Influence of acidity and pore geometry on the product distribution in the hydroisomerization of...

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Applied Catalysis A: General 288 (2005) 104–115

Influence of acidity and pore geometry on the product

distribution in the hydroisomerization of

light paraffins on zeolites

Rafael Roldan a, Francisco J. Romero a,*,Cesar Jimenez-Sanchidrian a,**,

Jose M. Marinas a, Juan P. Gomez b

a Departamento de Quımica Organica, Universidad de Cordoba, Campus de Rabanales,

Edificio Marie-Curie, Ctra. Nnal. IV, km 396, 14014 Cordoba, Spainb Centro de Tecnologıa Repsol-YPF, Ctra. Nnal. V, km 18, 28931 Mostoles, Spain

Received 4 January 2005; received in revised form 19 April 2005; accepted 20 April 2005

Available online 2 June 2005

Abstract

Several platinum supported zeolites with different topologies [beta (SiO2/Al2O3 = 25, 75, 150), USY(60), mordenite(20, 90), ferrierite(55)

and ZSM-5(80)] have been tested as catalysts for the hydroisomerization of n-hexane, cyclohexane and n-heptane. Pt/BETA(25) provided the

best results to convert C6 and C7 with high conversion and selectivity to isomers. The distribution of monobranched and multibranched

isomers with different sizes is influenced by the specific pore opening of each catalyst. All the samples showed an insufficient metal sites to

acid sites ratio, which promoted cracking as a consequence of further reactions of monobranched and multibranched isomers in the acid sites.

The transformation of 1-hexene was compared to that of n-hexane to evaluate the effects of a higher intermediate alkene concentration.

Considerations regarding n-hexane cracking mechanisms were also done. These unbalanced bifunctional catalysts promote the dimerization-

cracking mechanism. In fact, this was the prevailing cracking mechanism rather than classical b-scission for all the samples except for

Pt/BETA(25), for which some explanations are given. Our results suggest that the conversion is an acidity dependent parameter, whereas the

selectivity only depends on the conversion obtained for each catalyst and therefore it cannot be controlled by tailoring the catalyst acidity.

By comparison of different reactions performed by either the pure alkanes or their mixtures, cyclohexane was found to act as an inhibitor.

However, no changes in the product distribution were observed.

# 2005 Elsevier B.V. All rights reserved.

Keywords: Supported-metal catalysts; Zeolites; Isomerization; Cracking mechanism; Beta-scission; Dimerization; n-Hexane; n-Heptane; Cyclohexane; 1-

Hexene

1. Introduction

The hydroisomerization of light paraffins is a deeply

studied process with high industrial interest since the

obtained branched alkanes are used as octane boosters in

* Corresponding author. Tel.: +34 957 212 065/218 638;

fax: +34 957 212 066.

** Co-corresponding author.

E-mail addresses: [email protected] (F.J. Romero), [email protected]

(C. Jimenez-Sanchidrian).

0926-860X/$ – see front matter # 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.apcata.2005.04.029

gasoline [1]. Thus, isoparaffins are considered as an

alternative to the use of oxygenate and aromatic compounds,

whose maximum contents are subjected to strict regulations

in order to protect the environment.

Due to environmental concerns, platinum supported

chlorinated aluminas are not the best choice as catalysts for

isomerization processes because they require continuous

regeneration with chlorine. In this sense, zeolites, as in many

other reactions, have attracted a great interest due to their

useful properties, such as acidity, shape selectivity and stabi-

lity, as well as the availability of many different structures.

R. Roldan et al. / Applied Catalysis A: General 288 (2005) 104–115 105

Scheme 1. Illustration of some reaction pathways for the hydroisomerization of n-hexane over a bifunctional catalyst according to the classical unimolecular

mechanism. 1 and 2 indicate two possible successive isomerization reactions, while 3 is a possible cracking reaction.

These catalysts are bifunctional, i.e. they consist of a

metal supported on a zeolite, since the reaction mechanism

requires the dehydrogenation of the initial alkane to form an

intermediate alkene. This alkene can then proceed through a

carbocationic intermediate either to yield the isomerized

products or to undergo cracking through a b-scission to give

unwanted gaseous products (Scheme 1) [2,3]. For this kind

of bifunctional catalysts, Giannetto et al. [4] estimated an

optimum in the number of acid sites per available platinum

atom of 6. If this ratio is exceeded, the cracking reaction will

be favoured. Moreover, those catalysts without a proper

balance between the metallic and the acid functions are

expected to follow an alternative mechanistic pathway

involving bimolecular intermediates [2].

In general, catalytic activity and selectivity in this

reaction depend on the acidity and the pore structure of the

zeolites. Chica and Corma [5] reported the same isomeriza-

tion selectivities by using two different ways to obtain the

same conversion, varying either the temperature or the

contact time. Therefore, for a particular catalyst, there is an

unequivocal correspondence between selectivity and con-

version. When the hydro/dehydrogenation function is not

limiting, the activity of the zeolites is related to their acidity,

and so it would be possible to choose a specific catalyst by its

acidic properties in order to achieve the desired conversion

under certain conditions. Then, if acidity and, in turn,

conversion are fixed, and different catalysts are compared at

the same conversion, the differences in selectivity to isomers

must be explained in other terms apart from acidity. In this

sense, Patrigeon et al. [6,7] reported that the selectivity is

clearly governed by the pore structure and not by the acidity.

According to Kung et al. [8] the selectivity to cracking is

insensitive to differences in the acid strength among

different catalysts, whereas the differences found in the

activation energies were ascribed to variations in the

adsorption heats for n-hexane, i.e. a parameter dependent

on the zeolitic structure. Recently, Smirniotis et al. [9]

compared the selectivity to isomers of zeolites with

enhanced activity to that of their parent materials in the

hydroisomerization of n-heptane, and found that it was not

affected by the acidity or, in other words, by the Si/Al ratio.

Furthermore, they assert that the maximum isomer yield for

a catalyst is obtained when the metal and acidic functions of

the catalyst are well balanced and that it is not possible to

increase it beyond that maximum by modifying the catalyst

acidity. They admit, however, that the conversion can be

affected by other parameters, such as the generation of

mesopores by acid leaching, but this also affects the

accessibility of the acid sites, and in turn the acidity. Similar

results concerning selectivity have been also found for the

transformation of butanes [10].

In this work, a comparison of the performance of

different platinum supported zeolites in the hydroisome-

rization of light paraffins has been done in order to relate

catalyst properties to activity, as well as to confirm the

explicit dependence of the reaction selectivity. Zeolites

covering a wide spectrum of pore geometries have been

selected to examine the issue of shape selectivity and its

relationship with the catalytic activity. All the catalysts were

tested in the transformation of paraffins (n-hexane,

cyclohexane and n-heptane) and their mixtures, as well as

an olefin (1-hexene). The product distributions have been

studied in detail to examine the effects of hydrocarbon

branching and type of cracking mechanism.

