Synthesis and morphology research of framework Ti-rich TS-1 containing no extraframework Ti species in the presence of CO2

Article abstract of DOI:10.1016/j.inoche.2013.11.026

A new method to synthesis TS-1 has been developed using the carbon dioxide (CO₂) as an alkalinity regulator that resulted in the increased framework Ti contents. The prepared catalyst had a Si/Ti ratio as low as 40 in contrast to the ratio of 56 prepared through conventional synthesis. The twin crystals with the length of 2 μm were formed via introduction of CO ₂. The catalytic activity of TS-1 is remarkably enhanced compared with the conventional synthesis.

Full text of DOI:10.1016/j.inoche.2013.11.026

Inorganic Chemistry Communications 40 (2014) 129–132
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Synthesis and morphology research of framework Ti-rich TS-1 containing
no extraframework Ti species in the presence of CO2
a,b
a
c
b
b
b,
b
Guowei Zhu , Lei Ni , Wei Qi , Shuang Ding , Xiaoxin Li , Runwei Wang ⁎, Shilun Qiu
a
School of Chemical and Biological, Beihua University, Jilin 132013, China
State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130012, China
Oil Refinery of Jilin Petrochemical Company, Jilin 132022, China
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
A new method to synthesis TS-1 has been developed using the carbon dioxide (CO ) as an alkalinity regulator
that resulted in the increased framework Ti contents. The prepared catalyst had a Si/Ti ratio as low as 40 in con-
trast to the ratio of 56 prepared through conventional synthesis. The twin crystals with the length of 2 μm were
2
Received 8 September 2013
Accepted 21 November 2013
Available online 2 December 2013
2
formed via introduction of CO . The catalytic activity of TS-1 is remarkably enhanced compared with the conven-
tional synthesis.
Keywords:
©
2013 Elsevier B.V. All rights reserved.
Alkalinity regulator
Framework Ti content
Crystal morphology
Ti-silicalite-1 (TS-1) is a very active and versatile oxidation catalyst
in particular using diluted H as oxidant in various catalytic oxy-
reductive processes, such as selective oxidation of olefins to epoxies,
hydroxylations of aromatics, and ammoximation of cyclohexanone [1].
The major problem often encountered is during the synthesis of TS-1,
the presence of anatase reduces significantly the catalytic performance
transferred into a 50 ml Teflon-lined autoclave and subjected to a hy-
drothermal crystallization at 453 K for 3 days. Finally, the solid product
was recovered by centrifugation, washed, dried, and calcined at 823 K
for 6 h. This specimen is denoted by TS-1-a.
Procedure B. In contrast to Procedure A, after the resulted gel was
transferred into a Teflon-lined autoclave, the autoclave was pressurized
2 2
O
of TS-1, due to its promotion to the decomposition of H
2
O
2
[2], and
with CO
pressure liquid pump under stirring, agitating for 5 min and a certain
amount of CO was added in the gel, then the pressure was released.
2
up to comfortable pressure (1 M, 2 M, 3 M, 5 M) with high-
the maximum amount of Ti4 that can be incorporated in framework
positions in TS-1. It is known that the more framework Ti, the TS-1, con-
tains the higher catalytic performance it would present, e.g. Weibin Fan
and co-workers [3] have reported a new route to synthesis TS-1 using
+
2
(
4 2 3
NH ) CO as a crystallization-mediating agent, by which the frame-
work Ti content had been significantly improved without forming
extraframework Ti species. Also, it is well-known, zeolites with well-
controlled morphology are of great importance as devices and catalysts
in many applications [4–6]. However, most TS-1 materials reported
show poor crystal morphologies, mainly sphere-like, and morphology
modulation by adjusting alkalinity of the gel is absent. Therefore, devel-
oping synthetic strategies to regulate crystal size and morphology of TS-
1
with more framework Ti is more concerned. Herein, we present a fac-
ile method for preparation of framework Ti-rich TS-1 in the presence of
CO , with the controllable crystal size and morphology.
Synthesis of TS-1 via various procedures—Procedure A. In a conven-
tional synthesis, the molar composition of the reaction mixture was
SiO : 0.026 TiO : 0.40 TPAOH: 4.39 H : 47 H O, 8 g of TPAOH and
g of TEOS were dissolved in 5 g of deionized water, and 0.2 g TBOT
dissolved in 11 g of 30% aqueous H solution was added dropwise.
After stirring at room temperature for 24 h, the resulted gel was
2
2
2
2
O
2
2
5
2 2
O
⁎
Corresponding author. Tel./fax: +86 431 85168115.
E-mail address: rwwang@mail.jlu.edu.cn (R. Wang).
Fig. 1. XRD patterns of (a) TS-1-a, (b) TS-1-b, (c) TS-1-c, (d) TS-1-d, and (e) TS-1-e.
1387-7003/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.inoche.2013.11.026

