Catalytic wet air oxidation of pentachlorophenol over Ru/ZrO2 and Ru/ZrSiO2 catalysts

Article abstract of DOI:10.1016/j.cattod.2012.07.004

ZrSiO₂ and ZrO₂ supports loaded with active component Ru were unprecedentedly evaluated in catalytic wet air oxidation reaction of pentachlorophenol (PCP). The study results showed that the specific surface area of ZrSiO₂ which was prepared by high temperature aging method was much larger than that of ZrO₂, and it performed a better catalytic activity in catalytic wet air oxidation after being loaded with Ru. When the initial concentration of PCP was 125 mg L^-1, PCP conversion reached 92% after 90 min under the low temperature and pressure conditions of 180 °C and 0.1 MPa oxygen partial pressure. PCP conversion was increased by raising reaction temperature, increasing oxygen partial pressure, reducing the initial concentration of PCP and prolonging reaction time. The kinetics study of PCP in catalytic wet air oxidation showed that the catalytic wet air oxidation reaction of PCP obeyed first order kinetic model and its Arrhenius activation energy was 96.98 kJ mol^-1. The main intermediates of PCP in CWAO were acetic acid, oxalic acid and chlorine ion.

Full text of DOI:10.1016/j.cattod.2012.07.004

Catalysis Today 201 (2013) 49–56
Contents lists available at SciVerse ScienceDirect
Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Catalytic wet air oxidation of pentachlorophenol over Ru/ZrO and Ru/ZrSiO
2
2
catalysts
Huangzhao Weia,b, Xiaomiao Yan , Songbo He , Chenglin Sun
a
a
a,∗
a
Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, PR China
Graduate University of Chinese Academy of Sciences, Beijing 100049, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
ZrSiO2 and ZrO2 supports loaded with active component Ru were unprecedentedly evaluated in catalytic
wet air oxidation reaction of pentachlorophenol (PCP). The study results showed that the specific surface
area of ZrSiO2 which was prepared by high temperature aging method was much larger than that of
ZrO2, and it performed a better catalytic activity in catalytic wet air oxidation after being loaded with
Received 14 January 2012
Received in revised form 2 July 2012
Accepted 3 July 2012
Available online 9 August 2012
−1
Ru. When the initial concentration of PCP was 125 mg L , PCP conversion reached 92% after 90 min
◦
under the low temperature and pressure conditions of 180 C and 0.1 MPa oxygen partial pressure. PCP
Keywords:
conversion was increased by raising reaction temperature, increasing oxygen partial pressure, reducing
the initial concentration of PCP and prolonging reaction time. The kinetics study of PCP in catalytic wet
air oxidation showed that the catalytic wet air oxidation reaction of PCP obeyed first order kinetic model
Catalytic wet air oxidation
Pentachlorophenol
ZrSiO2
ZrO2
Kinetics
−1
and its Arrhenius activation energy was 96.98 kJ mol . The main intermediates of PCP in CWAO were
acetic acid, oxalic acid and chlorine ion.
Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved.
1
. Introduction
Since the 1930s, pentachlorophenol (PCP) is widely used as
common methods of AOPs used to treat PCP include photo-catalytic
oxidation process [7], supercritical oxidation process [8], ozonation
oxidation process [9], Fenton’s oxidation process [10] and electro-
catalytic oxidation process [11]. In AOPs, catalytic wet air oxidation
(CWAO) has many merits, including simultaneous treatment of
chemical oxygen demand (COD) and removal of nitrogen and sul-
fur compounds in one stage, low running cost, a compact plant
design for low space requirements, stably continuous and auto-
matic operation, deodorization and decolorization, the process is
extremely clean because it does not involve the use of any harm-
ful chemical reagents and the final products (if complete oxidation
is achieved) are carbon dioxide and water, no secondary pollu-
tants like sludge and ashes, the wastewater with COD of about
20,000 mg/L may be treated without supplying any auxiliary fuel,
the wastewater treated by CWAO may be reused and the steam
from the oxidation reaction of the wastewater may be recycled
into energy. Consequently, it is utilized to treat all kinds of organic
wastewater [12–14]. However, there has not been a report about
the PCP treatment by using CWAO.
wood preservatives, fruit trees pesticides or bactericide, whose
sodium salt is utilized as the medicine of killing oncomelania to
cure schistosomiasis. The properties of PCP are relatively stable,
and it is difficult to be degraded by using conventional wastewater
treatment methods such as physical, chemical and biological meth-
ods [1,2]. Besides, PCP has serious carcinogenic, teratogenic and
mutagenic effects. PCP has already been included in the blacklist of
priority pollutants, environmental endocrine disruptors and persis-
tent organic pollutants. Therefore, it is very important to develop a
safe and effective treatment technology of PCP.
