Catalytic oxidation of trichloroethylene over TiO2 supported ruthenium catalysts

Article abstract of DOI:10.1016/j.catcom.2015.12.015

Different types of TiO₂ (anatase, P25 and rutile) supported ruthenium catalysts were synthesized by wet impregnation and directly reduced in H₂. The distribution characteristics of ruthenium species were thoroughly studied before and after trichloroethylene oxidation. The results show that ruthenium oxide species are very unstable in the anatase phase, but quite stable in the rutile phase of TiO₂. This phenomenon results in different catalytic behaviors for the Ru/TiO₂ catalysts. The Ru/TiO₂ (P25) catalyst has the best catalytic performance among these catalysts. The complete conversion temperature of trichloroethylene is in the temperature range of 260-270°C.

Full text of DOI:10.1016/j.catcom.2015.12.015

Catalysis Communications 76 (2016) 13–18
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short communication
Catalytic oxidation of trichloroethylene over TiO2 supported
ruthenium catalysts
Jian Wang a,b, Xiaolong Liu a, , Junlin Zeng a,c, Tingyu Zhu a,
⁎
⁎
a
Beijing Research Centre of Process Pollution Control, National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Institute of Process Engineering, Chinese Academy of
Sciences, Beijing 100190, China
b
University of Chinese Academy of Sciences, Beijing 100049, China
School of Chemistry and Chemical Engineering, Guizhou University, Guiyang, Guizhou 550025, China
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Different types of TiO2 (anatase, P25 and rutile) supported ruthenium catalysts were synthesized by wet impreg-
nation and directly reduced in H2. The distribution characteristics of ruthenium species were thoroughly studied
before and after trichloroethylene oxidation. The results show that ruthenium oxide species are very unstable in
the anatase phase, but quite stable in the rutile phase of TiO2. This phenomenon results in different catalytic be-
haviors for the Ru/TiO2 catalysts. The Ru/TiO2 (P25) catalyst has the best catalytic performance among these cat-
alysts. The complete conversion temperature of trichloroethylene is in the temperature range of 260–270 °C.
© 2015 Elsevier B.V. All rights reserved.
Received 23 September 2015
Received in revised form 8 December 2015
Accepted 15 December 2015
Available online 17 December 2015
Keywords:
Ruthenium
Ru/TiO2
Catalytic oxidation
Trichloroethylene
Support effect
1. Introduction
(iii) Over et al. [10–14] provided ample evidences that CO can be
strongly adsorbed on the coordinatively unsaturated Ru sites
Volatile organic compounds (VOCs) are toxic and may cause a series
of environmental problems [1]. Catalytic oxidation is preferred for the
abatement of VOCs, because it does not implement the transfer of pol-
lutants but complete decomposition [2]. In the past decade, efforts
have been made to investigate the prospect of ruthenium-based cata-
lysts for the catalytic oxidation of VOCs, due to the low price and fasci-
nating properties of ruthenium [3–6]. Although the ruthenium-based
catalysts show high activities, catalyst deactivation is also widely re-
ported [4,6].
However, the knowledge about active state of ruthenium for oxida-
tion reactions is mostly obtained through CO oxidation over ideal single
crystal surfaces because of the simplicity [7–14]. The main viewpoints
can be summarized as follows:
(Rucus) of RuO2(110) and RuO2(100)-c(1 × 1) surface, and oxy-
gen atom on the bridge site (Obr)or on-top site (Oot) will react
with adsorbed CO. The activity loss is caused by phase transfor-
mation of the active RuO2 to an inert RuO2(100)-c(2 × 2) struc-
ture (without Rucus sites). And the RuO2(100)-c(2 × 2) is formed
by surface reconstruction of RuO2(100)-c(1 × 1).
Obviously, these conclusions are not fully consistent. Therefore,
there are heavy debates on the understanding regarding the activation
and the deactivation mechanism regarding actual ruthenium-based cat-
alysts [15–21]. The results of Rosenthal et al. [22] indicate that the be-
havior of polycrystalline Ru/RuO2 is very complicated, and the above
mechanism may coexist. Although the initial activities of ruthenium
may decrease, it has been reported that stable states can be eventually
achieved for ruthenium-based materials under relatively low tempera-
ture (e.g., b400 °C) in total oxidation reactions [3–5]. Thus, ruthenium-
based catalysts are promising candidates for the catalytic oxidation of
VOCs.
