Acidic property of FSM-16

Article abstract of DOI:10.1021/jp980675c

Siliceous FSM-16 possesses acid sites to catalyze but-1-ene isomerization to produce but-2-ene (cis/trans = 1.4-1.7) at 323 K and 2,6,6- trimethylbicyclo[3.1.1]hept-2-ene (α-pinene) isomerization at 303 K. Catalytic activity was dependent upon heat treatment and reached a maximum at 673 K. The maximum acid strength was invariably H₀ = -3.0 independent of the pretreatment temperatures. The acidity was much reduced by calcination at higher temperatures, but restored by water treatment at 353 K as long as the FSM-16 retained its structure.

Full text of DOI:10.1021/jp980675c

5830
J. Phys. Chem. B 1998, 102, 5830-5839
Acidic Property of FSM-16
Takashi Yamamoto, Tsunehiro Tanaka, Takuzo Funabiki, and Satohiro Yoshida*
Department of Molecular Engineering, Graduate School of Engineering, Kyoto UniVersity,
Kyoto 606-8501, Japan
ReceiVed: January 6, 1998; In Final Form: May 12, 1998
Siliceous FSM-16 possesses acid sites to catalyze but-1-ene isomerization to produce but-2-ene (cis/trans )
1.4-1.7) at 323 K and 2,6,6- trimethylbicyclo[3.1.1]hept-2-ene (R-pinene) isomerization at 303 K. Catalytic
activity was dependent upon heat treatment and reached a maximum at 673 K. The maximum acid strength
was invariably H0 ) -3.0 independent of the pretreatment temperatures. The acidity was much reduced by
calcination at higher temperatures, but restored by water treatment at 353 K as long as the FSM-16 retained
its structure.
Introduction
3-methylenebicyclo[2.2.1]heptane (camphene)24 and the migra-
tion of olefinic bonds of 1-methyl-4-(1-methylethynyl)cyclo-
FSM-16,1 MCM-41,2,3 and HMS4 are mesoporous silicas with
narrow pore size distribution, high specific surface area, and
high thermal stability up to 1273 K. These materials, synthe-
sized with cetyltrimethylammonium salts, have a quite similar
structure, a unique adsorption isotherm of nitrogen, high BET
specific surface area, a narrow pore size distribution, and a high
pore volume, although the XRD pattern of HMS is slightly
different from the others. While XRD patterns of FSM-16 and
MCM-41 may exhibit up to four well-defined peaks, that of
HMS exhibits only one broad peak attributed to the 100
reflection.5 The main difference between FSM-16 and MCM-
41 is the synthesis procedure and formation mechanism. Mobil
researchers proposed the formation mechanism of M41S materi-
als, such as MCM-41, based on a liquid crystal templating
model. The folding sheets mechanism was proposed for FSM-
16: intercalation of surfactants to layered polysilicate kanemite
with a primary d spacing of 10 Å and then the folding of layers
to form the specific hexagonal structure. On the other hand,
Monnier et al. proposed a layered intermediate with a primary
d spacing of 31 Å for the formation of MCM-41.6 In fact, an
in situ XRD study showed that the intermediate lamellar silica-
surfactant intercalate was formed during the synthesis of FSM-
16 from kanemite, whereas no intermediate phases were
observed during the formation of MCM-41.7
Silica is a generally catalytically inert material, and the surface
silanol groups are very weakly acidic in nature.8 Therefore,
FSM-16 and MCM-41 themselves are considered inactive
catalytically, and the introduction of Al to the framework was
often performed to generate acidity.3,6,9-13 Other metals or
cations are also added to FSM-16 and MCM-41 to generate
catalytic activity, as exemplified by incorporation of transition
metal cations such as Ti to the framework,5,14-16 introduction
of metal cations by ion exchange,17 direct incorporation of novel
metals via synthesis gel,18 and introduction of catalytically active
species into pores,19-23 and so forth.
hexene (limonene)25 were known to be acid-catalyzed reactions.
In contrast, solid bases such as CaO and SrO catalyze isomer-
ization of R-pinene to produce 6,6-dimethyl-2-methylenebicyclo-
[3.1.1]heptane (â-pinene), selectively.26 Therefore, isomeriza-
tion of R-pinene is an excellent test reaction for acid-base
properties of a catalyst.
Recently, catalysis by siliceous mesoporous materials was
reported. The selective dehydration of 2-methylbut-3-yn-2-ol
to 2-methylbut-3-yn-1-ene proceeded at 453 K over MCM-41.27
Cumene cracking was catalyzed over FSM-16 at 673 K.28
Furthermore, Yoshida et al. reported that FSM-16 evacuated
at 873 K catalyzes metathesis of propene under photoirradia-
tion.29 However, the first two papers did not focus on the
catalytic properties of siliceous mesoporous materials. There
have been no reports discussing the acidic properties of siliceous
mesoporous materials.
Experimental Section
Materials. FSM-16 was synthesized according to Inagaki’s
method.30 Prior to calcination, the Si/Na atomic ratio of water
glass (Osaka Keiso Co., LTD; SiO2 ) 31.93, Na2O ) 15.37,
Al ) 0.0098, Fe ) 0.0028 wt %; Si/Al ) 1463 atomic ratio)
was adjusted to 1.00 by addition of NaOH solution (Wako Pure
Chem. Ind., LTD). During synthesis, water glass successively
changed to δ-Na2Si2O5, kanemite (NaHSi2O5‚3H2O), and finally
FSM-16 via three steps. [C16H33(CH3)3N]Br (Tokyo Chem. Ind.
Co., LTD) was used as a template. The ion exchange of
kanemite to produce FSM-16 was carried out as follows. At
the beginning of ion exchange of kanemite, the concentration
of template was 0.10 M and a molar ratio of the template to Si
of kanemite was adjusted to 0.2. The ion exchange was carried
out at 343 K for 3 h with stirring. After cooling to room
temperature, the solid was filtered off and then dispersed in
distilled water again. After adjustment of the pH to 8.5 with 2
M HCl, it was heated to 343 K and stirred for 6 h while
maintaining pH at 8.5. Finally, ion-exchanged kanemite (FSM-
16) was calcined in a dry air stream at 823 K for 6 h. The
yield of FSM-16 based on SiO2 was 24%. After calcination,
FSM-16 was ground to powder under 100 mesh. The XRD
pattern (d100; 38 Å), the BET specific surface area (1078 m2
Here, we report that siliceous FSM-16 catalyzes isomerization
of but-1-ene and 2,6,6-trimethylbicyclo[3.1.1]hept-2-ene (R-
pinene) at 323 and 303 K, respectively. Isomerizations of
terpenes such as the rearrangement of R-pinene to 2,2-dimethyl-
* Fax: +81-75-753-5925. E-mail: yamamoto@dcc.moleng.kyoto-u.ac.jp.
