Fabrication and performance of noble metal promoted birnessite catalysts for complete oxidation of formaldehyde at low temperatures

Article abstract of DOI:10.1166/jnn.2015.9163

Noble metal (Au, Ag, Pd and Pt) promoted birnessite (Bir) catalysts were successfully prepared and tested for catalytic oxidation of formaldehyde (HCHO). The catalysts were characterized by means of X-ray diffraction (XRD),⁵transmission electron microscopy (TEM), hydrogen temperature programmed reduction (H ₂-TPR), inductively coupled plasma atomic emission spectroscopy (ICPAES) and N₂adsorption-desorption. The activities of noble metal (Au,Ag, Pd and Pt) promoted birnessite catalysts follow the order of 1.0Pt/Bir > 1.0Pd/Bir > Bir > 1.0Ag/Bir > 1.0Au/Bir, revealing that the loading of Pd and Pt improves the⁶catalytic activity of birnessite, but the loading of Ag and Au slightly decreases the catalytic activity of birnessite. Effects of the Pt loading amount were also investigated on the activity of Pt/Bir catalysts for HCHO oxidation. Pt/Bir with a Pt loading of 1.5 wt% (1.5 Pt/Bir), which has the best reduction properties, was found to be the most efficient catalyst. Over this catalyst,⁷HCHO could be completely oxidized into CO ₂and H ₂O at 70°. 1.5 Pt/Bir also shows good catalytic stability under the HCHO oxidation atmosphere. The differences in the catalytic activity of these materials are largely attributed to their reducibility as well as the dispersion of metal nanoparticles, but are not directly related to their specific surface areas.

Full text of DOI:10.1166/jnn.2015.9163

Article
Journal of
Nanoscience and Nanotechnology
Vol. 15, 2887–2895, 2015
Copyright © 2015 American Scientific Publishers
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Printed in the United States of America
Fabrication and Performance of Noble Metal Promoted
Birnessite Catalysts for Complete Oxidation of
Formaldehyde at Low Temperatures
Linlin Liu1ꢀ2, Hua Tian1, Junhui He1ꢀ∗, Donghui Wang3, Chunyan Ma4, and Qiaowen Yang2
1Functional Nanomaterials Laboratory and Key Laboratory of Photochemical Conversion and
Optoelectronic Materials, Technical Institute of Physics and Chemistry (TIPC),
Chinese Academy of Sciences, Beijing 100190, China
2School of Chemical and Environmental Engineering, China University of
Mining and Technology, Beijing 100083, China
3Research Institute of Chemical Defense, Beijing 100083, China
4Department of Environmental Nano-Materials, Research Center for Eco-Environmental
Sciences, Chinese Academy of Sciences, Beijing 100085, China
Noble metal (Au, Ag, Pd and Pt) promoted birnessite (Bir) catalysts were successfully prepared
and tested for catalytic oxidation of formaldehyde (HCHO). The catalysts were characterized by
means of X-ray diffraction (XRD), transmission electron microscopy (TEM), hydrogen temperature
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programmed reduction (H2-TPR), inductively coupled plasma atomic emission spectroscopy (ICP-
IP: 182.72.89.158 On: Mon, 18 Jan 2016 09:40:11
AES) and N2 adsorption–desorption. The activities of noble metal (Au, Ag, Pd and Pt) promoted
Copyright: American Scientific Publishers
birnessite catalysts follow the order of 1.0Pt/Bir > 1.0Pd/Bir > Bir > 1.0Ag/Bir > 1.0Au/Bir, revealing
that the loading of Pd and Pt improves the catalytic activity of birnessite, but the loading of Ag
and Au slightly decreases the catalytic activity of birnessite. Effects of the Pt loading amount were
also investigated on the activity of Pt/Bir catalysts for HCHO oxidation. Pt/Bir with a Pt loading of
1.5 wt% (1.5 Pt/Bir), which has the best reduction properties, was found to be the most efficient
catalyst. Over this catalyst, HCHO could be completely oxidized into CO2 and H2O at 70ꢀ. 1.5 Pt/Bir
also shows good catalytic stability under the HCHO oxidation atmosphere. The differences in the
catalytic activity of these materials are largely attributed to their reducibility as well as the dispersion
of metal nanoparticles, but are not directly related to their specific surface areas.
Keywords: Birnessite, Noble Metal, Formaldehyde Oxidation, Reducibility.
1. INTRODUCTION
on human health.5 Thus, great efforts have been made to
reduce the indoor concentration of HCHO for improving
the indoor environment.
The increasing concern about indoor environment leads to
great attention to the elimination of volatile organic com-
pounds (VOCs) emitted from building materials, furnish-
ings, cleaning compounds, flavoring agents, dry cleaning
agents, paints, glues, lacquers, cosmetics, textiles, and etc.,
because of their toxic, malodorous nature and significant
health risks.1–3 Among VOCs, formaldehyde (HCHO) is
regarded as one of the most dominating and serious indoor
pollutants for its irritation, carcinogenicity and teratogenic-
ity to human beings.3ꢀ4 Long-term exposure to indoor air
containing a few ppm of HCHO may cause adverse effects
Though conventional physical adsorption and/or chemi-
cal absorption were proved to be efficient for HCHO elim-
ination at field experiments, the effectiveness of adsorbents
and/or absorbents were limited for only a short period of
time due to their removal capacities.6–8 Catalytic oxida-
tion is considered to be a promising approach to effec-
tive and complete elimination of HCHO, with CO2 and
H2O being the harmless end products. As known, noble
metal nanoparticles (Au, Ag, Pd, and Pt) have high cat-
alytic activity and supported noble metal nanoparticles can
greatly improve the catalytic activity of metal oxides.9–12
Many researchers have also studied noble metal-containing
∗Author to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2015, Vol. 15, No. 4
1533-4880/2015/15/2887/009
doi:10.1166/jnn.2015.9163
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Fabrication and Performance of Noble Metal Promoted Birnessite Catalysts for Complete Oxidation of Formaldehyde
Liu et al.
catalysts for HCHO decomposition at low temperatures.
