A significant enhancement of catalytic activities in oxidation with H 2O2 over the TS-1 zeolite by adjusting the catalyst wettability

Article abstract of DOI:10.1039/c3cc48220k

Hydrophilic TS-1 (H-TS-1) with rich hydroxyl groups, which were confirmed by ²⁹Si and ¹H NMR techniques, exhibits much higher activities in the oxidation than conventional TS-1. This phenomenon is strongly related to the unique features of high enrichment of H₂O₂ on H-TS-1.

Full text of DOI:10.1039/c3cc48220k

ChemComm
View Article Online
View Journal | View Issue
COMMUNICATION
A significant enhancement of catalytic activities
in oxidation with H2O2 over the TS-1 zeolite by
adjusting the catalyst wettability†
Cite this: Chem. Commun., 2014,
50, 2012
Received 27th October 2013,
Accepted 9th December 2013
Liang Wang,a Jing Sun,b Xiangju Meng,*a Weiping Zhang,c Jian Zhang,a
Shuxiang Pan,a Zhe Shena and Feng-Shou Xiao*a
DOI: 10.1039/c3cc48220k
www.rsc.org/chemcomm
Hydrophilic TS-1 (H-TS-1) with rich hydroxyl groups, which microporous titanosilicate catalysts could effectively improve
were confirmed by 29Si and 1H NMR techniques, exhibits much the activity.
higher activities in the oxidation than conventional TS-1. This pheno-
In this work, we have synthesized the relatively hydrophilic TS-1
menon is strongly related to the unique features of high enrichment zeolite (H-TS-1) from dimethyl dimethoxy silane (DDS) in the
of H2O2 on H-TS-1.
starting gel. After crystallization of H-TS-1, the methyl groups were
introduced into the zeolite framework. After calcination at 550 1C to
The microporous titanosilicate zeolite of TS-1 with MFI-type frame- remove the organic template, the methyl groups were transformed
work structure has been widely used in liquid-phase oxidation using into hydroxyl groups. These samples were designated as H-TS-1-x,
H2O2 as a clean oxidant, which is considered a significant break- where x stands for the percentage of the DDS/SiO2 (total silica)
through in the fields of zeolites and catalysis.1–3 Considering the molar ratio in the starting gel (Scheme S1, ESI†).
great importance of the TS-1 zeolite, a further improvement of the
Fig. S2 (ESI†) shows XRD patterns of various TS-1 samples,
catalytic activities has been extensively investigated. For example, exhibiting good crystallinities associated with typical MFI
recent results show that the hydrophobic TS-1 zeolite is favorable for structure. Fig. S3 (ESI†) shows SEM images of these samples,
increasing catalytic activities in the oxidation, because the hydro- confirming the high crystallinities. Notably, H-TS-1-5, H-TS-1-7.5,
phobic titanosilicate surface could adsorb and enrich the organic H-TS-1-10, and H-TS-1-20 have crystal sizes of 298, 307, 500, and
hydrocarbon substrates, leading to high catalytic activities.4
1170 nm, which are obviously larger than that (212 nm) of C-TS-1.
On the other hand, it is also accepted that the first step in the N2 sorption isotherms (Fig. S4, ESI†) show that all H-TS-1-x samples
oxidation with H2O2 over the TS-1 zeolite is the activation of H2O2 give very similar sorption isotherms to that of C-TS-1, giving a typical
by Ti species.5 Therefore, it is also important to enrich H2O2, feature of crystalline microporous structure. These samples exhibit
another substrate in the oxidation, to nearby the Ti species, which similar Si/Ti ratios (52–60), microporous sizes (0.53–0.54 nm),
could effectively improve the activities.6 According to this idea, a and surface areas (403–435 m2 gÀ1), as presented in Table S1 (ESI†).
relatively hydrophilic TS-1 zeolite has been rationally synthesized. UV-visible spectroscopy shows that the H-TS-1-x samples have a
As we expected, the hydrophilic TS-1 zeolite is more active in the strong peak near 220 nm, which is related to the 4-coordinative Ti
oxidation with H2O2 than the conventional TS-1 zeolite.
species in the framework of the TS-1 zeolite (Fig. S5, ESI†).