S1089-5647(98)00675-0 CCC: $15.00 © 1998 American Chemical Society
Published on Web 07/07/1998

Acidic Property of FSM-16
J. Phys. Chem. B, Vol. 102, No. 30, 1998 5831
TABLE 1: Elemental Analysis of Catalystsa
elements (mass%)
catalyst
Na
Al
Ca
Fe
Mg
Ti
Si/Al atomic ratio
FSM-16
0.008
0.017
0.021
0.01
0.061
0.062
0.071
0.14
0.012
0.012
0.014
0.023
0.021
0.031
0.02
0.003
0.003
0.004
0.032
0.029
0.035
735
723
631
FSM-1173Hb
FSM-1373Hc
FSM-16d
320
H2Si2O5
SiO2 gel
0.005
0.002
0.008
<0.001
0.006
0.001
0.002
<0.001
0.001
<0.001
0.007
<0.001
5612
a Analyzed by ICP (inductively coupled plasma) and atomic absorption spectroscopy. b Hydrated at 353 K for 4 h followed by calcination at 773
K for 5 h. Before hydration, FSM-16 was calcined in a dry air stream at 1173 K for 2 h. c Hydrated at 353 K for 4 h followed by calcination at
773 K for 5 h. Before hydration, FSM-16 was calcined in a dry air stream at 1373 K for 2 h. d Supplied by Toyota Central R&D Labs., Inc. (lot
no. NG78-550).
g-1), the N2 adsorption isotherm, the pore volume (0.73 cm3
g-1; estimated by t-plot), and the pore diameter (27.6 Å;
estimated by the Clanston-Inkley method) were quite similar
to those reported in the literature.30,31
Characterization. NH3-TPD measurements were carried out
by a quadrupole-type mass spectrometer at a heating rate of 5
K min-1. Before TPD measurements, each 100 mg of sample
was evacuated at 673 K for 0.5 h and calcined under 6.66 kPa
of O2 for 1 h, followed by evacuation at the same temperature
for 1 h. The sample was exposed to 500 µmol of NH3 at room
temperature for 0.5 h followed by evacuation at the same
temperature for 1 h. The amount of desorbed gases (NH3; m/e
) 16) was normalized with that of introduced Ar (m/e ) 40)
as an internal standard.
Calcined and rehydrated FSM-16 was also prepared because
a hydration state of FSM-16 is closely related to catalytic
activities, as would be described below. Rehydrated catalysts
were prepared via two steps. Before rehydration, FSM-16 was
calcined once in a dry air stream at 1173 or 1373 K for 2 h
(FSM-1173, FSM-1373). At the next step, the calcined FSM-
16 was treated with water at 353 K for 4 h with stirring, followed
by calcination at 773 K for 5 h (FSM-1173H, FSM-1373H).
Silicon oxide hydrate (H2Si2O5) was synthesized from kane-
mite,32 which was the same material as used for FSM-16
synthesis. Kanemite dispersed in distilled water was converted
to H2Si2O5 keeping the pH at 1.2 at room temperature.
Adjustment of the pH was performed with 2 M HCl, and the
condition was maintained for 24 h with stirring. The precipitate
was washed with distilled water until Cl- was free based on
AgNO3 test. It was dried at 343 K for 12 h followed by
calcination at 773 K for 5 h. Formation of H2Si2O5 crystal was
confirmed by XRD (JCPDS file No. 27-606) for the dried
sample, which became amorphous upon calcination at 773 K.
TG-DTA analysis showed that H2Si2O5 released the interlayer
water molecules around at 473 K, and the loss of interlayer
water should account for the loss of crystallinity. This
phenomenon was consistent with previous works.33 Al-doped
δ-Na2Si2O5 and H2Si2O5 were also synthesized. To adjust the
Si/Al atomic ratio to be 16, whose value was to form 5 wt %
of Al2O3 containing SiO2-Al2O3 as a starting material, NaAlO2
was added to water glass.
SiO2 gel was synthesized from tetraethyl orthosilicate (Nacalai
tesque, EP-grade, once distilled) by hydrolysis in a water-
ethanol mixture at boiling point followed by calcination at 773
K for 5 h in a dry air stream.34 Before calcination, a dried
sample was ground to powder under 100 mesh. No crystalline
phases of SiO2 were detected by XRD analysis.
Other silicas used were Japan Reference Catalyst (JRC-SIO-
5, JRC-SIO-7), supplied by the Committee on Reference
Catalyst, Catalysis Society of Japan. JRC-SIO-5 contains 134
ppm Na, 122 ppm Al, 40 ppm Ca, 57 ppm Fe, and 100 ppm
Mg. JRC-SIO-7 contains 135 ppm Na, 195 ppm Al, 36 ppm
Ca, 72 ppm Fe, and 117 ppm Mg. The BET specific surface
area of JRC-SIO-5 and JRC-SIO-7 is 192 and 86 m2 g-1, res-
pectively. They were precalcined in dry air at 773 K for 3 h.
Reference catalysts used for R-pinene isomerization were
HZSM-5 (JRC-Z5-25H, -70H, -1000H; Si/Al atomic ratio are
12.3, 40.0, 623, respectively), NaY (JRC-Z-1), γ-Al2O3 (JRC-
ALO-4), ZrO2 (JRC-ZRO-1), TiO2 (JRC-TIO-4), Mg(OH)2
(Rare Metallic Co., 99%), Ca(OH)2 (Nacalai, GR), Nb2O5‚nH2O
(CBMM), and NiSO4‚nH2O (Nacalai, GR).
FTIR spectra were recorded with a Perkin-Elmer Paragon
1000 spectrometer in a transmission mode at room temperature.
IR spectra of adsorbed pyridine were recorded with a resolution
of 4 cm-1. Each sample (20-80 mg) was pressed into a self-
supporting wafer (20 mm in diameter) with a pressure of 100
kg cm-2 for 10 s. The wafer was pretreated in the same way
as that for NH3-TPD measurements and exposed to 27 Pa of
pyridine vapor at 423 K for 5 min followed by evacuation at
the same temperature for 1 h. The other spectra were recorded
with a resolution of 2 cm-1
.
Thermogravimetric analysis was carried out with Rigaku
Thermoflex TG 8110 in a dry N2 stream at a heating rate of 5
K min-1
.
X-ray diffraction patterns of samples were obtained with a
Rigaku Geigerflux diffractometer using Ni-filtered Cu KR
radiation (1.5418 Å).
The acid strength of catalysts was measured by various
Hammett indicators. The indicators used for the titration method
were 0.1 wt % benzene solution of methyl red (H0 ) +4.8),
p-dimethylaminoazobenzene (+3.0), benzenazodiphenylamine
(+1.5), dicinnamalacetone (-3.0), and benzalacetophenone
(-5.6).
Catalysis. But-1-ene isomerization was carried out in a
closed circulation system (dead volume, 200 cm3). Prior to each
run, 50 mg of FSM-16 was evacuated at a prescribed temper-
ature for 0.5 h and calcined under 6.66 kPa of O2 for 1 h,
followed by evacuation at the same temperature for 1 h. The
amount of substrate was 400 µmol, and the reaction temperature
was 323 K.
R-Pinene isomerization was carried out under dry N2 atmo-
sphere using a stirred batch reactor at 303 or 353 K. The
pretreatment procedure was the same as mentioned above. In
a typical experiment, the reactor was loaded with 2 mL (12.6
mmol) of R-pinene (Nacalai, EP, 99.8%) and 50 mg of catalyst.
Products were analyzed by GC and GC-MS (Shimadzu,
GCMS-QP5050).
Results and Discussion
Elemental Analysis. Table 1 summarizes elemental analysis
of prepared catalysts. Although the Si/Al atomic ratio of water

5832 J. Phys. Chem. B, Vol. 102, No. 30, 1998
Yamamoto et al.
Figure 1. Plots of initial rates for but-1-ene isomerization over FSM-
16 and BET specific surface area vs pretreatment temperatures. Dead
volume, 200 cm3; catalyst, 50 mg; but-1-ene, 400 µmol; reaction
temperature, 323 K.
glass was 1463, that of synthesized FSM-16 was 735. This
result shows that Al was slightly concentrated but the concentra-
tion was still quite low. Results of FSM-1173H and FSM-
1373H show that no treatment changes the original elemental
composition except for Na. Because H2Si2O5 was treated with
water of pH ) 1.2 during synthesis, almost all of the trace
elements were extracted off. SiO2 gel contained little other
elements.
