Coꢀbased catalysts derived from metal organic
storage/separation, chemical sensing, heterogeneous catalysis, frameworks are illustrated in Scheme 1. We use two typical MOFs
9
ꢀ10
bioimaging, and drug delivery and luminescence.
Inheriting these (CoꢀMOFꢀ74 and ZIFꢀ67) as the template to synthesize Co@C and
properties, MOFsꢀderived materials also exhibit high surface area, Co@NC composites as the catalysts for FischerꢀTropsch synthesis.
high pore volume and well dispersed nanosize metal particles, which Wellꢀdefined ZIFꢀ67 and CoꢀMOFꢀ74 are synthesized according to
14ꢀ15
does well to the performance of catalytic reaction. Recently Feꢀbased the published paper.
Specifically, ZIFꢀ67 is chosen from the
catalysts derived from FeꢀBTC show high CO conversion and stable
11ꢀ12
operation.
The obtained Fe@C features a high dispersion of Fe
nanoparticles confined within a porous carbon matrix. When used in
FTS, the Fe@C exhibits an excellent catalytic activity and superior
selectivity. Inheriting this idea, nitrogen species are further
introduced into the carbon matrix by carbonizing the nitrogenꢀrich
FeꢀMILꢀ88BꢀNH . In this work, nitrogen species are investigated to
2
13
tune the activity and selectivity of the final Feꢀbased catalyst.
Scheme 1 Schematic illustration for synthesis of Coꢀbased catalysts
by the pyrolysis of two typical MOFs.
These interesting results demonstrate that the MOFꢀmediated
synthesis strategy is a promising route for the preparation of
exceptionally dispersed Fe nanoparticles in a porous carbon matrix
with outstanding FTS performance. Until now, there are no reports
about Coꢀbased catalyst derived from MOFs for FTS.
nitrogenꢀrich precursor. In this MOFs, each cobalt cation is bridged
with four nitrogen atoms from the 2ꢀmethylimidazolate anions into
tetrahedral frameworks and further assembles into a sodalite (SOD)
1
6
topology. And CoꢀMOFꢀ74 is chosen from nitrogenꢀfree precursor.
Herein, we developed a new Coꢀbased FischerꢀTropsch catalyst
derived from MOFs. We investigated CoꢀMOFꢀ74 (w/o N) and ZIFꢀ
In this MOFs, the crystal structure is composed of infinite rods
3 3 2 3
Co O (CO ) and 2,5ꢀdioxidoterephthalate linkers, where each cobalt
67 (w/ N) as well as the derived Co@C and Co@NC
cation is coordinated with three carbonxyl, two hydroxyl groups and
nanocomposites to look into the influence of the structure of MOFs
precursors onto the structure and catalytic performance of the
derived Co catalysts. According to our results, CoꢀMOFꢀ74 derived
composites (Co@C) showed high CO conversion of 30%, high
17
a DMF or H O. The purity of the sample was confirmed by PXRD
2
patterns as shown in Fig. S1ꢀS2 (Supporting Information (SI)). And
from the N
2
adsorption test, we calculated the BrunauerꢀEmmettꢀ
Teller (BET) surface area for pure ZIFꢀ67 and CoꢀMOFꢀ74 as 1617
+
selectivity to C5 products of 65% and low selectivity of shortꢀchain
2
ꢀ1
2
ꢀ1
m g and 1025 m g , respectively (Fig. S3ꢀS4, SI). These results
2 4
hydrocarbons (C ꢀC ) of 10%. In comparison, ZIFꢀ67 deriving
confirm the high purity of the precursor.
composite (Co@NC) exhibited low CO conversion of 10%, low
To fabricate the FTS catalysts, we used the asꢀsynthesized MOFs as
sacrificial selfꢀtemplates and thermally treated them to carbonize the
organic components as well as reduce the metal species. The thermal
treatment procedure was designed according to thermogravimetric
analysis (TGA) results. From the TGA curves of ZIFꢀ67 under insert
+
selectivity to C5 products of 31% and high selectivity of shortꢀchain
2 4
hydrocarbons (C ꢀC ) of 37%, which means that the asꢀprepared Co
catalysts have significant differences based on the precursor chosen.