Debecker et al. [6] reported a nano-RuO2/TiO2 catalyst for propane
oxidation. They found that the homogeneously distributed RuO2 parti-
cles migrate from anatase to rutile phase of TiO2 at over 150 °C. Because
most of the applied noble metal catalysts are supported to increase the
exposure of active components, and also because TiO2 is an important
(i) Peden and Goodman [7] suggested that the Ru(0001)-(1 × 1)
oxygen surface is active for CO oxidation, and the formation of
RuO2 causes deactivation.
(ii) Böttcher et al. [8,9] proposed that a so called transient surface
oxide (TSO) is active, which can be described as oxygen after
completion of the Ru(0001)-(1 × 1) oxygen structure but before
the formation of ordered RuO2.
⁎
Corresponding authors.
E-mail addresses: liuxl@ipe.ac.cn (X. Liu), tyzhu@ipe.ac.cn (T. Zhu).
http://dx.doi.org/10.1016/j.catcom.2015.12.015
1566-7367/© 2015 Elsevier B.V. All rights reserved.

14
J. Wang et al. / Catalysis Communications 76 (2016) 13–18
commercial catalyst support, a clear understanding of the support effect
in TiO2 is important. The migration of ruthenium oxide species may
have a great influence on the catalytic performance because ruthenium
is easy to be oxidized. And to the best of our knowledge, no studies
concerning the support effect in different types of TiO2 supported ruthe-
nium catalysts for VOC oxidation have been reported.
In this article, Ru/TiO2 catalysts using different types of TiO2 (ana-
tase, P25 and rutile) as the supports were synthesized. Activity evalua-
tions and long-term stability tests were conducted for trichloroethylene
oxidation. The results suggest that the catalytic performance is greatly
influenced by the supports, which is due to the migration of ruthenium
oxide species.
where X is the conversion, C(in) and C(out) are the inlet and outlet con-
centration of the gaseous reactant and C(COx) (x=1,2) is the outlet
concentration of CO2 or CO (when mentioned as COx it is the summation
of these products).
The concentrations of HCl were on-line measured with a Fourier
transform infrared spectrometer (Nicolet 6700, Thermo Scientific)
equipped with a 2 m optical path gas cell. And the concentrations of
Cl2 were calculated by the effluent stream bubbling through a
0.0125 M NaOH solution followed by titration with ferrous ammonium
sulfate (FAS) using N,N-diethyl-p-phenylenedi-amine (DPD) as indica-
tor [23].
3. Results and discussion
2. Experimental
Table 1 shows the characterization data for various samples. The SBET
of the fresh catalysts decrease slightly compared with the supports. And
it was found that the actual ruthenium contents of the catalysts are sim-
ilar to the calculated values (within the error range). The XRD patterns
of the Ru/TiO2 catalysts (Fig. S1) reveal pure anatase phase and rutile
phase for the Ru1(WIR-450)/Anatase and Ru1(WIR-450)/Rutile catalysts,
respectively. And the data of the Ru1(WIR-450)/P25 catalyst shows typi-
cal binary phases. No diffraction peaks assignable to ruthenium species
can be found among these catalysts. TEM characterization for the Ru/
TiO2 catalysts was obtained. As shown in Fig. 1, ruthenium particles
are homogenously distributed, but the average particle size of metallic
ruthenium for each catalyst is not the same, which is between 1 and
2 nm (Table 1). Generally, the ruthenium particles on the support
with larger SBET are smaller compared with those on the support with
2.1. Catalyst preparation and characterization
Three types of TiO2 were calcined at 500 °C for 2 h. The resultant ma-
terials, referred to as Anatase (Aladdin, N99.5%; average particle size,
21 nm; specific surface area, 62.4 m2/g; anatase), P25 (Degussa,
N99.5%; average particle size, 24 nm; specific surface area, 51.3 m2/g;
anatase/rutile ≈ 84/16) and Rutile (Aladdin, N99.8%; average particle
size, 40 nm; specific surface area, 31.8 m2/g; rutile) were used as the
supports, and Ru(NO)(NO3)3 (1.5 mg/mL, Alfa-Aesar) was used as the
ruthenium precursor. Briefly, the respective TiO2 particles were stirred
with Ru(NO)(NO3)3 in solution at room temperature. After impregna-
tion, the samples were dried and reduced in a 5 vol.% H2/Ar stream at
450 °C for 6 h, affording TiO2 supported ruthenium catalysts denoted
as Rux(WIR-450)/Support, where x is the weight percentages of Ru (calcu-
lated), and Support is the type of TiO2 used.
