Effect of hydrohalogenation of metal/zeolite catalysts for cyclohexene hydroconversion -Part 3- Pd/H-ZSM-5 catalysts

Article abstract of DOI:10.1002/jccs.200700172

Cyclohexene (CHE) hydroconversion was performed in a flow reactor at atmospheric pressure and temperatures of 50-400 °C using: Pd/H-ZSM-5, Pd/H-ZSM-5(HCl), and Pd/H-ZSM-5(HF) catalysts. These catalysts were characterized for acid site strength distribution via NH₃ TPD, Pd dispersion via H₂ chemisorption, TPR via reduction of the metal oxide in the catalysts and XRD for tracing crystallinity. The hydroconversion steps proceeded as follows: CHE → Cyclohexane (CHA); CHE → Methylcyclopentenes (MCPEs) → Methylcyclopentane (MCPA); CHE → Cyclohexadienes (CHDEs) → Benzene → Alkylbenzenes; CHE and others → Hydrocracked products. The overall hydroconversion of CHE was achieved in the catalyst order: Pd/H-ZSM-5 > Pd/H-ZSM-5(HF) > Pd/H-ZSM-5(HCl). CHE hydrogenation step was the major reaction at low temperatures which significantly inhibited via HCl treatment, but slightly enhanced via HF treatment. At medium temperatures, on all catalysts, isomerisation to MCPEs and MCPA increase to a maximum then a decline with a further increase of temperature. The overall isomerisation of CHE was highest on the untreated catalyst. During the higher temperature range, dehydrogenation, alkylation and hydrocracking were increased with temperature. Dehydrogenation of CHE always yielded larger amounts of 1,3-CHDE than 1,4-CHDE. These cyclohexadienes were produced in the catalyst order: Pd/H-ZSM-5(HF) > Pd/H-ZSM-5(HCl) > Pd/H-ZSM-5. In general, benzene alkylation to toluene exceeded that of xylenes, indicating that the second methylation is more difficult than the first. However, the catalytic activities for benzene and toluene production were in the order: Pd/H-ZSM-5 ? Pd/H-ZSM-5(HCl) > Pd/H-ZSM-5(HF), whereas for xylenes production, Pd/H-ZSM-5 ? Pd/H-ZSM-5(HF) > Pd/H-ZSM-5(HCl). Intrapore diffusion plays an important role during the dehydrogenation reactions as well as during the interconversion of individual aromatic hydrocarbons.

Full text of DOI:10.1002/jccs.200700172

Journal of the Chinese Chemical Society, 2007, 54, 1211-1222
1211
Effect of Hydrohalogenation of Metal/Zeolite Catalysts for Cyclohexene
Hydroconversion†
-Part 3- Pd/H-ZSM-5 Catalysts
Noha A. K. Aboul-Gheit
Egyptian Petroleum Research Institute, Process Development Division,
Code 11787, P.O. box 9540, Nasr City, Cairo, Egypt
Cyclohexene (CHE) hydroconversion was performed in a flow reactor at atmospheric pressure and
temperatures of 50-400 °C using: Pd/H-ZSM-5, Pd/H-ZSM-5(HCl), and Pd/H-ZSM-5(HF) catalysts.
These catalysts were characterized for acid site strength distribution via NH3 TPD, Pd dispersion via H2
chemisorption, TPR via reduction of the metal oxide in the catalysts and XRD for tracing crystallinity. The
hydroconversion steps proceeded as follows: CHE ® Cyclohexane (CHA); CHE ® Methylcyclopentenes
(MCPEs) ® Methylcyclopentane (MCPA); CHE ® Cyclohexadienes (CHDEs) ® Benzene ® Alkyl-
benzenes; CHE and others ® Hydrocracked products.
The overall hydroconversion of CHE was achieved in the catalyst order: Pd/H-ZSM-5 > Pd/H-ZSM-
5(HF) > Pd/H-ZSM-5(HCl). CHE hydrogenation step was the major reaction at low temperatures which
significantly inhibited via HCl treatment, but slightly enhanced via HF treatment. At medium tempera-
tures, on all catalysts, isomerisation to MCPEs and MCPA increase to a maximum then a decline with a
further increase of temperature. The overall isomerisation of CHE was highest on the untreated catalyst.
During the higher temperature range, dehydrogenation, alkylation and hydrocracking were increased with
temperature. Dehydrogenation of CHE always yielded larger amounts of 1,3-CHDE than 1,4-CHDE.
These cyclohexadienes were produced in the catalyst order: Pd/H-ZSM-5(HF) > Pd/H-ZSM-5(HCl) >
Pd/H-ZSM-5. In general, benzene alkylation to toluene exceeded that of xylenes, indicating that the sec-
ond methylation is more difficult than the first. However, the catalytic activities for benzene and toluene
production were in the order: Pd/H-ZSM-5 >> Pd/H-ZSM-5(HCl) > Pd/H-ZSM-5(HF), whereas for
xylenes production, Pd/H-ZSM-5 >> Pd/H-ZSM-5(HF) > Pd/H-ZSM-5(HCl). Intrapore diffusion plays
an important role during the dehydrogenation reactions as well as during the interconversion of individual
aromatic hydrocarbons.