Today, the treatment methods of PCP are mainly physisorp-
tion [3,4], biodegradation [5,6] and advanced oxidation process
[
7–11] at home and abroad. Physisorption only transfers pollu-
tants from the aqueous phase to the surface of adsorbents. In fact,
it does not eliminate pollutants. Biodegradation has several disad-
vantages, such as the long time of the treatment, the large area of
devices taking up, the bad treatment effect and easily influenced by
seasons. Advanced oxidation processes (AOPs) possess the advan-
tages of quick degrading rate and no secondary pollution and so
on, so they are increasingly employed to treat PCP wastewater. The
ZrO2 is increasingly used as a support in catalyst. It has sev-
eral useful properties that favor its application in catalysis. Among
the physical properties that make it being a useful support under
◦
harsh conditions are its high melting point of 2370 C, low ther-
mal conductivity, and high corrosion resistance [15]. ZrO2 does
not dissolve in the acidic and alkaline solution, which makes it a
good catalyst support in CWAO reactions. The common methods
for the preparation of ZrO2 include direct calcination method [16],
∗ Corresponding author. Tel.: +86 411 84379326; fax: +86 411 84699965.
E-mail addresses: weihuangzhao@qq.com, clsun@dicp.ac.cn (C. Sun).
0
920-5861/$ – see front matter. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.cattod.2012.07.004

5
0
H. Wei et al. / Catalysis Today 201 (2013) 49–56
◦
precipitation method [17], azeotropic distillation method [18],
hydrolysis method [19], sol–gel method [20], reversed phase
micro-emulsion method [21], vapor phase hydrolysis at lower tem-
injection temperature was 200 C. The Detector temperature was
◦
300 C.
The carboxylic acid and Cl 1 were analyzed via ion chromatogra-
phy (IC). The ICS-3000 system produced by DIONEX was equipped
with an AS11-HC chromatographic column (4 mm × 250 mm). The
−
perature and extraction separation method used to prepare ZrO for
2
nuclear industry. Chuah and co-workers [22] found that the diges-
tion of the hydrous oxide may increase the thermal stability of the
◦
temperature of column and cell heater was 30 and 35 C, respec-
−
1
resulting ZrO . Sato et al. [23] and Miller et al. [24] found that silica
tively. The mobile phase was 30 mol L NaOH solution and the flow
2
−
1
dissolving in the solution from the glass vessel and re-depositing
on the zirconium hydroxide during the digestion process was the
rate was fixed at 1.2 ml min
.
main factor of high specific area ZrO2.
2.3. Catalytic wet air oxidation experiments
Catalysts containing noble metals exhibit usually higher activity
than base metal catalyst in CWAO reaction, particularly in respect to
carboxylic acids. Leaching of precious metals from CWAO catalysts
has not been reported [25]. In precious metal catalysts, Ru is much
cheaper than the other platinum group noble metals, so it has been
studied by many scholars [26–28].
In this paper, ZrO2 was prepared by precipitation method (PM)
and hydrolysis method (HM), and ZrSiO2 was prepared by deposi-
tion of silicate species on zirconia under hydrothermal conditions in
aqueous ammonia. Then all of them were loaded with active com-
ponent Ru and used to treat PCP in the autoclave. The effects on the
conversion of PCP from temperature, oxygen partial pressure, the
initial concentration of PCP, reaction time and PCP reaction kinetics
in CWAO were studied.
The reactions were performed in a 250 ml or 500 ml batch reac-
tor equipped with a magnetically driven stirrer and an electric
heating jacket. The reactor was CJF-0.25 or CJF-0.5 type autoclaves
made of titanium alloy supplied by Dalian Tongda Autoclave Plant.
2
.03 g PCP and 6.5 g NaOH were added into 1 L deionized water to
−1
prepare 2000 mg L PCP solution. In the standard procedure for a
CWAO experiment, 0.1 g catalyst and 100 ml PCP solution were put
into the 250 ml autoclave. The autoclave was closed, filled with a
certain pressure of oxygen (0.1–2.1 MPa) and checked whether it
was leak-free or not, then the heating-up program started. When
the set temperature was attained, the stirrer started at a speed
of 600 rpm. This time was taken as the zero time of reaction and
the reaction time was set as 90 or 120 min. When the sample
needed taking during the reaction, 250 ml autoclave was changed
into 500 ml to do the experiment. The amount of both the catalyst
and model compound solution was doubled. The liquid samples
were periodically withdrawn from the reactor, filtered to remove
any catalyst particle and finally analyzed.
