富山大学研究推進機構水素同位体科学研究センター研究報告 37：29－38，2017.

ノート

種結晶法による CHA 型ゼオライトの繰り返し合成と構造変化

田口 明*，中森拓実，米山優紀

富山大学

研究推進機構〒930-8555

水素同位体科学研究センター
富山市五福 3190

Synthesis and Structural Change of CHA Type Zeolite in the Repeated SeedGrowth Synthesis

Akira Taguchi*, Takumi Nakamaori, Yuki Yoneyama

Hydrogen Isotope Research Center
Organization for Promotion of Research, University of Toyama
Gofuku 3190, Toyama 930-8555(Received January 19, 2018; accepted June 22, 2018)

Abstract
The synthesis of CHA type zeolite using seed crystals was studied. CHA zeolite could beobtained by seeded growth synthesis, where the initial seeds of CHA zeolite were prepared by
the hydrothermal conversion of FAU zeolite. However, the subsequent use of the resultant
CHA zeolite as seed crystals resulted in a structure change to sanidine and analcine.

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田口

明・中森拓実・米山優紀

Research note
Zeolites have applications in a variety of fields including detergent builders,
adsorbents/desiccants and catalysts [1].

Recently, chabazite type zeolites, comprising 8-

membered rings and assigned the framework type CHA by the International Zeolite Association[2], have been attracting new attention. This is because high silica CHA zeolite (so-called SSZ13) or silicoaluminophosphate (SAPO-34) catalyzes the methanol-to-olefin reaction with higholefin (ethylene and propylene) selectivity [3-5]. More recent studies have shown that CHA
zeolite, especially, copper-ion exchanged SSZ-13 (Cu-SSZ-13), provides a high NOx reduction
activity using NH3 as a reductant (NH3-SCR) [6-8].
There are two main methods for the synthesis of CHA zeolite.

One is a widely known,

reliable method with potential applicability to the synthesis of SSZ-13, which uses N,N,Ntrimethyladamantammonium hydroxide as an organic structure directing agent (OSDA) [5,911].

The other is the structure conversion method, where a well-defined zeolite ishydrothermally converted to CHA zeolite.

Using FAU type zeolite as the starting material isprobably the most popular method for CHA synthesis [12].

We also prepared CHA zeolite(K+-type) from FAU (H-Y) zeolite, and found an intrinsic H2 and D2 sorption properties insubsequently Na+ or Ca2+ ion-exchanged CHA zeolites [13].
One drawback of this CHA zeolite synthesis, especially for SSZ-13, is the use of expensive
OSDA.

This underscores the importance of developing CHA zeolite synthesis without

requiring OSDA.

Using seed crystals of CHA zeolite in zeolite growth is a progressive

process, and Imai et al. successfully achieved seed-assisted CHA zeolite growth [14].

Also,

Liu et al. reported the ultrafast (within 10 min) synthesis of CHA zeolite by using a continuousflow reactor [15].

However, the initial seed crystals of CHA used in their experiments wereprepared using OSDA.

In the present report, we studied the seed-assisted growth of CHA

zeolite, where the initial CHA zeolite was prepared by structure conversion method from FAU

30

種結晶法による CHA 型ゼオライトの繰り返し合成と構造変化

zeolite.

: CHA: Sanidine

Potassium type CHA zeolite was prepared by
the hydrothermal conversion of FAU zeolite as
described in the literature [9,10]. To 16.1 mL of a(a)

KOH (45 wt%) aqueous solution, 15 g of HY-

Then, 119 mL of deionized water was poured,followed by vigorous shaking for 30 sec.

Intensityzeolite (HSZ-320HOA, Tosoh Corp.) was added.
(b)

The

mixed solution was kept static in an oven at 100 ºC
for 4 days.

(c)

After cooling to room temperature, theprecipitate was recovered by filtration, washed with(d)water, and dried overnight at 100 ºC. The white10

solid was calcined at 600 ºC for 3 h under air flow(ca. 100 cm3/min), with a ramp rate of 2 ºC/min.

