Controlling the Morphology and Titanium Coordination States of TS-1 Zeolites by Crystal Growth Modifier

TS ‑1 Zeolites by Crystal Growth Modi ﬁ er

Article

Controlling the Morphology and Titanium Coordination States of

Xiaojing Song, Xiaotong Yang, Tianjun Zhang, Hao Zhang, Qiang Zhang, Dianwen Hu, Xinyu Chang,

Yingying Li, Ziyi Chen, Mingjun Jia,* Peng Zhang,* and Jihong Yu*

Cite This: https://dx.doi.org/10.1021/acs.inorgchem.0c01518

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sı Supporting Information

ABSTRACT: Developing an eﬀective strategy to synthesize

perfect titanosilicate TS-1 zeolite crystals with desirable

morphologies, enriched isolated framework Ti species, and thus

enhanced catalytic oxidation properties is a pervasive challenge in

zeolite crystal engineering. We here used an amino acid L-carnitine

as a crystal growth modiﬁer and ethanol as a cosolvent to regulate

the morphologies and the Ti coordination states of TS-1 zeolites.

During the hydrothermal crystallization process, the introduced L-

carnitine can not only tailor the anisotropic growth rates of zeolite

crystals but also induce the formation of uniformly distributed

framework Ti species through building a suitable chemical

interaction with the Ti precursor species. Condition optimizations

could aﬀord the generation of perfect hexagonal plate TS-1 crystals

and elongated platelet TS-1 crystals enriched in tetrahedral framework Ti sites (TiO ) or mononuclear octahedrally coordinated Ti

species (TiO ). Both samples showed signiﬁcant improvement in catalytic activity for the H O -mediated epoxidation of alkenes. In

particular, the elongated platelet TS-1 enriched in “TiO ” species aﬀorded the highest activity in 1-hexene epoxidation, with a

−

turnover frequency (TOF) of up to 131 h , which is approximately twice as high as that of the conventional TS-1 zeolite (TOF: 65

h ) and even higher than those of the literature-reported TiO -containting TS-1 catalysts derived from the hydrothermal post-

−

treatment of TS-1 zeolites. This work demonstrates that the morphologies and the titanium coordination states of TS-1 zeolites can

be eﬀectively tuned by directly introducing suitable crystal growth modiﬁers, thus providing new opportunities for developing highly

eﬃcient titanosilicate zeolite catalysts for important catalytic applications.

INTRODUCTION

been utilized as crystal growth modiﬁers, which can eﬀectively

aﬀord the morphology control of zeolite crystals.

■

18−23

Zeolites have been extensively used as eﬃcient heterogeneous

catalysts in the petrochemical and ﬁne chemical industries

owning to their unique features, such as uniform micropores,

tunable acidities and redox properties, and high thermal and

Several easily available and inexpensive amino acids and

their derivatives such as lysine, L-carnitine, and arginine have

shown great advantages in modifying the morphology and

microstructure of zeolite crystals like NaA (LTA), Y (FAU),

hydrothermal stability. Modulation of the morphologies and

24−30

and ZSM-5 (MFI).

For instance, Hong’s group reported

active sites of zeolites plays a key role in enhancing their

−5

that introducing lysine, L-carnitine, or their salt derivatives

could generate disordered mesopores within single-crystalline

LTA zeolites; the resultant zeolites exhibited improved

catalytic properties.

Diverse strategies have been imple-

mented to alter the morphology and microstructure of zeolites,

such as adjusting synthesis conditions, adding seeds,

introducing additives, employing microwave irradiation, and

adsorption capacity for catalase enzyme. In 2017, the

successful synthesis of a core−shell zeolite Y containing an

ant-nest-like hollow interior was achieved by the same group

through introducing L-carnitine; the obtained zeolite exhibited

−15

adopting various post-treatment methods.

One of the most

eﬀective methods for zeolite crystal engineering is the

introduction of crystal growth modiﬁers, a special type of

additives in the zeolite synthetic system. Growth modiﬁers

commonly refer to the molecules that can interact with the

speciﬁc facets of zeolite crystals or associate with amorphous

precursors to regulate nucleation and growth kinetics, thus

Received: May 24, 2020

16,17

altering the crystal size and morphology.

So far, some

macromolecules like polymers, proteins, and peptides and

small organic molecules like lactams and amino acids have

XXXX American Chemical Society

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

Table 1. Compositions and Textural Parameters of Various TS-1 Zeolites

sample

TS-1#con

TS-1#A_15Et:0.4LC

TS-1#B_15Et:0.6LC

TS-1#C_0Et:0.6LC

Si/Ti

S_B_E_T(m /g)

S_m_i_c_r_o(m /g)

S_e_x_t(m /g)

V_m_i_c_r_o(cm /g)

V_m_e_s_o(cm /g)

RC %

34.3

35.2

38.3

41.1

410

384

349

387

275

272

265

286

135

111

0.13

0.12

0.13

0.09

0.10

0.12

0.06

100

Measured by inductively coupled plasma (ICP). S_B_E_T(total surface area) calculated using the BET method. S

external surface area), and V_m_i_c_r_o(micropore volume) calculated using the t-plot method. V

method (from adsorption). RC: Relative crystallinity is calculated through comparing the total intensity of the three characteristic peaks of the

samples.

(micropore area), S_e_x_t

micro

(

(mesopore volume) calculated using the BJH

meso

enhanced catalytic activity for the Friedel−Crafts reaction. In

019, Qin et al. reported that the crystal morphology of

silicalite-1 (MFI) could be tuned in a certain range by using

signiﬁcant subject to develop a more simple and eﬀective

strategy for the synthesis of TS-1 zeolites with preferential

crystal morphology and abundant mononuclear TiO species.

arginine as the growth modiﬁer. The authors found that the

introduced arginine could induce a reduction in the crystal size

through impeding the nanoparticle addition. Our recent work

also suggested that L-lysine could be used as a crystal growth

modiﬁer to generate nanosized zeolite single crystals or defect-

free hierarchical ZSM-5 nanocrystals through kinetic-modu-

Very recently, our group developed an eﬀective method for

the one-step fast synthesis of zeolites TS-1 with highly active

Ti species through seed-assisted microwave irradiation. The

addition of active seeds coupled to microwave irradiation can

produce plenty of highly coordinated Ti precursors that play

an important role in creating more active “TiO

(besides “TiO ” species) in the zeolite framework. The

resultant TS-1 zeolites showed enhanced catalytic activity for

1-hexene epoxidation, conﬁrming the higher activity of “TiO

species than that of “TiO ” species. This progress suggests that

highly active “TiO ” species may be directly created in the

” species

lated crystallization. These results have demonstrated that

amino acids may act as eﬀective crystal growth modiﬁers in

zeolite synthesis owing to their proximal binding moieties (i.e.,

amino and carboxyl groups) that can strongly interact with the

amorphous precursors or the speciﬁc crystal surface of zeolites.

As one of the most important heteroatom-containing zeolite

catalysts, titanosilicate zeolite TS-1 (MFI) has been widely

applied in the green synthesis of some nitrogen- and oxygen-

containing organic intermediates with H O as the oxi-

”

zeolite framework of TS-1 zeolites by optimizing the

hydrothermal synthesis method and conditions.

In this work, taking advantage of the unique features of L-

carnitine such as the high structure stability, solubility, and

diverse functional moieties (i.e., ammonio, carboxyl, and

hydroxyl groups), we utilized L-carnitine as a crystal growth

modiﬁer to control the synthesis of TS-1 zeolites with desirable

morphologies and Ti coordination states. By altering the

amounts of L-carnitine and ethanol (cosolvent with water), a

series of TS-1 crystals with diﬀerent morphologies and

titanium coordination states were hydrothermally synthesized.

