Reaction Pathways of 1-Cyclohexyloctane in Admixture with Dodecane on Pt/H-ZSM-22 Zeolite in Three-Phase Hydroconversion

Article abstract of DOI:10.1006/jcat.2000.3102

Isomerization and hydrocracking of a mixture of 1-cyclohexyloctane and dodecane were performed on Pt/H-ZSM-22 in a three-phase Robinson Mahoney reactor with complete internal mixing (T = 523-543 K, P=7-8 MPa, H2/HC =5). The reaction products from 1-cyclohexyloctane were analyzed in detail and compared with those obtained in the absence of dodecane in a fixed-bed vapor-phase reactor (T = 460 K, P = 0.45 MPa, H2/HC = 450). In the presence of dodecane, the main reaction pathway involved contraction of the six-membered ring to a five-membered ring with concomitant elongation of the octyl chain by one carbon. Subsequently, the nonyl chain underwent methyl branching at carbon positions far from the ring. Methyl branching rearrangements of the cyclohexane ring of 1-cyclohexyloctane were suppressed in the presence of dodecane. In the reaction product fraction of heptylmethylcyclohexanes, all cis-trans and positional isomers were formed except the 1,1'-heptylmethylcyclohexane isomer. The isomer distributions were explained with pore mouth and key-lock catalysis. Pt/H-ZSM-22 did not favor the paring reaction. The distribution of cracked products, and especially the abundant formation of alkylcyclopentanes, was in agreement with cracking through β-scission in the chain rather than by ring dealkylation typical of the paring reaction. Ring opening in 1-cyclohexyloctane and its isomers is a less important side reaction.

Full text of DOI:10.1006/jcat.2000.3102

Journal of Catalysis 198, 29–40 (2001)
doi:10.1006/jcat.2000.3102, available online at http://www.idealibrary.com on
Reaction Pathways of 1-Cyclohexyloctane in Admixture with Dodecane
on Pt/H–ZSM-22 Zeolite in Three-Phase Hydroconversion
J. A. Mun˜oz Arroyo, J. W. Thybaut, G. B. Marin, ,1 P. A. Jacobs,† J. A. Martens,† and G. V. Baron‡
Laboratorium voor Petrochemische Techniek, Universiteit Gent, Krijgslaan 281, B-9000 Gent, Belgium; †Centrum voor Oppervlaktechemie
en Katalyse, Departement Interfasechemie, K.U. Leuven, Kard. Mercierlaan 92, B-3001 Heverlee, Belgium; and ‡Departement Chemie
Ingenieurstechniek, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussel, Belgium
Received May 17, 2000; revised August 23, 2000; accepted October 13, 2000; published online February 8, 2001
The bifunctional reaction mechanisms were studied
by several research teams using model compounds and
laboratory-scale reactors (3–10). The reaction pathways of
paraffin and naphthene hydroisomerization and hydroc-
racking on bifunctional Y-type zeolite catalysts were ex-
plained in terms of alkylcarbenium ion chemistry in an
unconstrained molecular environment (3–7, 9). The carbe-
nium ions are formed by protonation of unsaturated hy-
drocarbons on the acid sites; the latter are formed by dehy-
drogenation of saturated compounds formed on the metal
function. Both saturated and unsaturated components can
be physisorbed prior to reaction. The reaction mechanism
of skeletal isomerisation involves the formation of proto-
nated cyclopropanes and larger cyclic alkylcarbonium ions
(3, 5, 9, 11). That mechanism is responsible for stepwise
changes in the degree of branching and is significantly
slower than ring contractions and expansions and posi-
tional shifts of alkyl groups along carbon rings and chains
(9, 11). Hydrocracking proceeds through -scission of car-
bon bonds in alkylcarbenium ions (12).
Souverijns et al. (9) studied the conversion pathways
of 1-cyclohexyloctane representing a typical naphthene
molecule contained in hydrotreated gasoil. They studied
this conversion using a Pt/H–Y zeolite catalyst in a vapor-
phase, continuous-flow, fixed-bed reactor (9). The primary
reaction step was methyl branching of the ring. Subse-
quently, the methyl group was shifted over the ring to the
10 position and transferred to the octyl chain. After methyl
group transfer from the ring to the first or second carbon
atom of the long alkyl chain, the molecule became suscep-
tible to dealkylation by -scission; this paring of methyl
groups from a ring is known as the paring reaction (7, 10).
Compared to those on Pt/H-Y, on Pt/H-ZSM-22 zeo-
lite catalyst the hydroisomerization reaction pathways of
1-cyclohexyloctane under similar reaction conditions were
significantly different (9, 11). Among the heptylmethylcy-
clohexanes which are important reaction products on Pt/H-
ZSM-22 as well as Pt/H-Y, the formation of 1,3-cis, 1,2-
trans, and 1,2-cis forms was kinetically suppressed in favor
Isomerization and hydrocracking of
a
mixture of 1-
cyclohexyloctane and dodecane were performed on Pt/H-ZSM-22
in a three-phase Robinson Mahoney reactor with complete internal
mixing (T = 523–543 K, P = 7–8 MPa, H2/HC = 5). The reaction
products from 1-cyclohexyloctane were analyzed in detail and
compared with those obtained in the absence of dodecane in a
fixed-bed vapor-phase reactor (T = 460 K, P = 0.45 MPa, H2/HC
= 450). In the presence of dodecane, the main reaction pathway
involved contraction of the six-membered ring to a five-membered
ring with concomitant elongation of the octyl chain by one carbon.
Subsequently, the nonyl chain underwent methyl branching at car-
bon positions far from the ring. Methyl branching rearrangements
of the cyclohexane ring of 1-cyclohexyloctane were suppressed
in the presence of dodecane. In the reaction product fraction of
heptylmethylcyclohexanes, all cis–trans and positional isomers
were formed except the 1,10-heptylmethylcyclohexane isomer. The
isomer distributions were explained with pore mouth and key–lock
catalysis. Pt/H-ZSM-22 did not favor the paring reaction. The
distribution of cracked products, and especially the abundant
formation of alkylcyclopentanes, was in agreement with cracking
through -scission in the chain rather than by ring dealkylation
typical of the paring reaction. Ring opening in 1-cyclohexyloctane
c
and its isomers is a less important side reaction.
2001 Academic Press
Key Words: hydrocracking; hydroisomerization; pore mouth
catalysis; key–lock catalysis; ZSM-22; 1-cyclohexyloctane; paring
reaction.
INTRODUCTION
Bifunctionalcatalystscomposed ofdispersed noble metal
and acidic oxide are used in several industrial processes re-
lated to petroleum refining and production of petrochemi-
cals such as hydrocracking, reforming, hydroisomerization,
and isodewaxing (1, 2). The converted hydrocarbon streams
are complex mixtures with paraffins and naphthenes as the
main compounds.
1 To whom correspondence should be addressed. Fax: (32)(0)92644999.
E-mail: Guy.Marin@rug.ac.be.
29
0021-9517/01 $35.00
c
Copyright
2001 by Academic Press
All rights of reproduction in any form reserved.