2. Experimental

The catalysts used in this work consist of platinum

supported by the incipient wetness impregnation method

(0.5 wt.%) on the calcined form (in air at 580 8C) of differ-

ent zeolites purchased from Zeolyst Int., viz. BETA(25)

(CP814E), BETA(75) (CP811E-75), BETA(150) (CP811E-

150), MOR(20) (CBV21A), MOR(90) (CBV90A), USY(60)

(CBV760), FER(55) (CP914), and ZSM-5(80) (CBV8014),

where the numbers in parentheses denote their SiO2/Al2O3

ratio, as well as a BETA(25) zeolite dealuminated with an

oxalic acid solution (0.5 M), named BETA(25)-OA [11].

Their characterization by different techniques, such as

elemental analysis, XRD, BET method, adsorption iso-

therms of pyridine in the liquid phase and TPDs of pyridine

adsorbed in the gas phase, both to determine the acidic

properties, as well as TPR and hydrogen chemisorption to

study the metallic phase has been already reported elsewhere

[12,13]. Solid state MAS 27Al NMR spectra were recorded

for MOR(20) and MOR(90) at room temperature in a Bruker

ACP-400 spectrometer (9.4 T) at a spin rate of 5.5 kHz. A

resonance frequency of 104.2 MHz, a recycle delay of 0.5 s

and a number of scans of 6000 were applied. Chemical shifts

were measured relative to Al(H2O)63+ (0 ppm).

R. Roldan et al. / Applied Catalysis A: General 288 (2005) 104–115106

Fig. 2. Yields (wt.%) to monobranched (*) and dibranched isomers (*)

and cracking products (!) vs. the total conversion for the hydroisomeriza-

tion of n-hexane (65 wt.%), cyclohexane (20 wt.%) and n-heptane

(15 wt.%) over Pt/BETA(25).

The catalytic tests were performed in a fixed-bed

continuous flow reactor (10 mm i.d.) connected by a

thermostated pipe to a gas chromatograph (Fisons 8000;

capillary column: methyl silicone 100 m � 0.25 mm i.d.

fused silica; oven program: 60–115 8C at 2 8C min�1). The

reactions were carried out under different conditions in order

to obtain a wide range of conversions: temperatures from

225 8C to 300 8C; atmospheric pressure; catalyst weight:

0.5–1.0 g; space velocities (WHSV): 1.9–3.7 h�1; carrier gas:

H2 (60 mL min�1) and H2/hydrocarbon molar ratio: 4–8.

The catalysts were pre-treated in the reactor by

calcination in oxygen followed by reduction in hydrogen,

both at 20 mL min�1 and 400 8C. The reactants used in this

work were pure hydrocarbons, i.e. n-hexane (nC6),

cyclohexane (cC6), n-heptane (nC7) or 1-hexene, and

ternary mixtures of n-hexane (65 wt.%), n-heptane

(15 wt.%) and cyclohexane (20 wt.%), as well as binary

mixtures of them with the same weight ratio as in the ternary

mixture.

3. Results and discussion

The hydroisomerization of the ternary hydrocarbon

mixture (nC6, cC6 and nC7) on the platinum-supported

zeolites studied gives rise to various n-hexane and n-heptane

isomers (monobranched and dibranched), methylcyclopen-

tane and, in some cases, benzene, thus increasing the octane

number of the mixture, as shown in Fig. 1. Among the

catalysts tested, platinum supported BETA(25) zeolite

exhibits the highest conversion and a high selectivity to

isomers (liquid products). Consequently, the yield to cracked

products (all of them gaseous except n-pentane and

isopentane) has been low on this catalyst.

Over a wide range of conversions, mono- (MB) and

multibranched (MuB) isomers and cracking products (CP)

Fig. 1. Total conversion (wt.%) (grey bar), research octane number (RON)

increment (%) (black bar) and yield (wt.%) to liquid products (C5+) (white

bar) for the hydroisomerization of n-hexane (65 wt.%), cyclohexane

(20 wt.%) and n-heptane (15 wt.%) over different Pt/zeolite catalysts.

Catalyst weight: 1 g; T = 275 8C; WHSV = 3.7 h�1; P = 1 bar.

exhibit a distribution similar to that of Pt/BETA(25) (Fig. 2).

Monobranched isomers appear from low conversions and

their fraction increases up to a point where multibranched

isomers and cracking products start to be significant. This

behaviour, also shown by all the other catalysts studied (not

shown), is one of the three possibilities depending on the

ratio between metallic and acid sites in the catalyst [4],

following the typical scheme for a platinum/acid site ratio

around 0.03:

n-paraffinÐðMB þ MuBÞ!CP

More in detail, in Fig. 3 both the nC6 and the nC7 isomers

compositions for the hydroisomerization of the multi-

component feed are separately plotted against n-hexane and

n-heptane conversions, respectively. A similar distribution

has been reported by Blomsma et al. [3] for n-heptane, using

different palladium contents on beta zeolite. The reactivity

of alkanes increases with the chain length due to enhanced

sorption properties; indeed, n-heptane provides higher

conversions under the same conditions, although in turn

much more cracking than n-hexane. Consequently, the

maximum in the curves of isomers formation is shifted to

lower conversions as the chain length increases, as seen for

instance for Pt/ZSM-5(80). However, the accurate contribu-

tion of each reactant to cracking cannot be calculated when

they are mixed and, therefore, the cracking products are

omitted in these plots. As shown in Fig. 2, monobranched

isomers predominate over the whole range of conversions.

Their formation increases together with that of multi-

branched isomers. The reaction scheme proposed above for

these catalysts describes both of them as primary products.

At a certain conversion – around the maximum of the curve –

they both start to react significantly to give secondary

products by cracking. Accordingly, the metallic function

would not be active enough to hydrogenate all the

intermediate alkenes before they reach a second acid site


and react there again. For our samples, the ratio between the

acid and metallic sites is higher than that reported as

optimum [4]. The ideal situation, i.e. a number of six acid

sites per available platinum atom (nPt=nHþ = 0.17), would

allow the paraffin to react in a sequential scheme and, in

turn, to decrease the cracking:

n-paraffinÐMBÐMuB!CP

Evidences on this failure to balance the bifunctionality of

the catalyst, caused by a deficient deposition of platinum on

the samples, as well as its implications in the reaction are

discussed later.

In order to obtain more information and clarify which

functions affect the catalytic activity and selectivity, the

comparison among different catalysts must be carried out at

the same conversions because both properties are mutually

dependent. Thus, the results obtained for several catalysts

based on zeolites with different topologies, whose channels

dimensions are given in Table 1, are shown in Fig. 4.

