The Role of Alkali Metal in α-MnO2 Catalyzed Ammonia-Selective Catalysis

Article abstract of DOI:10.1002/anie.201901771

The unexpected phenomenon and mechanism of the alkali metal involved NH₃ selective catalysis are reported. Incorporation of K⁺ (4.22 wt %) in the tunnels of α-MnO₂ greatly improved its activity at low temperature (50–200 °

Full text of DOI:10.1002/anie.201901771

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Accepted Article
Title: Can a poison be a gift? the role of alkali metal in the α-MnO2
catalyzed ammonia selective catalytic reaction
Authors: Zhifei Hao, Zhurui Shen, Yi Li, Haitao Wang, Lirong Zheng,
Ruihua Wang, Guoquan Liu, and Sihui Zhan
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201901771
Angew. Chem. 10.1002/ange.201901771
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10.1002/anie.201901771
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Can a poison be a gift? the role of alkali metal in the α-MnO2
catalyzed ammonia selective catalytic reaction
Zhifei Hao,[+][a] Zhurui Shen,[+][b] Yi Li,[c] Haitao Wang,[a] Lirong Zheng,[d] Ruihua Wang,[a] Guoquan Liu,[a]
and Sihui Zhan*[a]
Dedicated to the 100th anniversary of Nankai University
Abstract: The unexpected phenomenon and mechanism of the
alkali metal involved NH3-SCR catalyst were reported here. It is
found that the incorporation of K+ (4.22 wt %) in the tunnels of α-
MnO2 greatly improved its activity in low temperature (50-200 °C ,
100 % conversion of NOx vs. 50.6 % conversion over pristine α-
MnO2 at 150 °C ). Thereafter, experimental and theoretical evidences
demonstrated the atomic role of incorporated K+ in α-MnO2. Results
showed that K+ in the tunnels could form a stable coordination with
eight nearby Osp3 atoms. The columbic interaction between the
trapped K+ and O atoms can rearrange the charge population of
nearby Mn and O atoms, thus making the topmost five-coordinated
unsaturated Mn cations (Mn5c, the Lewis acid sites) more positive.
Therefore, the more positively charged Mn5c can better chemically
adsorb and activate the NH3 molecules compared with its pristine
counterpart, which is crucial for subsequent reactions.
The alkali metal species can also directly react with the out-
most surface of active sites and then change their
physiochemical properties.[1g] These advances have shed
light on further promotion of heterogeneous catalysis using
alkali metal species. However, restrictions are arising from
the limited knowledge of how the alkali metal species play
their roles at atomic-level. This is important for developing
novel catalysts and thus necessary to be investigated.
Lewis acid sites can dominate many important
homogeneous or heterogeneous catalytic reactions.[3] For
example, asymmetric organic synthesis,[3a] catalytic
polymerization toward macromolecules and heterogeneous
3c]
industrial catalytic reactions.[3b,
It is known that the
chemical nature of Lewis acid sites are positively charged
centers,[4] no-mater they are nonmetal (e.g. Boron),[4a] metal
(e.g. Ni2+, Ce3+) or atomic clusters (e.g. Ni, Au ),[4b, 4d] which
can attract the electrons and then initiate the reactions.
Therefore, it is crucial to understand and control the
electronic structure of Lew acid sites, which would bring new
strategy for better activating the Lewis acid sites.