Signiﬁcantly, elongated platelet TS-1 crystals with a high aspect

ratio were obtained through optimizing the synthesis

1−33

dant.

To enhance the catalytic properties of the TS-1

zeolites, great eﬀorts have been devoted to modulating the

morphology and crystal size, generating hierarchical pores, and

34−39

adjusting the coordination states of Ti species.

For

instance, Xiao and coworkers reported that TS-1 crystals with

sheet-like morphology could be synthesized by the addition of

urea to the starting gels; the resultant zeolites showed very high

catalytic activity in the Beckmann rearrangement of cyclo-

hexanone oxime. They proposed that the sheet-like TS-1

crystals with a short b-axis length (along the straight channels

of the MFI network) are more favorable for the diﬀusion and

conversion of cyclohexanone oxime. It was believed that the

generation of highly active Ti species is the most important

factor for improving the catalytic performance of TS-1. Ideally,

one perfect TS-1 zeolite crystal should have the isolated

^p^a^r^a^m^e^t^e^r^,^w^hⁱ^c^h^c^oⁿ^t^aⁱⁿ^s^a^b^uⁿ^d^aⁿ^t^m^oⁿ^oⁿ^u^c^l^e^a^r^“^Tⁱ^O6^”

species. The resultant TS-1 zeolites were characterized by

combining a variety of characterization means, including

powder X-ray diﬀraction (XRD), N adsorption/desorption

measurements, scanning electron microscopy (SEM), UV−

visible diﬀuse reﬂectance spectroscopy (UV−vis), UV Raman

spectroscopy, and X-ray absorption spectroscopy (XAS). As

expected, the elongated platelet TS-1 crystals enriched in

tetrahedral framework Ti species (TiO ) as much as possible

and, meanwhile, avoid the formation of extra-framework Ti

species, such as oligomeric six-coordinated Ti species or the

“

TiO ” species showed superior catalytic activity and stability

for the epoxidation of alkenes with H O as the oxidant.

anatase phase. Notably, several recent literature works

revealed that the mononuclear six-coordinated Ti species

(

TiO ), obtained by hydrothermally post-treating conventional

EXPERIMENTAL SECTION

■

TS-1 with basic agents like tetrapropyl ammonium hydroxide/

NaOH solutions, possessed very high catalytic oxidation

activity, in some cases, even higher than that of the framework

Chemicals and Materials. Tetraethylorthosilicate (TEOS),

ethanol (Et), and methanol were purchased from Beijing Chemical

Works. L-Carnitine (LC: 3-hydroxy-4-(trimethylammonio)butanoate)

was purchased from Tokyo Chemical Industry in Shanghai.

Tetrabutyltitanate (TBOT) and tetrapropylammonium hydroxide

1−43

“

TiO ” species.

In fact, such a hydrothermal post-

treatment method has been widely used to adjust the

morphology, porosity, and coordination states of Ti species

of the TS-1 zeolites to improve their catalytic activity and

(

25 wt %) were purchased from Sinopharm. Allyl chloride (98%), 1-

hexene (98%), 1-heptene (98%), cyclopentene (96%), and 1-octene

(98%) were purchased from Aladdin. All reagents were of analytical

grade and used as received.

1,41

selectivity.

However, the basic solution etching process

results in a considerable weight loss of the parent zeolite

crystals and, in some cases, may also form some undesirable

defect sites, thus decreasing the structure stability and catalytic

Synthesis of TS-1 Zeolites with L-Carnitine as the Modiﬁer.

TS-1 zeolites were hydrothermally synthesized from the starting gels

w i t h t h e o p t i m i z e d m o l a r c o m p o s i t i o n o f

SiO :0.033TiO :0.3TPAOH:124H O:xC H OH:yLC. (x and y rep-

activity of the TS-1 zeolites. Therefore, it remains a

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

24.4 °, conﬁrming the phase purity of the samples (Figure 1 ).

Article

^r^e^s^eⁿ^t^e^t^h^aⁿ^o^l^/^Sⁱ^O2 ^aⁿ^d^L^C^/^Sⁱ^O2 ratios in the synthesis gel,

respectively; x refers to the initially introduced ethanol without

considering that part of ethanol generated by the hydrolysis of

TEOS.) Typically, TPAOH (25 wt %) and deionized water were ﬁrst

mixed completely (solution A), while certain amounts of TEOS and

TBOT were dissolved in the ethanol to form solution B. Solution B

was added dropwise to the solution A under stirring. After that, a

certain amount of LC was dropped into the solution under stirring.

After 3 h, the initial gel was transferred to a Teﬂon-lined stainless-steel

autoclave and crystallized in a conventional oven at 180 °C for 48 h.

The as-synthesized TS-1 zeolites were centrifuged and fully washed

with water and ethanol and dried overnight at 80 °C in an oven. After

calcination at 550 °C for 8 h, the resulting products were obtained,

which are denoted as TS-1#A_15Et:0.4LC, TS-1#B_15Et:0.6LC, and

TS-1#C_0Et:0.6LC, as shown in Table 1. Besides, two other samples

with Si/Ti ratios of 74 and 58, named TS-1#B-58_15Et:0.6LC and

TS-1#B-74_15Et:0.6LC, respectively, were also synthesized by using

the same conditions as those of TS-1#B_15Et:0.6LC (Si/Ti = 33) for

the purpose of making the comparison of the catalytic properties with

the related literature.

RESULTS AND DISCUSSION

Three representative TS-1 zeolites, TS-1#A_15Et:0.4LC, TS-

#B_15Et:0.6LC, and TS-1#C_0Et:0.6LC, were hydrother-

mally synthesized by using TPAOH as the microporous

template and L-carnitine as the crystal growth modiﬁer in the

presence/absence of a certain amount of ethanol. The XRD

patterns of the resultant TS-1 zeolites exhibit the characteristic

peaks of the MFI structure at 2θ of 7.8, 8.8, 23.0, 23.9, and

■

The conventional TS-1 zeolite (TS-1#con) was synthesized

according to a literature preparation procedure. The molar

c o m p o s i t i o n o f t h e i n i t i a l g e l w a s a s f o l l o w s :

SiO :0.033TiO :0.3TPAOH:124H O, and the synthesis condition

was similar to that of the previously mentioned TS-1 zeolites, just

without the addition of ethanol and L-carnitine.

Characterization. Powder XRD patterns were recorded on a

Shimadzu XRD-6000 diﬀractometer (40 kV, 30 mA), using Ni-ﬁltered

Cu Kα radiation to characterize the crystallinity and phase purity of

the as-synthesized TS-1 zeolites. SEM was used to characterize the

crystal size and morphology of TS-1 zeolites by using a JSM-6700F

Figure 1. XRD patterns of various TS-1 samples and the simulated

pattern of MFI zeolite.

(

JEOL) electron microscope. Nitrogen adsorption−desorption

measurements were carried out on a Micromeritics 2020 analyzer at

7 K. Prior to the analysis, ∼50 mg samples were degassed at 350 °C

under vacuum overnight. Fourier transform infrared (FT-IR) spectra

were recorded on a Nicolet AVATAR 370 DTGS spectrometer in the

Compared with the samples of TS-1#con and TS-

#A_15Et:0.4LC, the relative intensity of the [020] reﬂection

−

(

000−500 cm

XANES) spectra at the Ti K-edge were performed using the Sector

0-BM beamline of the Advanced Photon Source at Argonne National

range. X-ray absorption near-edge structure

(

8.8°) of TS-1#B_15Et:0.6LC and TS-1#C_0Et:0.6LC

becomes stronger, indicating the presence of a preferential ac

45,46

plane in the crystals.

