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which may be caused by poor crystallinity and low surface
area of the nanocatalyst. Catalytic reactions using Mn@DVTA-2
and Mn@DVTA-3 were competitive in nature. More toluene
(32%) was transformed into the product if the reaction was
performed with octahedron-shaped Mn3O4 embedded on
DVTA (Mn@DVTA-3, Table 1, entry 16). tert-Butyl hydroperoxide
(TBHP) was employed to perform this toluene oxidation reac-
tion. The effective number of toluene oxidized is 12.5 for every
mole of TBHP expended. Higher catalytic performance of
Mn3O4 with octahedral morphology in Mn@DVTA-3 can be ex-
plained by its more exposed (101) crystallographic facets. In
this case, high-surface-energy (101) crystallographic facets are
more exposed than low-surface-energy (100) facets that only
exist in low percentage. More exposed crystalline planes of the
nanocatalyst can noticeably alter the catalytic property. Thus,
a high density of atomic steps, edges, kinks, and dangling
bonds on high-index crystalline facets facilitates the improve-
ment of catalytic activity. The adsorption followed by the acti-
vation of TBHP, O2, and reactant substrate is significantly assist-
ed by the interaction with the most exposed crystalline
planes.[25c]
Table 1. Screening of different catalysts for the solvent-free oxidation of
toluene using O2 as oxidant.
Entry[a]
Catalyst
T
[8C]
Conv.
[%]
Selectivity
[%]
ÀOH
ÀCHO
ÀCO2H
1
2
3
4
5
6
7
8
no catalyst
no catalyst
no catalyst
DVTA alone
MnCl2·4H2O
Mn(OAc)2·4H2O
MnSO4
60
80
100
80
80
80
0.1
0.1
0.2
0.2
1
1
1
1
15
15
13
15
14
12
15
13
76
78
38
62
65
68
75
78
8
7
49
23
21
20
10
9
80
80
MnO2
9[b]
10[c]
11[d]
12[e]
13
14
15
16
17[f]
18[f]
Fe/Al2O3
Mn/Al2O3
Zn/Al2O3
Au-Pd/TiO2
bare MnNP-3
Mn@DVTA-1
Mn@DVTA-2
Mn@DVTA-3
Mn3O4@SiO2
Mn3O4@C
190
190
190
80
80
80
80
80
80
80
1.1
1.4
1.8
5.3
2
4.3
12.5
11.5
16
32.3
39.1
41.6
37.3
45.5
35.6
95.7
87.5
88.5
32
66.6
47.2
47.9
55.5
45.9
53.9
0
0
0
52
3
13.5
9.5
7.2
8.6
10.5
3
17
32
18
20
[a] Reaction conditions: toluene (6 mL), catalyst (25 mg), TBHP (0.2 mL,
70 wt% in H2O, 0.00144 mol). O2 was the oxidant and TBHP was the ini-
tiator. O2 pressure was 1 atm. Substrate/initiator molar ratio was 39. Reac-
tion time was 12 h. Conversion was determined by GC analysis. ÀOH rep-
resents benzyl alcohol, ÀCHO benzaldehyde, and ÀCOOH benzoic acid.
[b–d] Toluene (0.47 mol) at 1908C and 1.0 MPa O2 on catalyst (1.0 g) for
2 h.[8a] [e] Ref. [8b]. [f] Mn3O4@SiO2 and Mn3O4@C catalysts were prepared
at 1608C solvothermal temperature.
Control experiments with mesoporous SiO2-supported
Mn3O4 (Mn3O4@SiO2) and porous carbon-supported Mn3O4
(Mn3O4@C) catalysts were performed for toluene oxidation,
which gave 18 and 20% conversions, respectively (Table 1, en-
tries 17, 18). Catalytic performances of the Mn3O4@SiO2 and
Mn3O4@C catalysts were also better than that of the bare
Mn3O4 nanoparticles. This result indicates that the supporting
matrix has a definite role for this oxidation reaction. Supported
matrix allows easy diffusion of organic substrate to interact
with the Mn3O4 catalytic centers, which facilitates improvement
of catalytic activity. Although the catalytic activity of the
Mn3O4@C catalyst is better than that of the Mn3O4@SiO2 cata-
lyst, it is still poorer than that of the Mn@DVTA-3 catalyst. This
result signifies that that hydrophobicity of supported matrix
may plays a decisive role in the catalytic reaction. The hydro-
phobic nature of the supporting matrix surface follows a trend
of porous polymer>porous carbon>porous SiO2. This trend
was established by performing contact-angle measurements
(Figure S14). The hydrophobic surface area enables hydropho-
bic and p–p stacking interactions between hydrophobic organ-
ic substrate and supporting matrix, leading to favorable ad-
sorption of the organic substrate into the nanoporous matrix
for catalytic reaction followed by desorption of the hydrophilic
product into the reaction mixture.[26] From these experimental
results, it can be concluded that the catalytic activity is acceler-
ated if a supporting matrix is used, and the porous-polymer-
supported nanocatalyst renders the best catalytic efficacy.
To explore the scope of the Mn@DVTA-3 nanocatalyst for
solvent-free oxidation of aromatic hydrocarbons, some of pe-
troleum compounds were employed for the catalytic conver-
sion under the optimized conditions (Table 2). Indane gave 8%
conversion in the presence of Mn@DVTA-3 with selectivities of
3% for 1-indanol and 95% for 1-indanone (Table 2, entry 1), re-
sulting in a turnover frequency (TOF) of 51 hÀ1. All the prod-
ucts were confirmed by using GC–MS analysis. The oxidation
of ethylbenzene afforded acetophenone exclusively with a con-
place (Table 1, entry 1). Then, the reaction temperature was in-
creased from 60 to 808C and then 1008C, and no improve-
ment in the conversion of toluene was achieved (entries 2 and
3). Triggered by these unsatisfactory results, we proceeded to
perform the reaction by using a catalyst to increase the yield.
The reaction with DVTA alone (entry 4) afforded 0.2% conver-
sion of the substrate. Several manganese salts and oxides in-
cluding MnCl2·4H2O, Mn(OAc)2·4H2O, MnSO4, and MnO2 were
used for the oxidation of toluene (entries 5–8). The products
were confirmed by GC–MS, and the conversion was deter-
mined by GC analysis with comparison to the authentic sam-
ples. In these cases, the conversion was only approximately
1%. Some heterogeneous catalysts such as Fe/Al2O3, Mn/Al2O3,
and Zn/Al2O3 have been considered to be poor catalysts for
aerobic oxidation of toluene.[8a] If the reaction was conducted
by using MnNP-3 (in the absence of nanoporous DVTA poly-
mer) with an octahedral morphology, the conversion was im-
proved to 2% (entry 13).[24,25] Catalytic reaction of synthesized
Mn3O4 nanoparticles without nanoporous polymer helped us
determine the catalytically active sites.
All the nanocatalysts Mn@DVTA-1, Mn@DVTA-2, and
Mn@DVTA-3 exhibited catalytic activity for aerobic toluene oxi-
dation with conversions ranging from 2 to 32% (Table 1, en-
tries 14–16). The nanoporous polymer itself was inactive to the
oxidation process. As bare MnNP-3 displays very low surface
area (BET surface area of 90 m2 gÀ1, Figure S8), low catalytic ac-
tivity was observed in this case. The Mn@DVTA-1 nanocatalyst
did not exhibit higher catalytic activity than bare MnNP-3,
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