Synthesis, characterization of FAU/EMT intergrowths and its catalytic performance in n-pentane hydroisomerization reaction

Article abstract of DOI:10.1016/j.molcata.2007.09.011

Zeolites FAU, EMT and their intergrowths were synthesized using 15-crown-5, 18-crown-6 and their equimolar mixture, respectively. The synthesized products were characterized by XRD, SEM-EDX, N₂ adsorption and TPD-NH₃. The solids obtained were all highly crystalline. The FAU samples were formed by octahedral submicrometric crystallites, EMT samples had hexagonal plate morphology of 2-5 μm. The intergrowth crystals were micrometric hexagonal plates through whose hexagonal faces, the octahedral FAU crystallites intergrow. The intergrowth proportion was evaluated by means of DIFFaX, resulting in different intergrowth proportions, depending on the molar ratio of template/Al₂O₃ and on the relative template proportion used in the synthesis gel. For a template/Al₂O₃ ratio of 0.70, a 50%FAU/50%EMT intergrowth proportion was obtained, with cluster-type stacking and for template/Al₂O₃ of 0.30 the intergrowth proportion was 12%FAU/88%EMT with two stacking arrangements: clusters and random. Platinum was incorporated to these zeolites and their intergrowths by solid ion exchange; the metal dispersion was evaluated by TEM. For most catalysts the platinum particles were between 4 and 10 nm. All the catalysts were active for n-pentane conversion. The activity was found to be a function of acidity. The intergrowth catalysts were the most active materials. The iso-pentane selectivity, at 350 °C and carrier gas composition of H₂:N₂ = 2:1, was 82% independent of time on stream, acidity, Pt/Al ratio and Pt dispersion. The selectivity increased with decreasing temperature and as carrier gas composition became richer in H₂. The catalytic remaining activity (at 10 min) decreased in the following order: FAU > EMT > intergrowth.

Full text of DOI:10.1016/j.molcata.2007.09.011

Available online at www.sciencedirect.com
Journal of Molecular Catalysis A: Chemical 281 (2008) 164–172
Synthesis, characterization of FAU/EMT intergrowths and its
catalytic performance in n-pentane hydroisomerization reaction
a
b
a
a
a
´
´
`
´
L.N. Belandrıa , C.S. Gonzalez , F. Aguirre , E. Sosa , A. Uzcategui ,
b
c
a
a,∗
´
´
G. Gonzalez , J. Brito , S.L. Gonzalez-Cortes , F.E. Imbert
a Laboratorio de Cine´tica y Cata´lisis, Facultad de Ciencias, Universidad de Los Andes (ULA), La Hechicera, Me´rida, Venezuela
b Laboratorio de Ciencias e Ingenier´ıa de Materiales, Dpto. Ingenier´ıa, Instituto Venezolano de Investigaciones
Cient´ıficas (IVIC), Carretera Panamericana Km 11, Altos de Pipe, Los Teques, Venezuela
c Laboratorio de cata´lisis y fisicoqu´ımica de superficies, Centro de Qu´ımica, Instituto Venezolano de Investigaciones
Cient´ıficas (IVIC), Carretera Panamericana Km 11, Altos de Pipe, Los Teques, Venezuela
Available online 14 September 2007
Abstract
Zeolites FAU, EMT and their intergrowths were synthesized using 15-crown-5, 18-crown-6 and their equimolar mixture, respectively. The
synthesized products were characterized by XRD, SEM-EDX, N2 adsorption and TPD-NH3. The solids obtained were all highly crystalline. The
FAU samples were formed by octahedral submicrometric crystallites, EMT samples had hexagonal plate morphology of 2–5 ␮m. The intergrowth
crystals were micrometric hexagonal plates through whose hexagonal faces, the octahedral FAU crystallites intergrow. The intergrowth proportion
was evaluated by means of DIFFaX, resulting in different intergrowth proportions, depending on the molar ratio of template/Al2O3 and on the
relative template proportion used in the synthesis gel. For a template/Al2O3 ratio of 0.70, a 50%FAU/50%EMT intergrowth proportion was obtained,
with cluster-type stacking and for template/Al2O3 of 0.30 the intergrowth proportion was 12%FAU/88%EMT with two stacking arrangements:
clusters and random. Platinum was incorporated to these zeolites and their intergrowths by solid ion exchange; the metal dispersion was evaluated
by TEM. For most catalysts the platinum particles were between 4 and 10 nm. All the catalysts were active for n-pentane conversion. The activity
was found to be a function of acidity. The intergrowth catalysts were the most active materials. The iso-pentane selectivity, at 350 ◦C and carrier
gas composition of H2:N2 = 2:1, was 82% independent of time on stream, acidity, Pt/Al ratio and Pt dispersion. The selectivity increased with
decreasing temperature and as carrier gas composition became richer in H2. The catalytic remaining activity (at 10 min) decreased in the following
order: FAU > EMT > intergrowth.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Intergrowth; FAU-EMT; Hydroisomerization; n-Pentane; Platinum
1. Introduction
structure with a space group P63/mmc, the stacking of layers
results in a ABAB sequence, with a reflection relation between
neighbouring layers. Its arrangement of sodalites cages creates
“hypocage” [3] (0.5 nm3) with three 12-member ring pore open-
ings and a larger cage – ‘hypercage’ [4] (1.3 nm3) – with five
12-member ring pore openings. The channel system is tridimen-
sional as in FAU structure, but the nature of the channel system
and of the larger cages in the EMT is significantly different.
