Operando Investigation of Toluene Oxidation over 1D Pt@CeO2Derived from Pt Cluster-Containing MOF

Article abstract of DOI:10.1021/jacs.0c08640

A unique 1D nanostructure of Pt@CeO2-BDC was prepared from Pt@CeBDC MOF. The Pt@CeO2-BDC was rich in oxygen vacancies (i.e., XPS Oβ/(Oα + Oβ) = 39.4%), and on the catalyst, the 2 nm Pt clusters were uniformly deposited on the 1D mesoporous polycrystalline CeO2. Toluene oxidation was conducted in a spectroscopic operando Raman-online FTIR reactor to elucidate the reaction mechanism and establish the structure-activity relationship. The reaction proceeds as follows: (I) adsorption of toluene as benzoate intermediates on Pt@CeO2-BDC at low temperature by reaction with surface peroxide species; (II) reaction activation and ring-opening involving lattice oxygen with a concomitant change in defect densities indicative of surface rearrangement; (III) complete oxidation to CO2 and H2O by lattice oxygen and reoxidation of the reduced ceria with consumption of adsorbed oxygen species. The Pt clusters, which mainly exist as Pt2+ with minor amounts of Pt0 and Pt4+ on the surface, facilitated the adsorption and reaction activation. The Pt-CeO2 interface generates reduced ceria sites forming nearby adsorbed peroxide at low temperature that oxidize toluene into benzoate species by a Langmuir-Hinshelwood mechanism. As the reaction temperature increases, the role of lattice oxygen becomes important, producing CO2 and H2O mainly by the Mars-van Krevelen mechanism.

Full text of DOI:10.1021/jacs.0c08640

pubs.acs.org/JACS
Article
Operando Investigation of Toluene Oxidation over 1D Pt@CeO2
Derived from Pt Cluster-Containing MOF
Qingyue Wang, Yuxin Li, Ana Serrano-Lotina, Wei Han, Raquel Portela, Ruixuan Wang,
Miguel A. Banares,* and King Lun Yeung*
̃
Cite This: https://dx.doi.org/10.1021/jacs.0c08640
Read Online
ACCESS
Metrics & More
Article Recommendations
*
sı Supporting Information
ABSTRACT: A unique 1D nanostructure of Pt@CeO −BDC was
2
prepared from Pt@CeBDC MOF. The Pt@CeO −BDC was rich in
2
oxygen vacancies (i.e., XPS O /(O + O ) = 39.4%), and on the
β
α
β
catalyst, the 2 nm Pt clusters were uniformly deposited on the 1D
mesoporous polycrystalline CeO . Toluene oxidation was conducted
2
in a spectroscopic operando Raman−online FTIR reactor to elucidate
the reaction mechanism and establish the structure−activity relation-
ship. The reaction proceeds as follows: (I) adsorption of toluene as
benzoate intermediates on Pt@CeO −BDC at low temperature by
2
reaction with surface peroxide species; (II) reaction activation and
ring-opening involving lattice oxygen with a concomitant change in
defect densities indicative of surface rearrangement; (III) complete
oxidation to CO and H O by lattice oxygen and reoxidation of the
2
2
reduced ceria with consumption of adsorbed oxygen species. The Pt clusters, which mainly exist as Pt with minor amounts of Pt0
2
+
4
+
and Pt on the surface, facilitated the adsorption and reaction activation. The Pt-CeO interface generates reduced ceria sites
2
forming nearby adsorbed peroxide at low temperature that oxidize toluene into benzoate species by a Langmuir−Hinshelwood
mechanism. As the reaction temperature increases, the role of lattice oxygen becomes important, producing CO and H O mainly by
2
2
the Mars-van Krevelen mechanism.
INTRODUCTION
Metal−organic frameworks (MOF) are interesting precur-
sors for catalyst preparation as it can preorganize catalytic
clusters and afford molecular-level mixing. This has been
illustrated in the high degree of aliovalent substitution of
■
Volatile organic compounds (VOCs) are ubiquitous in the
environment as a result of various human activities (e.g.,
smoking and cooking) as well as outgassing from assorted
products (e.g., furnishing and household products). An
ordinary home can expose the occupants to more than 900
different volatile chemical compounds. Many of these
compounds, particularly aromatic hydrocarbons, cause breath-
ing discomfort, trigger allergies and asthma, and are suspected
1
,2
copper in the CeCuO catalyst derived from bimetallic MOF
x
responsible for its excellent activity for VOC oxidation (i.e.,
14
3
toluene T = 150 °C). The CeCuO catalyst fully oxidizes o-
50 x
xylene and toluene to carbon dioxide and water at 200 °C and
acetone and methanol at 100 °C. Similarly, CoCeO prepared
x
4
−7
from bimetallic MOFs are also excellent catalysts for catalytic
contributors to lung cancer and Alzheimer’s disease.
removal and treatment pose a vital challenge. Catalytic
oxidation of VOCs is an attractive solution, but active catalysts
Their
15
8
oxidation of VOCs. MOF can also shape and form the
catalyst by manipulating MOF’s crystallization using different
14,15
9
,10
connective ligands.
This approach is used to prepare 1D
for low-temperature operation remain elusive.
Rational
ceria with predominantly (110) facets known for their high
design of highly active catalysts requires a comprehensive
understanding of the reaction mechanism. An operando
observation using advanced spectroscopic techniques can
unravel the structure−activity relationships of catalysts to
1
6,17
oxygen storage.
It is known that dispersed Pt on ceria can
18,19
improve its catalytic activity for oxidation reactions.
This
work describes a new route for preparing Pt-CeO catalyst by
2
11,12
guide future design and optimization.
It is possible since
Received: August 11, 2020
the operando methodology blends direct observation of
transient events occurring on the catalyst surface while
simultaneously tracking the reaction performance. However,
catalysts’ heterogeneity often complicates the interpretation of
overall reactivity in relation to localized events on the
1
3
surface.
©
XXXX American Chemical Society
https://dx.doi.org/10.1021/jacs.0c08640
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
A

Journal of the American Chemical Society
pubs.acs.org/JACS
Article
was conducted at a gas hourly space velocity (GHSV) of 34500 h−
1
introducing the Pt clusters during the crystallization of CeBDC
MOF. Their uniform incorporation in the prepared catalyst
promises stability and high reactivity for complete oxidation
reactions as the resulting grain boundaries create crystal defects
while isolating Pt from aggregation, as previously reported for
from 50 to 350 °C. Heating in a 25 °C increment, the reaction was
allowed to reach steady-state before measurements.
RESULTS AND DISCUSSION
■
1
19,20
similar materials.
The Pt@CeBDC and Pt@CeO −BDC
2
Pt@CeBDC MOF and Pt@CeO −BDC Catalyst. Figure
a illustrates the transformation of Pt@CeBDC to Pt@CeO −
2
samples are analyzed by a host of techniques to determine their
composition, structure, morphology, and textural properties.
Most importantly, an operando Raman with online FTIR rig is
2
BDC catalyst by oxidation in air at 400 °C. The Pt@CeBDC
MOF prepared by the solvothermal synthesis method forms
elongated crystals (Figure 1b) with surfaces uniformly
decorated with 2 ± 1 nm Pt clusters, as shown in Figure 1c.
The Pt@CeBDC measured 25 μm ± 5 μm in length with a
roughly square cross-section of 1.2 ± 1 μm by 0.9 ± 0.8 μm.
The atomic force microscope (AFM) image in Figure 1d
shows the general morphology of the MOFs crystal and the
crystal growth process along the crystal facet, indicating a
nucleation-crystallization. AFM also reveals the spatial
distribution of Pt clusters and their sizes (Figure 1e). The Pt
clusters form spontaneously after adding the solution of
chloroplatinic acid in acetic acid to the synthesis mixture of
ceria nitrate and terephthalic acid. During crystallization, the Pt
clusters deposition hinders crystal growth on these surfaces. It
results in elongated MOF (Figure S1) compared to its native
parallelepiped shape (Figure S2). Energy-dispersive X-ray
spectroscopy (EDX) elemental mapping (Figure S3) shows
the Pt clusters’ presence along the entire length of the MOF.