The ruthenium content was verified by an inductively coupled
plasma-optical emission spectrometer (ICP-OES, Optima 5300DV, Perkin
Elmer). The porous texture was characterized by N2 adsorption at 77 K in
an automatic surface area and porosity analyzer (Autosorb iQ,
Quantachrome). The X-ray diffraction (XRD) patterns were recorded
on a powder diffractometer (Rigaku D/Max-RA) using Cu Kα radiation
(40 kV and 120 mA). Transmission electron microscope (TEM), high-
resolution TEM (HR-TEM) were used with a FEI Tecnai G2 F20 field emis-
sion electron microscope operating at 200 kV, and X-ray photoelectron
spectroscopy (XPS) measurements were made on a photoelectron spec-
trometer (ESCALAB 250, Thermo Scientific) by using AlKα (1486.8 eV)
radiation as the excitation source (powered at 10 mA and 15 kV).
smaller SBET
.
The results of these catalysts for trichloroethylene oxidation are
shown in Fig. 2. The activity evaluation was carried out by heating at 1
°C/min and repeated for several cycles. The carbon balance ( 1%)
could be fulfilled when the temperature was above 150 °C. Fig. 2a
shows that the activity of the Ru1(WIR-450)/Anatase catalyst decreases
in each run. And the COx yields are not equal to trichloroethylene con-
versions, indicating the formation of organic by-products with a maxi-
mum amount of about 20%. Fig. 2b shows that the Ru1(WIR-450)/P25
catalyst can finally achieve stable-states as indicated by the catalytic
performance of the third and fourth runs. Again, the COx yields of this
catalyst are also much lower than the trichloroethylene conversions in
the temperature range of 210–260 °C. As for the Ru1(WIR-450)/Rutile
catalyst (Fig. 2c), the activity decreases continuously after each run.
But the extent of the decline is quite small after the first run. And it is in-
teresting that the formation of the organic by-products is obviously
decreased.
2.2. Catalytic oxidation of trichloroethylene
Catalytic reactions were carried out in a quartz tube, single-pass
fixed-bed micro reactor (4 mm i.d.) with a sieve plate in the middle.
The catalyst mixed with quartz sands was placed on the sieve plate.
The reactor was heated by an electric furnace, and the temperature
was monitored through a K-type thermocouple next to the catalyst
bed. Trichloroethylene/Ar was introduced from a gas cylinder, while
water vapor was introduced by passage of Ar through a heated satura-
tor. The reactant and products (CO2, CO and organic by-products)
were on-line analyzed with a gas chromatograph (GC 2010, Shimadzu)
equipped with a methanizer (MTN, Shimadzu) and two flame ioniza-
tion detectors, and off-line with a gas chromatograph–mass spectrome-
ter (GCMS-QP2010 Plus, Shimadzu). The inlet concentration of
trichloroethylene was calibrated at 500 5 ppm through a by-pass.
The conversion of trichloroethylene was calculated using Eq. (1) and
CO2 as well as CO yield was defined by Eq. (2), respectively.
Long-term stability tests for these catalysts after activity evaluations
were performed. As shown in Fig. 3, the conversion of trichloroethylene
over the Ru1(WIR-450)/Anatase catalyst decreases substantially with
Table 1
Characterization data for various samples.
Catalyst
Ruthenium content SBET
Pore volume dRu
(wt.%)a
(m2/g)b (cm3/g)c (nm)d
Ru1(WIR-450)/Anatase
Ru1(WIR-450)/P25
Ru1(WIR-450)/Rutile
Ru1(WIR-450)/Anatase
(used)
1.0 (0.98)
1.0 (1.02)
1.0 (1.05)
1.0 (1.03)
60.2
49.7
29.6
61.2
0.41
0.51
0.18
0.39
1.1
1.4
2.0
1–20
Ru1(WIR-450)/P25 (used)
Ru1(WIR-450)/Rutile (used) 1.0 (1.01)
1.0 (1.05)
49.1
30.1
0.52
0.18
2–7
2–3
a
The data in the parentheses show the accurate values.
The specific surface area (SBET) was calculated from the N2 adsorption isotherm using
b
½CðinÞ ꢀ CðoutÞꢁ
X ¼
ꢂ 100%
ð1Þ
ð2Þ
the Brunauer-Emmett-Teller (BET) equation.
CðinÞ
c
The pore volume was determined from the N2 desorption isotherm using the Barrett–
Joyner–Halenda (BJH) method.