For example, 0.4 wt% Pd–Mn/Al2O3 with 18.2 wt%
manganese loading could completelꢀy combust formalde-
hyde/methanol mixture at about 90 C.13 Ag and Pt pro-
moted MnOx–CeO2 catalysts were reported for complete
oxidation of HCHO, and Ag and Pt enhanced the effec-
tive activation of oxygen molecule on bare composite
oxides, which decreased the complete oxidization temper-
ature to 100 ꢀC and ambient temperature, respectively.14ꢀ15
Zhang et al.16 also reported that Pt/TiO2 could completely
oxidize HCHO into CO2 and H2O at ambient temper-
ature, exhibiting superior catalytic performance to Au
(Rh or Pd)/TiO2. In addition, Ni et al.17 reported that
Pt/Fe2O3 catalysts prepared by colloid-deposition method
possessed high catalytic activity with 100% HCHO con-
version at ambient temperature. It should be noted that
some manganese oxide materials without any noble metal
loaded have been proven to be effective for complete
oxidation of HCHO at low temperatures.18–20 Our previ-
ous works revealed that cryptomelane and birnessite man-
ganese oxides show significantly high catalytic activity,
and could completely decompose HCHO into CO2 and
H2O at very low temperatures.21ꢀ22
procedure, 6.0 g of KMnO4 was dissolved in 400 mL of
distilled water, and the mixture was fleetly stirred with a
rotational speed of 1200 rmp for ca. 30 min. A total of
8.0 mL of oleic acid was added dropwise, and a steady
emulsion formed. After the emulsion was maintained at
room temperature for 24 h, a brown-black product was
obtained, and washed several times with distilled water and
ethanol to remove any possible residual reactants. Finally,
ꢀ
the product was dried at 60 C for 24 h.
Noble metal (Au, Ag, Pd and Pt) promoted birnessite
catalysts were prepared by an impregnation method with an
ethanol solution of HAuCl4, AgNO3, H2PtCl6 and PdCl3,
respectively. A certain volume of noble metal precursor
solution was dispersed in 50 mL of ethanol, in which bir-
nessite was immersed for 2 h under vigorous stirring. Then
ꢀ
the temperature of the mixture was adjusted to 0 C and a
certain amount of aqueous KBH4 was dropped till the mole
ratio of KBH4 to noble metal was 15:1. After stirring for
another 2 h, the mixture was filtrated, wasꢀhed with distilled
water and ethanol, and then dried at 60 C for 24 h. The
obtained catalyst was labeled as wA/Bir, in which w repre-
sents the mass percentage of noble metal and A represents
the type of noble metal (Au, Ag, Pd and Pt).
Birnessite is a layered manganese oxide with poor
crystallinity,23 and has attracted significant interests in such
potential applications as adsorption,24ꢀ25 ion-exchange,26
battery electrodes,27 electrochemical materials28 and
magnetic materials.29 Catalytic activity of birnessite
has attracted wide attention in recent years for
N -demethylation oxidation, degradation of methylene
blue,30 acetone oxidation,31 complete oxidation of
HCHO21 and so on. The decoration of noble metals (such
as Au, Ag, Pd and Pt) on birnessite would enhance its cat-
alytic activity for HCHO oxidation, but few studies have
been reported so far on catalytic oxidation of HCHO by
noble metal promoted birnessite catalysts.
2.2. Characterization of Catalysts
X-ray diffraction (XRD) patterns of the samples were
recorded on a Bruker D8 Focus X-ray diffractometer using
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Cu Kꢁ radiation (40 mA, 40 kV). The data were collected
IP: 182.72.89.158 On: Mon, 18 Jan 2016 09:40:11
at a scanning rate of 0.1 sec/step over a 2ꢂ range from
Copyright: American Scientifꢀic Publishers
10–80 . Transmission electron microscopy (TEM) obser-
vations were carried out on a JEOL JEM-2100F trans-
mission electron microscope. A typical TEM specimen
was prepared by ultrasonically suspending catalyst pow-
der in ethanol followed by adding several droplets of the
suspension onto a carbon-coated copper grid. Elemental
analysis was performed by inductively coupled plasma
atomic emission spectroscopy (ICP-AES) on a Varian 710-
ES ICP Optical Emission Spectrometer. Hydrogen tem-
perature programmed reduction (H2-TPR) measurements
were carried out using a microreactor equipped with a
TCD detector. About 25 mg samples were loaded and pre-
treated with He at 120 ꢀC for about ten minutes to remove
adsorbed carbonates and hydrates. After cooling down to
room temperature and introducing the reduction agent of
5% H2/Ar with a flow rate of 50 mL/mꢀin, the tempera-
ture was then increased from 30 to 800 C at a ramp of
In our recent study,32 0.8% Pt-birnessite catalyst was
shown to be effective for HCHO oxidation, achieving
100% conversion of HCHO at relatively low temperatures.