2
. Experimental
2.1. Reagents
Experiments were carried out at temperatures ranging from
35 C to 195 C and oxygen partial pressures ranging from 0.1
Ruthenium Trichloride (37%Ru) was supplied by Shanghai Irid-
◦ ◦
1
ium Grain Plant. Zirconium(IV) oxychloride octahydrate (99.0%)
and PCP (98.5%) were supplied by Sinopharm Chemical Reagent
CO., Ltd. Ammonia solution (25.0%) was supplied by Tianjin Kermel
Chemical Reagent Co., Ltd.
to 2.1 MPa. When the effect of the initial concentration of PCP on
PCP conversion was studied, the experiment was carried out after
diluting the prepared PCP solution.
The catalyst life evaluation test of 48 h was carried out in a fixed-
bed reactor with upflow of PCP wastewater and air. The reaction
◦
condition was as follows: reaction temperature = 180 C, reaction
2.2. Analytical methods
−1
pressure = 2.0 MPa, catalyst dose = 10 ml, Vliquid = 0.33 ml min
,
−
1
Vgas = 40 ml min
.
Liquid samples taken from the reactor were analyzed by rou-
tine laboratory analyses, which were filtrated with 0.45 ␮m film to
remove any catalyst particles and solid residue. The total amount
of the organic substances in the aqueous phase was determined
by measuring the chemical oxygen demand (COD). The COD val-
ues of the samples were determined by GB 11914-89 potassium
clichromate methods. PCP concentration was analyzed via high
performance liquid chromatography (HPLC). The HPLC system pro-
duced by Dalian Elite Analytic Instruments Co., Ltd. was equipped
with an Elite C18 chromatographic column (4.6 mm × 250 mm,
2
2
.4. Catalyst preparation
.4.1. ZrO -PM
2
ZrOCl2 solution (0.3 mol L 1) was added into 5 mol L ammo-
−
−1
nia solution drop by drop. The preparation was aged for 12 h at
room temperature, filtrated under vacuum, washed with 1% dilute
ammonia solution to no Cl
AgNO3 solution and washed with deionized water at last. The fil-
ter cake was respectively dried for 12 h at 50 C and 100 C. Then it
was grinded with an agate mortar to sift through a 60 mesh sieve.
−
1
in it which was detected with 1%
◦
◦
5
␮m) and a UV-detector set at 320 nm. The mobile phase was
−1
methanol: ammonium acetate (2 g L ) = 85:15 (v/v) and the flow
◦
At last, it was calcined at 500 C for 2 h in a muffle furnace.
−1
rate was fixed at 1.0 ml min
.
Typically a 50 ml sample containing PCP and organic reaction
2
.4.2. ZrO -HM
products was acidified to pH < 2 with concentrated H SO4 solu-
2
2
ZrOCl2 solution (0.1 mol L 1) was boiled for 96 h in a round-
bottomed flask with a reflux device. The preparation was aged for
2 h at room temperature and boiled to a paste. The post treatment
−
tion, and then extracted twice using a total volume of 110 ml
chloroform and methanol at the ratios of 0.9:1:1 (v/v/v for
sample/chloroform/methanol). The combined extract was concen-
1
of the paste was as the same as the ZrO -PM.
trated to 2 ml using a gentle stream of N gas. The extract was stored
2
2
◦
at −10 C until analysis.
Extracted samples containing PCP, intermediates, and byprod-
ucts were analyzed using a gas chromatograph (GC) (Agilent
Technologies 7890A) equipped with a capillary column (HP-5ms,
2.4.3. ZrSiO2
ZrOCl (0.3 mol L−1) solution was added into ammonia solution
(5 mol L ) drop by drop. The preparation was digested for 96 h
at 100 C. The silica was dissolved from the glass round-bottomed
flask and re-deposit on the zirconia precipitate during the high tem-
perature aging process. The post treatment was as the same as the
2
−
1
◦
3
0 m × 0.25 mm × 0.25 ␮m, Agilent J&W GC Columns) and a flame
ionization detector (FID). A split injection of 5:1 was used with the
oven temperature programmed as follows: 45–60 C at 5 C/min,
◦
◦
◦
◦
◦
◦
◦
6
0 C for 1 min, 60–210 C at 3 C/min, 210–300 C at 20 C/min. The
ZrO -PM.
