Hierarchical SAPO-5 catalysts active in acid-catalyzed reactions

Article abstract of DOI:10.1016/j.jcat.2010.03.014

Crystalline silicoaluminophosphate (SAPO) of the AFI framework type with a bimodal pore system and high silicon content was hydrothermally synthesized using a soft template with a silicon-containing head group and cyclohexylamine to maintain microporosity. The structural and catalytic properties of the hierarchical structure were extensively characterized and compared to those of microporous SAPO-5 and H-ZSM-5. Temperature-programmed desorption of n-propylamine, isomerization of 2-methyl-2-pentene, and monomolecular cracking of propane indicated a large number of Bronsted acid sites and their high reactivity, similar to those of microporous H-SAPO-5. The catalytic activity of the hierarchical H-SAPO-5 was much higher in space-demanding alkylation of benzene with benzyl alcohol. At 353 K and under autogenous pressure, the conversion of benzyl alcohol over the hierarchical sample reached 98%, whereas the conversion over the microporous H-SAPO-5 was around 66% and over H-ZSM-5 below 10%. In contrast to H-ZSM-5, the external surfaces of H-SAPO-5 and H-SAPO-5M contribute to the alkylation reaction. Other procedures to yield mesoporous SAPO, such as hard-templating with carbon, soft-templating with amphiphilic surfactants, and phosphorus- or aluminum-containing molecules, resulted in impure, amorphous, non-mesoporous, or much less acidic materials.

Full text of DOI:10.1016/j.jcat.2010.03.014

Journal of Catalysis 272 (2010) 37–43
Contents lists available at ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Hierarchical SAPO-5 catalysts active in acid-catalyzed reactions
a
b
a,*
Nadiya Danilina , Frank Krumeich , Jeroen A. van Bokhoven
a
ETH Zurich, Institute for Chemical and Bioengineering, Wolfgang-Pauli-Str. 10, 8093 Zurich, Switzerland
ETH Zurich, Laboratory of Inorganic Chemistry, Wolfgang-Pauli-Str. 10, 8093 Zurich, Switzerland
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Crystalline silicoaluminophosphate (SAPO) of the AFI framework type with a bimodal pore system and
high silicon content was hydrothermally synthesized using a soft template with a silicon-containing head
group and cyclohexylamine to maintain microporosity. The structural and catalytic properties of the hier-
archical structure were extensively characterized and compared to those of microporous SAPO-5 and H-
ZSM-5. Temperature-programmed desorption of n-propylamine, isomerization of 2-methyl-2-pentene,
and monomolecular cracking of propane indicated a large number of Brønsted acid sites and their high
reactivity, similar to those of microporous H-SAPO-5. The catalytic activity of the hierarchical H-SAPO-
Received 2 February 2010
Revised 17 March 2010
Accepted 17 March 2010
Available online 18 April 2010
Keywords:
SAPO-5
Hierarchical
Mesoporous
Bimodal
5
was much higher in space-demanding alkylation of benzene with benzyl alcohol. At 353 K and under
autogenous pressure, the conversion of benzyl alcohol over the hierarchical sample reached 98%, whereas
the conversion over the microporous H-SAPO-5 was around 66% and over H-ZSM-5 below 10%. In
contrast to H-ZSM-5, the external surfaces of H-SAPO-5 and H-SAPO-5M contribute to the alkylation
reaction. Other procedures to yield mesoporous SAPO, such as hard-templating with carbon, soft-
templating with amphiphilic surfactants, and phosphorus- or aluminum-containing molecules, resulted
in impure, amorphous, non-mesoporous, or much less acidic materials.
Alkylation
Ó 2010 Elsevier Inc. All rights reserved.
1
. Introduction
Silicoaluminophosphates (SAPO) have considerable potential as
a new type of soft template for the synthesis of mesoporous zeo-
lites, such as ZSM-5 [9,15,16] and SAPO [8,17], has been described.
These so-called porogenes are surfactant molecules; they contain
silicon that enhances the interaction of the template with the
growing zeolite crystals and prevents phase segregation during
crystallization. Zeolites and zeotypes of high crystallinity and with
a hierarchical pore structure were obtained. It was shown that
such hierarchical materials have considerable catalytic potential
[8,16,18–20].
