Low-temperature catalytic oxidation of formaldehyde over Co3O4 catalysts prepared using various precipitants

Article abstract of DOI:10.1016/S1872-2067(15)61086-5

Co₃O₄ catalysts prepared with different precipitants (NH₃·H₂O, KOH, NH₄HCO₃, K₂CO₃ and KHCO₃) were investigated for the oxidation of formaldehyde (HCHO). Among these, KHCO₃-precipitated Co₃O₄ (KHCO₃-Co) was the most active low-temperature catalyst, and was able to completely oxidize HCHO at the 100-ppm level to CO₂ at 90 °C. In situ diffuse reflectance infrared spectroscopy demonstrated that hydroxyl groups on the catalyst surface were regenerated by K⁺ and CO₃^2-, thus promoting the oxidation of HCHO. Moreover, H₂-temperature programmed reduction and X-ray photoelectron spectroscopy showed that employing KHCO₃ as the precipitant increased the Co³⁺/Co²⁺ molar ratio on the surface of the Co₃O₄ catalyst, thus further promoting oxidation. Structural characterization revealed that catalysts precipitated with carbonate or bicarbonate reagents exhibited greater specific surface areas and pore volumes. Overall, these data suggest that the high activity observed during the Co₃O₄ catalyzed oxidation of HCHO can be primarily attributed to the presence of K⁺ and CO₃^2- on the Co₃O₄ surface and the favorable Co³⁺/Co²⁺ ratio.

Full text of DOI:10.1016/S1872-2067(15)61086-5

Chinese Journal of Catalysis 37 (2016) 947–954
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article (Special Issue on Environmental Catalysis and Materials)
Low‐temperature catalytic oxidation of formaldehyde over Co3O4
catalysts prepared using various precipitants
Zeyun Fan, Zhixiang Zhang, Wenjian Fang, Xin Yao, Guchu Zou, Wenfeng Shangguan*
Research Center for Combustion and Environment Technology, Shanghai Jiao Tong University, Shanghai 200240, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Co3O4 catalysts prepared with different precipitants (NH3·H2O, KOH, NH4HCO3, K2CO3 and KHCO3)
were investigated for the oxidation of formaldehyde (HCHO). Among these, KHCO3‐precipitated
Co3O4 (KHCO3‐Co) was the most active low‐temperature catalyst, and was able to completely oxidize
HCHO at the 100‐ppm level to CO2 at 90 °C. In situ diffuse reflectance infrared spectroscopy demon‐
strated that hydroxyl groups on the catalyst surface were regenerated by K+ and CO32−, thus pro‐
moting the oxidation of HCHO. Moreover, H2‐temperature programmed reduction and X‐ray photo‐
electron spectroscopy showed that employing KHCO3 as the precipitant increased the Co3+/Co2+
molar ratio on the surface of the Co3O4 catalyst, thus further promoting oxidation. Structural char‐
acterization revealed that catalysts precipitated with carbonate or bicarbonate reagents exhibited
greater specific surface areas and pore volumes. Overall, these data suggest that the high activity
observed during the Co3O4 catalyzed oxidation of HCHO can be primarily attributed to the presence
of K+ and CO32– on the Co3O4 surface and the favorable Co3+/Co2+ ratio.
Received 31 January 2016
Accepted 23 March 2016
Published 5 June 2016
Keywords:
Formaldehyde oxidation
Catalysis
Cobalt oxide
Precipitation method
Potassium ion
© 2016, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
1. Introduction
allows the ongoing degradation of low HCHO concentrations,
although the limited capacity of this approach and the inevita‐
Formaldehyde (HCHO) was classified as a human carcino‐
gen by the International Agency for Research on Cancer in June
2004 [1]. Long‐term exposure to parts per million (ppm) HCHO
concentrations thus represents a health hazard, and the
short‐term (30 min) exposure limit recommended by the
World Health Organization is 0.1 mg/m3 [2]. HCHO is released
from various products, such as chipboard, textiles, and decora‐
tive materials, and can also contribute to the formation of pho‐
tochemical smog [3]. Many efforts have been made to devise
methods of reducing indoor HCHO concentrations to satisfy the
stringent environmental regulations [4–6]. Conventional ab‐
sorbents (such as activated carbon) are a ready means of elim‐
inating HCHO, but the associated challenges of waste disposal
and frequent replacement cannot be ignored. Photocatalysis
ble formation of undesirable by‐products restricts its practical
application [7]. As such, high efficiency, low‐temperature cata‐
lytic oxidation is believed to represent the most promising
technology for HCHO removal [8,9].