2

H. Wei et al. / Catalysis Today 201 (2013) 49–56
51
Ru was introduced by incipient wetness impregnation using
aqueous solutions of ruthenium trichloride. To facilitate any com-
parison, the Ru content in all catalysts was fixed at 1 wt.%. After
impregnation, the preparations were dried under vacuum for 2 h
ZrSiO
◦
◦
ZrO -HM
at 60 C. At last, they were calcined at 350 C for 6 h in a muffle
furnace and labeled Ru/ZrO -PM, Ru/ZrO -HM and Ru/ZrSiO .
ZrSiO2
2
2
2
ZrO -PM
2
4
6
8 10
30 50 70 100
Pore diameter (nm)
2
2
.5. Catalyst characterization
ZrO -HM
.5.1. BET surface area
2
The specific surface area of ZrO2 was assessed by N2 adsorption
isotherms at 77 K using QUADRASORB SI instrument produced by
Quantachrome Company. The catalyst samples prior to the adsorp-
tion measurement were degassed at 300 C for 3 h under vacuum.
ZrO -PM
2
◦
The specific surface area was obtained by N2 adsorption isotherms
and BET equation.
0
.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure (P/P0 )
2.5.2. XRD
Specimens were prepared by packing the powder samples in a
Fig. 1. Nitrogen adsorption/desorption isotherms of the ZrO2 and ZrSiO2 supports.
glass samples holder. The X-ray diffraction (XRD) spectra of the
support was obtained with X’Pert PRO instrument produced by
higher specific surface area than ZrO -PM. This phenomenon indi-
cated that the high specific surface area ZrO2 reported by Chuah
and Jaenicke [29] was caused not by the removal of defects in the
2
PANalytical. The measurements were recorded in the 2ꢀ range of
◦
1
0–90 .
ZrO2 particles through the dissolution–deposition of ZrO , but by
2
2
.5.3. TPR and CO chemisorption
The interaction between RuOx and support was studied by
SiO2 (5.29%) coating the wet ZrO(OH)2 precipitates. The silica may
dissolve from the glass round-bottomed flask and re-deposit on
the zirconia precipitate during the high temperature aging process.
Since a SiO –ZrO composite has high alkali resistance, it is reason-
temperature-programmed reduction (TPR) using a Micromeritics
Auto-Chem II 2920 apparatus (American). Prior to the measure-
ment, the samples were pretreated in Ar (99.99%, 20 ml min ) at
−
1
2
2
able that the reverse reaction, dissolution of SiO2 from SiO –ZrO ,
◦
2
2
1
20 C for 2 h. After cooling to room temperature in Ar, the gas flow
hardly proceeds in the present ZrO2 system [23]. Miller et al. [24]
was switched to 10% H in Ar and the samples were heated from
5
consumption was determined by a thermal conductivity detector.
After the TPR experiment, CO chemisorption was determined at
5
technique, in which 0.1 ml CO/He (CO: 5 vol.%) pulses of each gas
were utilized. After the CO chemisorption, transmission electron
microscopy was determined.
2
has reported high-surface-area SiO –ZrO2 prepared by the sol–gel
◦
◦
◦
2
0 C to 300 C with a temperature ramp of 10 C/min. The hydrogen
method.
ZrO2 and ZrSiO2 isothermal adsorption–desorption curve was
shown in Fig. 1. According to Fig. 1, all the supports calcined at
◦ −1
0 C in a 20 ml min stream of He using a pulsed-chemisorption
◦
5
00 C for 2 h exhibited type IV adsorption isotherms, associated
with capillary condensation taking place in mesopores, and the lim-
iting uptake over a range of high p/p . The mesoporous texture was
0
also indicated from average pore size (Table 1). According to classi-
fication of hysteresis loops from IUPAC [30], they belonged to Type
H2 loop, attributed to a difference in mechanism between conden-
sation and evaporation processes occurring in pores with narrow
necks and wide bodies, and associated with “ink bottle” pores. The
2
.5.4. TEM
Transmission electron microscopy (TEM) images were obtained
using a HT7700 operated at 100 kV. The images were used to deter-
mine the particle size of the Ru metal. The samples were ground in
an agate mortar to fine particles and then dispersed ultrasonically
in ethanol. The sample was deposited on a Cu grid covered by a
holey carbon film.
hysteresis hoop of ZrSiO was wider than that of ZrO -PM and ZrO -
2
2
2
HM, which indicated that the pore size distribution of ZrSiO2 was
broader than that of PM-ZrO2 and HM-ZrO2.