Assuming that the hydrogenation function is limiting in

these samples, we still can compare them because, as will be

shown later, all of them are unbalanced in a similar degree.

Fig. 3. n-Hexane (left) and n-heptane (right) isomers distribution vs. partial n-alka

and n-heptane (15 wt.%) with different Pt/zeolite catalysts. n-Hexane isomers: 2-M

MC6 (&), 3-MC6 (^), 2,2-DMC5 (*), 2,4-DMC5 (*), 2,3-DMC5 (&), 3,3-D

Thus, the differences in selectivity can be related to their

pore geometry. As can be seen, BETA(25) and USY(60),

which are large pore zeolites (12 membered-rings), give

similar selectivities to isomers at the same overall

conversion, independently of the acidity and temperature.

Actually, both solids show not only different numbers of acid

sites but also very diverse acid sites strength distributions

[12]. Moreover, the same zeolite, BETA(25), dealuminated

in order to change its acidity (in both number and strength of

acid sites), BETA(25)-OA, also gives a similar selectivity.

All these results are in agreement with those reported by

Smirniotis et al. [9]. Mordenites (also with 12 MR pores) are

different to beta and faujasite because their channels possess

side pockets which are able to prolong the diffusion of the

intermediates, thus favouring their cracking [14–16]. In fact,

both mordenites are less selective towards isomerization

than beta and faujasite, with independence of acidity

(Fig. 4). On the other hand, medium pore zeolites, with 10

membered-rings, ferrierite and ZSM-5, yield less isomers

than beta and USY zeolites, even though the acidities of

ZSM-5 and USY are not very different. Furthermore, the

maximum in the curve of iC7 formation appears at around

50% for Pt/ZSM-5, while it does at ca. 70% for both Pt/

ne conversion after reaction of n-hexane (65 wt.%), cyclohexane (20 wt.%)

C5 (!), 3-MC5 (5), 2,2-DMC4 (*), 2,3-DMC4 (*); n-heptane isomers: 2-

MC5 (5), 2,2,3-TMC4 (!).


Fig. 3. (Continued ).

BETA(25) and Pt/BETA(75) (Fig. 3), which is consistent

with the fact that the selectivity is determined by the pore

geometry (see Section 1). The smaller size of the channels in

the MFI and FER structures does not allow the primary

reaction products to diffuse easily and, in consequence, they

undergo successive reactions, thus reducing the selectivity to

isomers. The difficulties of these hydrocarbons to diffuse

through the MFI structure have been studied by Choudhary

et al. [17–19].

Accordingly, significant differences must be also found

when the ratios of mono- and multibranched isomers formed

Table 1

Pore dimensions and acidic and metallic properties of the catalysts

Sample Topology Channels dimensions Aciditya

(mmol g�1)

Pt/BETA(25) BEA (7.6 � 6.4 A), circular 5.5 A 1010

Pt/BETA(25)-OA BEA (7.6 � 6.4 A), circular 5.5 A 700

Pt/BETA(150) BEA (7.6 � 6.4 A), circular 5.5 A 690

Pt/USY(60) FAU circular 7.4 A, (7.4 � 6.5 A) 670

Pt/MOR(20) MOR (7.0 � 6.5 A), (5.7 � 2.6 A) 830

Pt/MOR(90) MOR (7.0 � 6.5 A), (5.7 � 2.6 A) 640

Pt/FER(55) FER (5.4 � 4.2 A), (4.8 � 3.5 A) 140

Pt/ZSM-5(80) MFI (5.6 � 5.1 A), (5.5 � 5.1 A) 550a Spectrophotometric method.b TPD method.

in zeolites with different channel systems are compared

(Fig. 4). The thermodynamic equilibrium ratio at tempera-

tures below 300 8C for n-hexane and n-heptane isomers is

close to 1 [5]. However, inside the zeolites this ratio is

usually not reached due to pore restrictions on the diffusion

of the multibranched isomers and the formation of their

reaction intermediates. It is known that the hydrocarbons

sorption capability increases with molecular branching,

whereas their diffusivity decreases [20]. Therefore, the

formation of multibranched isomers is more difficult than

that of the monobranched ones, and, if the former were

Acidityb

(mmol g�1)

Acid sites (%) (py TPD) Dispersion

(%)

nPt=nHþ

Weak Medium Strong

910 32 52 16 52 0.013

386 10 19 71 – –

74 37 27 36 13 0.005

254 8 40 52 76 0.029

1158 20 35 45 57 0.018

391 43 35 22 64 0.026

12 0 0 100 49 0.090

212 10 29 61 70 0.033


Fig. 4. Selectivity to isomers (wt.%) (left black) for different Pt/zeolite catalysts compared at the same conversion (wt.%) (left grey) of nC6, cC6 and nC7, and

their population of acid sites (left white) measured by adsorption of pyridine (normalized taking that of BETA(25) as 100%). Mono/multibranched isomers

ratios (not percentages) are given for iC6 (right grey), iC7 (right black) and for both (iC6 + iC7) (right white). T = 225–275 8C; WHSV = 1.9–3.7 h�1; P = 1 bar.

produced, they would crack more easily. Different pore

systems will give rise to the formation of different isomers.

Compared to large pore zeolites, high mono/multi-branched

isomers ratios are shown by medium pore zeolites, thus

confirming the high reactivity of the bulkier multibranched

isomers in these pores. Once they are formed in the 10 MR

pores, probably in the pore intersections, they diffuse out

very slowly, having many opportunities to crack into smaller

molecules. Also, the dealuminated zeolite, BETA(25)-OA,

with half of the acidity of the non-dealuminated sample, still

exhibits similar MB/MuB ratios to the parent zeolite, since

its pore system remains unaltered. Finally, as shown above,

mordenites are unique since the MB/MuB ratios for them are

lower than those for BETA and USY. The longer time that

monobranched isomers spend diffusing through their

channels makes a second transformation to dibranched

ones more likely – and this is why the ratio is lower –, as well

as a subsequent scission to cracked products, which results

in a lower selectivity to isomers.

In this reaction, the ratios of the fractions of more or less

bulky isomers characterize the porous solids. The following

Fig. 5. 2-MC5/3-MC5 and 2-MC6/3-MC6 ratios for different Pt/zeolite catalysts v

cC6 and nC7: Pt/BETA(25) (*), Pt/BETA(75) (*), Pt/MOR(20) (!), Pt/MOR

parameters are defined, always dividing the less bulky

isomers by the bulkier ones [6]: the 2-MC5/3-MC5 ratio

and R = 2,3-DMC4/2,2-DMC4 for nC6 isomers, and the

2-MC6/3-MC6 ratio and R0 = (2,3-DMC5 + 2,4-DMC5)/

(2,2-DMC5 + 3,3-DMC5 + 2,2,3-TMC4) for nC7 isomers.

