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Catalysis
Science &
Technology
ISSN 2044-4761
Volume 11
Number 2
21 January 2021
Pages 361–690
PAPER
Raoul Naumann d’Alnoncourt et al.
Design of PtZn nanoalloy catalysts for propane
dehydrogenation through interface tailoring via atomic
layer deposition
Catalysis
Science &
Technology
PAPER
Cite this: Catal. Sci. Technol.,2021,
11,484
Received 30th July 2020,
Accepted 18th November 2020
DOI: 10.1039/d0cy01528h
rsc.li/catalysis
Design of PtZn nanoalloy catalysts for propane
dehydrogenation through interface tailoring via
atomic layer deposition†
Piyush Ingale,
a
Kristian Knemeyer,
a
Phil Preikschas,
a
Mengyang Ye,
b
Michael Geske,
a
Raoul Naumann d'Alnoncourt, *
a
Arne Thomas
b
and Frank Rosowski
ac
Supported Pt nanoparticles are widely used for the catalytic dehydrogenation of propane to propene.
Monometallic Pt catalysts are subject to fast deactivation. A successful strategy for stabilization is alloying Pt
with a second metal. In this study, we present a novel approach for the precise formation of bimetallic
nanoparticles via tailoring of the interface between metal nanoparticles and the support. An ultra-thin
functional layer of ZnO is deposited via atomic layer deposition on SiO
2
. The supported Pt nanoparticles
undergo a phase transformation and form Pt
1
Zn
1
alloy nanoparticles under reductive thermal treatment. The
resulting Pt
1
Zn
1
catalyst showed a high and stable selectivity to propene over 12 hours of time on stream. The
activity of the Pt
1
Zn
1
catalyst was 1.5 times higher than that of a catalyst of the same composition prepared by
incipient wetness impregnation. The nanoalloy formation causes electronic and geometric modification of Pt
which reduces side reactions and leads to a stable and active propane dehydrogenation catalyst.
Introduction
Propene is an important intermediate used in the production
of polypropene, propene oxide, acrylic acid, etc.
1
Propene is
mainly produced as a by-product of steam cracking and fluid
catalytic cracking.
2
As propene is a secondary product in both
processes, the demand for propene is often not met by its
production as cracking processes are volatile to gasoline
prices.
3
To answer the rising demand for propene due to e.g.
a growing middle class in developing countries, the on-
purpose production of propene is gaining attention. Propane
dehydrogenation (PDH) is a cost effective and efficient
technology for propene production. The non-oxidative
dehydrogenation of propane is an endothermic reaction
limited by thermodynamic equilibrium. Therefore, high
reaction temperatures (∼600 °C) are required to achieve
economically feasible conversions. However, high reaction
temperatures lead to several side reactions such as cracking,
isomerization and deep dehydrogenation of products.
4
Several dehydrogenation processes are applied in
industry. The most important are the Catofin process (CB&I
Lummus), the Oleflex process (UOP Honeywell) and the
STAR process (UHDE).
5
The Catofin process is based on
CrO
x
catalysts while the other processes are using bimetallic
Pt–Sn catalysts.
6
The use of chromium oxide-based catalysts
is an environmental challenge due to chromium's toxicity.
Therefore, noble metal-based catalysts are generally
preferred. However, platinum-based catalysts are subject to
fast deactivation due to sintering and coke formation.
7,8
The addition of a second inactive metal to a noble metal is
a widely used strategy in heterogeneous catalysis to improve
catalytic performance. An example for the PDH reaction is
the modification of Pt on alumina catalysts by adding
Sn.
9–11
The increased stability and selectivity of Pt–Sn
catalysts is due to the inhibition of hydrogenolysis, cracking
and coke formation.
12
The dehydrogenation of light alkanes
itself is a structure insensitive reaction where all Pt surface
atoms are active. However, side reactions such as
hydrogenolysis require larger Pt ensembles.
6
The Pt
ensemble size can be reduced by alloying with a second
non-active metal via a geometric effect. Thus, many alloy
phases have been studied in literature, e.g. Pt–Ga,
12,13
Pt–
Zn,
14–16
Pt–Cu,
17,18
Pt–Co,
19
Pt–Mn,
20
and Pt–Ti.
21
Catalytic
cracking is related to the Brønsted and Lewis acid sites of
catalysts due to formation of carbocation intermediates.
22
Zinc is a highly abundant, nontoxic and cheap raw
material. Therefore, Zn-based materials for catalytic
484 |Catal. Sci. Technol.,2021,11,484–493 This journal is © The Royal Society of Chemistry 2021
a
BasCat –UniCat BASF JointLab, Technische Universität Berlin, Berlin 10623,
Germany. E-mail: r.nauma[email protected]u-berlin.de
b
Functional Materials, Department of Chemistry, Technische Universität Berlin,
Berlin 10623, Germany
c
BASF SE, Process Research and Chemical Engineering, Heterogeneous catalysis,
Ludwigshafen 67056, Germany
†Electronic supplementary information (ESI) available. See DOI: 10.1039/
d0cy01528h
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applications are of special interest.
23
Several studies on Zn
based materials for PDH are reported in literature.
24,25
Single
site Zn
2+
species and ZnO nanoclusters were investigated for
activation of C–H bonds.
26–28
However, single site Zn
2+
species and ZnO nanoclusters are unstable under the harsh
conditions of PDH. Many strategies have been applied to
form bimetallic Pt/Zn nanoparticles.
14,24,25
However, most
synthesis methods result in an inhomogeneous distribution
of metals on the support. Atomic layer deposition (ALD) is a
synthetic method developed in the 1970's by Tuomo Suntola
in Finland.
29
Nowadays, ALD is widely used in the
semiconductor industry. The potential of ALD has been
widely investigated for catalyst development in the last two
decades.
30
ALD can be used to stabilize nanoparticles via
physical over-coating with an inert oxide layer,
31,32
formation
of metallic/core–shell nanoparticles,
33
deposition of
promoters on bulk catalysts,
34
and coating of powders with
functional materials.
35
Here, we use ALD to tailor the interface between Pt
nanoparticles and the SiO
2
used as support. The surface of
the SiO
2
is modified by homogenous deposition of a very thin
functional ZnO layer resulting in a high surface area support
with ZnO termination. ALD of zinc oxide is the second most
widely studied process after ALD of alumina.
36
A detailed
report of this process on powder substrates is given
elsewhere, along with characterization results for the ALD
modified materials.