Acidic Property. Figure 1 shows initial rates for but-1-ene
isomerization over FSM-16 pretreated at various temperatures
and BET specific surface areas of the FSM-16 samples. The
initial rate strongly depended on the pretreatment temperature.
Samples pretreated at temperatures from 473 through 673 K
showed similar initial rates. Once pretreatments were performed
at temperatures higher than 873 K, the initial rate drastically
decreased, although BET specific surface areas remained high.
No correlation between initial rates and surface areas was
observed. For example, only a 5% difference in surface area
was observed for the samples pretreated at 873 and 1073 K,
but the initial rates differed by 1.5 orders of magnitude. In all
cases, the ratios of the cis-isomer to the trans-isomer in produced
but-2-enes were 1.4-1.7, indicating that this reaction was
catalyzed by acids. No reaction proceeded over SiO2 gel
pretreated at 673 K.
A similar catalytic behavior was exhibited in isomerization
of R-pinene (Figure 2), as summarized in Table 2. It should
be noted that the selectivity did not change at all, whereas the
catalytic activity was drastically changed depending upon
pretreatment temperature. Main products were camphene and
limonene, and the selectivity to these two products was around
40%. Products of R-pinene isomerization can be classified into
three groups. The first group is â-pinene. Over solid base
catalysts, only equilibrium between R-pinene and â-pinene
would be observed.26 The second group consists of bicyclic
(camphene, R-fenchene, etc.) and tricyclic (tricyclene, etc.)
products. The last group is composed of monocyclic products
(limonene, terpinolene, R-terpinene, γ-terpinene, etc.). One
remarkable result of the present study is that the formation of
â-pinene was negligible over FSM-16. This result also revealed
that few basic sites existed on FSM-16, and this reaction was
catalyzed by acids. It was reported that monocyclic products
were formed more preferentially than bi- or tricyclic products
over strong acid catalysts.24 The independence of selectivity
Figure 2. Scheme of R-pinene isomerization.
TABLE 2: Results of r-Pinene Isomerization at 303 Ka
selectivityb (%)
pretreatment conversion
catalyst
FSM-16
temp/K
(%)
1
2
3
4
5
6
7
8
373
473
673
16.0
27.1
44.6
29.5
6.6
1.5
52.9
1
1
42
40
6
5
4
3
3
3
4
42
44
43
48
48
46
43
6
7
9
7
7
7
8
1
1
2
1
2
1
2
1
1
2
1
2
2
2
1
1
tr
1
1
tr
tr
tr 40
tr 39
1
4
873
1073
1273
673
37
37
FSM-16c
tr 39
a R-pinene, 2 mL; catalyst, 50 mg; reaction time, 0.5 h. b 1, â-pinene;
2, camphene; 3, R-fenchene; 4, limonene; 5, terpinolene; 6, R-terpinene;
7, γ-terpinene; 8, others. c Supplied by Toyota Central Lab., Inc. (lot
no. NG78-550).
for this reaction indicates that the maximum acid strengths were
not changed by pretreatment temperatures.
As shown in Table 3, over SiO2 gel, δ-Na2Si2O5, H2Si2O5,
JRC-SIO-5 and JRC-SIO-7, R-pinene isomerization hardly took
place even at 353 K. As-calcined H2Si2O5 pretreated at 373
and 473 K, which remained as a crystal structure, was also
inactive. The result of JRC-SIO-7 shows that silica containing
195 ppm of Al is not enough to catalog this reaction at the
temperature of 353 K. Furthermore, Al-doped H2Si2O5 showed
very low activity. Typical acid catalysts were also tested (Table
3). γ-Al2O3, TiO2, Nb2O5‚nH2O, and NiSO4‚nH2O were active
for this reaction at 353 K, but activities were quite low compared
to that of FSM-16. In the case of NiSO4‚nH2O, a selectivity
for bi- or tricyclic products was particularly high, 88%, which
coincides with the previous reports.24 It is very intriguing that
HZSM-5, the Si/Al atomic ratio of which was 12.3, known as
a strong acid catalyst, was less active than FSM-16 at least at
a temperature of 303 K. It may be due to its small pore size.
Although FSM-16 has a large mesopore of 28 Å, the MFI type
zeolite has a micropore in which the three-dimensional channel
system has straight 10-ring 5.2 × 5.7 Å channels connected by
a zigzag structure like 5.3 × 5.6 Å channels. In the case of
HZSM-5, a diffusion of substrates or products was suppressed

Acidic Property of FSM-16
J. Phys. Chem. B, Vol. 102, No. 30, 1998 5833
TABLE 3: Results of r-Pinene Isomerization at 353 Ka
selectivityb (%)
pretreatment
temp/K (%)
conversion
(%)
catalyst
FSM-16c
1
2
3
4
5
9
6
2
7
2
8
673
673
1073
673
673
673
673
673
673
673
673
673
673
673
673
673
673
373
673
873
873
77.8
0.0
0.0
0.0
0.0
0.0
1.7
<0.1
<0.1
3.4
0.6
0.0
18.8
6.1
18.0
0.2
21.1
6.5
54.5
2.1
0
4
41
4
41
1
SiO2 gel
δ-Na2Si2O5
d
Al-doped Na2Si2O5
H2Si2O5
d
Al-doped H2Si2O5
38
4
43
6
1
2
2
JRC-SIO-5
JRC-SIO-7
γ-Al2O3
33
31
44
43
2
2
17
13
2
3
1
1
1
3
tr
4
TiO2
ZrO2
HZSM-5 (12.3)c
HZSM-5 (40.0)c
HZSM-5 (623)
c
1
2
2
36
35
33
28
19
24
25
33
28
2
3
2
2
2
3
1
2
2
5
4
6
NaY
1
5
24
52
77
tr
2
5
3
55
26
7
9
5
2
3
2
1
5
2
tr
1
Nb2O5‚nH2O
NiSO4‚nH2O
MgOf
3
tr
100
95
10e
tr
CaOf
2.2
5
a R-Pinene, 2 mL; catalyst, 100 mg; reaction time, 3 h. b 1, â-pinene; 2, camphene; 3, R-fenchene; 4, limonene; 5, terpinolene; 6, R-terpinene;
7, γ-terpinene; 8, others. c Catalyst: 50 mg; reaction temperature, 303 K. d Si/Al atomic ratio was 16.1 as a starting material. e Tricyclene: 8%.
f Catalyst: 300 mg as M(OH)2 (M ) Mg, Ca).
TABLE 4: Results of â-Pinene Isomerizationa
especially at a low temperature of 303 K. These results indicate
that the effective surface area of MFI type zeolite for R-pinene
isomerization is much lower than that of FSM-16. FSM-16
could provide a reaction field for large molecules such as
R-pinene. In addition, HZSM-5 of Si/Al ) 623 was almost
inactive at 303 K and showed low activity even at 353 K,
although the Si/Al atomic ratios of the HZSM-5 and FSM-16
were almost the same. The second intriguing point is that the
selectivity for formation of R-fenchene was particularly high.
It results from restricted transition-state selectivity. Another
HZSM-5 of different Si/Al atomic ratio also showed high
selectivity for R-fenchene formation. In the small pore of the
MFI type zeolite, it is difficult for R-pinene isomerization to
bulky transition states to produce terpinolene, R-terpinene,
γ-terpinene, and so forth, compared to that of limonene. In
contrast, the FAU type zeolite has larger supercages of 13 Å,
and this restriction was no longer observed. It was reported
that NaY had acid sites, the maximum acid strength of which
range from H0 ) +1.5 to +4.0.35 Although NaY is a very weak
acid in nature, its specific surface area was estimated to be 973
m2 g-1 by Langmuir plot. The high activity of NaY was due
to the large surface area in comparison with other catalysts.