The Pt@CeBDC MOF transformation into the active Pt@
used to investigate toluene oxidation on the Pt@CeO −BDC
2
catalyst to identify the active sites and understand the reaction
mechanism. Comparison is made against a reference Pt
supported on CeO nanorods (Pt/CeO −NR).
2
2
EXPERIMENTAL METHODS
Catalyst Preparation, Characterization, and Reaction Stud-
ies. The Supporting Information (SI) provides a detailed description
■
of the preparation and characterization of CeBDC, CeO −BDC, Pt@
2
CeBDC, 1.0 wt % Pt@CeO −BDC as well as the reference CeO −
2
2
NR and 1.0 wt % Pt/CeO −NR catalysts. The SI also includes the
2
reactor setup and reaction conditions for the catalytic oxidation of
toluene in air.
Operando Investigation. Operando reaction study of the catalytic
oxidation of toluene was conducted in an operando spectroscopic
reactor made of optical-grade quartz material placed within a heating
21,22
unit (Scheme 1).
The temperature of the reactor cell was
Scheme 1. Schematic Diagram of the Custom-Made Reactor
for operando Raman−Online FTIR Investigation
CeO −BDC catalyst did not cause a substantial change in
morphology, and it retains the original size and shape of the
MOF crystals, as shown in Figure 1f. The high-resolution
2
image in Figure 1g shows that Pt@CeO −BDC catalyst
2
exposes well-oriented CeO (110) planes, recognized for their
2
17,23
reactivity,
on which Pt clusters and mesopores are evident.
The removal of the organic ligands by oxidation produces a
2
−1
mesoporous CeO with a specific surface area of 126 m g , as
2
seen in Table 1. The Pt@CeO −BDC was further charac-
2
terized by high-angle annular dark-field scanning transmission
electron microscopy (HAADF-STEM), and the results are
presented in Figure 2. A high-resolution image taken near the
tip of the Pt@CeO −BDC square rod reveals the details of the
2
catalyst structure. The surface is heavily riddled with slit-
shaped mesopores and uniformly decorated with 2.0 ± 0.5 nm
Pt clusters (Figure 2a). It is apparent from the micrograph that
some of the Pt clusters are embedded within the growing
crystal. Similarly, the elemental map of the catalyst in Figure 2b
taken by energy-dispersive X-ray spectroscopy (EDX) indicates
that Pt is present over the entire sample, suggesting that Pt
clusters are also in bulk. A closer examination (Figure 2c)
monitored and controlled by a Thermocoax K-type thermocouple and
a PID Eng&Tech programmable controller. A Renishaw Qontor
confocal Raman microscope observed the catalyst surface using a
LEICA DMILM microscope with a 20x long-distance objective lens.
The spectra were collected under 514 nm solid-state laser excitation at
an acquisition time of 30 s. A ThermoNicolet 6700 Fourier
transformed infrared (FTIR) spectrometer analyzed the reaction
gases leaving the reactor cell in a thermostatic (120 °C) gas cell.
shows that the Pt@CeO −BDC catalyst, as its precursor, is
2
−
1
composed of highly oriented CeO (110), as confirmed by the
2
Collecting the infrared spectra from 400 to 4000 cm at a resolution
of 4 cm−1 and a time interval of 9.85 s, it is possible to follow the
reaction in real-time by monitoring the characteristic wavelengths of
the reactants and products (Table S1 in the SI) down to a gas phase
concentration of 50 ppb.
fast Fourier-transform (FFT) pattern (Figure 2c, inset). The
FFT pattern also indicates the presence of Pt (111). Defects
can be seen along the interface of Pt (111) and CeO
Figure 2d. These defects could be related to oxygen vacancies
(110) in
2
24,25
Briefly, 0.150 g catalyst (32 to 60 mesh) was packed into the
operando reactor cell and sandwiched between beds of inert silicon
carbide (ca. 0.350 g) to enhance the heat transfer rate and decrease
the void volume. The packed bed was held in place with quartz wool.
The catalyst pretreatment involved heating to 200 °C in 100 sccm
synthetic air (20% O /80% N , Air Liquide) for 2 h. Bubbling dry
that facilitate oxidation of VOCs.
The Pt@CeBDC MOF has a XRD pattern similar to that of
CeBDC (cf. Figure S4a). It has a triclinic crystal structure P1
with a unit cell of a = 11.069(2) Å, b = 17.744(4) Å, c =
̅
14
2
9.089(6) Å, α = 87.13(3)°, β = 79.38(3)°, γ = 72.99(3)°. Pt
2
2
is mainly incorporated as clusters in Pt@CeBDC. Thermog-
ravimetric analysis in air flow (Figure S4b) shows Pt@CeBDC
decomposition at 367 °C, a slightly lower temperature than
CeBDC MOF (379 °C). Therefore, the Pt@CeBDC and
argon gas (UHP, Air Liquide) through toluene (Honeywell, 99.7%)
kept at 10 °C in a circulating oil bath (PolyScience 9106A12E)
produced toluene vapor to be blended with synthetic air to generate
1
000 ppm toluene in 18.8% O , 5.8% Ar, and 75.4% N . The reaction
2
2
B
https://dx.doi.org/10.1021/jacs.0c08640
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
pubs.acs.org/JACS
Article
Figure 1. (a) Schematic drawing of Pt@CeBDC transformation into Pt@CeO −BDC during heat treatment in air. (b and c) TEM micrographs of
2
Pt@CeBDC MOF showing (b) the morphology, and (c) deposited Pt clusters. (d and e) Atomic force microscope image of Pt@CeBDC MOF
showing (d) the morphology with an inset of the cross-section profile, and (e) Pt clusters on the surface with an inset of Pt cluster size distribution.
(
f and g) TEM micrographs of Pt@CeO −BDC derived from Pt@CeBDC MOF displaying (f) the morphology, and (g) Pt clusters (indicated by
2
arrows) and mesoporosity with a high magnification inset revealing atomic details of a Pt cluster and CeO .
2
Table 1. Crystal Size and Textural Properties of CeO −BDC and Pt@CeO −BDC Catalysts
2
2
crystal size of CeO [nm]
2
SBET [m g−1]
2
average pore size [nm]
total pore volume [cm g−1]
3
catalysts
XRD
TEM
I /I [%]
D
F2g
Pt@CeO −BDC
5.1
8.5
5 ± 1
8 ± 5
11.9
3.1
126.3
117.3
2.2
3.6
0.26
0.25
2
CeO −BDC
2
CeBDC MOFs were thermally treated at 400 °C to obtain the
The peak broadening is caused by photon confinement within
corresponding catalysts. The X-ray diffraction of Pt@CeO −
a smaller crystalline domain in Pt@CeO −BDC (i.e., 5.1 nm vs
2
2
27,28
BDC (Figure S4c) shows only the (111), (200), (220), and
8.5 nm).
The shift of the F2g vibration peak indicates a
(
331) diffraction peaks belonging to the cubic fluorite CeO2
distortion in CeO lattice and an increase in oxygen vacancies
2
with space group Fm3m and a lattice parameter of 5.411 Å
JCPDS file no. 43−1002). Pt diffractions are not evident from
29,30
induced by Pt insertion (cf. Figure S4d).
There are indeed
(
more defects in Pt@CeO −BDC as indicated by the higher I /
2
D
the data. The crystal size of CeO in Pt@CeO −BDC is 5.1
2
2
IF2g ratio of 11.9%, which is approximately four times greater
nm, smaller than 8.5 nm of CeO −BDC, as calculated by the
23
2
than such ratio for CeO −BDC (i.e., 3.1%; Table 1).
