Polyoxometalate as effective catalyst for the deep desulfurization of diesel oil

Article abstract of DOI:10.1016/j.cattod.2009.03.011

Aiming at the deep desulfurization of the diesel oil, a comparison of the catalytic effects of several Keggin type POMs, including H₃PW_xMo_12-xO₄₀ (x = 1, 3, 6), Cs_2.5H_0.5PW₁₂O₄₀, and H₃PW₁₂O₄₀, was made, using the solution of DBT in normal octane as simulated diesel oil, H₂O₂ as oxidant, and acetonitrile as extractant. H₃PW₆Mo₆O₄₀ was found to be the best catalyst, with a desulfurization efficiency of 99.79% or higher. Hence, it is promising for the deep desulfurization of actual ODS process. The role of the main factors affecting the process including temperature, O/S molar ratio, initial sulfur concentration, and catalyst dosage, was investigated, whereby the favourable operating conditions were recommended as T = 60 °C, O/S = 15, and a catalyst dosage of 6.93 g (H₃PW₆Mo₆O₄₀)/L (simulated diesel). With the aid of GC-MS analysis, sulfone species was confirmed to be the only product after reaction for 150 min. Furthermore, macro-kinetics of the process catalyzed by H₃PW₆Mo₆O₄₀ was studied, from which the reaction orders were found to be 1.02 to DBT and 0.38 to H₂O₂, and the activation energy of the reaction was found to be 43.3 kJ/mol. Moreover, the catalyst recovered demonstrated almost the same activity as the fresh.

Full text of DOI:10.1016/j.cattod.2009.03.011

Catalysis Today 149 (2010) 117–121
Contents lists available at ScienceDirect
Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Polyoxometalate as effective catalyst for the deep desulfurization of diesel oil
*
Rui Wang , Gaofei Zhang, Haixia Zhao
School of Environmental Science & Engineering, Shandong University, Jinan, 250100, PR China
A R T I C L E I N F O
A B S T R A C T
Article history:
Aiming at the deep desulfurization of the diesel oil, a comparison of the catalytic effects of several Keggin
type POMs, including H3PWxMo12ꢀxO40 (x = 1, 3, 6), Cs2.5H0.5PW12O40, and H3PW12O40, was made, using
the solution of DBT in normal octane as simulated diesel oil, H2O2 as oxidant, and acetonitrile as
extractant. H3PW6Mo6O40 was found to be the best catalyst, with a desulfurization efficiency of 99.79%
or higher. Hence, it is promising for the deep desulfurization of actual ODS process. The role of the main
factors affecting the process including temperature, O/S molar ratio, initial sulfur concentration, and
catalyst dosage, was investigated, whereby the favourable operating conditions were recommended as
T = 60 8C, O/S = 15, and a catalyst dosage of 6.93 g (H3PW6Mo6O40)/L (simulated diesel). With the aid of
GC–MS analysis, sulfone species was confirmed to be the only product after reaction for 150 min.
Furthermore, macro-kinetics of the process catalyzed by H3PW6Mo6O40 was studied, from which the
reaction orders were found to be 1.02 to DBT and 0.38 to H2O2, and the activation energy of the reaction
was found to be 43.3 kJ/mol. Moreover, the catalyst recovered demonstrated almost the same activity as
the fresh.
Available online 19 April 2009
Keywords:
Oxidative desulfurization
Hydrogen peroxide
Polyoxometalate
ß 2009 Elsevier B.V. All rights reserved.
1. Introduction
conditions of high temperature, high pressure and high hydrogen
consumption, as well as the use of more active catalyst or longer
The presence of sulfur compounds in transportation fuels is
recognized as a major source of SOx which contributes to air
pollution, acid rain and damages exhaust after-treatment devices.