As shown in Table 1, TS-

Laboratory (Argonne, IL). The beamline was equipped with a double-

crystal Si(111) monochromator. A 12-element Ge ﬂuorescence

detector was used to collect the spectra of the Ti K-edge. The

energy was calibrated according to the absorption edge of a pure Ti

foil as a reference. The acquired data were processed according to

standard procedures using the ATHENA module. The UV−vis

spectra were recorded on a Shimadzu UV-2400PC spectrophotometer

#A_15Et:0.4LC and TS-1#B_15Et:0.6LC have a relative

crystallinity (RC) of 97%, quite near that of the conventional

TS-1#Con (100%), whereas TS-1#C_0Et:0.6LC shows a

relatively low RC of 73%. These results suggest that

introducing a suitable amount of L-carnitine and ethanol may

retain the high crystallinity for TS-1 zeolites.

Figure 2 displays the SEM images of various TS-1 zeolites.

TS-1#con shows regular hexagonal prism morphology with an

average size of 0.7 μm and a uniform thickness of ∼0.5 μm

(Figure 2a). When a certain amount of LC or ethanol is

introduced into the sol−gel system, the thickness of the TS-1

crystals (along the b axis) obviously decreases to ∼0.3 μm

using a BaSO plate as a reference. Inductively coupled plasma/optical

emission spectroscopy (ICP/OES) was used to detect the chemical

compositions of samples on a PerkinElmer Optima 3300 DV ICP

instrument. UV Raman spectra with an excitation line at 260 nm were

recorded on a UV Raman spectrograph using a Jobin-Yvon T6400

−

triple-stage spectrograph with a spectral resolution of 2 cm . The line

at 260 nm was from the double-frequency of a DPSS 532 model 200

apparatus. The power of the 260 nm line of the samples was <1.0

mW.

(

Figure 2b−d). TS-1#A_15Et:0.4LC and TS-1#C_0Et:0.6LC

crystals show hexagonal plate-like morphology with a size of

about 0.8 and 0.9 μm, respectively (Figure 2b,d). A signiﬁcant

diﬀerence could be observed for TS-1#B_15Et:0.6LC, which

exhibits an interesting crystal shape of elongated platelet

morphology with well-developed ac planes and a short

dimension along the b axis (Figure 2c). The crystals of TS-

Catalytic Epoxidation of Alkenes with H O as the Oxidant.

The catalytic epoxidation of alkenes was carried out in a 25 mL

round-bottomed ﬂask equipped with a reﬂux condenser. The whole

device was immersed in a thermostated oil bath at the previously

designed temperature under vigorous stirring. Typically, 50 mg of

#B_15Et:0.6LC are uniform in the size of about 0.9 × 0.3 ×

.0 μm (a × b × c); signiﬁcantly, it has an average c/b aspect

catalyst, alkene (10 mmol), and CH OH (10 mL) were added to the

round-bottomed ﬂask. The catalytic reaction was initiated by adding

ratio of 10, which is one of the largest aspect ratios among the

0 mmol H O to the mixture at 60 °C. The quantitative analyses of

2 2

reported values for TS-1 crystals. As is known, there are two

channel systems in MFI-type zeolite: a straight 10-membered

ring channel (0.53*0.56 nm) parallel to the b axis, and a

sinusoidal channel (0.51*0.55 nm) parallel to the a axis. It is

the reagents and products were carried out by a GC-9790II gas

chromatograph with an HP-5 capillary column. The conversion of

alkenes and the selectivity of products were calculated on a C-atom

basis, and carbon balances were within 100 ± 5% in all tests.

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

samples are given in Figure 3 . All of the samples display the

Article

Figure 2. SEM images of (a) TS-1#con, (b) TS-1#A_15Et:0.4LC, (c)

TS-1#B_15Et:0.6LC, and (d) TS-1#C_0Et:0.6LC.

Figure 4. FT-IR spectra of TS-1#con, TS-1#A_15Et:0.4LC, TS-

1#B_15Et:0.6LC, and TS-1#C_0Et:0.6LC.

highly desirable to synthesize MFI zeolites with a very short b

axis, which could provide a short path along the straight 10-

membered ring channels for mass transfer, thus being

beneﬁcial for increasing the diﬀusional ﬂux of sorbate

UV−vis DRS spectra of various TS-1 zeolites are shown in

Figure 5 . All of the samples display a strong absorption peak at

molecules during a catalytic reaction process.

The N₂adsorption/desorption isotherms of the TS-1

Figure 5. UV−vis DRS spectra of TS-1#con, TS-1#A_15Et:0.4LC,

TS-1#B_15Et:0.6LC, and TS-1#C_0Et:0.6LC.

∼

207 nm, which is attributed to the isolated tetrahedral

framework Ti species (TiO ), originating from the charge

2−

transfer of the pπ−pπ transitions between O and Ti in the

framework of TS-1 zeolites.

42,43

An obvious absorption peak at

∼

330 nm can be observed in the TS-1#con and TS-

#C_0Et:0.6LC, which could be related to the formation of

Figure 3. N₂adsorption/desorption isotherms of TS-1#con, TS-

extra-framework bulk TiO . For TS-1#A_15Et:0.4LC, no

obvious absorption peak could be detected at 330 nm or

1#A_15Et:0.4LC, TS-1#B_15Et:0.6LC, and TS-1#C_0Et:0.6LC.

other positions, suggesting that the isolated TiO species are

type-I isotherms in the partial pressure range of 0.1 to 0.9 (P/

P₀), indicating the microporous characteristics of these zeolites.

The appearance of a weak uptake in the 0.9 to 1.0 range should

be a hint of a small number of meso- or macropores present in

the samples, which usually originate from the particle-piled

pores. The textural parameters of various TS-1 zeolites are

summarized in Table 1.

dominant in this material. Notably, for the sample of TS-

1#B_15Et:0.6LC, another wide and strong absorption band

center at ∼270 nm could be detected. The assignment of the

electronic transition in this region is quite complicated because

it might be related to diﬀerent kinds of Ti species, like

pentacoordinated and hexacoordinated Ti species either in

isolated form or in oligomeric form.

The FT-IR spectra of various TS-1 samples are shown in

Figure 4. The weak absorption band at 965 cm⁻¹is commonly

attributed to the stretching vibration of Si−O−Ti or Si−O

UV-Raman resonance spectroscopy with an excitation line at

260 nm was used to get further insights into the coordinative

states of Ti species in the TS-1 zeolites. As shown in Figure 6,

−1

perturbed by a Ti atom in the framework of TS-1. The bands

the typical bands at 380 and 800 cm detected in the four

at 1225 and 550 cm⁻are ascribed to the asymmetric

samples are the characteristic signals of siliceous zeolites (like

stretching and double-ring tetrahedral vibration of SiO and

silicalite-1) with a MFI structure. For the samples of TS-

1#con, TS-1#A_15Et:0.4LC, and TS-1#C_0Et:0.6LC, the

TiO tetrahedrals, respectively.

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

Figure 6. UV-Raman spectra of various TS-1 samples excited at 260

nm: (a) TS-1#con, (b) TS-1#A_15Et:0.4LC, (c) TS-

1#B_15Et:0.6LC, and (d) TS-1#C_0Et:0.6LC.