Both structures (i.e. FAU and EMT) have tridimensional sys-
tems of large pores and cages. These structures can relate one
to another, by changing one element of symmetry by the other
between neighbouring sheets. Solids with different stackings of
cubic and hexagonal sheets like ZSM-3 [5], ZSM-20 [6–8] and
CSZ-1 [9,10] have been reported. The distribution of the two
symmetry elements between the layers may be influenced by
The zeolite FAU is one of the most important zeolites for cat-
alytic applications, due to its pore size and acid site accessibility.
This zeolite has a cubic unit cell, a supercage (∼1.2 nm3) with
four 12-member ring pore openings (0.74 nm), its space group is
Fd3m, and can be described by the stacking of sodalite layers in
a ABCABC sequence [1]. These layers are related by center of
inversion in the double six-member rings. The EMT zeolite was
synthesized for the first time in 1990 [2]. This has a hexagonal
∗
Corresponding author. Tel.: +58 274 2401371; fax: +58 274 2401360.
E-mail addresses: gemagonz@ivic.ve (G. Gonza´lez), joabrito@ivic.ve
(J. Brito), imbert@ula.ve (F.E. Imbert).
1381-1169/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2007.09.011

L.N. Belandr´ıa et al. / Journal of Molecular Catalysis A: Chemical 281 (2008) 164–172
165
the template molecules and their proportion in the synthesis gel.
The geometry of the cage system is strongly dependent on the
actual stacking sequence. In this case the stacking faults do not
block the channels, but the local environments are slightly differ-
ent, so some of the properties of the intergrowth can differ from
those of the pure end members. For industrial applications the
preparation of metal catalysts should be as simple and econom-
ical as possible. Among the methods to introduce metals into
zeolites, impregnation and ion exchange are the most used. Ion
exchange results in high initial dispersion, while impregnation,
that involves mixing the zeolite with a solution of metal precur-
sor followed by evaporation, drying and calcination steps, leads
to rather weak metal support interaction [11]; thus, large parti-
cles are usually obtained. The conventional liquid ion exchange
is limited by precursors solubility, steric hindrance, due to bulky
hydration shell of the exchangeable cations and thermodynamic
equilibrium [12,13]. To overcome this drawback, some times
it is necessary to repeat the exchange procedure several times
and to undertake intermediate calcination in order to facilitate
cation migration [13,14]. Another disadvantage for industrial
applications is the handling of large volume of solution, dur-
ing the preparation process. The solid-state ion exchange is a
highly effective method to introduce cations into zeolite. In this
process, the metal cations are introduced into the zeolite by calci-
nation (usually in vacuum or under inert gas flow) of mechanical
mixture of the zeolite (usually in protonic form) and the metal
precursor (usually halide or oxide) [14]. The major advantage of
this method is to incorporate the metal in one step with high dis-
persion. Hence, in the present work, the solid-state ion exchange,
followed by H2 reduction was used to prepare bifunctional cat-
alysts. The FAU/EMT intergrowth synthesis has been reported
in the literature [15–18]. However, we have found a very few
reports on FAU/EMT intergrowth catalytic activity [19–22]. The
objective of the present work is to study the catalytic behavior
of FAU/EMT intergrowth and to compare with pure FAU and
EMT, on the n-pentane hydroisomerization reaction, which has
particular interest for hydrocarbon refining industry.
attached to the walls, to increase homogenization of the gel. Fol-
lowing the ageing period, the reactor is heated at 110 ◦C for 15
days. The resultant solid was filtered, washed and dried at 80 ◦C
for 16 h. In order to eliminate the template, the samples were
calcined at 600 ◦C for 16 h.
The catalysts were prepared from FAU, EMT and their inter-
growth by ion exchange with 2 M NH4NO3 solution, at 80 ◦C
for 24 h, filtered, washed, dried at 120 ◦C for 4 h and calcined at
450 ◦C for 4 h, in air; this procedure was repeated several times.
However, for EMT (0.33) and 50T1/50T2 (0.33) samples with
two different levels of exchange were prepared. One with 100%
exchange (no alkaline ions left on the sample), and another was
partially exchanged into acid form, that is, part of its exchange
positions are still occupied by alkaline ions, decreasing signifi-
cantlyitsacidity. InTable1asummaryofthepreparedsamplesis
given with the appropriate synthesis conditions. Once the zeolite
acid form was obtained, platinum (∼1 wt.%) was incorporated
by solid-state ion exchange with Pt(NH3)4Cl2·H2O at 500 ◦C for
4 h, under nitrogen flow. This method has several advantages:
avoids handling and disposal of large amounts of solution, cuts
down the cost of wasted chemicals as well as the associated
environmental impact.
