High selectivity of CO2 hydrogenation to CO by controlling the valence state of nickel using perovskite

Article abstract of DOI:10.1039/c8cc03829e

The selectivity of CO₂ hydrogenation can be significantly tuned by controlling the valence state of nickel using lanthanum-iron-nickel perovskites. Nickel with higher valence states weakens the binding of CO and increases the activation barrier for further CO hydrogenation, leading to a higher CO selectivity than the metallic nickel.

Full text of DOI:10.1039/c8cc03829e

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DOI: 10.1039/C8CC03829E.
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Reactivity differences of Sc
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High Selectivity of CO Hydrogenation to CO by Controlling the
2
Valence State of Nickel using Perovskite
Received 00th January 20xx,
Accepted 00th January 20xx
ab
bc
e
b
b
d
a
Baohuai Zhao,‡ Binhang Yan,‡ Zhao Jiang, Siyu Yao, Zongyuan Liu, Qiyuan Wu, Rui Ran,*
b
a
e
Sanjaya D. Senanayake, Duan Weng and Jingguang. G. Chen*
DOI: 10.1039/x0xx00000x
www.rsc.org/
The selectivity of CO
2
hydrogenation can be significantly tuned by the influence of the binding energies of the intermediates over Ni-
based catalysts on the product selectivity is still lacking. In our
previous studies, the correlation between the binding energies of
controlling the valence state of nickel using lanthanum-iron-nickel
perovskites. Nickel with higher valence states weakens the
binding of CO and increases the activation barrier for further CO
hydrogenation, leading to a higher CO selectivity than the metallic
nickel.
key intermediates and the product selectivity for CO
hydrogenation was established through combined experiments and
2
7, 12-14
DFT calculations over several other catalysts.
simply replacing the CeO or ZrO supports with TiO
based bimetallic catalysts, the ratio of CO/CH was increased since
the binding of C,O-bound and O-bound species at the PtCo-oxide
For example, by
2
2
2
for the PtCo-
4
Catalytic conversion of CO
2
has attracted increasing attention
in recent years, aiming at alleviating the global warming and
1
7
interface was weakened. Although the mechanism of CO
2
-3
ocean acidification.
CO2 hydrogenation with renewable
hydrogenation is complicated and might be very different over
various catalysts, it is generally accepted that CO is the key
hydrogen is proposed to utilize CO2 as a raw material to
4
, 11, 15, 16
produce valuable chemicals, such as CO, CH , and methanol. intermediate for CH4 formation over Ni-based catalysts.
4
Ni-based catalysts are identified as one of the most promising This suggests that the product selectivity of CO
2
hydrogenation can
catalysts for CO2 hydrogenation due to their considerable be potentially tuned by controlling the binding energies of CO on
the catalysts.
catalytic activity and lower cost compared to precious metal
4
,
5
It is well known that the binding energy of CO varies with the
valence state of nickel, which is much weaker on oxidized nickel
than that on metallic nickel. The weak binding energy of CO offers
catalysts.
favorable for the Sabatier methanation reaction for CH rather
However, Ni-based catalysts are generally
4
15
5, 6
than the reverse water gas shift (RWGS) reaction for CO. In
a
potential way to promote the CO selectivity for CO
2
many cases, CO is more desirable than CH as it offers more
4
hydrogenation over Ni-based catalysts. However, for the supported
Ni-based catalysts, nickel is more likely to be reduced to Ni under
hydrogenation conditions. Therefore, keeping Ni at higher valence
states under reaction conditions is a key challenge in promoting the
CO selectivity. Perovskites with the ideal general formula of ABO3
flexibility to produce oxygenates and synthetic fuels via the
7
methanol synthesis or Fischer-Tropsch reactions. Thus, it is
0
1
7
important to promote the selectivity of CO hydrogenation to
2
CO over Ni-based catalysts.
To date, many attempts have been made to increase the CO are known as versatile materials in which Ni ions can be located at
selectivity over Ni-based catalysts, such as alloying Ni with other the B sites. They could be reduced out of the perovskite lattice to
8
, 9
10
metals (Cu, Pt, and Pd et al.), controlling the loading of Ni, and form highly dispersed nanoparticles under particular environments,
1
1
18, 19
using promoters like K. However, a fundamental understanding of resulting in a strong metal support interaction (SMSI) effect.