The global need for clean fuels requires the minimization of the
sulfur level in transportation fuels. In the past decade, the
specifications for sulfur in diesel have undergone dramatic
revisions in many countries. According to the legislations in Japan
and Europe, the sulfur content in diesel was limited to a maximum
of 50 ppmw by 2005, and further to 10 ppmw by 2007 [1]. Whereas
in the US, the EPA regulations had cut the highway diesel fuel
sulfur from 500 ppmw down to 15 ppmw by June 2006 [2]. In the
long run, these restrictions are only a milestone before the society
at large stepping on the road of zero sulfur fuel.
To meet the requirements of more and more stringent
legislations, clean fuels research including ultra-deep desulfuriza-
tion of diesel is currently being conducted by worldwide
researchers as a challenging subject. The conventional process
for the removal of organosulfur is known as catalytic hydro-
desulfurization (HDS). HDS is highly efficient in removing thiols,
sulfides and disulfides, but less effective for dibenzothiophene
(DBT) and its derivatives with steric hindrance on the sulfur atom
(refractory organosulfur compounds) [3,4]. Severe operating
residence time are inevitably required for HDS to produce ultra-
low sulfur fuel. However, the implementation of these alternatives
requires huge capital investment. Hence, it is desirable to develop
alternative more energy-efficient deep desulfurization processes.
Potential deep desulfurization processes other than HDS
include, but are not limited to, adsorption [2,5], extraction [1],
oxidation [6–16], and bioprocesses [6]. Oxidative desulfurization
(ODS) combined with extraction, carried out in biphasic system, is
one of the most promising desulfurization processes [1,6,13].
Compared with conventional HDS, ODS requires very mild
conditions as ambient temperature and atmospheric pressure. In
the ODS process, the refractory organosulfur compounds can be
readily oxidized to their corresponding sulfoxides and sulfones,
which can be removed by extraction or adsorption. The commonly
used oxidant in ODS is H2O2, since it is cheap, environmentally
compatible, and commercially available. In very recent years,
polyoxometalates (POMs), renowned as green catalysts in many
processes, have been attracting worldwide attentions for their
effectiveness in ODS with H2O2 [11,13,17–21]. POMs belong to a
large class of nanosized metal-oxygen cluster anions, formed by a
self-assembly process typically in an acidic aqueous solution [22].
Among numerous applications of POMs, catalysis is by far the most
important. However, reported ODS processes catalyzed by POMs
are quite limited to date.
In this paper, several Keggin type POMs were evaluated as
catalysts for the oxidative removal of DBT from simulated diesel oil
* Corresponding author. Tel.: +86 531 88364513.
E-mail address: ree_wong@hotmail.com (R. Wang).
0920-5861/$ – see front matter ß 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.cattod.2009.03.011

118
R. Wang et al. / Catalysis Today 149 (2010) 117–121
in a biphasic system. H3PW6Mo6O40 was found to be the best
catalyst, with a desulfurization efficiency of 99.79% or higher.
Main factors affecting the process were investigated. Sulfone
species was confirmed to be the only product after reaction for
150 min. From macro-kinetic study of the process catalyzed by
H3PW6Mo6O40, values of the reaction orders and activation energy
were obtained. Moreover, the catalyst recovered demonstrated
almost the same effect as the fresh. As to the knowledge of the
authors, no similar report can be found in open literatures.
temperatures for GC-FID tests were set as 334 8C for both the
injector and the detector, and 280 8C for the oven. The concentra-
tion of DBT was quantified by external standard method. The
product derived from DBT oxidation by H2O2 was analysed using
Agilent HP-6890N/MS-5793 GC–MS analyser.
3. Results and discussion
3.1. POMs confirmation
2. Experimental
As to the H3PWMo11O40, H3PW3Mo9O40 and H3PW6Mo6O40
prepared, excluding the presence of Na+ by ICP analyses, the
cations were confirmed to be H+ only. Furthermore, the molar
ratios of P, W, Mo were confirmed to agree with the desired ratios.
