Catalytic wet air oxidation of aromatic compounds: Degradation in molybdovanadophosphoric polyoxometalates micellar system under room temperature conditions

Article abstract of DOI:10.1007/s13738-012-0132-1

Catalytic wet air oxidation process, enable to eliminate organic pollutants with non toxic by-product formation, was investigated in micellar system under room condition. Degradation of a series of aromatic compounds, including aromatic hydrocarbons, benzyl alcohol, benzaldehyde, benzoic acid, and some N-containing compounds was carried out based on molybdovanadophosphoric polyoxometalates [(C₁₆H₃₃)N(CH₃) ₃]_3+x PV _x Mo_12-x O₄₀ (x = 1, 2, 3) catalysts and surfactants. Outstanding results (60-96 % degradation efficiencies) were achieved for most of the tested substrates. And the POM micellar catalysts have an excellent stability and can be used as heterogeneous catalysts for about six times.

Full text of DOI:10.1007/s13738-012-0132-1

J IRAN CHEM SOC (2013) 10:123–129
DOI 10.1007/s13738-012-0132-1
ORIGINAL PAPER
Catalytic wet air oxidation of aromatic compounds: degradation
in molybdovanadophosphoric polyoxometalates micellar system
under room temperature conditions
•
Jie Zhu Peng-cheng Wang Ming Lu
•
Received: 12 December 2011 / Accepted: 19 June 2012 / Published online: 7 July 2012
Ó Iranian Chemical Society 2012
Abstract Catalytic wet air oxidation process, enable to
eliminate organic pollutants with non toxic by-product
formation, was investigated in micellar system under room
condition. Degradation of a series of aromatic compounds,
including aromatic hydrocarbons, benzyl alcohol, benzal-
dehyde, benzoic acid, and some N-containing compounds
was carried out based on molybdovanadophosphoric
polyoxometalates [(C16H33)N(CH3)3]3?xPVxMo12-xO40
(x = 1, 2, 3) catalysts and surfactants. Outstanding results
(60–96 % degradation efficiencies) were achieved for most
of the tested substrates. And the POM micellar catalysts
have an excellent stability and can be used as heteroge-
neous catalysts for about six times.
economically and technologically viable process for
wastewater treatment [2–5].
In the field of application of WAO process, i.e., catalytic
wet air oxidation (CWAO), strongly improves the degra-
dation of organic pollutants under mild conditions of
temperature and pressure. Pintar et al. [6] demonstrated
that the Ru/TiO2 catalysts enabled complete removal of
phenol and total organic carbon (TOC) without the for-
mation of carbonaceous deposits. Renard et al. [7] carried
out the CWAO of stearic acid over the noble metals (Ru,
Pd, Pt, and Ir) supported on CeO2 in a batch reactor and
found that the Pt/CeO2 catalyst was a very effective cata-
lyst in the degradation of stearic acid and extremely
selective to CO2 while the C–C bond splitting was much
more noticeable on the Ru/CeO2 catalyst. Besides, the
decomposition of a wide range of pollutants, including
nitrogen compounds, has been reported [8–12].
Keywords Micelle Á Degradation Á Aromatic
compounds Á CWAO Á Polyoxometalate
Polyoxometalates (POMs) or heteropolyacids (HPAs)
have been proved to be one of the most efficient and widely
used catalysts, with hydrogen peroxide or oxygen as oxi-
dant, in epoxidation of olefin [13–15], cleavage of double
bond [16–18], conversion of primary and secondary alco-
hol to carbonyl compounds under moderate condition [19–
21]. However, this homogeneous system has limited
industrial applications due to the difficulty of separation
and recovery of the catalyst. Earlier research showed that
the combination of surfactants and POMs provided a good
route for CWO process [22]. The oxidative desulfurization
of dibenzothiophene oxidized by O2 with amphiphilic
POM emulsion catalysts has been reported [23–25], which
helped to overcome the limited solubility of hydrophobic
substrates in water.
Introduction
Wastewaters from industries which contain hazardous and
refractory aromatic pollutants like phenol, xylene, etc.,
even in small concentrations pose a great threat to the
environment. Therefore, exploration of effective methods
for aromatic compound degradation represents an impor-
tant research aspect over the last two decades and various
alternative treatment technologies have been developed to
cost effectively meet environmental regulatory require-
ments. Wet air oxidation (WAO), which was proposed and
developed by Zimmermann [1], is one of the most
J. Zhu Á P. Wang Á M. Lu (&)
So far, few studies have been conducted to the appli-
cation of POM emulsion catalysts in wastewater treatment.