Based on these original ideas, we designed a method to synthe-
size microcrystalline SAPO with a high silicon content and bimodal
pore system using a soft template with a silicon-containing head
group [9] and an additional template cyclohexylamine to create
microporosity. We compared this method to alternative proce-
dures of obtaining mesoporous SAPO, such as a soft-templating
with phosphorus- and aluminum-containing molecules and
amphiphilic surfactants and a hard-templating with carbon nano-
particles. The catalytic activity of the hierarchical H-SAPO-5 was
evaluated in the liquid-phase alkylation of benzene with benzyl
alcohol, in monomolecular propane cracking, and in the isomeriza-
tion of 2-methyl-2-pentene. The monomolecular cracking of
propane yields the intrinsic reactivity of the Brønsted acid sites
[21–23]. The apparent activation barrier is a combined measure
of the heat of adsorption and the energy required to transfer the
proton from the zeolite to the alkane. The isomerization of
acidic catalyst for the conversion of hydrocarbons. Microporous
SAPO-5 is active in cumene synthesis [1], xylene isomerization
[
[
2], toluene alkylation by methanol [3], isopropylation of benzene
4], transalkylation of toluene with trimethylbenzenes [5], and
many other reactions. SAPO-5 is a 12-membered ring, wide-pore
zeolite with a pore size of 7.3 Â 7.3 Å. However, mesoporous or
hierarchical SAPOs could increase the external surface area and of-
fer more space for bulky molecules to diffuse and react. Unlike alu-
minosilicate zeolites, for which various methods exist to create
mesopores, little is known about the generation of mesopores in
SAPOs. Some mesoporous SAPO structures have been synthesized
[
6–9], but their catalytic properties have not been studied in depth.
The most important methods to synthesize mesoporous zeolites
and zeotypes are soft-templating [10], hard-templating [11], pillar-
ing/delamination [12], post-synthesis treatment [13], and use of
zeolite seeds as precursors in the preparation of mesoporous struc-
tures [14]. Mesoporous zeolites, which have the most desirable
properties for catalysis, such as high crystallinity, narrow pore size
distribution, uniform pores, hydrothermal stability, and zeolite-
like acidity, have been reported. Using a template enables the con-
trol of the shape and size of the solid and its pore system. Recently,
2
-methyl-2-pentene is a probe reaction to evaluate the acidity of
*
Corresponding author.
E-mail address: j.a.vanbokhoven@chem.ethz.ch (J.A. van Bokhoven).
solid acids [24]. The molar ratio of trans-3-methyl-2-pentene,
0
021-9517/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved.
doi:10.1016/j.jcat.2010.03.014

3
8
N. Danilina et al. / Journal of Catalysis 272 (2010) 37–43
obtained by the methyl shift, to trans- and cis-4-methyl-2-pentene,
obtained by the hydrogen shift reflects the acidity. The alkylation
of benzene with benzyl alcohol is a space-requiring acid-catalyzed
reaction, which allows the determination of active sites in the large
pores.
2.1.2.4. Soft-templating with amphiphilic surfactant. H-SAPO-S was
prepared in the same way as H-SAPO-5M. Instead of TPHAC, a mix-
ture of 1.01 g of dodecyltrimethylammonium bromide (Fluka,
>98%) and 1.14 g of tetramethylammonium hydroxide (Fluka,
25% in water) was added.
2
.1.2.5. Hard-templating with carbon black. SAPO-C was synthesized
as in Ref. [26]. A mixture of 2.04 g of aluminum isopropoxide and
mL THF was impregnated onto 1 g of carbon (Black Pearls 2000,
2
. Experimental
7
2
2
.1. Catalyst preparation
CABOT), which had an average particle diameter of about 12 nm.
The carbon black was dried at 383 K for 24 h prior to use. The car-
bonaceous material was left to dry at room temperature in a flow
of air for 6 h. A solution of 1.5 g phosphoric acid, 1.62 g triethyl-
amine, and 0.27 g hydrofluoric acid (Fluka, 48 wt.%) in 1 mL of
deionized water was prepared and stirred for 1 h. The dry carbon
material was impregnated with this solution and subsequently
with 0.87 g of TEOS (Fluka, >98%). Then, the material was put into
an open 10-mL Teflon bottle and placed in the PEEK liner filled with
.1.1. Microporous SAPO-5
Microporous SAPO-5 was hydrothermally synthesized from a
2 3 2 5 2 2
gel consisting of Al O :P O :0.24SiO :0.15cyclohexylamine:20H O.