The X-ray diffractograms were recorded in a diffractometer
´
˚
PHILLIPS PW 1050/25 using a Cu K␣ (λ = 1.5406 A) radia-
tion, in the 2θ interval from 5◦ to 70◦ and a path of 0.02◦. The
surface areas and pore volume were measured in a Micromerit-
ics analyser, model ASAP 2010 at liquid nitrogen temperature
(77 K). The EDX chemical semiquantitative analysis were made
in an EDAX system, model 8400. The scanning was done on a
Hitachi Field emission FE, model S-4500 and el transmission
electron microscopy analysis on a Philips, model CM10. The
acidity was evaluated by NH3-programmed thermodesorption
and metal dispersion by the CO chemisorption measurements,
both were carried out on a Micromeritics TPD/TPR 2900.
2.2. Catalytic test
The hydroisomerization reaction was investigated in the tem-
perature range of 250–350 ◦C, the effect of the carrier gas
composition was investigated for the H2:N2 = 30:0, 20:10, 10:20
at atmospheric pressure. A 30 mL/min flow of H2:N2 mixture
saturated with n-pentane at −3 ◦C, was fed to a pyrex down flow
continuous fixed bed reactor, in line with a gas chromatograph
(Perkin-Elmer, Auto System), equipped with an alumina/KCl
2. Experimental
2.1. Catalyst preparation and characterization
The zeolites FAU and EMT were synthesized using as tem-
plates (T) 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane)
(T1) and 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane)
(T2), respectively [15–18]. The intergrowths were obtained
by adding equimolar amounts of these templates to the
synthesis gel. The molar composition of the gel used
was 10 SiO2:Al2O3:2.1 Na2O:T1 15-Crown-5:T2 18-Crown-
6:140 H2O, where the template/alumina (T/Al2O3) molar ratio
employed were 0.70 or 0.33.
A sodium aluminate is added to sodium hydroxide under con-
tinuous agitation until complete dissolution was attained, then
the amount required of the specific template is added, under
agitation for 20 min, followed by the addition of colloidal sil-
ica. This solution is aged under continuous agitation for 24 h at
room temperature, using a special reactor with deflector blades
Table 1
Samples prepared
Sample
T/Al2O3
pH
exchange
HFAU (without template)
HFAU (pH = 9)
0
0.7
9
9
Fully
Fully
HFAU (pH = 11)
EMT (0.33)
HEMT (0.33)
0.7
11
9
9
Fully
Partially
Fully
0.33
0.33
0.7
HEMT (0.7)
9
Fully
FAU/EMT (0.33)
HFAU/HEMT (0.33)
HFAU/HEMT (0.7)
0.33
0.33
0.7
9
9
9
Partially
Fully
Fully

166
L.N. Belandr´ıa et al. / Journal of Molecular Catalysis A: Chemical 281 (2008) 164–172
Table 2
PLOT capillary column, a FID and an integrator PE Nelson
model 1022. Before each reaction, the catalyst was reduced
in situ, in a hydrogen flow of 30 mL/min at 450 ◦C for 4 h
[20–22].
Langmuir (Alang, m2/g), micropore (Am, m2/g) and external (Aext, m2/g)
specific surface areas, and micropore volume (Vm, cm3/g)
t-plot
Catalysts
ALang (m2/g) Am (m2/g) Aext (m2/g) Vm (cm3/g)
3. Results and discussion
FAU (without
template)
FAU (pH = 9)
EMT (0.33)
EMT (0.7)
FAU/EMT (0.33)
FAU/EMT (0.7)
998
986
12.4
0.34
3.1. Catalyst characterization
1061
998
1073
1044
1067
1060
985
1067
1035
1060
1.8
12.8
5.5
8.8
6.3
0.38
0.34
0.31
0.36
0.37
The zeolites FAU, EMT and their intergrowth highly crys-
talline were obtained, as shown by the powder X-ray diffraction,
scanning electron microscopy and specific surface areas. These
solids show nitrogen adsorption isotherms type I (Langmuir)
typical of micropore solids (see Fig. 1). In Table 2 are given the
specific surface area values for as-synthesized samples. As can
be seen in Table 2, these zeolites have high Langmuir surface
areas. The external surface areas are, as expected, very small.
The intergrowth does not affect the total pore volume or the
surface area.
Well-defined crystals for FAU and EMT were observed by
scanningelectronmicroscopy(SEM)(see Fig. 2). TheFAUcrys-
Fig. 1. Adsorption isotherms of N2 at 77 K, for (a) FAU (without template), (b) FAU (pH = 9), (c) EMT (0.33), (d) EMT (0.7), (e) FAU/EMT (0.33) and (f) FAU/EMT
(0.7).

L.N. Belandr´ıa et al. / Journal of Molecular Catalysis A: Chemical 281 (2008) 164–172
167
Fig. 2. SEM micrographs of (a) FAU, (b) EMT (0.33), (c) FAU/EMT (0.7) and (d) FAU/EMT (0.33).
tals are octahedral (<1 ␮m), while EMT crystals are hexagonal
plates (2–5 ␮m). The intergrowth crystals are shown in Fig. 2c
and d, where one can clearly see the FAU octahedral crystals
growing out from the hexagonal EMT plates. This is strong evi-
dence that supports the result obtained from the DIFFaX analysis
for the intergrowth FAU/EMT ‘clusters’ distribution.