For decades, the alkali metal species are highly involved in
the catalytic chemistry.[1] Besides as the active sites in the
organic homogeneous catalysis,[2] the alkali metal species
can also efficiently promote the performance of
heterogeneous catalysis via multiple ways. The recent
examples include: 1) The alkali metal cations can stabilize
the metastable active sites,[1a] e.g. mononuclear Au-O(OH)x
species were well stabilized by K+ or Na+.[1b] 2) In-situ formed
alkali metal compound coatings (e.g. the Li, K, Cs molten
salt) on active sites can elevate the catalytic activity by the
co-adsorption effect.[1c, 1d] 3) They can control the chemical
compositions of active sites and the corresponding catalytic
performance,[1e] e.g. the active sites can be changed into Cu-
Co alloy or Co/Co2C by changing the content of Na+.[1f] 4)
Herein, we have focused on NH3 selective catalytic
reactions (NH3-SCR) among various Lewis acid sites
correlated reactions, due to its importance for cleaning NOx
from power plants and mobile diesel vehicles.[5] It is known
that the alkali metal species can promote catalytic
performance in many conditions. However, they are typical
[5a,
poisons for most NH3-SCR catalysts e.g. V2O5-WO3/TiO2
and α-MnO2.[5c] Generally, the reaction temperature
5b]
should be above 300 °C to decompose the alkali metal
species, which is energy consuming. High conversion of NOx
at lower temperature is one of the key scientific issues for
NH3-SCR. Therefore, the anti-alkali metal ability of the
catalyst is usually necessary to achieve a lower reaction
temperature. Unexpectedly, in this study, we have found that
the incorporation of K+ (4.22 wt %) in the tunnels of α-MnO2
could greatly improve its activity at 150 °C in NH3-SCR
(100 % conversion of NOx vs. 50.60 % conversion over
pristine α-MnO2). Although several literatures have inserted
the K+ in the tunnels of α-MnO2, hardly any of them captured
similar phenomenon in the current work.[6] Thereafter,
experimental and theoretical evidences have demonstrated
the atomic role of incorporated K+ in α-MnO2, which brought
a K-O eight coordination and the charge rearrangement of
the nearby Mn and O atoms, resulted in more positively
charged and better activated Mn5c Lewis acid sites.
[a] Z.F. Hao, R.H. Wang, G.Q. Liu, Prof. H.T. Wang, Prof. S.H. Zhan
MOE Key Laboratory of Pollution Processes and Environmental Criteria
Tianjin Key Laboratory of Environmental Remediation and Pollution
Control
College of Environmental Science and Engineering, Nankai University
Tianjin 300350 (P. R. China)
E-mail: sihuizhan@nankai.edu.cn
[b] Prof. Z.R. Shen
School of Materials Science and Engineering, Nankai University
Tianjin 300350 (P. R. China)
[c] Prof. Y. Li
Tianjin Key Laboratory of Molecular Optoelectronic Sciences
Department of Chemistry, School of Science, Tianjin University
Collaborative Innovation Center of Chemical Science and Engineering
Tianjin, 300072 (P. R. China)
[d] Dr. L. Zheng
Beijing Synchrotron Radiation Facility, Institude of High Energy
Physics, Chinese Academy of Sciences
Beijing 100049 (P.R. China)
[+] These authors contributed equally to this work.
Supporting information for this article is given via a link at the end of the
documents.
Kinds of α-MnO2 nanorods were fabricated here as the
model catalysts for NH3-SCR reaction, including: K+ in its
tunnels (K-α-MnO2), K+ on its surface (K/α-MnO2) and pristine
α-MnO2 nanorod. The quantity of K+ was determined by the
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10.1002/anie.201901771
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energy-disperse X-ray spectroscopy (EDXS) on SEM, and
results show that 4.22 wt %, 4.64 wt % and negligible K+ are
based on the [100] atomic mode in Figure 1e. The EDXS of
TEM (Figure 1f, 1g and S6) further confirmed that K, Mn and
in K-α-MnO2, K/α-MnO2 and α-MnO2, respectively (Table S1). O were uniformly distributed over the K-α-MnO2, indicating
The SEM images show that K-α-MnO2, K/α-MnO2 and α-
MnO2 nanorods are with similar length of one to several
hundreds of nanometers and diameter of twenty to thirty
nanometers (Figure S1). Their specific surface areas are
quite close (Figure S2 and Table S2) and their crystalline
the successful incorprating of K+.
[7]
phases are all α -MnO2 (JCPDS No.44-0141) (Figure S3),
indicating that their morphology and size characteristic
resembles with each other, and should not leads to
significant difference in catalytic performance.
Figure 2. a) Rietveld refined XRD patterns of K-α-MnO2, K/α-MnO2 and α-
MnO2. b) Potassium K-edge XANES spectra of K-α-MnO2 and KCl. c)
Manganese K-edge XANES of K-α-MnO2 and α-MnO2 compared with Mn0 (Mn
foil) and Mn2+ (MnSO4) standards. d) Oxygen K-edge XANES spectra of K-α-
MnO2 and α-MnO2. e) Theoretical demonstration of K+ position in the tunnels
of α-MnO2 as well as site occupancy energy, CN represent the coordination
numbers of K+ with nearby O atoms.