3.1.2. XRD
2.5.5. TGA
The XRD patterns of ZrO2 and ZrSiO2 were shown in Fig. 2.
The weight loss mechanism of ZrSiO2 precursor was studied
According to Fig. 2, ZrO2 prepared with PM and HM had a good
crystal and it belonged to monoclinic crystal, while ZrSiO2 had no
obvious characteristic peak and was the amorphous structure. The
diffraction peaks of ZrO -PM were higher than ZrO -HM. The peaks
by thermogravimetric analysis instrument supplied by Sygate. The
◦
sample about 200 mg was heated from room temperature to 800 C
◦
−1
−1
at a heating rate of 3 C min in an air flow of 50 ml min .
2
2
at 2-Theta = 28.2 and 31.5 corresponded to the (1 1 1) reflection.
2.5.6. XRF
XRF was used to determine Silicon content in the ZrO2 sample
with Magix 601 equipment produced by PANalytical. The perform-
ing of each sample (1.5 g) was proceeded under 30 MPa condition
for the XRF measurement.
3.1.3. TPR and CO chemisorption
TPR profiles of the catalyst was presented in Fig. 3. This clearly
suggested that the reduction of ruthenium took place in two forms.
In the TPR profile of catalyst, the first peak could be attributed to
the reduction of well-dispersed RuOx or RuO2 particles [31]. It has
been found that RuCl3 can be oxidized at the surface by air exposi-
tion at room temperature. Moreover, color changes were observed
3. Results and discussion
3.1. Characterization
3.1.1. BET
when the RuCl impregnated catalysts were exposed upon air, indi-
3
cating the transformation of the chloride into an oxide and the
formation of ruthenium oxychloride [32]. The similar modifica-
tion was observed in the preparation of Ru/ZrO2 and Ru/ZrSiO2
As shown in Table 1, the specific surface areas of ZrO -PM and
2
ZrO -HM were low and near, while ZrSiO2 possessed four times
2

5
2
H. Wei et al. / Catalysis Today 201 (2013) 49–56
Table 1
BET surface area of the supports and metal dispersion of the catalysts.
SBET (N2) (m2
g
−1
)
Total pore volume
Average pore
diameter (nm)
Silica content
(wt.%)
Catalyst
Metal dispersion
(%)
Active particle
diameter (nm)
Support
3
−1
)
(
cm
g
ZrO2-PM
ZrO2-HM
ZrSiO2
60.79
63.77
251.15
0.17
0.17
0.43
9.03
9.16
5.67
0
0
5.29
Ru/ZrO2-PM
Ru/ZrO2-HM
Ru/ZrSiO2
13.96
14.17
21.82
9.55
9.40
6.11
3
.1.4. TEM
As shown in Fig. 4, the TEM image for each catalyst was obtained
to find out the particle size of Ru metals for the Ru/ZrO -PM,
2
Ru/ZrO -HM and Ru/ZrSiO2 catalysts. In the reports of Wang [34]
2
and Hamzah [35], the Ru loading was 3 wt.% and 5 wt.%, respec-
tively, and the TEM images were able to provide with a clear view
of the Ru particles. But it was hard to identify the Ru particle in
Fig. 4, which may be because the Ru loading was only 1 wt.% and
the Ru particle was too small. The ZrO2 (1 1 1) reflection was found
ZrO -PM
2
in Ru/ZrO -PM and Ru/ZrO -HM.
2
2
ZrO -HM
2
3
.1.5. TGA
According to TG–DTG curves in Fig. 5, it indicated that the
weight loss stage of ZrSiO precursor may be divided into two parts,
ZrSiO2
2
10
20
30
40
50
60
70
80
90
◦ ◦
00–400 C and 400–500 C, respectively. The weight loss of ZrSiO
2
1
2-theta (degree)
precursor was increased rapidly by enhancing temperature from
◦ ◦
1
00 C to 400 C, which was because both the adsorbed water and
Fig. 2. XRD patterns of ZrO2 and ZrSiO2 supports.
free water were removed. And the weight loss rate (DTG) reached
◦
maximum at 160 C. The weight loss was further produced when
◦
◦
the temperature was enhanced from 400 C to 500 C. And then the
weight of ZrSiO2 was approximately stable.
catalyst. Another peak may be related with the presence in this cat-
alyst of oxidized ruthenium species strongly interacting with the
support or more possibly located in the narrowest pores of the sup-
◦
port [31,33]. After the TPR experiments carried out up to 300 C, the
3.2. Effect of supports on catalytic activity of Ru catalysts
metal dispersion and mean particle diameter were determined by
CO chemisorption at 50 C. The corresponding mean particle diam-
eter was calculated assuming a stoichiometry CO:Ru = 1:1 and a
spherical shape of Ru particles. As shown in Table 1, higher Ru
dispersion was found for Ru/ZrSiO2.