2
Debye−Scherrer equation from XRD patterns (Tables S2 and
−
1
Moreover, the Raman band at 831 cm corresponding to
peroxides (O2 ) is more prominent in Pt@CeO −BDC. It is
consistent with the abundant oxygen vacancies created by the
Pt encapsulation. Both Pt@CeO −BDC and CeO −BDC
are mesoporous with type IV N physisorption isotherms
1
).
2−
2
The ex situ Raman spectra of Pt@CeO −BDC and CeO −
2
2
BDC (Figure S4d) show the second-order transverse acoustic
31
−
1
−1
(
2TA) mode at 254 cm , the F mode at 464 cm , the
2
2
2g
−
1
defect-related (D) mode at 595 cm , and second-order
longitudinal optical (2LO) mode at 1179 cm of CeO2.
Pt@CeO −BDC catalyst shows a 3 cm redshift and a
broadening of the F Raman peak attributed to the Pt clusters.
2
−
1
23,26
(Figure S5). Their textural properties, summarized in Table 1,
−
1
are comparable, with Pt@CeO
size (i.e., 2.2 nm vs 3.6 nm).
−BDC having a smaller pore
2
2
2g
C
https://dx.doi.org/10.1021/jacs.0c08640
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
pubs.acs.org/JACS
Article
4
+
2+
0
formed by stepwise reduction of Pt3 to Pt , and then to Pt
2
by DMF (Table 2 and Figure 3a). Platinum is reported to
interact with DMF by n → d* electron donation from N to Pt
cations in the mono- and multinuclear Pt (II) complexes. The
depositions of the Pt clusters on CeBDC is believed to drive
the anisotropic growth of Pt@CeBDC into elongated 1D rods
instead of the usual 3D parallelepiped of CeBDC MOF (cf.
Figures S1−S2). Pt@CeO −BDC obtained after heat treat-
2
2
+
ment at 400 °C mainly consists of Pt (47.2%), followed by
Pt (27.1%), and Pt (25.7%) on the surface. In oxidation
reactions, the ionic platinum Pt assists the adsorption of
0
4+
2
+
reactants and the formation of active sites on CeO in the
2
2+
19
vicinity of Pt . The transition from Pt@CeBDC to Pt@
CeO −BDC is believed to strip DMF from the Pt clusters and
2
allow them to form molecular bonds with the CeO surface. It
2
is also responsible for the formation of oxygen vacancies.
3
+
The cerium exists as Ce in Pt@CeBDC MOF (94.0%) and
4
+
mainly as Ce in the derived Pt@CeO −BDC catalyst
2
3
+
(
66.3%) (Figure S6 and Table 2). Ce content was higher
in Pt@CeO −BDC than CeO −BDC (23.1%). Meanwhile,
2
2
the O 1s spectra in Figure 3b exhibits two peaks belonging to
lattice oxygen (O ) at 529.6 eV and oxygen species adjacent to
α
33,34
oxygen vacancies (O ) at 531.5 eV.
The ratio O /(O +
Figure 2. High-resolution, high-angle annular dark-field (HAADF)
β
β α
O ) of Pt@CeO −BDC is 39.4%, which is also higher than
STEM images of (a) along the tip of the Pt@CeO −BDC catalyst and
β
2
2
(b) its STEM-EDS elemental mapping along with high-magnification
that of CeO −BDC (29.4%; Figure S7). The high concen-
2
3+
HAADF-STEM images of (c) the catalyst surface with its fast Fourier
transform (FFT) pattern in the inset and (d) Pt-CeO2 interface
structure.
tration of reduced Ce and O in Pt@CeO −BDC suggests
β
2
the formation of abundant oxygen vacancies as a result of Pt
interactions with CeO along the (110) plane. The formation
2
energy for oxygen vacancies for this plane (i.e., 1.99 eV) is
lower compared to 2.60 eV for CeO (111) and 2.27 eV for
X-ray photoelectron spectroscopy (XPS) in Figure 3
provides vital information on the catalyst’s surface composition
and chemistry. The platinum in Pt@CeBDC MOF (cf. Figure
2
35
CeO (100).
2
Catalytic Oxidation of Toluene. Figure 4a compares the
0
2+
catalytic activity for toluene oxidation of Pt@CeO −BDC to
S6) exists mainly as metallic Pt (48.4%) and as Pt (43.7%),
2
that of CeO −BDC, CeO nanorods (CeO −NR), and Pt
2
2
2
supported on CeO nanorods (Pt/CeO −NR). A detailed
2
2
description of the preparation and characterization of CeO −
2
NR and Pt/CeO −NR is presented in Figures S8−S11 and
2
Tables S2−S3. The CeO −NR prepared by hydrothermal
2
synthesis presents well-crystallized CeO (110) planes that are
2
17,23
recognized for their reactivity.
The reaction begins at 100
°
C in Pt@CeO −BDC, with 20% of conversion at 125 °C. The
2
temperatures for 50% and 90% conversion are 141 (T ) and
5
0
1
72 °C (T ), and the oxidation is complete to carbon dioxide
90
and water. CeO −BDC, without Pt clusters, is less active (T
2
50
of 169 °C and T of 250 °C) and produces measurable
9
0
quantities of partial oxidation byproducts (i.e., carbon
monoxide and benzaldehyde). The CeO −BDC is, in turn,
2
more active at temperatures below 200 °C than the reference
catalysts, Pt/CeO −NR (T = 203 °C) and CeO −NR (T =
2
50
2
50
2
09 °C). The Pt/CeO −NR being less active has T of 203
2
90
°
C, which is higher than Pt@CeO −BDC, while CeO −BDC
2
2
and CeO −NR have a comparable T .
2
90
Toluene oxidation catalyzed by Pt@CeO −BDC has an
2
−
1
activation energy of 48.9 kJ mol lower than for the reference
−
1
Pt/CeO −NR catalyst (i.e., 66.9 kJ mol ), as presented in
2
Figure S11. Pt@CeO −BDC differs from Pt/CeO −NR by
2
2
having smaller CeO particles (i.e., 5.1 nm vs 8.9 nm) with
2
more defects (i.e., I /I
proportion of reduced ceria (Ce = 33.7% vs 22.2%) and
more abundant oxygen vacancies (i.e., 39.4% vs 29.0%). Unlike
= 0.12 vs 0.08) and greater
D
F2g
3
+
Pt@CeO −BDC, the deposition of Pt clusters on CeO −NR
Figure 3. XPS spectra of (a) Pt 4f in Pt@CeO −BDC and (b) O 1s
2
2
2
in CeO −BDC and Pt@CeO −BDC. Note: the detailed XPS binding
barely changed the amount of reduced ceria and oxygen
2
2
energy assignments for data fitting are discussed in the SI.
vacancies in the underlying CeO −NR support. Prior
2
D
https://dx.doi.org/10.1021/jacs.0c08640
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
pubs.acs.org/JACS
Article
Table 2. Surface Species on Pt@CeBDC MOF, Pt@CeO −BDC, and CeO −BDC Catalysts (in %)
2
2
Ce /(Ce + Ce3+)
3
+
4+
O /(O + O )
Pt /Pt /Pt
0
2+
4+
sample
β
α
β
Pt@CeBDC
94.0
33.7
23.1
-
48.4:43.7:7.9
27.1:47.2:25.7
-
Pt@CeO −BDC
39.4
29.4
2
CeO −BDC
2
38
the reaction. Figure 4b shows that the activity of Pt@CeO −
2
BDC catalyst at 175 °C is stable in the presence of high water
vapor content (i.e., 69200 ppm) and similar to dry conditions.