˜
MUNOZ ARROYO ET AL.
30
of the 1,4-trans, 1,3-trans, and 1,4-cis substituted isomers. mouth mode, the long alkyl chain penetrates into the pore,
Another family of hydroisomerization products formed es- while the ring remains at the pore mouth as it cannot cross
pecially on Pt/H-ZSM-22 had a methyloctyl substituent on the first window of the pore. This was confirmed exper-
a five-membered ring. The methyl group was preferentially imentally by Denayer (13) who studied chromatographi-
positioned at carbon positions of the octyl chain far from cally the physisorption of naphthenes on ZSM-22. It was
the ring. On Pt/H-ZSM-22 direct branching of the long n- found that the Henry coefficient at 473 K of n-hexane is
alkyl side chain was a more important reaction pathway 14 times larger than that of cyclohexane. For larger
than that on Pt/H-Y. Hydrocracking in general and dealky- molecules such as n-octane and cyclooctane an even larger
lation in particular was suppressed on Pt/H-ZSM-22 since difference was found whereas for a non-shape-selective ze-
the formation of isomers with tertiary carbon atoms at the olite such as NaY the Henry coefficients of naphthenes are
first or second position in the chain counting from the ring comparable to those of paraffins. Moreover, on ZSM-22,
and which are particularly susceptible to cracking through the physisorption enthalpy of cycloalkanes is 20–30 kJ/mol
-scission did not occur.
lower than the corresponding n-alkane, pointing at a phy-
ZSM-22 has narrow parallel pores with windows that sisorption at the surface or the pore mouth. As the value of
cannot be crossed by cyclopentane nor cyclohexane rings cyclooctane isonlymarginallyhigher than that for cyclohex-
(11). The selectivity of Pt/H-ZSM-22 catalyst was explained ane (55.9 versus 54.2 kJ/mol), and considering the higher
by pore mouth and key–lock catalysis (Fig. 1). In the pore number of carbon atoms, this would point at a stronger
interaction at the pore mouth of cyclohexane than for cy-
clooctane. This seems reasonable, considering the size of
these molecules.
This physisorption behavior of cycloalkanes is not unex-
pected when examining the measurements for linear and
branched alkanes (14). Here it was shown that only lin-
ear alkanes can penetrate the pores of ZSM-22. Branched
alkanes adsorb only on the external surface and in the pore
mouths, and can only penetrate with their linear part into
the pore. This was evidenced most clearly from the phy-
sisorption enthalpies which correlate well with the length
of this linear part.
A further confirmation of this is found in the phy-
sisorption entropies which are 2 orders of magnitude higher
for branched alkanes than for n-alkanes. This cannot be
due to there being more physisorption sites available for
branched molecules, and one cannot imagine there being
more freedom of branched molecules in the pores. Hence,
branched alkanes and, by extension, naphthenes adsorb on
the external surface and at the pore mouths of ZSM-22.
They only have the linear chain part in the pore. These
findings were recently confirmed by very elaborate mea-
surements by IR and calorimetry (15).
Moreover, on the basis of all these findings from phy-
sisorption studies and using this surface physisorption
model, the gas-phase conversion of n-alkanes on Pt/H-
ZSM-22 could be very well rationalized (16).
Adsorbed in the pore mouth mode the only possible re-
action is a contraction of the ring and an elongation of the
alkyl chain by one carbon atom. In terms of alkylcarbenium
ion chemistry, this is a fast reaction, as it does not alter the
degree of branching. In the alternative pore mouth phy-
sisorption mode, the ring is located in the pore mouth, with
the chain outside the pore. This physisorption mode leads
to ring branching. In the key–lock mode two pore mouths
are involved (Fig. 1): the ring is located in one pore mouth,
with the alkyl chain stretched across the external crystal
surface reaching a neighboring pore mouth with the tail of
FIG. 1. Schematic representation of pore mouth and key lock phy-
sisorption and reaction of 1-cyclohexyloctane.