It suggests that the loading of Pt improves the catalytic
activity of birnessite. On the basis of these results, we
report in the present work a comparative study on birnes-
site catalysts loaded with different noble metals (Au, Ag,
Pd and Pt), and aimed to determine the most active cat-
alysts for HCHO oxidation at low temperature. Complete
conversion of HCHO into CO2 and H2O was achieved at
low temperatures over the Pt/Bir catalysts. The promoting
effect of Pt on birnessite was investigated in the HCHO
oxidation.
ꢀ
10 C/min. N2 adsorption–desorption measurements were
performed at 77 K using a Quadrasorb SI automated sur-
face area and pore size analyzer. The as-prepared products
ꢀ
were first dried at 100 C before analysis. Specific sur-
face areas were calculated by the Brunauer–Emmett–Teller
(BET) method.
2. EXPERIMENTAL DETAILS
2.1. Preparation of Catalysts
2.3. Measurement of Catalytic Activity
Catalytic activities of all the samples for HCHO oxidation
were measured in a fixed-bed reactor under atmospheric
Flaky birnessite (designed as Bir) was synthesized via a
simple soft chemistry route at room temperature, which is
also called “Baeyer test for unsaturation.”21 In a typical
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Liu et al.
Fabrication and Performance of Noble Metal Promoted Birnessite Catalysts for Complete Oxidation of Formaldehyde
pressure. The catalyst (100 mg, 40–60 mesh) was loaded
in a quartz tube reactor with a diameter of 4 mm. Gaseous
HCHO was generated by passing a purified air flow oꢀver
a HCHO saturated solution in an incubator kept at 0 C,
leading to a typical feed gas composition of 460 ppm
HCHO. The total flow rate was 50 mL/min in a space
velocity of GHSV = 30,000 mL/(g h). Effluents from
the reactor were analyzed with an on-line Agilent 6890
gas chromatograph equipped with FID and Ni catalyst
converter which was used for converting carbon oxides
quantitatively into methane in the presence of hydrogen
before the detector. In typical runs, the reaction data were
obtained after HCHO oxidation was performed for 1 h
in order to achieve the steady state. No other carbon
containing compounds except CO2 in the products were
detected for the tested catalysts. Thus, HCHO conversion
is expressed by the yield of CO2, and calculated as follows:
d
c
b
a
10
20
30
40
50
60
70
80
2θ/degree
Figure 2. XRD patterns of Pt/Bir catalysts with varied Pt loadings: (a)
0.5Pt/Bir, (b) 1.0Pt/Bir, (c) 1.5Pt/Bir and (d) 2.0Pt/Bir.
HCHO conversion ꢀ%ꢁ = CO2 yield (%)
ꢂCO2ꢃoutvol.%
(111), (200) and (311) planes of Au crystal (PDF #04-
0784). This result was attributed to larger crystal sizes
of the Au phase, which should be observed in its TEM
image. Other metals promoted Bir catalysts have similar
patterns to Bir, which reveals that the loading of Ag, Pd
and Pt did not change the crystalline phase of birnessite
(see Figs. 1 and 2). No diffraction peaks of Ag, Pd and
Pt could be observed, indicating that they must be highly
=
×100
ꢂHCHOꢃinvol.%
where [CO2]out is the CO2 concentration in the products
(vol.%), and [HCHO]in is the HCHO concentration in the
feed gas (vol.%).
3. RESULTS AND DISCUSSION
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dispersed on birnessite and have small crystal sizes, for the
3.1. Characterization of Catalysts
33
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lowest detection limit of the X-ray technique is ca. 4 nm.
In addition, increasing the Pt loading from 0.5% to 2.0%
does not alter the crystalline phase of birnessite either.
The morphologies of the birnessite samples were inves-
tigated by TEM, and are shown in Figures 3 and 4. It can
be seen in Figure 3(a) that birnessite displays flaky tex-
ture, which consists of nanoplatelets with lengths of 30–
50 nm. In the process of birnessite preparation, a stable
O/W emulsion formed, and the reaction named “Baeyer
test for unsaturation” occurred between KMnO4 and oleic
acid at the O/W interface,21 where birnessite nanoplatelets
were produced. At the stirring speed of 1200 rmp, the
diameters of emulsions were relatively large, and the shell
formed by lamellar birnessite platelets was loosely packed
and unstable. Therefore, removal of oleic acid and its
residual reaction products by ethanol resulted in collapse
of the shell into pieces, giving the flaky morphology.
Figures 3(b)–(d) and 4(b) display typical TEM images
of the noble metal (Au, Ag, Pd and Pt) promoted birnessite
catalysts with a loading of 1.0 wt%. Clearly, the morphol-
ogy of birnessite remained flaky after the loading of noble
metals. It could also be seen that Pd and Pt nanoparticles
are visually more and have a higher dispersion degree than
Au and Ag nanoparticles. The metal contents of 1.0Au/Bir
and 1.0Ag/Bir were measured by ICP-AES and are shown
Table I, which indicates that Au and Ag had been suc-
cessfully loaded onto birnessite with similar contents to
the designed values. The statistical size histograms of Pd
Copyright: American Scientific Publishers
Figures 1 and 2 show XRD patterns of birnessite and noble
metal (Au, Ag, Pd and Pt) promoted birnessite catalysts.