Figure 7. Normalized Ti K-edge XANES spectra for various TS-1

samples.

bands at 490, 530, 956, and 1125 cm⁻in the spectra could be

components are ascribable to the fraction of other Ti species

(e.g., bulk TiO and polymeric TiO species) suggests that

attributed to the asymmetric stretching and symmetric

stretching vibration of the framework TiO and Ti−O−Si

mononuclear hexacoordinated TiO₆species should be

prevalent in TS-1#B_15Et:0.6LC. Moreover, the Fourier-

transformed extended X-ray absorption ﬁne-structure spectrum

(FT-EXAFS) of TS-1#B_15Et:0.6LC shows only a major

signal of the Ti−O bond, whereas the signals of the Ti−O−Ti

bond are nearly negligible (Figure S1 ). These results provide

clear evidence that the dominating Ti species in TS-

1#A_15Et:0.4LC and TS-1#B_15Et:0.6LC are isolated TiO₄

species.

These four bands are very weak for TS-

#B_15Et:0.6LC, suggesting that the content of TiO species

in this sample should be quite low. Notably, an obvious band

at 695 cm

−

could be observed in the samples TS-

#B_15Et:0.6LC and TS-1#C_0Et:0.6LC. This signal has

recently been recognized as the characteristic of a mononuclear

hexacoordinated Ti species (TiO ), which is partially

coordinated with hydroxyl groups and H O, shown as

and mononuclear TiO species, respectively.

Ti(OSi) (OH) (H O) . Observably, the Raman band at

95 cm is the dominating signal in the spectrum of TS-

The above results demonstrate that TS-1 crystals with

diﬀerent morphologies and titanium coordination states could

be directly hydrothermally synthesized by introducing L-

carnitine as a crystal growth modiﬁer and ethanol as a

cosolvent. The amount of L-carnitine and ethanol in the

synthetic gel greatly aﬀects the crystal growth and the Ti

insertion into the MFI framework. In the case without the

addition of ethanol, the introduced L-carnitine may also

inﬂuence the morphology and the Ti coordination states of the

zeolites to a certain extent to generate hexagonal plate-like TS-

1 crystals containing both TiO₄and TiO₆species (TS-

1#C_0Et:0.6LC), whereas without L-carnitine, the addition of

a certain amount of ethanol does not have an obvious eﬀect on

the morphology and the crystal size of the TS-1 zeolites in

comparison with the conventional TS-1#con (Figure S2). It

should be mentioned that even without additional EtOH, a

certain amount of EtOH and BuOH could also be formed by

the hydrolysis of TEOS and TBOT during the hydrothermal

synthesis process, which may also inﬂuence the crystallization

process and the morphology of the resultant TS-1 zeolites to a

certain extent. In general, the insertion rate of Ti into the

zeolite framework must match well with the formation rate of

−

#B_15Et:0.6LC; it could be directly associated with the Ti

species that feature a strong adsorption band at ∼270 nm in

the UV−vis spectrum. These results suggest that such special

mononuclear TiO species are prominent in the sample of TS-

#B_15Et:0.6LC. It should be pointed out that TS-

#C_0Et:0.6LC did not give an obvious peak at 270 nm

(

UV−vis spectrum), although it gave a clear UV-Raman band

−1

of 695 cm . This might be an indication that the content of

the TiO species in this sample is not very high, whereas the

−

appearance of a relatively strong band of 695 cm should be

assigned to the resonance eﬀect that can selectively enhance

the Raman band associated with framework titanium atoms.

To further investigate the nature of the Ti species, X-ray

adsorption spectroscopy measurements were performed, and

the normalized Ti K-edge XANES spectra of various TS-1

zeolites are shown in Figure 7, together with Ti foil and anatase

TiO for references. All TS-1 zeolites exhibit a sharp pre-edge

peak at ∼4968 eV caused by the 1s → 3pd electronic transition

8,50

of Ti.

It was proposed that the pre-edge peak intensity

strongly depends on the symmetry around the Ti species.

Compared with the tetrahedrally coordinated Ti(IV) species,

the octahedrally coordinated Ti(IV) species are characterized

by a much lower intensity due to the small p−d hybridization

that occurs in octahedral symmetry. In the present case, TS-

the zeolite to generate isolated TiO species and inhibit the

formation of an unfavorable anatase phase. Our results

further demonstrate that the generation of a mononuclear

TiO species could also be eﬀectively achieved by introducing

#A_15Et:0.4LC shows the strongest pre-edge peak, reﬂecting

a growth modiﬁer of L-carnitine and a cosolvent of ethanol.

Notice that controlling the ratio of ethanol and L-carnitine

(e.g., 15Et:0.6LC) is a critical factor for aﬀording the formation

of the elongated platelet morphology and the generation of

the highest content of TiO species. The lowest peak intensity

of TS-1#B_15Et:0.6LC suggests that the content of TiO is

rather low, implying that the six-coordinated Ti species should

be dominant in this sample. The fact that no obvious spectral

abundant TiO species.

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

(Figure 8 ). Obvious diﬀraction peaks characteristic of the MFI

Article

To gain insight into the growth process of the elongated

platelet TS-1#B_15Et:0.6LC zeolite, time-resolved samples

were collected at diﬀerent crystallization stages (6−48 h). The

XRD patterns of the extracted solids from the early

crystallization stage (6 and 12 h) exhibit amorphous features

spectra (Figure S3). Although, experimentally, it is diﬃcult to

determine how the modiﬁer of L-carnitine impacts the

nucleation and crystal growth processes of TS-1 zeolites at

the molecular level owing to the complexity of zeolite

crystallization, our current results could still provide evidence

that modiﬁer−precursor interactions should be present, as the

morphology and Ti coordination states of the zeolites

obviously changed after L-carnitine was introduced. Previously,

it has been proposed that the coordinative actions of L-

carnitine onto the aluminosilicate framework may ﬁnally result

in the formation of a core−shell zeolite Y with an ant-nest-like

hollow interior. In the present case, the existence of

coordinative interactions between L-carnitine and Ti atoms

should also play a crucial role in generating mononuclear six-

coordination Ti species in the framework of TS-1 zeolites.

Hence our results suggest that L-carnitine can not only

functionalize as a common morphology modiﬁer by attaching

to speciﬁc surface sites of the crystal and by inhibiting the

nucleation during the hydrothermal synthesis process but also

act as a suitable ligand to adjust the coordination environment

of Ti species by building suitable coordination action with Ti

species throughout the entire crystal growth process. Although

additional work is still required to reveal the concrete

coordination interaction between Ti and L-carnitine in the

Figure 8. XRD patterns of TS-1#B_15Et:0.6LC samples with

diﬀerent crystallization times.

zeolitic synthesis system, the rapid formation of Ti−O bonds

between the amino acid and Ti in the presence of aqueous

alcohol has already been revealed in the literature work. In

the present case, the oxygen-containing groups in L-carnitine

should easily interact with the Ti species by forming Ti−O

bonds, which seems to be beneﬁcial for aﬀording the Ti species

in the state of mononuclear hexa-coordination, while

simultaneously modulating the incorporation rate of Ti to

match well with that of Si with the assistance of a certain

amount of ethanol cosolvent and, ﬁnally, resulting in the

structure start to appear in samples crystallized after 24 h, with

a gradual increase in intensity with time. As seen from SEM

images, extracted solids with a rough surface are observed after

crystallization for 12 h, whereas a large number of sheet-like

crystals covered with abundant small nanoparticles appear at

4 h (Figure 9 a,b). With further increasing the crystallization

formation of uniformed TiO species in the elongated platelet

TS-1 zeolites.

By comparing the thermogravimetric (TG) proﬁle and the

FT-IR spectrum of the as-synthesized TS-1 #B_15Et:0.6LC

(

without calcination) with that of LC (Figures S4 and S5 ), it

can be concluded that no detectable L-carnitine modiﬁers are

present in the as-synthesized TS-1#B_15Et:0.6LC crystals.