Keywords: Palladium; H-ZSM-5; Zeolite; Catalysts; Cyclohexene; Hydroconversion.
1. INTRODUCTION
originally strong acidic sites. This has been realized via us-
ing Pt/acid zeolite catalysts which may exclude continuous
Cl- ion injection in the reactor. The zeolite primarily used
commercially is H-mordenite (H-MOR), which is assumed
to acquire the strongest acid sites. In the present work, we
used H-ZSM-5 zeolite instead of H-MOR zeolite for sup-
porting Pt. The H-ZSM-5 zeolite seems advantageous over
H-MOR by virtue of acquiring a more efficient pore diffu-
sion capability, since H-MOR acquires a unidirectional
channel system which doesn’t permit molecular counter-
diffusion, whereas the channel system in H-ZSM-5 zeolite
is tridirectional 1 and permits counter-diffusion of even the
The industrial catalysts used in almost all petroleum
refineries for upgrading light and heavy naphthas via hy-
droisomerisation and catalytic reforming processes in-
clude, conventionally, Pt/g-alumina catalysts which are
promoted by a continuously injected low-molecular weight
chlorinated hydrocarbon mixed with the naphtha feed-
stock. The Cl- ions liberated in the reactor under the H2 op-
erating pressure enhance the catalyst acidity and improves
its Pt dispersion. However, Cl- ion is corrosive, which en-
forced the refineries to shift to using catalysts possessing
† Part 1 of this series is entitled “Cyclohexene hydroconversion on Ir/H-ZSM-5 Catalysts”, published in Appl. Catal. A: General 303
(2006) 141.

1212 J. Chin. Chem. Soc., Vol. 54, No. 5, 2007
Aboul-Gheit
most strongly adsorbed moleclules, and hence increasing
the effective diffusivity (Deff) along the catalytic pores.
Moreover, one of the three channels in H-MOR is very nar-
row (diameter of only 2.8 Å),2 wherein diffusion of any
molecules is impossible. In addition, there is no significant
superiority of the acid site strength in H-MOR over that in
H-ZSM-5 zeolite.
Scheme I Proposed scheme for pathways of cyclo-
hexene hydroconversion using the current
Re/H-ZSM-5 catalysts
Traditionally, Pt is combined with another metal (pro-
moter) such as Ir, Re, Ge, Ti, Sn, Zn, etc., in order to: (a)
protect well-dispersed Pt crystallites against sintering via
extended commercial use at high temperatures, (b) inhibit
catalyst poisoning by hetero-atoms, e.g., sulphur and nitro-
gen, and (c) reduce deactivation via carbon deposition on
the catalyst surface. Apart from Pt protection against deac-
tivation, the second metal is combined with Pt to promote
its catalytic efficiency. Palladium can successfully act as an
active promoter for Pt since it acquires higher hydrogena-
tion and dehydrogenation activities compared to Pt.3-5
Cyclohexene (CHE) is frequently selected as a probe
molecule for investigating catalyst preparation.3-11 It un-
dergoes various conversions depending on catalyst compo-
sition and operating conditions. In absence of H2, CHE
disproportionation12,13 and dehydrogenation14,15 reactions
take place. The former reaction produces benzene and cyc-
lohexane (CHA) (hydrogen transfer) using metal catalysts,
since CHE acts as hydrogen donor and acceptor. If the
metal is supported on Al2O3,4 the acid sites are weak Lewis
sites that can’t promote carbonium ion formation; there-
fore, isomerization and cracking reactions don’t occur on
alumina supported catalysts. Recently, Aboul-Gheit et al.16
investigated the kinetics of CHE hydrogenation and dehy-
drogenation using monometallic (Pt, Pd, Ir and Re) and bi-
metallic (Pt-Pd, Pt-Ir and Pt-Re) catalysts supported on
g-alumina, where no intermixing of these reactions occurs.
However, the H-zeolites possess strong Brönsted and Lewis
acid sites that promote CHE isomerization to a mixture of
MCPEs and cracking to lower molecular weight hydrocar-
bons, and the reaction scheme (Scheme I) becomes more
complicated. Treatment of cation-exchanged zeolites with
aqueous HCl acid leads to decationation and partial dealumi-
nation. Introduction of Cl- ion into alumina causes Brönsted
acid sites to form17 and skeletal isomerization and total
conversion greatly increases.18
aromatics,19 hydroconversion of n-paraffins in petroleum
light naphtha,20 CHA dehydrogenation21 and hydroiso-
merization, and hydrocracking and dehydrocyclization of
n-paraffins22 using Pt/Al2O3 catalysts promoted with other
metals (Rh, Ir, Re or U) and Cl- or F- ions. Other authors23-32
have studied CHE hydrogenation and/or dehydrogenation
using Ni, Pt, Rh and Pd catalysts. Moreover, CHE hydro-
conversion over catalysts containing 0.35 wt% of the mono-
metals Rh, Pt, Ir, Re or U and their combinations on g-
Al2O3 has been studied at temperatures of 50-250 °C in the
presence of H2.4 The effect of doping with 3.0 wt% of Cl- or
F- was examined. The bimetallic combinations on alumina
give more active catalysts than the monometallic partners.