In polyoxometalate chemistry, the IR spectroscopy is extensively
used for the purpose of finger printing and structural elucidation
[23]. The most characteristic region of the spectrum is 1100–
700 cmꢀ1 where adsorptions due to metal-oxygen stretching
vibrations occur. In the IR spectra of the H3PWxMo12ꢀxO40 (x = 1, 3,
6) prepared as shown in Fig. 1, broad peaks can be observed in the
region 3600–3100 cmꢀ1 and 1650–1550 cmꢀ1. These peak regions
correspond to those of water. Assignments for other peaks are
1070 cmꢀ1 for P–O, 965 cmꢀ1 due to Mo O, 873, 788 cmꢀ1 due to
Mo–O–Mo. The W–O adsorption peak is masked by that of the Mo–
O adsorption peak [24]. Hence, the desired phosphotungstomo-
lybdic acids with Keggin structure can be confirmed according to
the presence of these adsorption peaks as fingerprint. Similar to
many literature methods [22] for the preparation of mixed-
addenda POMs, each of the mixed-addenda POMs prepared in this
study is not pure substance but a mixture of Keggin heteropoly
acids, in which the species with the desired formula predominates.
The prepared Cs2.5H0.5PW12O40 retains the anion portion of the
parent compound used, i.e. H3PW12O40, and therefore possesses
the same Keggin structure. According to the ICP analysis results,
the Cs/P molar ratio was 2.5, therefore the desired product was
obtained.
2.1. Preparation of polyoxometalates
The POMs employed in this study include phosphotungstomo-
lybdic acids (H3PWxMo12ꢀxO40, x = 1, 3, 6), cesium phosphotung-
state (Cs2.5H0.5PW12O40) and phosphotungstic acid (H3PW12O40).
The phosphotungstic acid was purchased reagent, the rest were
prepared.
Phosphotungstomolybdic acids with various W content (x = 1,
3, 6) were prepared by the following procedure. Stoichiometric
amounts of Na2WO4, Na2MoO4 and H3PO4 were dissolved in
deionized water under agitation for 30 min. After adjusting the pH
value to 1.0 through the addition of 0.5 mol/L HCl solution, the
resultant solution was refluxed at 100 8C for 6 h, then cooled to
below 5 8C. Subsequently, an extractant of ethyl ether was added,
then a favourable amount of dilute HCl solution was dripped
slowly into the mixture under vigorous agitation. Thus, the desired
product was extracted as an ether-coordinated complex. Adding a
certain amount of dilute H2SO4 solution to the extracted complex,
removing the ethyl ether at 80 8C in a water bath by evaporation,
the phosphotungstomolybdic acids were crystallized in a drier and
collected by filtration.
The preparation of Cs2.5H0.5PW12O40 required the stoichio-
metric addition of Cs2CO3 solution drop by drop into the bulk
solution of H3PW12O40 under agitation at 50–80 8C for 1.5 h. As the
reaction proceeds, a white precipitate could be observed. The
resultant suspension was laid overnight, then the precipitate was
separated out by centrifugation. After having been washed for
several times with deionized water, the precipitate was dried first
at 85 8C in a water bath, then at 105 8C in a drying oven, before
stored for use.
3.2. Comparison of the POMs as desulfurization catalyst
A comparison of the catalytic effects of the prepared POMs on
the oxidation of DBT by H2O2 was made according to the
experiments carried out at 60 8C for 60 min, using the above-
mentioned experiment system with an initial sulfur concentration
of 500 ppmw and an O/S molar ratio of 15. The O/S molar ratio, viz.
the ratio of the number of moles of oxygen atom in H2O2 to that of
sulfur atom in sulfur compound, can be calculated as 2[H2O2]/[S],
where molar concentration is used. For all the experiments, unless
2.2. Characterization of the prepared POMs
The H3PWxMo12ꢀxO40 (x = 1, 3, 6) prepared were analysed using
a Thermo Nicolet Avatar 370 FT-IR instrument and a Perkin Elmer
ICP analyser, respectively. The Cs2.5H0.5PW12O40 prepared was
analysed using the ICP analyser only.