Only Zhao [22] reported the use of POMs in the CWAO of
School of Chemical Engineering, Nanjing University of Science
and Technology, Nanjing 210094, China
e-mail: luming302@126.com
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J IRAN CHEM SOC (2013) 10:123–129
phenol with air and micellar molybdovanadophosphoric
polyoxometalates under room condition. The application of
this method to other substrates, however, has not been
systematically studied. So the primary objective of our
work here was to further examine the degradation effi-
ciency of a series of organic compounds with oxygen and
micellar molybdovanadophosphoric polyoxometalates
under room condition.
Fig. 1 The reaction process
[26] and [(C16H33)N(CH3)3]Br (CTAB) were used as cat-
alyst, respectively, for the degradation of toluene. From
Table 1, it can be seen that CTAB hardly shows any
activity in the degradation of toluene and different het-
eropoly anions lead to different catalytic performances.
Among the catalysts we used, [(C16H33)N(CH3)3]6PV3Mo9
O40, with the highest contents of vanadium, exhibits the
best catalytic activity, while [(C16H33)N(CH3)3]4PVMo11
O40, with the lowest vanadium contents, shows a relatively
lower catalytic efficiency, indicating that vanadium plays
an important role in the degradation reaction.
Experiment
Materials and methods
All reagents were of commercial grade and were used
without further purification. The preparation and charac-
terization of [(C16H33)N(CH3)3]3?xPVxMo12-xO40 (x = 1,
2, 3), denoted as (C16TA)3?xPVxMo12-xO40 (x = 1, 2, 3),
were followed by Ref. [22].
Analysis of substrates during the reaction was per-
formed by high pressure liquid chromatogram (HPLC,
Shimadzu LC-20A) with a UV detector using a Shim-pack
VP-ODS (4.6 mm 9 150 mm, 5 lm) column. The mobile
phase was a mixture of 80 % water, and 20 % methanol
with a flow rate of 1 mL/min.
The explanation for the phenomenon may have two
aspects. First, the oxidation property of the catalyst may
have close relation to V(V) contents [27]. The catalytic
activity is ascribed to peroxide complexes of heteropoly
anions or VO(O2)? peroxo species resulted from the
interaction between the anion and O2. Rao [28] reported
that the lattice oxygen of the POM with vanadium in its
primary or secondary structure is more reactive than that
with no V, which might be the reason for high activity of
the vanadium containing molybdophosphoric acid com-
pared to simple molybdophosphoric acid. So the degrada-
tion efficiency increased with the number of vanadium
atoms. Moreover, the critical micelle concentration (CMC)
values for (C16TA)6PV3Mo9O40, (C16TA)5PV2Mo10O40,
and (C16TA)4PVMo11O40 are 1.8 9 10-4, 9.2 9 10-4 and
16.3 9 10-4mol/L, respectively [22]. That is to say, under
the same concentration, (C16TA)6PV3Mo9O40 is the easiest
to form micelles, so as to accelerate the reaction. So the
catalytic activities follow the order of (C16TA)6PV3
Mo9O40 [ (C16TA)5PV2Mo10O40 [ (C16TA)4PVMo11O40
under the same condition.
Catalytic experiments
A typical catalytic reaction was carried out as follows: the
substrate (2.0 mmol) was mixed with 50 mL water and the
catalyst (C16TA)5PV2Mo10O40 (0.92 mmol/L) in a 150 mL
roundbottom three-neck flask under magnetic agitation at
25 °C. The mixture was stirred for an hour and an emulsion
was gradually formed (hydrochloric acid was used to adjust
the pH of the solution to be about 2). Oxygen was inputted
into the bottom of the emulsion at a rate of 0.04 m3/h.
Within several hours accordingly, samples were withdrawn
periodically to be measured by high-performance liquid
chromatogram. As the total process took up just a few
hours, evaporation effect can be neglected. When the
reaction was finished, the catalyst was separated by cen-
trifuge in 10,000 rpm and washed with water for three
times before being reused.