However, the activities of monometallic catalysts were en-
hanced via Cl- incorporation. The effect of Cl- ion added,
either as a part of the Pt precursor or after noble metal im-
pregnation, on the catalytic activity of Pt/Al2O3 for com-
plete oxidation of toluene has been studied,33 and inhibition
by chlorine occurs and is assigned to the formation of oxy-
Hydrogenation and dehydrogenation of CHE are
much faster than hydrogenation of benzene and dehydro-
genation of CHA, particularly on noble metal catalysts.
Aboul-Gheit and coworkers have studied hydrogenation of

Hydrohalogenation of Pd/H-ZSM-5 Catalysts
J. Chin. Chem. Soc., Vol. 54, No. 5, 2007 1213
chlorided platinum species. Nevertheless, a highly dis-
persed 1.0 wt% Ir/Al2O3 catalyst doped with 1.0% Cl was
tested in n-hexane reactions at 180-330 °C;34 the Cl- con-
taining catalyst was considerably less active in this temper-
ature range (unfavorable for bifunctional reactions).
In the present work, we investigate the effect of dop-
ing a 0.35 wt% Pd/H-ZSM-5 catalyst with 3.0 wt% of HCl
or HF on the performance of CHE hydroconversion through
intermediate reaction steps including hydrogenation, dehy-
drogenation, isomerisation and hydrocracking at tempera-
tures of 50-400 °C in a fixed-bed flow type reactor.
revealed via X-ray diffraction analysis, where the 100%
diffraction peak in all samples (items 2.1.1-2.1.4) appeared
at 2q of 23.0°. However, a very slight increase of the dif-
fraction peak at 2q of 10.884° in the XRD diffraction pat-
terns (not given) of both hydrochlorinated and hydrofluo-
rinated catalysts indicated slight dealumination. The Pd
diffraction peaks didn’t appear due to the very low concen-
tration of Pd (0.35 wt%) incorporated.
2.2. Hydroconversion Reactor System and Product
Analysis
A silica-glass tube reactor containing 0.2 g of a cata-
lyst was used in the hydroconversion runs. The reactor was
electrically heated in an insulated wide silica tube jacket
and electronically thermostated to ±1 °C. Hydrogen gas of
a flow rate of 20 cm3 min-1 was used as a carrier-gas and si-
multaneously as a reactant in all runs. The CHE feed was
introduced into the reactor via continuous evaporation us-
ing a H2 flow passing into a closed jar thermostated at a
fixed temperature of 28 °C whereby the quantity of cyclo-
hexene was always 8.33 ´ 10-3 mole h-1; i.e., the H2/CHE
ratio was 6.4 in all runs. The amount of CHE condensed be-
tween saturator and reactor was always considered in cal-
culating the actual weight of CHE flowing to the catalyst.
Reaction temperatures of 50-400 °C were investigated. The
gaseous reaction effluent passing from the reactor was in-
jected in a Perkin-Elmer Autosystem XL gas-chromato-
graph using a 15 m capillary column of Carbowax 20 M
bonded in fused silica to be analysed. FID detector and a
Turbochrom Navigator Programme were used. Examina-
tion of the current catalysts for CHE hydroconversion for
time-on-stream of 180 minutes at 400 °C didn’t show any
decrease of the catalysts activities. Moreover, examination
of these catalysts for carbon deposition using temperature
programmed oxidation (TPO) in a differential scanning
calorimeter (DSC) didn’t give a CO2 peak.
2. EXPERIMENTAL
2.1. Preparation of the Catalysts
2.1.1. H-ZSM-5 Catalyst
This catalyst was prepared via exchanging Na-ZSM-
5 zeolite with 0.6 M NH4NO3 solution followed by drying
at 110 °C overnight and calcination at 530 °C for 4 h. The
mother Na-zeolite was kindly provided by the Süd Chemie,
München, Germany. The H-form (H-ZSM-5) acquired a
Si/Al ratio of 23.8, a surface area of 440 m2g-1, a pore vol-
ume of 0.16 cm3g-1 and a sodium content < 0.002%.
2.1.2. Pd/H-ZSM-5 Catalyst
A part of H-ZSM-5 zeolite prepared in 2.1.1. was im-
pregnated with an aqueous solution of palladium nitrate
containing the requisite quantity of Pd to obtain 0.35 wt%
Pd, dried at 110 °C overnight, calcined at 530 °C for 4 h
then reduced at 500 °C for 8 h in the reactor using a flow of
pure hydrogen gas.
2.1.3. Pd/H-ZSM-5(HCl) Catalyst
A part of the Pd/H-ZSM-5 zeolite catalyst, prepared
in 2.1.2. was doped with a solution containing the requisite
quantity of hydrochloric acid to acquire 3.0 wt% HCl. The
catalyst was dried, calcined and reduced in the reactor us-
ing a flow of pure hydrogen gas as in 2.1.2.