The toluene conversion remains unchanged over 60 h on-
stream with no detectable byproducts. Moreover, the water
feed is turned on and off three times without an observable
2
effect on the reaction. The Pt clusters are strongly anchored in
Pt@CeO −BDC (cf. Figure 2) giving it a higher resistance to
2
39
sintering in the presence of water. In comparison, Pt/CeO −
NR experiences a decrease in conversion in the presence of
water vapor (Figure S12 and Table S4).
2
Operando Raman−Online FTIR Study of Pt@CeO −
2
BDC. Toluene oxidation on Pt@CeO −BDC is investigated in
2
an operando Raman−online FTIR reactor system to bridge the
knowledge gap between catalyst surface and reaction. The goal
is to understand the role of the Pt clusters, Pt-CeO interface,
2
and oxygen vacancies in the reaction, as illustrated in Figure 5a.
Figure 5b plots the 3D operando Raman spectra obtained at
reaction temperatures of 50−350 °C, showing the Raman
signals of the catalyst, surface oxygen species, and adsorbed
toluene-derived species (e.g., benzyl and benzoate species).
The reaction composition is analyzed simultaneously by an
online FTIR spectrometer and presented as a contour plot in
Figure 5c, while the temperature program and the intensity of
the infrared bands of the gaseous reaction products are shown
in Figure 5d. The assignments of the characteristic infrared
bands are listed in Table S1. The contour plot shows that
toluene conversion starts at temperatures as low as 125 °C,
producing CO and H O. The primary products for toluene
Figure 4. Catalytic performance for toluene oxidation (a) toluene
conversion (solid symbols) and CO yield (open symbols) catalyzed
2
by Pt@CeO −BDC, CeO −BDC, and the reference Pt/CeO −NR
2
2
2
and CeO −NR catalysts at different reaction temperatures and (b)
2
2
2
toluene conversion catalyzed by Pt@CeO −BDC in the presence of
(PhCH ) oxidation remain CO and H O, with no detectable
2
3 2 2
6
9200 ppm water vapor at 175 °C. Note: [PhCH ] = 500 ppm,
benzyl alcohol (PhCH OH), benzaldehyde (PhCHO), ben-
3
2
−
1
mcatalyst = 0.150 g, gas hourly space velocity (GHSV) = 23000 h .
zoic acid (PhCOOH), or carbon monoxide (CO).
Figure 6 presents Raman spectra collected during toluene
2
1,36
reaction over Pt@CeO −BDC and CeO −BDC in the
studies
reported the essential role of surface defects and
2
2
operando reactor. The vibration mode assignments of the
Raman bands are summarized in Table S5. As observed by ex-
oxygen vacancies on the reaction, thereby explaining the higher
activity of the Pt@CeO −BDC catalyst. Moreover, Pt@
2
situ Raman (Figure S4d), Pt clusters distort the CeO lattice
CeO −BDC and Pt/CeO −NR have the same Pt loading,
2
2
2
−
1
causing a redshift of the CeO F mode from 463 to 460 cm
similar Pt size and comparable specific surface areas (i.e., 126
2
2g
2
−1
related to increased defects and oxygen vacancies (Figure
vs 114 m g ), but the former has narrower pores (i.e., 2.2 vs
.1 nm). The transport resistance in the narrow pores may
29,30,40
6
).
Toluene species adsorbed on Pt@CeO −BDC and CeO −
6
explain the slower ignition observed in Pt@CeO −BDC than
2
2
2
−
1
−1
BDC exhibit ν (1590 cm ), ν (1495 cm ), and ν (1003
cm ) vibration modes from ring stretching, as well as the ν9a
in less active Pt/CeO −NR. Other factors, such as the stronger
8a
19a
12
2
−
1
metal−support interaction of Pt@CeO −BDC (inherited from
2
−
1
Pt@CeBDC MOF) than Pt/CeO −NR (cf. Figure S8), also
(1166 cm ) from the in-plane C−H bending mode of the
2
20,37
21,41,42
contribute to its high activity.
aromatic ring (Figure 6).
CH stretching mode ν13 (1209 cm ) and the CH
mode (1380 cm ) suggests a distortion in the methyl group
The absence of both the Ph−
−1
CeO −BDC and CeO −NR are elongated 1D oxides of
3
bending
3
2
2
2
−1
−1
similar surface areas (i.e., 117 vs 108 m g ) despite having
smaller crystal size (i.e., 8.5 vs 11.7 nm) and narrower pores
4
1
following adsorption. Toluene molecule is adsorbed by π-
bonding on Pt@CeO −BDC with the aromatic ring parallel to
the surface as confirmed by the weak ν
stretching mode and broadening of the ν
(
i.e., 3.6 vs 7.7 nm). Defects and oxygen vacancies are more
2
−
1
abundant on CeO −BDC than CeO −NR and are responsible
2
(3068 cm ) C−H
−1
2
2
for its better catalytic activity. Unlike Pt@CeO −BDC, the
1
(651 cm ) ring-
It is deduced that toluene i−s
essentially adsorbed on Pt@CeO −BDC mainly as Ph−COO
2
4
3,44
deposition of Pt clusters on CeO −NR barely changed
breathing mode (Figure 6a).
2
reduced ceria and oxygen vacancies in the underlying CeO −
2
2
−1
43,44
NR support (Table S3).
from the broad peak at 1200 to 1350 and at 651 cm .
Toluene molecule adsorbs on CeO −BDC via π-interaction
It has been reported that water molecules compete against
toluene for adsorption sites on the catalyst, thereby inhibiting
2
−
1
with the aromatic ring (Figure 6b). The ν (2938 cm ) and ν
as
s
E
https://dx.doi.org/10.1021/jacs.0c08640
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
pubs.acs.org/JACS
Article
Figure 5. (a) Graphical illustration of Pt@CeO −BDC catalyst with oxygen vacancies (O ) investigated in the operando Raman−online FTIR
2
Vac
reactor. Reaction information presented in (b) 3D plot of the operando Raman spectra and (c) 3D contour plot of the online FTIR spectra, with
gas-phase characteristic peaks of toluene (black arrows), carbon dioxide (orange arrows), and water (white arrows). (d) Plots of reactor
temperature program and the corresponding concentration of carbon dioxide (CO ), carbon monoxide (CO), benzyl alcohol (PhCH OH),
2
2
benzaldehyde (PhCHO), benzoic acid (PhCOOH), and water (H O). Note: [PhCH ] = 1000 ppm, m = 0.150 g, gas hourly space velocity
2
3
catalyst
−
1
(
GHSV) = 34500 h ; OVac: oxygen vacancy; characteristic peaks of toluene (black arrows), carbon dioxide (orange arrows), and water (white
arrows).
1
(
2852 cm− ) −CH2 stretching modes and the CH
Figure 7 compares the behavior of Pt@CeO −BDC (left)
2
2
−
1
deformation mode (1474 cm ) indicate dehydrogenation of
and CeO −BDC (right); Figure 7a,b illustrates the evolution
2
+
2
42
the methyl group to form benzyl carbocation (Ph−CH ).
of the ceria F2g mode as a function of temperature in air (TPO-
Raman) and during the reaction (operando Raman); Figure
These benzyl species are apparent on Pt@CeO −BDC only
2
7
c,d illustrates the relative intensity of the defect band (595
below 125 °C, while they remain on CeO −BDC up to 300
2
−
1
−1
cm ) vs the F mode (ca. 460 cm ); Figure 7e,f plots the
°C.