1-CYCLOHEXYLOCTANE HYDROCONVERSION ON Pt/H–ZSM-22
31
the n-alkyl chain. The branching occurs in that part of the
chain that is located in a pore mouth.
The identification and quantification of the individual
components in the reaction products was performed us-
In a previous study dealing with skeletal isomerization of ing a GC–MS system equipped with an HP-PONA column
n-paraffins on Pt/H-ZSM-22, it was observed that the key– and using a Chrompack CP 9000 gas chromatograph with
lock mode was favored over the pore mouth mode when a TCD and FID detector, and previously established chro-
the catalyst was operated in the liquid phase under condi- matographic elution sequences (9, 11).
tions where the pores are filled with adsorbed n-paraffin
molecules (17).
In the present work we investigated the impact of pore
filling on the conversion of 1-cyclohexyloctane by admixing
dodecane and performing the reaction in the liquid phase.
The conversion of a component i, Xi, was defined by
Fi0 Fi
Xi =
(mol/mol),
[1]
Fi0
with Fi0 representing the inlet liquid molar flow rate and Fi
the outlet liquid molar flow rate.
The mean conversion between 1-cyclohexyloctane and
n-dodecane was defined by
EXPERIMENTAL
The ZSM-22zeolite wassynthesized accordingto a recipe
described elsewhere (18), calcined, exchanged with ammo-
nium cations, and impregnated with an aqueous solution of
Pt(NH3)4Cl2 to obtain a Pt loading of 0.5 wt% (19). The Pt
dispersion of such a sample is 30% . This low value indicates
that most of the platinum metal is present as large particles
on the external surface of the zeolite crystallites (20). Cata-
lyst pellets were prepared by compressing the dry zeolite
powder into flakes, which were crushed and sieved. Catalyst
pellets with diameters between 0.8 and 1.0 mm were used in
the reactor. These catalyst pellets were calcined in oxygen
and subsequently reduced in hydrogen at 400 C without in-
termittent cooling. The absence of mass transfer limitations
in the intercrystalline pores was verified.
1-Phenyloctane (Janssen, 99% ) was hydrogenated in
a batch reactor on Pd/carbon black catalyst. The 1-
cyclohexyloctane thus obtained was previously used as a
pure feed to a fixed-bed continuous-flow vapor-phase mi-
croreactor (9, 11), denoted in short as a vapor-phase reac-
tor. In these previous experiments the reaction pathways
of 1-cyclohexyloctane on both Pt/ZSM-22 and Pt/US-Y ze-
olite were investigated. In the present work, a mixture of
1-cyclohexyloctane with n-dodecane in a molar ratio of 5:95
was converted in a Robinson Mahoney type three-phase
reactor (17), denoted for convenience as the liquid-phase
reactor. The reaction conditions in the vapor- and liquid-
phase reactors are specified in Table 1.
P
NFEED
Fi0 Fi
i
¯
X =
(mol/mol),
[2]
P
NFEED
i=1
Fi0
in which i represents the feedstock components, i.e., n-
dodecane and 1-cyclohexyloctane. The yield of naphthene
branched isomers, naphthene cracked products, and ring-
opening products from 1-cyclohexyloctane was defined by
Fi MWi
NFEED
j=1
Y =
(kg/kg).
[3]
P
i
Fj0MWi
MWi represents the molecular weight of the particular feed
or product component i, and Fi0 represents the inlet liquid
molar flow rate and Fi the outlet liquid molar flow rate. It
was not possible to identify all the cracked products from
1-cyclohexyloctane. The production of C9–C11 naphthenes
was minimal and the formation of these compounds will not
be discussed. Moreover the identification of the C6, C7, and
C8 naphthenes was enough to explain the shape selective
on Pt/H-ZSM-22 catalyst. Paraffin cracked products were
produced from n-dodecane and 1-cyclohexyloctane, respec-
tively; therefore, the quantification of these compounds
produced by only 1-cyclohexyloctane was performed as fol-
lows: the moles of C6, C7, and C8 naphthene cracked prod-
ucts were accompanied by C8, C7, and C6 paraffin cracked
products, respectively. By this assessment the molar amount
of paraffin formed by cracking of 1-cyclohexyloctane can
be calculated. The molar amount of other paraffin cracked
products formed by secondary cracking of the ring-opening
products is calculated via the total mass balance of the 1-
cyclohexyloctane conversion.
TABLE 1
Range of Reaction Conditions for the Hydroconversion Experi-
ments of 1-Cyclohexyloctane in the Vapor-Phase and Liquid-Phase
Reactors
Vapor-phase reactor Liquid-phase reactor
RESULTS AND DISCUSSION
Fixed bed; plug-flow
Mixed flow
Pressure
Temperature (K)
H2/HC ratio (mol/mol)
W/F0
(Mpa)
0.45
460
450
7–8
523–543
5
The evolution of the individual conversions of 1-
cyclohexyloctane and dodecane with the mean conversion
is shown in Fig. 2. The C12 paraffin was more reactive than
the C14 naphthene. The skeletal isomerization products
(kg s/mol)
1,800
616

˜
MUNOZ ARROYO ET AL.
32
There was very little ring opening. In the liquid-phase re-
actor, isomerization was also the main conversion, but hy-
drocracking of C14 naphthenes was much more abundant
than that in the vapor-phase reactor. Ring-opening prod-
ucts and cracked products from ring-opening products were
formed in larger yields than in the vapor phase. This ring-
opening was probably catalyzed by the platinum metal and
favored in the presence of a low hydrogen concentration
in the liquid phase. Methane and ethane which are typical
FIG. 2. Individual conversion of 1-cyclohexyloctane and dodecane
against mean conversion (᭡, 1-cyclohexyloctane; ᭝, dodecane).
from dodecane exhibited the typical features previously re-
ported in detail (17, 23). The conversion of dodecane will
not be discussed further in this paper.
On the bifunctional Pt/USY zeolite catalyst there exists
a unique relationship between the selectivity and the to-
tal conversion (21, 22). On a shape selective catalyst the
selectivity may include a certain dependence on the reac-
tion conditions; however, these effects are expected to be
limited (19) so that the main differences in product distribu-
tions observed in this work are attributed to the difference
in aggregation state, i.e., the vapor or the liquid phase, and
to the presence or absence of an n-alkane solvent. In ad-
dition to the arguments presented in the Introduction to
explain why n-alkyl naphthenes only physisorb in the pore
mouth with the linear substituent, it has been measured
that linear paraffins such as dodecane physisorb much more
strongly than iso-paraffins and naphthenes (13, 14). Hence,
the dodecane in the admixture effectively will block the in-
tracrystalline pores and as no platinum is available there,
no reaction will occur in the pores. All reaction will occur
at the surface of the crystals. It can therefore be stated that
intracrystalline transport will not affect the reactions con-
sidered.
The reaction products from 1-cyclohexyloctane were
grouped in four product families, viz. (i) isomers which are
naphthenes with 14 carbon atoms, (ii) ring-opening prod-
ucts which are C14 normal and branched paraffins, (iii)
cracked products arising from C14 naphthenes, and (iv)
cracked products arising from C14 paraffins. The yields of
these product families in the liquid-phase reactor are re-
ported in Fig. 3a. Data previously obtained in a vapor-phase
reactor (11) are presented in Fig. 3b. In the vapor phase,
the isomer yields were high (Fig. 3b). Naphthene crack-
FIG. 3. Yield of reaction product lumps from hydrocracking
and isomerization of 1-cyclohexyloctane on Pt/H-ZSM-22 against 1-
cyclohexyloctane conversion in liquid-phase reactor (a) and vapor-phase
reactor (b): ᮀ, isomers; ᭛, cracked products from C14 naphthenes; ᭝,
ing became important only at conversions exceeding 80% . ring-opening products; ᭺, cracked ring-opening products.