2.3. Experimental method
The solution of DBT in normal octane was used as simulated
diesel oil, in which the sulfur content was set by fixing the dosage
of DBT. The oxidation reactions were carried out in a three-necked
250 mL round-bottomed flask immersed in a thermostatically
controlled water bath. The middle neck connected with a water
condenser tube; the other two side necks were closed with glass
stoppers. The liquid in the flask was continually and vigorously
stirred at
a constant speed by a magnetic agitator. The
polyoxometalate was dissolved in an aqueous hydrogen peroxide
with needed amount of H2O2 and mixed with 60 mL of acetonitrile.
The oxidation reactions were started by further addition of 60 mL
of the simulated diesel oil into the above mixture. During the
reactions, the DBT concentrations in the normal octane phase were
analysed by a GC-FID equipped with a capillary column. The
Fig. 1. IR spectra of the H3PWxMo12ꢀxO40 (x = 1, 3, 6) prepared: (a) H3PMo12O40
(purchased), (b) H3PWMo11O40, (c) H3PW3Mo9O40, (d) H3PW6Mo6O40
.

R. Wang et al. / Catalysis Today 149 (2010) 117–121
119
Table 1
Catalytic effects of POMs on the oxidation of DBT by H2O2.
POMs
Desulfurization efficiency (%)
H3PW12O40 (purchased)
Cs2.5H0.5PW12O40
H3PWMo11O40
99.23
70.50
98.80
99.22
99.79
H3PW3Mo9O40
H3PW6Mo6O40
otherwise specified, the amount of catalyst used was 1% the mass
of normal octane. The desulfurization efficiency in this study refers
to the percentage ratio of sulfur concentration decrease in the
normal octane phase to its initial sulfur concentration.
From the results listed in Table 1, it can be seen that the catalytic
performance of H3PWxMo12ꢀxO40 (x = 1, 3, 6) follows the order of
Fig. 3. The effect of O/S molar ratio. Experimental conditions: temperature, 60 8C;
initial sulfur concentration, 500 ppmw; catalyst dosage, 1% the mass of normal
octane.
H3PWMo11
O
40 < H3PW3Mo9O40 < H3PW6Mo6O40
.
The catalytic
performance of H3PW6Mo6O40 is superior to that of H3PW12O40
.
The transformation of phosphotungstic acid to its cesium
salt sharply weakens the catalytic effect, as verified by
Cs2.5H0.5PW12O40 < H3PW12O40. The substitution of W for Mo in
As a predominant factor, O/S molar ratio significantly affects the
oxidation of DBT by H2O2 (Fig. 3). Under otherwise identical
conditions, an increase of O/S molar ratio from 1 to 18 results in the
sharp increase of the desulfurization efficiency from 77.0% to 99.5%
after reaction for 30 min. In Fig. 3, corresponding to cases where
the O/S molar ratio exceeds 9, the desulfurization efficiencies were
found to be nearly identical as 99.5% or higher after reaction for
20 min.
the phosphomolybdic acid results in the enhancement of the
Bronstedacidity, and H3PW6Mo6O40 possessesthehighestoxidation
capacityamongallW–Moratios ofthesameseries,withtheaddition
of H3PW12O40 [23]. The best catalytic effect of H3PW6Mo6O40 can be
attributed to its high Bronsted acidity as well as the highest
oxidation capacity it has, under which the POM–H2O2 complex in
form of peroxo-POM intermediate [22] possesses the highest
oxidative capacity, namely the highest catalytic activity for the
oxidation of DBT. Compared to H3PW12O40, the insolubility of
Cs2.5H0.5PW12O40 significantly limits its catalytic activity.
Based on the results gained herein, H3PW6Mo6O40 was chosen
for further experiments on the effects of several operation factors,
including temperature, O/S molar ratio, initial sulfur concentration
and the dosage of catalyst.