Furthermore, over Brønsted acid catalysts, catalytic activity was
strongly related to the mobility of protons. From IR experi-
ments, Ward observed the delocalization of protons on HY in
the range 473-700 K.36 Baba et al. observed changes of the
line width of the 1H MAS NMR signal of acidic OH groups of
HZSM-5 with temperature and found a relation between line
widths and catalytic activities.37 They discussed that the mobil-
ity of protons depended on temperature and the same amounts
of protons would not necessarily exhibit the same activities.
MgO and CaO were also active for R-pinene isomerization.
The selectivities for â-pinene formation were almost 100%,
while they exhibited low conversion at 353 K (Table 3). The
selective isomerization between R-pinene and â-pinene is one
of the characteristics of solid base catalyst, and the low
conversions were due to the low equilibrium constant of
â-pinene to R-pinene.26 Table 4 summarizes isomerization of
â-pinene over FSM-16, MgO, and CaO. Over solid base
catalysts, only transformation between â-pinene and R-pinene
catalyst
FSM-16
MgO
CaO
pretreatment temperature/K
reaction temperature/K
weight/mg
673
353
50
873
423
300b
3
873
423
300b
3
time/h
0.5
conversion (%)
selectivity (%)
R-pinene
20.8
3.5
9.3
11
27
36
9
98
2
99
1
camphene
limonene
terpinolene
others
17
tr
tr
a â-Pinene: 2 mL. b As M(OH)2, (M ) Mg, Ca).
was electively catalyzed, and formation of other products was
negligible. In contrast, the reaction continuously proceeded via
R-pinene, and many kinds of secondary products were observed
over FSM-16. The result of â-pinene isomerization also
strongly suggests that not basic but acidic sites were the main
active sites on FSM-16. The lack of basic sites over FSM-16
was supported by the result of but-1-ene isomerization discussed
above. In general, solid base catalyzes but-1-ene and the cis/
trans ratio of produced but-2-ene is very large.38 In the case of
FSM-16, however, that ratio was between 1.4 and 1.7.
Figure 3 shows NH3-TPD profiles of FSM-16, SiO2 gel, and
H2Si2O5 pretreated at 673 K. SiO2 gel and H2Si2O5 exhibited
a single peak around at 370 and 360 K, respectively. The profile
of FSM-16 shows a peak above 400 K besides a peak at around
355 K; however the peak around at 473 K is not due to strong
acid sites.39 It clearly shows that the acid sites of FSM-16
pretreated at 673 K are different from those of the others. This
was supported by IR spectra. Figure 4 shows IR spectra of
adsorbed pyridine on SiO2 gel and FSM-16 pretreated at 673
K. Assignment of pyridine adsorption peaks was as follows.40
Peaks due to hydrogen-bonded pyridine were 1448 and 1598
cm-1, those due to pyridine adsorbed on Brønsted acid sites
were 1546 and 1638 cm-1, and those on Lewis acid sites were
1456 and 1624 cm-1. A peak at 1493 cm-1 was due to pyridine
adsorbed on both Brønsted and Lewis acid sites. SiO2 gel

5834 J. Phys. Chem. B, Vol. 102, No. 30, 1998
Yamamoto et al.
from hydrogen-bonded SiOH and free SiOH groups, and both
activation energies of desorption sites were similar to those of
amorphous silica. In fact, the reported pyridine desorption
profile for silica gel (Kieselgel 60; Merk NV) was quite
similar.43 The pyridine desorption profile for MCM-41 was also
quite similar to the NH3 desorption profile for FSM-16, although
it is very difficult to compare with the results of pyridine and
NH3-TPD experiment. Because the NH3-TPD profile for SiO2
gel was different from that for FSM-16, it could be possible
that the property of siliceous MCM-41 is similar to that of FSM-
16 demonstrated in the present work.
Contribution of Aluminum to Acidic Property. FSM-16
employed in the present work contains a trace amount of Al
(Si/Al ) 320, 735), which might be associated with the acid
sites. Van Roosmalen et al. reported the catalysis of but-1-ene
isomerization over silica gel.43 They concluded that activities
of silica gel were directly proportional to the concentration of
Al being present as a trace impurity at 600-700 K. In their
report, silica gel (Rhoˆne-Progil; Spherosil XOA-400, 361 m2
g-1, Si/Al ) 100-1000) showed a rate constant of 31 nmol
m-2 s-1 at 600 K and 1.1 × 105 Pa for but-1-ene, whereas in
the case of FSM-16, the activity comparable to that reported
was exhibited at a low temperature of 323 K and a low pressure
of 4.7 × 103 Pa for but-1-ene. Furthermore, we confirmed that
the amorphous silica prepared from the same water glass was
inactive. West et al. reported that many reactions catalyzed by
silica gel took place at impurity sites.45 They observed
improvement of activity more than 100 times for hex-1-ene
isomerization over Al(NO3)3 added to silica gel (120 ppm as
Al) than the original silica gel. However, the original silica
gel (Davison Grade 59 or Grade 70) contains 0.1% Al2O3, 0.01%
Fe2O3, 0.02% TiO2, 0.07% CaO, 0.06% Na2O, and 0.03% ZrO2,
and the rate of hex-1-ene isomerization was reported to be 0.2
mmol h-1 g-1 at 373 K.45 This value was about 60 times
smaller than the rate of but-1-ene isomerization over FSM-16
at 323 K. Although it is hard to compare them, we should
suppose that the acidity of FSM-16 is much higher than that of
silica gel containing 0.1% Al2O3.
Figure 3. NH3-TPD profiles of FSM-16 (a), SiO2 (b), and H2Si2O5
(c) pretreated at 673 K.
In the case of ZSM-5, it was reported that catalytic activities
of many reactions were directly proportional to the concentration
of Al and the proportional relations were applicable down to
10 ppm.46 The reported reactions were propylene polymeriza-
tion,47 n-hexane cracking,48-50 hex-1-ene isomerizations,49 and
so forth. However, all reactions were performed over 700 K.
On the other hand, isomerization of but-1-ene and R-pinene
proceeds over FSM-16 even at 323 K. There have been no
reports that butene isomerization proceeds at ambient temper-
ature on silica including such a trace amount of impurity at
measurable rates. In R-pinene isomerization, activities of FSM-
16 whose Si/Al atomic ratio was 320 and 735 were almost the
same. We emphasize again that the acidity of FSM-16 exhibited
by the present sample is not due to Al impurity.
Figure 4. FTIR spectra of adsorbed pyridine at 423 K. FSM-16 (21
mg) evacuated at 423 K (a), 473 K (b), 573 K (c), and 673 K (d) and
SiO2 gel (80 mg) evacuated at 423 K (e).
possessed only hydrogen-bonded sites, whereas FSM-16 pos-
sessed both Brønsted and Lewis acid sites besides hydrogen-
bonded sites. When FSM-16 adsorbing pyridine was evacuated
at 473 K, hydrogen-bonded pyridine and pyridine adsorbed on
Brønsted sites were desorbed. Almost all of the pyridine was
desorbed at 673 K with increasing evacuation temperature. IR
spectra of pyridine adsorbed on Al-containing MCM-41 were
measured by many researchers.9-11,41 Although Corma et al.
observed Brønsted acid sites on MCM-41 of Si/Al ) 100,9
Jentys et al. observed only Lewis acid sites on the same Si/Al
ratio’s material.11 Further, Jentys et al. and Mokaya et al.10
observed only hydrogen-bonded species on pure siliceous MCM-
41. While the Si/Al atomic ratio of synthesized FSM-16 was
735, both Lewis and Brønsted acid sites were observed on FSM-
16. The spectrum was quite similar to those of Al-MCM-41
(Si/Al ) 100). Although we have not compared directly the
acidic property between FSM-16 and MCM-41, IR spectra of
adsorbed pyridine suggest that the acidic property of FSM-16
is higher than, or at least equal to, those of MCM-41. Zhao et
al. performed pyridine TPD of siliceous MCM-41 and observed
two desorption peaks in the temperature range 323-523 K.42
They claimed that two peaks were due to desorbed pyridine
Dehydroxylation. As shown in Figure 1 and Table 2, FSM-
16 pretreated at 673 K showed maximum catalytic activity. The
activity was drastically reduced when FSM-16 was pretreated
at higher than 873 K. Sintering or the change of surface
property is thought to be the reason for deactivation. The
possibility that sintering causes deactivation can be excluded
from the result of BET measurements. Therefore, the change
of surface property should be the main reason for deactivation.