2.1.4. Pd/H-ZSM-5(HF) Catalyst
2.3. Temperature Programmed Desorption (TPD) of
Ammonia
A part of the Pd/H-ZSM-5 zeolite catalyst, prepared
in 2.1.2. was doped with an HF solution sufficient to con-
tain 3.0 wt% HF, dried, calcined then reduced as in 2.1.2.
Calcination and reduction temperatures of 530 and 500 °C,
respectively, didn’t cause a loss of either Cl- or F- in cata-
lysts as long as humidity was totally excluded.
Primarily, NH3 gas was chemisorbed on the catalyst
sample in a silica tube furnace after evacuation at 1.33 ´
10-3 Pa whilst heating at 500 °C followed by subsequent
cooling under vacuum to 50 °C. NH3 was introduced through
the catalyst bed at a flow rate of 50 cm3 min-1. Desorption
of NH3 from the catalyst was rapidly measured in a differ-
ential scanning calorimeter (DSC Mettler TA-3000) using
standard Al crucibles in nitrogen purge gas at a flow rate of
All catalysts prepared in items 2.1.2., 2.1.3. and 2.1.4.
were found to retain the majority of the crystallinity origi-
nally acquired by the H-ZSM-5 zeolite prepared in 2.1.1. as

1214 J. Chin. Chem. Soc., Vol. 54, No. 5, 2007
Aboul-Gheit
30 cm3min-1. The procedure of Aboul-Gheit35,36 using DSC
for detecting and measuring desorption of presorbed am-
monia from catalysts was applied. The heating rate was 10
Kmin-1 and a full-scale range of 25 mW. Two DSC endo-
thermic peaks appeared in all thermograms; a low tempera-
ture peak (~50-250 °C) represented NH3 desorption from
weak acid sites in the catalyst and a high temperature peak
(250-600 °C) represented NH3 desorption from strong acid
sites. The latter peak is relevant to this work. The values
obtained for the current catalysts include NH3 desorption
enthalpy values for the higher temperature endothermic
peak (Table 1) to correlate the number of acid sites, where-
as the peak temperature correlates the strength of these acid
sites.
Table 1. Ammonia TPD and palladium dispersion in the Pd/H-
ZSM-5 catalysts
Acid Sites Strength Distribution
Pd
DHd, Jg-1
Peak-temp.,°C
(**)
Catalysts
Dispersion,
%
(*)
H-ZSM-5
Pd/H-ZSM-5
Pd/H-ZSM-5(HCl) 084.8
Pd/H-ZSM-5(HF) 086.4
108.5
081.4
380.1
368.4
371.2
376.9
-----
63.1
60.9
68.6
(*) Proportional to acid sites number (**) Proportional to acid
sites strength
Table 2. Bulk and framework Si/Al, Al/u.c. and percent AlNF
Bulk Al
Framework Al
Catalysts
AlNF, %
Si/Al Al/u.c. Si/Al Al/u.c.
2.4. Palladium Fraction Exposed (Pd dispersion) in
the Catalysts
Pd/H-ZSM-5
Pd/H-ZSM-5(HCl) 23.9
Pd/H-ZSM-5(HF) 24.3
23.7
3.89
3.85
3.80
24.7
26.0
27.1
3.73
3.56
3.40
04.1
07.8
11.2
Pd dispersion in the current catalysts was determined
by H2 chemisorption in a pulse system described by Freel.37
A catalyst sample was heated in the chemisorption furnace
at 500 °C for 3 h in a flow of 50 cm3min-1 of pure hydrogen.
The flow was then replaced with O2-free nitrogen gas for 2
h at a flow rate of 30 cm3min-1 at 500 °C (degassing). The
furnace was shut off and the catalyst was cooled to room
temperature. Hydrogen was then pulsed into the nitrogen
carrier gas till saturation, i.e., till appearance of hydrogen
peaks equivalent to complete volumes of unchemisorbed
pulses. The hydrogen uptake was calculated as hydrogen
atoms chemisorbed per total Pd atoms (1:1 stoichiometry)
(Table 1).
tion,28 we applied this procedure to determine AlNF in
H-ZSM-5 zeolite after hydrothermal dealumination.
2.6. X-Ray Diffraction Patterns of the Catalysts
The X-ray diffraction patterns of the catalysts under
study were carried out using a Phillips X’Pert Diffractome-
ter PW 1390 at 40 kV and 30 mA with Ni Filter and Cu Ka
radiation. The XRD runs were carried out up to 2q of 60°.
The traditional XRD patterns (not given here) obtained for
the current catalysts show more or less similar intensities of
the diffraction peaks. The 100% crystallinity peak ap-
peared in all samples at 2q of 23.0°. However, the HCl and
HF doped samples show slightly higher relative intensities
of the lowest 2q peak indicating slight dealumination of the
zeolitic support.