Fig. 3a shows the simulated X-ray diffraction patterns of the
pure systems overlapped one over the other to show the positions
when both phases are present. The X-ray powder pattern does
not completely differentiate between the contributions from a
mixture of phases or from an intergrowth; in general the pres-
ence of defects affects the width and shape of the peaks profile.
In order to estimate the proportion and type of intergrowth the
DIFFaX programme [23] was used. This software generates the
X-ray powder diffraction patterns considering coherent planar
defects such as twins and stacking faults. DIFFaX computes
the average interference wave function scattered for each layer
from a faulted crystal with a random stacking sequence of lay-
ers. In real crystals not only stacking defects are present but also
dislocation, crystal size, domains, substitutional atoms, vacan-
cies, etc. also contribute to the diffraction pattern. Although, the
matching between the experimental X-ray powder pattern and
the simulated one are not completely accurate, a fair approxi-
mation is obtained. Fig. 3b and c shows the experimental X-ray
diffraction patterns of FAU/EMT intergrowth systems synthe-
sized with T/Al2O3 of 0.33 and 0.7, respectively. It can be
observed that the peaks present coincide with the correspond-
ing positions of FAU and EMT. The intergrowth proportion
was evaluated by matching the experimental X-ray diffraction
pattern with the simulated pattern generated by DIFFaX [23].
Fig. 4 shows the experimental X-ray pattern corresponding to
FAU/EMT synthesized with T/Al2O3 = 0.70 and the simulated
pattern obtained by DIFFaX, assuming a block type random dis-
tribution of 50%FAU–50%EMT. As can be seen there is a good
Table 3
Catalyst chemical composition (% atomic) by EDX
Catalysts
O (%)
Al (%)
Si (%)
Si/Al
Pt (%)
Na (%)
K (%)
Pt/HFAU (without template)
Pt/HFAU (pH = 9)
Pt/HFAU (pH = 11)
Pt/EMT(0.33)
Pt/HEMT(0.7)
Pt/FAU/EMT (0.33)
Pt/HFAU/HEMT (0.7)
57.8
50.8
57.7
52.2
56.6
53.7
58.4
11.1
8.11
8.32
9.73
7.72
9.33
6.95
31.0
38.2
33.8
35.3
35.5
33.6
34.4
2.8
4.7
4.1
3.6
4.6
3.6
4.9
0.13
0.11
0.25
0.21
0.19
0.21
0.18
–
–
–
2.56
–
–
–
–
–
–
0.63
–
2.90
–

168
L.N. Belandr´ıa et al. / Journal of Molecular Catalysis A: Chemical 281 (2008) 164–172
Fig. 4. (a) Experimental XRD pattern of intergrowth FAU/EMT,
(T1 + T2)/Al2O3 = 0.70. (b) Simulated XRD pattern of intergrowth with
stacking of clusters: ␣FF = 0.90; ␣EE = 0.90.
Fig. 3. (a) Simulated XRD diffraction patterns of FAU and EMT pure sys-
tems. (b and c) Experimental XRD patterns of intergrowth FAU/EMT for
(T1 + T2)/Al2O3 ratios 0.33 and 0.70, respectively.
agreement between both experimental and simulated patterns.
The inset shows an enlarged section of the 2θ = 5–7◦ in order to
visualize clearly the similarities between both patterns.
Fig. 5 shows the experimental and simulated patterns for
FAU/EMT synthesized with T/Al2O3 = 0.33. Two models of
intergrowth distribution were assumed, random stacking of
layers and cluster formation. The best fit was obtained for
random-stacking layers with a proportion 10%FAU/90%EMT
(Fig. 5b). A reasonable match was also obtained for a cluster
arrangement with a proportion of 12%FAU/88%EMT (Fig. 5c).
The diffractograms for the catalysts in their final reduced
state are shown in Fig. 6. Whatever the catalyst the crystallinity
is preserved, except for the FAU sample synthesized without
template (Fig. 6a). This sample lost most of its zeolite structure;
probably due to its low thermal stability, as a consequence of
its low Si/Al ratio. The incorporation of platinum, via solid ion
exchange onto all the prepared samples, was confirmed by the
peaks at 2θ = 39.9◦, 46.4◦ and 67.6◦, corresponding to metallic
platinum.
Fig. 5. (a) Experimental XRD pattern for intergrowth with
(T1 + T2)/Al2O3 = 0.33, (b) simulated for layers with random stackings
10%FAU/90%EMT, and (c) simulated for stacking of clusters of ␣FF = 0.3 and
␣EE = 0.9.
The chemical composition is given in Table 3. As can be
seen, all the samples were fully decationized, except the sam-

L.N. Belandr´ıa et al. / Journal of Molecular Catalysis A: Chemical 281 (2008) 164–172
169
Fig. 7. TEM micrograph of Pt/HEMT (0.70).