These results suggest that the L-carnitine does not distribute

inside the channels of the as-synthesized zeolites, further

conﬁrming that the introduced L-carnitine should mainly act as

a morphology modiﬁer for the formation of the TS-1 zeolite

rather than a template for the formation of zeolite framework.

On the basis of the above information, the role of L-carnitine in

the formation of the elongated platelet TS-1 crystals containing

abundant TiO species is schematically illustrated in Scheme 1.

In short, the soluble silicon/titanium monomer or oligomers in

the initial synthesis gel starts to agglomerate into small

amorphous nanoparticles upon heating; then, TS-1 crystals

gradually grow under the direction of the TPAOH template

through the molecule addition of soluble species (classical

path) or through the direct addition of amorphous nano-

particles on the crystal faces (nonclassical path). During this

process, the introduced L-carnitine could build coordinative

action with the monomer Si and Ti species as well as the

amorphous nanoparticles, and it may also act as an adsorbate

that can cover the preferential face of the crystal (i.e., the ac

face). In these cases, the crystal growth along the b orientation

may be considerably inhibited, thus ﬁnally resulting in the

Figure 9. SEM images of TS-1#B_15Et:0.6LC samples at diﬀerent

crystallization stages of (a) 12, (b) 24, (c) 30, and (d) 48 h.

time, the surface-deposited nanoparticles gradually disappear,

and perfect crystals with a smooth surface and a uniform

elongated platelet shape are observed after 48 h (Figure 9c,d).

These results clearly reveal that amorphous nanoparticle

precursors rapidly form in the initial growth stage; then,

these metastable species can act as Si and Ti sources for TS-1

crystal growth through a dissolution−recrystallization proc-

ess. Notably, the coordination states of the Ti species remain

constant throughout the synthesis period of 24 to 48 h, with

TiO as the dominant species, as shown in the UV−vis DRS

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

Scheme 1. Proposed Schematic of the Elongated Platelet

TS-1 Zeolite Growth in Classical (Molecule) and

Nonclassical (Nanoparticle) Pathways, Which Are Mediated

by L-Carnitine (Purple Curve) through Adsorbing on

Crystal Surfaces and Interacting with Amorphous

Nanoparticles

for the epoxidation of 1-hexene (Table S1). Their catalytic

activities were higher than those of the literature-reported

TiO -containting TS-1 catalysts (with similar Ti contents),

which were derived from the hydrothermal post-treatment of

41,42

conventional TS-1 with organic amine agents.

Notably,

under similar operation conditions, the TS-1#B_15Et:0.6LC

catalyst could give a much higher 1-hexene conversion and

H O utilization rate (see Table 2) than the previous reported

TS-1 zeolites synthesized through an active seed-assisted

microwave irradiation strategy (TS-1-AM), which also contain

a certain amount of “TiO ” species besides the “TiO ”

species.

This might be due to the fact that TS-

#B_15Et:0.6LC contains a greater concentration of highly

active “TiO ” species than does TS-1-AM.

Moreover, the catalytic properties of various TS-1 zeolites

were also studied for the oxidation of other alkenes, such as

allyl chloride, cyclopentene, and 1-heptene (Table S2 and

Figure S9 ). It was found that TS-1#B_15Et:0.6LC also showed

excellent catalytic activity for the epoxidation of allyl chloride

and cyclopentene. The relatively low selectivity for cyclo-

pentene epoxide (or high selectivity for glutaraldehyde) should

mainly be related to the presence of more acidic Ti−OH

formation of the elongated platelet TS-1 zeolite crystals with

dominant TiO species.

The catalytic properties of various TS-1 zeolites were ﬁrst

investigated for the 1-hexene epoxidation with H O as an

groups in TiO species of TS-1#B_15Et:0.6LC zeolites, which

oxidant, as shown in Table 2. TS-1#con and TS-

can lead to the side reaction of the ring opening of the

#C_0Et:0.6LC had relatively low catalytic activities, with 30

cyclopentene epoxide. The formation of the side product

glutaraldehyde could be signiﬁcantly inhibited when the weak

basic acetonitrile is used as the solvent, although an obvious

decrease in the catalytic activity of TS-1 #B_15Et:0.6LC

catalysts was observed (entry 4 in Table S2). As for the

epoxidation of 1-heptene, all of the TS-1 zeolites including TS-

and 25% conversion after 2 h of reaction, respectively, which

are consistent with the literature-reported TS-1 catalysts

synthesized by conventional hydrothermal methods. The

conversion of 1-hexene increased to 42% upon using TS-

#A_15Et:0.4LC as a catalyst, whereas the highest activity was

obtained over the catalyst of TS-1#B_15Et:0.6LC, with 55% 1-

hexene conversion and 96% epoxide selectivity, respectively.

The TOF over TS-1#B_15Et:0.6LC catalyst could reach 131

#B_15Et:0.6LC exhibited relatively low catalytic activity,

which provides indirect evidence that the active TiO species

−

should mainly distribute on the inner surface (or in the

under the test conditions, which was around two times as

framework) of TS-1 zeolites, similar to the TiO species.

high as that of the conventional TS-1#con zeolite (with TOF

−

The recycling experiments suggested that the TS-

#B_15Et:0.6LC catalyst can be easily recycled after simple

of 65 h ). On the basis of the above characterization results, it

can be proposed here that the presence of abundant “TiO₆”

active sites in TS-1#B_15Et:0.6LC should be mainly

responsible for its superior catalytic activity. The sheet-like

morphology of this catalyst may expose more geometric

surface area and catalytically active sites in the direction of the

ﬁltration, and its catalytic activity remained good after ﬁve

cycles (Figure 10). Additional characterization results based on

XRD, TEM, and UV−vis DRS spectra demonstrate that the

morphology, structure, and coordination states of the Ti

species of the used TS-1#B_15Et:0.6LC zeolite are well

remaining in comparison with the fresh one (Figure S10 −

(

010), owing to the larger c/b aspect ratio of 10, and may also

provide a shorter diﬀusion path for reactants along the straight

channel of the MFI network, thus being another favorite factor

for improving its catalytic property.

2,43

S12). According to the related literature,

it was known that

(H O) (OH) ,

the mononuclear TiO species like Ti(OSi)

In addition, the two other TS-1#B_15Et:0.6LC catalysts

with higher Si/Ti ratios of 74 and 58, which also possess

elongated platelet morphology and isolated TiO and TiO

which are generally derived from the hydrothermal post-

treatment of conventional TS-1 with basic agents, might be

easily converted into condensed Ti species or anatase TiO₂

with the neighboring defect sites of Si−OH or Ti−OH species

species, respectively (Figures S6 −S8), were also quite active

Table 2. Catalytic Results of 1-Hexene Epoxidation with H O as Oxidant over Diﬀerent TS-1 Samples

selectivity (%)

TOF (h⁻¹

catalyst

TS-1#con

TS-1#A_15Et:0.4LC

TS-1#B_15Et:0.6LC

TS-1#B-58_15Et:0.6LC

TS-1#B-74_15Et:0.6LC

TS-1#C_0Et:0.6LC

conversion (%)

epoxides

others

)

H O eﬃciency (%)

2 2

131

150

145

Reaction conditions: catalyst 50 mg, 1-hexene 10 mmol, H O 10 mmol, CH OH 10 mL, temperature 333 K, time 2 h. 2-Methoxyhexan-1-ol, 1-

methoxyhexan-2-ol, and 1,2-hexanediol. Turn over frequency (TOF) was calculated on the basis of the conversion of oleﬁn per hour divided by

the amount of Ti species in the TS-1 zeolite. Eﬃciency of H O for epoxides = (amount of epoxides/amount of H O consumed)*100%