Figure 1(a) displays four diffraction peaks at 2ꢄ = 12ꢅ29,
24.33, 36.60, and 65.67ꢀ, which can be well assigned to
the (001), (002), (100), and (110) planes of birnessite,
respectively.21 After Au was loaded (Fig. 1(b)), three new
diffraction peeks appeared, which were assigned to the
Au
e
d
c
Au(111)
Au(200)
Au(311)
b
a
10
20
30
40
50
60
70
80
2θ/degree
Figure 1. XRD patterns of birnessite and noble metal promoted bir-
nessite catalysts: (a) Bir, (b) 1.0Au/Bir, (c) 1.0Ag/Bir, (d) 1.0Pd/Bir and
(e) 1.0Pt/Bir.
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Fabrication and Performance of Noble Metal Promoted Birnessite Catalysts for Complete Oxidation of Formaldehyde
Liu et al.
(a)
(b)
20 nm
20 nm
(c)
(d)
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20 nm
20 nm
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Copyright: American Scientific Publishers
Figure 3. TEM images of birnessite and noble metal promoted birnessite catalysts: (a) Bir, (b) 1.0Au/Bir, (c) 1.0Ag/Bir and (d) 1.0Pd/Bir. Arrows
point to nanoparticles.
and Pt nanoparticles are shown in Figures 5(a) and (b),
which indicates that Pt nanoparticles have a smaller aver-
age particle size and are more homogeneously distributed
on birnessite than Pd nanoparticles. The average metal
nanoparticle sizes were estimated to be ca. 8.5 nm, 5.0 nm,
3.2 nm and 2.1 nm for 1.0Au/Bir, 1.0Ag/Bir, 1.0 Pd/Bir
and 1.0Pt/Bir, respectively.
TEM images and statistical Pt nanoparticle size his-
tograms of Pt/Bir with varied Pt loadings were also
obtained and are shown in Figures 4 and 5. The statistical
Pt nanoparticle size histogram of 0.5 Pt/Bir is not illus-
trated here because of its fewer Pt nanoparticles. The aver-
age Pt nanoparticle sizes were estimated to be ca. 2.8 nm,
2.1 nm, 2.8 nm and 3.2 nm for 0.5 Pt/Bir, 1.0Pt/Bir,
1.5 Pt/Bir and 2.0 Pt/Bir, respectively, indicating that the
average Pt nanoparticle size does not change much with
increase of the Pt loading.
the aggregation of nanoparticles.34ꢀ35 All promoted birnes-
site catalysts kept similar textures to the pure birnessite
after loading of varied amounts of Pt. All the catalysts
have larger BET specific surface areas (>100 m2/g) than
previously reported birnessite (<80 m2/g),21ꢀ27 which are
summarized in Table II. The surface areas of Pt/Bir cata-
lysts with a Pt loading less than 1.5% are slightly lower
than that of the pure birnessite, which may be related to
the blocking of some of birnessite pores by Pt nanoparti-
cles. When the Pt loading is 2.0 wt%, however, the surface
area of 2.0 Pt/Bir remarkably increases to 161 m2/g. This
phenomenon may be due to delamination and subsequent
rearrangement of birnessite by KBH4.
3.2. Catalytic Oxidation of HCHO
3.2.1. Effect of Varied Noble Metals
The catalytic oxidation of HCHO was performed and the
results are shown in Figure 7. The HCHO conversion at
N2 adsorption–desorption isotherms of Pt/Bir catalysts
with varied Pt loadings are shown in Figure 6. Clearly,
all the Pt/Bir catalysts exhibit typical type II isotherms
with type H3 hysteresis loops in the relative pressure range
of 0.4–1.0, suggesting the existence of slit–shaped meso-
pores with nonuniform shapes or sizes, probably due to
ꢀ
ꢀ
30 C (denoted as C30) and 100 C (denoted as C100), and
the temperatures for complete oxidation of HCHO (denoted
as T100%) over the promoted birnessite catalysts are used to
describe the catalytic activity. It can be seen that 1.0Pd/Bir
and 1.0Pt/Bir exhibited better catalytic performances than
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Liu et al.
Fabrication and Performance of Noble Metal Promoted Birnessite Catalysts for Complete Oxidation of Formaldehyde
(a)
(b)
20 nm
20 nm
(c)
(d)
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20 nm
20 nm
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Copyright: American Scientific Publishers
Figure 4. TEM images of Pt/Bir catalysts with varied Pt loadings: (a) 0.5Pt/Bir, (b) 1.0Pt/Bir, (c) 1.5Pt/Bir and (d) 2.0Pt/Bir. Arrows point to
nanoparticles.