During preparation, 6.808 g aluminum isopropoxide (Fluka, >98%)
was mixed with 3.27 g orthophosphoric acid (Merck, 85%), dis-
solved in 14 g of deionized water, and stirred for 1 h. A solution
of 0.99 g of cyclohexylamine was dissolved in 10 g of deionized
water and stirred for 1 h. Both solutions were then mixed and stir-
red for another hour. Finally, 0.96 g of silica aerosol Cab-osil M-5
2
0 mL of deionized water. The gel was hydrothermally crystallized
in a stainless-steel autoclave at 448 K for three days, after which the
product was filtered, washed with 2 L deionized water, and dried at
3
2
(
Riedel-de-Haën) was added, and the mixture was stirred for 2 h.
The gel was crystallized in 60-mL PEEK-lined stainless-steel auto-
claves at 473 K for 2 h and subsequently for 22 h at 463 K. The
product was recovered by filtration, washed with 2 L of deionized
water, dried at room temperature, and calcined in air at 823 K for
53 K overnight in a vacuum oven. The sample was calcined for
0 h at 873 K with a heating rate of 1 K/min in a flow of air.
SAPO-C was ion-exchanged to obtain H-SAPO-C after calcination.
2
0 h to remove the template. The sample was ion-exchanged three
times with 1 M NH NO (Fluka, >99%) for 2 h at 348 K and calcined
in nitrogen at 723 K for 4 h to give H-SAPO-5.
2
.2. Characterization
4
3
X-ray powder diffraction (XRD) was conducted on a STOE STA-
DI-P2 diffractometer in transmission mode using a flat sample
holder and Ge-monochromated Cu K
radiation. The instrument
was equipped with a position-sensitive detector with a resolution
2
2
.1.2. Mesoporous SAPO-5
.1.2.1. Soft-templating with organosilane. The synthesis procedure
a
1
was analogous to that of SAPO-5, with the exception that [3-
of ꢀ0.01° in 2h.
(
(
trimethoxysilyl)propyl]hexadecyldimethylammonium
TPHAC) was additionally used as a template to generate mesop-
chloride
Nitrogen sorption measurements were performed at the tem-
perature of liquid nitrogen on a Tristar 3000 apparatus of Microm-
eritics. Prior to the measurements, the samples were degassed at
10 Pa and 523 K for at least 2 h. The surface area was determined
by the BET method; the t-plot method was used to determine
the specific pore volume.
ores. A solution of 1.91 g TPHAC was added to the aqueous solution
of cyclohexylamine and stirred overnight before it was mixed with
the aluminophosphate solution. TPHAC was synthesized according
to a reported procedure [25]. The composition of the gel of the
hierarchical SAPO-5M was Al
2
O
3
2
:P O
5
:0.24SiO
2
:0.15cyclohexyl-
Atomic absorption spectroscopy (AAS) was performed on a Var-
ian SpectrAA 220 FS spectrometer to determine elemental consti-
amine:0.009TPHAC:20H O. The templates were removed by calci-
2
nation (see Section 2.1.1), and ion-exchange was performed
according to the procedure described earlier. The calcined sample
was labeled H-SAPO-5M.
3
tution. The samples were dissolved in an HF/HNO /water matrix
overnight. Quantification of the aluminum content was done by
the standard addition method. For silicon, individual calibration
curves were measured and used for quantification.
2
7
Al magic-angle spinning nuclear magnetic resonance (MAS
2.1.2.2. Soft-templating with a phosphorus-containing molecule. H-
NMR) experiments were carried out on a Bruker Avance 700
NMR spectrometer using a 2.5-mm double-resonance probe-head.
SAPO-P was prepared in the same way as H-SAPO-5M. Instead of
TPHAC, a mixture of 2.4 g of mono-n-dodecylphosphate (Alfa Ae-
sar) in 1 mL ethanol was added.
27
The resonance frequency for Al was 182.4 MHz and the pulse
length was 6
ls. The recycle delay was 1 s. All spectra were ob-
2
7
tained at a spinning speed of 15 kHz. The Al chemical shifts were
referenced to Alum ((NH
measurements were performed on a Bruker Avance 500 NMR spec-
O). 29Si and P MAS NMR
31
2
.1.2.3. Soft-templating with an aluminum-containing mole-
cule. SAPO-A was hydrothermally synthesized from a gel mixture
of composition Al :1.73P :1.21SiO :1.03Al-dihydroxo-mono-
heptadecylester:209.72H O. A solution of 2.512 g aluminum iso-
4
4
)Al(SO )
2
Á12H
2
2
9
2
O
3
2
O
5
2
trometer using a 4-mm probe-head. For Si MAS NMR, a spinning
frequency of 8 kHz and a relaxation delay of 10 s were employed.