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

The Supporting Information is available free of charge at

Article

by controlling the amount of the growth modiﬁer L-carnitine

and the cosolvent ethanol. The resultant hexagonal plate-like

TS-1#A_15Et:0.4LC and the elongated platelet TS-

#B_15Et:0.6LC zeolites contain abundant mononuclear

TiO and TiO species, respectively, which can be identiﬁed

by combining a variety of characterization means, including

UV−vis, UV Raman, and X-ray absorption spectroscopies. Our

results suggest that L-carnitine can act as a modiﬁer to

modulate the morphology of the zeolite TS-1 by mediating the

growth pathways of the crystals and to adjust the coordinative

environment of the Ti species in the zeolite framework by

building a suitable interaction with the precursor of the Ti

species during the hydrothermal synthesis process. Catalytic

tests demonstrate the superior catalytic activity and structural

stability of TS-1#B_15Et:0.6LC zeolites for the epoxidation of

alkene, which are attributed to the enriched mononuclear TiO₆

species and the perfect crystal morphology. This work oﬀers a

useful strategy to eﬀectively synthesize TS-1 zeolites with

desirable crystal morphology, Ti coordination states, and

excellent catalytic performance, which may bring new

opportunities to develop more eﬃcient titanosilicate zeolites

for catalytic applications.

Figure 10. Recycling experiments of 1-hexene epoxidation catalyzed

by TS-1#B_15Et:0.6LC with H O as the oxidant. Reaction

conditions: catalyst 50 mg, alkene 10 mmol, H O 10 mmol,

CH OH 10 mL, temperature 60 °C. Others: 1-methoxyhexan-2-ol, 2-

methoxyhexan-1-ol, 1,2-hexanediol.

(

caused by an etching process). In the present work, the high

stability of TS-1#B_15Et:0.6LC could be mainly attributed to

the uniform distribution of the framework TiO species in the

perfect zeolites with high crystallinity.

Above all, the catalytic epoxidation properties of the TS-1

zeolites are highly dependent on the coordinative states of the

Ti species and the morphology of the zeolites. Compared with

TS-1#con zeolites, the hexagonal plate TS-1#A_15Et:0.4LC

and elongated platelet TS-1#B_15Et:0.6LC have higher

catalytic activities for alkene epoxidation, which could be

mainly due to the well-deﬁned surface environments, such as

the short path along the (010) plane and the optimal active

TiO and TiO species. It was found that the eﬃciency of

ASSOCIATED CONTENT

sı Supporting Information

https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c01518.

■

Fourier transform Ti K-edge EXAFS ﬁtting curve, SEM

images, UV−vis DRS spectra, TG proﬁles, FT-IR

spectra, PXRD patterns, and catalytic results (PDF)

H O for epoxides could reach 53% when TS-1#B_15Et:0.6LC

was used as the catalyst, which is much higher than that of

other catalysts under the test conditions (Table 2). These

results suggest that the elongated platelet-like TS-

AUTHOR INFORMATION

■

Corresponding Authors

^#^B^_¹⁵^E^t^:⁰^.⁶^L^C^wⁱ^t^h^a^hⁱ^g^h^e^r^c^oⁿ^c^eⁿ^t^r^a^tⁱ^oⁿ^o^f^a^c^tⁱ^v^e^Tⁱ^O6

Mingjun Jia − Key Laboratory of Surface and Interface

Chemistry of Jilin Province, College of Chemistry, Jilin

University, Changchun 130012, P. R. China; orcid.org/

0000-0002-5826-8662 ; Phone: (+86)431-85155390;

Email: jiamj@jlu.edu.cn ; Fax: (+86)431-85168420

Peng Zhang − Department of Chemistry, Dalhousie University,

Halifax B3H4R2, Canada; orcid.org/0000-0003-3603-

0175 ; Email: peng.zhang@dal.ca

Jihong Yu − State Key Laboratory of Inorganic Synthesis and

Preparative Chemistry, College of Chemistry and International

Center of Future Science, Jilin University, Changchun 130012,

P. R. China; orcid.org/0000-0003-1615-5034;

Email: jihong@jlu.edu.cn

species could eﬃciently activate and utilize H O for the

epoxidation reaction. The relatively high utilization eﬃciency

of H O over this catalyst might be at least partly assigned to

the absence of unfavorable Ti species like anatase TiO , which

is responsible for the ineﬃcient decomposition of H O .

Notably, it seems unreasonable to ﬁnd that the sample of TS-

#C_0Et:0.6LC, which contains both catalytically active TiO₄

and TiO species, showed lower catalytic activity than TS-

#A_15Et:0.4LC and TS-1#B_15Et:0.6LC, even lower than

the conventional TS-1#con. This might be explained by the

presence of a portion of anatase TiO in TS-1#C_0Et:0.6LC,

which can accelerate the decomposition of H O , thus

decreasing the conversion of alkene. Concerning the fact that

both TS-1#A_15Et:0.4LC and TS-1#B_15Et:0.6LC catalysts

have similar common features in morphology and composition,

such as a high degree of crystallinity, similar Si/Ti ratios, and

well-developed (010) faces and approximate b-axis thickness

Authors

Xiaojing Song − State Key Laboratory of Inorganic Synthesis

and Preparative Chemistry, College of Chemistry, Jilin

University, Changchun 130012, P. R. China

Xiaotong Yang − Key Laboratory of Surface and Interface

Chemistry of Jilin Province, College of Chemistry, Jilin

University, Changchun 130012, P. R. China

(

∼300 nm), the relatively high catalytic activity of TS-

#B_15Et:0.6LC zeolite may suggest that TiO species are

more active than TiO species for alkene epoxidation.

Tianjun Zhang − State Key Laboratory of Inorganic Synthesis

and Preparative Chemistry, College of Chemistry, Jilin

University, Changchun 130012, P. R. China; Department of

Chemistry, Dalhousie University, Halifax B3H4R2, Canada

Hao Zhang − Key Laboratory of Surface and Interface

Chemistry of Jilin Province, College of Chemistry, Jilin

University, Changchun 130012, P. R. China

CONCLUSIONS

■

In summary, TS-1 zeolites with diﬀerent morphologies and

coordinative states of Ti species have been hydrothermally

synthesized by using L-carnitine as a crystal growth modiﬁer

and ethanol as a cosolvent. The zeolite morphology and the

coordinative states of Ti species could be eﬀectively modulated

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Dummer, N. F.; Perdjon, M.; Liu, J.; Hutchings, G. J. Inter-connected

Article

Qiang Zhang − State Key Laboratory of Inorganic Synthesis and

Preparative Chemistry, College of Chemistry, Jilin University,

Changchun 130012, P. R. China; orcid.org/0000-0002-

(11) Jiao, Y.; Adedigba, A. L.; He, Q.; Miedziak, P.; Brett, G.;

and open pore hierarchical TS-1 with controlled framework titanium

for catalytic cyclohexene epoxidation. Catal. Sci. Technol. 2018, 8,

837-8473

Liu, J.; Zhang, J.; Yu, J.; D ’Agostino, C.; Fan, X. Creation of Al-

211−2217.

12) Bai, R.; Song, Y.; Li, Y.; Yu, J. Creating Hierarchical Pores in

Zeolite Catalysts. Trend. Chem. 2019, 1, 601−611.

