Alkali-metal-promoted Pt/TiO2 opens a more efficient pathway to formaldehyde oxidation at ambient temperatures

Article abstract of DOI:10.1002/anie.201202034

Addition of alkali metal ions significantly promotes the activity of the Pt/TiO₂ catalyst for the HCHO oxidation reaction by stabilizing an atomically dispersed Pt-O(OH)_x alkali metal species and opening a new low-temperature reaction pathway. The atomically dispersed Na-Pt-O(OH) _x species can effectively activate H₂O and catalyze the facile reaction between surface OH and formate species to total oxidation products. Copyright

Full text of DOI:10.1002/anie.201202034

Angewandte
Chemie
DOI: 10.1002/anie.201202034
Catalytic Oxidation
Alkali-Metal-Promoted Pt/TiO2 Opens a More Efficient Pathway to
Formaldehyde Oxidation at Ambient Temperatures**
Changbin Zhang, Fudong Liu, Yanping Zhai, Hiroko Ariga, Nan Yi, Yongchun Liu,
Kiyotaka Asakura, Maria Flytzani-Stephanopoulos,* and Hong He*
Formaldehyde is emitted from building and furnishing
materials and consumer products,[1] and is known to cause
irritation of eyes and respiratory tract, headache, pneumonia,
and even cancer.[2,3] It is a dominant indoor air pollutant,
especially in developing countries, and significant efforts have
gone into indoor HCHO purification to meet environmental
regulations and human health needs.
was shown to be effective for HCHO oxidation at room
temperature, achieving 100% conversion of d = 100 ppm
HCHO to CO2 and H2O at a gas hourly space velocity
(GHSV) of 50000 hꢀ1. However, we also observed that this
type catalyst is not as active as needed for practical
applications, and deactivates with time-on-stream.
Herein, we report a novel alkali-metal-promoted Pt/TiO2
catalyst for the ambient destruction of HCHO. We show that
the addition of alkali-metal ions (such as Li+, Na+, and K+) to
Pt/TiO2 catalyst stabilized an atomically dispersed Pt-
O(OH)x–alkali-metal species on the catalyst surface and
also opened a new low-temperature reaction pathway,
significantly promoting the activity for the HCHO oxidation
by activating H2O and catalyzing the facile reaction between
surface OH and formate species to total oxidation products.
Figure 1a shows the HCHO conversion to CO2 as
a function of temperature over the x% Na-1% Pt/TiO2 (x =
0, 1, and 2) samples at a GHSVof 120000 hꢀ1 and HCHO inlet
of d = 600 ppm. All gas streams were humidified to a RH of
around 50%. Before each activity test, the samples were
reduced in H2 at 3008C for 30 min. The sodium-free catalyst
had low activity for the HCHO oxidation reaction, with
HCHO conversion being only about 19% at 158C. With 1%
Na addition, the HCHO conversion reached 96% at 158C and
100% at 408C. With 2% Na addition, 100% HCHO
conversion to CO2 and H2O was measured at 158C. The
effect of Na addition on the surface reducibility was examined
by H2 temperature-programmed reduction (TPR; Figure 1b).
The amounts of H2 consumption were about the same over all
the samples, but the addition of Na shifted the reduction peak
to lower temperatures, that is, from 28C for 1% Pt/TiO2 to
ꢀ68C for 1% Na-1% Pt/TiO2 and ꢀ118C for 2% Na-1% Pt/
TiO2. Thus, the sample reducibility correlates with the sample
activity. The most active 2% Na-promoted sample had
excellent stability as checked by long isothermal tests. For
example, at a GHSV of 300000 hꢀ1 and with the same other
reaction conditions, approximately 80% HCHO conversion
was maintained over a 72 h-long test (Figure 1a, inset). Li and
K were equally effective promoters to Na and imparted the
same high activity and stability to the Pt species (Supporting
Information, Figure S1). Water vapor and oxygen effects on
the activity of Na-Pt/TiO2 are important (Supporting Infor-
mation, Figures S2,S3).
Removal of HCHO by adsorbents has been investigated
extensively using potassium permanganate, activated carbon,
aluminum oxide, and some ceramic materials.[4–6] Sorbent
effectiveness is typically limited by low adsorption capacities.