The 2-MC5/3-MC5 and 2-MC6/3-MC6 ratios are plotted

against nC6 or nC7 conversions, respectively, in Fig. 5. As

conversion increases, the experimental ratios approach the

thermodynamic equilibrium (1.6 and 1.0, respectively).

Patrigeon et al. [6] reported that 3-MC6 should form more

likely than 2-MC6 although their ratio approaches that of

equilibrium (1.0) due to methyl rearrangements. Therefore,

the deviations from this equilibrium value must result from

the steric hindrance of different isomers in the zeolitic

channels. Our catalysts also give different results depending

on their pore system. Thus, for large pore zeolites, the

2-MC5/3-MC5 ratio tends to 1.6 and the 2-MC6/3-MC6

ratio to 1.0, which correspond to the values at the

thermodynamic equilibrium. However, for medium pore

zeolites, these ratios, even following a decreasing trend, are

higher than those for large pore zeolites, probably due to the

s. nC6 and nC7 conversions, respectively, in the hydroisomerization of nC6,

(90) (5), Pt/USY(60) (&), Pt/FER(55) (&), Pt/ZSM-5(80) (^).


shape-selectivity provided by these catalysts. R and R0 (not

shown) have higher standard deviations due to the small

fraction of dibranched isomers in the products. They

approach in a similar way to the equilibrium values (0.3

and 0.8, respectively) with marked differences between 12

MR and 10 MR catalysts.

As mentioned above, Pt/MOR(20) is a catalyst with a

particular behaviour because its great acidity causes a strong

deactivation in the early stages of the reaction. The 2-MC6/

3-MC6 ratios for the fresh catalysts (plotted in Fig. 5) did not

match those obtained for the same solids after some hours in

stream. Instead of a flat line, the aged catalysts give rise to an

increasing curve with the conversion, starting from a much

higher ratio (from 1.5 at a conversion of 11.8% up to 2.0 at

49.7%). The adsorption of several molecules, mainly coke

promoters, on the acid sites of MOR(20) reduces the

effective pore diameter and hinders the hydrocarbons

diffusion through the channels so that the terminal branching

is favoured, as it occurs in medium pore zeolites [21].

Actually, this explains the increase in the MB/MuB ratio for

the deactivated catalyst and the lower selectivity to isomers

presented by this catalyst compared to Pt/MOR(90), which

undergoes much less deactivation (Fig. 4). The increase of

the 2-MC6/3-MC6 ratio with the time on stream can be due

to a progressive poisoning of the catalyst. Alternatively, it

has been reported that channel blockage by extraframe-

work aluminium species is the reason to find a low

selectivity for bulkier isomers, which can be improved by

the generation of mesopores via acid leaching [9,22,23]. In

addition, it is known that this extraframework aluminium

promotes coking [24]. The 27Al MAS NMR spectra for

both mordenites are shown in Fig. 6, confirming the

existence of such a large amount of extraframework

aluminium (octahedral Al signal at 0 ppm) in MOR(20)

(43%), but not in MOR(90) (4%). Therefore, the low

selectivity in mordenites can be ascribed to the hampered

diffusion through their pores, MOR(20) showing an

additional ease to form coke due to its great framework

and extraframework acidity.

According to the classical unimolecular mechanism of

hydroisomerization, the equilibrium concentration of

Fig. 6. 27Al MAS NMR spectra for MOR(20) and MOR(90) zeolites.

alkenes is very small at the temperatures used. However,

with zeolitic catalysts possessing acidity that cannot be

countered by their hydrogenation–dehydrogenation activity,

bimolecular reactions of intermediate alkenes may be

significant [2,3]. So, catalysts with a low metal sites to acid

sites ratio are expected to show an important contribution of

the dimerization-cracking mechanism. Strong acid sites are

suggested to catalyze this dimerization while weak and

moderate acid sites are responsible for isomerization [25].

In order to obtain further information about this process,

we compared the transformation of n-hexane to that of

1-hexene.

Table 2 shows the results of the hydroisomerization of n-

hexane with different Pt/zeolite catalysts, compared to those

for the 1-hexene reaction, presented in Table 3. In agreement

with our previous results, Pt/BETA(25) is the most active

catalyst for the transformation of n-hexane, followed by Pt/

MOR(20), which does not show such a strong deactivation in

absence of cyclohexane. The results of Pt/MOR(20) for the

hydroconversion of n-hexane, as well as those for the other

metal/zeolites, are comparable to those reported in the

literature [26–34]. Table 1 also displays the metallic

dispersion (%) obtained by hydrogen chemisorption as well

as the metallic/acid sites molar ratio calculated from the

acidity determined elsewhere [12] by the adsorption

isotherm of pyridine in the liquid phase. This ratio takes

into account just the platinum atoms existing in the surface

of the particles. 1-Hexene reacts to produce n-hexane, iso-

hexanes and cracking products (C5�). With mordenites, C7

iso- and n-paraffins are formed, through dimerization-

cracking, and also C4–C6 alkenes were found. Conversion is

affected in a different way for each catalyst when feeding

with 1-hexene. However, although the conversion has been

previously defined as a function of the reactant, now the

most suitable parameters to establish a comparison between

these two series of data – alkane or alkene feed – are the

yields to isohexanes (YiC6), cracking products (YC5�) or the

sum of both (YiC6+C5�). We intend to compare the relative

catalytic activities among catalysts and therefore the

experiments were not carried out at constant conversion.

The yield to isomers is enhanced for Pt/USY(60) and Pt/

FER(55), especially for the latter in relative terms. Cracking

increases at the same rate as isomerization for Pt/USY,

though it is still very low, while for Pt/FER no cracking

products are present in any case. Pt/BETA(150) does not

show a significant conversion, while the more acidic Pt/

BETA(25) maintains the yield to isomers but increases the

yield to cracking products, that is, its conversion has

increased to produce mainly cracking products. This is

reasonable if we assume that a conversion higher than that

obtained for nC6 (70.7%) implies that the cracking

mechanism is thermodynamically favoured, as seen in

Fig. 2 for this catalyst. Consequently, the further – in

comparison – transformation of 1-hexene proceeds to form

cracking products from multibranched isomers, which are

found to be favoured too but less, and monobranched ones.