2
2
9
propoxide (Fluka, >98%) in 5.825 g deionized water was mixed
with 2.451 g orthophosphoric acid (Merck, 85%), dissolved in
The Si chemical shifts were referenced to octakis-(trimethylsil-
3
1
oxy)silsesquioxane. To record the P MAS NMR spectra, a spinning
frequency of 8 kHz and a relaxation delay of 1 s were employed.
5
4
.01 g of deionized water, and stirred for 1.5 h. A solution of
.304 g of aluminum-dihydroxo-mono-heptadecylester (Fluka,
1
3
The field was calibrated by measuring C MAS NMR of glycine.
Scanning electron microscopy (SEM) was performed on a LEO
1530 Gemini instrument (Zeiss) operated at 1 kV. The sample
was deposited onto a conductive carbon foil supported on an alu-
minum stub. Transmission electron micrographs (TEM) were ob-
tained on a Philips CM30 microscope with a point resolution of
0.2 nm at 300 kV. For TEM, the sample was ground, dispersed in
ethanol, and deposited on a holey carbon film supported on a cop-
per grid.
technical grade) was suspended in 5.032 g of deionized water,
added to the aluminophosphate solution, and stirred for 1.5 h. Fi-
nally, 1.7426 g of tetraethylorthosilicate (Fluka, >98%) was added
and the mixture was stirred overnight. The gel was crystallized
in 60-mL PEEK-lined stainless-steel autoclaves at 473 K for 20 h.
The product was recovered by filtration, washed with 2 L of deion-
ized water, dried at room temperature, and calcined in air at 823 K
for 20 h to remove the template.

N. Danilina et al. / Journal of Catalysis 272 (2010) 37–43
39
For the temperature-programmed desorption of propylamine
with thermogravimetric analysis (TPD–TGA), approximately
2
1
0 mg sample were activated overnight at a pressure below
À4
0
Pa by heating to 723 K with a ramp of 2 K/min. The sample
was then exposed to n-propylamine at 473 K for 2 h and cooled
to room temperature. The sample was evacuated for about 2 h to
remove physisorbed n-propylamine. The thermogravimetric
decomposition of n-propylamine was performed with a heating
rate of 10 K/min and in a flow of 20 mL/min Ar in a Mettler Toledo
TGA/SDTA851e instrument. The amount of decomposed n-propyl-
amine was obtained from the mass change in the TGA curves be-
tween 573 and 650 K.
2
2
.3. Catalytic tests
.3.1. Propane cracking
The monomolecular propane cracking was performed in a setup
Fig. 1. XRD of SAPO-5, SAPO-5M, SAPO-P, SAPO-A, SAPO-S, and SAPO-C and the
with six parallel-flow tubular quartz reactors. Ten percent propane
in argon was reacted between 723 and 873 K at 100 kPa total pres-
sure. About 100 mg of the catalyst was activated in a reactor in 10%
oxygen in argon at 878 K for 1 h with a heating ramp of 2 K/min. A
volumetric flow of 5 mL/min per reactor was used to keep the con-
version below 5%. The products were analyzed in the effluent gas
stream with an on-line Agilent 3000 MicroGC gas chromatograph
equipped with MolSieve 5A, PLOT U, and Alumina PLOT columns.
The procedure to determine the catalyst performance is described
in more detail elsewhere [21,19,23].
simulated pattern of AFI.
the whole 2h range, indicating that they contained a crystalline
phase. SAPO-5 and SAPO-5M had an AFI structure type. SAPO-P
was a mixture of two structures, AFI and CHA (Fig. S1, Supporting
information). The diffractogram of SAPO-A corresponded to that of
ALPO-H4 [27]. A background in the diffractogram of SAPO-A indi-
cated the presence of amorphous material. SAPO-S and SAPO-C
were of SOD and CHA structure types, respectively (Fig. S1, Sup-
porting information). No reflections were observed in the low 2h
range, indicating that the samples did not contain regular, uniform
mesopores.
2.3.2. Isomerization of 2-methyl-2-pentene
The gas phase isomerization of 2-methyl-2-pentene (2M2P)
Table 1 gives the results of nitrogen physisorption, elemental
[
24] was studied in a plug-flow reactor. A concentration of 0.1 g
of the catalyst was pretreated in flowing helium for about 1 h at
23 K prior to the reaction. The reaction was initially conducted
2
9
analysis, and the deconvolution of Si MAS NMR spectra. The
BET and the external surface area of SAPO-5M were about 10%
and 45% higher, respectively, than those of microporous SAPO-5.