Fig. 6. XRD patterns of Pt-modified zeolite: (a) Pt/HFAU (without tem-
plate), (b) Pt/HFAU (pH = 9), (c) Pt/HFAU (pH = 11), (d) Pt/EMT (0.33), (e)
Pt/HEMT (0.7), (f) Pt/FAU/EMT (0.33), (g) Pt/HFAU/HEMT (0.7), and (h)
Pt/HFAU/HEMT (75/25, 0.7).
3.2. Catalytic test
The catalysts were active for n-pentane conversion, particu-
larly for hydroisomerization into i-pentane. Fig. 8a shows the
behavior of Pt/zeolite catalysts prepared from gel composition
of T/Al2O3 = 0.7. The Pt/HFAU/HEMT (0.7) intergrowth cata-
lyst showed the highest initial activity for this series. The catalyst
preparedfromzeoliteFAU(pH = 11)wasthemostactiveandsta-
ble in the series of faujasites, probably due to the slightly higher
acidity than that for FAU (pH = 9). Comparing the catalytic per-
formance of the structures synthesized with T/Al2O3 = 0.7, the
intergrowth structure shows higher initial catalytic activity than
EMT or FAU structures alone, while FAU shows higher resid-
ual catalytic activity in the time scale studied (time on stream,
tos = 2–10 min) (see Fig. 8a). The Pt/HEMT sample, showed
slightly higher activity than the Pt/HFAU, both synthesized with
T/Al2O3 = 0.7 and at pH = 9, but less active than the Pt/HFAU
sample, synthesized with T/Al2O3 = 0.7 and at pH = 11. This
behavior is in agreement with the catalyst acidity (see Table 4
and Fig. 9), as reported elsewhere [16,24–26].
ples Pt/EMT(0.33) and Pt/FAU/EMT (0.33), which were only
partially exchanged (see Table 1). The Pt/H+ ratio, the unit
cell formula for the zeolites FAU and EMT and the acidity
(meqNH3/g) are given in Table 4. For FAU synthesized without
template, a higher Al content was obtained in the final prod-
uct. For the FAU structure synthesized with template, the pH
increase from 9 to 11 resulted in a slight increase in Al content
(lower Si/Al ratio), owing to a higher basicity in the synthe-
sis (see Table 4). The platinum incorporated is also higher for
the latter. For the EMT and FAU/EMT series, the increase in
T/Al2O3 ratio, from 0.33 to 0.7, decreases Al content (higher
Si/Al ratio). For these samples, the higher the Al content, the
higher the Pt/H+ ratio (see Table 4).
The high platinum dispersion was observed by TEM. Highly
dispersed platinum nanocrystals can be observed in Fig. 7,
for Pt/HEMT (0.7) sample. The crystal sizes were in the
range of 4–10 nm for most samples, except for Pt/FAU/EMT
(0.33), whose crystal sizes were between 1.5 and 3.5 nm,
and for Pt/EMT (0.33) with metal clusters of 20–50 nm (see
Table 5).
The catalyst prepared from the zeolite FAU (synthesized
without template) was the less active, due to the structural col-
lapse that occurred during catalyst preparation. This low thermal
and hydrothermal stability was a consequence of its low Si/Al
Table 5
Table 4
Metal dispersion measured by TEM (dPt, nm) and by CO chemisorption (D, %)
The Pt/H+ ratio, unit cell formula and acidity (mequiv.NH3/g)
Catalysts
dPt (nm)
D (%)
Catalysts
Pt/H+ Unit cell
mequiv.NH3/g
Pt/HFAU (without template)
Pt/HFAU (pH = 9)
Pt/HFAU (pH = 11)
Pt/EMT (0.33)
Pt/HEMT (0.33)
Pt/HEMT (0.7)
Pt/FAU/EMT (0.33)
Pt/HFAU/HEMT (0.33)
Pt/HFAU/HEMT (0.7)
4–7
4–8
4–10
20–50 clusters
–
5
1.5–3.5
–
6
1.1
31.1
42.0
17.6
7.53
57.9
9.58
10
Pt/HFAU (pH = 9)
Pt/HFAU (pH = 11)
Pt/EMT(0.33)
Pt/HEMT(0.33)
Pt/HEMT(0.7)
Pt/FAU/EMT (0.33)
Pt/HFAU/HEMT (0.33) 0.011
Pt/HFAU/HEMT (0.7) 0.026
0.014 H34Al34Si158O384
0.030 H38Al38Si154O384
0.021 Na5.5H15.5Al21Si75O192 1.57
2.06
2.35
0.030 H16.7Al16.7Si79.3O192
2.58
2.24
1.84
2.87
2.55
0.024
0.036
H
–
17Al17Si79O192
–
–
14.4

170
L.N. Belandr´ıa et al. / Journal of Molecular Catalysis A: Chemical 281 (2008) 164–172
low T/Al2O3 ratio the aluminum incorporation into the struc-
ture is favoured, with the corresponding increase in acidity (see
Table 4).