2g
intensity of the O2
2
−
peroxide Raman band; Figure 7g,h
The Raman spectra in Figure 6 also reveal several reactive
oxygen species present in the reaction.
cm ), adsorbed peroxides in the proximity of an isolated
oxygen vacancy, are the most abundant. Peroxides adsorbed on
line-defect (860 cm ) are more reactive and are only
observed on Pt@CeO −BDC below 125 °C. The consump-
tion of these peroxides coincides with the conversion of surface
benzyl species (3068, 2938, 2852, and 1474 cm ) into surface
ads
23,40
2−
plots the intensity of representative Raman bands of adsorbed
The O2
ads
(831
−1
−
1
toluene species (i.e., 3068, 2938, and 1590 cm ); and the gas-
phase concentrations from the online FTIR of toluene and
products are shown in Figure 7i,j. The F mode of the CeO2
−
1
40
2g
−1
fluorite phase near 460 cm represents the symmetric
2
vibration of oxygen with adjacent cations. This vibration is
closely correlated with the change in surface lattice oxygen and
−
1
3+
4+
46
the Ce /Ce redox cycle during oxidation. The observed
redshifts of F in Figure 7a,b are attributed to two phenomena.
−
1
benzoates (648, 1200, to 1350 cm ) on Pt@CeO −BDC.
The superoxide O2
2
2
g
−
−1
−
1
band at around 1130 cm is absent on
ads
The small redshifts, up to ca. −6 cm , are associated with
thermal lattice expansion and mode softening; such a shift is
apparent in both Pt@CeO −BDC and CeO −BDC during
2
3,40
both Pt@CeO −BDC and CeO −BDC catalysts.
The
2
2
2
−
O
are essential for adsorbed toluene oxidation and CeO
2
ads
2
2
2
−
2−
→ 2O− → 2O lattice.
2−
23,45
reoxidation via O2 ads → O2
heating in air (Figure 7a,b, respectively). The larger redshifts,
ads
ads
F
https://dx.doi.org/10.1021/jacs.0c08640
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
pubs.acs.org/JACS
Article
Figure 6. Operando Raman spectra of operando Raman−online FTIR
reactor study during toluene oxidation reaction on (a) Pt@CeO −
2
BDC and (b) CeO −BDC at reaction temperatures of 50 to 350 °C.
2
Note: [PhCH ] = 1000 ppm, m
velocity (GHSV) = 34500h .
= 0.150 g, gas hourly space
3
catalyst
−
1
Figure 7. Normalized operando Raman signals of Pt@CeO −BDC
2
(
left) and CeO −BDC (right) for (a and b) Raman shift of F mode
2
2g
in reaction condition (×) and in air (red circle); (c and d) defects
(
−
1
typically −6 to −12 cm , are associated with lattice expansion
2−
−1
ID/IF2g, red triangle); (e and f) O2
at 831 cm (blue ○); (g and
ads
and mode softening when oxygen vacancies are created in
−1
■
h) adsorbed toluene (ν (C−C) at 1590 cm - , ν(C−H) at
8
a
ring
ring
4
7
−
1
−1
ceria. Such a larger shift is apparent for both samples at
temperatures above ca. 250 °C in air and during the reaction
but are more intense for Pt@CeO −BDC. Pt@CeO −BDC
3068 cm - red × in a square, and ν(C−H)
at 2938 cm -yellow
CH2
⬒); and (i and j) the concentrations of PhCH (■), CO (orange
3
2
○), H O (blue ◆), CO (magenta ×), PhCH OH (purple ◮),
2
2
2
2
exhibits a large redshift at lower temperatures (ca. 125 to 250
PhCHO (green ▶), and PhCOOH (red ◀brown left pointing
triangle) according to online FTIR. Note: [PhCH ] = 1000 ppm,
°
C) under reaction, which is not observed during heating in
3
−
1
mcatalyst = 0.150 g, gas hourly space velocity (GHSV) = 34500 h .
air. It coincides with the conversion of benzyl species to
benzoates at ca. 125 °C (Figure 6a and 7g,h), then the redshift
progressively decreases until it equals the values in air at 250
oxidation of adsorbed toluene via a Langmuir−Hinshelwood
°
C when a total conversion is achieved (Figure 7i).
(L-H) mechanism. Above ca. 250 °C, both Pt@CeO −BDC
2
Conversely, benzyl species remain on CeO −BDC up to 300
and CeO −BDC behave similarly, suggesting that reaction
2
2
°
C. The different evolution of adsorbed toluene (benzyl on
Ce-BDC vs benzoate on Pt@CeO −BDC) results in highly
proceeds under a common mechanism. The surface peroxides
40
are no longer stable on ceria at these temperatures, and ceria
lattice oxygen becomes important. The Raman signals of
adsorbed toluene species decrease with heating and disappear
2
selective combustion at lower temperatures on Pt@CeO −
BDC (Figure 7i) than on CeO −BDC (Figure 7j). CeO −
2
2
2
BDC delivers CO2 along with partial oxidation products
with complete conversion at 250 °C for Pt@CeO −BDC and
2
(
Figures S13 and S14). These data show a close interplay
300 °C for CeO −BDC. Figure 7e,f insets show the CeO 2LO
2
2
−
1
between adsorbed peroxide and toluene species.
mode (1179 cm ) increasing with the consumption of
40
2−
The activity trend appears related to platinum’s role in
generating defects on ceria, shown in the XPS and Raman data,
that produces the surface peroxide species. The peroxides
O2 ads, indicating oxygen incorporation into the ceria lattice.
This observation is only valid at high temperatures as this band
overlaps with adsorbed toluene species at low temperatures. As
discussed, both catalysts display a redshift of F2g mode from
lattice expansion and mode softening associated with oxygen
readily oxidize benzyl to benzoates species on Pt@CeO −
2
BDC, leading to higher reactivity at low temperature than
47
CeO −BDC. This is consistent with the higher defects in ceria
vacancies during reaction. These observations are consistent
with a Mars-van-Krevelen (MvK) mechanism.
2
lattice (Figure 7c,d). On Pt@CeO −BDC, the adsorbed
2
peroxide species are rapidly consumed as reaction temperature
increases (Figure 7e,f), which is in line with its role in the
Toluene oxidation is believed to be activated at the Pt-CeO2
interface. The activation of molecular O is reported to occur
2
G
https://dx.doi.org/10.1021/jacs.0c08640
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
pubs.acs.org/JACS
Article
0
48
49
on Pt even at room temperature. Ye’s group found that the
Pt supported on CeO2 is the most active at the low
temperature for toluene oxidation, compared to Pt/Co O
reaction causes localized heating of the catalyst surface and
possible surface rearrangement. This could explain the abrupt
changes in ceria and oxygen species. Moreover, the Raman
3
4
and Pt/Al O , though at the same Pt loading (i.e., 0.5 wt %)
bands of toluene species on CeO suggest a change in the
configuration of the adsorbed molecule. After ignition, defects
became insensitive to reaction temperature and remained
2
3
2
and average particle size (i.e., 3.5 ± 0.2 nm). It implied that the
activation of toluene oxidation at a low temperature of 125 °C
occurs with the assistance of CeO support at the Pt-CeO
relatively constant at around 12.0% for Pt@CeO −BDC and
2
2
2
49
interface instead of isolated Pt clusters. This model is
consistent with the vacancies observed at ceria close to its
interface with platinum (Figures 2 and S15). The critical
difference between Pt@CeO −BDC and CeO −BDC is that
CeO −BDC. It is interesting to note that there is the same
2
defect density of CeO before the reaction. The Raman signals
2
2−
for adsorbed toluene species and surface O2
continue to
ads
diminish with increasing reaction temperature until complete
conversion. Above 250 °C, peroxide species are no longer
stable and both catalysts operate under the MvK mechanism
2
2
the Pt catalyst generates more reactive peroxide species at the
Pt-CeO interface that transform benzyl into benzoate species,
2
which readily burn to CO without producing partial-oxidation
byproducts. Thus, Figure 8 proposes the reaction mechanism
giving similar reaction performance. The appearance of CeO
2
2
−
1
2LO mode (1179 cm ) at higher temperatures indicates
−
2−
→ 2O−
efficient reoxidation of ceria via O
→ O2
→
2
ads
ads
ads
2−
23,45
2O
lattice.