Table 2

Catalytic results in the hydroisomerization of n-hexane

Feed: nC6 Pt/BETA(25) Pt/BETA(150) Pt/USY(60) Pt/MOR(20) Pt/MOR(90) Pt/FER(55) Pt/ZSM-5(80)

C1 0.1 0.1 0.1

C2 1.3 0.01 0.1 0.2

C3 0.01 4.5 0.1 2.1 0.5 0.3

iC4 0.9 0.1 3.2 0.3 0.2

nC4 2.1 0.5 0.3 0.2

iC5 0.01 1.0 0.01 1.8 0.3 0.2

nC5 0.02 0.8 0.1 0.5 0.2 0.2

2,2-DMC4 0.03 8.1 0.6 7.5 1.6 0.6

2,3-DMC4 0.1 8.0 1.2 7.0 5.5 1.2

2-MC5 1.3 26.7 1.5 8.2 24.7 23.4 4.4 32.9

3-MC5 1.2 17.9 0.8 6.1 15.7 15.0 2.3 17.5

nC6 97.3 28.4 97.5 82.8 36.9 52.3 93.3 46.6

XnC6 (%) 70.7 0.0 14.5 62.3 46.5 3.6 51.9

Yield iC6 (%) 59.7 – 14.2 53.8 44.5 3.6 50.8

Yield C5� (%) 11.0 – 0.3 8.5 2.0 0.0 1.1

Yield iC6+C5� (%) 70.7 – 14.5 62.6 46.5 3.6 51.9

Hydrogenolysis 4.6 (42) – 0.03 (9) 0.9 (11) 1.2 (60) – 0.0 (0)

b-Scission 4.6 (42) – 0.1 (30) 2.2 (26) 0.5 (25) – 0.3 (27)

Dimerization-cracking 1.8 (16) – 0.2 (61) 5.4 (63) 0.3 (15) – 0.8 (73)

The contributions to the different cracking mechanisms are given in yield (wt.%), with the total percentage in parentheses. Catalyst weight: 1 g;

WHSV = 3.7 h�1; T = 275 8C; P = 1 bar.

This agrees with Smirniotis et al. [9] who assert that the

maximum isomer yield cannot be controlled. Something

similar occurs for Pt/MOR(20) and Pt/ZSM-5(80), with a

higher overall yield, YiC6+C5�, in the 1-hexene reaction, but

Table 3

Catalytic results in the hydroisomerization of 1-hexene

Feed: 1-hexene Pt/BETA(25) Pt/BETA(150) P

C1 0.3

C2 2.8

C3 9.6

iC4 1.9

nC4 4.7

iC5 2.1

nC5 1.4

2,2-DMC4 9.6

2,3-DMC4 10.0

2-MC5 22.2 0.1 1

3-MC5 16.5 1.1 1

nC6 1.5 18.9 98.6 6

McC5

nC7 + iC7

Butenes

Pentenes

Hexenesa

1-Hexene 98.5

X1-hexene (%) 100.0 100.0 10

Yield iC6 (%) 58.6 1.2 3

Yield C5� (%) 23.5 0.0

Yield iC6+C5� (%) 81.5 1.2 3

Hydrogenolysis 10.5 (45) –

b-Scission 9.7 (41) –

Dimerization-cracking 3.2 (14) –

The contributions to the different cracking mechanisms are given in yield (

WHSV = 3.7 h�1; T = 275 8C; P = 1 bar.a 1-Hexene not included.

with even higher loss of selectivity, since not only the

cracking increases but also the isomerization decreases. Pt/

MOR(90) follows the same trend without experiencing such

total yield increment, which could be ascribed to the

t/USY(60) Pt/MOR(20) Pt/MOR(90) Pt/FER(55) Pt/ZSM-5(80)

0.1

0.2

0.03 6.3 1.7 8.5

0.03 12.9 4.5 5.8

0.06 3.3 1.5 7.7

0.1 9.0 3.9 2.5

0.03 3.1 1.3 8.6

2.2 5.3 0.6 0.2

4.3 4.8 3.4 0.4

8.9 17.0 16.5 14.3 16.0

3.4 10.8 9.8 7.8 6.2

0.3 26.4 51.5 77.9 43.5

0.2 0.4

0.6 1.1

0.1

0.2

2.8

0.3

0.0 100.0 99.7 100.0 100.0

9.0 37.9 30.3 22.1 22.9

0.5 34.9 12.9 0.0 33.5

9.5 72.8 43.2 22.1 56.4

0.0 (0) 1.2 (3) 0.0 (0) – 0.0 (0)

0.06 (13) 6.3 (18) 1.7 (12) – 8.3 (25)

0.4 (87) 28.0 (79) 12.3 (88) – 24.4 (75)

wt.%), with the total percentage in parentheses. Catalyst weight: 1 g;


deactivation caused by the olefin. Thus, none of the platinum

supported samples fulfils the required condition of the metal/

acid balance described by Giannetto et al. [4], since all of

them underwent an increase in conversion when using the

alkene as feed. In other words, the metal sites are not

supplying all the possible alkenic intermediates by

dehydrogenation of all the available n-hexane molecules.

This is the reason why conversion increases when 1-hexene

is fed. A possible explanation for the existence of such

unfavourable metal to acid sites ratio might be the

seggregation of platinum particles in the reduction step,

thus resulting in the formation of larger clusters with smaller

surfaces [35]. In addition, the available metallic content in

all the catalysts – see the nPt=nHþ ratios below 0.03 in most

cases – was effectively inefficient to rehydrogenate all the

alkenic intermediates before they crack. Particularly, the Pt/

BETA(150) catalyst possesses a low acidity which is

unbalanced to the metallic function, thus resulting in a

negligible conversion whichever the feed tested. The

different enhancements in total yield found for the catalysts

depend on how far each catalyst is from reaching the

equilibrium. This explains that the higher changes are found

for the catalysts with lower n-hexane conversions. On the

other hand, the differences in selectivity found between both

feeds are correlated with the conversion levels achieved, as

explained at the beginning of this discussion, and therefore

there is no explicit relationship between them and the alkene

concentration.

With regards to the branching of the isomers in the 1-

hexene reaction, the MB/MuB as well as the 2-MC5/3-MC5

and the 2,3-DMC4/2,2-DMC4 ratios are in agreement with

those previously found in the n-hexane reaction. All these

ratios or selectivities to isomers with different volumes can be

reasoned in terms of conversion level and pore geometry, as

explained before. For instance, the very low formation of

isomers, especially multibranched ones, for the USY(60)

zeolite when comparing to the BETA(25) sample, is only

due to the lower total conversion that USYexhibits at 275 8C,

but it is still higher than that in the n-hexane reaction.