130
G. Zhu et al. / Inorganic Chemistry Communications 40 (2014) 129–132
The corresponding pHs of gel are 10.7, 9.5, and 8.8, and when the CO
pressure is 5 M, pH cannot be determined due to the gel solidifying.
The following treating procedure was in accord with above for TS-1-a
2
To certify the morphology of prepared materials, SEM micrographs
were taken and shown in Fig. 2. Generally speaking, from TS-1-a to
TS-1-d, the regular spheroid morphologies are popular with an approx-
imate diameter of 400–800 nm, and particle sizes become larger upon
the increasing amount of the CO . In TS-1-e, almost all crystals are
2
double interpenetrated hexagonal with a twinning angle close to 90°
(
1
without CO
-c (2 M), TS-1-d (3 M), and TS-1-e (5 M).
The characterization and catalytic measurements of samples are de-
2
), and these specimens are denoted as TS-1-b (1 M), TS-
scribed in Supporting Information.
As it is shown in Fig. 1 of the XRD patterns, all the specimens are
crystalline with a set of diffraction peaks at 2θ = 7.9°, 8.8°, 23.1°,
in approximate dimensions of 1 ∗ 0.3 ∗ 2 μm (a ∗ b ∗ c). We believe
2
that the addition of CO to the synthesis gel lead to the changes of mor-
phology and crystal size as a result of decreasing the alkalinity of the
crystallization mixtures. It is well proved that more nuclei are formed
in higher alkalinity in the preparation of MFI type silicalite-1 [8],
which results in the formation of smaller crystals. While CO was used
2
as the alkalinity regulator, the TS-1 formation would exhibit a quite dif-
ferent behavior. We speculate the twin crystal formation mechanism as
2
3.9° and 24.4°, indicating the characteristic of MFI topological struc-
ture [7]. It is clear that the crystallinity of materials was promoted
along with the increasing addition of the CO (from TS-1-a to TS-1-e).
On the other hand, the crystallinity varies little when the amount of
the CO arrived 5 M and more (not reported here), which is probably
caused by the saturation dissolvation of CO
2
2
2
in the gel.
2
follows: with the increased addition of CO (TS-1-e), the prepared gel
a
b
c
d
e
c
a
b
Fig. 2. SEM micrographs of (a) TS-1-a, (b) TS-1-b, (c) TS-1-c, (d) TS-1-d, and (e) TS-1-e.