Initially, supported noble metal catalysts were applied to
HCHO oxidation at room temperature [10–13], but the high
cost of these metals restricts their large‐scale application. For‐
tunately, oxides of transition metals, including Mn, Co, and Cu,
also exhibit outstanding catalytic performance for low‐temper‐
ature HCHO oxidation. Among these, Co3O4 has been widely
investigated as a component of heterogeneous catalysts be‐
cause of its high performance [12–18]. Many researchers have
found that the catalytic activity of Co3O4 varies depending on
the method used to prepare the catalyst. Zhu et al. [19] synthe‐
* Corresponding author. Tel: +86‐21‐34206020; E‐mail: shangguan@sjtu.edu.cn
This work was supported by the National Natural Science Foundation of China (21577088).
DOI: 10.1016/S1872‐2067(15)61086‐5 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 37, No. 6, June 2016

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Zeyun Fan et al. / Chinese Journal of Catalysis 37 (2016) 947–954
sized a material consisting of Co3O4 supported on ZSM‐5
(Co3O4/ZSM‐5) for the oxidation of propane, using impregna‐
tion (IM), deposition precipitation (DP), and hydrothermal
(HT) methods. The catalytic activities of the resulting materials
were in the order of HT > DP > IM, and it was also determined
that the catalyst prepared with ammonium bicarbonate as the
precipitant was superior to one prepared with NaOH. Shi et al.
[20] produced a MnxCo3‐xO4 catalyst for HCHO oxidation as a
solid solution via both co‐precipitation and citric acid methods.
They found that the sample prepared by co‐precipitation ex‐
hibited the best catalytic performance and was able to com‐
pletely oxidize HCHO at 75 °C. The addition of specific alkali
elements, such as K and Na, has also proven to be effective for
promoting the catalytic oxidation of HCHO, by increasing the
concentration of OH on the catalyst surface [21–23].
The precipitation method is popular and also practical with
regard to eventual scaled‐up applications. Therefore, it is nec‐
essary to both research and develop the synthesis of transition
metal‐based catalysts utilizing different precipitation methods.
It would also be beneficial to further research the effect of the
precipitation method on catalyst performance for low‐temper‐
ature HCHO oxidation. Therefore, in the present study, various
precipitants were used to generate Co3O4 catalysts, and the
effects of these precipitants on the subsequent HCHO oxidation
performance were discussed.
ratus (Micromeritics) and X‐ray photoelectron spectroscopy
(XPS) spectra were acquired on an AXIS Ultra DLD instrument
(Kratos) at 300 W using Mg Kα excitation. H2 temperature‐pro‐
grammed reduction (TPR) data were obtained with a Chemi‐
sorb 2720 TPX apparatus (Micromeritics). In these tests, a 0.1‐g
sample (40−60 mesh) was pretreated under a N2 flow at 400 °C
for 30 min in a quartz reactor. The cooled sample was subse‐
quently reduced under a flow (40 mL/min) of 5 vol% H2 in Ar
from 20 to 700 °C (10 °C/min). In situ diffuse reflectance infra‐
red Fourier transform spectroscopy (DRIFTS) data were ac‐
quired on a Nicolet 6700 FTIR spectrometer equipped with an
MCT detector and a DRIFTS cell (Harrick), scanning from 4000
to 800 cm−1 with a resolution of 4 cm−1. Samples (30 mg) were
assessed under a flow of 100 ppm HCHO and 21 vol% O2 in N2
at 100 mL/min total flow. Prior to the FTIR characterization,
catalysts were pretreated under N2 for 1 h at 300 °C.