37
Fig. 1 summarizes the design strategy
for the final nanoalloy catalyst. After the ALD process, Pt
nanoparticles are deposited on the ZnO/SiO
2
support via
incipient wetness impregnation. This strategy ensures a
direct and intimate contact between all Pt nanoparticles and
ZnO. The formed Pt/ZnO
ALD
/SiO
2
is a precursor for the final
catalyst. Pt
1
Zn
1
nanoalloy particles are formed in situ under
activation treatment conditions in the reactor used for PDH.
Experimental
Materials
Silica powder [SiO
2
, high-purity grade ≥99% (Davisil Grade
636), average pore size 60 Å, 35–60 mesh particle size,
specific surface area 506 m
2
g
−1
, Sigma-Aldrich, Germany]
was used as ALD substrate and support for catalyst synthesis.
Zinc oxide nanopowder [ZnO, nanopowder, <100 nm particle
size, specific surface area 10–25 m
2
g
−1
, Sigma-Aldrich,
Germany] was used as support. Pt(NH
3
)
4
(NO
3
)
2
[99.995%
trace metal basis, Sigma-Aldrich, Germany] was used as metal
salt for impregnation. Diethylzinc [Zn(C
2
H
5
)
2
, DEZn, elec. gr.,
99.999% Zn, Strem Chemicals, Germany] and water (H
2
O,
CHROMASOLV®, for HPLC, Riedel-de Haen) served as ALD
precursors and were used without further purification. High
purity N
2
, Ar, and He (99.999%) were used as carrier and
purging gases.
Atomic layer deposition of ZnO on SiO
2
Atomic layer deposition experiments were conducted in a set-
up designed and constructed in-house. A detailed description
of the set-up is given elsewhere.
38,39
High surface area SiO
2
powder was filled into a tubular fixed bed reactor made of a
quartz tube. The ALD process was carried out under a
continuous total gas flow of 100 mL min
−1
at atmospheric
pressure and a deposition temperature of 80 °C. The
diethylzinc (Zn(C
2
H
5
)
2
) saturator was heated to 50 °C while
the water saturator was kept at room temperature. Both
reactants were sequentially fed into the reactor in a flow of
100 mL min
−1
carrier gas. The sequence used was (Zn(C
2
-
H
5
)
2
)/N
2
–Ar purge–H
2
O/He–Ar purge. The end of each half
cycle times was determined by on-line mass spectrometry.
Both reactants were dosed to the reactor until the mass traces
for m/z= 93 (DEZn) and m/z=18(H
2
O) reached constant
levels, respectively. The resulting material is denoted as
ZnO
ALD
/SiO
2
.
Synthesis of Pt/SiO
2
, PtZn
ALD
/SiO
2
, PtZn
IWI
/SiO
2
and Pt/ZnO
Platinum nanoparticles supported on SiO
2
and ZnO
ALD
/SiO
2
were prepared via incipient wetness impregnation. The
ZnO
ALD
/SiO
2
was calcined in synthetic air at 500 °C for 2 h
prior to the impregnation. The nominal metal loading of
platinum was 1.0 wt% for both samples. An amount of 60 mg
of tetraammineplatinum(II) nitrate (Pt(NH
3
)
4
(NO
3
)
2
) salt was
dissolved in 2.2 mL and 1.8 mL HPLC grade water,
respectively. The metal salt solution was added dropwise to 3
g of SiO
2
(2.2 mL) and ZnO
ALD
/SiO
2
support (1.8 mL) and
mixed thoroughly. The samples were left standing overnight
at room temperature. The samples were then dried at 70 °C
for 24 h. Finally, the samples were calcined at 500 °C for 2 h
(heating rate: 10 K min
−1
) in a flow of 20% O
2
/N
2
(500 mL
Fig. 1 Synthesis approach used for the precise development of Pt
1
Zn
1
nano-alloys via interphase tailoring using ALD.
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min
−1
). The samples in the state after calcination are denoted
as Pt/SiO
2
and Pt/ZnO
ALD
/SiO
2
.
The reference Pt/ZnO
IWI
/SiO
2
catalyst was synthesised by
sequential incipient wetness impregnation of Zn and Pt. An
amount of 1.36 g of Zn(NO
3
)
2
·6H
2
Owasmixedwith2.2mL
HPLC grade water and stirred at 400 rpm for 30 min. The Zn
metal salt solution was added dropwise to 3 g of SiO
2
.The
sample was then dried at 70 °C for 24 h, followed by
calcination at 500 °C for 2 h (heating rate: 10 K min
−1
) in a flow
of 20% O
2
/N
2
(500 mL min
−1
). The resulting material is
denoted as ZnO
IWI
/SiO
2
. An amount of 65 mg of
(Pt(NH
3
)
4
(NO
3
)
2
) salt was dissolved in 2.2 mL HPLC grade
water added dropwise to the ZnO
IWI
/SiO
2
. The sample was
dried again at 70 °C for 24 h followed by calcination at 500 °C
for 2 h (heating rate: 10 K min
−1
, 500 mL min
−1
of 20% O
2
/N
2
).
For a systematic comparison, Pt supported on ZnO
without any SiO
2
support was also prepared via incipient
wetness impregnation. The nominal metal loading of
platinum was kept at 1 wt%. An amount of 60 mg of
tetraammineplatinum(II) nitrate (Pt(NH
3
)
4
(NO
3
)
2
) salt was
dissolved in 0.2 mL HPLC grade water. The metal salt
solution was added dropwise to 3 g of ZnO powder and
mixed thoroughly. The sample was left standing overnight at
a room temperature followed by drying in an oven at 70 °C
for 24 h. The dried sample was calcined at 500 °C for 2 h
(heating rate: 10 K min
−1
) in a flow of 20% O
2
/N
2
(500 mL
min
−1
). The resulting material is denoted as Pt/ZnO.
Prior to the catalytic test, all catalysts were activated in situ
by a reduction in H
2
. The catalysts were reduced in 50 mL
min
−1
of 10% H
2
/He for 60 min at 600 °C with a heating rate
of 10 K min
−1
. The activated catalysts are designated as
PtZn
ALD
/SiO
2
, PtZn
IWI
/SiO
2
, Pt/SiO
2,ACT
, and Pt/ZnO
ACT
,
respectively.
Characterization of the catalysts
For determination of specific surface areas, nitrogen
physisorption was performed at 77 K using a Quadrasorb SI
device manufactured by Quantachrome. Samples were
degassed at 120 °C for 12 h prior to measurements. The
surface area was determined by the Brunauer–Emmett–Teller
(BET) method. The average pore size was calculated using
non-local density functional theory (NLDF) method.