1.0Au/Bir and 1.0Ag/Bir. Bir, 1.0Au/Bir and 1.0Ag/Bir
showed no activity for HCHO oxidation at 30ꢀC, while
C30 of 1.0Pd/Bir and 1.0Pt/Bir reached 10.2% and 24%,
respectively. T100% of 1.0Pd/Bir and 1.0Pt/Bir were 100 ꢀC
and 90ꢀꢀC, respectively. In contrast, the HCHO conversion
at 100 C over 1.0Au/Bir and 1.0Ag/Bir were only 44.9%
and 56.1%, respectively. It is evident that the order of cat-
alytic activity is 1.0Pt/Bir > 1.0Pd/Bir > Bir > 1.0Ag/Bir >
1.0Au/Bir. The addition of Pd and Pt led to improved per-
formance of birnessite catalysts, but Au and Ag promoted
birnessite catalysts were much less effective. The main rea-
son will be displayed later.
HCHO. And the effect of Pt loading varied from 0.5 wt%
to 2.0 wt% was thus evaluated on the catalytic activity
of Pt/Bir, and the results are displayed in Figure 8. C30
and T100% are also plotted as a function of the Pt loading
in Figure 9. Clearly, the Pt loading significantly improved
the catalytic activity of birnessite, and the catalytic activity
increases with increasing the amount of Pt loading, again
suggesting the promoting effect of Pt loading. 1.5Pt/Bir
has the highest catalytic activity than other catalysts. How-
ever, it should be noted that beyond this amount of Pt load-
ing, the catalytic activity of birnessite catalyst becomes
lower. As shown in Figure 9, C30 decreases from 28% of
2.0Pt/Bir to 23% of 1.5Pt/Bir.
3.2.2. Effect of Pt Loading
3.2.3. Reducibility of Noble Metal
From the above results, Pt is shown to be the most
active metal loaded on birnessite for catalytic oxidation of
Promoted Birnessite Catalysts
In order to better understand the effects of varied noble
metals and Pt loadings on the catalytic activity of the bir-
nessite catalysts, H2-TPR experiments were carried out
to investigate their reducibility, and the obtained results
are provided in Figure 10. The pure birnessite exhibits
two reduction peaks at 300ꢀ and 336ꢀ, indicating the
stepwise reduction of manganese oxides. According to
Table I. Metal contents of 1.0Au/Bir and 1.0Ag/Bir from ICP-AES
measurements.
Metal content
Ag or Au (wt%)
Mn (wt%)
1.0Au/Bir
1.0Ag/Bir
1.1
0.7
50.1
48.8
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Fabrication and Performance of Noble Metal Promoted Birnessite Catalysts for Complete Oxidation of Formaldehyde
Liu et al.
(a)
(b)
40
30
20
10
0
40
30
20
10
d = 3.2 nm
d = 2.1 nm
σ = 0.8 nm
σ = 0.5 nm
0
1.6
2.4
3.2
4.0
4.8
5.6
1.6
2.4
3.2
4.0
4.8
5.6
Diameter d (nm)
Diameter d (nm)
(c)
(d)
40
30
20
10
0
40
30
20
10
0
d = 3.1 nm
d = 2.8 nm
σ = 0.7 nm
σ = 0.7 nm
1.6
2.4
3.2
4.0
4.8
5.6
1.6
2.4
3.2
4.0
4.8
5.6
Diameter d (nm)
Diameter d (nm)
Figure 5. Statistical size histograms of Pd and Pt nanoparticles in promoted birnessite catalysts: (a) 1.0Pd/Bir, (b) 1.0Pt/Bir, (c) 1.5Pt/Bir and
(d) 2.0Pt/Bir.
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the literature,36–38 the low temperature (LT) peak may be
roughly assigned to the reduction of poorly crystalline
MnO2 to Mn3O4, whereas the high temperature (HT) peak
is attributed to the reduction of Mn3O4 to MnO. No pat-
tern can be attributed to the reduction of the noble metals,
due to their low amounts in the catalysts, which caused
very low consumption of hydrogen.39 After Au was loaded,
the temperatures of two reduction peaks slightly increased,
i.e., 305ꢀ for LT peak and 387ꢀ for HT peak, indicating
that the loading of Au slightly decreased the reducibility
Copyright: American Scientific Publishers
of birnessite. Meanwhile, with the addition of Ag, the
LT peak of 1.0Ag/Bir (Fig. 10(a)) becomes slightly left-
shifted but wider, and the HT peak is almost the same
as that of the pure birnessite, which means the loading
of Ag did not change the reducibility of birnessite sig-
nificantly. However, the loading of Pd and Pt dramati-
cally enhanced the reducibility of birnessite as shown in
Figures 10(a) and (b). Thꢀe H2-TPR profile of 1.0Pd/ꢀBir
shows a LT peak at 161 C with a shoulder at 279 C,
which are much lower than that of Bir. 1.0Pt/Bir exhibits
a sharp LT peak at 78 ꢀC with two weak and broad shoul-
der peaks at about 107 and 175ꢀ, respectively, suggesting
that the loading of Pt gave the highest reducibility for
birnessite materials. Meanwhile, the intensities of reduc-
tion peaks of 1.0Pt/Bir are apparently higher in compar-
ison to those of 1.0Pd/Bir, meaning higher amounts of
reducible species (thus, more reactive species and higher
reactivity). The reducibility order of noble metal pro-
moted birnessite catalysts is: 1.0Pt/Bir > 1.0Pd/Bir > Bir ≈
1.0Ag/Bir > 1.0Au/Bir, which is in accordance with their
catalytic activities for HCHO oxidation. This proves that
Table II. Specific surface areas (designated as SBETꢀ of birnessite and
0.0
0.2
0.4
0.6
0.8
1.0
noble metal (Au, Ag, Pd and Pt) promoted birnessite catalysts.