2.3. Catalytic activity measurements
Catalytic reactions were carried out in a U‐shape fixed‐bed
quartz tubular reactor with an inner diameter of 4 mm. The
catalyst sample (100 mg, 40–60 mesh) was placed between
two quartz wool layers in the tube and mass flow controllers
were used to set the gas flow rates. HCHO vapor was obtained
by passing a flow of N2 through a paraformaldehyde (99%,
SCRC) solution in a container within a water bath. The concen‐
tration of HCHO was adjusted by varying the N2 flow rate
and/or the temperature of the water bath. By mixing this N2
stream with a flow of O2 in N2, a typical feed gas composition
(100 mL/min, GHSV of 69000 h−1) containing 100 ppm HCHO
and 21 vol% O2 was obtained.
The concentrations of CO and CO2 in the outgoing gas
stream were measured by gas chromatography (GC 9560,
HUAAI, flame ionization detector with a CH4 conversion oven,
5Å molecule sieve and TDX‐01 packed columns). Experimental
data were recorded beginning at the point at which the reac‐
tion stabilized at each reaction temperature and data acquisi‐
tion continued over the span of 1 h. The HCHO conversion val‐
ues were calculated using the equation
2. Experimental
2.1. Catalyst preparation
All chemicals used in this work were analytical grade and
were purchased from the Sinopharm Chemical Reagent Co.
(SCRC). The NH3‐Co, KOH‐Co, NH4HCO3‐Co, K2CO3‐Co, and
KHCO3‐Co catalysts were prepared using a precipitation meth‐
od, employing five precipitants: NH3·H2O, KOH, NH4HCO3,
K2CO3, and KHCO3. In this method, a solution of the chosen pre‐
cipitant (2 mol/L) was added dropwise (10 mL/min) to a solu‐
tion of Co(NO3)2·6H2O (100 mL, 0.1 mol/L) with rapid stirring
at room temperature until the reaction solution had a pH value
of 9. After standing for 4 h, the resulting precipitate was re‐
moved by filtration and washed with deionized water until the
wash water was neutral, then dried at 100 °C for 10 h and cal‐
cined at 400 °C for 2 h. For comparison purposes, a sample
designated as PC/AHC‐Co was prepared by dispersing
HN4HCO3‐Co in a K2CO3 solution (2 wt%) with stirring for 30
min, followed by drying of the resulting product overnight at
100 °C.
HCHO conversion = [CO2]out/[HCHO]in  100%
where [CO2]out is the CO2 concentration in the outlet stream
(vol%), and [HCHO]in is the inlet HCHO concentration (vol%).
3. Results and discussion
3.1. Catalytic activity
Figure 1 summarizes the catalytic activities during HCHO
oxidation over different catalysts. It is evident that 100% of the
HCHO was oxidized to CO2 over the KHCO3‐Co and PC/AHC‐Co
at 90 °C, and so these two catalysts had the best low‐tempera‐
ture activity in this study. In contrast, the KOH‐Co and NH3‐Co
catalysts achieved 100% HCHO conversion at 120 and 130 °C,
respectively. The light off temperature (T10) obtained with the
KHCO3‐Co was only 60 °C, much lower than the values for the
NH4HCO3‐Co (90 °C) and NH3‐Co (110 °C). The PC/AHC‐Co
performance was significantly better than that of the
2.2. Catalyst characterization
All samples were pretreated at 200 °C for 1 h prior to cata‐
lytic trials. X‐ray diffraction (XRD) patterns of the catalysts
were acquired using a D8 ADVANCE (Bruker) X‐ray diffrac‐
tometer with Cu Kα radiation. The K content of each sample was
determined by atomic absorption spectroscopy (AAS). N2 ad‐
sorption‐desorption isotherms were obtained used the Bar‐
rett‐Joyner‐Halenda (BJH) method with a TriStar II 3020 appa‐

Zeyun Fan et al. / Chinese Journal of Catalysis 37 (2016) 947–954
949
Table 1
100
80
60
40
20
0
NH -Co
KOH-Co
NH4HCO3-Co
K2CO3-Co
KHCO3-Co
PC/AHC-Co
3
Chemical and physical parameters of catalysts prepared with different
precipitants.
BET surface BJH pore BJH pore
Crystallite
size b
(nm)
17.6
18.6
18.3
19.3
15.1
22.4
K a
(wt%)
Sample
area
(m2/g)
67.7
volume
(cm3/g)
0.135
0.105
0.393
0.337
0.411
0.216
size
(nm)
7.6
NH3‐Co
KOH‐Co
NH4HCO3‐Co
K2CO3‐Co
KHCO3‐Co
PC/AHC‐Co
0
0
0
0.07
1.15
1.06
54.8
7.6
95.4
78.7
97.9
88.3
16.5
14.2
16.8
9.8
a Determined by AAS.
b Determined using the Scherrer equation.