Phase analysis was done by powder X-ray diffraction (XRD)
measurements in Bragg–Brentano geometry on a D8 Advance
II theta/theta diffractometer (Bruker AXS) using Ni-filtered
Cu-Kαradiation and a position sensitive energy dispersive
LynxEye silicon strip detector.
For microstructural analysis, scanning transmission
electron microscopy (STEM) was conducted on a FEI Talos
F200X microscope. The microscope was operated at an
acceleration voltage of 200 kV. Elemental mappings were
recorded with a Super-X system including four silicon drift
energy-dispersive X-ray (EDX) detectors. All samples were
prepared on holey carbon-coated copper grids (Plano GmbH,
400 mesh).
Chemical analysis was carried out by X-ray fluorescence
spectroscopy (XRF) in a Bruker S4 Pioneer X-ray spectrometer.
Samples were prepared by melting pellets with a ratio of 100
mg sample to 8.9 g of Li
2
B
4
O
7
.
The electronic state of Pt in the catalysts was investigated
by X-ray photoelectron spectroscopy (XPS) measurements
using a ThermoScientific K-Alpha+ X-ray photoelectron
spectrometer. All samples were analysed using a micro-
focused, monochromatic Al-KαX-ray source (1486.68 eV; 400
μm spot size). The analyser had a pass energy of 200 eV
(survey), and 50 eV (high-resolution spectra), respectively. To
prevent any localized charge build-up during analysis the K-
α
+
charge compensation system was employed at all
measurements. The samples were mounted on conductive
carbon tape and the resulting spectra were analysed using
the Avantage software (ThermoScientific). All peaks were
calibrated by setting the binding energy (B.E.) for
adventitious carbon peak C1s to 284.8 eV to compensate for
the charging effect.
Catalytic experiments
The catalytic experiments were carried out at atmospheric
pressure and 600 °C in set-up designed by Integrated Lab
Solutions and equipped with a quartz tube as fixed bed
reactor. The applied reactor had an inner diameter of 10
mm. The used catalyst amount resulted in a bed height of
five mm. Catalyst amounts were fixed to 500 mg for all runs.
In an activation step, all catalysts were first in situ reduced
for 60 min at 600 °C in 50 mL min
−1
of 10% H
2
/He. After
purging with 50 mL min
−1
He for 5 min, the gas flow was
switched to 50 mL min
−1
of 20 vol% C
3
H
8
/He. The resulting
gas hourly space velocity (GHSV) was 6000 mL g
−1
h
−1
. The
effluent gas stream was analysed by an online gas
chromatograph (Agilent 7890A) equipped with a flame
ionization detector and a thermal conductivity detector.
Propane conversion, propene selectivity and a deactivation
factor were calculated according to eqn (1)–(3), respectively:
C3H8conversion %ðÞ¼ FC3H8in −FC3H8out
FC3H8in

×100 (1)
Selectivity %ðÞ¼ ni×Fiout
Pni×Fiout

×100 (2)
Deactivation factor %ðÞ¼
X0−X1
X0
×100 (3)
where irepresensts a hydrocarbon product of propane
dehydrogenation reaction in the effluent gas, n
i
represents
the number of carbon atoms of the component i, and F
i
is
the flow rate. X
0
and X
1
are propane conversion at 5 min and
12 h time on stream.
Results
The design strategy for the multistep synthesis applied in
this study is summarized in Fig. 1. In the first step, the SiO
2
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support is modified by a thin layer of ZnO via ALD. The
second step adds Pt nanoparticles via incipient wetness
impregnation. This results in a direct contact between Pt and
ZnO. The resulting Pt/ZnO
ALD
/SiO
2
material is then activated
by reduction to yield well defined Pt–Zn nanoalloy particles.
The ZnO ALD is carried out on a high surface area silica
powder via an AB type ALD process of (Zn(C
2
H
5
)
2
)/H
2
Oat80
°C in a tubular fixed bed reactor. An in situ gravimetric study
of the growth behaviour of ZnO on SiO
2
is reported
elsewhere.
37
In the ZnO ALD process, diethyl zinc (Zn(C
2
H
5
)
2
)
reacts with the surface hydroxyl groups forming surface
chemisorbed Zn(C
2
H
5
) species while releasing C
2
H
6
as by-
product during the first half cycle, while in the second half
cycle the surface hydroxyl groups are recreated by dosing
H
2
O to form surface Zn(OH)
x
species with C
2
H
6
as by-
product. The reaction will continue until all of the surface
groups are saturated.
Characterization of synthesized catalysts
The elemental analysis (XRF) of ZnO
ALD
/SiO
2
after one ALD
cycle gave a Zn content of 12.2 wt%. ZnO
ALD
/SiO
2
and the
original SiO
2
were used as support for Pt nanoparticles via
incipient wetness impregnation. The physicochemical
properties of the materials are reported in Table 1. The
specific surface area and average pore volume decreased
considerably after one ALD cycle of ZnO on SiO
2
and the
subsequent impregnation of Pt nanoparticles. A decrease in
specific surface area and total pore volume can be
rationalized by the coating of micro- and mesopores during
the ALD process. Furthermore, the observed decrease in the
specific surface area is partly due to the deposition of dense
ZnO on low density SiO
2
, as the specific surface area is
normalised to mass. The corresponding N
2
adsorption
isotherms are shown in Fig. S1.†The results for PtZn
ALD
/SiO
2
show a type IV isotherm with H1 hysteresis loop similar to
the isotherm of the original SiO
2
support, indicating the
overall conformal coating with ZnO of the mesopores of SiO
2
without loss of porosity due to pore blocking.