To investigate the structural and chemical nature of K+ in
the tunnels of K-α-MnO2, methods including Rietveld
refinement X-ray powder diffraction (XRD), the synchrotron
X-ray absorption spectra (XAS) and density functional theory
(DFT) were employed. Figure 2a shows the refined XRD
patterns of K-α-MnO2, α-MnO2 and K/α-MnO2, and the a, b
values (9.824 Å) of K-α- MnO2 are slightly larger than those
of pristine α-MnO2 and K/α-MnO2 (both are 9.769 Å). This
suggests that K+ in the tunnels of K-α-MnO2 leads to lattice
expansion along a, b axis and in line with the results of TEM
observations above. Moreover, the pre-edge features of X-
ray absorption near edge structure (XANES) spectra were
collected for K, Mn and O elements (Figure 2b-2d). As
shown in Figure 2b, the K-edge spectrum of K element for K-
α-MnO2 shows a lower intensity pre-edge at the 3602 to
3612 eV compared with that of KCl, which further confirm
that the K+ was in the 2 × 2 tunnels of K-α-MnO2.[6b] While for
O K-edge spectrum (Figure 2d), result shows that the peak
intensity of K-α-MnO2 is higher than that of pristine α-MnO2,
indicating the coordination environment of O atoms are
correlated with the incoming K+.[11] Then, the features of
XANES and EXAFS spectra of Mn K-edge (Figure 2c and
Figure S7) were also recorded for K-α-MnO2 and pristine α-
MnO2, appearing at the similar energy (6561 and 6572 eV).
Compared with the Mn foil and MnSO4, the Mn species of
Figure 1. a) TEM image of K-α-MnO2 and b) one K-α-MnO2 nanorod along
[001] direction. c) Its high-resolution HAADF-STEM image and FFT image and
d) the enlarged image of c). e) Its representative atomic model. The yellow
spots indicate Mn atoms, while red and purple represent O and K+. f) EDXS
mapping of K-α-MnO2 nanorod. g) EDXS spectrum of the K-α-MnO2.
Then, their microstructure, especially for K-α-MnO2, were
futher studied using transmittion electrons microscopy (TEM)
techniques. As shown in low-resolution TEM images (Figure
1a and 1b) and corresponding fast Fourier transform (FFT)
(Figure 1c inset), the K-α-MnO2 is monocrystalline and grown
along the [001] direction (Figure S4).[8] Then, the high-angle
annular
dark-field
scanning
transmission
electron
microscope (HAADF-STEM) discloses the atomic structure
of K-α-MnO2 with exposed [200] facet, and its d200 spacing is
4.95 Å (Figure 1c and 1d). By observing the d200 spacings of
K/α-MnO2 and α-MnO2 (Figure S5), it is shown that K+ in the
tunnels may silghtly leads to lattice expansion.[9] Moreover,
Figure 1d showed that the tunnels observed in K-α-MnO2
should be the 2 × 2 tunnels (dark stripes) surrounded by two
Mn atom columns (yellow spheres).[10] The K+ (purple
spheres) were probably traped in these 2 × 2 tunnels due to
the proper tunnel size (4.6 Å × 4.6 Å), which was depicited
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10.1002/anie.201901771
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the K-α-MnO2 and α-MnO2 are ascribed to the coexistence of
Mn4+ and Mn3+, suggesting the insertion of K+ could hardly
change the oxidation state of Mn in our case. This is
consistent with the results of XPS measurements (details in
S5). Generally, most NH3-SCR catalysts showed unsatisfied
performance when alkali metal species involved in the
reaction.[5] Nevertheless, in our case, the insertion of K+ in
the tunnels greatly enhanced the low temperature activity,
which inspired us to further study the atomic role of inserted
K+ as follow.
Figure S8 and Table S3). Besides,
a filter washing
experiment of K+ was used to further confirm that the K+
successfully incorporated in the tunnels of K-α-MnO2 (Figure
S9 and Table S4). Furthermore, a DFT simulation is
conducted (Figure 2e), and the results show that K+
coordinated with eight nearby Osp3 atoms with the
coordination numbers (CN) of 8 is more energy favourable
than that K+ coordinated with four nearby Osp2 atoms.
Figure 3. a) NOx conversion ratio as a function of temperature over K-α-MnO2,
K/α-MnO2 and α-MnO2. b) thermal stability test of K-α-MnO2, K/α-MnO2 and α-
MnO2 at 150 °C , c) H2O resistance, d) SO2 tolerance. Reaction conditions:
[NH3] = [NO] = 500 ppm, [O2] = 5 vol%, [H2O] = 10 vol% (when used), [SO2] =
100 ppm (when used), N2 balance, GHSV of 60,000 h-1.