Relative pressure (P/P0)
Catalyst
Bir
0.5Pt/Bir
104
1.0Pt/Bir
118
1.5Pt/Bir
115
2.0Pt/Bir
161
Figure 6. N2 adsorption–desorption isotherms of birnessite and Pt/Bir
catalysts with varied Pt loadings: (ꢀ) Bir, (•) 0.5Pt/Bir, (ꢁ) 1.0Pt/Bir,
(ꢂ) 1.5Pt/Bir, (+) 2.0Pt/Bir.
SBET (m2/g)
132
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Fabrication and Performance of Noble Metal Promoted Birnessite Catalysts for Complete Oxidation of Formaldehyde
(a) (b)
100
80
60
40
20
0
1.0Pd/Bir
1.0Pt/Bir
1.0Pd/Bir
1.0Ag/Bir
1.0Au/Bir
Bir
100 200 300 400 500 600 700
Temperature (ºC)
200
400
20
30
40
50
60
70
80
90
100
Temperature (ºC)
(c)
Figure 7. Effects of noble metal loaded on birnessite catalysts on CO2
yield at varied temperatures. (ꢀ) Bir, (+) 1.0Au/Bir, (ꢁ) 1.0Ag/Bir,
(ꢂ) 1.0Pd/Bir, (•) 1.0Pt/Bir. Reaction conditions: HCHO 460 ppm, O2
21 vol%, total flow rate of 50 mL/min, and GHSV 30,000 mL/(g h).
2.0Pt/Bir
1.5Pt/Bir
1.0Pt/Bir
100
80
0.5Pt/Bir
Bir
60
100 200 300 400 500 600 700
Temperature (ºC)
40
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lysts, (b) magnified H2-TPR profile of 1.0Pd/Bir, and (c) H2-TPR profiles
20
0
IP: 182.72.89.158 On: Mon, 18 Jan 2016 09:40:11
Copyright: American SocfiePtn/BtiifriccaPtaluybstlsiswhitehrvsarious Pt loadings.
with higher reducibility, the promoted birnessite exhibits
higher catalytic activity for HCHO oxidation.
20
30
40
50
60
70
80
90
100
Temperature (ºC)
With increase of the Pt loading amount to 1.5 wt%,
the ꢀtemperature of reduction peaks markedly decreased to
Figure 8. Effects of the Pt loading amount on CO2 yield over Pt/Bir
catalysts at varied temperatures. (×) Bir, (•) 0.5Pt/Bir, (ꢀ) 1.0Pt/Bir,
(ꢂ) 1.5Pt/Bir, (ꢁ) 2.0Pt/Bir. Reaction conditions: HCHO 460 ppm, O2
21 vol%, total flow rate of 50 mL/min, and GHSV 30,000 mL/(g h).
ꢀ
65 C with a shoulder peak at ca. 100 C. When the Pt
loading amount further increased to 2.0 wt%, the tempera-
ꢀ
ture of reduction peaks increased slightly to 69 C. These
H2-TPR observations agree well with the catalytic activity
measurements.
30
300
TLTP
3.2.4. Stability Test of 1.5Pt/Bir
25
20
15
Besides activity, stability is another important index for
catalyst performance. Based on the above results, we
focused study on the stability of 1.5Pt/Bir for catalytic
oxidation of HCHO. Figure 11 illusꢀtrates the HCHO
conversion with time-on-stream at 70 C over 1.5Pt/Bir.
Complete decomposition of HCHO into CO2 and H2O
remained unchanged and no deactivation was observed in
48 h. Therefore, the 1.5Pt/Bir catalyst is quite stable under
the HCHO oxidation atmosphere.
250
200
150
100
50
10
5
C30
T 100%
0
0.5
1.0
1.5
2.0
Pt loading (wt%)
3.3. Discussion
Figure 9. Relationship between (ꢃ) C30, (•) T100% , (ꢀ) TLTP and the
Pt loading amount on birnessite. C30: the CO2 yield at 30 ꢀC; T100%: The
temperature for complete oxidation of HCHO; TLTP : The temperature of
LT peak according to the H2-TPR profiles.
The introduction of noble metal nanoparticles on birnessite
greatly affects the activities of catalysts, and the promot-
ing effect of noble metal is dependent on their type and
J. Nanosci. Nanotechnol. 15, 2887–2895, 2015
2893

Fabrication and Performance of Noble Metal Promoted Birnessite Catalysts for Complete Oxidation of Formaldehyde
Liu et al.
the specific surface area of 1.5Pt/Bir is not the largest
among the Pt/Bir catalysts, it has the largest catalytic activ-
ity of HCHO oxidation. 2.0Pt/Bir has the largest specific
surface area; however, it shows a lower catalytic activity
than 1.5Pt/Bir. Very interestingly, the adsorption capacity
of nitrogen molecules also increases with increase of the
Pt loading amount from 0.5% to 1.5, and decreases with
further increase of the Pt loading amount (Fig. 6), cor-
responding to the order of catalytic activity of the Pt/Bir
catalysts for HCHO oxidation.