As a model of oxidation, 1-hexene oxidation with H2O2 was
Fig. 1 shows 29Si and 1H MAS NMR spectra of C-TS-1 and H-TS-1-
chosen because of the great importance of the 1,2-epoxyhexene 7.5 samples. Both samples exhibit strong signals at À113 and
product in industry.7 Interestingly, it is observed that over the À116 ppm in the 29Si spectra (Fig. 1A), which are associated with
conventional TS-1 catalyst (C-TS-1) both 1-hexene and H2O2 typical Si(OSi)4 species. However, the signal at À103.5 ppm, assigned
concentrations are very sensitive to the activity (Fig. S1, ESI†), to the Si species functionalized by hydroxyl groups, is stronger
suggesting that the enrichment of both reactants in the in the spectrum of H-TS-1-7.5 (Fig. 1A-a) than that of C-TS-1
(Fig. 1A-b).6a,8 Upon deconvolution and integration of the 29Si MAS
a Key Laboratory of Applied Chemistry of Zhejiang Province, Zhejiang University,
Hangzhou 310028, China. E-mail: fsxiao@zju.edu.cn, mengxj@zju.edu.cn
b State Key Laboratory of Inorganic Synthesis and Preparative Chemistry,
Jilin University, Changchun 130012, China
NMR spectra, the molar ratio of hydroxyl-attached Si can be obtained
as 3.5% and 7.6% for C-TS-1 and H-TS-1-7.5, respectively. Further-
more, 1H MAS NMR spectroscopy (Fig. 1B) shows that both samples
exhibit obvious signals at 1.7 and 2.0 ppm, which are attributed to
the Si–OH species in the samples. Notably, H-TS-1-7.5 (Fig. 1B-a)
has stronger signals than C-TS-1 (Fig. 1B-b), demonstrating that
H-TS-1-7.5 has more rich hydroxyl groups than C-TS-1.
c State Key Laboratory of Fine Chemicals, Dalian University of Technology,
Dalian 116024, China
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c3cc48220k
2012 | Chem. Commun., 2014, 50, 2012--2014
This journal is ©The Royal Society of Chemistry 2014

View Article Online
Communication
ChemComm
conditions, the influence of H2O2 concentration on r0 over the
H-TS-1-7.5 catalyst is little, giving the reaction kinetic order at only
0.11 (Fig. S8, ESI†). These results suggest that the H-TS-1-7.5 catalyst
with more hydroxyl groups could efficiently enhance catalytic
activities in epoxidation of 1-hexene, compared with C-TS-1.
To understand the role of the hydroxyl groups in the reaction, we
have measured the adsorption of H2O2 on H-TS-1-7.5 and C-TS-1
catalysts (Scheme S2, ESI†). As a result, it was found that the H2O2
reactant in the reaction can be significantly enriched in H-TS-1-7.5
because of its superior wettability for water.6a For example, the H2O2
concentration in the pores of H-TS-1-7.5 is about 10.8 times of that
in the reaction liquor, while this value is only 2.7 on the C-TS-1
catalyst. On the other hand, the H-TS-1-7.5 and C-TS-1 catalysts
exhibit similar wettability to 1-hexene (another reactant in the
reaction, Fig. S6, ESI†), giving similar contact angles of 1-hexene
on the catalyst surface. As a result, 1-hexene adsorption tests (Fig. S9,
ESI†) show that the H-TS-1-7.5 and C-TS-1 catalysts have similar
adsorption capacity for 1-hexene. These results indicate that the
introduction of hydroxyl groups in the H-TS-1-7.5 catalyst does not
influence the adsorption of 1-hexene, but greatly enriches the H2O2
concentration. This phenomenon leads to a significant enhance-
Fig. 1 (A) 29Si and (B) 1H MAS NMR spectra of (a) H-TS-1-7.5 and (b) C-TS-1
samples.