The study suggests the presence of Pt on CeO2
provides sites for oxygen adsorption as peroxides at low
temperatures, promoting adsorbed toluene to benzoate species
that can readily burn to CO . It also facilitates the
2
replenishment of the lattice oxygen of CeO2.
CONCLUSIONS
■
The 1D Pt@CeO −BDC prepared by incorporating platinum
2
clusters during the synthesis of Ce-BDC is a stable and active
catalyst for oxidation of toluene in air. Toluene conversion
catalyzed by Pt@CeO −BDC starts at 100 °C, with T of 141
2
50
°
C, indicating that this catalyst is much more active than
CeO −BDC and the reference catalysts, Pt/CeO −NR and
2
2
−
1
Figure 8. Proposed reaction mechanism for toluene oxidation over
Pt@CeO −BDC and CeO −BDC catalysts.
CeO −NR at GHSV of 23000 h . Toluene is completely
2
oxidized at 200 °C, and unlike the other catalysts, the reaction
produces only carbon dioxide and water. Moreover, it
maintains high reactivity even in the presence of water
2
2
of toluene oxidation on Pt@CeO −BDC and CeO −BDC.
vapor. Pt@CeO −BDC is characterized by its uniformly
2
2
2
50−52
Toluene adsorbs on both catalysts through dehydrogenation.
dispersed 2 nm Pt clusters known for its high reactivity.
Pt@CeO −BDC, having more defects, adsorbs more toluene
It also has smaller CeO crystals and more oxygen vacancies
2
2
than CeO −BDC. Peroxide species on the line-defects (860
contributing to its excellent catalytic activity.
2
−
1
−1
cm ) at the Pt-CeO interface start to react and convert Ph−
Operando study at GHSV of 34500 h confirmed the role of
2
+
−
CH to Ph−COO via the L-H mechanism at low
Pt clusters, defects, and oxygen vacancies in the reaction. The
Pt is responsible for toluene forming benzoate species on Pt@
2
temperature of 50 °C. These peroxides are more reactive
than peroxide species on the proximity of isolated oxygen
CeO −BDC by reaction with adsorbed peroxide at low
2
−
1
40
vacancies (831 cm ), and account for the higher reactivity
temperatures. Platinum sites also catalyze the reoxidation of
+
2
of Pt@CeO −BDC. The Ph−CH is barely seen on Pt@
the lattice oxygen in CeO at higher temperature by pumping
2
2
−
CeO −BDC at 125 °C, when the converted Ph−COO is
adsorbed peroxide species into ceria lattice, thus enhancing the
reaction. The defects and oxygen vacancies participate as
adsorption sites for the reactants and as the active sites for the
reaction. The operando results confirm that toluene oxidation
2
further oxidized to produce CO and H O. On the other hand,
2
2
+
2
Ph−CH remains on CeO −BDC even at high temperatures
ca. 300 °C). The progressive loss of surface peroxide species
2
(
with temperature is compensated by an increasing role of
lattice oxygen in the reaction, thus describing a transition from
over Pt@CeO −BDC occurs via the L-H mechanism
2
producing surface benzoate intermediate. Above 125 °C,
adsorbed toluene (i.e., benzoate species) reacts with CeO2
lattice oxygen according to the MvK mechanism, and Pt acts as
an oxygen pump to replenish the lattice oxygen. Therefore, a
progressive transition from predominantly L-H to MvK
a predominantly L-H to MvK mechanism on Pt@CeO −BDC
2
from 125 to 250 °C.
−
1
On the CeO −BDC, the peroxides (831 cm ) become
2
highly active only as the temperature reaches 150 °C. Their
low oxidation capacity leads CeO −BDC to insufficiently
reaction mechanism is observed from on Pt@CeO −BDC
2
2
convert benzyl into benzoate species. Toluene adsorbed as
catalyst.
+
2
+
Ph−CH with the methylene cation (−CH ) balances the
2
extra electron on the phenyl ring. This configuration favors the
formation of the aromatic byproducts. The less efficient
ASSOCIATED CONTENT
sı Supporting Information
■
*
reoxidation of CeO −BDC without the noble metal (Figure
2
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/jacs.0c08640.
S16) leads to incomplete combustion and the generation of
CO. The reaction rate of CeO −BDC increases slowly with
2
Experimental details, supplementary figures, and supple-
mentary tables as mentioned in the text (PDF)
temperature until ignition occurs with a sharper transition from
a slow to a fast reaction. The heat released by the exothermic
H
https://dx.doi.org/10.1021/jacs.0c08640
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
pubs.acs.org/JACS
Article
(
3) Chan, K. H. Assessment of Air Quality and Performance of
Central Ventilation System. J. Perform. Constr. Fac. 2011, 25 (4),
26−335.
AUTHOR INFORMATION
■
Corresponding Authors
3
Miguel A. Ban
Instituto de Catálisis y Petroleoquímica, E-28049 Madrid,
Spain; Email: miguel.banares@csic.es
̃
ares − Spectroscopy and Industrial Catalysis,
(4) Billionnet, C.; Gay, E.; Kirchner, S.; Leynaert, B.; Annesi-
Maesano, I. Quantitative Assessments of Indoor Air Pollution and
Respiratory Health in a Population-Based Sample of French
Dwellings. Environ. Res. 2011, 111 (3), 425−434.
King Lun Yeung − Department of Chemical and Biological
Engineering and Division of Environment and Sustainability,
The Hong Kong University of Science and Technology,
Kowloon, Hong Kong SAR, China; Guangzhou HKUST Fok
Ying Tung Research Institute, Guangzhou, China;
orcid.org/0000-0002-6970-8483; Email: kekyeung@
ust.hk
(5) Nurmatov, U. B.; Tagiyeva, N.; Semple, S.; Devereux, G.; Sheikh,
A. Volatile Organic Compounds and Risk of Asthma and Allergy: A
Systematic Review. Eur. Respir. J. 2015, 24 (135), 92−101.
(6) Phillips, M.; Gleeson, K.; Hughes, J. M. B.; Greenberg, J.;
Cataneo, R. N.; Baker, L.; McVay, W. P. Volatile Organic Compounds
in Breath as Markers of Lung Cancer: A Cross-Sectional Study. Lancet
1
(
999, 353 (9168), 1930−1933.
7) Mazzatenta, A.; Pokorski, M.; Sartucci, F.; Domenici, L.; Di
Authors
Giulio, G. Volatile Organic Compounds (VOCs) Fingerprint of
Alzheimer’s Disease. Respir. Physiol. Neurobiol. 2015, 209, 81−84.
(8) Revah, S.; Morgan-Sagastume, J. M. Methods of Odor and VOC
Control. In Biotechnology for Odor and Air Pollution Control;
Shareefdeen, Z., Singh, A., Eds.; Springer Berlin Heidelberg: Berlin,
Heidelberg, 2005; pp 29−63.
Qingyue Wang − Department of Chemical and Biological
Engineering, The Hong Kong University of Science and
Technology, Kowloon, Hong Kong SAR, China; Institute of
Zhejiang University - Quzhou, 324000 Quzhou, China
Yuxin Li − Division of Environment and Sustainability, The
Hong Kong University of Science and Technology, Kowloon,
Hong Kong SAR, China; orcid.org/0000-0002-3355-
(9) Yang, C.; Miao, G.; Pi, Y.; Xia, Q.; Wu, J.; Li, Z.; Xiao, J.
Abatement of Various Types of VOCs by Adsorption/Catalytic
Oxidation: A Review. Chem. Eng. J. 2019, 370, 1128−1153.
0
397
(10) Wang, Q.; Yeung, K. L.; Banares, M. A. Ceria and Its Related
Ana Serrano-Lotina − Spectroscopy and Industrial Catalysis,
Instituto de Catálisis y Petroleoquímica, E-28049 Madrid,
Spain; orcid.org/0000-0001-7498-7491
Wei Han − Division of Environment and Sustainability, The
Hong Kong University of Science and Technology, Kowloon,
Hong Kong SAR, China; Guangzhou HKUST Fok Ying
Tung Research Institute, Guangzhou, China; orcid.org/
Materials for VOC Catalytic Combustion: A Review. Catal. Today
020, 356, 141.