Considering the fact that the advantage of (C16TA)6
PV3Mo9O40 over (C16TA)5PV2Mo10O40 is not very obvi-
ous, but the yield according to Ref. [13] is much lower (38
vs. 50 %), (C16TA)5PV2Mo10O40 is chosen as the catalyst
for the following experiment.
The reaction process is shown as in Fig. 1.
Results and discussion
Influence of catalyst concentration
Influence of the type of catalyst
For toluene, as the degradation efficiency was very high
even when catalyst concentration is at CMC, the regularity
between degradation efficiency and catalyst concentration
cannot be illustrated clearly. So aniline instead was chosen
To examine the influence of the type of catalyst,
(C16TA)6PV3Mo9O40, (C16TA)5PV2Mo10O40, (C16TA)4
PVMo11O40, Na5PV2Mo10O40, [C7H7N(CH3)3]3PMo4O16
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125
Table 1 Degradation efficiency of toluene by different catalysts at room condition for 3 h
Catalyst
Substrate
CH
CHO
OH
NH
2
3
CTAB
Trace
5.3
Trace
5.5
9.6
8.7
Na5 PV2Mo10O40
[C7H7N(CH3)3]3PMo4O16
(CTA)6PVMo11O40
(CTA)5PV2Mo10O40
(CTA)4PV3Mo9O40
14.6
11.4
72.6
83.9
85.7
10.8
10.0
60.3
74.1
74.9
Trace
78.8
95.9
96.9
Trace
70.5
91.1
93.4
100 mL of 2.0 mM toluene solution, with the catalyst concentration 0.92 mM and O2 flowing rate 0.04 m3/h
area between catalyst and O2, leading to a relatively low
reaction rate and conversion of aniline. When the POM
micelles are formed, aniline is solubilized into the micelles,
and the interface area magnifies suddenly along with the
rate of reaction occurred at the interface of organic phase/
catalyst/O2 accelerated sharply, so the conversion showed a
break point at CMC. Above CMC, the number of micelles
increases with the increase of catalyst concentration, so the
rate of reaction speeds up and the conversion is enhanced.
At the same time, it can be found that the conversion
reaches the maximal value when the concentration of cat-
alyst is 10CMC. The facts are in line with the characteristic
of micellar catalytic reactions [29–31].
88
86
84
82
80
78
76
74
72
70
68
10CMC
CMC
-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2
Log c (mol/L)
Seeing that when catalyst concentration increased from
CMC to 10CMC, there is only a moderate increase in the
degradation efficiency (from 74.1 to 85.4 %), CMC value
of (C16TA)5PV2Mo10O40 is considered to be the optimum
condition. Though the increase of catalyst concentration
leads to a larger number of micelles, the arrangement of
micelles and substrates solubilized in it becomes tighter,
decreasing the contact opportunity between substrates/cat-
alysts/O2.
Fig. 2 Influence of catalyst concentration on degradation of aniline at
room condition, 50 mL of 2.0 mmol/L aniline solution in the
presence of (C16TA)5PV2Mo10O40, with the O2 flowing rate
0.04 m3/h
as the model substrate to study the influence of the catalyst
concentration. Prior to oxidation of aniline with O2, pre-
liminary experiment was performed at 25 °C and atmo-
spheric pressure in the presence of O2 but no catalysts, in
which almost no aniline degradation was detected. Figure 2
shows the degradation ratio of aniline varied with the
change of the surfactant concentration while other vari-
ables are kept constant. As seen in Fig. 2, when the con-
centration of catalyst is below critical micelle
concentration (CMC), the conversion of aniline after 3 h
was 64 %, and hardly varies with the increase of catalyst
concentration. However, once its concentration attains
CMC, the conversion increases with the increase of the
catalyst concentration, and levels off after the surfactant
concentration reaching 10CMC.
Influence of substrate concentration
To study the effect of the amount of substrate, experiments
are performed using different concentrations of toluene,
benzaldehyde, phenol and aminobenzene (0.04, 0.08, 0.12,
0.16 mol/L) while other variables are kept constant. From
Fig. 3, it can be found that degradation efficiency decreases
quickly when initial concentration increases. Under the
same micellar system, the number of micelles is limited, so
is the solubilization capacity. The interface area or active
site decreases when excessive substrates are solubilized
into micelles and substrates are arranged more closely,
leading to a reduction of degradation rate. On the other
hand, further reduction of substrate concentration may be
of less significance to industrial wastewater treatment.