7
at 473 K for 1 h, while a flow of 15 mL/min of 7 vol.% 2M2P in he-
lium at atmospheric pressure was passed over the catalyst. The
feed was then switched to helium and the catalyst cooled to
3
The micropore volumes of SAPO-5 (0.1 cm /g) and SAPO-5M
3
(
0.09 cm /g) were similar, and both were high. These values were
in good agreement with those reported in the literature [28]. Fur-
thermore, SAPO-5M had a large mesopore volume of 0.73 cm /g.
The BET surface area and the micropore volume of SAPO-P were
relatively high. This is explained by the presence of the CHA impu-
rity. The external surface area was 47 m /g and the mesopore vol-
ume was only 0.06 cm /g, indicating only a small number of
mesopores. The BET surface area of SAPO-A was 148 m /g, almost
as large as its external surface area. Porosity was not detected.
The BET surface area of SAPO-S (68 m /g) was low. The whole sur-
face area of the sample was the external surface area; the sample
was non-porous. This is in agreement with the results of XRD,
which showed that SAPO-A and SAPO-S were of the ALPO-H4
and SOD structure type, respectively, which are dense phases.
SAPO-C showed a very high surface area of 613 m /g and micropo-
rous volume of 0.26 cm /g, typical of materials of CHA structure
type (SAPO-34). The external surface area of SAPO-C was very
small and mesoporosity was not observed, indicating that micro-
porous SAPO with a CHA structure was obtained. The isotherm of
SAPO-5 was typical of microporous material (Fig. 2); SAPO-5M
contained a hysteresis of type IV, typical of mesoporous material
4
48 K and then to 423 K. The samples were taken 10 min after
3
switching on the feed at 473, 448, and 423 K. The products were
analyzed on-line with an Agilent 6890 GC with an FID detector
using a 50-m HP5 packed column.
2
3
2.3.3. Alkylation of benzene with benzyl alcohol
2
Alkylation of benzene with benzyl alcohol was performed in 25-
mL Berghof autoclaves BR-25. A concentration of 0.11 g of the cat-
alyst was activated ex situ at 523 K in a flow of nitrogen, transferred
to the reactor in a flow of nitrogen, and covered with 14.9 g ben-
2
zene (Sigma–Aldrich, puriss.), which was dried over a mol sieve
Ò
(
(
ZEOCHEM Purmol from Uetikon Chemie AG). Benzyl alcohol
0.26 g) (Fluka, puriss.) was added, resulting in a molar ratio of
2
benzene to benzyl alcohol of around 80. The reactor was purged
with nitrogen and a permanent pressure of 25–27 bars was main-
tained during the reaction to keep the reactants in the liquid phase
at the reaction temperature of 433 K. The mixture was stirred at
3
1
250 rpm throughout the run, which was determined to be suffi-
ciently fast. Small liquid samples were withdrawn periodically
and analyzed using a GC–MS setup equipped with a capillary HP-
PONA (Agilent Technologies) column.
[
29]. The shape of the hysteresis suggested presence of aggregates
of platy particles with pores of different shape and size. The pore
size distribution of SAPO-5M (Fig. 2, inset) showed two maxima,
one at 3.8 nm, which is probably attributed to the so-called tensile
strength effect [30], and a relatively broad one centered at about
12 nm, representing the mesopores.
3
. Results
3.1. Synthesis and characterization
AAS indicated that SAPO-5, SAPO-5M, SAPO-P, and SAPO-A con-
tained a considerable amount of silicon. The deconvolution of 29Si
MAS NMR spectra (Fig. S2, Supporting information) revealed that,
for SAPO-5, SAPO-5M, and SAPO-P, most of the silicon was in the
Fig. 1 shows X-ray diffractograms of SAPO-5, SAPO-5M, SAPO-P,
SAPO-A, SAPO-S, and SAPO-C and a simulated diffractogram of the
AFI zeolite structure. The samples showed sharp reflections over

4
0
N. Danilina et al. / Journal of Catalysis 272 (2010) 37–43
Table 1
Results of characterization of SAPO-5, SAPO-5M, SAPO-P, SAPO-A, SAPO-S, and SAPO-C.