Catalytic oxidation is the most effective technology for
volatile organic compound (VOC) abatement because
VOCs can be oxidized to CO2 over certain catalysts at much
lower temperatures than in thermal oxidation.[7–9] Supported
noble metal catalysts (Pt, Pd, Rh, Au, Ag) or metal oxide
catalysts (Ni, Cu, Cr, Mn) have been used for the catalytic
oxidation of VOCs.[8–22] Complete oxidation of HCHO over
catalysts occurs above 1508C on clean and oxidized films of
Ni, Pd, and Al[15] and over silver–cerium composite oxide,[16]
above 1008C over Ag/MnOx-CeO2 and Au/CeO2,[19] and
[18]
above 858C over Pd-Mn/Al2O3[17] and Au/FeOx.[20]
As catalytic oxidation at even lower temperatures is
desirable for indoor air purification, the development of
a catalyst for total HCHO oxidation at room temperature is of
great interest. In our recent study,[21,22] 1% Pt/TiO2 catalyst
[*] C. Zhang, F. Liu, Y. Liu, Prof. H. He
Research Center for Eco-Environmental Sciences
Chinese Academy of Sciences
Shuangqing Road 18, Beijing, 100085 (China)
E-mail: honghe@rcees.ac.cn
Y. Zhai, N. Yi, Prof. M. Flytzani-Stephanopoulos
Department of Chemical and Biological Engineering
Tufts University, Medford, MA 02155 (USA)
E-mail: mflytzan@tufts.edu
H. Ariga, Prof. K. Asakura
Catalysis Research Center, Hokkaido University (Japan)
[**] The authors appreciate the valuable advices of Emeritus Prof. Ken-
ichi Tanaka of Tokyo University and the aberration-corrected
HAADF/STEM tests performed by Dr. David Bell of the School of
Engineering and Applied Sciences, Harvard University. This work
was supported by the National Natural Science Foundation of China
(50921064 and 21077117), the Program of the Ministry of Science
and Technology of China (2010AA064905), the Photon Factory, KEK
(Japan) (2009G177), and the BL14W1 beam line, Shanghai
Synchrotron Radiation Facility. Work at Tufts University was
supported by the U.S. Department of Energy (DOE)/Basic Energy
Sciences (BES) Grant No. DE-FG02-05ER15730.
Deionized-water washing of the samples was performed
to check the alkali-metal and Pt interaction. While most of the
Na was removed from the Na- containing catalysts, a residual
amount remained (Supporting Information, Table S1). Activ-
ity test results (Supporting Information, Figure S1) showed
that the washed catalyst had identical activity for HCHO
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201202034.
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stabilized hydroxyl species in close proximity to the Pt
site.[23,24]
Huang et al.[25,26] also studied the catalytic oxidation of
HCHO over Pt/TiO2 and Pd/TiO2 catalysts at ambient
temperatures. They observed that the NaBH4-reduced Pd/
TiO2 samples showed higher catalytic activity than H2-
reduced ones; but did not discuss the activity enhancement
as an alkali-metal promotion. It would be worth exploring
whether a sodium promotion effect as the one described here
for Pt is also manifested for Pd catalysts.
Detailed catalyst sample characterization was conducted
and is shown in the Supporting Information, Figure S5–S14.
XAFS measurements were conducted to study the structure
of samples before/after Na addition and before/after H2
reduction under atmospheric pressure. The XANES and
EXAFS of Ti-K and Pt-LIII edges were recorded in trans-
mission mode at room temperature. Both XANES and
EXAFS results of the Ti-K edge in x% Na-Pt/TiO2 catalysts
(Supporting Information, Figure S7–S9) showed no change
before and after Na addition or H2 reduction. In contrast,
clear distinctions were observed for the Pt-LIII edge with and
without Na addition. From the Pt-LIII XANES spectra and
their first-order derivatives (Supporting Information, Fig-
ure S10–S12), we can see that before H2 reduction, the Pt
species in all samples were in oxidized state by comparing the
white line intensity with those of Pt foil and PtO2. The Pt
species were reduced to metallic state after in situ reduction.
With further exposure to ambient air, the Pt species became
partially oxidized. In particular, the Pt species in the Na-
doped samples were more oxidized than those in Pt/TiO2,
which is probably due to the formation of Pt-(ONa)x species
with strong association.[23,24]
The curve fitted k3-weighted EXAFS oscillations of the Pt
LIII edges along with the corresponding transformations into
R space and as measured k3-weighted EXAFS oscillations are
presented in the Supporting Information, Figures S13 and
S14, and the fitting parameters are given in Table 1. Prior to
H2 reduction, all of the Pt was coordinated with O or Cl, and
the Pt-Pt coordination was zero on all catalysts. After in situ
H2 reduction at 3008C, all of the Pt species were reduced to
the metallic phase, yet the Pt-Pt coordination number was
monotonically lowered with an increase in the amount of Na.