Results and Discussion
2
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atmosphere, a large weight loss around 500 °C is contributed by the larger size with a rod shape as shown in Fig. 1e. After thermal
destruction of MOFs structures (Fig. S5, SI). Meanwhile, from the treatment, the obtained Co@Cꢀ550 nanocomposites also keep the
TGA curves of CoꢀMOFꢀ74 under insert atmosphere, the first weight rod shape as shown in the SEM image (Fig. 1f). According to the
loss before 150 °C comes from the evaporation of remnant solvents TEM test of a fragment obtained by sonication (Fig. 1g), there are
like DMF and methanol, and the second weight loss around 500 °C also well dispersed NPs with size of 8 nm embedded in the carbon
is contributed by the destruction of MOFs structures (Fig. S6, SI). matrix in the composites. The lattice space value of 0.205 of the NPs
Therefore, to ensure the complete reduction of Co species and keep in the HRTEM image also indicates the NPs as Co species (Fig. 1h).
the small size of the Co nanoparticles (NPs), a high temperature of
550 °C is chosen for the thermal treatment. After the treatment, two
asꢀsynthesized composites, Co@Cꢀ550 and Co@NCꢀ550, are used
as the catalysts for the FTS.
The morphology of two MOFs precursors and their corresponding
MOFꢀderived composites were characterized by SEM, TEM and
HRTEM (Fig. 1). It is obvious that ZIFꢀ67 precursor has wellꢀ
defined polyhedral shape with particle size about 300 nm (Fig. 1a).
After thermal treatment, the morphology of the Co@NCꢀ550
composite retains as that of the precursor (Fig. 1b). Moreover,
uniformly distributed NPs with size of 6 nm can be seen in the
carbon matrix as shown in Fig. 1c. Based on HRTEM, the NPs have
lattice space value of 0.205 nm as shown in Fig. 1d, which fits well
Fig.
2
(a) PXRD patterns of Co@NCꢀ550 and Co@Cꢀ550
adsorptionꢀdesorption isotherms and pore size
composites. (b) N
2
distribution of Co@NCꢀ550 and Co@Cꢀ550 composites.
The crystal structure and pore texture of the asꢀsynthesized Co@Cꢀ
5
50 and Co@NCꢀ550 composites were evaluated by PXRD and N
2
sorption experiments (Fig. 2). It is obvious that all the PXRD peaks
of Co@Cꢀ550 and Co@NCꢀ550 composites can be assigned to
metallic cobalt (Fig. 2a). The broad and low intensity nature of the
peaks indicate the tiny size of the cobalt particles. And from the N2
adsorption test, Co@NCꢀ550 composites exhibit BET surface area
18
to the Co (111), suggesting the NPs as Co species. In comparison,
CoꢀMOFꢀ74 precursor synthesized by solvothermal method shows
2
ꢀ1
of 309 m g (Fig. 2b). The high uptake at low relative pressure
19
indicates the large amount of micropores. Meanwhile, Co@Cꢀ550
2
ꢀ1
composites exhibit surface area of 341 m g which shows larger
hysteresis (type H3) between adsorption and desorption branches
than Co@NCꢀ550 composites, indicating the presence of large
amount of mesoporous cavities. The total pore volume for Co@Cꢀ
Fig. 1 SEM images of (a) ZIFꢀ67 and (b) Co@NCꢀ550 composites.
3
ꢀ1
5
50 and Co@NCꢀ550 composites are 0.58 and 0.37 m g , in which
(
c) TEM images of Co@NCꢀ550 composites. (d) Highꢀresolution
high pore volume of the catalysts may expose more active metal to
the reaction gas for the catalysis. From the NLDFT model, Co@Cꢀ
TEM (HRTEM) images of Co@NCꢀ550 composites. SEM images
of (e) CoꢀMOFꢀ74 and (f) Co@Cꢀ550 composites. (g) TEM images
of Co@Cꢀ550 composites. (h) HRTEM images of Co@Cꢀ550
composites.