2
2
3
3
a
b
Sample
BET surface area (m /g)
S
ext (m /g)
V
micro (cm /g)
V
meso (cm /g)
Sibulk (wt.%)
SiSAPO (wt.%)
SAPO-5
SAPO-5M
SAPO-P
SAPO-A
SAPO-S
SAPO-C
325
367
441
148
68
93
0.10
0.09
0.17
0
0
0.26
0.12
0.73
0.06
0
0
0
5.6
5.3
4.9
12
n.d.
n.d.
3.3
3.7
3.2
3.4
n.d.
n.d.
170
47
138
68
7
c
613
a
b
c
Determined by AAS.
Si in SAPO domains determined from deconvolution of 29Si MAS NMR spectra (Fig. S1, Supporting information).
Not determined.
rich regions of H-SAPO-5 and H-SAPO-5M. Both samples showed
2
7
peaks in the Al MAS NMR spectra at around 50 and 0 ppm, corre-
sponding to tetrahedrally and octahedrally coordinated aluminum,
respectively (Fig. 3b). The mesoporous sample contained more
octahedral aluminum, which could be of framework or extraframe-
work nature. The peak at 17 ppm in the spectrum of H-SAPO-5M is
3
1
attributed to pentacoordinated aluminum. P MAS NMR spectra
showed only one peak at around 30 ppm (Fig. 3c), which is attrib-
uted to phosphorus in the framework. This peak was asymmetrical
and had a tail toward lower chemical shift.
Fig. 4a shows the SEM of a SAPO-5M particle, which in fact was
an agglomerate of about 100 nm thin platelets. Fig. 4b–d shows
TEM micrographs of SAPO-5M. Bright spots appeared due to differ-
ences in thickness (Fig. 4b), which correspond to mesopores (thick-
ness contrast). Their diameter was between 8 and 30 nm. Their size
is in a good agreement with the average pore size obtained from
nitrogen physisorption. Zeolite lattice fringes were easily recogniz-
able in micrographs of high magnification (Fig. 4c, inset). The sam-
ple contained round and tail-shaped cavities (Fig. 4c and d), which
may have accommodated the porogenous template molecules.
Table 2 gives an overview of the results of TPD–TGA of n-pro-
pylamine, monomolecular propane cracking, and isomerization of
2-methyl-2-pentene for H-SAPO-5 and H-SAPO-5M. Both samples
chemisorbed roughly the same amount of n-propylamine, indicat-
ing that the number of acid sites was similar. The reaction rate and
the activation energy for the monomolecular cracking of propane,
obtained from the slope of the Arrhenius plots (Fig. S3, Supporting
information), were very similar for the microporous H-SAPO-5 and
the mesoporous H-SAPO-5M, which indicates that the catalytically
active sites in this reaction are the same. Assuming that in the
isomerization of 2-methyl-2-pentene, the molar ratio of trans-3-
methyl-2-pentene, obtained by methyl shift, to trans- and cis-4-
methyl-2-pentene, obtained by hydrogen shift reflects the acidity,
equal acidity was observed: at similar conversion of about 60%, the
molar ratio was 1.3.
Fig. 2. Nitrogen sorption isotherms of SAPO-5 and SAPO-5M and pore size
distribution of SAPO-5M.
framework (vide infra). Most of the silicon in SAPO-A was of extra-
framework nature. However, because there were several possibili-
ties to deconvolute the spectra, the values are significantly
uncertain with regard to the silicon content in the framework.
2
9
27
31
Fig. 3 shows Si, Al, and P MAS NMR spectra of H-SAPO-5
and H-SAPO-5M. SAPO consists of aluminosilicate regions with a
Si(2Al, 2Si) configuration, which is also observed in zeolites [31],
and of silicon-rich regions or silicon-islands [32]. These different
regions result from different possibilities of substitution of alumi-
num and phosphorus atoms by silicon during its incorporation into
2
9
the framework [33]. The Si MAS NMR spectra (Fig. 3a) of H-SAPO-
and H-SAPO-5M were broad and asymmetrical, indicating the
5
presence of different silicon species. We assign the intense peak
at about À90 ppm to framework silicon atoms, which were located
in the aluminosilicate region of the sample [6,34]. The resonances
at higher chemical shifts represented silicon located in the silicon-
Fig. 3. 29Si (a), 27Al (b), and 31P (c) MAS NMR of H-SAPO-5 and H-SAPO-5M, Ã denote spinning side bands.