The contribution of different mechanisms to the

transformation of paraffins was estimated by Blomsma

et al. [2] for the cracking of n-heptane assuming that b-

scission is not the only possible mechanism but also a

bimolecular one. In the last case, an intermediate alkene

reacts with a carbocation to give a dimeric C14 reaction

intermediate (possibly in a pore intersection) which under-

goes isomerization and finally cracking. Hydrogenolysis is

the only way to generate C1 and C2 fragments because their

formation involves unstable primary carbocations. In

consequence, C6 and C5 fragments will not be formed by

b-scission. On the contrary, they can be formed by a

dimerization-cracking mechanism as well as by hydroge-

nolysis. As classical mechanism produces equimolar

amounts of C3 and C4 fragments, they supposed that the

excess of C4 over C3 was due to the bimolecular mechanism

and therefore that all the C3 fragments came from b-scission.

The situation for n-hexane is similar, being not possible to

discriminate the origin of C3 fragments. However, as these

authors, we can assume that all the C3 molecules come from

b-scission, given that the rate of this mechanism is much

faster [2]. On the other hand, the total C4 and C5 produced

by dimerization-cracking will be C4–C2 and C5–C1,

respectively, whereas all the C7 found comes obviously

from this mechanism. Therefore, the yield to hydrogenolysis

products is equal to 2(C1 + C2), the yield to b-scission

products is equal to C3 and the yield to dimerization-

cracking products is (C4–C2) + (C5–C1) + C7. The molar

yields have been converted to weight yields, Yx, which are

given in Tables 2 and 3. Similar calculations have been also

performed by Onyestyak et al. [36] for the hydroconversion

of cyclohexane and methylcyclopentane. In opposition to our

scheme, they consider that b-scission can lead to C4 and C5

fragments, or in other words, they lump the hydrogenolysis

and the b-scission together. Notwithstanding, C7 fragments

do not appear in the Onyestyak study, where they found that

the dimerization-cracking mechanism prevails rather than

the b-scission mechanism in large pore zeolites, but not in

those with medium pores. According to Tables 2 and 3,

dimerization-cracking is the main mechanism for cracking of

n-hexane in all the catalysts except for Pt/BETA(25),

although Pt/MOR(90) also produces more b-scission but

only with n-hexane as feed. Blomsma et al. [2] also reported

a very high contribution of b-scission compared to the

bimolecular mechanism for a Pd/Beta catalyst. Evidently, as

seen for Pt/ZSM-5, the pore dimensions are not restrictive for

the formation of the bimolecular intermediate, which can

happen by addition of the alkene to a carbocation in the

intersection of channels [3]. This is not in contradiction with

the fact that the formation of multibranched isomers is

hindered in medium pore zeolites because, if they were

formed, they would probably crack, thus being absent in the

reaction products. Other reasonable way to form this

intermediate in medium pore zeolites would involve a

scheme of pore-mouth catalysis, which has been discussed

by other authors for one-dimensional medium pore

materials [37–40]. Therefore, if the space inside both

kinds of pore systems, i.e. 10 and 12 MR channels, is enough

to form the dimeric intermediate, other reason must be

involved in the differences found between beta and the rest of

zeolites. We can also observe that hydrogenolysis is much

more significant for Pt/BETA(25). Some arguments are given

later.

Both Pt/Mordenites, mainly MOR(20), gradually deac-

tivate with time on stream in the reaction with n-hexane but

with 1-hexene as reactant this deactivation is very fast. In the

1-hexene reaction, other alkenes (branched alkenes) appear

among the reaction products with Pt/MOR(90). With Pt/

MOR(20) these alkenes are not present in the initial stages of

the reaction (see the data of the first run in Table 3) but in

further analysis, after the initial deactivation, their formation

increases, whereas the formation of the rest of products

decreases, as can be seen in Fig. 7. The strong acidity


Fig. 7. Yield to different products in the hydroconversion of 1-hexene over

Pt/MOR(20): C1–C5 (*), iC6 (*), nC6 (!), alkenes (1-hexene not

included) (5), 1-hexene (&), C7 (&). Catalyst weight: 1 g; T = 275 8C;

WHSV = 3.7 h�1; P = 1 bar.

previously referred for this zeolite favours the formation of

coke promoters which adsorb in the catalyst active sites and

platinum particles thus preventing the hydrogenation of the

alkenes. These coke promoters would easily form due to the

high olefin concentration. In this way, as the catalyst is

poisoned, alkenes progressively appear among the reaction

Table 4

Effluent composition for the hydroisomerization of individual alkanes or their m

zeolite

Feed

nC6 nC7 cC6

C2 0.2 0.1

C3 1.4 4.5

iC4 0.1 5.5

nC4 0.6 0.5

iC5 0.1 0.2

nC5 0.3 0.3

2,2-DMC4 2.6

2,3-DMC4 3.1

2-MC5 20.0 0.1

3-MC5 12.6 0.1

nC6 58.7 0.2

2,2-DMC5 2.4

McC5 0.2 3.6 31.7

2,4-DMC5 0.3

Benzene 0.6

3,3-DMC5 1.0

cC6 67.2

2-MC6 18.0

2,3-DMC5 3.9

3-MC6 17.0

nC7 41.5

XnC6 (%) 39.4

XnC7 (%) 58.0

XcC6 (%) 32.5

Selectivity to isomers (%) 93.1 79.4 98.1

Selectivity to C5� (%) 6.9 20.6 0

Selectivity to benzenea (%) 0 0 1.9

Catalyst weight: 1 g; WHSV = 3.7 h�1; T = 250 8C; P = 1 bar.a Calculated only for cC6, which yields McC5 and benzene.

products. Although the deactivation is not so strong for Pt/

MOR(90), the increase in the formation of alkenes, mainly

hexenes, is similarly found, indicating that the strong acid

sites are playing a similar role in this catalyst.

Concerning the dependence of the cracking mechanism

on the conversion, we found in the reaction with 1-hexene

that, as the conversion increases with respect to the n-hexane

reaction, dimerization-cracking increases with respect to b-

scission for all the catalysts, except for Pt/BETA(25) and Pt/

ZSM-5(80). Kung et al. also reported this increment for

cracking of n-hexane with USY [8]. This enhancement in the

bimolecular mechanism reaction rate is a consequence of the

higher concentrations of alkenes and, in turn, carbocations

on the catalyst, which is already accepted according to the

previous statements. For the Pt/ZSM-5 catalyst, the

dimerization-cracking/b-scission ratio does not increase,

thus supporting the limitation for the formation of the

dimeric intermediates in the channel intersections. On the

other hand, beta zeolite should not cause higher diffusional

obstacles than mordenites. This reason and the higher

contribution of b-scission suggest that this zeolite might be

different to the rest of catalysts in some features apart from

the overall acidity and the channel system. Thus, some

explanations should be considered to justify the main

mechanism in beta zeolite. One possibility is to assume that

ixtures (weight ratios: nC6/cC6 = 3.25, nC6/nC7 = 4.33) with BETA(25)