5
50 composites have larger pore size of 7 nm while the Co@NCꢀ550
have the pore size of 3 nm. It is worth mention that, based on early
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report, larger pore of carbon support can facilitate the diffusion of (Fig. 3c), it is obvious that Co@NCꢀ550 samples contain two peaks
2
0
liquid longꢀchain hydrocarbons.
located at 780.4 eV (Co 2p 3/2) and 796.2 eV (Co 2p 1/2) along with
XPS characterizations are conducted to analyze the surface the two satellite peaks are contributed by the divalent Co or CoNx,
elemental composition as well as the chemical bonding environment which indicates that the surface Co atoms that may have interaction
24ꢀ25
of the asꢀsynthesized composites as shown in Fig. 3. In particular, N with the nitrogen doped carbon matrix.
Meanwhile, Co@Cꢀ550
species are viewed as efficient electron donor to enhance the CO shows Co species corresponding to metallic Co (778.5 eV) from
2
6
adsorptionꢀdissociation process and tune the selectivity of the final XPS spectra of Co 2p (Fig. 3d).
21
products for FischerꢀTropsch synthesis. From the full spectra of
Co@Cꢀ550 and Co@NCꢀ550 composites shown in Fig. 3a, only
Fig. 4 (a) Simulated FTꢀEXAFS data for Co@NCꢀ550 (blue dot
line) as a sum of contribution from nitrogen scattering (black ■) and
coblat scattering (red ●). (b) Experimental FTꢀEXAFS pattern
obtained for fresh Co@NCꢀ550 catalysts. (c) Simulated FTꢀEXAF
data for Co@Cꢀ550 (blue dot line) as a sum of contribution from
carbon scattering (black ■) and coblat scattering (red ●). (d)
Experimental FTꢀEXAFS pattern obtained for fresh Co@Cꢀ550
catalysts.
Fig. 3 XPS full spectra of (a) the Co@Cꢀ550 and Co@NCꢀ550
EXAFS is used to investigate the fine structure of the samples in Fig.
composites, (b)N 1s in Co@NCꢀ550 composites，(c) Co 2p in
4
. For verification, the theoretical Fourier transformed EXAFS (FTꢀ
Co@NCꢀ550 composites, and (d) Co 2p in Co@Cꢀ550 composites.
Co@NCꢀ550 samples show existence of N species which is
consistent with the ZIFꢀ67 texture properties. Then we used highꢀ
resolution N 1s spectrum to investigate the states of N species in
Co@NCꢀ550 (Fig. 3b). The spectra can be deconvoluted into three
peaks of pyridinic N (398.7 eV), pyrrolic N (400.0 eV), graphitic N
EXAFS) pattern of the first two coordination shells of Co@NCꢀ550
and Co@Cꢀ550 is fitted using the program IFEFFIT. In Fig. 4a, the
blue fitted line is a joint contribution of Co−N scattering in the first
Co−N coordination shell (black square) and CoꢀCo scattering in the
first CoꢀCo coordination shell (red circle). And the experimental
curve shown in Fig. 4b is in good agreement with the simulated. The
other peaks in the experimental pattern represent the outer
coordination shells of Co/CN. The corresponding CoꢀN and CoꢀCo
bond lengths were determined to be 2.01 and 2.49 Å (Table S1, SI),
respectively. As for the Co@Cꢀ550 composites, the blue fitted line is
22
(
401.2 eV). Pyridinic N is founded to be the prominent species in
Co@NCꢀ550 samples. It is suggested that cobalt preferentially
2
aggregate on the sp ꢀtype nitrogen sites to nucleate and grow due to
2
3
the strong interaction between cobalt and π electrons. This
indicates that species in carbon support facilitates the
immobilization of the cobalt species. From the XPS spectra of Co 2p
N
a
joint contribution of Co−C scattering in the first Co−C
coordination shell (black square) and CoꢀCo scattering in the first
4
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CoꢀCo coordination shell (red circle) in Fig. 4c. The experimental composites is larger than Co@NCꢀ550 composites. Moreover, wider
curve also showed a good agreement with the simulated curve as pore mesoporous distribution of Co@Cꢀ550 is also beneficial to the
shown in Fig. 4d. The corresponding CoꢀC and CoꢀCo bond lengths diffusion of gas and mass diffusion in the carbon matrix, resulting in
2
7
were determined to be 2.11 and 2.50 Å (Table S1, SI), respectively. a higher catalytic activity. However, as the formation of longꢀchain
From the EXAFS result, it is obvious that there is CoN species in hydrocarbons, active sites may be covered by these products in the
the Co@NCꢀ550 composites. This results are consistent with the narrow pore supports, which lead to the deactivation of the
x
2
8
XPS results which confirm that the existence of CoN species in the catalyst. It is obvious that Co@Cꢀ550 composites deactivate more
x
Co@NCꢀ550 composites again.