In literatures [22,25], peroxo-POM has been widely recognized
as active intermediate for POM-catalyzed oxidations of many
organic compounds by H2O2, such as epoxidation of alkenes and
oxidation of organosulfur (e.g. DBT and thioether). In our
experiments carried out according to the above-mentioned
procedures, H3PW6Mo6O40 was dissolved in H2O2 solution before
mixing with acetonitrile and simulated diesel oil, resulting in a
good activity on the oxidation of DBT. However, no activity was
observed when mixing all the reagents simultaneously. This is in
agreement with the phenomena reported by Bregeault and co-
workers [26]. Hence, it can be concluded that, the quick oxidation
of DBT lies in the formation of an active peroxo-POM intermediate,
i.e. peroxo-phosphotungstomolybdic acid, upon pre-dissolving of
H3PW6Mo6O40 in H2O2 solution. With the increase of the O/S molar
ratio under fixed initial sulfur concentration, more and more
excess H2O2 were added into the reaction system, leading to the
enhancement in DBT conversion by direct oxidation. From the
results, the favourable O/S molar ratio can be recommended as 15.
Initial sulfur concentration also plays an important role in the
oxidation of DBT. Under otherwise identical conditions, increasing
3.3. Role of main factors affecting the process
Using the same experiment system, the effect of temperature
was investigated under otherwise identical conditions as men-
tioned above. The oxidation of DBT by H2O2 was found to show an
apparent dependence on temperature (Fig. 2). Within the
temperature increase from 40 8C to 70 8C, the desulfurization
efficiency increases from 98.8% to nearly 100% after reaction for
20 min, and an identical efficiency of 99.7–100% can be achieved
after 120 min. From the results, the favourable temperature can be
recommended as 60 8C.
Fig. 2. The temperature dependence of the process. Experimental conditions: initial
sulfur concentration, 500 ppmw; O/S molar ratio, 15; catalyst dosage, 1% the mass
of normal octane.
Fig. 4. The effect of initial sulfur concentration. Experimental conditions:
temperature, 60 8C; O/S molar ratio, 15; catalyst dosage, 1% the mass of normal
octane.

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R. Wang et al. / Catalysis Today 149 (2010) 117–121
H3PW6Mo6O40 was finished accordingly. Filtering off the cation
exchange resin, the H3PW6Mo6O40 solution was retrieved as filter
liquor. The H3PW6Mo6O40 can be extracted from solution with
ethyl ether and recovered as solid by evaporating ethyl ether at
60 8C. Using the recovered H3PW6Mo6O40 for the same experiment
as Table 1, a desulfurization efficiency of 99.61% was achieved in
60 min, which is quite close to that obtained with the fresh
catalyst.
3.6. Macro-kinetics of the process
Based on the experimental data, the overall process comprising
mass transfer and chemical reaction can be simplified and
described as follows:
In the moment of the start of the mixing of the two liquid
phases, due to the vigorous agitation and the comparatively higher
solubility of DBT in acetonitrile, the mass transfer of DBT extraction
from n-octane phase to acetonitrile phase is significantly fast, and
the resultant concentration of DBT in acetonitrile phase can be
considered as closing to its equilibrium value. As a result, a large
portion of DBT is extracted into the acetonitrile phase, leading to
the quick drop of the mass transfer rate, meanwhile, the
H3PW6Mo6O40 catalyzed oxidation of DBT by H2O2 initiates at a
considerable high rate in acetonitrile phase. Consequently, the rate
of the chemical reaction process reaches that of the mass transfer
process instantaneously, and the steady state of the overall process
is thereupon achieved and maintained till the completion of the
chemical reaction.
Fig. 5. The effect of catalyst dosage. Experimental conditions: temperature, 60 8C;
initial sulfur concentration, 500 ppmw; O/S molar ratio, 15.
initial sulfur concentration from 100 ppmw to 500 ppmw and
further to 800 ppmw, the desulfurization efficiency was found to
increase from 96.5% to 99.5% and further to 99.7% at a reaction time
of 10 min, and maintained 99.8% or higher 40 min later (Fig. 4). As a
whole, both the effects of the O/S molar ratio and that of the initial
sulfur concentration fall in with the law of mass action.