2.5. Framework and non-Framework Aluminium in
the Current Catalysts
The Si/Al ratio was determined via chemical analysis
of the Pd/H-ZSM-5, Pd/H-ZSM-5(HCl) and Pd/H-ZSM-
5(HF) catalysts, and the number of bulk Al per unit cell in
these catalysts was calculated according to {(Na or H)n
Si96-n AlnO192.16 H2O}. After selective extraction of the
non-framework Al (AlNF) with an aqueous solution con-
taining the requisite quantity of ammonium hexafluorosili-
cate (NH4)2F6Si) using reflux at 70 °C, the solid material
was washed, dried at 110 °C then calcined at 530 °C for 3
h.25,26 The procedure depends on the faster extraction of
AlNF than of AlF from zeolites. The Si/Al in the catalysts
were then determined whereby the framework aluminium
(AlF) was calculated for the current catalysts. The calcu-
lated values are given in Table 2. In a previous publica-
3. RESULTS AND DISCUSSION
Distribution of the hydroconversion products of CHE
using the current Pd/HZSM-5, Pd/HZSM-5(HCl) and Pd/
HZSM-5(HF) catalysts (Figs. 1a, 1b and 1c, respectively)
show significant transformation levels from the beginning
of reaction at 50 °C till 400 °C. Obviously, Figs. 1a-1c
show that transformation of CHE to CHA is the major reac-
tion in the low temperature region (50-200 °C). During the
intermediate temperature region, MCPEs and MCPA are

Hydrohalogenation of Pd/H-ZSM-5 Catalysts
J. Chin. Chem. Soc., Vol. 54, No. 5, 2007 1215
formed and increase to reach a maximum at around 300 °C,
beyond which these products decline with a further in-
crease of temperature. However, during the high tempera-
ture region, CHDEs, aromatics and hydrocracked prod-
ucts (lower molecular weight hydrocarbons) continually
increase as a function of reaction temperature up to 400
°C.
temperatures of 50-200 °C. Although the differences be-
tween the activities of the current catalysts for the overall
hydroconversion as a function of temperature don’t appear
large (Fig. 2), the variation of the intermediate products is
greatly significant (Figs. 3-11), indicating interconversions
of these intermediates rather than their complete disappear-
ance.
3.1. Overall Hydroconversion of CHE
3.2. Hydrogenation of CHE
The overall hydroconversion of CHE using the three
current catalysts as a function of reaction temperature is
compared in Fig. 2. The untreated catalyst exhibits superior
activity, compared to the two hydrohalogenated versions.
Nevertheless, the hydrochlorinated catalyst can be said to
acquire the lowest activity among the current catalysts at
The authors have found that the hydrogenating activ-
ity of Pd either supported on g-alumina4 or on H-ZSM-5 ze-
olite is exceptionally higher at low temperatures than on
various other noble metals.3 Fig. 3 shows that when using
the untreated Pd/H-ZSM-5 catalyst, CHA production is as
high as 81.4% at 50 °C and slowly increases to a maximum
Fig. 1a. Product distribution of cyclohexene hydro-
conversion using Pd/H-ZSM-5 catalyst.
Fig. 1c. Product distribution of cycohexene hydro-
conversion using Pd/HZSM-5(HF) catalyst.
Fig. 2. Hydroconversion of cyclohexene using Pd/H-
ZSM-5 catalysts.
Fig. 1b. Product distribution of cyclohexene hydro-
conversion using Pd/H-ZSM-5(HCl) catayst.

1216 J. Chin. Chem. Soc., Vol. 54, No. 5, 2007
Aboul-Gheit
of 84.6% at 100 °C, beyond which it decreases steadily to
7.9% at 300 °C. However, using the Pd/H-ZSM-5(HF) cat-
alyst, CHE hydrogenation is a little bit more increased over
that on the untreated catalyst, attaining 83.8% at 50 °C and
slowly enhanced to a maximum of 86.7% at 75 °C.
attributed to agglomeration of the Ir crystallites. The be-
haviour of Ir in references 33 and 37 very closely resembles
the behaviour of Pd in the present work. On the contrary,
the authors have recently found that7 the dispersion of Pt in
a Pt/H-ZSM-5 catalyst and its hydrogenation activity in
CHE hydroconversion have been significantly enhanced.
This indicates that HCl doping in catalysts primarily con-
taining varying single noble metals supported on H-ZSM-5
will respond differently. These behaviours have to be stud-
ied more extensively to clarify the suitability of metals dur-
ing industrial applications.
During the lower temperature region (50-200 °C),
where the hydrogenation activity is primarily a function of
the metal sites in the catalyst, CHE hydrogenation activi-
ties on the current catalysts can be arranged in order (1):
Pd/HZSM-5(HF) > Pd/HZSM-5
>> Pd/HZSM-5(HCl)
(1)
Although the Pd/HZSM-5(HCl) catalyst acquires the
lowest hydrogenation activity during the low temperature
range, it acquires the highest activity during the higher tem-
perature range (250-400 °C) (Fig. 3) which can be attrib-
uted to the role of acid sites in creating and strengthening
Brönsted acid sites that act as hydrogenation sites39-41 at
higher temperatures. Table 1 shows that doping Pd/HZSM-
5 with 3.0% HCl has increased the NH3 desorption en-
thalpy (which is proportional to the number of acid sites)
from 81.4 to 84.8 Jg-1 and increased the NH3 desorption
peak temperature (which is proportional to the strength of
acid sites) from 368.4 to 371.2 °C. Several authors prove
that Brönsted acid sites act as hydrogenation sites at high
temperatures: Sano et al.38 show that 95% of ethylene hy-
drogenates to ethane at 535 °C on an unloaded H-ZSM-5
catalyst. Kanai et al.40 and Senger and Radom41 proved that
Brönsted acid sites act as hydrogenation sites for alkenes at
higher temperatures. Furthermore, our recent publication,6
gives more evidence that doping H-ZSM-5 zeolite with
HCl or HF increased acid sites number and strength, and
hence, enhanced the CHE hydrogenation activity.