13) Jiao, Y.; Forster, L.; Xu, S.; Chen, H.; Han, J.; Liu, X.; Zhou, Y.;

Dianwen Hu − Key Laboratory of Surface and Interface

Chemistry of Jilin Province, College of Chemistry, Jilin

University, Changchun 130012, P. R. China

Xinyu Chang − Key Laboratory of Surface and Interface

Chemistry of Jilin Province, College of Chemistry, Jilin

University, Changchun 130012, P. R. China

Yingying Li − Department of Chemistry, Dalhousie University,

Halifax B3H4R2, Canada

Ziyi Chen − Department of Chemistry, Dalhousie University,

Halifax B3H4R2, Canada

(

Enriched mesoporous ZSM-5 nanoboxes with high catalytic activity:

converting tetrahedral extra-framework Al into framework sites via

post treatment. Angew. Chem., Int. Ed. 2020, 59, 2−11.

(14) Zhang, R.; Zhong, P.; Arandiyan, H.; Guan, Y.; Liu, J.; Wang,

N.; Jiao, Y.; Fan, X. Using ultrasound to improve the sequential post-

synthesis modification method for making mesoporous Y zeolites.

Front. Chem. Sci. Eng. 2020, 14, 275−287.

Complete contact information is available at:

https://pubs.acs.org/10.1021/acs.inorgchem.0c01518

(15) Abdulridha, S.; Jiao, Y.; Xu, S.; Zhang, R.; Garforth, A.; Fan, X.

Mesoporous zeolitic materials (MZMs) derived from zeolite Y using a

microwave method for catalysis. Front. Chem. 2020 , No. 482.

Notes

(

16) Jones, F.; Ogden, M. Controlling crystal growth with modifiers.

CrystEngComm 2010, 12, 1016−1023.

17) Ma, W.; Lutsko, J.; Rimer, J.; Vekilov, P. Antagonistic

cooperativity between crystal growth modifiers. Nature 2020, 577,

97−515.

18) Liu, Z.; Dong, X.; Zhu, Y.; Emwas, A. H.; Zhang, D.; Tian, Q.;

The authors declare no competing ﬁnancial interest.

Han, Y. Investigating the influence of mesoporosity in zeolite beta on

ACKNOWLEDGMENTS

■

(

We acknowledge the ﬁnancial support by the National Natural

Science Foundation of China (grants 21920102005, 21835002,

its catalytic performance for the conversion of methanol to

hydrocarbons. ACS Catal. 2015, 5, 5837−5845.

1621001, and 21173100), the National Key Research and

Development Program of China (grant 2016YFB0701100),

and the 111 Project (B17020). The APS was operated for the

U.S. DOE Oﬃce of Science by Argonne National Laboratory,

and the CLS@APS facilities (Sector 20) were supported by the

U.S. DOE under contract no. DEAC02-06CH11357 and the

Canadian Light Source and its funding partners.

(19) Lv, G.; Deng, S.; Zhai, Y.; Zhu, Y.; Li, H.; Wang, F.; Zhang, X.

P123 lamellar micelle assisted construction of hierarchical TS-1

stacked nanoplates with constrained mesopores for enhanced

oxidative desulfurization. Appl. Catal., A 2018, 567, 28−35.

20) Li, R.; Smolyakova, A.; Maayan, G.; Rimer, J. D. Designed

peptoids as tunable modifiers of zeolite crystallization. Chem. Mater.

017, 29, 9536−9546.

21) Davis, T. M.; Snyder, M. A.; Krohn, J. E.; Tsapatsis, M.

Nanoparticles in lysine-silica sols. Chem. Mater. 2006, 18, 5814−5816.

22) Zhao, D.; Wang, Y.; Chu, W.; Wang, X.; Zhu, X.; Li, X.; Xie, S.;

REFERENCES

■

1) Li, Y.; Yu, J. H. New stories of zeolite structures: their

descriptions, determinations, predictions, and evaluations. Chem. Rev.

(

014, 114, 7268−7316.

Wang, H.; Liu, S.; Xu, L. Direct synthesis of hollow single-crystalline

zeolite Beta using a small organic lactam as a recyclable hollow-

directing agent. J. Mater. Chem. A 2019, 7, 10795−10804.

2) Lupulescu, A. I.; Kumar, M.; Rimer, J. D. A facile strategy to

design zeolite L crystals with tunable morphology and surface

architecture. J. Am. Chem. Soc. 2013, 135, 6608 −6617.

(23) Chen, C.; Zhai, D.; Dong, L.; Wang, Y.; Zhang, J.; Liu, Y.;

Chen, Z.; Wang, Y.; Qian, W.; Hong, M. Organic anion facilitates in

3) Serrano, D. P.; Escola, J. M.; Pizarro, P. Synthesis strategies in

situ synthesis of mesoporous LTA zeolites. Chem. Mater. 2019, 31,

the search for hierarchical zeolites. Chem. Soc. Rev. 2013, 42, 4004−

035.

4) Perego, C.; Millini, R. Porous materials in catalysis: challenges

for mesoporous materials. Chem. Soc. Rev. 2013, 42, 3956−3976.

5) Choi, M.; Na, K.; Kim, J.; Sakamoto, Y.; Terasaki, O.; Ryoo, R.

24) Watanabe, R.; Yokoi, T.; Tatsumi, T. Synthesis and application

528−1536.

of colloidal nanocrystals of the MFI-type zeolites. J. Colloid Interface

Sci. 2011, 356, 434−441.

Stable single-unit-cell nanosheets of zeolite MFI as active and long-

(25) Chen, Z.; Zhang, J.; Yu, B.; Zheng, G.; Zhao, J.; Hong, M.

lived catalysts. Nature 2009, 461, 246−249.

Amino acid mediated mesopore formation in LTA zeolites. J. Mater.

Chem. A 2016, 4, 2305−2313.

6) Deng, X. J.; Wang, Y. N.; Shen, L.; Wu, H. H.; Liu, Y. M.; He, M.

Y. Low cost synthesis of Titanium Silicalite-1 (TS-1) with highly

catalytic oxidation performance through a controlled hydrolysis

process. Ind. Eng. Chem. Res. 2013, 52, 1190−1196.

(26) Zhang, J.; Chen, Z.; Wang, Y.; Zheng, G.; Zheng, H.; Cai, F.;

Hong, M. Influence of the nature of amino acids on the formation of

mesoporous LTA-type zeolite. Microporous Mesoporous Mater. 2017,

(

7) Li, H.; Jin, J.; Wu, W.; Chen, C.; Li, L.; Li, Y.; Zhao, W.; Gu, J.;

(

52, 79−89.

Chen, G.; Shi, J. L. Synthesis of a hierarchically macro-/mesoporous

zeolite based on a micro-emulsion mechanism. J. Mater. Chem. 2011,

27) Zhang, J.; Bai, S.; Chen, Z.; Wang, Y.; Dong, L.; Zheng, H.; Cai,

F.; Hong, M. Core −shell zeolite Y with antnest like hollow interior

constructed by amino acids and enhanced catalytic activity. J. Mater.

Chem. A 2017, 5, 20757−20764.

(

1, 19395.

8) Xin, H.; Zhao, J.; Xu, S.; Li, J.; Zhang, W.; Guo, X.; Hensen, E.;

Yang, Q.; Li, C. Enhanced catalytic oxidation by hierarchically

(28) Qin, W.; Agarwal, A.; Choudhary, M. K.; Palmer, J. C.; Rimer,

structured TS-1 zeolite. J. Phys. Chem. C 2010 , 114 , 6553 −6559.

J. D. Molecular modifiers suppress nonclassical pathways of zeolite

crystallization. Chem. Mater. 2019, 31, 3228−3238.