◦
−1
Under the reaction conditions of 2000 mg L PCP initial con-
◦
centration, 1.1 MPa oxygen partial pressure and 180 C, the CWAO
experiments were carried out, and the results were shown in
Fig. 6(a and b). According to Fig. 6(a), the PCP conversion rate rose
with the time moving on. PCP conversion rate reached 79.1% after
3
0 min over Ru/ZrSiO2 catalyst, while it was only 57.3% and 47.5%
over Ru/ZrO -HM and Ru/ZrO -PM catalysts, respectively. When
2
2
0
0
0
0
0
0
0
0
.18
.16
.14
.12
.10
.08
.06
.10
Ru/ZrO -PM
2
the linear fitting was done between ln(mAo/mAf) and time (mAo
:
the initial concentration of PCP, mAf: PCP concentration in reac-
tion process), it was found that PCP reaction in CWAO obeyed
the first order kinetic model [36] and the linear slope was the
reaction rate constant k of PCP in CWAO. According to Fig. 6(b),
the relationship of catalysts on reaction rate constants was as fol-
lows: kRu/ZrSiO2 ꢀ k
≈ k
. Thus, it showed that
Ru/ZrSiO2 catalyst had the higher catalytic activity in CWAO, which
Ru/ZrO -HM
Ru/ZrO -PM
2
2
Ru/ZrO -HM
2
was because the ZrSiO had the higher specific surface area. Accord-
2
ing to Fig. 6(b), the PCP reaction rate constant k of Ru/ZrSiO2 was
0
0
.08
.06
1
.6 times larger than that of Ru/ZrO -PM.
2
3.3. Effect of the calcination temperature of ZrSiO2 precursor on
catalytic activity
0
0
.04
.15
Ru/ZrSiO2
◦
Under the low temperature and pressure conditions of 180 C
and 0.1 MPa oxygen partial pressure, the effect of the calcination
temperature of ZrSiO2 precursor on catalytic activity was stud-
ied. The results were shown in Fig. 7. According to Fig. 7(a), the
catalytic activity gradually decreased as the calcination tempera-
0
0
0
.10
.05
.00
ture increased. According to Fig. 7(b), when the ZrSiO precursor
2
◦
was calcined at 400 C, the reaction rate constant of PCP was twice
larger than that of 800 C. This was because the specific surface
◦
5
0
100
150
200
250
300
o
area of ZrSiO2 decreased as the calcination temperature went up
Temperature ( C)
[
22], leading to lower catalytic activity eventually. Although the
◦
Fig. 3. TPR profiles of the catalysts.
ZrSiO2 precursor which was calcined at 400 C and loaded with Ru

H. Wei et al. / Catalysis Today 201 (2013) 49–56
53
220
215
210
205
200
195
190
185
180
TG DTG
0.56
0.48
0.40
0.32
0.24
0.16
0.08
0.00
-0.08
0
100 200 300 400 500 600 700 800
T (
)
Fig. 5. TG–DTG curves of the ZrSiO2 precursor.
possessed the highest catalytic activity, the catalyst broke into pow-
der after the CWAO reaction. According to TGA plot (Fig. 5) of ZrSiO2
◦
precursor, 500 C was chosen as the best calcination temperature.
3
.4. Effects of reaction conditions on PCP conversion
.4.1. Effect of reaction temperature
3
0
.1 MPa oxygen (1.4 times of stoichiometric oxygen demand)
was filled into a 250 ml autoclave, and then the effect of different
temperature on PCP conversion was studied. The results in Fig. 8(a)
showed that the temperature had a great effect on PCP conversion
◦
rate. PCP had no obvious conversion at 135 C and the conver-
sion rate was only 14% after 90 min. As the reaction temperature
rose, PCP conversion rate also gradually went up, and it showed an
approximate linear relationship. PCP conversion rate reached even
◦
1
00% at 195 C. As the temperature rose, PCP molecules in the solu-
tion moved more quickly which made the increasing collision and
adsorption probability between PCP and the catalytic active site,
and then resulting in the high PCP conversion.
2
1
1
1
1
1
8
6
4
2
000
800
600
400
200
000
00
00
00
00
0
(a)
1
9
8
7
00
0
0
0
Ru/ZrO -PM
2
60
Ru/ZrO -HM 50
2
40
30
20
10
0
Ru/ZrSiO
2
0
15
30
45
t(min.)