This order is fairly compatible with the order of Pd disper-
sion in the catalysts (Table 1). The lower dispersion of Pd in
the hydrochlorinated catalyst than in the two other versions
can be assumed to result through interaction of the well dis-
persed (63.1%) Pd supported on the H-ZSM-5 zeolite with
HCl forming larger Pd agglomerates. Nevertheless, Paulis
et al.32 found that Cl- ions added, either as a part of the Pt
precursor or after noble metal impregnation, a decrease of
the catalytic toluene oxidation activity of Pt/Al2O3 catalyst
and that this inhibition is assigned to the formation of oxy-
chlorided platinum species. However, Majeste et al.34 have
prepared and tested a highly dispersed 1.0 wt% Ir/Al2O3
catalyst doped with 1.0% Cl- for n-hexane reactions at 180-
330 °C and found that after Cl- doping the catalyst was con-
siderably less active than before chlorination. Recently, the
authors38 have found that doping of Ir/H-ZSM-5 catalyst
with HCl enhanced its acid sites number and strength but
reduced the metal dispersion as well as the hydrogenation
activity in CHE hydroconversion. This inhibition has been
The Pd/HZSM-5(HF) catalyst acquires the highest Pd
dispersion, as well as the highest acid sites number and
strength among the current catalysts; however, its hydroge-
nation activity doesn’t differ significantly from that of the
untreated catalyst (which acquires the lowest dispersion of
Pd and lowest acidity). This can be attributed to formation
of the highest extra-framework (AlNF) fluoro-aluminium
debris (11.2% of Al in the catalyst, Table 2) in the channels
of the Pd/HZSM-5(HF) catalyst, causing significant diffu-
sion restriction on the reaction. On the other hand, the sig-
nificantly lower activity of Pd/HZSM-5(HCl) than that of
untreated Pd/HZSM-5 can evidently be attributed to high
diffusion restriction caused by extra-framework (AlNF
)
Fig. 3. Cyclohexane production using Pd/H-ZSM-5
catalysts.
chloro-aluminium debris in the zeolitic channels. However,
this debris is lower (7.8% of Al in the catalyst, Table 2) than

Hydrohalogenation of Pd/H-ZSM-5 Catalysts
J. Chin. Chem. Soc., Vol. 54, No. 5, 2007 1217
that formed in the Pd/HZSM-5(HF) catalyst. Relatively,
the untreated catalyst contains the lowest debris
(hydroxy-aluminium debris (4.1% of Al formed during the
zeolite synthesis, Table 2) than the hydrohalogenated ver-
sions of Pd/HZSM-5. However, the higher dispersion of Pd
in H-ZSM-5 treated with HF than the untreated one may be
attributed to the leaching action of the acid on the zeolitic
components (Al and Si) surrounding Pd crystallites, where-
as HCl decreases Pd dispersion via causing agglomeration
of the metal crystallites as revealed by SEM examination
(not given).
bered ring isomers of CHE, unsaturated and saturated (Fig.
6), which is in the catalyst order (5):
Pd/HZSM-5 >> Pd/HZSM-5(HF)
³ Pd/HZSM-5(HCl)
(5)
Dwyer et al.,42 Tjandra and Zaera43 and Jolly et al.44 sub-
stantiate the assumption that the sum of MCPEs plus MCPA
in a product equals the overall hydroisomerisation of CHE.
Although hydroisomerisation is a reaction typically
catalysed by bifunctional catalysts containing strong acid
sites and strong hydrogenation sites, it is evident that the
catalytic action of the metal sites (palladium sites) over-
3.3. Isomerisation of CHE
The isomers of CHE don’t only include MCPEs in a
product, obtained via rearranging the 6-membered ring
cycloolefin to 5-membered ring cycloolefins (CHE ®
MCPEs) (Fig. 4), but also include the yield of MCPA pro-
duced via hydrogenation of a part of MCPEs (Fig. 5). Fig. 4
shows that MCPEs in a product using the current catalysts
are in the order:
Pd/HZSM-5(HF) > Pd/HZSM-5(HCl)
> Pd/HZSM-5
(3)
whereas Fig. 5 shows that MCPA in the product is in the or-
der:
Pd/HZSM-5 >> Pd/HZSM-5(HCl)
Fig. 5. Methylcyclopentane production using Pd/H-
ZSM-5 catalysts.
> Pd/HZSM-5(HF)
(4)
The sum of the quantities of MCPEs + MCPA produced
during the whole temperature range investigated using the
current catalysts gives the overall production of the 5-mem-
Fig. 4. Methylcyclopentenes production using Pd/H-
ZSM-5 catalysts.