G. Zhu et al. / Inorganic Chemistry Communications 40 (2014) 129–132
131
Fig. 3. The FT-IR spectra of (a) TS-1-a, (b) TS-1-b, (c) TS-1-c, (d) TS-1-d, and (e) TS-1-e.
Fig. 4. The UV–vis spectra of (a) TS-1-a, (b) TS-1-b, (c) TS-1-c, (d) TS-1-d, and (e) TS-1-e.
was solidified, the massive dry-gel aggregation was formed, and the dis-
sociation and rearrangement/restructuring of this initial solid gel result-
ed in a secondary gel [9,10]. In crystallization process, nucleation and
excluded the possibility of the presence of amorphous Ti species, it is
undoubtedly accepted that most of the Ti species present in the speci-
mens have been incorporated into the framework. The sample a has
the lowest extraframework Ti species, because optimal alkalinity can in-
hibit extraframework Ti species [3]. As for sample d, we speculate that it
+
crystal growth occur at the interface of gel particles and liquid, TPA dif-
fuses from solution to the crystal/gel interface, inducing the crystal
growth which was preferentially along certain planes, finally gave
twin crystals.
is caused by the combined action of alkalinity and CO
have made the relevant experiment about the effect of CO
When the autoclave was pressurized with CO up to comfortable pres-
2
pressure. We
The infrared spectra of calcined specimens were shown in Fig. 3, and
2
pressure.
−
1
the MFI structure was certified as well. The peak at 960 cm is often
referred to Ti\O\Si band and is taken as good indication of titanium
substitution into the zeolite framework [11]. The bands at 550 and
2
sure (6 MPa, 8 MPa, 10 MPa, 15 MPa) with high-pressure liquid
pump, it is obvious that extra-framework Ti species are present in the
specimens. It showed that the greater pressure has a negative effect
on inhibiting extraframework Ti species. So the sample TS-1-e (5 M)
has more extraframework Ti species.
The catalytic activities of the specimens from TS-1-a to TS-1-e have
been evaluated by the phenol hydroxylation with hydrogen peroxide
and the result is listed in Table 2. The catalytic performance of TS-1-a
is the worst, while the catalytic ability of TS-1-d is the best. It is likely
that the framework Ti content in TS-1-d is highest. Although the frame-
work Ti in TS-1-e is similar with TS-1-d, due to the higher concentration
−
1
8
00 cm are assigned to δ(Si\O\Si) and ν(Si\O\Si), respectively.
−
1
The relative intensity of the 960–800 cm peak has often been used
to estimate the titanium incorporation in TS-1 specimens [12]. In anoth-
er word, the larger the relative intensity (I960/I800) presents, the
higher framework Ti contains. It is clear in Table 1 that the framework
Ti content is the highest in the TS-1-d and TS-1-e, which indicates that
2
CO helps in increasing the amount of Ti incorporated into framework
of TS-1. It is also in agreement to the results of ICP-AES (characteriza-
tions of Ti contents in the specimens). From data of IR (Table 1), we
can find out that the TS-1-d and TS-1-e prepared is with highest frame-
work Ti content. From Fig. 2 and Table 1, it is in accordance with the re-
sults reported by Cundy et al. that incorporation of more Ti into the
framework resulted in the formation of larger crystals [13].
Fig. 4 shows the UV–vis spectra of the five specimens. All specimens
show a main absorption around 210 nm, substantiating the existence of
framework Ti [14]. The band at 250–280 nm is considered as a charge-
2
of anatase TiO , as well as the larger size of crystals, the catalytic perfor-
mance of TS-1-e is reduced.
In the present work, we have characterized that through alkalinity
reduction of the initial gel, not only promotion on the crystallization of
TS-1, favorable incorporation of Ti into the framework and altering mor-
phology of the crystal, from small spheroid to larger twin crystals were
achieved, but also enhancing the catalytic activities of TS-1. The opti-
4 3
transfer process in isolated [TiO ] or [HOTiO ] units, which are assigned
mum cooperation of alkalinity and CO
2
pressure (TS-1-d) can inhibit
to the amorphous Ti species. The absorption at 330 nm originated from
the anatase phase. Comparing the spectrum of TS-1-a, d with those of
b–e, it is obvious that extraframework Ti species are present in the spec-
extraframework Ti species, in particular the formation of anatase TiO ,
2
the catalytic activity of the specimen TS-1-d is the best. We have provid-
ed a promising method to study the positive effect of alkalinity for the
synthesis of transition metal-rich zeolite.
2
imen b–e, especially anatase TiO . Although TS-1-a and d cannot be
Table 2
Comparison of catalytic performances over specimens TS-1-a–TS-1-e.
Table 1
Specimens
Conversion (mol%)
PHE
Selectivity (mol%)
The chemical compositions and values of I960/I804 of specimens.
CAT
HQ
PBQ
Specimens
Molar ratio Si/Ti in TS-1
I960/I800
TS-1-a
TS-1-b
TS-1-c
TS-1-d
TS-1-e
19.66
22.80
21.23
26.10
20.88
51.22
44.06
46.03
48.11
48.63
48.63
55.28
52.50
51.78
50.64
0.15
0.66
1.47
0.11
1.73
TS-1-a
TS-1-b
TS-1-c
TS-1-d
TS-1-e
56
44
40
43
40
1.7
1.8
1.7
2.0
2.0
2 2
Reaction conditions: Phenol/H O = 2/1 (molar ratio); catalyst/phenol = 10% (weight
ratio); temp = 80 °C; time = 5 h; acetone as a solvent. PHE = phenol; CAT =
catechol; HQ = hydroquinone; PBQ = para-benzoquinone.
Ratios I960/I800 for the 960 and 800 cm− absorption bands in the FT-IR spectra of
specimens.
1

132
G. Zhu et al. / Inorganic Chemistry Communications 40 (2014) 129–132
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