CðCOxÞ
d
The average particle size of ruthenium (dRu)was determined after the used catalysts
COx yields ¼
ꢂ 100%ðx ¼ 1; 2Þ
½2 ꢂ CðinÞꢁ
being reduced in H2.

J. Wang et al. / Catalysis Communications 76 (2016) 13–18
15
Fig. 1. TEM micrographs of the Ru/TiO2 catalysts. (a) Ru1(WIR-450)/Anatase. (b) Ru1(WIR-450)/P25. (c) Ru1(WIR-450)/Rutile.
time. In contrast, the activity of the Ru1(WIR-450)/P25 catalyst is stable.
These observations are consistent with the above temperature cycle re-
sults. However, the activity of the Ru1(WIR-450)/Rutile catalyst decreases
at first, but then increases slightly. Nevertheless, no obvious changes can
be observed in ruthenium content, SBET and pore volume of the used
catalysts compared with the fresh ones (Table 1). Therefore, the used
catalysts were characterized by TEM (Fig. S2), but ruthenium species
cannot be found. And it is because of that, the metallic ruthenium is ox-
idized into ruthenium oxide species (see the XPS results in Fig. S3),
which often have a low contrast.
Hence, the used catalysts were reduced in a 5 vol.% H2/Ar flow at 300
°C, and then characterized by TEM and HR-TEM as shown in Fig. 4. In
Fig. 4a, the used Ru1(WIR-450)/anatase catalyst shows significant
sintering (some small ruthenium particles still exist). It should be point-
ed out that the ruthenium species of the used catalysts are oxidized, and
the severely sintered Ru1(WIR-450)/anatase catalyst shows the diffrac-
tion peaks of RuO2 (Fig. S1). In Fig. 4c, it is also found that aggregation
of ruthenium species occurs for the used Ru1(WIR-450)/P25 catalyst,
but this system can be described as moderate sintering. Fig. 4d shows
clear lattice fringes of the TiO2 particles and metallic ruthenium (corre-
sponding to the yellow dotted line area in Fig. 4c). The lattice spacing of
the sample with ruthenium is 0.21 nm, and the lattice spacing of the
sample containing a few ruthenium species is 0.35 nm, which is consis-
tent with that of the rutile (210) and anatase (101) crystal planes of
TiO2, respectively. Therefore, the ruthenium species are mostly distrib-
uted in the rutile phase of P25, and the ruthenium oxide species can
be described as being captured by the rutile phase of P25 (about 20%
of the P25-TiO2 is the rutile phase). In Fig. 4e, there is only a small degree
of sintering for the Ru1(WIR-450)/Rutile catalyst. These results indicate
that the rutile phase of TiO2 can better maintain the original morpholo-
gy of ruthenium oxide species.
Fig. 2. Trichloroethylene conversion as a function of temperature for the Ru/TiO2 catalysts
(500 ppm trichloroethylene, 20 vol.% O2, balance Ar; 100 mg catalyst; WHSV
60,000 mL g−1 h−1, 1 °C/min).
Fig. 3. Long-term stability tests for the Ru/TiO2 catalysts at 240 °C (500 ppm trichloroeth-
ylene, 20 vol.% O2, balance Ar; 100 mg catalyst; WHSV 60,000 mL g−1 h−1).

16
J. Wang et al. / Catalysis Communications 76 (2016) 13–18
Fig. 4. TEM and HR-TEM micrographs of the used Ru/TiO2 catalysts after reduction. (a–b) Ru1(WIR-450)/Anatase. (c–d) Ru1(WIR-450)/P25. (e–f) Ru1(WIR-450)/Rutile.
As suggested by Over et al. [16], the deactivation of ruthenium spe-
Ru1(WIR-450)/Rutile catalysts because of being severely sintered. How-
ever, the ruthenium oxide species of the Ru1(WIR-450)/Rutile catalyst
seem to undergo slow sintering even at the end of the stability test, be-
cause the particle sizes of the ruthenium oxide species of this catalyst
are very small. The migration of ruthenium oxide species in the rutile
phase of TiO2 does not occur when the particle size of ruthenium
oxide species is above 2–3 nm. So the Ru1(WIR-450)/P25 catalyst exhibits
the highest stability.