Sanidine
Analcime

The obtained sample was denoted as CHA-HT. Fig. 1

20
2θ / º30

40

XRD patterns of (a) CHA-HT, (b)CHA-Seed1, (c) CHA-Seed2 and (d) CHA-

Figure 1 (a) shows the XRD (X-ray diffraction) Seed3. The lengths of the arrows beside (a) topatterns of CHA-HT. The diffraction signals were (d) each correspond to 100 cps. The expected
positions of signals from sanidine and analcime

assignable to those from the CHA structure [2], are schematically drawn at the bottom.
suggesting the successful preparation of CHA
zeolite.

Using CHA-HT as seed crystals, the growth of CHA zeolite with an amorphousaluminosilicate gel under hydrothermal conditions was investigated.

Here, the mixed solutionof fumed silica (1.0 g, Cab-O-Sil (M-5); Cabot Corporation, USA), NaAlO2 (0.13 g), NaOH
(0.47 g), KOH (0.17 g; all from Wako Pure Chemical Industries, Ltd.) in H2O (30 mL) was used
for preparing synthetic aluminosilicate gel according to the literature [14].

The molar

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田口

Table 1

明・中森拓実・米山優紀

Preparation and Si/Al ratio estimated by EDS and 29Si MAS NMR measurements

Sample name Synthetic conditions
CHA-HT
CHA-Seed1
CHA-Seed2
CHA-Seed3

Hydrothermally synthesized
Synthesized using CHA-HT as a seed
Synthesized using CHA-Seed1 as a seed
Synthesized using CHA-Seed2 as a seed

Yield
/g
0.45
0.47
0.41

Si/Al ratio
EDS
NMR
2.5
2.17
3.0
2.73
3.4
2.76
4.0
n.d.

composition of this synthetic aluminosilicate gel corresponded to 1.0 SiO2 : 0.1 NaAlO2 : 0.7
NaOH : 0.18 KOH : 100 H2O. To this synthetic solution, CHA-HT (20 wt%, corresponding
to about 0.36 g) as the seed crystals was added, and the mixture was hydrothermally treated at
170 ºC for 24 h with tumbling at 20 rpm using a hydrothermal synthesis reactor instrument(HIRO COMPANY).

The product, denoted as CHA-Seed1 (see Table 1 for a summary ofsample names), was obtained by filtration, drying and calcination in the same manner as
mentioned above.

The yield of CHA-Seed1 was higher than the weight of the seed crystals

used, indicating that crystal growth from the synthetic alminosilicate gel had occurred.
The XRD pattern of CHA-Seed1 was as shown in Figure 1 (b).

The diffraction signals

were assignable to those from the CHA structure. Also, the diffraction signals were sharperand considerably more intense as compared with CHA-HT, suggesting that the crystallinity of
CHA zeolite had been improved.

The crystalline morphology of CHA-Seed1 observed by FE-

SEM (JEM-6701F, JEOL) is represented in Figure 2 (b), together with that of CHA-HT (Figure
2 (a)).

CHA-HT was composed from an aggregation of cube shaped crystals, the size of which

generally ranging from several ten to 100 nm.

On the other hand, CHA-Seed1 comprised ofa stack of slab shaped crystals. The size of slabs was not uniform, ranging from several ten to
several hundred nm.

These were significantly different from those of CHA-HT, and the large

sizes of crystals were consistent with the intense diffraction signals from CHA-Seed1.
In this study, further growth of CHA zeolites was also studied. CHA-Seed2 was preparedfrom the synthetic aluminosilicate gel in the same manner as mentioned above. Here, 20 wt%
of CHA-Seed1 was used as seed crystals (Table 1).

32

Subsequently, the resulting CHA-Seed2

種結晶法による CHA 型ゼオライトの繰り返し合成と構造変化(a) CHA-HT(b) CHA-Seed1

100 nm(c) CHA-Seed2

100 nm(d) CHA-Seed3

100 nmFig. 2100 nmFE-SEM pictures of (a) CHA-HT, (b) CHA-Seed1, (c) CHA-Seed2 and (d) CHA-Seed3.

was used as seed crystals for the preparation of CHA-Seed3.

The XRD patterns of theobtained CHA-Seed2 and CHA-Seed3 were as shown in Figure 1.

For the CHA-Seed2,

although well-resolved and intense diffraction signals from the CHA structure could be
confirmed, the diffraction signals assignable to sanidine (general formula; (K,Na)(Si,Al)4O8,
JCPDS: 025-0618), for example, at 20.9, 23.5, 26.8, 27.7, 29.8 and 32.2º (2θ) were observed(marked signals in Figure 1 (c)). The latter signals, as well as other signals that appeared
newly or had been hidden in the signals from CHA-Seed2, dominated in CHA-Seed3 (Figure 1(d)).