The X-ray diffractograms of all materials in the state as
synthesized and after activation are shown in Fig. 2. In the state
before activation, no indications for Pt nanoparticles are
observed in the diffractograms of Pt/SiO
2
and Pt/ZnO
IWI
/SiO
2
.A
very broad peak at 2θ∼39.2°, corresponding to the (111)
reflection of the face centered cubic (FCC) structure of Pt, can
be found in the diffractogram of Pt/ZnO
ALD
/SiO
2
. A peak at the
same position, although much sharper, can be found in the
diffractogram of Pt/ZnO. After the activation step a Pt (111)
diffraction peak can be found in the diffractogram of Pt/
SiO
2,ACT
. The peaks observed in the diffractograms of Pt/
ZnO
ALD
/SiO
2
and Pt/ZnO are shifted to 2θ= 40.6°in the
diffractograms of PtZn
ALD
/SiO
2
and Pt/ZnO
ACT
. This shift can be
rationalized by the formation of an alloy phase as literature
reportsa2θvalue of 40.6°for the (111) diffraction peak of the
tetragonal Pt
1
Zn
1
alloy (PDF-04-016-2848, spacing group P4/
mmm). In contrast, the diffractogram of PtZn
IWI
/SiO
2
shows no
peaks indicating any Pt nanoparticles. The absence of such
peaks can be rationalized by an average crystallite domain size
for Pt below 5 nm, indicating either large polycrystalline
nanoparticles, e.g. with stacking faults or twin faults, or highly
dispersed, small nanoparticles.
The HAADF-STEM images and the corresponding EDX
mappings of the catalysts in the state after synthesis and
after activation are shown in Fig. S2†and 3, respectively. The
STEM image of Pt/SiO
2
(Fig. S2a†) shows highly dispersed Pt
nanoparticles supported on SiO
2
. The average particle size of
the Pt nanoparticles is about 5 nm, in agreement with the
XRD results. A representative STEM image and corresponding
EDX mappings for Pt/ZnO
ALD
/SiO
2
are shown in Fig. S2(b and
d).†No indications for phase separation and formation of
ZnO crystallites were found. The EDX mappings clearly show
the well-dispersed distribution of Zn over the support
indicating a homogenous coating of SiO
2
with ZnO. The
STEM-EDX analysis also confirms that all supported Pt
Table 1 Physicochemical analysis of as synthesized materials
Material Surface area (m
2
g
−1
) Pore size (nm) Pore volume (mL g
−1
) Pt content (wt%) Zn content (wt%)
SiO
2
505 4.9 0.75 0 0
Pt/SiO
2
465 4.6 0.71 1.15 0
PtZn
ALD
/SiO
2
400 4.8 0.56 1.15 12.2
PtZn
IWI
/SiO
2
381 4.7 0.66 1.1 10
Pt/ZnO 13 2.8 0.04 1.2 78
Specific surface area calculated by BET method, pore size from NLDFT method and Pt and Zn content calculated by XRF analysis.
Fig. 2 X-ray diffractograms of (a) as synthesized and (b) activated
materials.
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nanoparticles are in direct and intimate contact with ZnO. The
formation of PtZn nanoparticles during activation can be seen
in a representative STEM image and the corresponding EDX
mappings of PtZn
ALD
/SiO
2
shown in Fig. 3(a–c). The alloy
formation can be deduced from the fact that in the EDX
mappings Zn is enriched in the areas were Pt is concentrated.
The average particle size of the supported PtZn nanoalloy
particles is 8.6 nm. In contrast, the electron microscopy results
for PtZn
IWI
/SiO
2
cannot be summarized in a representative
micrograph as the material is far too heterogeneous. The
STEM images and corresponding EDX mappings shown in
Fig. 3(d–i) indicate the presence of segregated ZnO
nanoparticles with sizes up to 200 nm (Fig. 3i) as well as
regions with finely dispersed ZnO agglomerates on SiO
2
(Fig. 3f). The EDX mappings also show that Pt is not
homogeneously distributed either. There are regions with very
low Pt concentration (Fig. 3h) as well as regions with
homogeneously dispersed Pt nanoparticles (Fig. 3e). It can be
clearly seen that Zn is not enriched in the locations of Pt
nanoparticles (Fig. 3e and f). The heterogeneous distribution
of Pt and Zn can already be seen in STEM image and the
corresponding EDX mappings of Pt/ZnO
IWI
/SiO
2
in the state
after synthesis shown in Fig. S2(e–g).†Therefore, it can be
assumed that the segregation of ZnO observed in PtZn
IWI
/SiO
2
is not due to the activation step but rather the way of ZnO
deposition. The electron microscopy results regarding Pt/ZnO
and Pt/ZnO
ACT
are in full agreement with the corresponding
XRD results. It can be clearly seen in Fig. S2(h–j)†that the IWI
of Pt onto unsupported ZnO resulted in the formation of large
Pt nanoparticles. The micrograph shows several Pt particles in
an orientation without underlying ZnO, at the edge of a large
ZnO particle. EDX mappings clearly show that these Pt
nanoparticles contain no significant amount of Zn. In
contrast, a similarly oriented Pt nanoparticle in Fig. 3(j–l)
shows a high Zn content. Thus, the via XRD macroscopically
observed phase transformation of Pt to Pt
1
Zn
1
during
activation can also be confirmed in microstructural analysis
on the nm scale. The main difference to the other Pt
containing catalysts is the size of the supported metal
particles. The low specific surface area of the unsupported
ZnO favours the formation of large Pt particles in the range
above 10 nm. The differences between PtZn
ALD
/SiO
2
and
PtZn
IWI
/SiO
2
can be rationalized by the fact that ALD is based
on chemisorption while IWI proceeds mainly via
physisorption. Chemisorbed Zn species are more strongly
bound to the SiO
2
surface and therefore supposedly stay well
dispersed during the calcination step prior to Pt impregnation.
In contrast, physisorbed Zn species are more mobile on the
SiO
2
surface and thus may form easily ZnO aggregates and
nanoparticles. The results obtained for Pt/ZnO
ACT
support the
idea that Pt which is in close contact to ZnO transforms into a
PtZn upon activation as postulated in our design strategy.
Fig. 3 HAADF-STEM image and EDX maps of Pt and Zn in (a–c) PtZn
ALD
/SiO
2
showing homogenously dispersed Zn signal on SiO
2
and Pt
nanoparticles in direct contact with ALD deposited ZnO; (d–f) PtZn
IWI
/SiO
2
, indicating the inhomogeneous dispersion of Zn and Pt, where Zn is
either in apart or in close proximity of Pt nanoparticles; (g–i) PtZn
IWI
/SiO
2
, where severe Zn aggregation can be visualised indicating poor
dispersion of ZnO during impregnation; (j–l) Pt/ZnO
ACT
, indicating larger Pt nanoparticles supported on bare ZnO support.