40
60
80
100
120
140
Temperature (oC)
Fig. 1. HCHO conversions over catalysts prepared with different pre‐
cipitants. Reaction conditions: 100 ppm HCHO, 21 vol% O2/N2, GHSV =
69000 h‒1.
and a type H1 hysteresis loop, indicating that the catalyst pores
had a narrow distribution and that these materials each had a
mesoporous (2 to 50 nm) structure [24]. The BET surface are‐
as, total pore volumes and pore sizes were found to vary de‐
pending on the precipitant. Comparing the NH3‐Co and KOH‐Co
with catalysts precipitated using carbonate and bicarbonate
reagents, the latter had the higher physical parameters. The
significant increase in the adsorption capability indicates that
the specific surface area was enhanced due to the decomposi‐
tion of cobalt carbonate during the calcination process. The
PC/AHC‐Co catalyst shows reduced structural parameters
compared with the NH4HCO3‐Co, which is attributed to either
clogging or covering of the NH4HCO3‐Co pores after K2CO3
loading [16]. The residual K concentration in the KHCO3‐Co was
15 times that of the K2CO3‐Co, although the peak position
demonstrates that the K+ cations did not enter the bulk phase
Co3O4 or replace the Co2+ ions because of the space (rK+ = 0.152
nm, rCo2+ (hs) = 0.0885 nm and rCo3+ (hs) = 0.075 nm) [25] and
charge factors. That is, if the Co2+ ions in the Co3O4 lattice had
been replaced by K+, the lattice parameters of the Co3O4 would
have been altered accordingly. These results are similar to
those reported previously by Wu et al. [26] and Park et al. [27].
As a result of the formation of carbonic acid and hydroxide
ions, a hydrogen carbonate solution will slowly generate CO2 at
room temperature [28]. In the presence of Co2+, the hydrolyza‐
NH4HCO3‐Co because of the immersion process applied during
the preparation of the catalyst.
3.2. Catalyst characterization
3.2.1. Structural characterization
The textures of the catalysts were characterized by XRD and
N2 physisorption, and the XRD patterns of the as‐prepared
Co3O4 samples are shown in Fig. 2. The peaks at 2θ = 31.3°,
36.8°, 38.5°, 44.8°, 55.6°, 59.5°, 65.2° and 77.3° correspond to
the (220), (311), (222), (400), (422), (511), (440) and (533)
planes, respectively. All these diffraction peaks are in good
agreement with those of spinel Co3O4 (JCPDS 65‐3103) and do
not indicate any impurity phases. The average crystal sizes of
these catalysts, as calculated from the XRD data (FMWH of the
(311) peak) using the Scherrer equation, ranged from 17 to 23
nm (Table 1).
The N2 adsorption‐desorption isotherms of the catalysts are
shown in Fig. 3. Each catalyst generated a typical IV isotherm
(311)
(511)
(422)
(220)
(440)
(222)(400)
(533)
(1)
NH3-Co
250
KOH-Co
(2)
(3)
NH4HCO3-Co
200
K2CO3-Co
KHCO3-Co
PC/AHC-Co
150
100
50
(4)
(5)
(6)
20
30
40
50
2/( o
60
70
80
0
0.0
)
0.2
0.4
0.6
0.8
1.0
Relative pressure (p/p0)
Fig. 2. XRD patterns of catalysts prepared with different precipitants.
(1) NH3‐Co; (2) KOH‐Co; (3) NH4HCO3‐Co; (4) K2CO3‐Co; (5) KHCO3‐Co;
(6) PC/AHC‐Co.
Fig. 3. N2 adsorption‐desorption isotherms of catalysts prepared with
different precipitants.

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Zeyun Fan et al. / Chinese Journal of Catalysis 37 (2016) 947–954
Table 2
283
266
Surface chemical compositions and element molar ratios of different
catalysts.