1-CYCLOHEXYLOCTANE HYDROCONVERSION ON Pt/H–ZSM-22
33
hydrogenolysis products were indeed observed. The lower
yield of primary products (isomers) and the higher yield of
secondary products (cracked products) in the liquid phase
compared to the case in the vapor phase can be explained by
a difference in physisorption mechanism (Fig. 1).On the ba-
sis of a simplified consecutive reaction scheme the influence
of the reactor type on the selectivity pattern was calculated
(24) and it was found to be negligible at the conversion level
investigated.
Hydroisomerization Pathways
The isomerization of 1-cyclohexyloctane led to products
with a five-membered ring or a six-membered ring. The
distribution of isomers according to ring type obtained
in the liquid and vapor phases is shown in Figs. 4a and
4b, respectively. Despite the presence of a significant frac-
tion of unidentified isomers, it was possible to conclude
that the formation of substituted cyclopentanes was fa-
vored in the liquid phase; the formation of substituted cy-
clohexanes was favored in the vapor phase. On the Pt/Y
in the vapor phase an even lower amount of cyclopen-
tanes was formed (9). The only possible isomer the forma-
tion of which does not involve a branching rearrangement
of carbon skeleton is 1-cyclopentylnonane. Unfortunately,
this isomer had the same chromatographic retention time
as 1-cyclohexyloctane. Its presence in the GC peak of 1-
cyclohexyloctane was evidenced with MS, but due to the
overlapping with the larger peak stemming from the uncon-
verted feed, its formation could not be quantified. The 1-
cyclopentylnonane was accounted for with the unconverted
feed. Allother identified isomerscontained two tertiarycar-
bon atoms next to secondary and primary carbon atoms and
consequently had a branching degree of two, compared to a
branching degree of one for the feed molecule. Isomers with
a quaternary atom were not formed in measurable quanti-
ties. The distribution ofisomersaccordingto the presence of
either two n-alkyl substituents, or one isoalkyl substituent
on the ring in liquid- and vapor-phase reactors, is presented
in Figs. 5a and 5b, respectively. Rings with one isoalkyl sub-
stitutent were most abundantly formed in the liquid-phase
reactor; rings with two n-alkyl substituents were most abun-
dant in the vapor-phase reactor.
FIG. 4. Distribution of 1-cyclohexyloctane isomers according to the
type of ring against 1-cyclohexyloctane conversion in liquid-phase reactor
(a) and vapor-phase reactor (b).
alkanes decreased as follows (Table 2):
heptylmethylcyclohexanes > heptylethylcyclopentanes
> hexylethylcyclohexanes > hexylpropylcyclopentanes
The distribution of di-n-alkyl substituted cycloalkanes at
two conversion levels in the liquid- and vapor-phase re-
actors is reported in Table 2. Specific cyclopentanes and This sequence reflects consecutive ring contractions and
cyclohexanes with two n-alkyl substituents were formed, expansions and a shortening long n-alkyl substituent with
namely cyclohexanes with methyl and heptyl, or ethyl and concomitant elongation of the short one. The formation of
hexyl substituents and cyclopentanes with ethyl and heptyl, pentylbutylcyclopentanes, requiring still more isomeriza-
propyl and hexyl, and butyl and pentyl substituents. For all tion steps, was observed in the vapor-phase reactor (11),
these isomers the positional and the cis–trans isomers were but not in the liquid-phase reactor.
formed.
The distribution of positional and cis–trans heptyl-
At conversion levels of ca. 8% and 34% in vapor- and methylcyclohexane isomers obtained at three conversion
liquid-phase reactors, the formation of di-n-alkylcyclo- levels in the two reactors is reported in Table 3. The

˜
MUNOZ ARROYO ET AL.
34
TABLE 2
Distribution of Di-n-alkyl-Substituted Cycloalkane Feed Iso-
mers (mol%) at Different 1-Cyclohexyloctane Conversion Levels
on Pt/H-ZSM-22 and on Pt/H-Y
Pt/H-ZM-22,
Pt/H-Y,
Pt/H-ZM-22,
Pt/H-Y,
Vapor Liquid Vapor
phasea phase
Vapor Liquid Vapor
phasec
phasec phasea phase
Conversion (% )
Heptylmethyl-
cyclohexanesb
Heptylethyl-
cyclohexanes
Hexylethyl-
cyclohexanes
Hexylpropyl-
cyclopentanes
Pentylbutyl-
cyclopentanes
Others
9
53.0
8
52.6
10
68.5
34
51.2
35
49.6
35
65.4
27.0
9.5
3.5
7.0
—
30.2
16.5
5.3
—
—
1.9
—
17.6
12.3
3.5
23.3
20.1
6.9
—
—
3.7
—
2.7
26.8
15.4
—
2.5
26.7
—
—
a Data obtained from (11).
b Overlapped with methyloctylcyclopentane.
c Data obtained from (9).
1,10-heptylmethylcyclohexane isomer was not formed in
any of the experiments with Pt/H-ZSM-22. On Pt/H-Y ze-
olite, this isomer represents 10% of this product fraction,
independent of the total conversion, since on Pt/H-Y cata-
lyst the thermodynamic equilibrium is achieved for the hep-
tylmethylcyclohexane isomers (Table 3). The formation of
1,3 and 1,4 substituted cyclohexanes was favored on Pt/H-
ZSM-22 in the liquid phase as well as in the vapor phase
(Table 3), confirming the pore mouth catalysis. Cis isomers
were more abundant in the reaction products obtained in
the liquid-phase compared to those in the vapor phase.
The isomers having a monoisoalkyl-substituted ring were
mostly cyclopentanes. This product fraction was also ana-
lyzed in detail and compared with the results from previ-
ous experiments in the vapor-phase reactor (Table 4). The
FIG. 5. Distribution of 1-cyclohexyloctane isomers according to the
number of alkyl substituents on the ring against 1-cyclohexyloctane con-
version in liquid-phase reactor (a) and vapor-phase reactor (b).
TABLE 3
Distribution of Positional and Cis–trans Heptylmethylcyclohexane Vapor and Liquid Reaction Products as a Function of the
Conversion on Pt/H-ZSM-22 and the Equilibrium on Pt/H-Y
Pt/H-ZSM-22
Pt/H-ZSM-22
Pt/H-ZSM-22
Pt/H-Y
Vapor
phasea
Liquid
phase
Vapor
phasea
Liquid
phase
Vapor
phasea
Liquid
phase
Vapor
phaseb
Conversion (% )
7
—
—
21.8
12.5
65.7
8
—
—
26.3
25.7
48.0
20
—
0.5
24.5
11.8
63.2
21
—
—
18.2
37.4
44.6
34
—
1.0
29.0
10.0
60.0
35
—
—
49.7
16.8
33.5
Equil.
9.5
1.0
41.5
5.0
43.0
1,10-Heptylmethylcyclohexane
1,2-c-Heptylmethylcyclohexane
1,3-c-Heptylmethylcyclohexane
1,4-c-Heptylmethylcyclohexane
1,4-t + 1,3-t + 1,2-t-Heptylmethylcyclohexane
a Data obtained from literature (11).
b Data obtained from literature at equilibrium (9, 11).