N. Danilina et al. / Journal of Catalysis 272 (2010) 37–43
41
Fig. 4. SEM (a) and TEM (b–d) micrographs of SAPO-5M.
Table 2
Results of TPD–TGA, monomolecular propane cracking, and isomerization of 2-methyl-2-pentene for H-SAPO-5 and H-SAPO-5M.
a
propane
cr
b
propane
A
c
3MP/4MPd
Sample
n
n-PA (mmol/g)
r
(mol/g s bar)
E
(kJ/mol)
X
2M2P (%)
À7
H-SAPO-5
H-SAPO-5M
0.79 ± 0.02
0.83 ± 0.02
2.41 Â 10
2.26 Â 10
189
188
61
66
1.3
1.3
À7
a
b
c
Mole of decomposed n-propylamine.
Cracking rate of propane at 848 K.
Conversion of 2-methyl-2-pentene.
d
Molar ratio of 3-methyl-2-pentenes to 4-methyl-2-pentenes.
Fig. 5a shows the conversion plot in the alkylation of benzene
H-SAPO-5M at a conversion of 55%. The mesoporous sample
showed higher selectivity to the bulkier products, dibenzyl ether
and dibenzyl benzene, which indicates that the reaction took place
in the mesoporous domains. Over H-ZSM-5 only diphenylmethane
formed.
with benzyl alcohol for H-SAPO-5, H-SAPO-5M, and H-ZSM-5. H-
Ò
ZSM-5 (ZEOcat PZ-2/50 H) was obtained from Zeochem AG, Ueti-
kon, Switzerland. The Si/Al ratio was 25 and the BET surface area
2
4
00 m /g. After 3.5 h of reaction, the conversion of benzyl alcohol
over H-SAPO-5M reached 98%, whereas the conversion over the
microporous H-SAPO-5 was around 66%, and over H-ZSM-5 it
was below 10%. Assuming that the reaction was of first-order,
the reaction rates of all the samples were determined (Fig. 5b).
Table 3 gives the rate constants and selectivities. The rate for
H-SAPO-5M was more than three times higher than that for the
microporous H-SAPO-5 and roughly 35 times higher than for
H-ZSM-5. The selectivity was calculated for H-SAPO-5 and
4. Discussion
The dual templating method, with cyclohexylamine and an
organosilane with a long hydrocarbon chain, yielded a crystalline
SAPO-5 with a high micro- and mesoporosity. The organosilane
TPHAC is already known to act as a mesopore-directing template

4
2
N. Danilina et al. / Journal of Catalysis 272 (2010) 37–43
Fig. 5. Conversion of benzyl alcohol (XBA) vs. time (a) and rate constant in the alkylation of benzene with benzyl alcohol (b) for H-ZSM-5 (d), H-SAPO-5 (j), and H-SAPO-5M
N).
(
Table 3
pattern for silicon in SAPO molecular sieves is known to be sensi-
tive to many synthesis parameters, such as total silicon content,
Results of alkylation of benzene with benzyl alcohol (BA) over H-ZSM-5, H-SAPO-5,
and H-SAPO-5M.
template/Al
and temperature [7,37,38].
2 3 2 5 2 3
O ratio, P O /Al O ratio, pH, and crystallization time,
a
À1
Selectivityb (%)
Sample
X
BA (%)
k (min
)
DPMc
DBEd
DBBe
The acidity expressed by the conversion of 2-methyl-2-pentene
and the 3MP/4MP ratio was similar for H-SAPO-5 and H-SAPO-5M.
In comparison, over ZSM-5, the conversion was almost the same,
whereas the 3MP/4MP ratio over SAPO was lower (1.3) than over
ZSM-5 (1.9) [16]. The number of Brønsted acid sites and their
intrinsic reactivity, determined by the TPD/TGA of n-propylamine
and propane cracking, were similar for the micro- and the meso-
porous samples. The intrinsic activation energy is a measure of
acidity and equals the apparent activation energy minus the heat
of reactant adsorption. The strength of the adsorption depends
on the fit of the reactant within the pore: the better the fit, the
higher the heat of adsorption [39]. Therefore, the size and shape
of the pores, in which the reaction occurs, are the main factors in
determining the cracking activity of Brønsted acid sites. For the
AFI structure, the heat of adsorption was À36 kJ/mol [40], similar
to that obtained for FAU (À31 kJ/mol) [41], which has a similar
pore size. The identical activation barrier of propane cracking for
the micro- and the mesoporous SAPO (188–189 kJ/mol) suggests
equal strength of catalytically active sites, indicating that they
are most probably located in the micropores of both samples. Typ-
ical values of the apparent activation energy of cracking for zeolites
are between 146 kJ/mol for MFI and 165 kJ/mol for FAU [41] and
for amorphous silica-alumina (ASA) between 182 and 186 kJ/mol
[42]. Assuming that the active sites for propane cracking are within
the microporous SAPO domain, which might be an approximation
(vide infra), the intrinsic activation barrier in SAPO is higher than
for zeolites. The activity per Brønsted acid site in propane cracking
is calculated from the rate of cracking of propane and the number
of Brønsted acid sites determined by TPD/TGA of n-propylamine.