For this series, one can see that the catalyst activity increases
with its acidity, as can be seen in Fig. 9, where the ini-
tial conversion (%) (at 2 min) is plotted versus total acidity
(mequiv.NH3/g). In the range studied, neither the Pt/H+ ratio
nor the metal dispersion had an observable effect on activity. On
the contrary, the intergrowth structures do have a pronounced
effect on activity. Thus, the FAU/EMT (0.33) has an intergrowth
proportion of 10%FAU/90%EMT, whereas FAU/EMT (0.7) has
50%FAU/50%EMT, and this is reflected in the activity. This
appears to suggest that the intergrowth enhances the catalyst
activity. The lower activities for Pt/EMT (0.33) or Pt/FAU/EMT
(0.33) are due to the presence of alkaline cations that limit the
acidity (see Tables 3 and 4), stressing the key role played by the
acid sites in determining the catalyst activity [28–31].
At 350 ◦C and with a carrier gas flow composition of
H2:N2 = 2:1, the iso-pentane yield appeared to be a direct func-
tion of conversion, as shown in Fig. 10, for whatever structure
(i.e. FAU, EMT or FAU/EMT) and at different times on stream.
The slope of this curve is the selectivity; therefore, it appears to
be independent of structure, time on stream, acidity, Pt/H+ ratio
and metal dispersion, for this series of catalysts under these con-
ditions (given temperature and carrier gas composition). From
the slope is obtained a value of 82% selectivity, which is slightly
higher than the one reported in the literature (72%) [32]. This
value compares very well with that calculated, using a Gibbs
free energy of −1.18 kcal/mol [33]. In fact, for Pt/MOR cata-
lyst, it has been reported that the selectivity is a function both of
conversion and of the degree of deactivation [34].
Fig. 8. Conversion (%) as function of the time on the stream (os, min) for
(a) zeolites Pt/HFAU: (ꢀ) pH = 11; (ꢁ) pH = 9; (♦) without template, (ꢂ)
Pt/HFAU/HEMT (0.7) and (᭹) Pt/HEMT (0.7) and (b) (ꢀ) zeolites Pt/HEMT
(0.33); (
(0.33).
) Pt/EMT (0.33); (ꢁ) Pt/HFAU/HEMT (0.33); (
) Pt/FAU/EMT
ratio [27]. However, the catalyst shows some activity, probably
associated to the presence of platinum active sites.
The behavior of Pt/EMT (0.33) and Pt/FAU/EMT (0.33) cat-
alysts, with different amount of alkaline cation (see Table 3),
is shown in Fig. 8b. For both partially and totally decationized
samples the intergrowth structures are more active. The higher
the degree of proton exchange, the higher the activity for EMT
and for the intergrowth structure. Therefore, not only the acid
sites in the supercages for FAU and in the hypercages for EMT
structures, but also the acid sites in the hypocages for EMT
structures do participate in the reaction. The Pt/HFAU/HEMT
(0.33) intergrowth catalyst showed the highest activity for this
series. In general, it appears that the structures synthesized with
a T/Al2O3 = 0.33 are more active than those synthesized with
a T/Al2O3 = 0.7. This is probably related to the fact that at
The residual activity at 10 min, measured as the ratio of con-
version (X10, %) at 10 min to initial conversion at 2 min (X2,
%) is given in Table 6. For such short range of time, the resid-
ual catalytic activity is in the order FAU > EMT > intergrowth.
Dougnier et al. [16] reported similar results for the cracking of
Fig. 10. Iso-pentane yield (%) as function of conversion (%) for zeolites
Pt/HFAU: (ꢁ) pH = 11; (ꢀ) pH = 9; (♦) without template; (ꢀ) zeolites Pt/HEMT
(0.7); (᭹) Pt/EMT (0.33); and intergrowths: (ꢁ) Pt/HFAU/HEMT (0.7) and (ꢂ)
Pt/FAU/EMT (0.33).
Fig. 9. Conversion (%) as function of acidity (mequiv.NH3/g) for all catalysts.

L.N. Belandr´ıa et al. / Journal of Molecular Catalysis A: Chemical 281 (2008) 164–172
171
Table 6
Remaining activity at 10 min (X10/X2)
Catalysts
X10/X2
Pt/FAU (without template)
Pt/HFAU (pH = 9)
Pt/HFAU (pH = 11)
Pt/EMT (0.33)
Pt/HEMT (0.33)
Pt/HEMT (0.70)
Pt/FAU/EMT (0.33)
Pt/HFAU/HEMT (0.33)
Pt/HFAU/HEMT (0.7)
0.38
0.85
0.90
0.72
0.73a
0.76
0.65
0.92
0.62
a
The remaining activity was calculated at 8 min on stream, X8/X2.
n-heptane and Berreghis et al. [28] for the hydrocracking of n-
heptane. However, for Pt/HFAU/HEMT (0.33) residual activity
is comparable with that of template-synthesized Pt/HFAU.
The increase in the H2:N2 carrier composition, leads to higher
activity, stability and selectivity, as shown in Fig. 11, due to the
increase in the hydrogenation of olefins. This fact inhibits the
coke precursor formation, which is the main cause of catalyst
deactivation and enhances the selectivity to isoparaffins through
hydrogenation of intermediate branched olefins.