The diffraction signals were assignable to sanidine and analcime (ANA, general formula;Na(Si2Al)O6·H2O, JCPDS: 041-1478) based on their peak positions illustrated in Figure 1.
The drastic change of crystalline structure in CHA-Seed3 could be confirmed by FE-SEM study.

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田口

明・中森拓実・米山優紀

The crystalline morphology of CHA-Seed3, an aggregation of nonuniform ellipsoid-shaped
crystals with the size of about several hundred to 1,000 nm, was totally different from that of
CHA-HT or CHA-Seed1 (Figure 2). Thus, it was found that the seeded growth of CHA zeolite
under hydrothermal conditions caused the collapse of specific CHA structures.

Actually, the

FE-SEM study of CHA-Seed2 showed large ellipsoid-shaped crystals rarely (e.g. on the rightside in Figure 2 (c)), while the main product was slab shaped crystals.
The Si/Al ratio estimated by EDS (Energy-dispersive) spectroscopy (JEOL, JED-2300)
combined with FE-SEM increased from 2.48 in CHA-HT to 2.97, 3.44 and 3.96 in CHA-Seed1,
CHA-Seed2 and CHA-Seed3, respectively, showing an increase in Si content by thesubsequence growth of CHA zeolite (Table 1).

Imai et al. reported that the seed crystals

mostly dissolved in this synthetic aliminosilicate gel in 1 h (170 ºC) [14].

Thus, the above

results are consistent with the dissolution-recrystallization growth of CHA zeolite.
zeolites are not in a thermodynamically stable phase but in a metastable phase [16].

Also,

Therefore,

the non-optimal synthetic conditions in this study is considered to have resulted in the formationof undesired aluminosilicates from CHA zeolite during repeated synthesis. It should be notedthat the hydrothermal synthesis of aluminosilicate gel without seed crystals resulted in theformation of PHI type zeolite [2,14].
The growth and the structural change of CHA zeolite were investigated by using MAS(magic-angle spinning) NMR spectroscopy (at 6 kHz spinning, ECX-500, JEOL).
shows the single-pulse spectra of 29Si MAS NMR.
observed at about -88, -92, -98, -103 and -108 ppm.

Figure 3

Mainly, the resonance signals wereThese signals were assignable to Si(4Al),

Si(3Al), Si(2Al), Si(1Al) and Si(0Al), respectively. Here, n in Si(nAl) indicates the numberof Al atoms bonding to Si via O.

One interesting point is that the relative intensities of Si(0Al)and Si(1Al) of CHA-Seed1 increased in comparison with those of CHA-HT.

34

In addition, the種結晶法による CHA 型ゼオライトの繰り返し合成と構造変化

relative intensities of Si(3Al) and Si(4Al) decreasedin CHA-Seed1.

This suggests an increase in thenumber of Si-O-Si bonds in CHA zeolite made byseeded growth.

CHA-Seed3, on the other hand,showed broadening of signals.

As the XRD

CHA-HTmeasurement revealed, CHA-Seed3 was a mixtureof sanidine and analcime. Thus, the overlappingof

Si(2Al)signals

from

two

CHA-Seed1

different

aluminosilicates gave rise to the broadening of
signals.

CHA-Seed2

Besides, sanidine is a polymorph crystal.

CHA-Seed3

This suggests that the heterogeneity of the Si
tetrahedral environment led to the broadening of-60.0

resonance signals.

-80.0-100.0 -120.0 -140.0

Chemical shift / ppm from TMS

The framework Si/Al ratio can be determined Fig. 3
from signal intensities using the following equation
[17]:

29

Si MAS NMR spectra of (a) CHA-

HT, (b) CHA-Seed1, (c) CHA-Seed2 and (d)CHA-Seed3.

4

4

n=0

n=0

n
(Si⁄Al) = ∑ ASi (n Al) ⁄ ∑ ASi (n Al)
4Here, A is the signal area of Si(nAl). The Si/Al ratio was estimated to be 2.17, 2.73 and 2.76
for CHA-HT, CHA-Seed1 and CHA-Seed2, respectively (Table 1). An increase in the Si/Al
ratio from CHA-HT to CHA-Seed1 was clearly observed, corresponding to the increase insignal intensity of Si(0Al) and Si(1Al). Also, it was found that these values were close to theones obtained by EDS study (Table 1).