Dehydration and condensation of SiOH groups should relate
closely to the change of specific property.
Figure 5 shows a thermogravimetric analysis and H2O-TPD
profile of FSM-16. The weight loss completely corresponded

Acidic Property of FSM-16
J. Phys. Chem. B, Vol. 102, No. 30, 1998 5835
6b shows spectra of isolated silanol groups. In the case where
the evacuation temperature was below 773 K, positions of the
peak maximum were 3742 cm-1. As evacuation temperature
increases, the peak position was shifted to higher frequency.
When FSM-16 was evacuated at 1073 K, the peak position was
finally reached at 3745 cm-1. Morrow et al. reported that
observed bands of isolated silanol groups were a combination
of two species.52 One was truly isolated silanol (ν(SiO-H) of
species I: 3750 cm-1), and the other was weakly perturbed
vicinal pairs of silanols (ν(SiO-H) of species II: 3740 cm-1).
Morrow et al. also reported that fumed silica and precipitated
silica have different peak frequencies and bandwidths of isolated
silanol because different preparation methods caused the ratio
of the two isolated silanols to differ. If the concentration of
weakly perturbed vicinal pairs of silanol is high, the peak
position should be near 3740 cm-1. On the contrary, if the
concentration of truly isolated silanol is high, the peak position
should be near 3750 cm-1. From the band position of FSM-
16, we conclude that isolated silanol groups on FSM-16 are
rich in species II (weakly perturbed vicinal pairs of silanol).
Ishikawa et al. observed a silanol band at 3740 cm-1 over FSM-
16 and estimated the surface concentration.53 The wavenumber
also indicates that almost all the silanol groups are weakly
perturbed, although their concentration was lower than that of
ordinary silica gel. Over siliceous MCM-41, the band due to
isolated silanol groups was confirmed at 3738 cm-1 which was
also close to the band of species II.42
Figure 5. Thermogravimetric analysis and H2O-TPD profile of FSM-
16. Prior to TPD measurement, 20 mg of FSM-16 was evacuated at
373 K for 1 h.
When FSM-16 was evacuated at above 773 K, weakly
perturbed vicinal pairs of silanol (species II) were selectively
dehydroxylated to form truly isolated silanol (species I). The
blue shift of the isolated silanol band on FSM-16 was due to a
change of their ratio. These phenomena were more clearly
shown in difference spectra, as shown in Figure 7. Below 673
K, broad bands of strongly hydrogen bonded silanol groups were
mainly weakened. The difference spectrum between 573 and
673 K has the largest band area. It corresponded to the first
peak of tje H2O-TPD profile and a gravimetric decrease (Figure
5). Above 773 K, the position of the weakened band was shifted
to higher frequency. The most typical case was the difference
spectra between 873 and 1073 K. The positions of weakened
and strengthened peaks were 3741 and 3748 cm-1, respectively.
In this region, elimination of silanol groups occurred. We
observed a new band generation at around 892 cm-1 in
accordance with blue shift of isolated silanol bands (Figure 6c).
Morrow et al. observed generation of new two bands at 908
and 888 cm-1 on fumed silica. New bands appeared when silica
was evacuated at temperatures higher than 873 K, and these
intensities reached a maximum at 1473 K.54-56 They assigned
these peaks to a reactive strained siloxane bridge formed by
condensation of isolated silanol groups. Further, Bunker et al.
assigned them to an edge-shared silicate tetrahedral ring.57 In
the second derivative of the IR spectrum, a trace peak and a
Figure 6. FTIR spectra of FSM-16 evacuated at various temperatures.
to desorption of H2O. Since large part of physisorbed H2O was
eliminated below 373 K, a TPD experiment was performed after
preevacuation at 373 K for 1 h. Because FSM-16 was once
calcined at 823 K in a synthesis step, the signal intensity of
m/e ) 18 below 773 K was small. Dehydroxylation continu-
ously proceeded over 773 K. A large quantity of H2O evolution
over 773 K was due to dehydroxylation of a silanol group to
form a siloxane bridge,51 and catalytic activities were drastically
lowered in this region.
IR spectra of FSM-16 showed similar behavior, as shown in
Figure 6. With increasing evacuation temperature, a very broad
band at around 3500 cm-1 gradually decreased and a new
window at around 900 cm-1 appeared. The band at around 3500
cm-1 is due to strongly hydrogen bonded silanol groups. Figure
distinct peak were observed on FSM-16 at 912 and 892 cm-1
,
respectively. IR behavior exhibited by FSM-16 resembles that
previously reported on fumed silica, although the new band on
FSM-16 was almost single. The IR result suggests that weakly
perturbed vicinal pairs of silanols on FSM-16 condensed to
produce siloxane bridges, similar to those on fumed silica and
silica gel.51 Therefore the dehydroxylation of surface silanol
groups of FSM-16 was responsible for the deactivation. The
temperature of 673 K is the point where catalytic activity of
FSM-16 decreased. Matsumura et al. reported that silica gel
pretreated above 1000 K was active for selective ethanol
dehydrogenation and the active site was an active siloxane bridge

5836 J. Phys. Chem. B, Vol. 102, No. 30, 1998
Yamamoto et al.
TABLE 5: Change of the Activity of r-Pinene
Isomerization over FSM-16a
selectivityb (%)
pretreatment conversion
catalyst
temp/K
(%)
1
2
3
4
5
6
7
8
FSM-16
673
673
673
673
44.6
8.8
48.1
<0.1
tr 40
36
tr 42
4
4
4
43
46
43
9
8
7
2
2
2
2
2
1
tr
1
1
FSM-1173
FSM-1173H
FSM-1373H
1
a R-Pinene: 2 mL. Catalyst: 50 mg. Reaction temperature: 303 K.
Reaction time: 0.5 h. b 1, â-pinene; 2, camphene; 3, R-fenchene; 4,
limonene; 5, terpinolene; 6, R-terpinene; 7, γ-terpinene; 8, others.
Figure 7. Difference IR spectra of FSM-16 evacuated at various
temperatures: between 373 K and room temperature (a), 473 and 573
K (b), 573 and 673 K (c), 673 and 773 K (d), 773 and 873 K (e), and
873 and 1073 K (f).
Figure 8. FTIR spectra of adsorbed pyridine at 423 K: fresh FSM-
16 (21 mg) (a), FSM-1073pre (20 mg) (b), FSM-1173H (30 mg) (c),
and FSM-1373H (80 mg) (d).
formed by the dehydration of silanol groups.58,59 In contrast,
the siloxane bridge on FSM-16 did not concern the isomerization
because no increase in activity was observed for FSM-16
evacuated at higher temperatures. The isolated silanol band
observed on FSM-16 was only one and the wavenumber was
around 3742 cm-1, so-called neutral. We conclude that the
active sites were surface silanol groups of species II themselves
and/or silanol-related sites, although they were not so-called
acidic silanol bands around 3600 cm-1. This presumably results
from the synthesis method and the crystal structure of FSM-
16, on which the silanol groups were supposed to be regularly
arrayed. There are very few reports in which neutral silanol
groups are active sites for any reactions. Sato et al. claimed
that Beckmann rearrangement of cyclohexanone oxime was
catalyzed by neutral silanol groups, whose wavenumber was
3740 cm-1, on the external surface of highly siliceous MFI type
zeolites.60 Although they did not discuss the silanol groups in
detail, we suspect that the silanol groups should be weakly
perturbed vicinal pairs.