The intergrowth FAU/EMT is a highly active and selective
catalyst. For the intergrowth Pt/HFAU/HEMT (0.33), the con-
version increases withthereaction temperature, whileselectivity
to i-pentane increases and approaches 100% with decreasing
temperature, as shown in Fig. 12. The isomerization at low
temperature is enhanced, since this is an exothermic reaction.
While at higher temperatures the endothermic reactions such as
cracking become more important.
Fig. 12. (a) Conversion (%) as a function of tos (min). (b) selectivity (%) as a
function of conversion (%), for T = 350 ◦C (ꢀ); 300 ◦C (♦); 275 ◦C (ꢁ); 250 ◦C
(ꢀ); H2:N2 = 2:1, on Pt/HFAU/HEMT (0.33).
methane, ethane, propane, i-butane and n-butane, were reported
as cracking products, pentenes reported as dehydrogenation
products, and those with carbon numbers higher than five
are reported as C5+. In Fig. 13, minor product distribution
is presented. The presence of cracking and C5+ fractions
can be explained by C5 disproportionation to C4 + C6 and
to C3 + C7. C6 and C7 can undergo cracking to C3 and C4.
These products can also be explained by C5 dimerization to
C10, followed by a fast isomerization and cracking to C4 + C6
and to C3 + C7. Comparing the catalysts Pt/HEMT(0.33),
Pt/EMT(0.33), Pt/HFAU/HEMT(0.33)andPt/FAU/EMT(0.33),
it can be seen that the cracking activity increases with the degree
of protonic exchange. This probably is due to the increase in the
amount and strength of accessible acid sites.
The studied catalyst was highly selective to i-pentane. How-
ever, some minor products were also observed. Among them,
Fig. 11. (a) Conversion (%) as a function of time on stream (min). (b) selectivity
(%) as a function of conversion (%), at T = 350 ◦C, H2:N2 = 30:0 (ꢀ); 20:10 (♦);
10:20 (ꢂ); for Pt/HFAU (0.7).
Fig. 13. Cracking (%), dehydrogenation (%) and C5+ (%) yield at 350 ◦C,
H2/N2 = 20/10.

172
L.N. Belandr´ıa et al. / Journal of Molecular Catalysis A: Chemical 281 (2008) 164–172
[3] J.A. Martens, P.A. Jacobs, in: E.G. Derouane, F. Lemos, C. Naccache,
F.R. Ribeiro (Eds.), Zeolite Microporous Solids: Synthesis, Structure and
Reactivity, NATO ASI Ser. C, Vol. 352, Kluwer, Dordrecht, 1992, p. 511.
[4] J.M. Thomas, M. Audier, J. Klinowski, J. Chem. Soc., Chem. Commun.
(1981) 1221.
[5] G.T. Kokotailo, J. Ciric, Adv. Chem. Ser. 101 (1971) 109.
[6] J. Ciric, US Patent 3,972,983 (1976).
[7] V. Fu¨lo¨p, G. Bobe´ly, H.K. Beyer, S. Ernst, J. Weitkamp, J. Chem. Soc.,
Faraday Trans. 85 (1989) 2127.
[8] M.M.J. Treacy, J.M. Newsam, D.E.W. Vaughan, K.G. Strohmaier, W.J.
Mortier, J. Chem. Soc. Chem. Commun. (1989) 493.
[9] D.E.W. Vaughan, M.G. Barret, US Patent 4,309,313 (1982).
[10] M.M.J. Treacy, J.M. Newsam, R.A. Beyerlein, M.E. Leonowicz, D.E.W.
Vaughan, J. Chem. Soc. Chem. Commun. (1986) 1211.
[11] P. Canizares, A. de Lucas, F. Dorado, A. Duran, I. Asencio, Appl. Catal.
A: Gen. 169 (1998) 137.
Fig. 14. Typical cracking product distribution.
[12] G. Kinger, A. Lugstein, R. Swagera, M. Ebel, A. Jentys, H. Vinek, Micro-
por. Mesopor. Mater. 39 (2000) 307.
The Fig. 14 shows the typical cracking product distribution
observed for these catalysts. The major component is i-butane,
while CH4 and C2H6 are present at trace level, indicating that
the hydrogenolysis reaction is practically insignificant.
[13] Ch. Jia, P. Beaunier, P. Massiani, Micropor. Mesopor. Mater. 24 (1998) 69.
[14] C. Stolz, A. Sauvage, P. Massiani, R. Kramer, Appl. Catal. A: Gen. 167
(1998) 113.
[15] N. Hanif, M.W. Anderson, V. Alfredsson, O. Terasaki, Phys. Chem. Chem.
Phys. 2 (2000) 3349.
[16] F. Dougnier, J. Patarin, J.L. Guth, D. Anglerot, Zeolites 12 (1992) 160.
[17] C.S. Gonza´lez, S´ıntesis y caracterizacio´n de sistemas de intercrecimiento
FAU/EMT, Tesis de Maestr´ıa, Instituto Venezolano de Investigaciones
Cient´ıficas (IVIC), 2004.
[18] G. Gonza´lez, C.S. Gonza´lez, Proceedings of XVII Simpo´sio Iberoameri-
cano de Cata´lisis, Margarita (Venezuela), 2002, p. 150.