The facts indicate that the effective micellar system is
formed by the POM micellar catalysts. When catalyst
concentration is below CMC, the reaction system is a
suspension or emulsion and the interface area between
organic phase and catalyst is very small, so is the interface
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J IRAN CHEM SOC (2013) 10:123–129
100
80
60
40
20
0
benzaldehyde
toluene
phenol
100
80
60
40
20
0
toluene
4-isopropyl toluene
4-tert-butyltoluene
o-xylene
m-xylene
p-xylene
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
2
4
6
8
10 12 14 16 18
Reaction time (h)
Substrate concentration (10-2 mol/L)
Fig. 4 Degradation efficiency of aromatic hydrocarbons at room
condition, 50 mL of 2.0 mmol/L solution in the presence of
(C16TA)5PV2Mo10O40, with the O2 flowing rate 0.04 m3/h
Fig. 3 Influence of substrate concentration on degradation at room
condition, 50 mL of 2.0 mmol/L solution in the presence of
(C16TA)5PV2Mo10O40, with the O2 flowing rate 0.04 m3/h
So the following experiments are conducted with substrate
concentrations fixed on 2.0 mmol/L.
Degradation of aromatic alcohol, aldehyde
and carboxylic acid
Degradation of aromatic compounds
Benzyl alcohol, benzaldehyde and benzoic acid are chosen
as substrates to study the degradation of aromatic alcohols,
aldehydes and carboxylic acid. It can be found in Fig. 5
that benzaldehyde gives the best result (with a conversion
of 91.1 %), probably due to its higher reactivity compared
to benzyl alcohol and benzoic acid. It almost completes the
degradation in 3 h with an efficiency of 82.4 %. As for
benzyl alcohol and benzoic acid, it is noteworthy that
benzoic acid shows a higher degradation rate at first but
gives lower degradation conversion in the end. The deg-
radation efficiency of benzoic acid reaches 49.4 % in 3 h
and then increases slowly in the following hours. We fur-
ther extended the degradation time of benzyl alcohol, and
found that its degradation efficiency increased from 63.0 %
(6 h) to 86.7 % (12 h).
Degradation of aromatic hydrocarbons
Degradation of toluene, 4-tert-butyltoluene, 4-isopropyl
toluene, o-xylene, m-xylene, p-xylene was investigated. As
shown in Fig. 4, 4-tert-butyltoluene has the highest
degradation efficiency, which exhibits a conversion of
97.1 % in 3 h. Reactivity of substrates varied in the order
of 4-tert-butyltoluene * 4-isopropyl toluene * p-xylene[
m-xylene [ o-xylene. This may be due to the effect of
electron donating groups on benzene ring. Tert-butyl acti-
vates the benzene ring most so that 4-tert-butyltoluene
shows a relatively higher efficiency. As for xylene,
although methyl somewhat also activates the benzene ring,
more groups are in need of being attacked before degra-
dation. Thus, lower degradation efficiency was exhibited
compared with toluene.
The experimental results indicate that benzyl alcohol is
partly degraded directly and partly oxidized into benzal-
dehyde first before further degradation. The HPLC data
also confirm this conclusion. The oxidation of benzyl
alcohol to benzaldehyde gradually helped to promote the
degradation. In other words, compared with benzoic acid,
benzyl alcohol is easier to be oxidized but harder to be
degraded. This may explain the fact that benzyl alcohol
decomposes more slowly than benzoic acid at first while
showing higher degradation efficiency in the end.
Degradation of toluene was equally directed to methyl
group and the ring, preferably to ortho-position, and
2-methyl-1,4-benzoquinone is supposed to be the major
intermediate. In the degradation of xylene, however, ortho-
position is supposed to be more easily attacked compared
to methyl group since p-xylene has a higher degradation
efficiency than o-xylene. Moreover, the number of ortho-
position of xylene is p-oxylene [ m-oxylene [ o-oxylene,
probably forcing p-oxylene to be attacked most likely and
o-xylene the least. The intermediates in this CWAO pro-
cess with POM micellar system are similar to that reported
by Kuznetsova [32] on the distribution of oxidation prod-
ucts of toluene oxidized by hydrogen peroxide with het-
eropoly compounds as catalyst.