The relationship between Pt particle size and Pt-Pt coordi-
nation number determined by EXAFS is well-established,[27]
whereby the metal–metal coordination number is a function
of the total number of metal atoms in one particle and
a smaller coordination number corresponds to a smaller
particle size.[28] Thus, the EXAFS findings show that Na
addition effectively reduces the particle size of Pt from 10 ꢀ
(Na-free), to 6.8 ꢀ (1% Na), to 4.8 ꢀnm (2% Na). With
higher (2%) amount of Na as in the most active catalyst
sample, the decrease of Pt cluster size was also confirmed by
the STEM images and corresponding particle size distribu-
tions (Supporting Information, Figure S6). Single Pt atoms or
ions are also stabilized on these surfaces. Once the prere-
duced catalysts were exposed to air, as in realistic operation
for HCHO oxidation, surface structures were changed owing
to oxygen adsorption[29] and the structural differences were
substantial among three samples. The Na-free Pt/TiO2 sample
Figure 1. a) HCHO conversion h over x wt% Na-1 wt% Pt/TiO2 (x=0,
1, and 2) catalysts as a function of temperature T. Reaction conditions:
HCHO d=600 ppm, O2 20 vol%, relative humidity: about 50%, He
balance, total flow rate of 50 cm3 minꢀ1, and GHSV 120000 hꢀ1 (inset:
stability test of 2% Na-1% Pt/TiO2 at 258C, GHSV 300000 hꢀ1 with
same other reaction conditions). b) H2 TPR profiles of x wt% Na-1%
Pt/TiO2 (x=0, 1, and 2).
oxidation to the unwashed sample. Thus, only a small amount
of Na is needed to promote the Pt on the surface (9.6 at.% Na
for 1.2 at.% Pt; Supporting Information, Table S1). In turn,
the Pt binds the residual Na and stabilizes it. Indeed, it is the
Pt, not the TiO2 surface, that binds the Na, because in the
absence of Pt all Na is removed by washing (see the
Supporting Information for the washing procedure). The
residual amount of Na on the sample surface, measured by
XPS (Supporting Information, Table S1), was significantly
higher for the most active catalyst sample corresponding to
a Na/Pt atomic surface ratio of 8:1. These findings are similar
to what has been reported for Pt/SiO2, when promoted by
alkali-metal oxides.[23] In that work it was shown that the Na-
O-Pt interaction is present only for the sub-nm size Pt species.
Pt-O(OH)x-Na clusters were proposed as the active sites for
the water-gas shift reaction.[23] The promoted catalyst differs
from the unpromoted catalyst in that it has alkali-metal-
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Table 1: Fitting parameters of the curve fitted k3-weighted EXAFS
analysis of x% Na-1% Pt/TiO2 (x=0, 1, 2).[a]
Samples
Shell
CN
R [ꢀ]
DW [ꢀ]
R factor
(ꢁ0.01)
Pt-foil
PtO2
Pt-Pt
Pt-O
Pt-O-Pt 4.0ꢁ1.0
12.0ꢁ2.3 2.77
0.077ꢁ0.010 0.8
0.061ꢁ0.020 3.0
0.061ꢁ0.012
6.0ꢁ1.2
2.02
3.14
2.02
2.30
2.02
2.02
2.77
2.77
2.77
2.77
2.30
2.77
2.02
2.02
[b]
1Pt/TiO2
Pt-O
Pt-Cl
Pt-O
Pt-O
Pt-Pt
Pt-Pt
Pt-Pt
Pt-Pt
Pt-Cl
Pt-Pt
Pt-O
Pt-O
3.7ꢁ1.2
2.3ꢁ1.0
6.0ꢁ1.3
5.4ꢁ1.2
5.6ꢁ1.2
3.8ꢁ0.8
2.4ꢁ0.5
4.7ꢁ1.0
0.6ꢁ0.2
2.7ꢁ0.6
1.3ꢁ0.3
2.8ꢁ0.6
0.061ꢁ0.020 0.6
0.051ꢁ0.057
1Na-1Pt[b]
2Na-1Pt[b]
1Pt/TiO2
1Na-1Pt[c]
2Na-1Pt[c]
1Pt/TiO2
1Na-1Pt[d]
2Na-1Pt[d]
0.061ꢁ0.020 4.1
0.061ꢁ0.020 8.7
0.097ꢁ0.010 1.3
0.097ꢁ0.010 2.3
0.097ꢁ0.010 7.2
0.097ꢁ0.010 0.4
0.051ꢁ0.057
[c]
[d]
0.097ꢁ0.010 11.6
0.061ꢁ0.020
0.092ꢁ0.010 9.8
[a] CN=coordination number, R=bond length, DW=Debye–Waller
factor, Pt-Pt is the coordination shell in Pt metal, Pt-O is the first
coordination shell in PtO2, Pt-O-Pt is the second coordination shell in
PtO2. [b] Samples calcined in static air, 4008C, 2 h. [c] Samples after
in situ H2 reduction in 10% H2/Ar at 3008C for 30 min. [d] Samples
exposed to ambient air after H2 reduction.