[19] J.A. Martens, P.A. Jacobs, J. Mol. Catal. 78 (1993) L47–L52.
[20] L.N. Belandria R., Trabajo Especial de Grado, Universidad de Los Andes,
Me´rida-Venezuela, 2004.
4. Conclusions
The intergrowths of zeolites FAU/EMT were synthesized
usingmixturesof15-crown-5and18-crown-6astemplatesinthe
synthesis gels. Well-dispersed platinum was successfully incor-
porated onto the zeolite via solid-state ion exchange procedure.
The catalytic activity of the FAU/EMT intergrowth structure
was higher than that for the pure EMT or FAU structures under
the same reaction conditions. The structure order of activity was
FAU/EMT > EMT ≥ FAU, forsamplessynthesizedatpH = 9and
T/Al2O3 = 0.7. The structure synthesized with lower T/Al2O3
incorporated more aluminum and were more active. The synthe-
sis of FAU structure at pH = 11 lead to a more acidic samples;
and consequently, more active. The acidity and the presence of
intergrowth structure were the key factors that control the activ-
ity. The catalytic remaining activity at 10 min follows the order
FAU > EMT > intergrowths FAU/EMT. The selectivity obtained
at 350 ◦C, and a carrier gas flow composition of H2:N2 = 2:1 was
82% independent ofstructure, timeon stream, acidity, Pt/Al ratio
or metallic dispersion. The selectivity is, however, a function of
temperature and carrier gas composition. Thus, the selectivity
increases as the temperature decreases and/or hydrogen content
increases in the gas carrier.
[21] L.N. Belandr´ıa, C.S. Gonza´lez, J.C. Herna´ndez, A. Uzca´tegui, G. Gonza´lez,
J. Brito, A. Calafat, F. Arenas, F. Imbert, Proceedings of 13◦ Congreso
Brasilero de Cata´lisis and 3◦ Congreso de Cata´lisis del Mercosur, Foz de
Iguazu-Brasil, 2005.
[22] L.N. Belandr
´ıa, C.S. Gonza´lez, J.C. Herna´ndez, A. Uzca´tegui, G. Gonza´lez,
J. Brito, A. Calafat, F. Arenas, F. Imbert, Proceedings of XX Simposio
Iberoamericano de Catalisis, Gramados, Brazil, 2006.
[23] M.M.J. Treacy, J.M. Newsam, M.W. Deˆem, Proc. Roy. Soc. Lond. A 433
(1991) 499.
[24] G. Lischke, E. Schreier, B. Parlitz, I. Pitsch, U. Lohse, M. Woettke, Appl.
Catal. A: Gen. 129 (1995) 57.
[25] Y. Cao, R. Kessas, C. Naccache, Y. Ben Taarit, Appl. Catal. A: Gen. 184
(1999) 231.
[26] T. Rorvik, H. Mostad, O. Henrik Ellestad, M. Sto¨cker, Appl. Catal. A: Gen.
137 (1996) 235.
[27] G. Giannetto, A. Montes, G. Rodr´ıguez, Zeolitas: Caracter´ısticas,
PropiedadesyAplicacionesIndustriales, EditorialInnovaci
UCV, Caracas, Venezuela, 2000.
o´nTecnolo´gica,
[28] A. Berreghis, P. Magnoux, M. Guisnet, Proceedings of 12th Interna-
tional Zeolite Conference, vol. IV, Baltimore, USA, July 5–10, 1998, pp.
2719–2726.
Acknowledgements
[29] L.O. Almanza, T. Narbeshuber, P. d’Araujo, C. Nacache, Y.B. Taarit, Appl.
Catal 178 (1999) 39.
The authors are grateful to the following institu-
[30] A. Hollo´, J. Hancso´k, D. Lallo´, Appl. Catal. 229 (2002) 93.
[31] M. Weihe, M. Hunger, M. Breuninger, H.G. Karge, J. Weitkamp, J. Catal.
198 (2001) 256.
[32] F. Schmidt, E. Kohler, in: M. Guisnet, P. Gilson (Eds.), Zeolites for Cleaner
Technologies, Imperial College Press, London (Great Britain), 2002, p. 153
(chapter 7).
[33] D. Stull, E. Westrum, G. Sinke, The Thermodynamics of Organic Com-
pounds, New York (USA), 1969.
[34] A. Corma, A. Mart´ınez, in: M. Guisnet, P. Gilson (Eds.), The Chemistry
of the catalytic process, in Zeolites for Cleaner Technologies, Imperial
College Press, London (Great Britain), 2002, p. 29 (chapter 2).
´
tions FONACIT: Agenda Petroleo CONICIT-CONIPET No.
97003795, G-2000001537 and CDCHT-ULA (C-1231-04-08-
B), for the financial support.
References
[1] H. van Bekkum, E.M. Flanigen, P.A. Jacobs, J.C. Jansen (Eds.), Intro-
duction to Zeolite Science and Practice, 2nd ed., Elsevier, Amsterdam,
2001.
[2] F. Delprato, L. Demontte, J.L. Guth, L. Huve, Zeolites 10 (1990) 546.