These features of Ni-containing perovskites were widely
investigated and the related catalysts, such as LaNiO , LaFe1-xNi
and SrTi1-xNi , were used for many reactions including dry
reforming or steam reforming of methane.
al. investigated the parameters for the regeneration behavior of the
perovskite (LaFe1-xNi ) structure, using CO hydrogenation as a
probe reaction. However, to the best of our knowledge, there are
3
x 3
O ,
x 3
O
1
8, 20
Recently, Steiger et
x
O
3
2
2
1
no discussions about controlling the selectivity of CO
hydrogenation using perovskites.
2
Herein, this study demonstrates how the selectivity of CO
2
hydrogenation can be tuned by changing the valence state of
nickel using different lanthanum-iron-nickel perovskites. The
catalytic performance using a flow reactor is shown in Fig. S1
and S2 (ESI†) and results obtained after the reaction reached a
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steady-state at 14 hours at 673 K are summarized in Table 1. It
is noticed that LaNiO mainly produces CH rather than CO
while very little CH is formed over LaFe0.5Ni0.5 . Table S1
ESI†) compares the catalytic performance of a series of
perovskites with different Fe/Ni ratios. LaFeO shows poor
activity with the lowest CO and H conversions. After doping
3
4
4
O
3
(
3
2
2
Ni into the perovskites their activity is significantly increased,
indicating that Ni-related species should be responsible for the
production of CH
is known that the selectivity of CO
based catalysts often varies with CO
4
or CO over the Ni-containing perovskites. It
hydrogenation over Ni-
conversion, which
2
2
depends on the gas space velocity and temperature. Here the
CO conversion of LaNiO was controlled at a similar level with
2
3
LaFe0.5Ni0.5O , i.e. 18.1%, and the selectivity is also listed in
3
Table 1. It can be seen that even at similar CO conversion
2
LaNiO still shows a much higher selectivity of CH (71.4%)
4
3
compared to LaFe0.5Ni0.5O (3.2%).
3
Table 1: Summary of flow reactor data for CO
2
hydrogenation over
3 3
LaNiO and LaFe0.5Ni0.5O (calculated by averaging data points in 12–14
-
/Ar = 5/10/25 mL min ).
1
h on stream, CO
Catalyst
2
/H
2
a
a
b
LaNiO
39.7
3
LaFe0.5Ni0.5
O
3
LaNiO
18.1
3
Conversion
CO
2
2
16.3
(%)
H
2
75.5
11.4
28.4
TOF
mol molNi
min )
CO
0.20
0.75
0.15
0.21
1.03
3.19
-1
(
-1
H
2
CO
3.2
36.5
8.0
15.8
0.5
5.1
Fig. 1 TEM images and particle size distributions of the spent catalysts (a–c)
LaNiO ; (d–f) LaFe0.5Ni0.5O .
3 3
Yield
(%)
CH
4
12.9
28.2
71.4
Selectivity
%)
CO
96.6
3.2
(
CH
4
92.0
a
b
00 mg catalyst, T = 673 K. 15 mg catalyst, T = 623 K.
1
Fig. 1 shows the TEM images and particle size distributions
of the spent catalysts. In Fig. 1a and d the Ni-related particles
can be found on the surface of both spent catalysts, while no
such particles are observed on the fresh catalysts (Fig. S3,
ESI†), indicating that Ni ions were exsolved from the
perovskite lattice to form surface nanoparticles. The magnified
images in Fig. 1b and e reveal that the nanoparticles are
closely attached to the perovskite host. The size distributions
of the nanoparticles are shown in Fig. 1c and f. The average
particle size in the spent LaNiO
3 3
and LaFe0.5Ni0.5O are 6.5 and
4.5 nm, respectively. However, according to the general view
of the catalysts derived from perovskites, the particles on the
surface usually interact strongly with the support and their
Fig. 2 Results of the in-situ XRD measurements during the temperature
ramping stage, (a) and (b) patterns of LaNiO ; (c) and (d) lattice expansion
. Fig. b and d show regions where Ni diffraction
1
8,
properties are significantly influenced by their parent lattice.
2
3
1
Thus, the oxidation states of Ni in the nanoparticles are still and patterns of LaFe0.5Ni0.5
O
3
peaks would be expected.
unknown.