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XPS gives results in agreement with XRD and electron
microscopy. The Pt 4f
7/2
binding energy (B.E.) is different for
Pt/SiO
2,ACT
and PtZnALD/SiO
2
in the XPS spectra shown in
Fig. 4 the Pt 4f
7/2
B.E. for standalone Pt/SiO
2,ACT
is 71.2 eV
indicating the presence of metallic Pt
0
. The Pt 4f
7/2
peak for
PtZn
ALD
/SiO
2
is at 71.7 eV. This positive shift of 0.5 eV in B.E.
can be rationalized by the enhancement of the electrostatic
field around Pt nuclei due to the vicinity of alloying Zn
atoms. The alloying of Pt with Zn results in a reduction of
the density of Pt 5d states around the Fermi level which leads
to a shift of the Pt 5d band and the 4f core levels to higher
binding energies.
40,41
Propane dehydrogenation
The propane dehydrogenation (PDH) experiments were
conducted in a single tube quartz reactor at the reaction
temperature of 600 °C. The catalytic performance of Pt/
SiO
2,ACT
, PtZn
ALD
/SiO
2
, PtZn
IWI
/SiO
2
and Pt/ZnO
ACT
are shown
in Fig. 5 and Table 2. All four catalysts initially show a higher
C
3
H
8
conversion followed by deactivation within 0.5 h time
on stream (TOS) and finally a stable performance for 12 h.
To compare the different catalysts regarding their stability,
a deactivation factor (D) was calculated according to eqn (3).
The performance of the reference Pt/SiO
2,ACT
catalyst is in
general agreement with literature. An initial C
3
H
8
conversion
of 37% decreases within 0.5 h TOS giving a deactivation
factor of 86% after 12 h time on stream. The C
3
H
6
selectivity
decreases over 12 h TOS from 77% to 61%. The second
reference catalyst, Pt/ZnO
ACT
, exhibits a much lower initial
conversion of 8% and reaches a similar low performance
after 12 h TOS. The lower initial performance is not
surprising and can be clarified by the large size of the
supported Pt nanoparticles and the resulting low dispersion
of Pt.
Modification of the interface between Pt and SiO
2
by
deposition of ZnO before Pt is supported improves
significantly the performance of the catalysts PtZn
ALD
/SiO
2
and PtZn
IWI
/SiO
2
. PtZn
ALD
/SiO
2
shows an initial C
3
H
8
conversion of 53% and a low deactivation factor of 7.5% after
12 h TOS, with the complete deactivation occurring in the
first 0.5 h. The C
3
H
6
selectivity is at a high level 97% over the
complete 12 h TOS. PtZn
IWI
/SiO
2
shows an initial C
3
H
8
Fig. 4 XPS analysis of Pt/SiO
2
and PtZn
ALD
/SiO
2
after activation
treatment in 10% H
2
/He at 600 °C for 1 h.
Fig. 5 (a) C
3
H
8
conversion, (b) C
3
H
6
selectivity and (c) different
product distributions at the end of 12 h time on stream; propane
dehydrogenation was carried out at 600 °C under 20 vol% C
3
H
8
/He
flow and 500 mg of catalyst.
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conversion of 40% and a higher deactivation factor of 22.5%.
The C
3
H
6
selectivity of PtZn
IWI
/SiO
2
is comparable to the
selectivity shown by PtZn
ALD
/SiO
2
at a constant level of 96%.
The product distribution measured for all catalysts in the
state after 12 h TOS is given in Fig. 5c. The deactivated state
of Pt/SiO
2,ACT
and Pt/ZnO
ACT
is very similar. The main
product is propene with selectivities of 61% and 52%,
respectively. Ethylene and methane are major byproducts,
only minor amounts of ethane are found. One clear
difference is the fact that the carbon balance for Pt/ZnO
ACT
is
not closed indicating ongoing formation of carbonaceous
deposits. The byproduct distribution indicates hydrogenolysis
of propene. Pt–Pt ensembles are known to perform deep
dehydrogenation of alkanes followed by hydrogenolysis.
42,43
On the other hand, Pt/ZnO
ACT
shows the same product
distribution. The results of a blank test using the quartz
reactor filled with SiO
2
are shown in Fig. S3.†The measured
values for conversion of 3% and for propene selectivity of
53% can be attributed to homogeneous gas phase reaction.
The values are in the same order of magnitude as measured
for Pt/SiO
2,ACT
and Pt/ZnO after 12 h TOS, therefore the
performance of these two catalysts after 12 h TOS cannot be
reliably interpreted. The product distribution for PtZn
ALD
/
SiO
2
and PtZn
IWI
/SiO
2
is nearly identical, only small amounts
of byproducts are found, in both cases methane, ethene and
ethane. This can be taken as indication that the active sites
are in both catalysts of the same nature. The difference in
activity for the both catalysts can be rationalized by a
different amount of active sites, with PtZn
ALD
/SiO
2
having
more active sites than PtZn
IWI
/SiO
2
. An explanation could be
that Pt
1
Zn
1
nanoalloy particles are the active phase, while Pt
nanoparticles are subject to fast deactivation. The macro-
and microstructural analysis of the catalysts in the state as
synthesized and after activation showed that the ZnO is more
homogeneously distributed in the ALD modified samples,
and that PtZn
ALD
/SiO
2
contained exclusively Pt
1
Zn
1
nanoalloy
particles while PtZn
IWI
/SiO
2
contained a possibly some PtZn
nanoalloy particles and mainly Pt nanoparticles. A hypothesis
would be that the Pt nanoparticles in PtZn
IWI
/SiO
2
are partly
transformed into active Pt
1
Zn
1
nanoalloy particles and partly
deactivate in the form of Pt nanoparticles. In order to clarify
whether ZnO supported on SiO
2
has a positive contribution
to the target reaction, Zn
ALD
/SiO
2
without Pt content was
activated and tested. The results are shown in Fig. S4.†The
C
3
H
8
conversion is stable at a level of 8%, but the propene
selectivity decreased within 4 h TOS from 98% to 65%. The
activity is higher than that of pure SiO
2
, but the selectivity is
poor, and thus the contribution of the exposed ZnO surface
is in total not beneficial for the overall propene yield.