(6)
(5)
Surface content (at%)
Surface molar ratio
Sample
Co
O
K
0
Co3+/Co2+
0.24
Oads/Olatt
1.08
290
NH4HCO3‐Co 39.1
56.7
59.8
60.4
(4)
(3)
(2)
(1)
KHCO3‐Co
PC/AHC‐Co
36.8
36.3
3.4
3.3
0.35
0.96
300
308
0.42
1.33
examined, while the NH3‐Co had the highest peak. The reduc‐
tion temperatures of the others were in the order of KOH‐Co >
NH4HCO3‐Co > K2CO3‐Co > PC/AHC‐Co, which is in good
agreement with the observed differences in their catalytic
HCHO oxidation activities. There have been several literature
reports that the amount of Co3+ on the catalyst surface is relat‐
ed to the catalytic activity [35–37]. In the present work, it can
be seen that the reduction temperature shifts from 300 to 283
°C upon applying a coating of K2CO3 (2 wt%) on the
NH4HCO3‐Co catalyst. The reason for this shift is explained be‐
low, based on XPS analysis.
310
I
II
0
100
200
300
400
500
600
Temperature (oC)
Fig. 4. H2‐TPR profiles of NH3‐Co (1), KOH‐Co (2), NH4HCO3‐Co (3),
K2CO3‐Co (4), KHCO3‐Co (4), and PC/AHC‐Co (6) catalysts.
tion rate will increase substantially and so more CO2 will be
released. The CO2 gas bubbles thus produced could provide
aggregation centers for the precipitation reaction, creating
loose hydroxide carbonate precursors that might include K+
[29]. During the calcination process, these hydroxide carbonate
precursors will decompose to CO2 and H2O, refining the particle
size and increasing the porosity of the powder [30].
3.2.3. XPS results
Taking into account the structures and residual K contents
of these catalysts, the KHCO3‐Co, NH4HCO3‐Co and PC/AHC‐Co
were chosen to investigate the effect of the precipitant on the
surface chemical state. The Co 2p, K 2p and O 1s XPS data for
these materials are presented in Fig. 5, and associated values
are summarized in Table 2. As can be seen from Fig. 5(a) and
Table 2, K was found in the KHCO3‐Co and PC/AHC‐Co, but not
in the NH4HCO3‐Co. The amounts of K on the surfaces of the
KHCO3‐Co and PC/AHC‐Co were both approximately 3.3 at%,
demonstrating the presence of residual K following the use of
KHCO3 as the precipitant. Fig. 5(b) indicates two major oxygen
species with O 1s binding energy (BE) values of 529.8 and
3.2.2. H2‐TPR results
In Fig. 4, two obvious reduction peaks can be observed in
the low (I) and high (II) temperature regions. There are differ‐
ent opinions concerning the reduction mechanism of Co3O4.
Arnoldy et al. [31] stated that the reduction of Co3O4 consisted
of only a single step, while many other researchers [32–34]
regarded the reduction of Co3O4 as a two‐step process involv‐
ing the intermediate reduction of CoO. In the low temperature
region, the Co3+ in Co3O4 was presumably reduced to Co2+ with
the sample transitioning to CoO as an intermediate. In the high
temperature section, this intermediate was further reduced to
metallic cobalt. Peak I (at 290 °C) is therefore attributed to the
reduction of Co3+ to Co2+, while peak II (at 400 °C) resulted
from the reduction of CoO to Co. The KHCO3‐Co showed the
lowest reduction temperature (266 °C) among all the samples
530.8 eV. The former results from surface lattice oxygen (Olatt
)
contained in the Co3O4 [38], while the latter is attributed to
adsorbed surface oxygen (Oads) [39]. The Oads/Olatt ratio in the
KHCO3‐Co was 0.96 (Table 2), a value that is slightly lower than
that of the NH4HCO3‐Co (1.08). The Oads/Olatt ratio of the
PC/AHC‐Co (1.33) was relatively high, which is attributed to
the presence of surface hydroxyl (OH) groups resulting from
(b) O 1s
(a) K 2p
(c) Co 2p
Co2+
Olatt
Oads
(1)
Co3+
(1)
(1)
(2)
(3)
(2)
(3)
(2)
(3)
528
530
532
534
536
290
292
294
296
298
774 780 786 792 798 804 810
Binding energy (eV)
Binding energy (eV)
Binding energy (eV)
Fig. 5. XPS patterns of NH4HCO3‐Co (1), KHCO3‐Co (2), and PC/AHC‐Co (3) catalysts.