2
(11) Guerrero-Perez, M. O.; Banares, M. A. Operando Raman Study
of Alumina -Supported Sb−V−O Catalyst during Propane Ammox-
idation to Acrylonitrile with on-Line Activity Measurement. Chem.
Commun. 2002, 12, 1292−1293.
(
12) Banares, M. A. Operando Spectroscopy: The Knowledge Bridge
̃
to Assessing Structure-Performance Relationships in Catalyst Nano-
0
000-0002-4808-0711
particles. Adv. Mater. 2011, 23 (44), 5293−5301.
Raquel Portela − Spectroscopy and Industrial Catalysis,
Instituto de Catálisis y Petroleoquímica, E-28049 Madrid,
Spain; orcid.org/0000-0002-1882-4759
Ruixuan Wang − Division of Environment and Sustainability,
The Hong Kong University of Science and Technology,
Kowloon, Hong Kong SAR, China
(
13) Portela, R.; Perez-Ferreras, S.; Serrano-Lotina, A.; Banares, M.
̃
A. Engineering Operando Methodology: Understanding Catalysis in
Time and Space. Front. Chem. Sci. Eng. 2018, 12 (3), 509−536.
(
14) Wang, Q.; Li, Z.; Banares, M. A.; Weng, L.-T.; Gu, Q.; Price, J.;
̃
Han, W.; Yeung, K. L. A Novel Approach to High-Performance
Aliovalent-Substituted Catalysts2D Bimetallic MOF-Derived Ce-
CuO Microsheets. Small 2019, 15 (42), 1903525.
x
Complete contact information is available at:
https://pubs.acs.org/10.1021/jacs.0c08640
(
15) Li, Y.; Han, W.; Wang, R.; Weng, L.-T.; Serrano-Lotina, A.;
̃
Banares, M. A.; Wang, Q.; Yeung, K. L. Performance of an Aliovalent-
Substituted CoCeO Catalyst from Bimetallic MOF for VOC
x
Notes
Oxidation in Air. Appl. Catal., B 2020, 275, 119121.
The authors declare no competing financial interest.
(16) Mai, H.-X.; Sun, L.-D.; Zhang, Y.-W.; Si, R.; Feng, W.; Zhang,
H.-P.; Liu, H.-C.; Yan, C.-H. Shape-Selective Synthesis and Oxygen
Storage Behavior of Ceria Nanopolyhedra, Nanorods, and Nano-
cubes. J. Phys. Chem. B 2005, 109 (51), 24380−24385.
ACKNOWLEDGMENTS
■
The authors are grateful for the financial support from the
National Natural Science Foundation of China/Research
Grants Council Joint Research Scheme [N_HKUST626/13]
and Research Grants Council - General Research Fund
(17) Trovarelli, A.; Llorca, J. Ceria Catalysts at Nanoscale: How Do
Crystal Shapes Shape Catalysis? ACS Catal. 2017, 7 (7), 4716−4735.
(18) Peng, R.; Sun, X.; Li, S.; Chen, L.; Fu, M.; Wu, J.; Ye, D. Shape
Effect of Pt/CeO Catalysts on the Catalytic Oxidation of Toluene.
2
Chem. Eng. J. 2016, 306, 1234−1246.
[16307014], Innovation and Technology Fund [ITS/300/
(19) Nie, L.; Mei, D.; Xiong, H.; Peng, B.; Ren, Z.; Hernandez, X. I.
1
8], the Spanish Ministry [CTM2017-82335-R], and Guangz-
P.; DeLaRiva, A.; Wang, M.; Engelhard, M. H.; Kovarik, L.; Datye, A.
K.; Wang, Y. Activation of Surface Lattice Oxygen in Single-Atom Pt/
hou Collaborative Innovation Key Program [201704030074].
We also acknowledge the staff from MCPF, AEMF, CBE from
HKUST, and CSIC-ICP, especially Dr. Yuan Cai for her
technical support.
CeO for Low-Temperature CO Oxidation. Science 2017, 358 (6369),
2
1419−1423.
(20) Ta, N.; Liu, J.; Chenna, S.; Crozier, P. A.; Li, Y.; Chen, A.;
Shen, W. Stabilized Gold Nanoparticles on Ceria Nanorods by Strong
Interfacial Anchoring. J. Am. Chem. Soc. 2012, 134 (51), 20585−
20588.
REFERENCES
■
(
1
1) Brooks, B. O. Understanding Indoor Air Quality; CRC Press,
991.
(21) Wang, Q.; Yeung, K. L.; Banares, M. A. Operando Raman-
̃
Online FTIR Investigation of Ceria, Vanadia/Ceria and Gold/Ceria
(
2) Chin, J.-Y.; Godwin, C.; Parker, E.; Robins, T.; Lewis, T.;
Catalysts for Toluene Elimination. J. Catal. 2018, 364, 80−88.
Harbin, P.; Batterman, S. Levels and Sources of Volatile Organic
Compounds in Homes of Children with Asthma. Indoor Air 2014, 24
4), 403−415.
(22) Banares, M. A.; Guerrero-Perez, M. O.; Fierro, J. L. G.; Cortez,
̃
́
G. G. Raman Spectroscopy during Catalytic Operations with On-Line
Activity Measurement (Operando Spectroscopy): A Method for
(
I
https://dx.doi.org/10.1021/jacs.0c08640
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
pubs.acs.org/JACS
Article
Understanding the Active Centres of Cations Supported on Porous
(40) Pushkarev, V. V.; Kovalchuk, V. I.; d’Itri, J. L. Probing Defect
Materials. J. Mater. Chem. 2002, 12 (11), 3337−3342.
Sites on the CeO Surface with Dioxygen. J. Phys. Chem. B 2004, 108
2
(23) Wu, Z.; Li, M.; Howe, J.; Meyer, H. M.; Overbury, S. H.
(17), 5341−5348.
Probing Defect Sites on CeO2 Nanocrystals with Well-Defined
(41) Busca, G. Infrared Characterization of the Hydrocarbon
Intermediates in the Oxidation of Toluene and Xylenes over
Vanadia-Titania Catalysts. J. Chem. Soc., Faraday Trans. 1993, 89
(4), 753.
Surface Planes by Raman Spectroscopy and O Adsorption. Langmuir
2
2
(
010, 26 (21), 16595−16606.
24) Liu, H.-H.; Wang, Y.; Jia, A.-P.; Wang, S.-Y.; Luo, M.-F.; Lu, J.-
(42) Lin-Vien, D.; Colthup, N.; Fateley, W.; Grasselli, J. The
Q. Oxygen Vacancy Promoted CO Oxidation over Pt/CeO2
Handbook of Infrared and Raman Characteristic Frequencies of Organic
Molecules; Elsevier, 1991.
Catalysts: A Reaction at Pt−CeO Interface. Appl. Surf. Sci. 2014,
2
3
(
14, 725−734.
(43) Gao, P.; Weaver, M. J. Surface-Enhanced Raman Spectroscopy
25) Aranifard, S.; Ammal, S. C.; Heyden, A. On the Importance of
as a Probe of Adsorbate-Surface Bonding: Benzene and Mono-
substituted Benzenes Adsorbed at Gold Electrodes. J. Phys. Chem.
Metal−Oxide Interface Sites for the Water−Gas Shift Reaction over
Pt/CeO Catalysts. J. Catal. 2014, 309, 314−324.
2
1
(
985, 89 (23), 5040−5046.
(26) Schilling, C.; Hofmann, A.; Hess, C.; Ganduglia-Pirovano, M.