Figure 4. a) NH3-TPD profiles and b) normalized amount of Lewis acid site of
pyridine adsorption for K-α-MnO2, α-MnO2 and K/α-MnO2 at 150 °C and
230 °C. c) and d) In situ DRIFT spectra over K-α-MnO2 in a flow of NO + O2
/NH3 after the catalyst was pre-adsorbed NH3 / NO + O2. e) and f) In situ
DRIFT spectra over α-MnO2 in a flow of NO + O2 /NH3 after the catalyst was
pre-adsorbed NH3 / NO + O2.
Thereafter, the NH3-SCR reactions were performed over
as-prepared K-α-MnO2, α-MnO2 and K/α-MnO2 to evaulate
the effect of K+ incorporation (Figure 3). The NOx conversion
as a function of temperature (50-300 °C ) were firstly plotted
(Figure 3a). Unexpectedly, compared with pristine α-MnO2,
the K-α-MnO2 exhibited much better deNOx performance in
the low temperature of 50-200 °C . Its NOx conversion
achieved 100 % at 150 °C, which is c.a. one time higher than
that of pristine α-MnO2. Only when the temperature
approaching 300 °C , the NOx conversion of pristine α-MnO2
can reach 100 %. While for K/α-MnO2, it showed poor activity
in the whole temperature range due to covering of the active
sites by K+ on the surface.[12] Figure 3b showed the thermal
stability test of the catalysts at 150 °C, and the NOx
conversion of K-α-MnO2, α-MnO2 and K/α-MnO2 maintained
stable at 100 %, 50.6 % and 23.2 % during 48 h, respectively.
Then, their H2O and SO2 tolerance (Figure 3c, 3d) were also
test with additional feeding of 10 vol% H2O vapor or 100 ppm
SO2 at 150 °C . The results show that K-α-MnO2 exhibited an
acceptable H2O and SO2 tolerance. Besides, the N2
selectivity (Figure S10) and apparent activation energy
based on arrhenius plots (Figure S11) of K-α-MnO2 and
pristine α-MnO2 were also analyzed, and K-α-MnO2
performed better for both two parameters. Moreover, the
structure and morphology of K-α-MnO2 can remain
unchanged after reaction (details in Figure S12-13 and Table
To explore the surface chemistry and monitor the crucial
intermediates, spectra mainly including the NH3-temperature
programmed desorption (NH3-TPD), FT-IR spectra of
pyridine adsorption (Py-IR) and the in situ DRIFT are
performed and demonstrated here (Figure 4, Figure S14-
S16). As shown in NH3-TPD spectra (Figure 4a), the amount
of NH3 adsorbed on K-α-MnO2 is much larger than those
over α-MnO2 and K/α-MnO2, indicating its more abundant
acid sites. The peaks at 150 and 213 °C of K-α-MnO2 were
ascribed to the NH3 chemically adsorbed on surface acid
sites. The pristine α-MnO2 showed a moderate desorption
peak at 226 °C, indicating its characteristic surface acid sites.
While for the K/α-MnO2, there was almost no desorption
peak in the whole temperature range (50-400 oC).These
results are consistent with their NH3-SCR performance,
indicating the surface acid sites are highly correlated with
their catalytic activity. To further disclose the acidic types and
amount of surface acid sites, the Py-IR was then conducted
(Figure 4b, Figure S14 and Table S6). Results show that the
type of surface acid sites are mainly Lewis acid sites with few
Brønsted acid sites for all of the three samples (Figure S14).
The amount of Lewis acid of K-α-MnO2 (158.66 μmol/g) is
one time higher than that of pristine α-MnO2 (70.81 μmol/g)
and four times higher than that of K/α-MnO2 (34.08 μmol/g)
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at 150 °C. When the temperature increasd to 230 °C, the
amount of Lewis acid of K-α-MnO2 (188.40 μmol/g) is still the
largest, and the amount of Lewis acid of pristine α-MnO2
increased to 153.04 μmol/g. However, the amount of Lewis
acid of K/α-MnO2 kept almost unchanged. These results
were in line with their catalytic performance and indicated
that the incorpration of K+ will significantly enhanced the
Lewis acid sites on the surface at low temperature, crucially
for its enhanced catalytic performance.