STEM micrographs and corresponding EDX mappings of
spent catalysts are shown in Fig. 6. The elemental mapping
of PtZn
ALD
/SiO
2
and Pt/ZnO
ACT
shows that the PtZn nanoalloy
particles observed in Fig. 3 can still be seen in
Fig. 6(a–c) and (j–l), respectively. There is no hint for any
phase segregation into Pt and ZnO. The results for the spent
PtZn
ALD
/SiO
2
also show no hint for any aggregation or
sintering of ZnO. The STEM images for PtZn
IWI
/SiO
2
and the
corresponding EDX mappings indicate clearly the presence of
PtZn nanoalloy particles in Fig. 6(d–f) and Zn nanoparticles
in Fig. 6(g–i). The results of the XRD analysis of all spent
catalysts are shown in Fig. S5.†A peak at 2θ= 40.6°indicates
the presence of Pt
1
Zn
1
nanoalloy particles in PtZn
ALD
/SiO
2
,
PtZn
IWI
/SiO
2
, and Pt/ZnO
ACT
, in agreement with the results
from electron microscopy. To investigate whether the
nanoalloy particles observed macroscopically by XRD and
microscopically by STEM have the same composition, further
STEM experiments were carried out investigating spent
PtZn
ALD
/SiO
2
. Many micrographs were analysed to find
nanoalloy particles that are oriented at the edge of the
supporting particles without any particles lying beneath or on
top. The results are shown in Fig. S7.†Two suitable
nanoparticles were chosen, and EDX analysis was performed.
The results show that in both cases the mass fractions of Pt and
Zn match very well the composition of the Pt
1
Zn
1
nanoalloy
particles observed by XRD. Therefore, it can be safely assumed
that Pt
1
Zn
1
nanoalloy particles are the active phase, and the
under reaction conditions most stable alloy phase.
Discussions
Previous studies reported that Zn
2+
species are active in
propane dehydrogenation.
26,28,44–47
However, homogeneously
coated Zn
ALD
/SiO
2
performed not very well and cannot be
considered a relevant catalyst. Pt nanoparticles supported on
SiO
2
without ZnO exhibited a fast decrease of activity and
selectivity. Bimetallic PtZn catalysts synthesized via ALD and
IWI showed a high and stable activity and with high
selectivity to C
3
H
6
. The promotional effect of Zn on Pt
Table 2 Catalytic performance of reference and ALD modified catalysts
Name of
catalyst
C
3
H
8
conversion
X(%)
C
3
H
6
selectivity
S(%) Deactivation
factor D(%)
Carbon
balanceX
0a
X
1b
S
0a
S
1b
Pt/SiO
2,ACT
37 5 77 61 86 98
PtZn
ALD
/SiO
2
53 49 97 97 7.5 99
PtZn
IWI
/SiO
2
40 31 97 96 22.5 99
Pt/ZnO
ACT
8 5 63 52 37.5 95
a
X
0
&S
0
: conversion of propane and selectivity towards propene at 5 min TOS.
b
X
1
&S
1
: conversion of propane and selectivity towards
propene at 12 h TOS; carbon balance was calculated at end of 12 h TOS.
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catalysts was clearly observed. The formation of Pt
1
Zn
1
nanoalloy particles during activation or reaction was
confirmed for all bimetallic catalysts. The alloy formation
results in electronic modification of Pt but separation of
larger Pt ensembles by Zn atoms may also play a role.
15
The
hydrogenolysis of propane to lower alkanes is favoured by
larger Pt ensembles. Separation of Pt ensembles by Zn atoms
via alloy formation is considered to be the main reason of
the high propene selectivity of PtZn catalysts.
48
The present
study shows that the method used to deposit ZnO has a
strong influence on the activity of a PtZn catalyst. It is crucial
to bring all Pt nanoparticles in direct contact with ZnO to
allow formation Pt
1
Zn
1
nanoalloy particles under reducing
conditions. ALD leads to a homogeneous dispersion of ZnO
on SiO
2
, completely coating the whole surface of the SiO
2
support with strongly chemisorbed ZnO species. In contrast,
IWI yields more mobile and inhomogeneously dispersed ZnO
particles on the SiO
2
support. Only the homogeneously
dispersed ZnO gave a direct contact between all Pt species
and ZnO and thus ensured the complete formation of PtZn
nanoalloy particles.
V. J. Cybulskis et al.,
15
studied the effect of promoting Pt
with Zn for the catalytic dehydrogenation of ethane by in situ
X-ray absorption and synchrotron X-ray diffraction. The study
indicated that the addition of Zn to Pt nanoparticles lowers
the energy level of occupied Pt 5d orbitals thereby weakening
the bond between the Pt 5d orbital and adsorbates (reactant
and product). Thus, the main dehydrogenation product will
quickly desorb from surface of Pt, avoiding deep
dehydrogenation and other side reactions. The geometric
and electronic effect of promoting Pt with another element is
also studied for Fe,
48
Ce,
49,50
Co,
19
and Mn.
20
In general, an
increase in olefin selectivity is observed when Pt is combined
with another element.
Many different strategies such as impregnation,
14
ion
exchange,
41
and a single source precursor approach using
bimetallic metalorganic precursors
51
were investigated to
form PtZn nanoalloy particles on different supports.
Impregnation and ion exchange techniques typically lead to
inhomogeneous deposition of Pt and Zn on the support. The
single source precursor approach yields precisely formed
PtZn nanoalloy particles.
51
However, the single source
precursor approach already requires immense efforts when a
scale-up to the range of 10 to 25 g of catalyst is considered.
One previous study also used an ALD approach to
synthesize a PtZn catalyst for butane dehydrogenation.
52
However, the study focussed on the catalytic performance
rather than the synthesis. Pt and Zn were both deposited via
ALD, and it is not clear whether the observed effects are due
to Zn or Pt ALD. The authors did not investigate the
homogeneity of ZnO deposition in detail. The fact that Zn
loading was varied by changing the Zn deposition
temperature from 175 °C to 100 °C and the amount of
substrate by a factor of ∼3 may be an indication for
inhomogeneous deposition. The main reason for the
homogeneity of via ALD prepared materials is the self-
Fig. 6 HAADF-STEM image and EDX maps of Pt and Zn in spent (a–c) PtZn
ALD
/SiO
2
showing formed Pt
1
Zn
1
nanoalloys; (d–f) PtZn
IWI
/SiO
2
,
indicating formed Pt
1
Zn
1
nanoalloys as well as (g–i) severe aggregation of Zn away from Pt; (j–l) Pt/ZnO
ACT
, indicating formed Pt
1
Zn
1
alloy particles.
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limitation of the reaction leading to a saturation of the
surface. Generally, the independence of the loading from
temperature and amount of dosed precursor is taken as proof
that the conditions for ALD are fulfilled and the process
operates within the ALD window.
53–56
Furthermore, Libera
et al.,
57
reported that the deposition of Zn via ALD on SiO
2
particles at temperatures above 150 °C yields metallic Zn and
ZnO simultaneously. The presence of metallic Zn is reported
as an indication of a chemical vapour deposition (CVD)
process occurring in parallel. Please note that in general CVD
leads to less homogeneously distributed deposition.