9) Fang, Y. M.; Hu, H. Q.; Chen, G. H. In situ assembly of zeolite

nanocrystals into mesoporous aggregate with single crystal like

morphology without secondary template. Chem. Mater. 2008, 20,

(29) Zhang, Q.; Mayoral, A.; Terasaki, O.; Zhang, Q.; Ma, B.; Zhao,

C.; Yang, G.; Yu, J. H. Amino Acid assisted construction of single-

crystalline hierarchical nanozeolites via oriented aggregation and

intraparticle ripening. J. Am. Chem. Soc. 2019, 141, 3772−3776.

(30) Zhang, Q.; Chen, G.; Wang, Y.; Chen, M.; Guo, G.; Shi, J.; Luo,

J.; Yu, J. H. High-quality single-crystalline MFI-Type nanozeolites: A

(

670−1672.

10) Dai, C.; Zhang, A.; Li, L.; Hou, K.; Ding, F.; Li, J.; Mu, D.;

Song, C.; Liu, M.; Guo, X. Synthesis of hollow nanocubes and

macroporous monoliths of silicalite-1 by alkaline treatment. Chem.

Mater. 2013, 25, 4197−4205.

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

performance of TS-1 in the hydrogen peroxide to propylene oxide

Article

facile synthetic strategy and MTP catalytic studies. Chem. Mater.

reaction. J. Phys. Chem. C 2018, 122, 9021−9034.

(49) Li, C.; Xiong, G.; Xin, Q.; Liu, J.-k.; Ying, P.-l.; Feng, Z.-c.; Li,

J.; Yang, W.-b.; Wang, Y.-z.; et al. UV resonance raman spectroscopic

identification of titanium atoms in the framework of TS-1 zeolite.

Angew. Chem., Int. Ed. 1999, 38, 2220−2222.

018, 30, 2750−2758.

31) Prech, J. Catalytic performance of advanced titanosilicate

selective oxidation catalysts − a review. Catal. Rev.: Sci. Eng. 2018, 60,

1−131.

32) Bregante, D. T.; Flaherty, D. W. Periodic trends in olefin

epoxidation over group IV and V framework substituted zeolite

catalysts: A kinetic and spectroscopic study. J. Am. Chem. Soc. 2017,

(50) Dong, J.; Zhu, H.; Xiang, Y.; Wang, Y.; An, P.; Gong, Y.; Liang,

Y.; Qiu, L.; Zheng, A.; Peng, X.; Lin, M.; Xu, G.; Guo, Z.; Chen, D.

Toward a unified identification of Ti location in the MFI framework

of high-Ti-loaded TS-1: combined EXAFS, XANES, and DFT study.

J. Phys. Chem. C 2016, 120, 20114−20124.

(

39, 6888−6898.

33) Jin, S.; Wang, Z.; Tao, G.; Zhang, S.; Liu, W.; Fu, W.; Zhang,

B.; Sun, H.; Wang, Y.; Yang, W. UV resonance raman spectroscopic

insight into titanium species and structure-performance relationship in

boron-free Ti-MWW zeolite. J. Catal. 2017, 353, 305−314.

(

51) Chrissanthopoulos, A.; Klouras, N.; Ntala, Ch.; Sevastos, D.;

Dalas, E. Inhibition of hydroxyapatite formation in the presence of

titanocene −aminoacid complexes: an experimental and computa-

tional study. J. Mater. Sci.: Mater. Med. 2015, 15.

(

34) Shan, Z.; Wang, H.; Meng, X.; Liu, S.; Wang, L.; Wang, C.; Li,

F.; Lewis, J. P.; Xiao, F. S. Designed synthesis of TS-1 crystals with

controllable b-oriented length. Chem. Commun. 2011, 47, 1048 −1050.

35) Deng, Z.; Yang, Y.; Lu, X.; Ding, J.; He, M.; Wu, P. Studies on

the epoxidation of methallyl chloride over TS-1 microsphere catalysts

in a continuous slurry reactor. Catal. Sci. Technol. 2016, 6, 2605−

36) Du, S.; Li, F.; Sun, Q.; Wang, N.; Jia, M.; Yu, J. H. A green

615.

surfactant-assisted synthesis of hierarchical TS-1 zeolites with

excellent catalytic properties for oxidative desulfurization. Chem.

Commun. 2016, 52, 3368−3371.

37) Du, S.; Sun, Q.; Wang, N.; Chen, X.; Jia, M.; Yu, J. H. Synthesis

of hierarchical TS-1 zeolites with abundant and uniform intracrystal-

line mesopores and their highly efficient catalytic performance for

oxidation desulfurization. J. Mater. Chem. A 2017, 5, 7992−7998.

(

38) Bai, R.; Sun, Q.; Song, Y.; Wang, N.; Zhang, T.; Wang, F.; Zou,

Y.; Feng, Z.; Miao, S.; Yu, J. Intermediate-crystallization promoted

catalytic activity of titanosilicate zeolites. J. Mater. Chem. A 2018, 6,

39) Zhang, T.; Chen, X.; Chen, G.; Chen, M.; Bai, R.; Jia, M.; Yu, J.

757−8762.

Synthesis of anatase-free nano-sized hierarchical TS-1 zeolites and

their excellent catalytic performance in alkene epoxidation. J. Mater.

Chem. A 2018, 6, 9473−9479.

40) Guo, Q.; Sun, K.; Feng, Z.; Li, G.; Guo, M.; Fan, F.; Li, C. A

thorough investigation of the active titanium species in TS-1 zeolite

by in situ UV resonance raman spectroscopy. Chem. - Eur. J. 2012, 18,

(

3854−13860.

41) Wu, L.; Tang, Z.; Yu, Y.; Yao, X.; Liu, W.; Li, L.; Yan, B.; Liu,

Y.; He, M. Facile synthesis of a high-performance titanosilicate

catalyst with controllable defective Ti(OSi) OH sites. Chem.

Commun. 2018, 54, 6384−6387.

(

42) Wu, L.; Deng, X.; Zhao, S.; Yin, H.; Zhuo, Z.; Fang, X.; Liu, Y.;

He, M. Synthesis of a highly active oxidation catalyst with improved

distribution of titanium coordination states. Chem. Commun. 2016,

(

2, 8679−8682.

43) Xu, L.; Huang, D. D.; Li, C. G.; Ji, X.; Jin, S.; Feng, Z.; Xia, F.;

Li, X.; Fan, F.; Li, C.; Wu, P. Construction of unique six-coordinated

titanium species with an organic amine ligand in titanosilicate and

their unprecedented high efficiency for alkene epoxidation. Chem.

Commun. 2015, 51, 9010−9013.

44) Xu, W.; Zhang, T.; Bai, R.; Zhang, P.; Yu, J. A one-step rapid

synthesis of TS-1 zeolites with highly catalytically active mononuclear

TiO species. J. Mater. Chem. A 2020, 8, 9677−9683.

45) Fan, W.; Fan, B.; Shen, X.; Li, J.; Wu, P.; Kubota, Y.; Tatsumi,

T. Effect of ammonium salts on the synthesis and catalytic properties

of TS-1. Microporous Mesoporous Mater. 2009, 122, 301−308.

46) Liu, M.; Chang, Z.; Wei, H.; Li, B.; Wang, X.; Wen, Y. Low-cost

synthesis of size controlled TS-1 by using suspended seeds: from

screening to scale-up. Appl. Catal., A 2016 , 525 , 59 −67.

47) Du, Q.; Guo, Y.; Wu, P.; Liu, H. Synthesis of hierarchically

porous TS-1 zeolite with excellent deep desulfurization performance

under mild conditions. Microporous Mesoporous Mater. 2018, 264,

(

72−280.

48) Signorile, M.; Crocella,

Bonino, F.; Bordiga, S. Effect of Ti speciation on catalytic

V.; Damin, A.; Rossi, B.; Lamberti, C.;