60
75
90
5
4
.0
.5
.0
.5
.0
.5
.0
.5
.0
.5
.0
(
b)
2
Ru/ZrO -PM y=0.029x-0.098 R =0.9980
2
2
4
3
3
2
2
1
1
0
0
Ru/ZrO2-HM y=0.028x+0.058 R =0.9973
2
Ru/ZrSiO y=0.046x+0.148 R =0.9986
2
Fig. 4. TEM images of the catalysts.
0
15
30
45
t (min.)
60
75
90
Fig. 6. Effect of supports on catalytic activity of Ru catalysts.

5
4
H. Wei et al. / Catalysis Today 201 (2013) 49–56
a) 100
5
(
(a)
2
155
165
175
185
y=0.008x-0.007 R =0.9939
90
80
70
60
50
40
30
20
10
0
2
y=0.012x+0.054 R =0.9976
4
3
2
y=0.023x+0.078 R =0.9958
2
y=0.047x+0.176 R =0.9953
4
500
00
=1.1MPa
2
600
700
800
2
1
0
o
-1
C
PCP=200 mg·L
T=180
Po =0.1MPa
2
0
15
30
45
60
75
90
0
15
30
45
t (min.)
60
75
90
Reaction time (min.)
(
b) 4.5
2
400
500
600
700
800
y=0.032x+0.405 R =0.9904
(b)
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
2
4.8
4.5
y=0.029x+0.267 R =0.9973
2
y=0.027x+0.200 R =0.9971
2
y=0.023x+0.237 R =0.9872
4.2
3.9
3.6
3.3
3.0
2
y=0.016x+0.189 R =0.9981
2
y=96.98x-22.32 R =0.9808
Po =1.1MPa
2
0
15
30
45
60
75
90
0
.260
0.264
0.268
0.272
000/RT
0.276
0.280
t (min.)
1
Fig. 7. Effects of ZrSiO2 precursor calcination temperature on catalytic activity.
Fig. 9. Kinetic plots for PCP in CWAO.
The effect of different reaction temperature on COD removal
was studied and the results were shown in Fig. 8(a). According to
Fig. 8(a), the temperature also had a great effect on COD removal
group Cl, resulting in the electron density of the benzene ring
reducing. So it was not easy for the free radical OH to attack the
◦
•
rate. The removal rate of COD still was 0% at 135 C after 90 min. As
reaction temperature rose, COD removal rate gradually went up.
COD removal rate reached only 44% at 195 C. It may because that
the group H of benzene was substituted by withdrawing electron
benzene ring and very difficult to form aromatic oxygen free rad-
ical and open the benzene ring [37], leading to relatively low COD
removal rate.
◦
00
(
a)100
(b) 1
PCP conversion
COD removal
90
80
70
60
50
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
Po =0.1MPa t=90min
2
o
=2000 mg·L-1
C
PCP
%
%
4
3
2
1
0
0
0
0
0
PCP conversion
COD removal
T=180
t=90min
o
-1
C
PCP=2000 mg·L
1
35
150
165
T
180
195
0.0 0.3 0.6 0.9 1.2 1.5 1.8 2.1
PO2 (MPa)
c) 1
00
100
90
(d)
155
165
(
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
1
1
75
85
80
70
C
=2000 mg·L
60 Po =1.1MPa
-
1
50
40
30
20
10
0
1
2
5
1
2
25 mg·L
50 mg·L
00 mg·L
-1
-1
-1
-1
000 mg·L
000 mg·L
Po =0.1MPa T=180ഒ
2
-
10
-10
0
15
30
45
60
75
90
0
15
30
45
t (min.)
60
75
90
t (min.)
Fig. 8. Effect of reaction conditions on PCP conversion and COD removal.

H. Wei et al. / Catalysis Today 201 (2013) 49–56
55
Fig. 10. Degradation pathways of PCP in CWAO.
3
.4.2. Effect of oxygen partial pressure
At 180 C, the effect of oxygen partial pressure on PCP conver-
and the collision probability between PCP and catalyst active site
became larger. Therefore, the decomposition of PCP in CWAO
became faster.
◦
sion in CWAO was studied and the results were shown in Fig. 8(b). It
indicated that oxygen partial pressure had a relatively great effect
on PCP conversion rate when it was less than 1.1 MPa. When oxy-
gen partial pressure was enhanced from 0.1 MPa to 1.1 MPa, the
PCP conversion rate was increased by about 20%. This was because
as oxygen partial pressure rose, the oxygen concentration in the
solution increased according to Henry’s law, and then the reaction
rate was raised. When oxygen partial pressure reached 1.1 MPa,
PCP conversion rate was 99%.