Zeyun Fan et al. / Chinese Journal of Catalysis 37 (2016) 947–954
951
the hydrolysis of K2CO3 [22]. The peaks in the Co 2p XPS spec‐
tra (Fig. 5(c)) at 795.0 and 780.1 eV could represent Co 2p1/2
and Co 2p3/2 spin‐orbital peaks [19, 40]. In this work, the Co 2p
spin‐orbit splitting value of the Co3O4 catalysts was 14.9 eV,
which is close to that of Co3+ (15.0 eV) [41], therefore, the cata‐
lysts likely consisted of Co3O4. The Co3+/Co2+ ratio for the
NH4HCO3‐Co was 0.24, a value that is less than that of the
PC/AHC‐Co (0.42), indicating that a greater amount of Co3+ was
present on the PC/AHC‐Co surface exposed after the K2CO3
immersion. This could explain the shift in the reduction tem‐
perature, which decreased from 300 to 283 °C when K2CO3 was
coated onto the NH4HCO3‐Co catalyst. The Co3+/Co2+ ratio of the
KHCO3‐Co was 0.35, which is between the values for the
NH4HCO3‐Co and PC/AHC‐Co. It appears that less of the
KHCO3‐Co surface was covered with K2CO3 compared with the
PC/AHC‐Co. Despite the much higher Co3+/Co2+ ratio of the
PC/AHC‐Co, the relatively low specific surface area of this ma‐
terial (Table 1) might explain why its catalytic activity was sim‐
ilar to that of the KHCO3‐Co.
in the NH4HCO3‐Co spectrum, thus the HCHO was oxidized as
soon as it was adsorbed on the surface of the catalyst. The
peaks at 1593 and 1575 cm–1 are attributed to the asymmetric
(COO) stretching vibration of formate species, while those at
1360, 1315 and 1276 cm–1 are assigned to the corresponding
symmetric (COO) stretch [42]. The absorbance bands at 1480,
1434, 1132, 1097 and 1055 cm–1 are ascribed to dioxymeth‐
ylene (DOM) species [43,44] and are seen to increase signifi‐
cantly over the first few minutes, while those due to OH species
at 3400 and 3342 cm–1 increased slightly. In addition, the ab‐
sorptions at 3633, 3568, 3542, and 3373 cm–1 ascribed to other
hydroxyl groups decreased to give negative peaks, presumably
as these groups were consumed during the oxidation. When O2
was introduced and the temperature increased, similar spectra
were obtained, as shown in Fig. 6(b). The bands resulting from
DOM species were significantly weakened as the temperature
increased. As well, the monodentate formate species (1593 and
1276 cm–1) appear to have been converted to bidentate for‐
mate (1575 and 1360 cm–1) [45] as the temperature was raised
to 200 °C, with the simultaneous appearance of a new mono‐
dentate species (1506 and 1248 cm–1). Surface carbonate and
bicarbonate species (1543, 1335 and 1210 cm–1) [45,46] were
formed at 80 °C and the absorbance of the two types of hydrox‐
yl groups returned to their initial values.
3.2.4. FT‐IR
Figure 6 shows the in situ DRIFT spectra acquired during
HCHO oxidation over the NH4HCO3‐Co and KHCO3‐Co catalysts.