Another interesting phenomenon is that, the activity of the
Ru1(WIR-450)/Rutile catalyst which has the best ruthenium dispersion
is lower than that of the Ru1(WIR-450)/P25 catalyst. This phenomenon
can be explained through particle size effect which may exist in ruthe-
nium oxide species. For instance, Pt0 atoms exposed to the outmost
layer of large Pt0 particles are far more active than the ones in the
cies can be attributed to the formation of the inert RuO2(100)-c(2 × 2)
structure. So the initial activity losses for the Ru/TiO2 catalysts could
have resulted from the oxidation in the activity evaluations, and chlori-
nation of the catalysts may also play an important role. But the Ru1(WIR-
450)/P25 catalyst can eventually achieve stable states. Hence, this indi-
cates that the activity changes for the other two catalysts are caused
by the migration of ruthenium oxide species. The ruthenium oxide spe-
cies are quite unstable in the anatase phase of TiO2, but quite stable in
the rutile phase. A reasonable explanation is that, the rutile phase of
TiO2 has plenty of lattice defects on the surface and shares similar crystal
cell parameters with RuO2, thus the interaction between them is
extremely strong [24]. Therefore, the stability of Ru1(WIR-450)/Anatase
catalyst is poor compared with that of the Ru1(WIR-450)/P25 and

J. Wang et al. / Catalysis Communications 76 (2016) 13–18
17
same position of small Pt0 particles [25] because the abilities to activate
tetrachloroethylene and
a
small amount of pentachloroethane
the reactants are stronger. Thus, it is possible that the catalyst with large
metal or metal oxide particles is more active than that with small ones,
even though the latter exposes more active sites. Sintering will reduce
the number of the active sites on the one hand and change (speculative-
ly increase) the activities of the ruthenium oxide species exposed on the
outmost layer on the other hand. Hence, the combined effects lead to
the change of the activities for the Ru/TiO2 catalysts. Therefore, the ac-
tivity of the Ru1(WIR-450)/Anatase catalyst is the lowest due to lack of
active sites, and the Ru1(WIR-450)/P25 catalyst is more active than the
Ru1(WIR-450)/Rutile catalyst because of the moderate sintering. It can
also be noticed that the Ru1(WIR-450)/Anatase and Ru1(WIR-450)/P25
catalysts produce more by-products than the Ru1(WIR-450)/Rutile cata-
lyst (Fig. 2), indicating that the large ruthenium oxide particles may act
as “moderate” adsorption sites. These results suggest that particle size
effect exists for ruthenium oxide species. And it also indicates that the
activity of a rutile-TiO2 supported ruthenium catalyst can be promoted
by altering the particle size of ruthenium species.
Generally, water vapor exists in the inlet feed of VOCs when a cata-
lyst is actually applied, which may have great effects [26]. Therefore, we
studied the effects of water vapor on trichloroethylene oxidation over
the Ru1(WIR-450)/P25 catalyst as shown in Fig. 5. The selectivity to chlo-
rinated by-products can be deduced from the differences between the
trichloroethylene conversions and COx yields at various temperatures.
In the absence of additional water vapor (Fig. 5a), CO2 holds an abso-
lutely majority in the COx yields, but tens of ppm of CO can also be de-
tected, and approximately 25% of the trichloroethylene is converted to
organic by-products in the outlet stream at 230 °C. With the increase
of temperature, the ratio of HCl in inorganic chlorine decreases to
about 10%, and the organic by-products mainly consist of
(Fig. 5b). In the presence of additional water vapor (Fig. 5c), it can be ob-
served that the activity of the catalyst is suppressed, and a reasonable
explanation is that the additional water vapor can compete with the re-
actants (trichloroethylene and O2) for the active sites. However, the COx
yields are almost equal to the trichloroethylene conversions in the
whole studied temperature, and there is hardly any CO that can be de-
tected. Meanwhile, the ratio of HCl in inorganic chlorine increases com-
pared with that in the absence of additional water vapor (Fig. 5d), but
the overall trend is not changed. Besides, the formation of the organic
by-products (especially tetrachloroethylene) is greatly reduced. Com-
pared with the one used in the absence of additional water vapor, no ob-
vious changes in ruthenium oxide species can be found, but the organic
and inorganic chlorine species are reduced (Fig. S3 and Table S1). These
results indicate that the chlorine species on the catalyst surface can be
removed by water vapor. Thus, it will inhibit the formation of the organ-
ic by-products. The formation of pentachloroethane may be due to the
tetrachloroethylene and HCl addition or trichloroethylene and Cl2 addi-
tion, so the introduction of additional water vapor will change the rela-
tive ratios of the by-products. Based on the above results, the major
effects of water vapor on the reaction can be summarized as follows:
(i) compete with the reactants for the active sites; (ii) improve the se-
lectivities to COx and HCl; and (iii) change the relative ratios of the or-
ganic by-products.