According to the curve between COD removal rate and time in
Fig. 8(b), when the oxygen partial pressure was less than 1.1 MPa,
it had a relatively great effect on COD removal rate. COD removal
rate rose from 28% to 46% when the oxygen partial pressure went
up from 0.1 MPa to 1.1 MPa. This was because the rising of oxygen
concentration in the solution increased COD removal rate. How-
ever, when oxygen partial pressure was more than 1.1 MPa, COD
removal rate was not raised any more. The oxygen on the surface
of catalyst was saturated and the concentration of the hydroxyl free
radial was kept constant. Therefore, higher oxygen partial pressure
would not have an effect on COD removal.
3.5. The study of reaction kinetics on PCP in CWAO
The degradation process of PCP in CWAO may be as follows:
PCP was adsorbed to the surface of Ru/ZrSiO catalyst and oxidized
2
•
by the hydroxyl radical OH produced by oxygen at the catalyst
surface. The polyphenols or quinones were gradually produced by
the dechlorination reaction of PCP, and then they were mineralized
•
after opening the benzene ring [10]. Acetyl radical CH COO was
3
formed at the catalyst surface and then underwent a decarboxyla-
tion reaction which was usually a slow step. The methyl radicals
were eventually oxidized to CO2 [25].
According to the data in Fig. 8(d), the linear fitting was done
between ln(mAo/mAf) and time, and the results were shown in
Fig. 9(a). The reaction rate constant k of PCP in CWAO was obtained
according to the slope of the fitted line. According to the Arrhenius
equation ln k = −Ea/RT + ln A, the linear fitting was done between
−
ln k and 1000/RT. The result in Fig. 9(b) indicated that Arrhe-
nius activation energy of PCP degradation reaction in CWAO was
−
1
9
6.98 kJ mol
.
3
.4.3. Effect of initial concentration of PCP
The effect of the initial concentration of PCP on PCP conversion
3
.6. Degradation pathways of PCP in CWAO
rate was studied under the condition of low oxygen partial pressure
of 0.1 MPa. The results were shown in Fig. 8(c). According to Fig. 8(c),
during the same reaction time, as the initial concentration of PCP
increased, PCP conversion rate gradually decreased. PCP conversion
rate was 73% after 90 min when the initial concentration of PCP was
In Fig. 10, only PCP was detected and no other specific peaks
were identified in all reaction processes by GC–MS. This may be
because the unknown intermediates were very unstable or there
was only a little during the reaction processes. The acetic acid, oxalic
acid and chlorine ion were identified by IC.
−1
2
000 mg L , while it was 92% when the initial concentration of PCP
−1
was 125 mg L . PCP concentration in the environment was gener-
ally lower, so Ru/ZrO2 catalyst prepared with HTAM could degrade
most PCP in the environment after 90 min under the conditions of
relatively low temperature and pressure.
3
.7. Life evaluation test
Life evaluation test of Ru/ZrSiO2 catalyst was carried out in
3
.4.4. Effect of reaction time
The effect of reaction time on PCP conversion rate was shown
CWAO, and the results were shown in Fig. 11. The test result
indicated that at the reaction conditions of reaction temper-
◦
in Fig. 8(d). According to Fig. 8(d), PCP conversion rate gradually
increased as the reaction time moved on and it reached respectively
6
ature = 180 C, reaction pressure = 2.0 MPa, catalyst dose = 10 ml,
−
1
−1
Vliquid = 0.33 ml min
and Vgas = 40 ml min , the PCP conversion
◦
◦
8.2% and 99% after 90 min at 165 C and 185 C.
Compared with the reaction condition of 165 C, the kinetic
was kept essentially constant. The catalyst life was more than 48 h,
indicated that the catalyst possessed a high stable performance in
CWAO.
◦
◦
energy of molecules in the solution was relatively larger at 185 C

5
6
H. Wei et al. / Catalysis Today 201 (2013) 49–56
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5
10 15 20 25 30 35 40 45 50
[
[
[
Run time (h)
5
Fig. 11. Life evaluation test of Ru/ZrSiO2 catalyst in CWAO.
1
(
4
. Conclusions
[
[
In CWAO reaction, it was found that the PCP conversion rate was
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5
2
[
(
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◦
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1
7
2
2
[
bility in the fixed-bed reactor with upflow of PCP wastewater and
air.
9
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This work was financially supported by Major State Basic
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