nitrate species were reactive in the SCR reaction. Meanwhile,
in situ DRIFT spectra of pristine α-MnO2 sample in a flow of
NO + O2/ NH3 after pre-adsorbed NH3 /NO + O2 were shown
in Figure 4e, 4f and S16. It is found that the ammonia
species and nitrate species on the surface of α-MnO2 were
essentially the same as those on the K-α-MnO2, implied that
they have the same main reaction process. Furthermore,
compared with conditions of pre-adsorption of NH3 or NO+O2
(Figure 4c, d and S15), results show that: 1) the pre-
adsorbed peak intensity of NH3 was much stronger than that
of NOx, 2) the NH3 reacted with the pre-adsorbed NO+O2
more easily than the reverse condition. It provided that NH3
adsorption and activation should be the critical step of the
NH3-SCR in our case, which is greatly enhanced by the
incorporation of K+ of K-α-MnO2.
On account of NH3 adsorption and activation is the initial
and critical step of the SCR process.[15] To uncover the
atomic role of K+ for K-α-MnO2, the chemical adsorption of
NH3 and dissassociation of N-H bond was calculated based
on DFT method (Figure 5). Experimentally, NH3 molecules
mainly adsorbed on Lewis acid sites provided by unsaturated
coordinative Mn atoms with or witihout oxygen vacancies.[6c]
Therefore, two aspects were considered for building the
models (Figure 5a, 5b, S17 and S18): 1) The adsorption of
NH3 at the original formed five-coordinated unsaturated Mn
cations (Mn5c, the Lewis acid site) on the (001) surface of K-
α-MnO2 and α-MnO2, respectively (Figure 5a). 2) Oxygen
vacancy is introduced by removing a two-coordinated bridge
oxygen (Obri) atom, then forming a new Mn5c site on the
surface with original Mn5c site coexisted (Figure 5b).
Figure 5. a) Structure of the α-MnO2 and K-α-MnO2 [001] surface, optimized
adsorption configurations of Lewis acid Mn5c site. b) Structure of the α-MnO2
and K-α-MnO2 [001] surface after introducing the oxygen vacancy, optimized
configurations of new (A) and original (B) Mn5c site. c-d) The electron
difference density analysis of K-α-MnO2 and α-MnO2. e) Energy profiles of NH3
dissociation on the Mn5c site of K-α-MnO2 and α-MnO2 for the processes NH3*
+ Obri → NH2*+ ObriH. f-g) Energy profiles of NH3 dissociation on the new and
original Mn5c site of K-α-MnO2 and α-MnO2.
Firstly, as shown in Figure 5e, S19 and S20, K+ insertion
increased the adsorption energy of NH3 on vacancy-free α-
MnO2 (-2.17 eV vs. -1.35 eV) significantly. Generally, the
NH3* ( * stands for the active site on the surface) was firstly
activated, dissociated and then reacted with the gaseous or
adsorbed NO.[16] Whereafter, the N−H bond is breaked by
Obri species and NH3* transformed into NH2* and H* through
dehydrogenation process (NH3* + Obri → NH2* + Obri H), the
transition states were shown in Figure 5f, 5g, S19 and S20.
When interfacial oxygen vacancy was formed, it is also found
that no matter NH3 absorbed on the newly formed Mn5c site
or original Mn5c site, the adsorption energy on K-α-MnO2-x (x
for the oxygen vacancy) was significantly higher than that of
α-MnO2-x, which is consistent with the results of NH3-TPD.
For the K-α-MnO2-x, the adsorption energy of NH3 (−1.87 eV)
on the original Mn5c site was higher than the new Mn5c site
(−1.76 eV). While the N-H dissociation energy barrier of the
original Mn5c site (0.82 eV) is lower than that of the new Mn5c
site (1.01 eV). However, the former process is an
endothermic process and the later is an exothermic process.
Thereafter, in situ DRIFT spectra of K-α-MnO2 and pristine
α-MnO2 were performed to better understand their NH3/NOx
adsorption/decomposition process in SCR process (Figure
4c, f and and S15, 16). For K-α-MnO2, it was first treated with
NH3/N2 for 30 min and then followed by purging with N2 for
30 min at 150 °C (Figure 4c and S15a), the peaks appearing
at 1419 and 1300 cm−1 were attributed to coordinated NH3
bound to Lewis acid sites,[13] whereas no obvious bonds
linked to Brønsted acid sites were observed. It is noteworthy
that
the
amide
species
(–NH2)
resulting
from
dehydrogenation of adsorbed NH3 was also detected (1540
cm-1),[14] which can react directly with gaseous or weakly
adsorbed NO to form NH2NO and finaly decompose into N2
and H2O. After switching the gas atmosphere to NO + O2,
coordinated NH3 (1419 and 1300 cm−1) and the amide
species (–NH2) were decreased rapidly within 5 min. These
results show that the adsorbed NH3 species can quickly
participate in the NH3-SCR reaction. Meanwhile, some new
peaks ascribed to NOx species appeared, including the
monodentate nitrate(1295, 1264 cm-1),[14a] bidentate nitrate
The similar phenomenon was also observed on the α-MnO2-x
.