Regeneration of Acid Sites. In the previous section, we
mentioned that catalytic activity of the highest FSM-16 was
exhibited by pretreatment at 673 K and deactivation was due
to dehydroxylation of silanol groups. To examine whether
silanol groups of FSM-16 participate in acidic property or not,
we prepared calcined and rehydrated FSM-16. If only silanol
groups were the active sites, rehydrated FSM-16 should exhibit
the same activity as fresh catalyst. Table 5 summarizes results
of R-pinene isomerization over variously treated FSM-16.
Pretreatments were performed at 673 K in all cases. The catalyst
noted simply as FSM-16 in Table 5 was the fresh catalyst, which
was the same catalyst as listed in Table 2. FSM-16 calcined at
1173 K (FSM-1173) was less active than the fresh catalyst, but
the activity was slightly higher than that pretreated at 1073 K.
As expected, the activity of the less active catalyst was
completely restored by hydration of the catalyst at 353 K
followed by calcination at 773 K (FSM-1173H). The selectivity
was not changed. These results indicate that hydration to restore
silanol groups on FSM-16 regenerates acidic sites. The reason
FSM-1173 was more active than FSM-16 pretreated at 1073 K
was explained as follows. By moisture in atmosperic air, partial
rehydration proceeded on FSM-1173 during the storage. Re-
hydrated FSM-16 having been calcined at 1373 K (FSM-1373H)
did not catalyze isomerization of R-pinene, in contrast to the
result of FSM-1173H. This indicates that FSM-1373H no
longer had the same properties as fresh FSM-16. The reason
for the difference of catalytic activity between FSM-1173H and
FSM-1373H is considered as follows. The possible first reason
may be that the active elements such as Al and Ti on FSM-16
were lost during various treatments. The first reason can be
excluded because no change of elemental composition was
found (Table 1). The second is the fundamental structural
change of FSM-16. This is only sintering.
To investigate the difference of acidic properties more in
detail, IR spectra of adsorbed pyridine were recorded. Figure
8 shows those of four typical variously treated FSM-16. The
four catalysts are the fresh one, FSM-16 pretreated at 1073 K
(FSM-1073pre), FSM-1173H, and FSM-1373H. Brønsted py-
ridine was observed on the fresh FSM-16, while not on FSM-
1073pre. Although as many Lewis acid sites existed on the
surface as on fresh FSM-16, FSM-1073pre was inactive for

Acidic Property of FSM-16
J. Phys. Chem. B, Vol. 102, No. 30, 1998 5837
but-1-ene and R-pinene isomerization. The band at around 1492
cm-1 was assigned to overlapping 19a bands of both Lewis and
Brønsted pyridine. The intensity ratio of the band at 1492 cm-1
to a 19b band of Lewis pyridine at 1456 cm-1 was quite different
from fresh FSM-16 and FSM-1073pre. The ratio of Lewis and
Brønsted acid sites ([L]/[B] ratio) can be calculated from the
band area of adsorbed pyridine at 1455 and 1492 cm-1 63
The
.
calculated [L]/[B] ratio of fresh FSM-16 was 2.6, and that of
FSM-1073pre was 5.6. This suggests that the fraction of
Brønsted sites was decreased by pretreatment at 1073 K. The
majority of acid sites were Lewis acid, however, Lewis acid
sites are inactive for the catalysis of the isomerization of
R-pinene and but-1-ene. The IR spectrum of adsorbed pyridine
on FSM-1173H was quite similar to that on fresh FSM-16, and
the [L]/[B] ratio of FSM-1173H was 2.6. This is in good
accordance with the results of the catalysis. In other words,
the surface property of FSM-1173H was the same as that of
fresh FSM-16. On the other hand, FSM-1373H was quite
different. Only hydrogen-bonded pyridine was observed in the
IR spectrum of adsorbed pyridine on FSM-1373H, and it was
quite similar to that of SiO2 gel (Figure 4). This strongly
suggests that FSM-1373H was fundamentally different from that
of fresh FSM-16 and FSM-1173H. From the results of catalytic
activities and IR spectra, we conclude that the surface property
of FSM-1373H is similar to that of ordinary silica gel rather
than that of FSM-16.
To clarify the difference of each structure, we measured the
XRD pattern of these samples. Figure 9 shows those of
variously treated FSM-16 listed in Table 5. The XRD pattern
of fresh FSM-16 exhibited four peaks and the primary d spacing
was 38 Å. This profile is identical with that reported previ-
ously.30 All peaks observed on FSM-1173 were shifted to
higher degree. This was due to shrinkage of the lattice, and
the shrunk primary d spacing was 32 Å. FSM-1173 and FSM-
1173H still kept the structure of FSM-16, although the fourth
peak disappeared. The result of XRD measurements shows that
a series of rehydration procedures scarcely influenced the
structure of FSM-1173. In the case of FSM-16 calcined at 1373
K, peaks below 10 degrees completely disappeared and no peaks
were observed in all regions. This clearly shows that FSM-
1373H became amorphous. From XRD results, we conclude
that acidic properties appeared on only the crystal FSM-16. This
result strongly suggests that the active site of FSM-16 was not
due to impurity.
Figure 9. Cu KR XRD patterns of fresh FSM-16 (a), FSM-1173 (b),
FSM-1173H (c), and FSM-1373 (d).
completely restored by rehydration procedures. This was
supported by results of R-pinene isomerization, as shown in
Table 5. The difference between our experiments and reported
results was due to rehydration processes. The rehydration has
been attempted at ambient temperature with 100% relative
humidity,61,62 whereas FSM-16 was rehydrated in water at 353
K. To investigate the property of catalysts further, we measured
the maximum of acid strength of catalysts by Hammett
indicators. Table 6 summarizes maximum acid strength and
BET specific surface area. Once SiO2 gel (BET specific surface
area was 650 m2 g-1) was calcined at 1173 K, the surface area
was reduced to 445 m2 g-1. Even if calcined silica gel was
rehydrated in water at 353 K, complete regeneration of silanol
groups was impossible because of its sintering. In contrast, the
surface area of FSM-1173 was maintained at 965 m2 g-1. FSM-
16 was stable at temperatures up to 1273 K and possessed high
surface area even for a rehydrated sample calcined at 1173 K
(Table 6). The rigid structure of FSM-16 made it possible to
complete reversible dehydroxylation of isolated silanols.
Over FAU type zeolites, Severino et al. reported that the
change of the [L]/[B] ratio around 1.0 caused an abrupt change
of selectivity to camphene in R-pinene isomerization.64 They
concluded that the reaction rate catalyzed by Brønsted sites was
higher than that by Lewis sites and that Lewis sites preferentially
catalyzed to produce bicyclic products such as camphene. In
the case of FSM-16, selectivity for camphene was independent
of pretreatment temperature. Further, low-temperature-treated
niobic acid, known to be a typical Brønsted acid, gave a high
selectivity for camphene. The suggestion by Severino et al.
was not applicable to our experiments. The majority of acid
sites on FSM-16 were Lewis sites, but Lewis sites did not
participate in the catalysis of both but-1-ene and R-pinene
isomerization. Therefore, we concluded that Brønsted acid sites
were active sites for both reactions and that the sites were weakly
perturbed vicinal pairs of silanol groups (species II).