1-CYCLOHEXYLOCTANE HYDROCONVERSION ON Pt/H–ZSM-22
35
TABLE 4
sition most remote from the ring. The formation of iso-
mers with the methyl group close to the five-membered
ring, and especially 2-cyclopentylnonane, was suppressed.
At the same conversion level, this suppression was more
pronounced in the vapor-phase than in the liquid-phase ex-
periments. The behavior of Pt/H-ZSM-22 was totally dif-
ferent from that of Pt/H-Y, on which the formations of 1-
cyclopentyl-2-methyloctane and 2-cyclopentylnonane are
kinetically favored, viz. Table 4. On the Pt/H-Y zeolite with
wide pores, the methyl groups are generated by contraction
of the ring and subsequently transferred to the long alkyl
side chain (9).
In conclusion, inspection ofallthese detailed product fea-
tures on Pt/H-ZSM-22 showed that in the liquid phase in
the presence of dodecane, some reaction pathways are fa-
vored and others suppressed (see Fig. 6). The main isomers
were cyclopentanes with one isoalkyl substituent. Their for-
mation from 1-cyclohexyloctane requires a ring contrac-
tion and concomitant side chain elongation followed by
branching of the nonyl chain. This reaction pathway was
more important than the generation of a second side chain
on the ring, which was the dominant reaction pathway in
the vapor-phase experiments (11). On a Pt/H-Y zeolite,
the six-membered ring of 1-cyclohexyloctane was much
more reactive toward branching than the side chain (9).
On the Pt/H-ZSM-22 zeolite under vapor-phase reaction
conditions, the side chain was already relatively more reac-
tive toward branching (11). Under the present liquid-phase
Distribution of 1-Cyclopentyl-m-methyloctanes (mol %) as a
Function of the Conversion of 1-Cyclohexyloctane on Pt/H-ZSM-
22 and on Pt/H-Y
Pt/H-ZSM-22 Pt/H-Y Pt/H-ZSM-22 Pt/H-Y
Vapor Liquid Vapor Vapor Liquid Vapor
phasea phase phaseb phasea phase phaseb
Conversion (% )
1-Cyclopentyl-7-
methyloctane
1-Cyclopentyl-6-
methyloctane
1-Cyclopentyl-5-
methyloctane
1-Cyclopentyl-4-
methyloctane
1-Cyclopentyl-3-
methyloctane
1-Cyclopentyl-2-
methyloctane
14.0
32.3
8.0
32.1
13.4
0
34.0
23.2
35.0
32.3
35.0
0
N.D.c 18.4
N. D.
10.9
11.1
10.9
40.8
26.4
N. D.
15.4
21.1
14.5
13.6
12.2
5.8
20.6
20.7
11.2
3.4
N.D.
18.0
16.0
23.5
29.5
13.0
16.9
22.1
14.8
13.8
0
27.8
8.3
3.1
5.1
3.5
2-Cyclopentylnonane
5.9
a Data obtained from literature (11).
b Data obtained from literature (9).
c N.D., not detected.
fraction comprises 1-cyclopentyl-m-methyloctanes, with m
in the range from 2 to 7, together with 2-cyclopentylnonane.
The following observations were made: the preferred iso-
mer had the methyl group at the C7 position, i.e., the po-
FIG. 6. 1-Cyclohexyloctane isomerization pathways occurring on Pt/H-ZSM-22 zeolite.