100
80
60
40
20
0
0
10
20
30
40
50
Time (h)
4. CONCLUSIONS
Complete oxidation of HCHO at very low temperature
could be obtained over noble metal (Au, Ag, Pd and Pt)
promoted birnessite catalysts. The catalytic behavior of
birnessite strongly depends on the type of loaded noble
metal and the catalyst reducibility. Pt and Pd nanoparticles
greatly improve the catalytic activity of birnessite, while
the loading of Ag and Au leaded to deactivation of birnes-
site catalysts. The activities of catalysts with varied noble
metals follow the order of 1.0Pt/Bir > 1.0Pd/Bir > Bir >
1.0Ag/Bir > 1.0Au/Bir, which is the same as the reducibil-
ity order of these catalysts. The Pt loading amount also
affects the catalytic performance of Pt/Bir catalysts, and
the optimal Pt loading is 1.5%. HCHO over 1.5Pt/Bir can
be completely oxidized into CO2 and H2O at a tempera-
Figure 11. Variation of CO2 yield with time-on-stream over 1.5Pt/Bir
at reaction temperature of 70 ꢀC.
loading amount for HCHO oxidation. For 1.0Pt/Bir and
1.0Pd/Bir catalysts, the promoting effects of these noble
metals are significant, but the addition of Ag and Au even
lowers the catalytic activity of birnessite. The catalytic
activity increases with increase of the Pt loading amount,
with 1.5Pt/Bir having the highest catalytic activity. How-
ever, further increase of the Pt loading amount results in
slight decrease in catalytic activity. These differences in
catalytic behaviors would to be related to the significant
differences in the structural and chemical properties of the
birnessite catalysts, including the reducibility of materials.
ꢀ
Delivered by Publishing Technology to: Chinese University of Hong Kong
ture as low as 70 C. Stability test further suggested that
The H2-TPR results show that the loading of Au causes
slight decrease of the reducibility of birnessite, which leads
IP: 182.72.89.158 On: Mon, 18 Jan 2016 09:40:11
1.5Pt/Bir is quite stable in an extended period of HCHO
Copyright: American Scientific Publishers
oxidation. This work suggests that high reducibility and
to the lower catalytic activity of 1.0Au/Bir than that of
birnessite. After the addition of Ag, the reduction peaks of
birnessite do not significantly change, suggesting that the
promoting effect of Ag is negligible on the reducibility and
catalytic activity of birnessite. In addition, the loading of
Ag nanoparticles may block some of birnessite pores and
result in its lower catalytic activity for HCHO oxidation, as
compared with the pure birnessite. The reducibility of bir-
nessite is enhanced with increase of the Pt loading amount
to 1.5 wt%, but slightly decreases with further increase
of the Pt loading amount. The enhancement of catalyst
reducibility is doubtlessly beneficial to the catalytic oxida-
tion of HCHO.
good dispersion of noble metal nanoparticles are favor-
able for the promoted catalytic activity of birnessite mate-
rials. But the surface area of material is not crucial for
excellent catalytic performance toward complete oxidation
of HCHO. All of these results may give strong support
to the catalyst designment for promoting low-temperature
catalytic oxidation of HCHO.
Acknowledgment: This work was supported by the
National Natural Science Foundation of China (Grant
20871118, 21007076), the Knowledge Innovation Pro-
gram of the Chinese Academy of Sciences (CAS) (Grant
KSCX2-YW-G-059), the National Basic Research Pro-
gram of China (Grant 2010CB934103), and “Hundred Tal-
ents Program” of CAS.
Based on the literature,39–41 the introduction of Pt and
Pd facilitates the spillover of hydrogen atoms from noble
metal to birnessite or leads to the enhanced mobility of bir-
nessite lattice oxygen, which may result in the significantly
lowered reduction temperatures of 1.0Pt/Bir and 1.0Pd/Bir
catalysts. Pt nanoparticles have a smaller average particle
size and exhibit more homogeneous distribution than Pd
nanoparticles (Fig. 5), which should also contribute to the
higher catalytic activity of 1.0Pt/Bir than that of 1.0Pd/Bir.
The specific surface area usually plays an important role
in determining the catalytic activity of a catalyst. However,
it is not the case in the current systems, i.e., the catalytic
activity for HCHO oxidation is not directly related with
the specific surface area of catalysts (Table II). Though
References and Notes
1. R. Kostiainent, Atmos. Environ. 29, 693 (1995).
2. M. A. Parra, D. Elustondo, R. Bermejo, and J. M. Santamaría, Sci.
Total Environ. 404, 18 (2008).
3. D. A. Sarigiannis, S. P. Karakitsios, A. Gotti, I. L. Liakos, and
A. Katsoyiannis, Environ. Int. 37, 743 (2011).
4. Y. Shen, X. Yang, Y. Wang, Y. Zhang, H. Zhu, L. Gao, and M. Jia,
Appl. Catal. B 79, 142 (2008).
5. Y. Sekine, Atmos. Environ. 36, 5543 (2002).
6. Q. Wen, C. Li, Z. Cai, W. Zhang, H. Gao, L. Chen, G. Zeng, X. Shu,
and Y. Zhao, Bioresource Technol. 102, 942 (2011).
2894
J. Nanosci. Nanotechnol. 15, 2887–2895, 2015

Liu et al.
Fabrication and Performance of Noble Metal Promoted Birnessite Catalysts for Complete Oxidation of Formaldehyde
7. Z. Jiao, P. Luo, Y. Wu, S. Ding, and Z. Zhang, J. Hazard. Mater. B
134, 176 (2006).