To understand the structural evolution of the catalysts, in-
situ XRD experiments for LaNiO under
reaction conditions were performed. Fig. 2a shows the
strongest diffraction peak around 2θ = 5.0° of LaNiO as a
3
and LaFe0.5Ni0.5O
3
3
function of temperature from 300 to 673 K. It can be seen that
the peaks start to slightly shift to lower angle position at 553 K
2
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due to the exsolution of Ni ions and the phase transformation seen that LaFe0.5Ni0.5
from LaNiO
the diffraction peaks of metallic Ni centered at 2θ = 6.8° start
to appear at 653 K, right after the phase transformation. These spectroscopy (AP-XPS) experiments was to detect the oxidation
results suggest that a portion of the Ni ions in the LaNiO states of surface Ni. They were carried out under 10 mTorr pressure
perovskite is converted into metallic Ni under reaction of reactants (CO /H = 1/2) and the Ni 3p spectra are adopted in
, its perovskite this work since the Ni 2p3/2 and La 3d3/2 spectra strongly interfere
O
3
truly has the ability to maintain Ni in a
3
to LaNiO2.5 takes place at about 625 K. In Fig. 2b higher valence state than the supported catalyst.
The aim of in-situ ambient pressure X-ray photoelectron
3
2
2
2
1
conditions. In the case of LaFe0.5Ni0.5O
3
2
2
structure is still maintained after the reaction (Fig. S4, ESI†). In with each other. The Ni 3p spectra in Fig. 3c and d show changes
Fig. 2c there is an abrupt volume expansion occurred between in valence states between the catalyst at 300 K and during the
5
3 3
20 and 615 K on top of the upward-sloping background line reaction at 673 K. The spectra of LaNiO -300 K and LaFe0.5Ni0.5O -
3
+
3+
2+
from the thermal effect, demonstrating that there are Ni ions 300 K show co-existence of Ni and Ni , with their 3p3/2 peaks
1
9, 21
22-25
coming out of the perovskite lattice.
0
noted that the diffraction peak of metallic Ni is almost invisible Ni 3p3 peak as indicated by the dashed line (65.5 eV) is absent in
However, it should be appearing at approximately 70.9 and 67.0 eV, respectively.
The
/2
2
5, 26
in the XRD patterns in Fig. 2d. The H -TPR results (Fig. S6, ESI†) both fresh catalysts.
2
For the spectrum of LaNiO -673 K, the
3
are also consistent with that the LaFe0.5Ni0.5O perovskite is overall peak shifts to a lower binding energy range (Fig. S8, ESI†)
3
3
able to stabilize Ni in the oxidized states until a higher due to a decrease in the intensity peaks assigned to Ni and Ni ,
+
2+
0
temperature range than LaNiO3. When changing the together with the appearance of the Ni peaks. In contrast, such a
atmosphere to H +He at 673 K, the strongest diffraction peak peak shift does not occur obviously between the two spectra of
2
3
+
in both catalysts are without further change (Fig. S5, ESI†), LaFe0.5Ni0.5O . The intensity of the peaks assigned to Ni decreases
3
demonstrating that the changed structures are stable to in the spectrum of LaFe0.5Ni0.5O -673 K compared to that of
3
0
endure such a reaction condition.
LaFe0.5Ni0.5O -300 K. However, the peaks attributed to Ni are very
3
weak in LaFe0.5Ni0.5O -673 K. As summarized in Table S3 and S4
3
0
(
ESI†), the peak area of Ni in the spectrum of LaNiO -673 K
3
accounts for 29.1% of the total peak area, while it is only 3.0% of
the total peak area of LaFe0.5Ni0.5O -673 K. It should be noted that
3
some metallic Ni might come from the Ni nanoparticles over the
LaFe0.5Ni0.5O3 surface. However, Ni in the nanoparticles of this
sample should likely be in a mixed states of metallic Ni and Ni ions,
2
0
as the nanoparticles strongly interact with the perovskite support
and the electronic properties of Ni in the nanoparticles should also
be modified. Based on the in-situ XRD, XANES, and AP-XPS results, it
is suggested that LaFe0.5Ni0.5O3 is able to maintain the surface Ni
species at a higher valence state in the reducing atmosphere.
Fig. 3 In-situ XANES spectra of Ni K-edge of (a) LaNiO
3
and (b) LaFe0.5Ni0.5
at 300 K
and 673 K, peak A and B correspond to the 3p3/2 and 3p1/2 of Ni , peak C and
3
O .
3 3
In-situ AP-XPS spectra of Ni 3p of (c) LaNiO and (d) LaFe0.5Ni0.5O
0
2
+
D correspond to the 3p3/2 and 3p1/2 of Ni , peak E and F correspond to the
3
+
3
p
3/2 and 3p1/2 of Ni .