˜
MUNOZ ARROYO ET AL.
36
reaction conditions, the alkyl group was more reactive than of dodecane and its aliphatic cracked products in the liquid-
the six-membered ring toward branching. phase experiments rendered the analysis of the aliphatic
The suppressed reactivity of the ring toward branching cracked products from 1-cyclohexyloctane and its isomers
in the liquid-phase experiments can be quantitatively ex- impossible. The discussion on the cracking of the C14 naph-
plained with physisorption according to the pore mouth thenes in the liquid phase will be based on the formation of
and key–lock model (Fig. 1) and competition with dode- alicyclic cracked products. The C5, C6, C7, and C8 naphthene
cane. For steric reasons, the five-membered ring or six- reaction products were analyzed in detail. The distribution
membered ring of the naphthene molecules cannot cross of the C6, C7, and C8 naphthene reaction products obtained
the 10 oxygen atom window of the ZSM-22 zeolite (11). in the liquid phase is given in Table 5. The molar yield of
The acid catalytic centers responsible for ring branching C6, C7, and C8 naphthenes per 100 moles of feed molecules
are located inside the micropore. To enable reaction, the cracked is plotted against the 1-cyclohexyloctane conver-
naphthene molecule must be adsorbed with its ring in the sion in Fig. 7.
pore mouth. This physisorption mode with only a limited
In the liquid-phase experiments, cyclopentane was
number of carbon atoms of the molecule in contact with not formed. In principle, it could be formed by dealkyla-
the zeolite micropore is expected to be energetically dis- tion of 1-cyclopentylnonane, which is an intermediate in the
favored in the presence of large concentrations of linear transformation of1-cyclohexyloctane into 1-cyclopentyl-m-
alkane molecules such as dodecane that can much better in-
teract with the micropore. In the alternative reaction modes
of naphthene molecules, i.e., the key–lock mode and pore
mouth mode with the chain inside (Fig. 1), interaction of
alkyl chains of the naphthene molecule with a micropore
is established. In these modes the physisorption of naph-
thene molecules is expected to be less suppressed by com-
petitive physisorption and reaction of dodecane. Reactions
of the alkyl chain according to the pore mouth and key–
lock mode lead to the formation of 1-cyclopentylnonane
and isomers with methyl branching in the chain. According
to this model, the significant differences observed between
the vapor- and liquid-phase experiments are caused by the
presence of dodecane.
Hydrocracking Pathways
The Pt/H-ZSM-22 catalyst shows low hydrocracking ac-
tivity toward long n-alkanes, a property that is at the basis
of its excellent isodewaxing properties (25). The low ten-
dency to cracking of the skeletal isomerization products
from long n-alkanes can be explained by the position of
the methyl branchings in the isomers, and the pore mouth
and key–lock catalysis concept (26, 27). Hydrocracking pro-
ceeds through -scission of alkylcarbenium ions. The fastest
-scissions involve tertiary or secondary alkylcarbenium
ions with a tertiary or quaternary carbon atom in the
position. The Pt/H-ZSM-22 catalyst does not favor the for-
mation of skeletal isomers with tertiary or quaternary car-
bon atoms separated by one methylene carbon atom, sus-
ceptible to such cracking via fast -scissions (19). In such
isomers, the distance between the branchings is too short
for a favorable interaction with the zeolite according to the
key–lock mode. On Pt/H-ZSM-22, hydrocracking of paraf-
fins proceeds via -scissions of secondary or tertiary alkyl-
carbenium ions into smaller secondary alkylcarbenium
ions (19).
FIG. 7. Molar yield of C6, C7, and C8 naphthenes per 100 total moles
Hydrocracked products from 1-cyclohexyloctane and its
isomers comprise paraffins and naphthenes. The presence version: ᭛, C6; ᮀ, C7; ᭝, C8.
of naphthene cracked products as a function of 1-cyclohexyloctane con-

1-CYCLOHEXYLOCTANE HYDROCONVERSION ON Pt/H–ZSM-22
37
formed (Table 5). This molecule can be formed through a
-scission that does not correspond to a dealkylation, but
a scission of a carbon–carbon bond in the chain (Fig. 8,
Eq. 3).
C7 naphthenes are abundant cracked products (Fig. 7).
The cyclic C7 fraction of the cracked products comprises
ethylcyclopentane, methylcyclohexane, and dimethylcy-
clopentanes (Table 5). Ethylcyclopentane is the main prod-
uct of this fraction (Table 5). Its content in the C7 naphthene
fraction decreases with conversion, while that of methyl-
cyclohexane and dimethylcyclopentanes increases, indicat-
ing that ethylcyclopentane is a primary cracked product.
Methylcyclohexane and dimethylcyclopentanes are at least
partially formed by secondary isomerization of this pri-
mary cracked product. Ethylcyclopentane can be formed
through -scissions in the chain of alkylcarbenium ions
derived from 1-cyclopentylmethyloctanes (Fig. 8, Eqs. 7
TABLE 5
Distribution of Cracked Products in Liquid Phase as a Function of
1-Cyclohexyloctane Conversion on Pt/H-ZSM-22
Conversion (% )
6
8
21
35
C6 Fraction
86.6
MeCyC5
CyC6
90.1
9.9
96.1
3.9
92.6
7.4
13.4
C7 Fraction
N.D.c
14.1
1,10-Dimethylcyclopentane
1-t-3-Dimethylcyclopentane
1-c-3-Dimethylcyclopentane
1-t-2-Dimethylcyclopentane
Methylcyclohexanea
N.D.
15.9
13.1
1.1
16.9
52.9
N.D.
17.6
14.6
1.2
17.2
49.4
N.D.
17.0
18.0
1.7
19.5
43.6
10.0
0
14.4
61.4
Ethylcyclopentane
C8 Fractionb
—
1,1,3-Trimethylcyclopentane
N.D.
0
N.D.
0
N.D.
1.9
N.D.
0
0.6
4.6
N.D.
7.8
10.6
N.D.
N.D.
N.D.
42.6
1.2
N.D.
0.7
N.D.
0
N.D.
7.4
N.D.
1.4
N.D.
0
N.D.
0.8
N.D.
4.1
N.D.
10.3
4.1
1-t-2-c-4-Trimethylcyclopentane
1-c-2-t-4-Trimethylcyclopentane
1,1,2-Trimethylcyclopentane
1-c-2-c-4-Trimethylcyclopentane
1-c-2-t-3-Trimethylcyclopentane
1,1-Dimethycyclohexane
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
1-c-3-Dimethylcyclohexane
1,3-Dimethylcyclohexane
FIG. 8. Mechanism of naphthene cracking reactions performed on
Pt/H-ZSM-22 zeolite.
4.7
8.2
1-t-4-Dimethylcyclohexane
1-t-2-Dimethylcyclohexane
1-Ethyl-3-methylcyclopentane
1-Ethyl-3-methyl-c-cyclopentane
1-Ethyl-2-methylcyclopentane
1-Ethyl-1-methylcyclopentane
iso-Propylcyclopentane
2.1
N.D.
11.2
15.2
N.D.
N.D.
N.D.
43.2
7.4
N.D.
15.0
15.9
N.D.
N.D.
N.D.
38.5
9.1
methyloctanes. Hence, dealkylation of the five-membered
ring, involving a -scission on a secondary alkylcarbenium
ion into a secondary cyclic alkylcarbenium ion (Fig. 8,
Eq. 1) was a very slow reaction.
n-Propylcyclopentane
C6 naphthenes are formed, but less abundantly than C7 Ethylcyclohexane
and C8 naphthenes (Fig. 7). Cyclohexane formation corre-
a Overlapped with 1-c-2-dimethylcyclopentane.
sponds to a dealkylation of the ring (Fig. 8, Eqs. 5 and 6),
and is a very slow process in comparison to cyclopentane
formation. Methylcyclopentane is the main C6 naphthene
b At conversion of 6% , too few C8 cracked products were analyzed to
form a representative distribution.
c N.D., not detected.