slowly than Co@NCꢀ550 composites because the larger pore size of
Co@Cꢀ550 composite facilitates the diffusion of longꢀchain
+
hydrocarbons like C5 products. The product selectivities for two
typical catalysts are shown in Fig. 5b. After 100 h test, the selectivity
+
of C
5
products for Co@Cꢀ550 samples reaches 65% while
+
Co@NCꢀ550 composites only exhibits a selectivity towards C5 of
3
1%. It is known that Coꢀbased FTS catalysts usually has higher
+
+
selectivity towards C
5 5
products. And the lower C selectivity of
Co@NCꢀ550 is because that the small pore size of Co@NCꢀ550
composites impedes the transportation of longer chain hydrocarbons
on one hand. On the other hand, the nitrogen species act as the
electron donor which can change the valence state of the cobalt, and
thus, promote the synthesis of shortꢀchain hydrocarbons in FTS.
Fig. 5 FTS catalytic performance. (a) Overall CO conversion of
Co@Cꢀ550 and Co@NCꢀ550 catalysts. (b) Products selectivity of
4
Co@Cꢀ550 and Co@NCꢀ550 composites after 100 h test. CH and
2
9ꢀ31
Similar effect was observed by previous reports.
From the
CO selectivity of (c) Co@Cꢀ550 and (d) Co@NCꢀ550.
2
characterization of our MOFs derived catalysts, it was obvious that
nitrogen species in the carbon matrix which might introduce the
formation of CoNx confirmed by our XPS and EXAFS test. Then
the changed Co surface state could tune the products selectivity for
FTS. To provide more details about the selectivity of products, the
time on stream selectivity of CH and CO are shown in Fig. 5c,5d.
We used the asꢀsynthesized Co@Cꢀ550 and Co@NCꢀ550
composites for the catalysts of FTS. The CO conversion and
products selectivity of the composites for FTS are shown in Fig. 5.
The catalytic performance are calculated on the actual weight of Co
content in the composites (calculated from ICP test as summarized in
Table S2, SI). Both catalysts experienced deactivation process
during the initial stage in Fig. 5a. After that, CO conversion of
Co@Cꢀ550 composites maintains 30%, while the CO conversion of
Co@NCꢀ550 composites only maintains 10% conversion after 100 h
test. The higher CO conversion of Co@Cꢀ550 should be attributed to
higher loading percentage and abundant porosity than those of
4
2
Both catalysts show low CO
2
selectivity as Coꢀbased catalyst
exhibited lower water gas shift activity. And the selectivity of CH
for Co@NCꢀ550 and Co@Cꢀ550 composites are almost the same.