58,59
The
ALD process applied in this study for the deposition of ZnO
on SiO
2
particles was carefully developed and thoroughly
investigated to ensure maximum homogeneity of the Zn
distribution. Details and descriptions are given elsewhere.
37
Therefore, to the best of our knowledge, this study is the first
study that uses ALD of ZnO to synthesize in a controlled way
a bimetallic PtZn nanoalloy catalyst for dehydrogenation of
alkanes.
Conclusions
In summary, we applied a clear synthesis strategy to tailor
the interface between Pt and SiO
2
by deposition of a thin
layer of ZnO. The direct contact between Pt and ZnO resulted
in the complete transformation of all Pt nanoparticles into
Pt
1
Zn
1
nanoalloy particles under reducing conditions. The
activated PtZn
ALD
/SiO
2
catalyst showed exceptional activity
and stability in the reaction of propane dehydrogenation.
Incorporation of Zn into Pt results in electronic as well as
geometric modification of the active catalyst surface, which
leads to a very high propene selectivity of 96%. Only one ALD
cycle was needed to deposit a sufficient amount of ZnO for
the boost in propane dehydrogenation performance. The
present study established a novel yet easily scalable synthetic
approach to design an interface between metal nanoparticles
and the support with a functional layer in between. This
synthesis strategy can be easily transferred to other catalyst
systems where nanoalloy particles or strong metal support
interactions (SMSI) play an important role.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
The authors are grateful for the support by the Einstein
Foundation Berlin (ESB) –Einstein Center of Catalysis (EC
2
).
The work was conducted in the framework of the BasCat –
UniCat BASF JointLab. The authors gratefully acknowledge
the support by C. Eichenauer (AK Thomas, TU Berlin, N
2
physisorption measurements), Dr. F. Girgsdies (FHI, Berlin,
XRD measurements), Dr. B. Frank (BasCat, thermodynamic
calculations), and Jan Meissner (BasCat, technical support).
References
1 J. C. Bricker, Top. Catal., 2012, 55, 1309–1314.
2 B. V. Vora, Top. Catal., 2012, 55, 1297–1308.
3 S. Kim, S. Jeong and E. Heo, Energy Sources, Part B, 2019, 14,
49–66.
4 M. M. Bhasin, J. H. McCain, B. V. Vora, T. Imai and P. R.
Pujadó, Appl. Catal., A, 2001, 221, 397–419.
5 D. E. Resasco and G. L. Haller, Catalysis, ed. J. Spivey and
S. Agarwal, Royal Society of Chemistry, 2007, vol. 11, pp.
379–411.
6 J. J. H. B. Sattler, J. Ruiz-Martinez, E. Santillan-Jimenez and
B. M. Weckhuysen, Chem. Rev., 2014, 114, 10613–10653.
7 H. Z. Wang, L. L. Sun, Z. J. Sui, Y. A. Zhu, G. H. Ye, D. Chen,
X. G. Zhou and W. K. Yuan, Ind. Eng. Chem. Res., 2018, 57,
8647–8654.
8 Q. Li, Z. Sui, X. Zhou, Y. Zhu, J. Zhou and D. Chen, Top.
Catal., 2011, 54, 888–896.
9 J. J. H. B. Sattler, A. M. Beale and B. M. Weckhuysen, Phys.
Chem. Chem. Phys., 2013, 15, 12095–12103.
10 H. N. Pham, J. J. H. B. Sattler, B. M. Weckhuysen and A. K.
Datye, ACS Catal., 2016, 6, 2257–2264.
11 S. Sahebdelfar, M. T. Ravanchi, F. Tahriri Zangeneh, S.
Mehrazma and S. Rajabi, Chem. Eng. Res. Des., 2012, 90,
1090–1097.
12 J. J. H. B. Sattler, I. D. Gonzalez-Jimenez, L. Luo, B. A. Stears,
A. Malek, D. G. Barton, B. A. Kilos, M. P. Kaminsky,
T. W. G. M. Verhoeven, E. J. Koers, M. Baldus and B. M.
Weckhuysen, Angew. Chem., Int. Ed., 2014, 53, 9251–9256.
13 K. Searles, K. W. Chan, J. A. Mendes Burak, D. Zemlyanov, O.
Safonova and C. Copéret, J. Am. Chem. Soc., 2018, 140,
11674–11679.
14 C. Chen, M. Sun, Z. Hu, J. Ren, S. Zhang and Z. Y. Yuan,
Catal. Sci. Technol., 2019, 9, 1979–1988.
15 V. J. Cybulskis, B. C. Bukowski, H. T. Tseng, J. R. Gallagher,
Z. Wu, E. Wegener, A. J. Kropf, B. Ravel, F. H. Ribeiro, J.
Greeley and J. T. Miller, ACS Catal., 2017, 7, 4173–4181.
16 G. Liu, L. Zeng, Z. J. Zhao, H. Tian, T. Wu and J. Gong, ACS
Catal., 2016, 6, 2158–2162.
17 Z. Han, S. Li, F. Jiang, T. Wang, X. Ma and J. Gong,
Nanoscale, 2014, 6, 10000–10008.
18 Z. Ma, Z. Wu and J. T. Miller, Catal., Struct. React.,
2017, 3(1–2), 43–53.
19 L. G. Cesar, C. Yang, Z. Lu, Y. Ren, G. Zhang and J. T. Miller,
ACS Catal., 2019, 5231–5244.
20 Z. Wu, B. C. Bukowski, Z. Li, C. Milligan, L. Zhou, T. Ma, Y.
Wu, Y. Ren, F. H. Ribeiro, W. N. Delgass, J. Greeley, G. Zhang
and J. T. Miller, J. Am. Chem. Soc., 2018, 140, 14870–14877.
21 F. Jiang, L. Zeng, S. Li, G. Liu, S. Wang and J. Gong, ACS
Catal., 2015, 5, 438–447.
22 N. Rahimi and R. Karimzadeh, Appl. Catal., A, 2011, 398,
1–17.
23 A. Kolodziejczak-Radzimska and T. Jesionowski, Materials,
2014, 7, 2833–2881.
24 O. B. Belskaya, L. N. Stepanova, T. I. Gulyaeva, S. B.
Erenburg, S. V. Trubina, K. Kvashnina, A. I. Nizovskii, A. V.
Catalysis Science & TechnologyPaper
Open Access Article. Published on 18 November 2020. Downloaded on 3/11/2021 12:04:16 PM.