Fig. 6. CHE isomerization products using Pd/H-ZSM-
5 catalysts.

1218 J. Chin. Chem. Soc., Vol. 54, No. 5, 2007
Aboul-Gheit
compensates for the action of the acid sites, although mo-
lecular rearrangement is a carbonium ion acid catalysed re-
action. The acid sites (both number and strength) in the
hydrohalogenated catalysts exceed those acquired by the
untreated Pd/H-ZSM-5 catalyst (Table 1); the latter cata-
lyst is more significantly active than the hydrohalogenated
ones (Fig. 6). The maximum overall isomers obtained us-
ing the Pd/HZSM-5 catalyst amounts to 64.9% at 250 °C,
whereas using the HF and HCl treated catalysts, this maxi-
mum amount rose to 57.0 and 55.7%, respectively, at 300
°C. This can be attributed to the lower deposited AlNF de-
bris in the zeolitic channels of the untreated Pd/HZSM-5
catalyst.
pared to the total dehydrogenation products which com-
prise as high as 22.2% using the Pd/HZSM-5 catalyst at
400 °C (Fig. 8), Subtraction of CHDEs (Figs. 7a and 7b)
from the total dehydrogenation products (Fig. 8) gives the
total aromatics production (Fig. 9). During the high tem-
perature region, CHDEs in product are in the catalyst order:
Pd/HZSM-5(HF) > Pd/HZSM-5(HCl)
> Pd/HZSM-5
(6)
whereas the dehydrogenation products and total aromatics
produced are in the catalyst order:
Pd/HZSM-5 > Pd/HZSM-5(HCl)
3.4. Dehydrogenation of CHE to CHDEs
> Pd/HZSM-5(HF)
(7)
CHDEs are intermediates in CHE dehydrogenation in
its way to be converted to benzene. CHDEs in a product are
relatively low, not exceeding 2.0% (Figs. 7a and 7b), com-
Since the order of CHDEs produced is in the reverse order
compared to producing benzene, it can be assumed that
Fig. 7a. 1,3-CHDE in product using Pd/H-ZSM-5 cata-
lysts.
Fig. 7c. Ratio of 1,3-/1,4-CHDEs vs. temperature.
Fig. 8. CHE dehydrogenation product using Pd/H-
ZSM-5 catalysts.
Fig. 7b. 1,4-CHDE in product using the Pd/H-ZSM-5
catalysts.

Hydrohalogenation of Pd/H-ZSM-5 Catalysts
J. Chin. Chem. Soc., Vol. 54, No. 5, 2007 1219
CHDEs conversion can be considered the rate determining
step in the overall dehydrogenation of CHE. The lower the
CHDEs level produced, the higher the production of ben-
zene.
1,3-CHDE isomer seem to require higher temperatures
than the un-conjugated ones in 1,4-CHDE for conversion.
3.5. Benzene and Alkylbenzene Production during
CHE Hydroconversion
1,3- and 1,4-CHDEs are very low at temperatures of
50-250 °C, beyond which they increase with a further in-
crease of temperature (endothermic reaction) to reach a
maximum then decrease with a further increase of tempera-
ture. Fig. 7a shows that 1,3-CHDE reaches a maximum of
1.3% at 350 °C, 0.7% also at 350 °C and 0.3% at 325 °C us-
ing the Pd/HZSM-5(HF), Pd/HZSM-5(HCl) and Pd/HZSM-
5 catalysts. However, the 1,4-isomer attains a maximum of
0.7% at 350 °C, 0.4% at 325 °C and 0.2% at 300 °C using
these catalysts, respectively (Fig.7b). Evidently, using the
Pd/HZSM-5 or Pd/HZSM-5(HCl) catalysts at the lower
temperatures, the 1,3-isomer is almost zero, whereas the 1,4-
isomer is slightly higher, such that the ratio of 1,3-/1,4-
CHDEs (Fig. 7c) amounts to zero up to 175-200 °C, where-
as, using the HF treated catalyst, this ratio ranges between
0.7 and 0.9 at 50-225 °C and increases to 1.1-2.3 at 300-400
°C, respectively: In other words, the formation of 1,3-
CHDE may be slower than the 1,4-isomer at the lower tem-
peratures, whereas it is faster at higher temperatures. A log-
ical alternative is that the conversion of the 1,4-isomer in a
product to benzene is somewhat slower than the 1,3-isomer
at the lower temperatures, but more rapidly converted at
higher temperatures. Accordingly, the higher temperature
region, which is thermodynamically favored for dehydro-
genating CHDEs to benzene, will be more favorable for the
1,3-isomer to become larger than twice the 1,4-isomer in
product. The conjugated single and double bonds in the
The total aromatics produced during CHE dehydro-
genation include benzene, toluene and xylenes. Once ben-
zene forms (Fig. 10a) on the catalyst surface, it can react
(alkylate) with a methyl fragment produced via cracking of
an adsorbed molecule on an acid site on the surface of the
H-ZSM-5 zeolite producing toluene (Fig. 10b). Both crack-
ing and alkylation occur via carbonium ion formation on
acid sites. Toluene can again be further alkylated to give a
mixture of ortho-, meta- and para-xylenes (Fig. 10c). Fig.