When a water droplet was brought into contact with the surface ment of the catalytic activities, in good agreement with the reactant
of the C-TS-1 zeolite, the contact angle was measured to be 171. In enrichment in carbon nanotubes9 and porous polymer catalysts.10
contrast, the water droplet contact angles were much smaller on
Table 1 presents the catalytic data in oxidation of 1-hexene,
the H-TS-1-x samples (Fig. S6, ESI†). For example, the contact angle hexane, and phenyl alcohol over various catalysts. In the 1-hexene
is lower than 51 on H-TS-1-7.5, indicating its relatively hydrophilic oxidation, the C-TS-1 catalyst is catalytically active, giving the
surface as compared with C-TS-1. This conclusion is strongly 1-hexene conversion of 21.2% (TON of 132.3, entry 1 and Fig. S10,
supported by the IR spectra of the samples in the region of ESI†). Very interestingly, H-TS-1-5 and H-TS-1-7.5 catalysts show
3100–3700 cmÀ1 associated with adsorbed water, as well as the much higher activities at 32.4 and 35.0 (TON of 213.8 and 243.6,
water adsorption capacities (Fig. S7, ESI†). These results are reason- entries 2 and 3 and Fig. S10, ESI†), which is reasonably assigned to
ably attributed to the presence of rich hydroxyl groups on the the enrichment of H2O2 concentration in the catalysts. These results
framework of H-TS-1-x samples, compared with C-TS-1.
indicate that increasing the hydrophilicity of TS-1 could efficiently
Fig. 2 shows dependences of the reaction rate on H2O2 improve its catalytic activities. However, when a large amount of
concentration over C-TS-1 and H-TS-1-7.5 catalysts in the oxida- hydroxyl groups existed in the catalyst, the H-TS-1-20 catalyst exhibits
tion of 1-hexene. Very clearly, at the same H2O2 concentration a low conversion of 12.5% (TON of 85.5, entry 5), compared with
the reaction rate over H-TS-1-7.5 is always higher than that over C-TS-1. In consideration of the similar wettability of 1-hexene on the
C-TS-1. More importantly, at relatively low H2O2 concentration TS-1 samples (Fig. S6 and S9, ESI†), this phenomenon might be
(CH O o 0.33 mol LÀ1), the reaction rate (r0) over C-TS-1 obviously related to their distinguishable crystal size of the H-TS-1-20 catalyst
2
2
decreased with the H2O2 concentration, giving the reaction kinetic of 1120 nm, which is much larger than that of C-TS-1 (220 nm).
order at about 0.71 (Fig. S1, ESI†). In contrast, under the same Larger crystal sizes have stronger limitation of mass transfer in the
reaction process, giving lower catalytic activities.11 Moreover, when
the external active sites are poisoned by bulky molecules of
2,4-dimethylquinoline, the H-TS-1-7.5 catalyst still shows much higher
conversion of 1-hexene (33.3%, entry 7) than the C-TS-1 catalyst (18.7%,
entry 6), which indicates that the higher activity of H-TS-1-7.5
than C-TS-1 should have originated from the internal active sites
in the micropores, rather than those in the external surface.
Similarly, the enhancement of the catalytic activities over
TS-1-x catalysts with rich hydroxyl groups is also extended to
the oxidation of n-hexane and benzyl alcohol (entries 8–14). In
the n-hexane oxidation, H-TS-1-5 and H-TS-1-7.5 exhibit much
higher conversion (23.8 and 27.9%, entries 9 and 10, TON of
78.5 and 97.1, Fig. S10, ESI†) than C-TS-1 (16.0%, entry 8, TON
of 49.9, Fig. S10, ESI†). In addition, it is also found that the
H-TS-1-x catalysts have higher 2- and 3-hexanone selectivity
Fig. 2 Dependences of the catalytic rate (r0) on H2O2 concentration over
(A) C-TS-1 and (B) H-TS-1-7.5 catalysts.
(71.0–85.0%, entries 9–12) than the C-TS-1 catalyst (66.0%, entry 8).
This journal is ©The Royal Society of Chemistry 2014
Chem. Commun., 2014, 50, 2012--2014 | 2013

View Article Online
ChemComm
Communication
Table 1 Catalytic activities and selectivities in oxidation of 1-hexene,
The obtained H-TS-1-7.5 catalyst shows a significant enhance-
ment of catalytic activities in oxidation of hexene, hexane, and
benzyl alcohol, compared with the conventional TS-1 catalyst.
This phenomenon is reasonably related to the presence of
hydroxyl groups in the H-TS-1-7.5 catalyst, which efficiently
enrich the concentration of H2O2 in the micropores. Considering
the wide applications of the TS-1 catalyst in industrial processes, a
significant enhancement of catalytic activities by adjusting the
catalyst hydrophilicity would be of great importance for the produc-
tion of fine chemicals in the future. The method in this work would
open a new door for developing more alternative active catalysts,
such as hydrophilic ZSM-5 catalysts (Fig. S13–S16, ESI†).
hexane, and benzyl alcohol over various catalystsa
Conv.