showed a Pt-Pt coordination shell in Pt metal and a small
residual Pt-Cl coordination shell (the absence of residual Cl
effect on the activity of Na-Pt/TiO2 is shown and discussed in
the Supporting Information, Table S3, Figure S4). Addition of
Na into the catalyst clearly decreased the Pt-Pt and elimi-
nated the Pt-Cl shell fraction, while it increased the Pt-O shell
fraction. With 2% Na added, only a Pt-O shell was detected,
hence 2% Na addition can completely suppress the formation
of Pt-Pt bonds in the presence of O2 and stabilizes atomically
dispersed Pt-O species on the TiO2 surface. Furthermore, the
Pt-O coordination number in this sample was only about 3;
that is, much lower than the normal coordination number in
PtO2. A Bader charge closer to PtO was calculated by DFT[23]
for the single Pt cation-centered K6PtO4(OH)2 cluster that
was proposed as the active site for the low-temperature water-
gas shift reaction. A similar structure may be responsible for
the ambient HCHO oxidation reaction.
Qiao et al. recently reported a novel catalyst that con-
sisted of atomically dispersed Pt atoms on FeOx support for
CO oxidation.[30] As the catalyst was prepared with a co-
precipitation method using sodium carbonate as precipitant
and H2PtCl6·6H2O as Pt precursor, the presence of Na species
possibly also played an important role in the fabrication of
this single-atom Pt catalyst.
The reaction mechanism of HCHO oxidation on Na-free
Pt/TiO2 catalysts has been investigated at room temper-
ature.[22] As shown in Figure 2a, formate species (1570,
1359 cmꢀ1 for u(COOꢀ) and 2956, 2868, 2740 cmꢀ1 for
u(CH))[22,31] were formed and were dominant on Pt/TiO2
after the catalyst was exposed to a flow of O2 + HCHO +
He + H2O for 60 min. With helium purging for 60 min, the
formate species completely decomposed into CO species
(2058, 1769 cmꢀ1).[22] Upon catalyst exposure to O2, the CO
species were converted into CO2 and desorbed from the
Figure 2. In situ DRIFTS over a) 1% Pt/TiO2 and b) 2% Na-1% Pt/
TiO2 after 1) a flow of He+HCHO+O2 +H2O for 60 min followed by
2) He purging for 60 min, and finally 3) O2 purging for 30 min at room
temperature. For the dynamic time sequence of the DRIFTS spectra,
see the Supporting Information, Figure S15. Reaction conditions:
HCHO d=600 ppm, O2 20 vol%, about 50% relative humidity, He
balance, total flow rate of 50 cm3 minꢀ1
.
surface. Therefore, it was concluded that the HCHO oxida-
tion reaction on sodium-free samples follows the formate
(HCOOꢀ) decomposition route (HCHO!HCOOꢀ!CO!
CO2), with formate decomposing into CO being the rate-
determining step.[22] Kim et al. also reported a similar reaction
mechanism of HCHO oxidation over Pt/TiO2 catalyst at room
temperature.[32]
Here, the reaction mechanism of HCHO oxidation over
Na-promoted Pt/TiO2 catalysts was studied using in situ
DRIFTS (Figure 2b; Supporting Information, Figure S15).
After the samples were exposed to a flow of O2 + HCHO +
He + H2O for 60 min, surface formate (1596, 1352 cmꢀ1 for
u(COOꢀ) and 2807, 2703 cmꢀ1 for u(CH),[33] were dominant
at steady-state. Two kinds of surface hydroxyl (OH) groups at
ca. 3695 and 3600 cmꢀ1 were observed on the catalyst surface.