11 depicts the total production of alkylaromatics; i.e., tolu-
ene + xylenes, as a function of reaction temperature.
Fig. 10a. Benzene production using Pd/H-ZSM-5 cata-
lysts.
Fig. 10b. Toluene production using Pd/H-ZSM-5 cata-
lysts.
Fig. 9. Total aromatics production using Pd/H-ZSM-5
catalysts.

1220 J. Chin. Chem. Soc., Vol. 54, No. 5, 2007
Aboul-Gheit
3.5.1. Benzene Production
Since Pd is principally the active catalytic component
for CHE dehydrogenation, it may be assumed that the low-
est benzene production observed during the temperature
range 150-275 °C using the Pd/H-ZSM-5(HCl) catalyst can
be attributed to acquiring the lowest Pd dispersion (Table 1)
among the current catalysts (Fig. 10a).
Fig. 10a shows that benzene production is insignifi-
cant on all catalysts up to 150 °C, but increases in product
with increasing temperature up to 400 °C using the Pd/H-
ZSM-5 and Pd/H-ZSM-5(HCl) catalysts in a more or less
similar fashion, i.e., with some slowing down in the me-
dium temperature region. However, using the Pd/H-ZSM-
5(HF) catalyst, the increase of benzene is modest up to 250
°C, beyond which its increase with temperature is insignifi-
cant up to 400 °C. Evidently, benzene production is highest
at all reaction temperatures using the untreated catalyst by
virtue of acquiring the lowest extra-framework Al debris
(Table 2) and hence encountering the lowest diffusion re-
sistance. On the contrary, the Pd/H-ZSM-5(HF) catalyst
encounters the highest diffusion resistance due to acquiring
the largest quantity of debris. Using the Pd/H-ZSM-5(HCl)
catalyst, benzene production in general occupies an inter-
mediate activity due to acquiring an intermediate quantity
of the extra-framework Al debris.
3.5.2. Toluene Production
Although toluene production via benzene alkylation
(with methyl groups resulting from hydrocracking of vari-
ous hydrocarbon species) is an acid catalysed reaction, it
exhibits a distinct higher activity using the untreated Pd/H-
ZSM-5 catalyst (Fig. 10b) in comparison with the two hy-
drohalogenated catalysts which possess higher acid sites
number and strength than the untreated one. This can be
principally attributed to diffusion limitation by extra-frame-
work Al debris deposited in the pores of the hydrohalo-
genated catalysts which thus overcompensates the acidity
effect. The two hydrohalogenated catalysts exhibit almost
equal toluene yields since beginning at 50 °C up to 350 °C,
beyond which the toluene yield declines using the Pd/H-
ZSM-5(HF) catalyst faster than using the Pd/H-ZSM-
5(HCl) catalyst which can be attributed to a larger content
of debris deposited in the pores of the HF-treated catalyst
than the HCl-treated one.
3.5.3. Xylenes Production
Xylenes in product are also significantly higher using
the untreated Pd/H-ZSM-5 catalyst than on the hydrohalo-
genated ones (Fig. 10c). However, the higher acid sites
number and strength (Table 1) of the HF-promoted catalyst
compared to those of the HCl-promoted one exhibits some
more effectiveness for enhancing xylenes formation than
using the HCl-promoted one at temperatures up to 350 °C.
The second methyl group has more difficulty alkylating a
toluene molecule than the first methyl group to alkylate a
benzene molecule and hence, requires higher acidity. Nev-
ertheless, beyond 350 °C, the effect of the larger amount of
debris deposited in the pores of the Pd/H-ZSM-5(HF) cata-
lyst than in the Pd/H-ZSM-5(HCl) one seems to have over-
compensated the effect of the higher acidity of this catalyst,
whereby xylenes on the HCl-treated catalyst exceeded those
using the HF-treated catalyst. Comparing the data in Figs.
10b and 10c concerning the HF- and HCl-promoted cata-
lysts, the effect of molecular sizes of the produced alkyl
aromatics (toluene and xylenes) becomes more evident.
Toluene produced on the HF- and HCl-promoted catalysts
deviates from equality and declines in product beyond 350
°C, whereas the xylenes with their larger molecular sizes
Fig. 10c. Xylenes production using Pd/H-ZSM-5 cata-
lysts.
Fig. 11. Hydrocracked product of cyclohexene using
Pd/H-ZSM-5 catalysts.

Hydrohalogenation of Pd/H-ZSM-5 Catalysts
J. Chin. Chem. Soc., Vol. 54, No. 5, 2007 1221
decline faster on the HF-promoted catalyst (more diffusion
restricted) than on the HCl-promoted one, although the
xylenes were higher on the HF-promoted catalyst during
the lower temperature range where the diffusion effect is
not so significant.
valuable liquid yield.
Received December 25, 2006.
3.6. Hydrocracking Reactions
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CHE hydrogenation is a metal-catalysed reaction at
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