(%)
Selectivity (%)
Othersa
Entry Substrate
Catalyst
1b
2b
3b
4b
5b
6b
7b
1-Hexene
1-Hexene
1-Hexene
1-Hexene
1-Hexene
1-Hexene
1-Hexene
C-TS-1
H-TS-1-5
21.2
32.4
35.0
25.3
12.5
18.7
97.0
98.5
97.8
98.0
99.0
97.9
97.5
3.0
1.5
2.2
2.0
1.0
2.1
2.5
H-TS-1-7.5
H-TS-1-10
H-TS-1-20
C-TS-1-poisonedc
H-TS-1-7.5-poisonedc 33.3
This work was supported by the National Natural Science
Foundation of China (21273197, and U1162201), the National
High-Tech Research and Development program of China
(2013AA065301), and Fundamental Research Funds for the
Central Universities (2013XZZX001).
8d
9d
Hexane
Hexane
C-TS-1
16.0
23.8
27.9
16.1
2.0
66.0
74.2
72.6
71.0
85.0
34.0
25.8
27.4
29.0
15.0
H-TS-1-5
H-TS-1-7.5
H-TS-1-10
H-TS-1-20
10d Hexane
11d Hexane
12d Hexane
Notes and references
1 (a) G. Bellussi and M. S. Gigutto, Stud. Surf. Sci. Catal., 2001,
137, 911; (b) T. Tatsumi, M. Nakamura, S. Negishi and
H. Tominaga, Chem. Commun., 1990, 476.
13e Benzyl alcohol C-TS-1
17.6 >99.0
35.5 >99.0
14e Benzyl alcohol H-TS-1-7.5
a
b
The C6 alcohols, ketones, and some others. Reaction conditions:
2 (a) D. R. C. Huybrechts, L. De Bruycker and P. A. Jacobs, Nature,
1990, 345, 240; (b) A. Corma, J. Catal., 2003, 216, 298; (c) F. T. Fan,
Z. C. Feng and C. Li, Chem. Soc. Rev., 2010, 39, 4794.
3 (a) Q. Guo, K. J. Sun, Z. C. Feng, G. N. Li, M. L. Guo, F. T. Fan and
C. Li, Chem.–Eur. J., 2012, 18, 13854; (b) L.-H. Chen, X.-Y. Li, G. Tian,
Y. Li, J. C. Rooke, G.-S. Zhu, S.-L. Qiu, X.-Y. Yang and B.-L. Su, Angew.
Chem., Int. Ed., 2011, 50, 11156.
60 1C, 4 h, 0.05 g of catalyst, 10 mL of methanol, 10 mmol of 1-hexene,
c
10 mmol of H2O2. 1 mmol of 2,4-dimethylquinoline into the reaction
d
mixture. Reaction conditions: 60 1C, 4 h, 0.1 g of catalyst, 10 mL of
e
methanol, 10 mmol of cyclohexane, 20 mmol of H2O2. Reaction
conditions: 80 1C, 4 h, 0.05 g of catalyst, 3 mL of water, 5 mmol of
phenyl alcohol, 10 mmol of H2O2.
4 (a) W. B. Fan, R.-G. Duan, T. Yokoi, P. Wu, Y. Kubota and
T. Tatsumi, J. Am. Chem. Soc., 2008, 130, 10150; (b) A. Corma,
J. L. Jorda, M. T. Navarro and F. Rey, Chem. Commun., 1998, 1899;
(c) T. Tatsumi, K. A. Koyano and N. Igarashi, Chem. Commun., 1998,
2211; (d) J. Jarupatrakorn and T. D. Tilley, J. Am. Chem. Soc., 2002,
124, 8380; (e) A. Bhaumil, P. Mukherjee and R. Kumar, J. Catal.,
1998, 178, 101; ( f ) A. Bhaumik and T. Tatsumi, Chem. Commun.,
1998, 463.