Degradation of phenol and phenolic substances
Experiments are conducted to study the degradation of
phenol, catechol, hydroquinol, and resorcinol and the
results are shown in Fig. 6. All of the four types of phe-
nolic substances can be degraded well or excellently. The
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J IRAN CHEM SOC (2013) 10:123–129
127
100
80
60
40
20
0
100
80
60
40
20
0
o-phenylenediamine
m-phenylenediamine
p-phenylenediamine
trinitrotoluene
nitrobenzene
aniline
benzaldehyde
benzoic acid
benzyl alcohol
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Reaction time (h)
0
1
2
3
4
5
6
Reaction time (h)
Fig. 7 Degradation efficiency of N-containing compounds at room
condition, 50 mL of 2.0 mmol/L solution in the presence of
(C16TA)5PV2Mo10O40, with the O2 flowing rate 0.04 m3/h. For
trinitrotoluene, a few drops of acetonitrile was added
Fig. 5 Degradation efficiency of aromatic alcohol, aldehyde and
carboxylic acid at room condition, 50 mL of 2.0 mmol/L solution in
the presence of (C16TA)5PV2Mo10O40, with the O2 flowing rate
0.04 m3/h
little gray green, especially for catechol. This may be due
to the side reactions among which the trimerization of
phenolic substances to form tricyclic aromatic substance is
predominant [33, 34] and the substances may inhibit fur-
ther degradation of phenol.
80
60
40
Degradation of aromatic N-containing compounds
catechol
hydroquinol
resorcinol
phenol
20
0
The catalytic system can be also applied to the degradation
of N-containing compounds such as nitrobenzene, aniline,
p-phenylenediamine, o-phenylenediamine (Fig. 7). The
best result is achieved when p-phenylenediamine is used as
substrate (96.5 %). And even deactivated compound
nitrobenzene can be degraded to the extent of 58.5 %
in 3 h.
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Reaction time (h)
Fig. 6 Degradation efficiency of phenol and phenolic substances at
room condition, 50 mL of 2.0 mmol/L solution in the presence of
(C16TA)5PV2Mo10O40, with the O2 flowing rate 0.04 m3/h
During the degradation of aniline and p-phenylenedi-
amine, some kind of black substances are generated, which
are supposed to be aniline black or its analog, as aniline
and p-phenylenediamine may turn into a series of colored
compounds and finally aniline black when they are exposed
to air. The o- and m-phenylenediamine, however, do not
show this phenomenon. Besides, it has been confirmed that
the degradation of POM catalyst will take place if the pH
value of reaction solution is higher than its ‘‘nature’’ one
[26]. Since aniline and phenylenediamine are slightly
alkaline compounds, the addition of hydrochloric acid to
adjust the pH value is of great importance and is further
studied. Table 2 reveals the effect of pH value on the
degradation of aniline.
degradation efficiency is arranged as follows: phe-
nol [ hydroquinol [ resorcinol [ catechol. It is of interest
that the sequence of the degradation efficiency of diphenol
is different from that of xylene. The degradation efficiency
of resorcinol is a little similar with that of catechol, while
hydroquinol shows a higher efficiency compared with both
of them. The degradation mechanism of phenol in the
presence of POM micelle has been reported to undergo a
free radical process, and active oxidative species involved
1
in this CWAO system is either O2 or OHÁ [22]. Phenol is
oxidized first into hydroquinone and catechol and then into
p-benzoquinone, o-benzoquinone, and maleric acid. The
intermediates disappear as they are further oxidized into
CO2 and water.
The initial by-products of N-organic are essentially
nitrophenol, aminophenol, nitrobenzene and condensed
oligomers like azo-, azoxy-benzene and hydrazo-benzene.