This article is licensed under a
Creative Commons Attribution-NonCommercial 3.0 Unported Licence.
View Article Online
Catal. Sci. Technol., 2021, 11,484–493 | 493This journal is © The Royal Society of Chemistry 2021
Kalinkin, V. I. Zaikovskii, V. I. Bukhtiyarov and V. A.
Likholobov, J. Catal., 2016, 341,13–23.
25 Z. Nawaz, T. Xiaoping and W. Fei, Korean J. Chem. Eng.,
2009, 26, 1528–1532.
26 C. Chen, Z. Hu, J. Ren, S. Zhang, Z. Wang and Z. Y. Yuan,
ChemCatChem, 2019, 11, 868–877.
27 T. Gong, L. Qin, J. Lu and H. Feng, Phys. Chem. Chem. Phys.,
2016, 18, 601–614.
28 J. Camacho-Bunquin, P. Aich, M. Ferrandon, A. “Bean”
Getsoian, U. Das, F. Dogan, L. A. Curtiss, J. T. Miller, C. L.
Marshall, A. S. Hock and P. C. Stair, J. Catal., 2017, 345,
170–182.
29 S. M. George, Chem. Rev., 2010, 110, 111–131.
30 B. J. Oneill, D. H. K. Jackson, J. Lee, C. Canlas, P. C. Stair,
C. L. Marshall, J. W. Elam, T. F. Kuech, J. A. Dumesic and
G. W. Huber, ACS Catal., 2015, 5, 1804–1825.
31 J. Lu, B. Fu, M. C. Kung, G. Xiao, J. W. Elam, H. H. Kung
and P. C. Stair, Science, 2012, 335, 1205–1208.
32 P. Ingale, C. Guan, R. Kraehnert, R. Naumann d’Alnoncourt,
A. Thomas and F. Rosowski, Catal. Today, DOI: 10.1016/j.
cattod.2020.04.050.
33 K. Cao, Q. Zhu, B. Shan and R. Chen, Sci. Rep., 2014, 5, 8470.
34 V. E. Strempel, D. Löffler, J. Kröhnert, K. Skorupska, B.
Johnson, R. Naumann d'Alnoncourt, M. Driess and F.
Rosowski, J. Vac. Sci. Technol., A, 2016, 34, 01A135.
35 J. S. Jur and G. N. Parsons, ACS Appl. Mater. Interfaces,
2011, 3, 299–308.
36 J. Lu, J. W. Elam and P. C. Stair, Surf. Sci. Rep., 2016, 71,
410–472.
37 P. Ingale, K. Knemeyer, M. P. Hermida, R. Naumann
d'Alnoncourt, A. Thomas and F. Rosowski, Nanomaterials,
2020, 10, 981.
38 V. E. Strempel, R. Naumann D'Alnoncourt, M. Driess and F.
Rosowski, Rev. Sci. Instrum., 2017, 88.
39 V. E. Strempel, K. Knemeyer, R. Naumann d’Alnoncourt, M.
Driess and F. Rosowski, Nanomaterials, 2018, 8(6), 365.
40 J. A. Rodriguez and M. Kuhn, J. Chem. Phys., 1995, 102,
4279–4289.
41 T. Iida, D. Zanchet, K. Ohara, T. Wakihara and Y. Román-
Leshkov, Angew. Chem., Int. Ed., 2018, 57, 6454–6458.
42 J. H. Sinfelt, J. Phys. Chem., 1964, 68, 344–346.
43 R. D. Cortright, R. M. Watwe and J. A. Dumesic, J. Mol.
Catal. A: Chem., 2000, 163,91–103.
44 S. M. T. Almutairi, B. Mezari, P. C. M. M. Magusin, E. A.
Pidko and E. J. M. Hensen, ACS Catal., 2012, 2,71–83.
45 T. Gong, L. Qin, J. Lu and H. Feng, Phys. Chem. Chem. Phys.,
2016, 18, 601–614.
46 S. M. T. Almutairi, B. Mezari, P. C. M. M. Magusin, E. A.
Pidko and E. J. M. Hensen, ACS Catal., 2012, 2,71–83.
47 N. M. Schweitzer, B. Hu, U. Das, H. Kim, J. Greeley, L. A.
Curtiss, P. C. Stair, J. T. Miller and A. S. Hock, ACS Catal.,
2014, 4, 1091–1098.
48 E. C. Wegener, B. C. Bukowski, D. Yang, Z. Wu, A. J. Kropf,
W. N. Delgass, J. Greeley, G. Zhang and J. T. Miller,
ChemCatChem, 2020, 12, 1325–1333.
49 Y. Qiu, X. Li, Y. Zhang, C. Xie, S. Zhou, R. Wang, S. Z. Luo, F.
Jing and W. Chu, Ind. Eng. Chem. Res., 2019, 58,
10804–10818.
50 W. Cai, R. Mu, S. Zha, G. Sun, S. Chen, Z. J. Zhao, H. Li, H.
Tian, Y. Tang, F. Tao, L. Zeng and J. Gong, Sci. Adv., 2018, 4,
eaar5418.
51 L. Rochlitz, K. Searles, J. Alfke, D. Zemlyanov, O. V. Safonova
and C. Copéret, Chem. Sci., 2020, 11, 1549–1555.
52 J. Camacho-Bunquin, M. S. Ferrandon, H. Sohn, A. J. Kropf,
C. Yang, J. Wen, R. A. Hackler, C. Liu, G. Celik, C. L.
Marshall, P. C. Stair and M. Delferro, ACS Catal., 2018, 20,
10058–10063.
53 A. W. Weimer, J. Nanopart. Res., 2019, 21,9.
54 N. E. Richey, C. De Paula and S. F. Bent, J. Chem. Phys.,
2020, 152, 40902.
55 L. Cao and J. Lu, Cite this Catal. Sci. Technol., 2020, 10,
2695.
56 J. Lu, J. W. Elam and P. C. Stair, Surf. Sci. Rep., 2016, 71,
410–472.
57 J. A. Libera, J. W. Elam and M. J. Pellin, Thin Solid Films,
2008, 516, 6158–6166.
58 H. H. Sønsteby, A. Yanguas-Gil and J. W. Elam, J. Vac. Sci.
Technol., A, 2020, 38, 020804.
59 G. L. Doll, B. A. Mensah, H. Mohseni and T. W. Scharf,
J. Therm. Spray Technol., 2010, 19, 510–516.
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