5 (a) J. Zhuang, G. Yang, D. Ma, X. Lan, X. Liu, X. Han, X.-H. Bao and
U. Mueller, Angew. Chem., Int. Ed., 2004, 43, 6377; (b) M. G.
Clerici and P. Ingallina, J. Catal., 1993, 140, 71; (c) S. Bordiga,
A. Damin, F. Bonino, G. Ricchiardi, C. Lamberti and A. Zecchina,
Angew. Chem., Int. Ed., 2002, 41, 4734; (d) B. Notari, Adv. Catal., 1996,
41, 253.
6 (a) F.-S. Xiao, B. Xie, H. Y. Zhang, L. Wang, X. J. Meng, W. P. Zhang,
X. H. Bao, B. Yilmaz, U. Muller, H. Gies, H. Imai, T. Tatsumi and
D. De Vos, ChemCatChem, 2011, 3, 1442; (b) A. Corma, P. Esteve and
A. Martinez, J. Catal., 1996, 161, 11.
7 (a) W. Fan, P. Wu and T. Tatsumi, J. Catal., 2008, 256, 62; (b) K. Na,
C. Jo, J. Kim, W.-S. Ahn and R. Ryoo, ACS Catal., 2011, 1, 901;
(c) L. Xu, H. Peng, K. Zhang, H. Wu, L. Chen, Y. Liu and P. Wu, ACS
Catal., 2013, 3, 103.
8 Y. Han, D. Li, L. Zhao, J. Song, N. Li, Y. Di, C. Li, S. Wu, X. Xu,
X. Meng, K. Lin and F.-S. Xiao, Angew. Chem., Int. Ed., 2003, 42, 3633.
9 Z. J. Chen, Z. H. Guan, M. R. Li, Q. H. Yang and C. Li, Angew. Chem.,
Int. Ed., 2011, 50, 4913.
10 F. Liu, L. Wang, Q. Sun, L. Zhu, X. Meng and F.-S. Xiao, J. Am. Chem.
Soc., 2012, 134, 16948.
11 (a) J. Wang, L. Xu, K. Zhang, H. Peng, H. Wu, J.-G. Jiang, Y. Liu and
P. Wu, J. Catal., 2012, 288, 16; (b) X. Zhang, D. Liu, D. Xu, S. Asahina,
K. A. Cychosz, K. V. Agrawal, Y. Al Wahedi, A. Bhan, S. Al Hashimi,
O. Terasaki, M. Thommes and M. Tsapatsis, Science, 2012,
336, 1684; (c) Y. J. Lee, J. H. Kim, S. H. Kim, S. B. Hong and
G. Seo, Appl. Catal., B, 2008, 83, 160.
This feature might be related to that the presence of rich
hydroxyl groups on H-TS-1-x catalysts is favorable for the adsorp-
tion of 2- and 3-hexanol, re-oxidizing to 2- and 3-hexanone
products. Similar to the phenomenon observed in the oxidation
of 1-hexene, the H-TS-1-20 catalyst exhibits very low activity in
the oxidation of n-hexane (conversion at 2.0%, entry 12, TON of
6.8, Fig. S10, ESI†), which might also be related to the bulky
crystal size of H-TS-1-20. In the oxidation of benzyl alcohol, the
H-TS-1-7.5 catalyst exhibits much higher conversion (35.5%,
entries 14) than C-TS-1 (17.0%, entry 13). These results suggest
wide applications of the H-TS-1-x catalysts in a series of catalytic
oxidation with H2O2 in the future.
Fig. S11 (ESI†) shows a dependence of catalytic data in 1-hexene
conversion and 1,2-epoxyhexene selectivity on reaction time over
the H-TS-1-7.5 catalyst in a fixed-bed reactor. Very importantly,
the H-TS-1-7.5 catalyst always retains much higher 1-hexene
conversion than the C-TS-1 catalyst for a long time (100 h).
These results confirm that the H-TS-1-7.5 catalyst has stable high
activity, which offers a good opportunity for potential industrial
applications of the highly active H-TS-1-7.5 catalyst in the future
(Fig. S12, ESI†).
In summary, the TS-1 zeolite with rich hydroxyl groups
(H-TS-1-x) was rationally designed and successfully synthesized
by introducing methyl groups into the zeolite framework, followed
by calcination to transform methyl groups to hydroxyl groups.
2014 | Chem. Commun., 2014, 50, 2012--2014
This journal is ©The Royal Society of Chemistry 2014