However, a large difference was found between the

Si/Al ratios determined by EDS and MAS NMR for CHA-Seed2, due to the presence ofsanidine as evidenced by XRD.

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田口

明・中森拓実・米山優紀

Figure 4 shows the 27Al MAS NMR spectraof CHA zeolites.

The chemical shift of* : spinning side bands

tetrahedrally coordinated Al atoms was found at
58.1, 58.6, 58.6 and 59.1 ppm for CHA-HT, CHASeed1,

CHA-Seed2

respectively.

and

CHA-Seed3,

CHA-HT**

The absence of the signals fromoctahedrally coordinated Al (around 0 ppm)

CHA-Seed1

suggests that Al atoms exist in the zeolite
framework.

The signal width became wider in*

CHA-Seed2**

CHA-Seed3*

CHA-Seed3 (9.108 ppm) as compared with CHAHT (4.060), CHA-Seed1 (3.992) and CHA-Seed2(4.449).

Such broadening of resonance signals

in CHA-Seed3 was consistent with the results of
29

the Si MAS NMR study.

100.0
50.0
0.0
Chemical shift / ppm (1.0M Al(NO3)3aq.)
27

Fig. 4Al MAS NMR spectra of (a) CHA-HT,(b) CHA-Seed1, (c) CHA-Seed2 and (d) CHA-

Finally, the N2 adsorption isotherm of CHA Seed3.

Instruments, USA) were shown in Figure 5.
The N2 adsorption isotherm of CHA-HT did notindicate the occurrence of micropore filling (P/P0
below 0.1), but showed a linear increase in N2
adsorption up to about 0.8 (P/P0) [13], suggesting
the hindered access of N2 molecules to120

Vol. adsorbed (cm3-STP/g)zeolites at 77 K (Autosorb-1MP, Quantachrome

CHA-Seed1

100

80

CHA-Seed2

60
40
20
0
0.0

Fig. 5

CHA-HT
CHA-Seed3
0.2

0.4
0.6
0.8
Relative pressure

1.0

Nitrogen adsorption isotherm of (a)micropores due to the presence of relatively large CHA-HT, (b) CHA-Seed1, (c) CHA-Seed2 andpotassium cations (K+).

The K/Al ratio(d) CHA-Seed3.

estimated by EDS was 1.1, 0.7 and 0.6 for CHA-HT, CHA-Seed1 and CHA-Seed2, respectively,36

種結晶法による CHA 型ゼオライトの繰り返し合成と構造変化

suggesting K+ ions were filled almost fully in the cages of CHA-HT.

As expected, CHA-

Seed1 and CHA-Seed2 with lower K/Al ratios showed obvious micropore filling (type I by
IUPAC classification) [18]. The N2 sorption amount of CHA-Seed2 was slightly smaller thanthat of CHA-Seed1. This is due to the presence of non-porous sanidine in CHA-Seed2.

For

the mixture of sanidine and analcime (CHA-Seed3), the N2 sorption amount was low in thewhole (P/P0) region.

The BET (Brunauer-Emmett-Teller) surface area for CHA-HT, CHA-

Seed1 and CHA-Seed2 was estimated to 14.0, 389.2 and 344.0 m2/g, respectively. The surface
area of CHA-Seed3 was lower than the value for detection limit (below 10 m2/g).
In conclusion, CHA type zeolite was synthesized by seeded growth method, where OSDAfree CHA zeolite was used as seed crystals.

The XRD measurements and 29Si and 27Al MAS

NMR studies revealed that the obtained CHA zeolite were highly crystalized as compared with
the initial material.

However, the subsequent use of resultant CHA zeolite as seed crystals wasfound to be inappropriate, since other aluminosilicates – sanidine and analcime – were formed,
resulting in a structure change.
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明・中森拓実・米山優紀[11] M. Bourgogne, J. L. Guth and R. Wey, U.S. Patent 4,503,024, March 5, 1985.
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38

編集委員

阿

部

鈴

木

萩

原

波多野
宮

孝

之

片

岡

弘

炎

田

口

明

英

久

橋

爪

隆

雄

治

原

﨑

正

章

富山大学水素同位体科学研究センター研究報告

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