The effect of catalyst lies mainly in the formation of peroxo-
POM intermediate, which possesses much higher oxidation
capacity than H2O2, and therefore facilitates the oxidation of
DBT. Consequently, knowledge on the effect of catalyst dosage is
very important to the process optimization. From the results as
shown in Fig. 5, it is evident that higher catalyst dosage leads to
higher desulfurization efficiency. Under otherwise identical
conditions, after reaction for 60 min, a higher desulfurization
efficiency of 99.8% can be achieved at the catalyst dosage of ca. 1%
the mass of normal octane, compared to that of 99.1% achieved at
the catalyst dosage in half. Hence, the favourable catalyst dosage
can be recommended as 1% the mass of normal octane, equivalent
to 6.93 g (H3PW6Mo6O40)/L (simulated diesel).
In the light of the above assumptions, using the equilibrium
formula, we have
yA
K ¼
(1)
xA
where K is the equilibrium constant, and xA, yA, the mole fractions
of DBT in n-octane phase and acetonitrile phase, respectively.
With the transformation of xA, yA into XA, YA through the
following Eqs. (2) and (3), we can finally turn Eq. (1) into a new
form, i.e. Eq. (4).
nA;1
nn
xA
XA
¼
¼
(2)
3.4. Reaction product
1 ꢀ xA
-
o
where nn-o and nA,1 are the mole amount of n-octane and that of
DBT in n-octane phase, respectively.
With the aid of GC–MS analysis, the product of DBT oxidation by
H2O2 after 150 min was confirmed to contain the corresponding
sulfone species only, regardless of the POM catalyst used. Hence,
the overall reaction equation can be expressed as
nA;2
nac
yA
YA
¼
¼
(3)
1 ꢀ yA
where nac and nA,2 are the mole amount of acetonitrile and that of
DBT in acetonitrile phase, respectively.
KXA
YA
¼
(4)
1 þ ð1 ꢀ KÞXA
As XA is very small, Eq. (4) can be approximately expressed as
YA ¼ KXA (5)
3.5. Catalyst recovery
The used catalyst can be recovered and reused with almost the
same effect as the fresh. When the reaction was finished, the
resultant mixture was kept still for 20 min. Then the acetonitrile
phase was separated out and distilled at 85 8C to recover
acetonitrile (with some water) at the top of the distillator by
cooling. The remaining in the distillator, i.e. a mixture of sulfone,
water and H3PW6Mo6O40, was withdrawn and put into a beaker.
With the addition of KCl aqueous solution, a precipitate of
K3PW6Mo6O40 can be observed in the beaker. The precipitate was
isolated by decantation, and washed twice with deionized water.
Then, the precipitate was treated by mixing with a favourable
amount of H-type cation exchange resin particles in deionized
water under mild and continuous agitation at 70 8C. When the
precipitate dissolved completely, conversion of K3PW6Mo6O40 to
Since acetonitrile and n-octane are mutually unsoluble, forming
a distinct biphase system, and H3PW6Mo6O40 and H2O2 exist
merely in acetonitrile phase [13], so, what we need is the
distribution of DBT in the biphase system. In the absence of
H3PW6Mo6O40 and H2O2, no chemical reaction occurs, and the
total amount of DBT remains the original of nA0. That is
nA;1 þ nA;2 ¼ nA0
(6)
Combining Eqs. (2), (3) and (5) yields
nac
nA;2 ¼ K
nA;1
(7)
nn
-o

R. Wang et al. / Catalysis Today 149 (2010) 117–121
121
Further combination of the above two equations leads to
in the presence of the H3PW6Mo6O40 catalyst. Hence, the macro-
kinetic results derived from this study should lay a solid foundation
for better understanding and optimum design of the overall process.