8. S. Srisuda and B. Virote, Environ. Sci. 20, 37 (2008).
9. F. Niu, D. Zhang, L. Shi, X. He, H. Li, H. Mai, and T. Yan, Mater.
Lett. 63, 2132 (2009).
25. H. Chen and J. He, J. Phys. Chem. C 112, 17540 (2008).
26. Y. Kim, Y. Hong, M. G. Kim, and J. Cho, Electrochem. Commun.
9, 1041 (2007).
27. M. Nakayama, T. Kanaya, J. W. Lee, and B. N. Popov, J. Power
Sources 179, 361 (2008).
10. A. M. Venezia, L. F. Liotta, G. Deganello, Z. Schay, D. Horváth,
and L. Guczi, Appl. Catal. A 211, 167 (2001).
11. R. Yamamoto, Y. Sawayama, H. Shibahara, Y. Ichihash,
S. Nishiyama, and S. Tsuruya, J. Catal. 234, 308 (2005).
28. P. Yu, X. Zhang, Y. Chen, and Y. Ma, Mater. Lett. 64, 1480 (2010).
29. H. T. Zhu, J. Luo, H. X. Yang, J. K. Liang, G. H. Rao, J. B. Li, and
Z. M. Du, J. Phys. Chem. C 112, 17089 (2008).
30. M. Zaied, S. Peulon, N. Bellakha, B. Desmazières, and A. Chaussé,
Appl. Catal. B 101, 441 (2011).
31. D. Frías, S. Nousir, I. Barrio, M. Montes, T. López, M. A. Centeno,
and J. A. Odriozol, Mater. Charact. 58, 776 (2007).
32. L. Liu, H. Tian, J. He, D. Wang, and Q. Yang, J. Environ. Sci.
1117, 24 (2012).
12. C. Zhang, H. He, and K. Tanaka, Appl. Catal.
(2006).
B 65, 37
13. M. C. Álvarez-Galván, B. Pawelec, V. A. de la Peña O’Shea, J. L.
G. Fierro, and P. L. Arias, Appl. Catal. B 51, 83 (2004).
14. X. Tang, J. Chen, Y. Li, Y. Li, Y. Xu, and W. Shen, Chem. Eng. J.
118, 119 (2006).
15. X. Tang, J. Chen, X. Huang, Y. Xu, and W. Shen, Appl. Catal. B
81, 115 (2008).
33. C. Zhang, H. He, and K. Tanaka, Catal. Commun. 6, 211 (2005).
34. X. Chen, Y. Shen, S. L. Suib, and C. L. O’Young, Chem. Mater.
14, 940 (2002).
16. C. Zhang and H. He, Catal. Today 126, 345 (2007).
17. N. An, Q. Yu, G. Liu, S. Li, M. Jia, and W. Zhang, J. Hazard. Mater.
186, 1392 (2011).
35. Y. Ding, X. Shen, S. Sithambaram, S. Gomez, R. Kumar, V. M.
B. Crisostomo, S. L. Suib, and M. Aindow, Chem. Mater. 17, 5382
(2005).
18. C. Lahousse, A. Bernier, P. Grange, B. Delmon, P. Papaefthimiou,
T. Ioannides, and X. Verykios, J. Catal. 178, 214 (1998).
19. D. Zhao, T. Ding, X. Li, J. Liu, C. Shi, and A. Zhu, Chinese J. Catal.
33, 396 (2012).
36. E. R. Stobbe, B. A. de Boer, and J. W. Geus, Catal. Today 47, 161
(1999).
37. T. S. Park, S. K. Jeong, S. H. Hong, and S. C. Hong, Ind. Eng.
Chem. Res. 40, 4491 (2001).
20. Y. Sekine and A. Nishimura, Atmos. Environ. 35, 2001 (2001).
21. H. Chen, J. He, C. Zhang, and H. He, J. Phys. Chem. C 111, 18033
(2007).
22. H. Tian, J. He, X. Zhang, L. Zhou, and D. Wang, Micropor. Mesopor.
Mater. 138, 118 (2011).
38. L. Wang, Q. Liu, X. Huang, Y. Liu, Y. Cao, and K. Fan, Appl.
Catal. B 88, 204 (2009).
39. M. Ferrandon, J. Carnö, S. Järås, and E. Björnbom, Appl. Catal. A
180, 141 (1999).
40. J. Carnö, M. Ferrandon, E. Björnbom, and S. Järås, Appl. Catal. A
155, 265 (1997).
41. S. Hamoudi, A. Sayari, K. Belkacemi, L. Bonneviot, and F. Larachi,
Catal. Today 62, 379 (2000).
23. Q. Feng, L. Liu, and K. Yanggisawa, J. Mater. Sci. Lett. 19, 1567
(2000).
24. C. L. Peacock and D.DMe.lSivheerrmeadn,bCyhePmu. bGleioslh. i2n3g8, T94e(c2h00n7o).logy to: Chinese University of Hong Kong
IP: 182.72.89.158 On: Mon, 18 Jan 2016 09:40:11
Copyright: American Scientific Publishers
Received: 25 April 2013. Accepted: 5 November 2013.
J. Nanosci. Nanotechnol. 15, 2887–2895, 2015
2895