nC6, cC6 nC6, nC7 cC6, nC7 nC6, cC6, nC7

0.1 <0.1 <0.1

<0.1 2.0 1.0 0.8

0.1 2.0 1.4 0.9

<0.1 0.3 0.1 0.1

0.1 0.1 0.1 0.1

0.2 0.3 <0.1 0.2

0.8 1.5 <0.1 0.6

1.9 2.4 <0.1 1.3

13.2 16.1 0.2 10.0

7.5 9.6 0.1 5.9

53.1 51.5 0.8 47.5

<0.1 0.5 0.7 0.4

10.9 0.9 24.9 9.2

0.1 <0.1 <0.1

0.1 0.2 0.3 <0.1

0.2 0.1

12.8 <0.1 33.6 11.5

<0.1 3.3 8.8 2.7

<0.1 0.7 1.4 0.5

<0.1 3.1 7.7 2.5

<0.1 5.7 19.9 6.5

27.0 33.7 23.3

69.8 52.3 56.7

48.0 40.9 44.2

98.9 88.3 88.0 91.9

1.1 11.7 12.0 8.1

0.8 1.1 0.5


Table 5

Yields (wt.%) for the cracking mechanisms in reactions with different feeds

on Pt/BETA(25)

Feed

nC6 nC7 nC6, cC6 cC6, nC7

Hydrogenolysis 0.6 (22.2) 0.4 (3.5) 0.0 (0.0) 0.1 (3.8)

b-Scission 1.4 (51.9) 10.5 (90.5) 0.03 (7.0) 1.0 (38.5)

Dimerization-cracking 0.7 (25.9) 0.7 (6.0) 0.4 (93.0) 1.5 (57.7)

The total percentage for each cracking mechanism is given in parentheses

(see Table 4).

its smaller crystal size, compared to other zeolites [41],

allows faster hydrocarbon diffusion through its pores, thus

dimerization at the intersection channels being more

difficult. This is supported by the fact that the whole

cracking process is minimized when using a nanocrystalline

beta zeolite [5,42]. Other possible explanation is related to

the strength of the acid sites. If strong, and not weak or

moderate, acid sites effectively cause dimerization [25], it

would be conceivable that BETA(25) displays a lower

cracking through this mechanism because, as it was found by

TPD of pyridine (Table 1), it is the solid with the lowest

strong to total acid sites ratio, followed by MOR(90), which

also gives b-scission [12]. The acid strength would then

control the cracking mechanism in the reaction but not the

total selectivity to cracking products. Broadly speaking, the

b-scission and dimerization-cracking mechanisms will be

related to medium and strong acid sites, respectively,

whereas the metallic sites will play the key role in the

absence of these sites, promoting the cracking through

hydrogenolysis reactions (Tables 1–3).

Finally, it is interesting to examine how the reaction of

mixtures of hydrocarbons rather than individual reactants

could affect the products distribution. Table 4 shows the

effluent composition, conversion and selectivities in the

hydroisomerization of n-hexane, n-heptane or cyclohexane

as well as their binary and ternary mixtures on Pt/BETA(25).

Although the reactivity order for the different alkanes in Pt/

BETA(25) follows the order nC7 > cC6 > nC6 both for the

binary mixtures and for the ternary one, when they are

individually fed then the sequence is nC7 > nC6 > cC6.

Hollo et al. [43] reported that in mixtures of alkanes (C5–

C7) the component with a higher boiling point exerts a

higher inhibition on the hydroisomerization rates with

mordenite. In our case, the inhibition by cyclohexane and n-

heptane over n-hexane is higher than vice versa. However,

cyclohexane shows the highest inhibitory effect, due to its

well known preferential adsorption in the zeolite [44]. This

adsorption may be responsible for the decrease in its

conversion when it is the only component in the feed.

On the other hand, the transformation of binary or ternary

mixtures of these hydrocarbons does not show any

difference on the products distribution with relation to that

of the pure hydrocarbons. Thus, the MB/MuB, 2-MC5/3-

MC5 and 2-MC6/3-MC6 ratios are close to those previously

reported.

Table 5 shows the contribution of the different cracking

mechanisms for the reactions with different feeds. The

cyclohexane cracking is negligible under the reaction

conditions and so it is possible to make similar calculations

to those described above. However, the mechanisms for the

mixtures containing both n-hexane and n-heptane are not

presented due to the impossibility to discriminate the origin

of the cracking products. As expected, the contribution of

the dimerization-cracking reaction relative to the unim-

olecular reaction decreases with increasing chain length of

the hydrocarbon [45]. In addition, when cyclohexane is

added to the feed, not only the conversion decreases, but

also the dimerization-cracking/b-scission ratio markedly

increases, resulting in a predominance of the bimolecular

mechanism. As b-scission is the faster reaction, the

blockage of some of the active sites by the cyclohexane

molecules (or the reaction intermediates formed) must

affect this reaction mainly, favouring the reaction between

molecules rather than single molecules reacting on an

acid site. Thus, the bimolecular mechanism would finally

prevail.

4. Conclusions

Several platinum supported zeolites have been tested in

the hydroisomerization of n-hexane, cyclohexane and n-

heptane. The metal impregnation and the activation

conditions, even if a typical method was used, led to

catalysts whose acidity cannot be countered by their

hydrogenation-dehydrogenation activity, so that cracking

is favoured. Notwithstanding, the distribution of reaction

products could confirm different relevant aspects. Conver-

sion depends on acidity, whereas selectivity is clearly

governed by the pore system. Selectivity, in turn, depends on

the conversion level reached, but at a given conversion,

attempts to control the selectivity by tuning acidic properties

will fail, irrespectively of whether changes affect either the

number or the strength of the acid sites. According to this, it

would be erroneous to assert that a zeolite is very selective to

cracking because it is very acidic or it has many strong acid

sites, since it will depend on the reaction conditions. These

conclusions lump several previous suggestions given in the

literature.

Several calculations have been made to distinguish the

contributions of the different cracking mechanisms. Also,

the transformation of 1-hexene has been compared to that of

n-hexane to confirm that the metal supported on the zeolites

does not show the optimal performance in hydro-dehy-

drogenation. These unbalanced bifunctional catalysts

promote dimerization-cracking, which is the prevailing

mechanism in all of them except for Pt/BETA(25). Some

arguments regarding crystal size and acid strength are given

to explain the differences among the catalysts. However,

irrespective of the cracking mechanism, selectivity is only a

function of conversion.


The transformation of mixtures of hydrocarbons on Pt/

BETA(25) did not change the products distribution, although

some inhibitory effects were observed, in particular of

cyclohexane on the paraffins, which even affect the cracking

mechanism.