The adsorption energy and energy barriers of NH3 on new
Mn5c site (−1.04 eV/0.80 eV) and original Mn5c site (−1.03
eV/0.79 eV) are close, but the former process is endothermic
(0.38 eV) and the later process is exothermic (−0.67 eV).
These results revealed that incorporating K+ could enhance
NH3 adsorption and activation via both thermo-dynamics and
kinetics way (Table S7). Moreover, the calculated Hirshfeld
charge population on topmost Mn5c before and after K+
incorporation are 0.44 and 0.47, respectively (Figure 5c and
5d), indicating that the valence electron decreases due to the
charge rearrangement.[9] This resulted in a more positively
(1026 cm-1) and the disproportionation of NO bridging
14b]
nitrates (1135 cm-1).[13a,
In contrast, the in situ DRIFT
spectra of reaction between pre-adsorbed NO + O2 with NH3
was also collected (Figure 4d and S15b). After the
introduction of NH3, both monodentate nitrate (1408 cm-1)
and the disproportionation of NO bridging nitrates (1212 cm-
1) showed rapid decrease in intensity, indicating that these
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[4]
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charged Mn5c stie, which is more facile to adsorb and
activate the NH3 with lone pair eletrons. This charge
difference is consistent with the features of Mn K-edge
XANES spectra (Figure 2c inset), where the Mn3+/Mn4+ of K-
α-MnO2 tend to move more postive valence weakly.
In summary, an unexpected phenomenon was found and
demonstrated here about the alkali metal involved NH3-SCR
catalysts. As an example, after insertion of 4.22 wt% K+ (a
common posion agent) in the tunnels, the so-called K-α-
MnO2 exhibited much better deNOx performance than that of
pristine α-MnO2 in the temperature of 50-200 oC (100 %
conversion vs. 50.6 % conversion at 150 °C). Spectroscopic
and theoretical methods were then performed to study the
atomic role of K+ in the NH3-SCR. Results showed that K+ in
the tunnels coordinated with eight nearby Osp3 atoms and
then making the charge rearrangement of nearby Mn and O
atoms via the columbic interactions. That resulted in more
positively charged topmost five-coordinated unsaturated Mn
cations (Mn5c, the Lewis acid site). Therefore, these more
positively charged Mn5c would better adsorb and activate the
NH3 molecules, which is crucial for the subsquent reaction
steps confirmed by in situ DRIFT spectra. This work is
beneficial for further understanding the atomic role of alkali
metals in Lewis acid sites dominated catalysis. Besides, it
also offers a kind of potential NH3-SCR catalyst with
excellent performance at low temperature.
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Acknowledgements
The authors gratefully acknowledged the financially
support by the Natural Science Foundation of China as
general projects (grant Nos. 21722702 and 21872102), and
the Tianjin Commission of Science and Technology as key
technologies R&D projects (grant Nos. 16YFXTSF00440,
16ZXGTSF00020, 16YFZCSF00300, 18YFZCSF00730,
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Keywords: atomic insights • alkali metal • Lewis acid sites •
NH3-SCR • charge rearrangement
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This article is protected by copyright. All rights reserved.

10.1002/anie.201901771
Angewandte Chemie International Edition
COMMUNICATION
COMMUNICATION
The K+ incorporated in the tunnels of
α-MnO2, which brought a K-O eight
coordination structure and the
charge rearrangement of the nearby
Mn and O atoms, resulted in more
positively charged Mn5c Lewis acid
sites and an unexpectedly enhanced
low temperature performance in
NH3-SCR.
Zhifei Hao[+][a], Zhurui Shen[+][b], Yi Li[c],
Haitao Wang[a], Lirong Zheng[d],
Ruihua Wang[a], Guoquan Liu[a], and
Sihui Zhan[a]*
Page No. – Page No.
Can a poison be a gift? the role of
alkali metal in the α-MnO2 catalyzed
ammonia selective catalytic reaction
This article is protected by copyright. All rights reserved.