˜
MUNOZ ARROYO ET AL.
38
and 8). The reaction of Eq. 7 is similar to the preferred as was observed in the composition of the group of methyl-
cracking pathway of isoparaffins: the positive charge is on heptylcyclohexanes isomers.
a secondary carbon atom of a linear alkyl group, which
The C8 naphthene reaction products are composed of
can be positioned inside the pore and stabilized by the propylcyclopentane, ethylcyclohexane, dimethylcyclohex-
atoms of the pore wall. In Eq. 8, the charged carbon is anes, ethylmethylcyclopentanes, and trimethylcyclopen-
located between the ring and the branching in the chain. tanes(Table 5). The abundant formation ofpropylcyclopen-
There is no way to locate the charged carbon atom inside tane in this fraction can be explained by considering the
the zeolite micropore. The formation of methylcyclohex- different possibilities for cracking through -scission in a
ane via cracking in a chain has to proceed via the reaction chain (Fig. 8, Eqs. 11–17). Propylcyclopentane, ethylcyclo-
of Eq. 9, Fig 8. The parent molecule, viz. a 1-cyclohexyl- hexane, methylethylcyclopentane, and trimethylcyclopen-
m-methylheptane, is much less abundantly formed than tanes can all be formed through two types of -scissions in
1-cyclopentyl-m-methyloctane (Fig. 4a), explaining the the chain, converting a secondary alkylcarbenium ion into
low formation of methylcyclohexane compared to ethylcy- a smaller secondary carbenium ion and a smaller olefin,
clopentane. Dimethylcyclopentanes represent a significant or a tertiary alkylcarbenium ion into a smaller secondary
fraction of the C7 naphthenes (Table 5). The formation carbenium ion and an olefin.
of 1,3-dimethylcyclopentanes is favored. Their formation
The formation of a particular C8 naphthene is depen-
can be explained by cracking in the chain of the group of dent on the formation of the specific parent feed isomer.
1-methylcyclopentyl-m-methylheptanes (Fig. 8, Eq. 10) in Propylcyclopentane is the main C8 naphthene product
which the formation of the 1,1 and 1,2 forms is disfavored, obtained from the abundantly formed 1-cyclopentyl-m-
TABLE 6
Distribution of Cracked Products in the Vapor Phase as a Function of 1-Cyclohexyloctane Conversion on Pt/H-ZSM-22
Conversion (% )
33
46
62
76
80
88
90
93
C6 Fraction
83.8
MeCyC5
CyC6
100
0
100
0
79.4
20.6
75.1
24.9
65.6
34.4
52.8
47.2
48.7
51.3
16.2
C7 Fraction
N.D.
19.6
1,10-Dimethylcyclopentane
1-t-3-Dimethylcyclopentane
1-c-3-Dimethylcyclopentane
1-t-2-Dimethylcyclopentane
Methylcyclohexanea
N.D.d
20.4
15.4
0
40.1
24.1
N.D.
19.7
15.7
0
39.7
24.8
N.D.
16.4
13.4
2.9
48.8
18.3
N.D.
14.6
11.8
3.3
54.2
15.7
N.D.
11.6
9.6
3.9
62.2
12.6
N.D.
10.6
8.8
4.3
64.4
11.9
N.D.
10.2
8.6
5.6
63.9
11.6
15.3
0
42.3
22.8
Ethylcyclopentane
C8 Fraction
1,1,3-Trimethylcyclopentane
1-t-2-c-4-Trimethylcyclopentane
1-c-2-t-4-Trimethylcyclopentane
1,1,2-Trimethylcyclopentane
1-c-2-c-4-Trimethylcyclopentane
1-c-2-t-3-Trimethylcyclopentane
1,1-Dimethycyclohexane
0
0
N.D.
0
N.D.
0
0
0
0
N.D.
0
N.D.
0
0
0
0
N.D.
0
N.D.
0
0
0
0
N.D.
0
N.D.
0
0
0
0
N.D.
0
N.D.
0
0
0.9
1.3
N.D.
1.2
N.D.
2.3
0
1.1
1.6
N.D.
1.3
N.D.
2.3
0
1.2
2.1
N.D.
1.9
N.D.
2.6
0.9
1-c-3-Dimethylcyclohexane
1,3-Dimethylcyclohexane
—
—
26.0
0
20.6
16.5
0
0
0
—
36.9
—
—
16.8
0
23.7
20.1
0
0
0
—
39.4
—
—
18.6
0
22.9
10.2
0
0
0
—
40.3
—
—
13.4
0
21.8
17.1
0
0
0
—
47.6
—
—
—
—
—
—
—
—
10.6
8.4
8.6
7.8
2.9
3.6
1.0
1-t-4-Dimethylcyclohexaneb
1-t-2-Dimethylcyclohexane
1-Ethyl-3-methylcyclopentane
1-Ethyl-3-methyl-c-cyclopentane
1-Ethyl-2-methylcyclopentane
1-Ethyl-1-methylcyclopentane
iso-Propylcyclopentane
17.2
8.4
16.3
12.6
0
2.6
0
—
13.7
9.8
11.9
10.6
1.7
2.7
0
12.4
9.2
10.2
9.1
2.1
2.6
0.9
—
n-Propylcyclopentane
—
43.8
—
47.9
Ethylcyclohexanec
42.9
47.0
a Overlapped with 1-c-2-dimethylcyclopentane.
b Overlapped with 1,3-c-dimethylcyclohexane and 1,3-dimethylcyclohexane.
c Overlapped with n-propylcyclopentane.
d N.D., not detected.