’
1 þ
nA;2
¼
nA0
(8)
(9)
’
where
4. Conclusions
nac
’
¼ K
nn
The catalytic performance of H3PWxMo12ꢀxO40 (x = 1, 3, 6) was
found to follow the order of H3PWMo11O40 < H3PW3Mo9O40 <
-
o
The constant K is slight dependant on temperature within the
temperature range of the experiment conditions and can therefore
be regarded as fixed. As for nac and nn-o, the amounts of acetonitrile
H3PW6Mo6O40. Moreover, H3PW6Mo6O40 was also found to be
superior to H3PW12O40. The transformation of phosphotungstic acid
to its cesium salt sharply weakens the catalytic effect, as verified by
and n-octane are identical for all the experiments. Hence
w can be
Cs2.5H0.5PW12O40 < H3PW12O40. Under the simulated system with
regarded as an identical constant for all the experiments.
an initial sulfur concentration of 500 ppmw, the ODS process
catalyzed by H3PW6Mo6O40 can proceed very efficiently at 60 8C
and an O/S molar ratio of 15, achieving a desulfurization efficiency of
99.79% or higher after 60 min. Hence, H3PW6Mo6O40 is promising for
thedeepdesulfurizationofactualODSprocess.Theprocessefficiency
can be improved by an increase in any of the factors including
temperature, O/S molar ratio, and catalyst dosage, whereby the
favourable operating conditions were recommended as T = 60 8C, O/
S = 15, and a catalyst dosage of 6.93 g (H3PW6Mo6O40)/L (simulated
diesel). The effects of both the O/S molar ratio and the initial sulfur
concentration conform to the law of mass action. With the aid of GC–
MS analysis, sulfone species was confirmed to be the only product
after reaction for 150 min. Furthermore, macro-kinetics of the
process catalyzed by H3PW6Mo6O40 was studied, from which the
reactionorderswerefoundtobe1.02toDBTand0.38toH2O2,andthe
activation energy of the reaction was found to be 43.3 kJ/mol.
Moreover, the used catalyst can berecoveredand reused withalmost
the same activity as the fresh.
Owing to the equal volume of n-octane and acetonitrile used in
all the experiments, according to Eq. (8), the concentration of DBT
in acetonitrile phase can be written as
’
1 þ
CA;2
¼
CA0
(10)
’
where CA0 is the initial concentration of DBT in n-octane phase.
From the experimental test, the value of was determined as 1.17.
w
In the presence of H3PW6Mo6O40 and H2O2 (B) in acetonitrile
phase, the irreversible oxidation of DBT will proceed at the initial
rate of
ri ¼ kCAm;2CBn
(11)
where the kinetic factor k can be expressed in terms of activation
energy E and temperature T as the well-known Arrhenius equation
ꢀ
ꢁ
E
k ¼ A exp
ꢀ
(12)
(13)
(14)
RT
Acknowledgement
Combining Eqs. (10)–(12) yields
ꢀ
ꢁ
E
ri ¼ A0 exp ꢀ
CAm0CBn
Financial support from the Ministry of Education of China under
New Century Excellent Talents Project (NCET-05-0584) is grate-
fully acknowledged.
RT
where
ꢀ
ꢁ
m
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’
1 þ
A0 ¼ A
’
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DBT concentration of CA0–CA,2, rather than CA0
.
In the above experimental results, by means of variable
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obtained. Based on these results, setting Eq. (13) as objective
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against CA,2, ln ri against CA,2, and further ln ri against 1/T, the
values of m, n, E in Eq. (13) were determined as follows:
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m ¼ 1:02 ðR ¼ 0:996Þ
n ¼ 0:38 ðR ¼ 0:989Þ
E ¼ 43:3 kJ=mol ðR ¼ 0:992Þ
Meanwhile, the value of A0 was determined as
(1.01 ꢁ 0.06) ꢂ 107 (mol/L)ꢀ0.40 minꢀ1
.
Hence, the H3PW6Mo6O40 catalyzed oxidation of DBT by H2O2 is
1st order to DBT and 0.4th order to H2O2. Therefore, it can be drawn
fromthisstudythat,whenhighO/Smolarratioareused, thereaction
can simply be taken as a pseudo-1st order reaction. The activation
energy of 43.3 kJ/mol indicates that the reaction process is quite fast
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