In our experiment at room condition, aminophenol (nitro-
phenol) is suggested to be the major intermediate for
It is worth mentioning that during the experimental
process, the solution for phenolic substances turns into a
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J IRAN CHEM SOC (2013) 10:123–129
Table 2 The effect of pH on the degradation of aniline
pH
Degradation efficiency (%)
1.65
2.58
3.31
4.44
5.62
7.55
8.59
75.3
74.9
74
71.7
67.2
65.5
63.9
100 mL of 2.0 mM toluene solution with the catalyst concentration
0.92 mM and O2 flowing rate 0.04 m3/h
toluene
benzaldehyde
aniline
Scheme 1 The mechanism of degradation reaction in micellar
system
100
80
60
40
20
0
O
O
OH
CH3
O
R=CH3, NO2
CH3
OH
NH2
NH
OH
O
O
R=NH2
NO+
NHOH
N N
OH
O
R
1
2
3
4
5
6
CO2
Recycling times
OH
O
O
R=OH
Fig. 8 Recycling times in the degradation of toluene, benzaldehyde
and aniline at room condition, 50 mL of 2.0 mmol/L solution in
the presence of (C16TA)5PV2Mo10O40, with the O2 flowing rate
0.04 m3/h
OH
OH
O
CHO
......
aniline degradation when aniline (nitrobenzene) is attacked
1
R=CH2OH
OH
OH
O
by O2 or OHÁ just like phenol. Some of the intermediates
CH2OH
CH2OH
including ammonium ions, molecular nitrogen and unde-
sirable nitrite and nitrate ions are generated as by-products
to complete nitrogen balance, which is similar to the
CWAO process of aniline over the Ru/CeO2 catalyst at
high temperature [35].
O
Scheme 2 Simplified procedure for the catalytic degradation
aniline gives a relatively obvious decrease in activity
(degradation efficiency falls from 74.1 to 64.6 %), which
may have relation to the formation of aniline black that
deactivated the catalyst.
Recycle of catalyst
After the catalytic experiment, the catalyst was separated
by centrifuge in 10,000 rpm and washed with water for
three times before being reused. Figure 8 describes deg-
radation efficiency of toluene, benzaldehyde and aniline
versus recycling times (phenol was mentioned in Ref. [22]
and was not tested here), with (C16TA)5PV2Mo10O40 used
as catalyst. It reveals that for all the substrates tested,
(C16TA)5PV2Mo10O40 maintains efficiency after 6 repeated
experiments, without great loss in catalytic activity. Only
Possible pathway for aromatic compound degradation
The high activity of micellar POM catalysts is attributed to
the solubilization of substrates in the POM micellar system.
Zhao et al. [22] reported that it was hydrogen bonding
interaction between hydroxyl groups from phenol and O
atom from POMs that leads to the absorption of reactants
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J IRAN CHEM SOC (2013) 10:123–129
129
on catalyst, so as to accelerate the degradation. In this
study, the fact that the catalytic system can be applied to
aromatic hydrocarbons as well indicates that the hydrogen
bonding may not be the key factor for the rate acceleration,
while the micelle behavior may even play a more important
role. In Fig. 2, break points were shown at CMC and
10CMC, which prove to be a micellar catalytic system.
Once catalyst concentration attains to CMC, the micellar
system is formed. Then lipophilic reactants are solubilized
in the micelles of surfactants, and the swelling micelles
disperse in water phase containing hydrophilic reactants, so
that the reaction interface area between organic phase
reactants and water phase reactants is enlarged greatly. The
interface magnifying effect as well as concentrating effect
results in dramatic increases of reaction rates [36–38].
Scheme 1 illustrates a probable pathway for the degra-
dation reaction of aromatic compounds in the POM
micellar system. First, the catalyst accumulates to form
micellar aggregates once its concentration attains to CMC.
Then substrate can be solubilized into micelles due to the
hydrophobic effect, and the solubilization amounts increase
with surfactant concentrations. Second, at the micellar
interface, the catalyst is reduced by substrate to generate
the reduced form POMred (in particular the valent change
of V, Scheme 1). And at the same time, substrate is oxi-
dized to initiate the degradation. Finally, the catalytic cycle
is completed by the reoxidation of POMred to the oxidized
form of POMox using O2. Simplified procedure for the
catalytic degradation is generalized as shown in Scheme 2.
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In this work, POM micellar catalysts [(C16H33)N
(CH3)3]3?xPVxMo12-xO40 (x = 1, 2, 3) have been synthe-
sized and used as catalysts and surfactants in the CWAO
process of aromatic compounds under room condition. A
series of aromatic compounds, including hydrocarbons,
alcohols, aldehydes, carboxylic acid, phenolic substances
and N-containing compounds can be degraded to a well or
excellent degree in the presence of the catalysts. The
influence of the catalyst types, catalyst concentration,
substrate concentration and possible mechanism has also
been investigated. It was found that [(C16H33)N(CH3)3]6
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