Acknowledgements

The authors wish to acknowledge funding of this research

by Spains DGI, Ministerio de Educacion y Ciencia, within

the framework of Project CTQU2004-02200, as well as by

Fondos Feder, Junta de Andalucıa and Repsol-YPF. R.R.

acknowledges Ministerio de Educacion y Ciencia of Spain

for his grant.

References

[1] C. Jimenez, F.J. Romero, J.P. Gomez, Recent Res. Dev. Pure Appl.

Chem. 5 (2001) 1–21.

[2] E. Blomsma, J.A. Martens, P.A. Jacobs, J. Catal. 155 (1995) 141.

[3] E. Blomsma, J.A. Martens, P.A. Jacobs, J. Catal. 159 (1996) 323.

[4] M. Guisnet, F. Alvarez, G. Giannetto, G. Perot, Catal. Today 1 (1987)

415–433.

[5] A. Chica, A. Corma, J. Catal. 187 (1999) 167–176.

[6] A. Patrigeon, E. Benazzi, Ch. Travers, J.Y. Bernhard, Catal. Today 65

(2001) 149.

[7] P. Raybaud, A. Patrigeon, H. Toulhoat, J. Catal. 197 (2001) 98.

[8] S.M. Babitz, B.A. Williams, J.T. Miller, R.Q. Snurr, W.O. Haag, H.H.

Kung, Appl. Catal. A: Gen. 179 (1999) 71–86.

[9] S. Gopal, P.G. Smirniotis, J. Catal. 225 (2004) 278–287.

[10] J. Engelhardt, J. Catal. 164 (1996) 449–458.

[11] R. Giudici, H.W. Kouwenhoven, R. Prins, Appl. Catal. A: Gen. 203

(2000) 101.

[12] C. Jimenez, F.J. Romero, R. Roldan, J.M. Marinas, J.P. Gomez, Appl.

Catal. A: Gen. 249 (2003) 175–185.

[13] R. Roldan, F.J. Romero, C. Jimenez, V. Borau, J.M. Marinas, Appl.

Catal. A: Gen. 266 (2004) 203–210.

[14] A. Chica, A. Corma, P.J. Miguel, Catal. Today 65 (2001) 101.

[15] J.-K. Lee, H.-K. Rhee, Catal. Today 38 (1997) 235.

[16] A. van de Runstraat, J.A. Kamp, P.J. Stobbelaar, J. van Grondelle, S.

Krijnen, R.A. van Santen, J. Catal. 171 (1997) 77–84.

[17] V.R. Choudhary, D.B. Akolekar, J. Catal. 117 (1989) 542–548.

[18] V.R. Choudhary, D.B. Akolekar, J. Mol. Catal. 60 (1990) 173–188.

[19] V.R. Choudhary, T.V. Choudhary, Chem. Eng. Sci. 52 (1997) 3543–

3552.

[20] V. Fierro, Y. Schuurman, C. Mirodatos, J.L. Duplan, J. Verstraete,

Chem. Eng. J. 90 (2002) 139–147.

[21] C.L. Li, O. Novaro, E. Munoz, J.L. Boldu, X. Bokhimi, J.A. Wang, T.

Lopez, R. Gomez, Appl. Catal. A: Gen. 199 (2000) 211–220.

[22] M. Tromp, J.A. van Bokhoven, M.T.G. Oostenbrink, J.H. Bitter, K.P.

de Jong, D.C. Koningsberger, J. Catal. 190 (2000) 209.

[23] S. van Donk, A. Broersma, O.L.J. Gijzeman, J.A. van Bokhoven, J.H.

Bitter, K.P. de Jong, J. Catal. 294 (2001) 272–280.

[24] Q.L. Wang, G. Giannetto, M. Guisnet, J. Catal. 130 (1991) 471–

482.

[25] D. Li, M. Li, Y. Chu, H. Nie, Y. Shi, Catal. Today 81 (2003) 65–

73.

[26] F. Ribero, C. Marcilly, M. Guisnet, J. Catal. 78 (1982) 275–280.

[27] M. Guisnet, V. Fouche, M. Belloum, J.P. Bournonville, C. Travers,

Appl. Catal. 71 (1991) 283–293.

[28] M.M. Otten, M.J. Clayton, H.H. Lamb, J. Catal. 149 (1994) 211–

222.

[29] T. Yashima, Z.B. Wang, A. Kamo, T. Yoneda, T. Komatsu, Catal.

Today 29 (1996) 279–283.

[30] R.M. Mao, T.B. Lin, J.R. Chang, J. Catal. 161 (1996) 222–229.

[31] K.J. Chao, H.C. Wu, L.J. Leu, Appl. Catal. A: Gen. 143 (1996) 223–

243.

[32] J.K. Lee, H.K. Rhee, Catal. Today 38 (1997) 235–242.

[33] M.T. Tran, N.S. Gnep, G. Szabo, M. Guisnet, Appl. Catal. A: Gen. 170

(1998) 49–58.

[34] K.I. Patrylak, F.M. Bobonych, Y.G. Voloshyna, M.M. Levchuk, V.G.

Ilin, O.M. Yakovenko, I.A. Manza, I.M. Tsupryk, Appl. Catal. A: Gen.

174 (1998) 187–198.

[35] S. Yuvaraj, T.-H. Chang, C.-T. Yeh, J. Catal. 221 (2004) 466–473.

[36] Gy. Onyestyak, G. Pal-Borbely, H.K. Beyer, Appl. Catal. A: Gen. 229

(2002) 65–74.

[37] W. Souverijns, J.A. Martens, G.F. Froment, P.A. Jacobs, J. Catal. 174

(1998) 177–184.

[38] J.F. Denayer, G.V. Baron, G. Vanbutsele, P.A. Jacobs, J.A. Martens,

Chem. Eng. Sci. 54 (1999) 3553–3561.

[39] J.A. Munoz Arroyo, G.G. Martens, G.F. Froment, G.B. Marin, P.A.

Jacobs, J.A. Martens, Appl. Catal. A: Gen. 192 (2000) 9–22.

[40] G. Sastre, A. Chica, A. Corma, J. Catal. 195 (2000) 227–236.

[41] C. Woltz, J. Macht, A. Jentys, J.A. Lercher, Abstracts on the 13

International Catalysis Congress, Paris, 2004.

[42] M.A. Arribas, A. Martınez, Catal. Today 65 (2001) 117–122.

[43] A. Hollo, J. Hancsok, D. Kallo, Appl. Catal. A: Gen. 229 (2002)

93–102.

[44] A. Voorhies, W.J. Hatcher, Ind. Eng. Chem. Prod. Res. Dev. 8 (1969)

361.

[45] J. Abbot, B.W. Wojciechowsky, Can J. Chem. Eng. 63 (278) (1985)

451–462.

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