In-situ X-ray absorption near-edge structure (XANES)
measurements were performed to further understand the
evolution of Ni ions in the perovskites. The XANES spectra of Ni K-
edge for the two catalysts are shown in Fig. 3a and b. Ni in reduced
oxidation states can be identified by the decreased white line in the
spectra. The compositions are estimated by a linear combination
fitting method and summarized in Table S2 (ESI†). The results
indicate that metallic Ni exists (11%) in LaNiO3 under reaction
2 4 2
Fig. 4 The partial pressures of CO, H , CH , and CO during the CO
conditions, and its amount further increases to 41% when cutting hydrogenation reaction for (a) LaNiO and (b) LaFe0.5Ni0.5O . Potential energy
3
3
off CO2 in the stream. In contrast, the Ni-related species in diagram for the reaction routes of *CO+H on Ni(111) and NiO(111). The DFT
optimized geometries of *H, *CO, transition states (TS), and *CHO on
Ni(111) and NiO(111), are shown as insets in (c) and (d), Ni: blue, O: red, C:
gray, H: white.
LaFe0.5Ni0.5O3 are almost without metallic Ni under both reaction
and reduced conditions. As mentioned above, the Ni in supported
catalyst is easy to be reduced to the metallic state. Here, a
Density functional theory (DFT) calculations combined with the
CO hydrogenation experiments were carried out to understand how
comparison between the Ni K-edge spectra of LaFe0.5Ni0.5O3 and
Ni/ZrO under reaction condition is given in Fig. S7 (ESI†). It can be
2
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the valence states of Ni control the selectivity of CO
hydrogenation. Fig. 4a and b show the CO, H , CH , and CO partial
pressures during the CO+2H reaction on LaNiO
LaNiO is active for the further hydrogenation of the CO product;
both CO and H start to react at 525 K, and their pressures keep
decreasing with a simultaneous increase in the CH pressure. In
contrast, LaFe0.5Ni0.5 is inactive for CO hydrogenation in the
entire temperature range. The results confirm that CO is a key
intermediate for CO hydrogenation to CH and its reactivity is quite
different over LaNiO
2
Notes and references
2
4
2
1
S. Choi, B. I. Sang, J. Hong, K. J. Yoon, J. W. Son, J. H. Lee, B. K.
Kim and H. Kim, Sci. Rep., 2017, 7, 41207-41216.
2
3 3
and LaFe0.5Ni0.5O .
3
2
M. D. Porosoff, B. Yan and J. G. Chen, Energy Environ. Sci., 2016,
2
9
, 62-73.
4
3 F. Wang, S. He, H. Chen, B. Wang, L. Zheng, M. Wei, D. G. Evans
and X. Duan, J. Am. Chem. Soc., 2016, 138, 6298-6305.
4 W. Lin, K. M. Stocker and G. C. Schatz, J. Am. Chem. Soc., 2017,
139, 4663-4666.
O
3
2
4
5
6
7
R. Zhou, N. Rui, Z. Fan and C.-j. Liu, Int. J. Hydrogen Energ.,
016, 41, 22017-22025.
W. Wang, S. Wang, X. Ma and J. Gong, Chem. Soc. Rev., 2011,
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Y. Liu and D. Liu, Int. J. Hydrogen Energ., 1999, 24, 351-354.
3
3
and LaFe0.5Ni0.5O .
2
DFT calculations were performed to correlate the binding energy
of CO with the product selectivity by using Ni(111) and NiO(111)
model surfaces simulating Ni oxidation states. According to
previous studies, the RWGS + CO-Hydro pathway with key
4
7
, 11, 12, 27, 28
intermediates of CO and CHO is employed.
The optimized
8
9
geometries and binding energies of CO and CHO species are shown
in Fig. S9 and Table S5 (ESI†), respectively. According to the RWGS + 10 H. C. Wu, Y. C. Chang, J. H. Wu, J. H. Lin, I. K. Lin and C. S. Chen,
CO-Hydro mechanism, the formed *CO either desorbs to produce
Catal. Sci. Technol., 2015, 5, 4154-4163.
gas phase CO or undergoes subsequent hydrogenation reaction to 11 T. K. Campbell and J. L. Falconer, Appl. Catal., 1989, 50, 189-198.
1
1
1
1
1
2 S. Kattel, B. Yan, J. G. Chen and P. Liu, J. Catal., 2016, 343, 115-
26.