À3
À3
À3
H-ZSM-5
H-SAPO-5
H-SAPO-5M
9
66
98
0.2 Â 10
2.4 Â 10
7.9 Â 10
100
87
74
0
11
23
0
2
3
a
b
c
After 3.5 h of reaction.
At 55% conversion of BA.
DPM – diphenylmethane.
DBE – dibenzyl ether.
d
e
DBB – dibenzyl benzene.
in the synthesis of several hierarchical zeolite structures, such as
AEL [8], AFI [8], LTA [9], MFI [9,16], and MOR [35]. Materials syn-
thesized by alternative templating procedures did not crystallize
in a pure AFI structure or did not contain mesopores, indicating
that, during synthesis, phase segregation may have occurred. Syn-
theses of mesoporous SAPO with a high silicon content with
amphiphilic molecules are reported in the literature [6,7]. Amor-
phous or partially crystalline structures, which did not have an
AFI structure, were obtained. Compared to mesoporous ZSM-5
[
16] and ALPO-5 [8], synthesized in the presence of TPHAC as a
template, H-SAPO-5M had a much larger mesoporous volume,
although the same or even smaller amount of TPHAC was used
for its synthesis. The microporous volume is in good agreement
with that of hierarchical H-ALPO-5 reported in the literature [8].
The pore size of roughly 12 nm was around four times higher than
that observed for hierarchical ZSM-5, suggesting a different order-
ing of the mesopore-directing template. As revealed by the EM
images and nitrogen physisorption, the mesopores consisted of
both intra- and intercrystalline voids between crystalline domains.
The crystallinity and the microporosity of the hierarchical
SAPO-5M are properties typical of zeolites and zeotypes. Combined
with the high silicon content in the framework, these features are
responsible for the high acidity and activity of the mesoporous
sample. H-SAPO-5M had a high silicon content in the SAPO do-
main, equal to that of H-SAPO-5. The deconvoluted 29Si MAS
NMR spectra (Fig. S2, Supporting information) showed peaks be-
tween À98 and À110 ppm, which are also assigned to silicon with
one or two aluminum neighboring atoms. Such zeolitic domains
may also be acidic and, thus, contribute to catalytic activity [36].
It is known from the literature that, with increasing amount of sil-
icon in the synthesis gel, the content of the aluminosilicate domain
increases [36]. At 0.28 equivalents of silicon in the framework,
about 25% of it may have a zeolitic environment. The substitution
À1
For H-SAPO-5, it was 3.05 ± 0.02 mol (mmol s bar) and for H-
À1
SAPO-5M, 2.72 ± 0.02 mol (mmol s bar)
.
The role of the mesopores was revealed by space-requiring
alkylation of benzene with benzene alcohol. Although it has almost
the same number and strength of Brønsted acid sites as its micro-
porous analog, H-SAPO-5M was roughly three times more active
than H-SAPO-5. This significant difference in catalytic activity indi-
cates that the reaction occurs in the mesoporous domain, in agree-
ment with the large external surface area. The presence of very
bulky products also indicates that at least a part of the reaction
takes place at the external surface. H-ZSM-5 showed 35 times less
catalytic activity, in spite of its higher acidity and no bulky reaction
2
products. H-ZSM-5, with an external surface area of 123 m /g and a
2
BET surface area of 399 m /g, which are higher than that of H-

N. Danilina et al. / Journal of Catalysis 272 (2010) 37–43
43
SAPO-5, showed very low activity. Therefore, most of its catalyti-
cally active sites are located in the micropores, and the external
surface did not contribute significant to the reaction. The alumino-
silicate domains in SAPO-5M are the most likely candidates for cat-
alytic activity in the alkylation reaction. They are probably located
at or near the external surface of the crystal.
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