FSM-16 pretreated at 673 and 1073 K exhibited medium acid
strength of H0 ) -3.0. This value is almost the same as those
for SiO2-MgO 65,66 and NiSO4‚nH2O,67 but much weaker than
that of SiO2-Al2O3, which is stronger than H0 ) -8.2.65,66
FSM-16, with Si/Al atomic ratios of both 735 and 320, showed
the same value of maximum acid strength. The maximum acid
Survey of Catalyst Property. It was reported that reversible
dehydroxylation of silanols occurred below 673 K and irrevers-
ible dehydroxylation of isolated silanols occurred above 923
K.51 On the other hand, silanol groups of FSM-1173 were

5838 J. Phys. Chem. B, Vol. 102, No. 30, 1998
Yamamoto et al.
TABLE 6: Maximum Acid Strength and BET Specific
Surface Area
Conclusion
FSM-16 catalyzes but-1-ene isomerization at 323 K and
R-pinene isomerization at 303 K in the liquid phase. Catalytic
activity of FSM-16 was dependent upon pretreatment temper-
atures and showed a maximum at 673 K. The activity of FSM-
16 calcined at higher than 773 K was much reduced, but it could
be restored by rehydration procedures as long as the samples
maintained the crystal structure. The active sites were weakly
perturbed silanol groups and a trace amount of Al of FSM-16
did not affect acidic property. Maximum acid strength was
invariably H0 ) -3.0, independent of pretreatment temperatures.
These properties are related to the regular structure of FSM-
16.
pretreatment
temp/K
surface area/
m2 g-1
catalyst
FSM-16
H0 max
-3.0c
-3.0
473
673
873
1073
1273
673
673
673
673
673
1078
1045
1026
815
965
874
37
960
650
490
144
-3.0
-5.6
-3.0
-3.0
-3.0c
-3.0
+4.8
+3.0
+3.0c
FSM-16a
FSM-1173H
FSM-1373H
FSM-16b
SiO2
1073
673
H2Si2O5
a Calcined in a dry air stream at 1173 K for 2 h. b Supplied by Toyota
Central R & D Labs., Inc. (lot no. NG78-550). c Hammet indicator was
faintly colored.
Acknowledgment. We thank Dr. S. Inagaki (Toyota Central
R & D. Labs., Inc.) for the supply of FSM-16 (lot no. NG78-
550) and elemental analysis, Dr. R. Ohnishi (Hokkaido Uni-
versity) for the offer of terpenes (tricyclene, bornylene), and
Mr. R. Kuma (Kyoto University) for his assistance with TPD
measurements.
strengths of SiO2 gel were much weaker than those for FSM-
16. Werner et al. reported that crystalline silicates have much
stronger acid sites than those of silica gel. For example, H2-
Si2O5 and H2Si14O29‚5H2O exhibited a maximum acid strength
of H0 ) +2.3 to +3.3 and -5 to -3, respectively.68 They
discussed that the high acidity resulted from regular and
extended hydrogen-bonding systems including the surface water
molecules. The maximum acid strength of synthesized H2Si2O5
was the same as the reported value of H0 ) +3.0, although
calcined H2Si2O5 became amorphous. From elemental analysis,
the Al concentration of H2Si2O5 was estimated to be only 80
ppm (Table 1); however, its maximum acid strength of H0 )
+3.0 was higher than that of SiO2 gel of +4.8. These results
show that almost pure siliceous materials have the possibility
to exhibit acidic properties. Thus, we conclude that but-1-ene
and R-pinene isomerizations were catalyzed by Brønsted acid
sites with an acidic strength of H0 < +3.0. In the case of FSM-
16, the selectivity of R-pinene isomerization and the maximum
acid strength were independent of the pretreatment temperature.
This result indicates that the change of catalytic activity of FSM-
16 does not depend on the change of the acid strength but on
the number of acid sites. IR and H2O desorption experiments
showed that active sites on FSM-16 were blocked by hydrogen-
bonded adsorbed water when FSM-16 was pretreated at below
673 K. This was supported by the result that addition of water
to pretreated FSM-16 drastically lowered catalytic activity.
Although FSM-16 pretreated at 1273 K showed the maximum
acid strength of H0 ) -5.6, the number of the strongest acid
sites was quite small because no change of selectivity for
R-pinene isomerization was observed and activities for R-pinene
and but-1-ene isomerization were quite low. Although FSM-
1373H was amorphous, it still possessed a small number of acid
sites whose H0 max was -3.0. As shown in Table 5, the activities
of FSM-1373H and fresh FSM-16 were different from each
other by over 400 times. On the other hand, the BET specific
surface area of FSM-1373H was about 3% of the fresh one.
The reduction of catalytic activity was far from that of the
surface area. Therefore, the possibility that sintering was the
main reason for deactivation is excluded. The structure of FSM-
16 is indispensable to acidic property, although the mechanism
of generation of acid sites is not clear. This is supported by
the fact that FSM-16, having become amorphous, could not
regenerate the acidic property by the rehydration process.
We suppose that the structure of FSM-16 is indispensable to
acidic property, especially to its thin wall and regularly arrayed
silanol groups.
References and Notes
(1) Inagaki, S.; Fukushima, Y.; Kuroda, K. J. Chem. Soc., Chem.
Commun. 1993, 680.
(2) Kresge, C. T.; Lenowicz, M. E.; Roth, W. J.; Vartuli, J. C.; Beck,
J. S. Nature 1992, 359, 710.
(3) Beck, J. S.; Vartuli, J. C.; Roth, W. J.; Lenowicz, M. E.; Kresge,
C. T.; Schmitt, K. D.; Chu, C. T.-W.; Olson, D. H.; Sheppard, E. W.;
McCullen, S. B.; Higgis, J. B.; Schlenker, J. L. J. Am. Chem. Soc. 1992,
114, 10834.
(4) Tanev, P. T.; Chibwe, M.; Pinnavaia, T. J. Nature 1994, 368, 321.
(5) Zhang, W.; Fro¨ba, M.; Wang, J.; Tanev, P. T.; Wong, J.; Pinnavaia,
T. J. J. Am. Chem. Soc. 1996, 118, 9164.
(6) Monnier, A.; Schu¨th, F.; Huo, Q.; Kumar, D.; Margolese, D.;
Maxwell, R. S.; Stucky, G. D.; Krishnamuty, M.; Petroff, P.; Firouzi, A.;
Janicke, M.; Chmelka, B. F. Science 1993, 261, 1299.
(7) O’Brien, S.; Francis, R. J.; Price, S. J.; O’Hare, D.; Clark, S. M.;
Okazaki, N.; Kuroda, K. J. Chem. Soc., Chem. Commun. 1995, 2423.
(8) Tanabe, K.; Misono, M.; Ono, Y.; Hattori, H. New Solid Acids
and Bases; Kodansha, Elsevier: Tokyo, 1989; pp 91-105.
(9) Corma, A.; Fornes, V.; Navarro, M. T.; Pe´rez-Pariente, J. J. Catal.
1994, 148, 569.
(10) Mokaya, R.; Jones, W.; Luan, Z.; Alba, M. D.; Klinowski, J. Catal.
Lett. 1996, 37, 113.
(11) Jentys, A.; Pham, N. H.; Vinek. H. J. Chem. Soc., Faraday Trans.
1996, 92, 3287.
(12) Inagaki, S.; Fukushima, Y.; Okada, A.; Kurauchi, T.; Kuroda, K.;
Kato, C. Proc. 9th Int. Zeolite Conf., I 1992, 305.