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4
form CH . As shown in Fig. 4c the hydrogenation of *CO to *CHO on
1
Ni(111) has an activation barrier (Ea) of 1.78 eV, while the
formation of CO should overcome a desorption energy (Ed) of 1.93
eV, which is equal the BE of *CO on Ni(111). Such a strong binding
makes the desorption of *CO difficult and thus it is more favorable
2
9
4
for its further hydrogenation to *CHO and subsequently to CH . On
the other hand, the hydrogenation of *CO to *CHO on NiO(111) has
an Ea of 1.96 eV, while the Ed for CO is only 1.53 eV. Thus, the *CO
desorption is more favorable than its hydrogenation to *CHO on the
NiO(111) surface. Overall, the DFT calculations predict that the
NiO(111) surface should be more selective than Ni(111) for CO 17 B. Mutz, H. W. P. Carvalho, S. Mangold, W. Kleist and J.-D.
Grunwaldt, J. Catal., 2015, 327, 48-53.
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1
8 D. Neagu, T. S. Oh, D. N. Miller, H. Menard, S. M. Bukhari, S. R.
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In conclusion, the combined in-situ experimental and
theoretical investigations have shown that by changing the
2015, 6, 8120.
valence state of Ni, the product selectivity of CO
hydrogenation can be tuned over lanthanum-iron-nickel
2
1
2
9 J. Deng, M. Cai, W. Sun, X. Liao, W. Chu and X. S. Zhao,
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Penner, J. Catal., 2016, 337, 26-35.
perovskites. LaNiO
3
shows high selectivity toward CH
4
3
,
.
whereas CO is preferentially formed on LaFe0.5Ni0.5
O
According to the in-situ XRD, XANES, and AP-XPS analysis,
metallic Ni is formed over LaNiO
while the Ni-related species present higher valence states in
. DFT calculations reveal that CO binds weakly on
NiO(111) where *CO desorption is more favorable over its
further hydrogenation to CH , leading to a much higher CO
3
under reaction conditions, 21 P. Steiger, R. Delmelle, D. Foppiano, L. Holzer, A. Heel, M.
Nachtegaal, O. Krocher and D. Ferri, ChemSusChem, 2017, 10,
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LaFe0.5Ni0.5O
3
2
2
4
selectivity. This correlates well with the experimental results
that Ni-related species in higher valence states could produce
more CO. These findings establish new correlations between
the catalytic performance and structural properties of Ni-
based catalysts and provide catalyst synthetic strategies for
controlling the metal oxidation state to achieve the selectivity
2
2
2
2
in CO hydrogenation reactions.
This work was supported by the U.S. Department of Energy 27 T. Avanesian and P. Christopher, ACS Catal., 2016, 6, 5268-5272.
DOE, DE-SC0012704 and DE-AC02-05CH11231). Baohuai Zhao 28 T. Avanesian, G. S. Gusmão and P. Christopher, J. Catal., 2016,
(
343, 86-96.
acknowledges the financial support from the China Scholarship
Council (201606210159).
4
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3
Fig. 1 TEM images and particle size distributions of the spent catalysts (a–c) LaNiO ; (d–f)
3
LaFe0.5Ni0.5O .

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Fig. 2 Results of the in-situ XRD measurements during the temperature ramping stage, (a) and (b)
patterns of LaNiO ; (c) and (d) lattice expansion and patterns of LaFe0.5Ni0.5 . Fig. b and d show
regions where Ni diffraction peaks would be expected.
3
O
3
3 3
Fig. 3 In-situ XANES spectra of Ni K-edge of (a) LaNiO and (b) LaFe0.5Ni0.5O . In-situ AP-XPS spectra of
Ni 3p of (c) LaNiO
3
and (d) LaFe0.5Ni0.5
O
3
at 300 K and 673 K, peak A and B correspond to the 3p3/2 and
0
2+
3
3
p
1/2 of Ni , peak C and D correspond to the 3p3/2 and 3p1/2 of Ni , peak E and F correspond to the
3
+
p
3/2 and 3p1/2 of Ni .

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Fig. 4 The partial pressures of CO, H , CH , and CO during the CO hydrogenation reaction for (a)
2
4
2
3 3
LaNiO and (b) LaFe0.5Ni0.5O . Potential energy diagram for the reaction routes of *CO+H on Ni(111)
and NiO(111). The DFT optimized geometries of *H, *CO, transition states (TS), and *CHO on Ni(111)
and NiO(111), are shown as insets in (c) and (d), Ni: blue, O: red, C: gray, H: white.

ChemComm
Page 8 of 8
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DOI: 10.1039/C8CC03829E
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The product selectivity of CO hydrogenation can be significantly tuned by controlling the valence
2
state of Ni using perovskites.