In Fig. 6(a), no peaks associated with adsorbed HCHO are seen
(a) HCHO+N
2
(b) HCHO+O
2
+N
2
1055
1097
1055
1097
1132
1315
1360
1335
1360
1434
1575
1593
3542
3400
1543
1506
1664
3542
3568
1132
1284
3568
3633
250 oC
1575
3373
3342
3400
3373
3342
1434
1210
1276
3633
1480
60 min
30 min
15 min
5 min
200 oC
160 oC
120 oC
80 oC
2 min
40 oC
0 min
4000 3600 3200 2000 1800 1600 1400 1200 1000 800
Wavenumber (cm1)
4000 3600 3200 2000 1800 1600 1400 1200 1000 800
Wavenumber (cm1)
1132
(c) HCHO+N
2
1099
(d) HCHO+O
2
+N
2
1376
1412
1434
1543
1132
1099
1060
1060
1376
1412
1593
1434
1593
1346
1346
3373
3623
3373
3623
60 min
1543
200 oC
30 min
160 oC
15 min
5 min
2 min
0 min
120 oC
80 oC
40 oC
4000 3600 3200 2000 1800 1600 1400 1200 1000 800
Wavenumber (cm1)
4000 3600 3200 2000 1800 1600 1400 1200 1000 800
Wavenumber (cm1)
Fig. 6. In situ DRIFTS spectra obtained during HCHO adsorption (a) and HCHO oxidation (b) on NH4HCO3‐Co, and during HCHO adsorption (c) and
HCHO oxidation (d) on KHCO3‐Co.

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Zeyun Fan et al. / Chinese Journal of Catalysis 37 (2016) 947–954
The behavior of the KHCO3‐Co was simple. As shown in Fig.
found that the KHCO3 precipitated material (KHCO3‐Co) exhib‐
its the best catalytic efficiency, and is able to provide 100%
conversion of HCHO to CO2 at 90 °C. The AAS and XPS data in‐
dicate that the KHCO3‐Co surface holds residual K. The struc‐
tures of the Co3O4 catalysts obviously vary with different types
of precipitants, such that those catalysts precipitated using
6(c), the peak due to one type of hydroxyl group (3623 cm–1)
decreased slightly with increasing temperature, while the other
type (3373 cm–1) increased greatly during HCHO adsorption.
The intensities of the DOM peaks (1434, 1412, 1132, 1099 and
1060 cm–1) increased rapidly in the initial stage, and the peaks
from one type of bicarbonate (1593 and 1376 cm–1) also in‐
creased rapidly up to 60 min. At the oxidation stage shown in
Fig. 6(d), the relative intensities of the surface carbonate spe‐
cies peaks (1543 and 1346 cm–1) were found to change, alt‐
hough no new peaks were generated. The hydroxyl species
(3373 cm–1) and the formate species (1593 and 1376 cm–1)
initially increased in intensity and then decreased on going
from 40 to 160 °C, while the peaks due to DOM decreased con‐
tinuously. At 200 °C, the KHCO3‐Co spectrum indicates the
presence of only a few OH groups (3373 cm–1), as well as DOM
and carbonate species.
2–
–
reagents containing CO3 or HCO3 ions have higher BET sur‐
face areas and BJH pore sizes. H2‐TPR and XPS analyses show
that the KHCO3‐Co and PC/AHC‐Co have higher oxidizing abili‐
ties due to their relatively high surface Co3+/Co2+ molar ratios.
In situ DRIFTS results suggest that few DOM species are con‐
verted to formate species due to the absence of OH groups,
2–
which can be regenerated by K+ and CO3 loaded on the sur‐
face of the Co3O4.
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At lower temperatures (80 °C), few DOM species could be
converted to formate species due to absence of hydroxyl
groups on the NH4HCO3‐Co. In contrast, at higher temperatures
(> 80 °C), the decomposition of formate species became the key
step. In the case of the KHCO3‐Co, the DOM species generated
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Graphical Abstract
Chin. J. Catal., 2016, 37: 947–954 doi: 10.1016/S1872‐2067(15)61086‐5
Low‐temperature catalytic oxidation of formaldehyde over Co3O4 catalysts prepared using various precipitants
Zeyun Fan, Zhixiang Zhang, Wenjian Fang, Xin Yao, Guchu Zou, Wenfeng Shangguan*
Shanghai Jiao Tong University
100
80
60
40
20
0
NH3-Co
KOH-Co
NH4HCO3-Co
K2CO3-Co
KHCO3-Co
PC/AHC-Co
H2O
H2O
+
CO2
−
DOM OH−
K2CO3
HCO3
Co3O4
O2
+
HCHO
OH−
40
60
80
100
120
140
Temperature (C)
The K+ and CO32– on the surface of Co3O4 would regenerate hydroxyl groups consumed in the reaction, which would be helpful for catalyt‐
ic oxidation of HCHO.

Zeyun Fan et al. / Chinese Journal of Catalysis 37 (2016) 947–954
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