Angewandte
Chemie
Structure-Directing Agents
Hot Paper
Synthesis of Silicate Zeolite Analogues Using Organic Sulfonium
Compounds as Structure-Directing Agents
Changbum Jo, Sungjune Lee, Sung June Cho, and Ryong Ryoo*
Abstract: A microporous crystalline silica zeolite of the MEL
structure type and three other zeolite analogues composed of
germanosilicate frameworks were synthesized using tributyl-
sulfonium, triphenylsulfonium, or tri(para-tolyl)sulfonium as
the structure-directing agent. The germanosilicates thus
obtained had ISV, ITT, or a new zeolite structure depending
on the synthesis conditions. The structure of the new germa-
nosilicate was solved using X-ray powder diffraction data with
the aid of a charge-flipping method. The solution indicated
a crystal structure belonging to the P63/mmc space group with
cell parameters of a = 16.2003 and c = 21.8579 . After
calcination, the new germanosilicate material exhibited two
types of accessible micropores with diameters of 0.61 and
0.78 nm.
hydrothermal reaction temperature, by using organic struc-
ture-directing agents (SDAs), and by crystal seeding.[7]
Among them, the most versatile method entails the use of
SDAs, typically organic ammonium compounds.[8,9] The
cationic form of the SDAs provides tight electrostatic binding
to the silicate anions under hydrothermal synthesis condi-
tions. The SDA cations remain in tight proximity while the
silicate anions are polymerized into a three-dimensional
zeolite framework. The SDA cations remain embedded in the
polymerized silicate framework, stabilizing the metastable,
porous zeolite phase. Hence, the choice of SDA is the most
important factor affecting the framework topologies of the
final zeolite products, although the inverse molecular top-
ologies are not precisely imprinted to the zeolite frame-
work.[10] Previous studies have shown that ammonium cations
with C/N+ values between 11 and 15 are the most effective for
a variety of high-silica zeolites.[9] Cyclic ethers[11] and metal
complexes[12] were also used as zeolite SDAs although they
are less common than the ammonium species. Recently,
Corma and co-workers synthesized zeolitic materials with
new framework structures (e.g., ITQ-27, ITQ-34, ITQ-47, and
ITQ-52) using phosphonium,[13,14] phosphazene[15] and amino-
phosphonium[16] cations. In our work, we explored the
possibility of using organic sulfonium compounds as SDAs
for the synthesis of zeolites and zeolite analogues. In
particular, we focused on the possibility of synthesizing
germanosilicates with extra-large pores.
Three organosulfonium compounds (triphenylsulfonium,
tri(para-tolyl)sulfonium, and tributylsulfonium) were tested
for the synthesis of crystalline microporous materials in this
study (see the Supporting Information for the synthesis of the
organosulfonium compounds and Figure S1 for their molec-
ular structures). The properties of the microporous materials
obtained with the sulfonium compounds are summarized in
Table 1. Crystalline germanosilicates of three structure types
(ISV, ITT, and an unknown structure) could be synthesized
using triphenylsulfonium and tri(para-tolyl)sulfonium as
SDAs in fluoride media. The germanosilicate zeolite analogue
with the unknown structure is hereafter referred to as
Z
eolites and zeolite analogues are a family of crystalline
microporous materials, for which more than 220 structure
types have been discovered to date.[1] Their microporous
structures are built of silicate or phosphate frameworks to
retain uniform micropores with specific pore shapes, diame-
ters, and connectivity, which depend on the structure type.[2]
These microporous materials can discriminate adsorbate
molecules that are larger than their specific pore apertures.
The frameworks can incorporate various elements, which
often yield strongly acidic or other catalytic functionalities.[3,4]
Chemical reactions at these catalytic sites can occur in
a shape-selective manner, as the reactants and products
should be small enough to diffuse through the pore aper-
tures.[5] Owing to the porous textural properties of the
inorganic frameworks and their high stability, many zeolite-
based catalysts are currently used in oil-refinery and petro-
chemical processes.[6] Many of these applications are still in
need of zeolites with new porous textures (i.e., pore shapes
and diameters, connectivity, and framework constituents).
The zeolite structure can be controlled by adjusting the
synthesis conditions, such as the gel composition or the
[*] Dr. C. Jo, S. Lee, Prof. R. Ryoo
Center for Nanomaterials and Chemical Reactions
Institute for Basic Science (IBS)
Daejeon 305-701 (Korea)
E-mail: rryoo@kaist.ac.kr
Table 1: Synthesis of crystalline microporous materials using organo-
sulfonium SDAs.[a]
S. Lee, Prof. R. Ryoo
Department of Chemistry, KAIST
Daejeon 305-701 (Korea)
SDA
Structure type
triphenylsulfonium
triphenylsulfonium
tri(para-tolyl)sulfonium
tributylsulfonium
ISV
Prof. S. J. Cho
unknown (GeZA)
ITT
MEL
Department of Applied Chemical Engineering
Chonnam National University
Gwangju 500-207 (Korea)
Supporting information for this article is available on the WWW
[a] Synthesis procedures and detailed results highlighting the effect of
the gel composition are provided in Figure S2.
Angew. Chem. Int. Ed. 2015, 54, 12805 –12808
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
12805