(13) Inagaki, S.; Yamada, Y.; Fukushima, Y. Stud. Surf. Sci. Catal. 1996,
105, 109.
(14) Tanev, P. T.; Chibwe, M.; Pinnavaia, T. J. Science 1994, 368, 321.
(15) Corma, A.; Navarro, M. T.; Pe´rez Pariente, J. J. Chem. Soc., Chem.
Commun. 1994, 147.
(16) Rhee, C. H.; Lee, J. S. Catal. Lett. 1996, 40, 261.
(17) Ryoo, R.; Ko, C. H.; Kim, J. M.; Howe, R. Catal. Lett. 1996, 37,
29.
(18) Junges, U.; Jacobs, W.; Voigt-Martin, I.; Krutzsch, B.; Schu¨th, F.
J. Chem. Soc., Chem. Commun. 1995, 2283.
(19) Shinoda, T.; Izumi, Y.; Onaka, M. J. Chem. Soc., Chem. Commun.
1995, 1801.
(20) Huber, C.; Moller, K.; Bein, T. J. Chem. Soc., Chem. Commun.
1994, 2619.
(21) Maschmeyer, T.; Rey, F.; Sanker, G.; Thomas, M. Nature 1995,
378, 159.
(22) Macquarrie, D. J.; Jackson, D. B. Chem. Commun. 1997, 1781.
(23) Liu, C.-J.; Li, S.-G.; Pang, W.-Q.; Che, C.-M. Chem. Commun.
1997, 65.
(24) Ohnishi, R.; Tanabe, K.; Morikawa, S.; Nishizaki, T. Bull. Chem.
Soc. Jpn. 1974, 47, 571.
(25) Tanaka, T.; Iatagaki, A.; Zhang, G.; Hattori, H.; Tanabe, K. J. Catal.
1990, 122, 384.
(26) Ohnishi, R.; Tanabe, K. Chem. Lett. 1974, 207.
(27) Galarneau, A.; Barodawalla, A.; Pinnavaia, T. J. Chem. Commun.
1997, 1661.

Acidic Property of FSM-16
J. Phys. Chem. B, Vol. 102, No. 30, 1998 5839
(28) Hamaguchi, K.; Hattori, H. React. Kinet. Catal. Lett. 1997, 61, 13.
(29) Yoshida, H.; Kimura, K.; Inaki, Y.; Hattori, T. Chem. Commun.
1997, 129.
(30) Inagaki, S.; Koiwai, A.; Suzuki, N.; Fukushima, Y.; Kuroda, K.
Bull. Chem. Soc. Jpn. 1996, 69, 1449.
(49) Haag, W. O.; Lago, R. M.; Weisz, P. W. Nature 1984, 309, 589.
(50) Derouane, E. G.; Baltusis, L.; Dessau, R. M.; Schmitt, K. D. Stud.
Surf. Sci. Catal. 1985, 20, 135.
(51) Chuang, I.-S.; Maciel, G. E. J. Phys. Chem. B 1997, 101, 3052,
and references therein.
(31) Branston, P. J.; Kaneko, K.; Setoyama, N.; Sing, K. S.; Inagaki,
S.; Fukushima, Y. Langmuir 1996, 12, 599.
(32) Beneke, K.; Lagaly, G. Am. Mineral. 1977, 62, 763.
(33) Lagaly, G. AdV. Colloid Interface Sci. 1979, 11, 105.
(34) Yoshida, S.; Matsuzaki, T.; Kashiwazaki, T.; Mori, K.; Tarama,
K. Bull. Chem. Soc. Jpn. 1974, 47, 1564.
(52) Morrow, B. A.; McFarlan, A. J. J. Phys. Chem. 1992, 96, 1395.
(53) Ishikawa, T.; Matsuda, M.; Yasukawa, A.; Kandori, K.; Inagaki,
S.; Fukushima, Y.; Kondo, S. J. Chem. Soc., Faraday Trans. 1996, 92,
1985.
(54) Morrow, B. A.; Devi, A. J. Chem. Soc., Faraday Trans. 1 1972,
68, 403.
(35) Klading, W. J. Phys. Chem. 1976, 80, 262.
(36) Ward, J. W. J. Catal. 1970, 16, 386.
(37) Baba, T.; Inoue, Y.; Ono, Y. J. Catal. 1996, 159, 230.
(38) Tanabe, K.; Misono, M.; Ono, Y.; Hattori, H. New Solid Acids
and Bases; Kodansha, Elsevier: Tokyo, 1989; pp 215-220.
(39) Niwa, M.; Iwamoto, M.; Segawa, K. Bull. Chem. Soc. Jpn. 1986,
59, 3735.
(55) Morrow, B. A.; Cody, I. A. J. Phys. Chem. 1975, 79, 761.
(56) Morrow, B. A.; Cody, I. A. J. Phys. Chem. 1976, 80, 1995.
(57) Bunker, B. C.; Haaland, D. M.; Ward, K. J.; Michalske, T. A.;
Binkley, J. S.; Melius, C. F.; Malfe, C. A. Surf. Sci. 1989, 210, 406.
(58) Matsumura, Y.; Hashimoto, K.; Yoshida, S. J. Chem. Soc., Chem.
Commun. 1987, 1559.
(59) Matsumura, Y.; Hashimoto, K.; Yoshida, S. J. Catal. 1989, 117,
135.
(40) Parry, E. R. J. Catal. 1963, 2, 371.
(41) Climent, M. J.; Corma, A.; Iborra, S.; Navarro, M. C.; Primo, J. J.
Catal. 1996, 161, 783.
(42) Zhao, X. S.; Lu, G. Q.; Whittaker, A. K.; Millar, G. J.; Zhu, H. Y.
J. Phys. Chem. B 1997, 101, 6525.
(43) Gillis-D’Hamers, I.; Cornelissens, I.; Vrancken, K. C.; Van Der
Voort, P.; Vansant, E. F. J. Chem. Soc., Faraday Trans. 1992, 88, 723.
(44) Van Roosmalen, A. J.; Hartmann, M. C.; Mol, J. C. J. Catal. 1980,
66, 112.
(60) Sato, H.; Hirose, K.; Nakamura, Y. Chem. Lett. 1993, 1987.
(61) Brinker, C. J.; Kirkpatrick, R. J.; Tallant, D. R.; Bunker, B. C.;
Montez, B. J. Non-Cryst. Solids 1988, 99, 418.
(62) Le´onardelli, S.; Facchini, L.; Fretigny, C.; Tougne, P.; Legrand,
A. P. J. Am. Chem. Soc. 1992, 114, 6412.
(63) Anderson, M. W.; Klinowsky, J. Zeolites 1986, 6, 455.
(64) Severino, A.; Esculcas, A.; Rocha, J.; Vital, J.; Lobo, L. S. Appl.
Catal. A General 1996, 142, 255.
(45) West, P. B.; Haller, G. L.; Burwell, R. L., Jr. J. Catal. 1973, 29,
486.
(46) Haag, W. O. Stud. Surf. Sci. Catal. 1994, 84, 1375.
(47) Weisz, P. B. Ind. Eng. Chem. Fundam. 1986, 25, 53.
(48) Olsen, D. H.; Haag, W. O.; Lago, R. M. J. Catal. 1980, 61, 390.
(65) Benesi, H. A. J. Am. Chem. Soc. 1956, 78, 5490.
(66) Benesi, H. A. J. Phys. Chem. 1957, 61, 970.
(67) Tanabe, K.; Takeshita, T. AdV. Catal. 1967, 17, 315.
(68) Werner, Von H.-J.; Beneke, K.; Lagaly, G. Z. Anorg. Allg. Chem.
1980, 470, 118.