The negative peak of OH species at 3695 cmꢀ1 suggests that
the formation of surface HCOOꢀ consumed some OH species
(Supporting Information, Figure S15A). With He purging
(Supporting Information, Figure S15B), the intensities of the
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HCOOꢀ and OH peaks at 3600 cmꢀ1 dropped simultaneously.
After 60 min, the HCOOꢀ species completely disappeared
from the surface and the OH peak at 3600 cmꢀ1 became
negative (Figure 2b), indicating the complete reaction
between formate and active OH groups. In contrast, surface
carbonate and bicarbonate species (1970, 1620, 1540, 1400,
and 1325 cmꢀ1)[34] remained unchanged and gradually
increased with formate consumption (Figure 2b). A further
O2 purge did not alter the spectra, showing that no further
reaction occurred. Based on these results, we conclude that
HCHO oxidation over the promoted 2% Na-1% Pt/TiO2
catalyst follows a new pathway, that is, the direct formate
oxidation (HCHO!HCOO + OH!H2O + CO2), and the
reaction between surface hydroxyls and formate is preferred
over the decomposition of formate to CO followed by CO
oxidation.
To further check for the new HCHO oxidation pathway,
we carried out kinetics tests with both the sodium-free and
sodium-promoted Pt/TiO2 catalysts. Figure 3 shows Arrhe-
nius-type plots for the rates of HCHO oxidation over the 1%
Pt/TiO2 and 2% Na-1% Pt/TiO2 (unwashed and washed)
samples. The apparent activation energy of the reaction on
the sodium-free sample is (30 ꢁ 4) kJmolꢀ1; however, over the
Na-Pt/TiO2 catalyst, in both the unwashed and washed state,
the reaction was easier to activate, with apparent activation
energy of about (13 ꢁ 4) kJmolꢀ1, thus providing further
evidence that the reaction pathway was changed on the
sodium-promoted samples.
Figure 4. Profiles of species detected by temperature-programmed
desorption of HCHO from a) 1% Pt/TiO2 and b) 2% Na-1% Pt/TiO2
samples as a function of temperature (0–1208C). For detailed exper-
imental information, see the Supporting Information.
room temperature (Figure 4b), indicating that Na addition
changes the reaction pathway. Additionally, we observed that
a small amount of CO and H2 was produced at higher
temperatures (> 708C) over the sodium-doped catalyst. This
can be explained by the dehydrogenation pathway becoming
more dominant (easier) at high temperatures. Thus, we again
conclude that the preferred ambient temperature pathway for
HCHO oxidation is through formate oxidation by the
abundant associated hydroxyl groups on the Pt-O(OH)xNa-
type clusters.
Cyclic CO-TPR was performed to check whether on the
sodium-promoted Pt/TiO2 catalyst the activation of the
surface OH species is enhanced (Supporting Information,
Figure S16). Only a small amount of active OH groups existed
on the 1% Pt/TiO2 surface to react with CO to produce CO2
and H2 (2CO + 2OH!2CO2 + H2) at about 1508C. By
contrast, a considerable number of active OH groups were
present on the sodium-promoted sample, which could react
with CO at about 1008C, indicating that Na addition
increased the concentration of surface OH groups. With
intermittent rehydration at ambient conditions, the second
CO-TPR cycle was identical to the first. Thus, the OH groups
were fully regenerated on the catalyst surface. These findings
are the same as what has been reported for sodium-promoted
Pt/SiO2 for the low-temperature water-gas shift reaction.[23]
The promotion is structural in the WGS reaction; that is, the
CO + OH reaction is similarly activated on all Pt catalysts and
is independent of the type of support. A similar apparent
activation for promoted and unpromoted Pt catalysts was
reported.[23] However, the case of HCHO oxidation on the
same type catalyst is distinct in that the addition of alkali
metal alters the pathway from the HCHO decomposition
followed by CO oxidation to that of direct formate oxidation.
When a catalyst lacks OH groups, the formate species tend to
decompose into surface CO (HCOO-M!CO-M + OH-
M).[22] However, when a large amount of nearby OH groups
is present, the formate decomposition is inhibited and the
direct formate oxidation (HCOO-M + OH-M!H2O +
Figure 3. HCHO oxidation rate R over 1% Pt/TiO2, 2% Na-1% Pt/
TiO2 and 2% Na-1% Pt/TiO2-washed catalysts.