44) Kwon, Y. J.; Son, D. H.; Ahn, S. J.; Kim, M. S.; Kim, K.
V. Raman Spectra of Polycrystalline CeO : A Density Functional
2
Vibrational Spectroscopic Investigation of Benzoic Acid Adsorbed on
Theory Study. J. Phys. Chem. C 2017, 121 (38), 20834−20849.
Silver. J. Phys. Chem. 1994, 98, 8481−8487.
(27) Spanier, J. E.; Robinson, R. D.; Zhang, F.; Chan, S.-W.;
(
45) Trovarelli, A. Catalytic Properties of Ceria and CeO -
2
Herman, I. P. Size-Dependent Properties of CeO2‑y Nanoparticles as
Studied by Raman Scattering. Phys. Rev. B: Condens. Matter Mater.
Phys. 2001, 64 (24), 245407.
Containing Materials. Catal. Rev.: Sci. Eng. 1996, 38 (4), 439−520.
(46) Zhang, X.; Deng, Y.-Q.; Tian, P.; Shang, H.; Xu, J.; Han, Y.-F.
Dynamic Active Sites over Binary Oxide Catalysts: In Situ/Operando
Spectroscopic Study of Low-Temperature CO Oxidation over MnOx-
̈
(28) Ozkan, E.; Cop, P.; Benfer, F.; Hofmann, A.; Votsmeier, M.;
Guerra, J. M.; Giar, M.; Heiliger, C.; Over, H.; Smarsly, B. M. Rational
Synthesis Concept for Cerium Oxide Nanoparticles: On the Impact of
Particle Size on the Oxygen Storage Capacity. J. Phys. Chem. C 2020,
CeO Catalysts. Appl. Catal., B 2016, 191, 179−191.
2
(47) Lee, Y.; He, G.; Akey, A. J.; Si, R.; Flytzani-Stephanopoulos, M.;
Herman, I. P. Raman Analysis of Mode Softening in Nanoparticle
CeO2−δ and Au-CeO2−δ during CO Oxidation. J. Am. Chem. Soc.
1
(
24 (16), 8736−8748.
29) Lee, J.; Ryou, Y.; Chan, X.; Kim, T. J.; Kim, D. H. How Pt
2
(
011, 133 (33), 12952−12955.
48) Gan, T.; Chu, X.; Qi, H.; Zhang, W.; Zou, Y.; Yan, W.; Liu, G.
Pt/Al O with Ultralow Pt-Loading Catalyze Toluene Oxidation:
Interacts with CeO under the Reducing and Oxidizing Environments
2
at Elevated Temperature: The Origin of Improved Thermal Stability
2
3
of Pt/CeO Compared to CeO . J. Phys. Chem. C 2016, 120 (45),
2
2
Promotional Synergistic Effect of Pt Nanoparticles and Al O
2
3
2
(
5870−25879.
Support. Appl. Catal., B 2019, 257, 117943.
30) Gulyaev, R. V.; Kardash, T. Yu; Malykhin, S. E.; Stonkus, O. A.;
(49) Zhang, Q.; Mo, S.; Li, J.; Sun, Y.; Zhang, M.; Chen, P.; Fu, M.;
Ivanova, A. S.; Boronin, A. I. The Local Structure of Pd Ce1−xO
x
2−x−δ
Wu, J.; Chen, L.; Ye, D. In Situ DRIFT Spectroscopy Insights into the
Reaction Mechanism of CO and Toluene Co-Oxidation over Pt-
Based Catalysts. Catal. Sci. Technol. 2019, 9 (17), 4538−4551.
Solid Solutions. Phys. Chem. Chem. Phys. 2014, 16 (26), 13523−
3539.
31) Wu, Z.; Rondinone, A. J.; Ivanov, I. N.; Overbury, S. H.
1
(
(50) Wang, H.; Liu, J.-X.; Allard, L. F.; Lee, S.; Liu, J.; Li, H.; Wang,
Structure of Vanadium Oxide Supported on Ceria by Multiwavelength
J.; Wang, J.; Oh, S. H.; Li, W.; Flytzani-Stephanopoulos, M.; Shen, M.;
Goldsmith, B. R.; Yang, M. Surpassing the Single-Atom Catalytic
Activity Limit through Paired Pt-O-Pt Ensemble Built from Isolated
Pt1 Atoms. Nat. Commun. 2019, 10 (1), 3808.
(51) Ding, K.; Gulec, A.; Johnson, A. M.; Schweitzer, N. M.; Stucky,
G. D.; Marks, L. D.; Stair, P. C. Identification of Active Sites in CO
Oxidation and Water-Gas Shift over Supported Pt Catalysts. Science
2015, 350 (6257), 189−192.
(52) Peng, R.; Li, S.; Sun, X.; Ren, Q.; Chen, L.; Fu, M.; Wu, J.; Ye,
D. Size Effect of Pt Nanoparticles on the Catalytic Oxidation of
Raman Spectroscopy. J. Phys. Chem. C 2011, 115 (51), 25368−25378.
(32) Liu, H.; Chang, L.; Chen, L.; Li, Y. In Situ One-Step Synthesis
of Metal−Organic Framework Encapsulated Naked Pt Nanoparticles
without Additional Reductants. J. Mater. Chem. A 2015, 3 (15),
8
(
028−8033.
33) Lopez, J. M.; Gilbank, A. L.; García, T.; Solsona, B.; Agouram,
́
S.; Torrente-Murciano, L. The Prevalence of Surface Oxygen
Vacancies over the Mobility of Bulk Oxygen in Nanostructured
Ceria for the Total Toluene Oxidation. Appl. Catal., B 2015, 174−
1
(
75, 403−412.
34) Chen, A.; Yu, X.; Zhou, Y.; Miao, S.; Li, Y.; Kuld, S.; Sehested,
J.; Liu, J.; Aoki, T.; Hong, S.; Camellone, M. F.; Fabris, S.; Ning, J.;
Jin, C.; Yang, C.; Nefedov, A.; Woll, C.; Wang, Y.; Shen, W. Structure
Toluene over Pt/CeO
2
Catalysts. Appl. Catal., B 2018, 220, 462−470.
̈
of the Catalytically Active Copper−Ceria Interfacial Perimeter. Nat.
Catal. 2019, 2 (4), 334−341.
(
35) Nolan, M.; Parker, S. C.; Watson, G. W. The Electronic
Structure of Oxygen Vacancy Defects at the Low Index Surfaces of
Ceria. Surf. Sci. 2005, 595, 223−232.
(36) Liotta, L. F.; Ousmane, M.; Di Carlo, G.; Pantaleo, G.;
Deganello, G.; Marcì, G.; Retailleau, L.; Giroir-Fendler, A. Total
Oxidation of Propene at Low Temperature over Co O −CeO Mixed
3
4
2
Oxides: Role of Surface Oxygen Vacancies and Bulk Oxygen Mobility
in the Catalytic Activity. Appl. Catal., A 2008, 347 (1), 81−88.
(37) Spencer, M. S. Models of Strong Metal-Support Interaction
(
SMSI) in Pt on TiO Catalysts. J. Catal. 1985, 93 (2), 216−223.
2
(
38) Xie, S.; Dai, H.; Deng, J.; Liu, Y.; Yang, H.; Jiang, Y.; Tan, W.;
Ao, A.; Guo, G. Au/3DOM Co O : Highly Active Nanocatalysts for
3
4
the Oxidation of Carbon Monoxide and Toluene. Nanoscale 2013, 5
22), 11207−11219.
39) Pask, J. A. Effect of Water Vapor on Sintering of Ceramic
(
(
Oxides. In Sintering Key Papers; Somiya, S., Moriyoshi, Y., Eds.;
̅
Springer Netherlands: Dordrecht, 1990; pp 579−592.
J
https://dx.doi.org/10.1021/jacs.0c08640
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX