Novel aluminophosphate (AlPO) bound ZSM-5 extrudates with improved catalytic properties for methanol to propylene (MTP) reaction

Article abstract of DOI:10.1016/j.apcata.2009.11.019

Novel aluminophosphate (AlPO) binders consisting of dense phases of alpha-cristobalite and tridymite were prepared by the treatment of pseudo-boehmite (AlO(OH)) with phosphoric acid. The ZSM-5 extrudates prepared by using AlPO binders have been characterized by XRD, N₂ sorption, NH₃-TPD, ²⁷Al and ³¹P NMR techniques to elucidate the changes that occurred in the textural properties of the catalyst and their implications on the catalytic activity of the resultant ZSM-5-based extrudates towards methanol to propylene (MTP) reaction. XRD indicated the chemical interaction of P with the alumina binder to form a highly dense crystalline phase of aluminophosphate, alpha-cristobalite. N₂ adsorption, while NH₃-TPD studies revealed the changes in pore morphology of AlO(OH) binder and acidity of ZSM-5 in phosphorus containing extrudates. The drastic decrease in mesoporosity of the AlO(OH) observed after phosphorus addition indeed envisions the disappearance of inter-crystalline voids in the AlO(OH), probably due to a change in its morphology from the crystalline phase to amorphous AlPO phase. ²⁷Al and ³¹P NMR studies further confirmed the formation of AlPO in these samples. The resultant ZSM-5-based extrudates exhibited enhanced properties of hydrothermal stability, mechanical strength, propylene yield and coke resistance in methanol to propylene (MTP) reaction. The positive aspect of P addition was continuously increased with P amount; at optimum P/Al (binder) ratio of ～0.8, the catalyst exhibited about 80% yield to C₂-C₄ olefins with the major component being propylene (～50%) at near 100% methanol conversion. The catalyst also exhibited the stable performance in the studied period of 150 h.

Full text of DOI:10.1016/j.apcata.2009.11.019

Applied Catalysis A: General 374 (2010) 18–25
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Novel aluminophosphate (AlPO) bound ZSM-5 extrudates with improved catalytic
properties for methanol to propylene (MTP) reaction
Yun-Jo Lee *, Ye-Won Kim, Nagabhatla Viswanadham, Ki-Won Jun *, Jong Wook Bae
Petroleum Displacement Technology Research Center, Korea Research Institute of Chemical Technology (KRICT), P.O. Box 107, Sinseongno 19, Yuseong, Daejeon 305-600,
Republic of Korea
A R T I C L E I N F O
A B S T R A C T
Article history:
Novel aluminophosphate (AlPO) binders consisting of dense phases of alpha-cristobalite and tridymite
Received 8 June 2009
were prepared by the treatment of pseudo-boehmite (AlO(OH)) with phosphoric acid. The ZSM-5
Received in revised form 12 November 2009
Accepted 16 November 2009
Available online 20 November 2009
27
2 3
extrudates prepared by using AlPO binders have been characterized by XRD, N sorption, NH -TPD, Al
31
and P NMR techniques to elucidate the changes that occurred in the textural properties of the catalyst
and their implications on the catalytic activity of the resultant ZSM-5-based extrudates towards
methanol to propylene (MTP) reaction. XRD indicated the chemical interaction of P with the alumina
Keywords:
binder to form a highly dense crystalline phase of aluminophosphate, alpha-cristobalite. N
2
adsorption,
Aluminophosphate
ZSM-5
while NH -TPD studies revealed the changes in pore morphology of AlO(OH) binder and acidity of ZSM-5
3
in phosphorus containing extrudates. The drastic decrease in mesoporosity of the AlO(OH) observed
after phosphorus addition indeed envisions the disappearance of inter-crystalline voids in the AlO(OH),
Acidity control
Mechanical strength
MTP
2
7
probably due to a change in its morphology from the crystalline phase to amorphous AlPO phase. Al
31
and P NMR studies further confirmed the formation of AlPO in these samples. The resultant ZSM-5-
based extrudates exhibited enhanced properties of hydrothermal stability, mechanical strength,
propylene yield and coke resistance in methanol to propylene (MTP) reaction. The positive aspect of P
addition was continuously increased with P amount; at optimum P/Al (binder) ratio of ꢀ0.8, the catalyst
exhibited about 80% yield to C
2
–C
4
olefins with the major component being propylene (ꢀ50%) at near
1
1
00% methanol conversion. The catalyst also exhibited the stable performance in the studied period of
50 h.
ß 2009 Elsevier B.V. All rights reserved.
1
. Introduction
The distinct acidity demonstrated by the systematic arrange-
representation for the reaction pathway of methanol conversion
consists of several consecutive reaction steps initialized by the
dehydration of methanol to dimethyl ether (DME), followed by its
further dehydration to form light olefins, which are reactive
enough to form several hydrocarbon end-products such as
paraffins, oligomers, aromatics and even the coke precursors
responsible for the catalyst deactivation [1]. Recent studies reveal a
much clearer insight into the reaction aspects [5,6]. The key step in
effective conversion of methanol to propylene lies in controlling
the reaction at the olefin formation stage, where the acidity of the
catalyst plays a vital role.
Variation of framework Si/Al ratio by pre or post synthesis
methods is a generally adopted procedure for tuning the zeolite
acidity. However, the powder form of zeolite needs to be shaped
with the help of an inert binder material to achieve the mechanical
strength required for using it in industrial reactors for catalytic
applications [7,8]. The binder material used for shaping the zeolites
is also observed to contribute to the acidity and porosity of the
zeolites [9]. Though the binder is not active as a catalyst but can
change the acid properties of the zeolite by altering its proton-
exchange efficiencyorbyphysicaloccupationofzeolite poresduring
the pelletization process [10,11]. For example, the aluminum in an
ment of silicon and aluminum tetrahedral units in zeolites
provides a platform for a variety of hydrocarbon conversions to
produce industrially important petroleum and petrochemical
components such as olefins, iso-paraffins and aromatics. Conver-
sion of methanol to light olefins especially propylene is gaining
importance, due to its applications in the production of various
petrochemicals. This reaction also provides an alternative source to
traditional resources such as natural gas, coal and biomass, for the
production of light olefins [1–3]. The well-known Lurgi process
operates for the production of propylene from methanol, where
gasoline, LPG and fuel gas appear as byproducts that limit the
maximization of propylene yields in once-through operation. The
hydro process of UOP/Norsk operates for the selective production
of light olefins from methanol on a SAPO based catalyst [2,4]. But
achieving high yields of propylene is still challenging. The classical
*
Corresponding authors. Tel.: +82 42 860 7630; fax: +82 42 860 7388.
E-mail addresses: yjlee@krict.re.kr (Y.-J. Lee), kwjun@krict.re.kr (K.-W. Jun).
0926-860X/$ – see front matter ß 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2009.11.019

Y.-J. Lee et al. / Applied Catalysis A: General 374 (2010) 18–25
19
alumina binder can interact with zeolite to form additional acid sites
12,13]. In a similar way, the silica binders decrease the acidity of the
of 2 mm inner diameter. The extrudates are dried at 110 8C
followed by calcinations at 600 8C for 6 h. A similar procedure is
applied to obtain the binder with varying P/Al molar ratios from 0.2
to 1.2. The samples prepared with varying phosphorus content
[
protonic form of zeolites [14,15]. Clay such as Bentonite exhibits
poor binding properties in itsacidic form and hence needsto be used
in alkali form for making extrudates, followed by the treatment of
clay-zeolite agglomerates to their protonic form. This makes the
process tedious [16]. Pseudo-boehmite is generally used as binder
for the preparation of zeolite extrudates [17]. Modification of ZSM-5
acidity by loading phosphorus compounds viz. trimethylphosphite
and phosphoric acid is observed to improve the catalytic properties
of ZSM-5 [18,19]. Since, addition of binder material is obvious for
achieving the desired mechanical strength and diluting the acid
density of the ZSM-5, addition of P to the binder may have direct
influence on the properties of binder and resultant extrudates. Few
Studies are available on the incorporation of P into the binder
material in the development of catalysts. Recently, Freiding et al.
x
were designated as ZAlPO , where x represents the P/Al molar ratio
in the AlPO binder.
Some P-free alumina based ZSM-5 extrudates were also
prepared by the same method except for the acid, where nitric
acid is used in place of phosphoric acid for the treatment of
pseudo-boehmite. The P-free bound ZSM-5 sample was designated
as ZAl. Throughout the studies, the zeolite to binder ratio is kept at
a constant value of 80:20 by wt%.
2.2. Characterization of the catalysts
The XRD patterns of the synthesized samples were recorded on
[
20] used amorphous aluminophosphate hydrate as binder for
a Rigaku D/MAX IIIB X-ray diffractometer with Cu K
The surface acidity of the samples was measured by temperature
programmed desorption of ammonia (NH -TPD) using a BEL-CAT
a radiation.
preparation of ZSM-5 extrudates of improved properties. However,
the materials have not been proven to be available for improved
catalytic applications.
In the present study, the effects of P addition on the properties
of AlO(OH) binder and on the properties of ZSM-5 extrudates have
been studied, with special reference to its applications to the MTP
reaction. The present study deals with the following aspects of the
catalysts for MTP reaction:
3
PCI 3135 with TCD detector. In a typical analysis, 0.2 g of the
calcined sample was pretreated at 500 8C for 3 h to remove
adsorbed water and then saturated with ammonia at 100 8C for 1 h.
After saturation, the sample was purged with helium for 30 min to
remove the weakly adsorbed ammonia on the surface of the
catalyst. The temperature of the sample was then raised from 100
À1
to 700 8C at a heating rate of 10 8C min . The curves obtained at
1
.
Preparation of AlPO binder by the addition of various amounts of
P to the pseudo-boehmite and shaping the ZSM-5 for extrudate
preparation.
Effect of binder composition on mechanical strength, acidity,
porosity and their implications on MTP reaction.
Hydrothermal stability, coke resistance and long time perfor-
mance of catalysts.
two regions, 100–325 8C (I region, weak acid) and 325–580 8C (II
region, strong acid) were integrated and calibrated with standard
À1
sample (NH
4
–ZSM-5, 0.99 Æ 0.1 mmol g ). BET surface area mea-
2
3
.
.
surements and pore volume measurements were obtained from N
2
adsorption–desorption isotherms conducted at À196 8C using a
TriStar 3000 (Micromeritics) instrument. Prior to the adsorption–
desorption measurements, all the samples were degassed at 300 8C in
vacuum for 4 h. Thermo-gravimetric analysis (TGA) was conducted
on the spent catalysts to analyze coke amounts using a TA Instrument
(DMA, SDT 2960), where the samples are heated up to 800 8C at a
heating rate of 10 8C/min under controlled air flow (100 mL/min). The
compressive mechanical strength of the cylindrical extrudates (6 mm
diameter and 12 mm length) was measured using a Universal Testing
Machine (UTM, Instron 4482) with 10 kN load cell at a crosshead
Here we report the successful development of an AlPO binder
based ZSM-5 catalyst exhibiting tuned properties of acidity for
selective production of propylene manifested by the effective
interaction of P with the AlO(OH) as well as with the ZSM-5
framework to produce as high as 45% propylene at near 100%
conversion of methanol. The transformation of pseudo-boehmite
crystalline phase into amorphous AlPO phase by P addition and its
conversion into highly dense alpha-cristobalite with calcination
gave exceptionally high mechanical strength to the catalyst even at
lower binder (20 wt%) content in the extrudates. At optimized
reaction conditions, the catalyst exhibited stable performance in
the studied period of 150 h.
À1
speed of 0.1 mm min until failure occurred.
Solid-state magic angle spinning (MAS) NMR experiments were
performed on a Varian Unity INOVA 600 MHz (14.09 T) spectrom-
eter with a 4 mm zirconia MAS probe at a rotation rate of 14 kHz.
2
7
The Al MAS NMR spectra were obtained at a Larmor frequency of
156.4 MHz using a short RF pulse length of 1.0 s and a recycle
delay of 2 s. Chemical shifts of the Al spectra were referenced to
m
2
7
3
+
31
2
. Experimental
[Al(H
2 6
O) ] (0 ppm). The P MAS NMR spectra were obtained at
Larmor frequencies of 242.7 MHz using a short RF pulse length of
31
2.1. Catalyst preparation
4.0 ms and a recycle delay of 8 s. Chemical shifts of the P spectra
3 4
were referenced to 85% H PO .
In order to change the properties of the AlO(OH) binder, we
added P to the binder before mixing it with the zeolite for shaping.
The amount of P in the binder is varied from P/Al mole ratio of 0.0–
2.3. Catalytic activity
1
.2. The catalyst preparation is made in two steps: (1) peptization
Catalytic activity of all the samples towards methanol conver-
sion was measured in a fixed bed micro-reactor (316 stainless steel
tubing, I.D. = 1 cm and length = 30 cm) at atmospheric pressure in
the temperature range of 300–550 8C. The catalyst particles (1–
2 mm size) were loaded into the reactor and activated at 500 8C for
of pseudo-boehmite by treatment with acid and (2) mixing the
peptized binder with zeolite to obtain extrudates. Nitric acid and
phosphoric acid are used as peptizing agents for the preparation of
P-free and P-containing extrudates respectively. In a typical
procedure, the ZSM-5 extrudates having aluminophosphate of P/
Al = 1.0 mole ratio have been prepared by the following method:
1 h in a N
into the reactor with corresponding WHSV of 2.55 h . N
diluent gas was co-fed with MeOH:N ratio of 1:9 (v/v). The
2 2
flow. Methanol feed containing 20 mol% H O was fed
À1
2
as a
6
.55 g phosphoric acid is added to 3.86 g of pseudo-boehmite
2
containing 11.7 g of water with constant stirring to obtain a well-
mixed paste of aluminophosphate. This paste is then added to
effluent gas from the reactor was analyzed by an online gas
chromatograph (Donam GC 6100) employing GS-Q capillary
columns for hydrocarbons and oxygenates, respectively. Product
compositions were calculated based on a standard gas mixture.
2
4.9 g of ZSM-5 (Zeolyst CBV 8014, Si/Al = 40), followed by
thorough mixing and extruding the resultant paste with a syringe

2
0
Y.-J. Lee et al. / Applied Catalysis A: General 374 (2010) 18–25
3
. Results and discussion
3.1. Changes in textural properties of pseudo-boehmite by P addition
X-ray diffraction patterns of the pseudo-boehmite binder
before (Al) and after the P addition (AlPO) are given in Fig. 1.
The parent binder (Al) after calcination exhibits the structure of
gamma-alumina. As shown in Fig. 1, phosphorus addition to the
pseudo-boehmite followed by its calcination changed the struc-
ture to the crystalline aluminophosphate phases of alpha-
cristobalite and tridymite (AlPO 0.8). This change clearly envisions
the effective interaction of P with the aluminum of pseudo-
boehmite to form an entirely new chemical phase of aluminopho-
sphate.
The MAS NMR results also support the interaction of P with the
aluminum in the binder to form aluminophosphate (AlPO). The
27
Al NMR spectra of the P-containing and P-free extrudates are
given in Fig. 2(a). The P-free ZSM-5 extrudates (ZAl) exhibit a signal
at 53.8 ppm corresponding to the framework aluminum (Al(OSi)
4
)
of the ZSM-5. In addition, two signals at 69 and 8.7 ppm were also
observed in the sample. These can be attributed to the aluminum
present in the pseudo-boehmite in tetra-(Al(OAl)
4
) and hexa-
coordination (Al(OAl) ), respectively [21,22]. In phosphorus
6
containing (ZAlPO) samples, the intensities of these two signals
are decreased with P loading and they are almost disappeared at
higher phosphorus loadings (ZAlPO 1.2). This is accompanied by
the simultaneous formation of two new signals at 39 ppm and
À13.7 ppm in ZAlPO samples; the intensities of these new signals
are also increased with the P amount in the samples. Thus the
signals that appeared in the present study clearly suggest the
4 6
formation of Al(OP) and Al(OP) species by the interaction of P
with the pseudo-boehmite in the P-loaded samples [22,23]. In
addition the signal at 53.8 ppm is also decreased with the increase
of P content in ZAlPO samples. The framework aluminum can be
combined with phosphate to form aluminum species of (Al(O-
Si)
which overlaps with the signal of binder Al(OP)
The interaction between phosphorus and aluminum was also
3
(OP)) where the signal of 53.8 ppm can shift to around 39 ppm
4
[24].
31
reflected in P NMR (Fig. 2(b)), where the P-containing samples
(
ZAlPO) exhibited a band at À31 ppm representing the P(OAl)
4
27
31
Fig. 2. (a) Al and (b) P MAS NMR spectra of the samples.
species. At lower P loadings, the band is broad; the sharpness of the
signal is increased with the P amount. This observation along with
2
7
Al supports the interaction of P with the binder aluminum. At
Nitrogen adsorption–desorption isotherms of the samples also
indicate the changes in the textural properties of the binder by P
addition (Fig. 3(a)). The pseudo-boehmite (Al) exhibits type IV
adsorption isotherm with H1 hysteresis loop, as defined by IUPAC
25]. A loop at about P/P = 0.5–1.0 representing the presence of a
higher P loadings, the samples also exhibited the low energy signals
at 6, À6.3 and À45 ppm representing the formation of minute
amounts of pyrophosphate and polyphosphate species [22,23].
0
[
considerable amount of mesopores created by inter-crystalline
voids of the alumina crystallites is observed in this sample. The
shape of hysteresis loop indicates the presence of ink-bottle type
pores. But, the pseudo-boehmite that includes some phosphorus
(
AlPO 0.8) exhibits very negligible amounts of mesopores. That
means the addition of P to the alumina binder has completely
removed the mesopore structure of the material. Since the inter-
crystalline voids are the origin of mesoporosity in the pseudo-
boehmite binder, the decrease in mesoporosity by P addition
suggests a change in morphology of the alumina crystals in the
binder. This can be explained by the effective interaction of P with
the pseudo-boehmite to modify its structure and inter-crystalline
voids. The addition of P to the pseudo-boehmite facilitates the
chemical interaction between P and aluminum, and the interaction
causes the change in morphology of the alumina crystallites to form
amorphous aluminophosphate gel with no specific crystalline
structure and hence no inter-crystalline voids. The resultant
amorphous material yields a dense phase of AlPO up on calcination.
As shown in Fig. 1, the X-ray diffraction patterns of AlPO binder
Fig. 1. X-ray diffraction patterns of binder and bound zeolite samples. T: tridymite;
C: alpha-cristobalite; A: gamma-alumina.

Y.-J. Lee et al. / Applied Catalysis A: General 374 (2010) 18–25
21
indeed exhibit the peaks correspond to dense phase of alpha-
cristobalite and tridymite. This observation supports the phase
transformation of less-dense pseudo-boehmite into more-dense
AlPO binder phase upon P addition that is responsible for the
considerable decrease in mesoporosity of the binder. A significant
2
À1
decreaseinsurface area(from236 to1.9 m g )ofthealuminaafter
the P addition also supports the formation of high-density AlPO.
The phenomenon of P-induced transformation of pseudo-
boehmite into amorphous phase of aluminophosphate (and its
conversion to high-density AlPO phase upon calcination) is
expected to improve the mixing properties of the binder with
zeolite. Moreover, the decrease of large pores in the binder is also
known to improve the mechanical strength of the extrudates; such
improvement is highly desirable for commercial applications
[26,27]. Hence the extrudates are thoroughly studied for their
physico-chemical properties and catalytic activity in MTP reaction.
3.2. Properties of AlPO bound ZSM-5 extrudates
In order to understand the role of phosphorus, we prepared
various ZSM-5-based extrudates by varying the P amount in the
pseudo-boehmite binder. The molar composition of binder is
varied from P/Al = 0 (P-free pseudo-boehmite) to P/Al = 0.2, 0.4,
0.6, 0.8, 1.0 and 1.2 (P-containing pseudo-boehmite samples).
During preparation of the binder-mixed-ZSM-5 extrudates, the
percent of binder is always kept constant at 20 wt%. The resultant
extrudates are characterized to understand the effect of P addition
to the binder on the overall properties of the extrudates.
X-ray diffraction patterns of the samples given in Fig. 1 indicate
that all the samples possess ZSM-5 structure. No distinguishable
change is observed in the intensities of the samples with the
addition of the binder or with the variation in composition of the
binder. However, the samples show different adsorption isotherms
(Fig. 3(a)). The extrudates prepared by mixing 20 wt% of pseudo-
Fig. 3. (a) Nitrogen adsorption–desorption isotherm and (b) pore size distribution of
boehmite in the ZSM-5 (ZAl) exhibits the isotherm similar to that
of the pure binder (Al), while the isotherms of P-containing
extrudates (ZAlPO) show a reduction in the capillary condensation
in mesopores. With increasing P content in the binder, the
the samples measured by BJH method.
Fig. 4. SEM images of (a) ZSM-5, (b) ZAl and (c) ZAlPO 0.8 samples.

2
2
Y.-J. Lee et al. / Applied Catalysis A: General 374 (2010) 18–25
Table 1
Physico-chemical properties and coke analysis of extruded ZSM-5 catalysts.
À1
Sample
Composition
Nitrogen adsorption
NH
3
-TPD acidity (mmol g
)
TGA results
a
of binder
BET surface
Pore volume
Micropore
Weak
Strong
Total
Reaction
time (h)
Coke (wt%)
2
À1
3
À1
3 À1
area (m g
)
(cm g
)
volume (cm g )
(100–325 8C)
(325–580 8C
ZAl
Al0.293
Al0.229
Al0.188
Al0.160
Al0.139
Al0.123
Al0.110
P
P
P
P
P
P
P
0
O
x
392.4
368.9
349.4
340.1
328.9
325.0
314.5
236.1
1.9
0.311
0.263
0.236
0.216
0.198
0.195
0.193
0.457
0.017
0.092
0.095
0.091
0.091
0.086
0.085
0.082
0
0.291
0.309
0.318
0.311
0.286
0.275
0.269
0.232
0.219
0.215
0.162
0.112
0.069
0.025
0.523
0.528
0.533
0.473
0.398
0.344
0.294
80
–
27.3
–
ZAlPO 0.2
ZAlPO 0.4
ZAlPO 0.6
ZAlPO 0.8
ZAlPO 1.0
ZAlPO 1.2
Al
0.046
0.075
0.096
0.111
0.123
0.132
O
x
O
x
O
x
O
x
O
x
O
x
80
18.1
20.0
15.6
9.9
150
150
150
100
5.2
AlOOH only
AlPO only
AlPO 0.8
0
a
y
All the bound catalysts contain a ZSM-5 of Al0.022Si1.0O composition.
extrudates exhibit decreases in mesoporosity. Above the value of
P/Al = 0.6, mesopores in the sample have almost disappeared and
the sample does not exhibit any loop representing the mesopor-
osity. The aspect of mesopore decrease is further appreciated from
the pore diameter measurements (BJH method) of samples shown
in Fig. 3(b). The trends in pore diameter of the P-loaded samples
clearly reveal the systematic decrease in pore volume specifically
enhancement in the mechanical strength of extrudates. The
mechanical strength of the extrudates is indeed increased from
3.1 MPa of ZAl to 8.2 MPa of ZAlPO 0.8, by the addition of P to the
alumina binder. The intrusion of P-containing amorphous binder
was also observed to alter the acidic properties of ZSM-5. At P/Al of
1.2 (ZAlPO 1.2), the sample exhibited 20% decrease in surface area
and 40% decrease in pore volume when compared to ZAl sample.
The ammonia TPD plots of the calcined samples (Fig. 5(a))
exhibit a two-peak pattern: a low temperature peak at ꢀ200 8C and
a high temperature peak at ꢀ450 8C. The former originates from
the weakly acidic silanol groups that cover the external surface of
˚
at the pore diameter range of 50–300 A related to the mesopores.
Overall, the alumina binder (Al) as well as alumina bound ZSM-5
extrudates (ZAl) exhibit prominent mesoporosity, while the
mesoporosity decreases with phosphorus addition in ZAlPO
samples. The phenomenon of mesopore reduction in extrudates
can be attributed to the role of P in converting the pseudo-
boehmite crystals into amorphous alumina phase having no inter-
crystalline voids responsible for mesoporosity. This is also
reflected in the SEM images of the samples. The SEM images of
the pure ZSM-5 zeolite and two binder-mixed-ZSM-5 extrudates
with P/Al = 0 (ZAl) and 0.8 (ZAlPO 0.8) are shown in Fig. 4. The ZAl
sample exhibits the presence of small granular phases of alumina
on the zeolite crystals. But the ZAlPO 0.8 shows a clean morphology
of zeolite. This may be due to the uniform distribution of fine
amorphous particles of AlPO on the ZSM-5 crystals in the latter
sample. This means that the interaction of P is responsible for the
change in morphology of the alumina binder.
Textural properties of the samples prepared by P-containing
alumina (AlPO binders) are given in Table 1. The phosphorus free
sample (ZAl) exhibits higher surface area and pore volume. With
the addition of phosphorus to the binder, the resultant ZAlPO
extrudates exhibit a decrease in surface area from 392 to
2
À1
3
3
0
14 m g and a decrease in total pore volume from 0.311 to
À1
.193 cm g . This can be attributed to the formation of high-
density AlPO by the interaction of phosphorus with the low-
density alumina binder in the samples. Hence, the decreases in
adsorption properties and surface area of the ZAlPO samples are
due to the change in properties of the binder component, but are
not due to the change in zeolite component. This aspect is further
appreciated from the properties of the zeolite-free AlPO (AlPO 0.8)
sample. The sample exhibits significant decrease in surface area
and pore volume (Table 1). The pseudo-boehmite sample (Al)
2
À1
exhibits the surface area of 236 m g which is decreased to as
2
À1
low as 1.9 m g by P addition (AlPO 0.8). The micropore volume
representing zeolitic pores is also slightly decreased from 0.092 to
3
À1
0
.082 cm g . The major decreases in total pore volume and
mesoporosity of the extrudates with marginal decreases in
micropore volume and surface area clearly indicate that the added
P has a major influence on the binder properties but not on the
zeolite properties. However, the slight decrease in micropore
volume observed in ZAlPO samples may be due to the increased
inclusion of amorphous binder alumina inside the porous structure
of zeolite with the increase of P amount in the binder. Such a close
interaction between binder and zeolite will provide significant
Fig. 5. NH -TPD of extrudates: (a) before hydrothermal treatment and (b) after
3
hydrothermal treatment at 700 8C for 5 h under 100% steam.

Y.-J. Lee et al. / Applied Catalysis A: General 374 (2010) 18–25
23
Table 2
Product distribution at 10 h reaction time in methanol conversion over extruded ZSM-5 catalysts.
Sample
ZAl
ZAlPO 0.4
100
ZAlPO 0.6
100
ZAlPO 0.8
100
ZAlPO 1.0
100
ZAlPO 1.2
98.1
MeOH/DME conversion
100
Hydrocarbon distribution (yield, C-mol%)
(I) C
1
4.6
1.3
0.7
0.4
0.3
0.35
=
=
(
II) C
2
–C
4
2À
2
(C –C
4
paraffins)
72.6(11.3)
20.8(0.3)
37.0(3.2)
14.8(7.6)
11.4
77.3(5.7)
16.9(0.16)
41.5(2.5)
18.9(3.0)
16.5
82.9(2.6)
14.7(0.09)
46.9(1.25)
21.7(1.3)
37.7
84.9(2.05)
12.6(0.06)
48.6(0.8)
23.6(1.1)
55.0
83.3(1.2)
8.1(0.03)
51.1(0.3)
24.0(0.7)
156.4
74.1(0.47)
4.0(0.02)
43.9(0.1)
26.0(0.44)
439.0
=
=
=
=
=
C
C
C
C
C
2
3
4
3
3
(C
(C
(C
)
3À
4À
3À
)
)
/C
=
/C
2
1.7
2.5
3.2
3.8
6.2
10.8
(III) C5+
11.3
15.7
13.8
12.5
15.1
23.1
the crystals and from lattice defects, while the latter peak arises
from the Bronsted acid sites related with the framework aluminum
of the ZSM-5. The strong and weak acidity of the samples are
quantified based on the millimoles of ammonia desorbed at higher
and lower temperatures, respectively (Table 1). All the samples
exhibit the two-peak pattern but the intensity of high temperature
peak representing strong acidity decreases with the increase of P in
the binder. This observation clearly emphasizes the effective
interaction of P with the binder and zeolite aluminum.
These observations suggest the positive role of P in the binder
=
for improved selectivity of C –C olefins, especially C . Continuous
2
4
3
=
increase of the C3 /C ratio reveals the significant increase in the
3
olefinicity of the C3 hydrocarbon product with P loading. The
=
=
difference observed in the yields of C3 and C2 clearly support that
the formation and consumption of individual olefins are governed
at different rates of the reactions. Earlier studies indicated that
higher Si/Al of zeolite is better for increasing the propylene yields
[28,29]. As the acidity decreases with the increase of Si/Al ratio, the
moderate acidity in high Si/Al samples is responsible for the
improved formation of propylene. The improved propylene yields
obtained in the present study can be ascribed to the decrease in
acidity of ZSM-5 caused by its mixing with AlPO binder. The TPD
data indeed supports the decrease in strong acidity of AlPO bound
ZSM-5 extrudates.
+
The P in the binder seems to interact with the Al–OH –Si
groups of the zeolite and reduces the strong acidity; the
phenomenon progresses with the P loading. This point can be
clearly assessed from the data given in Table 1, where the strong
acidity of the extrudates slightly decreased up to the P loading of
P/Al = 0.4, whereas a drastic decrease in acidity is observed at
higher P loadings (P/Al = 0.6–1.2). The strong acidity is decreased
but the weak acidity is almost constant at all the levels of P
loading. This observation suggests the effective interaction of the
P in the binder with the framework aluminum (Bronsted acid
sites) of the ZSM-5. Thus the AlPO based ZSM-5 sample with low
acidity is expected to exhibit improved catalytic properties in
terms of propylene yield, hydrothermal stability and coke
resistance in MTP reaction.
The positive aspect of P for improving propylene yield is
continued up to the P/Al of 1.0 (Table 2). However, above this value,
P addition caused decreases in overall conversion and product
yields of the catalyst. In order to understand the optimum amount
of P needed for catalyst performance in methanol conversion, we
studied all the P-containing catalysts for their long time
performance. Fig. 6 shows that the conversion of methanol is
comparable on all the catalysts at the initial time of reaction. But
the performance is varied depending on the amount of P loaded in
the binder alumina. The ZAl and ZAlPO 0.4 exhibited decrease in
conversion after 25 and 50 h of reaction time, respectively. While
the performance is improved with the increase of phosphorus
loading up to ZAlPO 0.8, the catalyst performance is again
decreased at higher phosphorus loadings i.e., ZAlPO 1.0 and ZAlPO
3.3. Catalyst performance in methanol to propylene (MTP) reaction
The well-known mechanism for methanol conversion consists
of the consecutive reaction steps of methanol dehydration to form
DME; the resultant equilibrium mixture of methanol and DME
undergoes further dehydration to produce light olefins, oligomers,
paraffins and aromatics. The P modified binder in the catalyst is
expected to control the strong acidity responsible for the formation
of oligomers through the control of reaction at olefin formation
stage. Performance of various catalysts in MTP reaction was
studied and the product obtained after 10 h reaction time over
these catalysts is given in Table 2. The product obtained is
=
=
classified into C
Emphasis is given to maximize the formation of C
special reference to propylene. All the catalysts exhibited near
00% conversion of methanol, but the product yields are changed.
1
, light olefins (C
2
–C
4
) and C5+ hydrocarbons.
2
–C olefins with
4
1
With increasing P amount in the binder, the following changes are
observed in the product yields:
=
1
2
.
.
C
C
1
and C
2
continuously decreased.
=
3
increased up to P/Al = 1.0 and then decreased at higher P
loadings.
=
3
4
.
.
4
C continuously increased.
=
=
The C
2 4
–C yields increased up to P/Al of 0.8 and then decreased
above the value of 1.2.
=
=
5.
Both C
3
/C
3
and C
3
/C
2
ratios have increased with the P loading.
Fig. 6. Time-on-stream performances of catalysts in MTP reaction.

2
4
Y.-J. Lee et al. / Applied Catalysis A: General 374 (2010) 18–25
Table 3
Product distribution at 80 h reaction time in methanol conversion over extruded ZSM-5 catalysts.
Sample
ZAl
ZAlPO 0.4
69.7
ZAlPO 0.6
93.6
ZAlPO 0.8
100
ZAlPO 1.0
93.1
ZAlPO 1.2
78.5
MeOH/DME conversion
44.4
Hydrocarbon distribution (Yield, C-mol.%)
(I) C
1
16.4
2.8
1.8
1.4
1.0
0.6
=
=
(
II) C
2
–C
4
(C
2
–C
4
, saturated)
26.4(0.45)
1.2(0.2)
1.3(0.05)
23.8(0.2)
24.5
48.9(2.97)
5.4(0.17)
18.0(0.6)
25.4(2.2)
29.8
66.8(5.7)
10.4(0.1)
37.9(0.7)
18.4(4.9)
48.6
81.2(0.97)
9.4(0.07)
50.2(0.4)
21.5(0.5)
123.3
68.5(0.94)
4.3(0.04)
37.8(0.1)
26.3(0.8)
275.5
54.4(0.39)
1.7(0.02)
27.5(0.05)
25.1(0.32)
550
=
=
=
=
=
2À
3À
4À
C
2
C
3
C
4
C
3
C
3
(C
(C
(C
)
)
)
3À
/C
=
2
/C
1.0
3.3
3.6
5.3
8.6
15.6
(III) C5+
0.9
15.0
19.1
16.2
22.5
23.0
1
.2. The C
2
–C
4
olefin yields shown in Fig. 6 also followed a similar
acidity after the hydrothermal treatment with the exception to
the ZAlPO 0.8 sample. However, the low temperature peak
representing weak acid sites is in some extent protected in P-
loaded samples and the amount of weak acidity remaining in the
samples is increased with P loading i.e. from ZAlPO 0.4 to 1.2. The
amount of weak acidity preserved after the treatment is also
increased to some extent with the P loading. The ZAlPO 0.8
exhibited highest amount of stable acid sites after hydrothermal
treatment. This may be due to the increased resistance of
phosphorus-interacted aluminum sites in ZSM-5 against the
dealumination. The X-ray diffraction patterns indicated no loss in
crystallinity after the hydrothermal treatment.
The amount of coke formed on the catalysts after several hours
of reaction was measured by TGA method. The P-free pseudo-
boehmite containing catalyst (ZAl) exhibited a drastic decline in
activity within 50 h of reaction time, whereas ZAlPO catalysts
showed the reaction stability for 150 h. The amount of coke on the
ZAl catalyst is also high even after 50 h reaction time. The data
given in Table 1 indicates a decrease in formation of coke on the
catalysts with increasing P amount. At the P loading of P/Al = 1.2
(ZAlPO 1.2), the catalyst exhibited the lowest amount of coke
(ꢀ5 wt%). This is in accordance with the acidity values of the
samples, where, the presence of P in the binder caused a decrease
in strong acidity; hence, the amount of coke is also decreased on
these catalysts.
trend with conversions. Among the various P-loaded catalysts,
ZAlPO 0.8 exhibited the superior conversion and light olefin yields.
The detailed product pattern obtained over this catalyst in
methanol conversion is shown in Fig. 7. There is a slight increase
in C5+ hydrocarbon yield, while a simultaneous decrease in
ethylene is observed with reaction time on this catalyst. However,
propylene yield is constant throughout the reaction time of 100 h.
The results emphasize the exceptional improvement in reaction
performance of the P-loaded catalyst. The improved performance
of P-loaded catalyst may be due to the improvement in
hydrothermal stability of the ZSM-5 facilitated by the interaction
of P. Since, the presence of P in the binder decreased the acidity of
the catalysts, the lower coke formation tendency of the resultant
catalyst is also responsible for its long time stability in MTP
reaction (Table 3).
3.4. Hydrothermal stability and coke resistance
The hydrothermal stability of the samples is studied by
characterizing the structural and acidic properties of the catalysts
after the treatment with water at high temperatures (700 8C) for
5
acidity after the hydrothermal treatment (when compared to the
untreated samples shown in Fig. 5(a)). Especially, the high
temperature peak representing strong acidity is significantly
decreased after the hydrothermal treatment of P-free (ZAl)
sample. But the P-containing (ZAlPO) samples mostly lost strong
h. As shown in Fig. 5(b), all the samples exhibited decreases in
4. Conclusions
Novel AlPO binders with amorphous phases are prepared by the
treatment of pseudo-boehmite with phosphoric acid. The materi-
als are identified as extremely suitable binders for the extrusion of
ZSM-5 catalysts applied for methanol to propylene reaction. The
advantage of the new amorphous binder lies in its effective
interaction with the ZSM-5 to give extra-ordinary mechanical
strength. Upon calcinations, the AlPO binder exhibits dense phases
of alpha-cristobalite as major along with some tridymite phase.
The undesired inherent properties of pseudo-boehmite, such as its
self-catalytic activity and the possible interaction of aluminum in
the binder with zeolite to form additional acid sites are nullified by
the presence of phosphorus. In contrast to the conventional
pseudo-boehmite, the AlPO binder exhibits no alumination and
acidity increase to the zeolite. Rather, a decrease in strong acidity is
observed in this catalyst due to the interaction of P with the zeolite.
The acidity of the samples can be tailored through the optimization
of the P loading in the binder to minimize side reactions of olefins
to improve the propylene yield. At optimized P amount and
reaction conditions, the catalyst Exhibits 50% yield to propylene at
near 100% conversion of methanol.
Apart from the product yield, the presence of P in the binder
also causes improved hydrothermal stability of the ZSM-5 catalyst
Fig. 7. Detailed product trends in MTP reaction over ZAlPO 0.8 catalyst.

Y.-J. Lee et al. / Applied Catalysis A: General 374 (2010) 18–25
25
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[
Acknowledgements
2
The authors would like to acknowledge funding from the Korea
Ministry of Knowledge Economy (MKE) through ‘‘Project of next-
generation novel technology development’’ of ITEP. Dr. N.
Viswanadham is thankful to Korea Federation of Science &
Technology (KOSEF) for awarding a Brain-Pool fellowship.
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