HCHO temperature-programmed desorption (HCHO-
TPD) tests were conducted to further probe how the
mechanism of HCHO oxidation is altered by Na addition
onto Pt/TiO2. Figure 4 presents the HCHO-TPD profiles
collected from the 1% Pt/TiO2 and 2% Na-1% Pt/TiO2
samples as a function of temperature (0–1208C). Over the
sodium-free sample (Figure 4a), CO was the only carbon-
containing product and no CO2 was detected, showing that
over the sodium-free sample the HCHO dehydrogenation
route (HCHO!H2 + CO) is followed. By contrast, CO2 is the
major product over the sodium-modified sample even at
4
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[4] B. Eriksson, L. Johanssin, I. Svedung, The Nordest Symposium
CO2 + 2m) is facilitated. We found that the OH groups are
regenerated by the H2O vapor on stream. Therefore, we
conclude that the regenerable OH provided by Na addition
on the Na-Pt/TiO2 sample, are responsible for altering the
HCHO oxidation reaction pathway.
On the basis of the above results, we propose that the key
steps for HCHO oxidation over the alkali-metal-promoted Pt/
TiO2 catalyst (including O2, HCHO, and H2O activation) take
place on the atomically dispersed Pt-O(OH)x alkali-metal
species, which alters the ambient-temperature HCHO oxida-
tion pathway by promoting the reaction between surface OH
and formate species at room temperature, and thus greatly
enhancing the HCHO oxidation activity. Such OH activation
by alkali-metal ion addition may apply to other volatile
organic compound oxidation reactions and to other metals.
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Experimental Section
The x wt% Na-1 wt% Pt/TiO2 (x = 0, 1, and 2) catalysts were
prepared at room temperature by excess solution impregnation of an
anatase TiO2 powder (Millennium Inorganic Chemicals, BET surface
area of 69 m2gꢀ1), using an aqueous solution of PtCl4 (Sigma–Aldrich)
and Na/K carbonate or LiNO3 solution (Sigma–Aldrich). After
impregnation, excess water was removed in a rotary evaporator at 30–
608C under vacuum until dryness. Samples were dried at 1108C for
12 h and calcined at 4008C in static air for 2 h (58Cminꢀ1). After
calcination, the samples were subjected to 10% H2/Ar (50 mLminꢀ1
)
reduction at 3008C for 30 min before testing.
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The activity tests and kinetics measurements for the catalytic
oxidation of HCHO over the catalysts were performed in a fixed-bed
quartz flow reactor. The feed gas composition for the activity tests
was HCHO/O2/He = 600 ppm/20 vol%/balance and 50% relative
humidity (total flow 50 mLminꢀ1) at a gas hourly space velocity of
120000/300000 hꢀ1 (W/F = 0.018/0.0072 gscmꢀ3). For kinetics mea-
surement, the feed gas composition was HCHO/O2/He = 700 ppm/
20 vol%/balance and 50% relative humidity (total flow
175 mLminꢀ1) for the reactor operated in a differential mode,
keeping the HCHO conversion below 15%. The inlet and outlet
gases were monitored by FTIR (Nicolet 380) equipped with IR-cells
with 2 m of light pass.
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Received: March 14, 2012
Revised: June 10, 2012
Published online: && &&, &&&&
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Keywords: alkali metals · catalytic oxidation · formaldehyde ·
platinum · titanium dioxide
.
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Angew. Chem. Int. Ed. 2012, 51, 1 – 6
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!

.
Angewandte
Communications
Communications
Catalytic Oxidation
Addition of alkali metal ions significantly
promotes the activity of the Pt/TiO2
catalyst for the HCHO oxidation reaction
by stabilizing an atomically dispersed Pt-
O(OH)x alkali metal species and opening
a new low-temperature reaction pathway.
The atomically dispersed Na-Pt-O(OH)x
species can effectively activate H2O and
catalyze the facile reaction between sur-
face OH and formate species to total
oxidation products.
C. Zhang, F. Liu, Y. Zhai, H. Ariga, N. Yi,
Y. Liu, K. Asakura,
M. Flytzani-Stephanopoulos,*
H. He*
&&&& — &&&&
Alkali-Metal-Promoted Pt/TiO2 Opens
a More Efficient Pathway to
Formaldehyde Oxidation at Ambient
Temperatures
6
www.angewandte.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
These are not the final page numbers!