Communication
DOI: 10.1002/bkcs.12049
BULLETIN OF THE
H. S. Lee et al.
KOREAN CHEMICAL SOCIETY
Effect of Mesoporosity on Methanol-to-Olefin Reactions over
Organosilane-Directed Mesoporous SSZ-13 Zeolites
†,
Hae Sol Lee,† Sung Chan Nam,‡, and Changbum Jo
*
*
†Department of Chemistry and Chemical Engineering, Inha University, Incheon 22212, South Korea.
*E-mail: jochangbum@inha.ac.kr
‡Greenhouse Gas Laboratory, Korea Institute of Energy Research, Daejeon 34129, South Korea.
*E-mail: scnam@kier.re.kr
Received February 19, 2020, Accepted April 22, 2020
Keywords: Methanol-to-olefin, Mesoporous zeolite, SSZ-13 zeolites, Chabazite, Deactivation
Methanol to olefin (MTO) reactions are among the most
promising pathways in C1 chemistry, which provides
value-added olefins from synthesis gas via methanol. Tre-
mendous research efforts have been devoted to MTO reac-
tions since they were proposed by Mobil in 1977.1 In
particular, significant progress has been made in under-
standing reaction kinetics and mechanisms, and in the
developments of efficient catalysts. Currently, the MTO
process has been demonstrated on plant scale, and a
methanol-to-propene process, developed by Lurgi, is ready
for commercialization.2
have several advantages over conventional zeolites, which
include the rapid diffusion of reactants through mesopores. For
this reason, mesoporous zeolites can provide significantly
enhanced catalytic lifetimes over conventional zeolites in some
reactions, which include MTO.19 However, it has been
recently reported that mesoporous zeolites typically possess
framework defects that reduce acid strength and hydrothermal
stability,20–21 and for MTO reactions, hydrothermal stability is
important as it enhances catalyst lifetime because the water
produced as a byproduct damages zeolites.22,23 From this point
of view, the generation of mesoporosity does not guarantee
enhanced MTO catalyst stability.
Zeolites are a class of crystalline microporous alumino-
silicates and are widely used as solid acid catalysts in petro-
chemistry because they possess catalytically active acid
sites onto micropores and high (hydro)thermal stabilities.3
Zeolites can exhibit shape-selective functionality in some
acid-catalyzed reactions, and shape-selectivity can be con-
trolled using zeolite pore size, shape, and connectivity.4–6
However, microporous networks can retard the diffusion
rates of chemical reagents due to their too narrow pore
diameters and this causes pre-cokes to remain in micro-
pores and thereby accelerate deactivation.7 For example,
SSZ-13 zeolite with chabazite structure (micropore diame-
ter, 0.37 nm × 0.42 nm)8 is rapidly deactivated during
MTO reaction due to the deposition of carbonaceous cokes,
which prevent methanol accessing active sites.9,10 There-
fore, MTO processes typically require frequent catalyst
regeneration, and unfortunately, catalyst regeneration irre-
versibly damages active acid sites, which further reduces
initial catalytic activities.11,12 To avoid this situation, zeo-
lite structures should be investigated in detail to prevent
coke deposition and catalyst deactivation.
The present study was undertaken to investigate the effect of
mesoporosity on the MTO catalyst lifetimes.20,24,25 Accord-
ingly, mesoporous SSZ-13 zeolites were synthesized using
organosilane surfactants (i.e., C18H37-N+(Me)2-C3H6-Si(OMe)3)
as the mesopore generator at a gel composition of 400 SiO2:
10 Al2O3: x organosilane surfactant (x = 1, 2, 4, 6): 100 N,N,
N-trimethyladamantan-1-ammonium hydroxide (TMAdOH):
9000 H2O.24 Amounts of organosilane surfactants were varied
to produce SSZ-13 zeolites with different mesoporosities. The
resultant zeolites are denoted by x-MP-SSZ, where x represents
the amount of organosilane molecule in the gel composition.
The catalytic lifetimes of these zeolites in MTO reactions were
investigated for the textural properties of zeolites, which were
derived from N2 adsorption isotherms.
Figure 1 shows X-ray diffraction (XRD) patterns and N2
adsorption–desorption isotherms of a xMP-SSZ-13 series.
Bulk SSZ-13 zeolite is displayed for comparison purposes.
As shown in Figure 1(a), a series of xMP-SSZ zeolites
exhibited several reflection XRD peaks with positions iden-
tical to those of bulk SSZ-13 zeolite. Other than for these
diffraction peaks, no other XRD peak was observed in the
wide-angle region, which indicated the zeolite samples
obtained in the present work were pure and highly crystal-
line chabazite. Pore structures were investigated using N2
adsorption–desorption isotherms (Figure 1(b)). Bulk SSZ-
13 zeolite showed a sharp increase at <P/P0 of 0.01. This
abrupt increase observed at such a low-relative pressure
was attributed to N2 condensation within micropores.
Hierarchically mesoporous-microporous zeolites (hereafter,
referred to as denoted by mesoporous zeolites) are aluminosili-
cates with the characteristics of secondary mesoporosity and
crystalline microporous structures. Several routes such as post-
synthetic modification13 and the use of multiammonium-
surfactants as crystal-growth inhibitors14,15 and organosilanes
as mesopore-generating agents16,17 have been devised for the
production of high-quality mesoporous zeolite.18 These zeolites
Bull. Korean Chem. Soc. 2020, Vol. 41, 595–598
© 2020 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Wiley Online Library
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