Just as the small molecule CH was easy to be transported in the
pores of the carbon matrix. But the selectivity of CH and CO for
4
4
4
2
Co@Cꢀ550 composites are suppressed in comparison to Co@NCꢀ
2
Co@NCꢀ550. From the N sorption test, the pore size of Co@Cꢀ550
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50 composites, which is highly desired for obtaining the maximum Conclusion
Journal Name
5
production of longꢀchain hydrocarbons. After 100 h test, the PXRD In summary, we synthesized two Coꢀbased FTS catalysts derived
peaks of Co@Cꢀ550 and Co@NCꢀ550 composites are consistent from MOFs and investigated the influence of pore texture and
with metallic cobalt respectively as shown in Fig. S7ꢀS8 (SI). This nitrogen species on the catalytic performance. The asꢀsynthesized
result confirms that the metal phase is assigned to metallic cobalt. catalysts equipped with well dispersed Co NPs embedded in carbon
The morphology is characterized by TEM and HRTEM for Co@Cꢀ matrix which provide the catalysts with unique feature like pore
550 and Co@NCꢀ550 composites after 100 h test (Fig. S9, SI). structure and large surface area. Notedly, large pore size of the
There are well dispersed nanoparticles embedded in the carbon support can facilitate the diffusion of hydrocarbons, thus enhance the
+
matrix in the Co@Cꢀ550 composites in Fig. S9a (SI). The lattice CO conversion and C
5
selectivity of the catalysts. While the
space value of 0.205 nm of the particles in the HRTEM image nitrogen species in carbon matrix can tune the products selectivity
indicates the particles as Co species (Fig. S9b, SI). It is obvious that towards shortꢀchain hydrocarbons through the electronic effect. In
+
Co@NCꢀ550 composites still retain the polyhedral shape with small order to get high CO conversion with high C
5
selectivity and low
particle can be seen in carbon matrix as shown in Fig. S9c (SI). shortꢀchain hydrocarbons selectivity, larger pore size carbon matrix
Based on HRTEM, the particles have lattice space value of 0.205 nm without nitrogen species may be chosen. These findings provide a
as shown in Fig. S9d (SI), which fits well to the Co (111), new route for the designing of high performance Coꢀbased FTS
suggesting the particles as Co species.
catalysts.
Up to now, there are only a few cases about MOFꢀderived FTS Experimental Section
1
1ꢀ13,32
catalysts as shown in Table S3 (SI).
The first MOFꢀderived Feꢀ Preparation of the Catalyst
based FTS catalyst exhibits high CO conversion and superior Synthesis of CoꢀMOFꢀ74: The synthesis is carried out by following
14
stability under the operating temperature near to 340 °C. Compared published paper with a minor modification. 0.241 g H
with Feꢀbased catalysts, Coꢀbased catalysts have many advantages (2,5ꢀdihydroxyterephthalic acid) and 1.1885 g Co(NO
such as the enhanced activity, higher chain growth probability and added a mixture DMFꢀEthanolꢀH O (v/v/v=1:1:1, 100 mL, DMF=
4
DOBDC
3
)
2
·6H O is
2
2
lower water gas shift activity. Notedly, the Co@Cꢀ550 catalyst N,Nꢀdimethylformamide) in a 125 mL Teflonꢀlined steel autoclave,
+
shows high selectivity to C
5
in a relative low reaction temperature and heated at 100 °C for 24 h. The as prepared crystals are filtered
of 230 °C. Until now, there is one published paper about Coꢀbased out and washed by DMF, methanol, finally dried at 150 °C for 12 h.
catalysts by using MOF as Co nanoparticles carrier, namely Synthesis nano ZIFꢀ67: The procedure is carried out by our precious
3
2
15
Co@MILꢀ53(Al). Generally, MOF substrates usually shows the method: 1.43 g Co(NO ) ·6H O is dissolved in 100 mL methanol
3
2
2
limited stability to highꢀtemperature gasꢀphase catalytic reaction. forming homogeneous solution. And 3.244 g 2ꢀmethylimidazole is
Furthermore, the nitrogenꢀfree Co@Cꢀ550 catalyst exhibits dissolved into 100 mL methanol respectively. The two solution are
ultrasmall Co nanoparticles embedded in hierarchically porous mixed at room temperature and stirring for 15 min, and then stand
carbon by the inꢀsitu pyrolysis of CoꢀMOFs, which displays for 24 h. Final products are collected by centrifugation and washed
+
enhanced CO conversion with high selectivity of C
5
and low with methanol for three times, followed by vacuum drying at 150 °C
for 12 h.
selectivity of C ꢀC .