As shown in Table 2, the 90% conversion temperature (T90) of tri-
chloroethylene over the Ru1(WIR-450)/P25 catalysts is much lower
than that of the previously reported catalysts even in the case of the
highest space velocity. Co is easy to combine with chlorine, resulting
in the activity losses. The advantage of V2O5/TiO2 catalysts in the catalyt-
ic oxidation of Cl-VOCs is that VOx species have a strong ability to resist
Fig. 5. Trichloroethylene conversion, COx yields, distribution of the organic by-products and ratio of HCl in inorganic chlorine as a function of temperature over the Ru1(WIR-450)/
P25catalyst in the (a–b) absence and (c–d) presence of additional water vapor (1.5 vol.%). (500 ppm trichloroethylene, 20 vol.% O2, balance Ar; 100 mg catalyst; WHSV
60,000 mL g−1 h−1, steady-states).

18
J. Wang et al. / Catalysis Communications 76 (2016) 13–18
Table 2
Data of research articles on trichloroethylene oxidation.
Catalyst
Concentration (ppm)
WHSV (mL g−1 h−1
)
T90 (°C)
Ref. no.
Co2AlOx
1000
1000
1091
1091
500
35,300
30,000
46,800
46,800
60,000
340
372
495
375
249
[32]
[33]
[34]
[35]
3.5 wt.% V2O5/TiO2
0.5 wt.% Pt/γ–Al2O3
0.5 wt.% Ru/γ–Al2O3
1 wt.% Ru/TiO2 (P25)
This work
chlorine poisoning. But the catalytic activities of these catalysts are rel-
atively low, giving a large amount of CO as one of the oxidation products
[27,28]. Pt-based materials exhibit high activities in the catalytic oxida-
tion of non-chlorinated VOCs, but the activities of these catalysts are
also strongly inhibited by chlorine. For example, the total conversion
temperature (T100) of toluene over a Pt/γ–Al2O3 catalyst can be lower
than 230 °C [29], but the T100 of chlorobenzene is above 375 °C [27].
According to the previous report [3], the Ru/γ–Al2O3 catalyst will
show severe sintering during the calcination or oxidation process,
which is very similar with the Ru1(WIR-450)/Anatase catalyst, thus γ-
Al2O3 is not a good catalyst support for ruthenium species in oxidation
reactions at high temperature. Therefore, the Ru1(WIR-450)/P25 catalyst
reported in this paper can retain a relatively good dispersion of rutheni-
um oxide species, and also because ruthenium oxide species can effec-
tively remove chlorine from the active sites (industrially applied as
active species for the Deacon process, 2 HCl + 1/2 O2 = Cl2 + H2O
[24]), thus having good performance in the catalytic oxidation of tri-
chloroethylene. In this work, the fresh catalysts with relatively small
particles of metallic ruthenium were fully oxidized (Fig. S3). With Cl-
VOCs as reactants, the ruthenium oxide species are chlorinated, so the
active species can be described as chlorinated ruthenium oxide species.
Over et al. [30] reported RuO2 as active species for the Deacon process
and suggested that Obr of RuO2 can be replaced by Cl. Meanwhile, the
adsorbed HCl and O2 (dissociated into O atoms) on Rucus sites can
react with each other through the Langmuir–Hinshelwood mechanism
[31]. We believe that the Deacon process and the reaction proposed in
this article may possess a similar pathway. The verification test is cur-
rently being performed in our laboratory.
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.catcom.2015.12.015.
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4. Conclusions
Different types of TiO2 (anatase, P25 and rutile) supported rutheni-
um catalysts with homogeneously distributed ruthenium particles
were synthesized. These catalysts are very active for trichloroethylene
oxidation, but it was found that ruthenium oxide species formed during
the reaction are very unstable in the anatase phase of TiO2. The rutile
phase of TiO2 has a similar structure with RuO2, thus better maintaining
the morphology of ruthenium oxide species. And particle size effect ex-
ists for ruthenium-based materials. Besides, the existence of additional
water vapor will increase the formation of HCl and greatly reduce the
amount of tetrachloroethylene and pentachloroethane as the organic
by-products, but also suppress the catalytic activity.
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This work was supported by the Strategic Priority Research Program
of the Chinese Academy of Sciences (No. XDB05050100) and the Na-
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