2
4
6
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Synthesis of Co@Cꢀ550 composites: The as prepared CoꢀMOFꢀ74 is loaded in a stainless steel tube lined with a quartz layer. The gas
3
ꢀ1
are carbonized at 550 °C for two hours under Ar with a heating rate hourly space velocity (GHSV) of the reaction is set at 20 cm min .
ꢀ
1
of 5 °C min . For comparison, Co@NCꢀ550 composites are just For the Co@C and Co@NC catalysts, no H
2
or CO activation is
carbonizing ZIFꢀ67 at 550 °C for 2 h under Ar with a heating rate of adapted. The pressure of the reactor is set at 3 MPa, and the
ꢀ
1
ꢀ1
5
°C min .
temperature is raised from 303 K to 503 K at 3 K min , the products
Materials Characterization
can be directly detected just as the temperature goes up to the setting
number. The product with large molecular weight is collected in a
The powder Xꢀray diffraction (PXRD) patterns of composites are
recorded on a Bruker D8 Advanced diffractometer using Cu Kɑ cold trap. Hydrocarbons are analyzed using a 6820 GC with an HPꢀ5
radiation (λ=1.5405Å) and operating at 40 KV and 100 mA. capillary column and an FID, and oxygenates in water are analyzed
BrunauerꢀEmmettꢀTeller (BET) surface area and pore volume of the using a 6820 GC with an HPꢀINNOWax capillary column and an
materials are evaluated by nitrogen sorption measurement at 77 K FID. The selectivity of final products are all on a carbon basis.
using a Quantachrome AutosorbꢀIQ gas adsorption analyzer. Before Products analysis
the adsorption test, MOFꢀ74 are activated under vacuum at 250 °C The final product and reactant in the gas are detected by Agilent
for 5 h and ZIFꢀ67 are activated under vacuum at 150 °C for 5 h. 6890 GC. C
ꢀC
1 4
products are analyzed by a plot Al
2
O
3
capillary
BET surface area are calculated from the gas adsorption curves and column with a flame ionization detector (FID); CO, CO
2
, CH and
4
pore size distribution are obtained from Quenched Solid Density Ar are analyzed using a Porapak Qꢀ and 5A molecular sieveꢀpacked
Functional Theory (QSDFT). Thermogravimetric analysis (TGA) is column with a thermal conductivity detector. The 5% Ar in the
carried out using a TA Instrument SDT Q600 analyzer under syngas is used as an internal standard for the calculation of CO.
nitrogen flow. Scanning electron microscopy (SEM) images are Acknowledgements
recorded using a Hitachi Sꢀ4800. Transmission electron microscopy B. Q. and C. Y. contributed equally to this work. This work was
(
TEM) images are taken on a FEI Tecnai F20 microscope. XPS financially supported by the National Natural Science Foundation of
measurement are performed on a Kratos Axis Ultra imaging China (No. 21371014) and National Program for Support of Topꢀ
Photoelectron Spectrometer using monochromatic Al Kα line notch Young Professionals.
ǂ
(1486.7 eV). A Leeman prodigy inductively coupled plasma optical
Note: Current address of Ce Yang : Argonne National Laboratory,
emission spectrometer (ICPꢀOES) is used to determine the Co Chemical Science and Engineering division, 9700 South Cass
content in the hybrids. Extended Xꢀray absorption fine structure Avenue, Lemont, IL 60439, United States.
(
EXAFS) was characterized on beamline BL14W1ꢀXAFS at the References
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FTS experiments are performed in a twoꢀchannel fixed bed flow
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at the temperature of 503 K for 100 h. Briefly, 50 mg sample catalyst
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Table of Content Entry:
Ultrasmall Co nanoparticles embedded in hierarchically porous carbon are in-situ made from
metal-organic frameworks and used as the catalysts for Fischer-Tropsch synthesis.