1-CYCLOHEXYLOCTANE HYDROCONVERSION ON Pt/H–ZSM-22
TABLE 8
39
methyloctane isomers through Eqs. 11 and 12, Fig. 8. This
cracking mode fits the pore mouth model. Ethylcyclohex-
ane can be formed through a similar -scission (Eqs. 13
and 14, Fig. 8), but the 2-cyclohexyloctane isomer in-
volved is formed in trace amounts only. The formation of
ethylmethylcyclopentanes starts from tribranched substi-
tuted cyclopentanes, necessitates an additional branching
step, and is less important (Fig. 8, Eqs. 15 and 16). Four
branchings in the parent naphthene are required to obtain
trimethylcyclopentane as cracked product (Fig. 8, Eq. 17).
Trimethylcyclopentanes are most likely obtained through
secondary isomerization of less branched C8 naphthenes.
It is concluded that on the Pt/H-ZSM-22 catalyst, crack-
ing in a branched C8 or C9 alkyl substituent is favored over
ring dealkylation. In the liquid phase, chain branching is
more important than ring branching, explaining why the
isomerization is rapidly followed by cracking (Fig. 3a). The
opposite situation was encountered in the vapor phase. In
the vapor phase, ring branching was more important than
chain branching, explaining why cracking was much more
suppressed than in the liquid phase (Fig. 3b).
In the vapor phase, the naphthene cracked product dis-
tributions (Table 6) were significantly different from those
in the liquid phase. Especially the formation of alkyl-
substituted cyclohexaneswasmore important. It reflectsthe
more abundant formation of isomers with six-membered
rings in the vapor phase (Fig. 4b). Unfortunately, in the
vapor-phase experiments, it was not possible to determine
in sufficient detail the composition of the feed isomers
at the very high conversion levels where cracking sets in.
Such information would have made it possible to detect
whether these cyclohexanes are formed through cracking
in an isoalkyl ring substituent, or by ring dealkylation.
The molar yield of C5–C9 aliphatic and alicyclic hydro-
carbons per 100 moles of feed cracked in the vapor-phase
experiment is shown at 30% cracking yield in Table 7. Un-
der these conditions, there is little ring-opening (Fig. 3b).
If there were pure primary cracking, the molar yield of C5
Distribution of Cracked Products in Vapor Phase as a Function of
1-Cyclohexyloctane Conversion on Pt/H-Y
Conversion (% )
32.6
61.6
81.8
91.7
C6 Fraction
72.0
MeCyC5
CyC6
80.0
20.0
81.0
19.0
81.5
18.5
28.0
C7 Fraction
N.D.b
5.8
1,10-Dimethylcyclopentane
1-1-3-Dimethylcyclopentane
1-c-3-Dimethylcyclopentane
1-t-2-Dimethylcyclopentane
Methylcyclohexanea
N.D.
9.7
14.3
8.6
62.7
4.7
N.D.
12.3
16.6
10.7
53.6
6.8
N.D.
13.9
15.4
12.6
48.7
9.4
9.2
5.2
79.8
0.0
Ethylcyclopentane
C8 Fraction
0.0
1,1,3-Trimethylcyclopentane
3.8
5.4
0.0
0.0
1.5
0.3
1.2
8.4
5.4
24.1
7.1
15.2
3.9
0.0
2.4
18.2
2.9
3.5
5.4
0.0
0.2
1.5
3.5
1.6
8.9
5.1
22.8
6.3
13.6
4.1
0.2
1.4
16.3
5.6
3.1
5.1
0.2
0.0
1.1
3.5
3.0
10.9
3.7
24.8
3.9
11.2
5.8
0.1
1.8
15.7
6.2
1-t-2-c-4-Trimethylcyclopentane
1-c-2-t-4-Trimethylcyclopentane
1,1,2-Trimethylcyclopentane
1-c-2-c-4-Trimethylcyclopentane
1-c-2-c-3-Trimethylcyclopentane
1,1-Dimethycyclohexane
1-c-3-Dimethylcyclohexane
1-t-3-Dimethylcyclohexane
1-t-4-Dimethylcyclohexane
1-t-2-Dimethylcyclohexane
1-c-2-Dimethylcyclohexane
1-Ethyl-2-methylcyclopentane
iso-Propylcyclopentane
4.6
0.0
0.0
0.0
0.0
0.0
4.5
5.5
23.9
7.6
17.2
4.2
0.0
n-Propylcyclopentane
Ethylcyclohexane
Other C8 naphthenes
3.0
27.1
0.0
a Overlapped with 1-c-2-Dimethylcyclopentane.
b N.D. not detected.
paraffins and C9 naphthenes should be equal. The same
holds for C6 paraffins and C8 naphthenes, C7 paraffins and
C7 naphthenes, C8 paraffins and C6 naphthenes, and C9
paraffins and C5 naphthene. This symmetry is absent, indi-
cating that there was some secondary cracking of the heav-
iest cracked products.
TABLE 7
On the Pt/H-Y catalyst, in contrast to the Pt/ZSM-22, all
the -scission cracking mechanisms are possible, especially
the (t,t) -scission which requires branchings in the , ,
positions with respect to the charged carbon atom. Table 8
shows the distribution of C6, C7, and C8 naphthene cracked
products obtained in the vapor phase on the Pt/H-Y cata-
lyst.
Methylcyclopentane is also the main C6 naphthene
formed as it occurred on Pt/H-ZSM-22; however, in Table 8
a higher formation of cyclohexane with respect to that on
Pt/H-ZSM-22at the same conversion levelcan be observed.
Dealkylation reactions starting from secondary or tertiary
alkyl carbenium ions lead to this molecule (Fig. 8, Eqs. 5
and 6).
Carbon Number Distribution of Cracked Prod-
ucts at Cracking Yield of 30% in the Vapor-Phase
Reactor
Cracked products
Moles/100 moles cracked
C5 paraffins
C9 naphthenes
C6 paraffins
C8 naphthenes
C7 paraffins
C7 naphthenes
C8 paraffins
28.8
22.2
23.1
19.5
19.1
22.2
6.8
C6 naphtenes
C9 paraffins
11.0
2.2
C5 naphthenes
0.0

˜
40
MUNOZ ARROYO ET AL.
For the C7 fraction the very high formation of methyl- Eerste Minister—Federale diensten voor wetenschappelijke, technische
en culturele aangelegenheden.
cyclohexane is attributed to the more abundant formation
of six-membered-ring isomers of 1-cyclohexyloctane and
especially the heptylmethyl-cyclohexanes compared to the
five-membered-ring isomers (Table 2). By secondary iso-
merization of methylcyclohexane the formation of ethyl-
and dimethylcyclopentanes increases with the conversion.
The non-shape-selective character of the Pt/H-Y is evi-
denced by the higher amount of 1,2-dimethylcyclopentane
formed than on Pt/H-ZSM-22 (Tables 5 and 6) where in
particular at low conversion this component is not formed.
1,10-Dimethylcyclopentane which is normally formed on
Pt/US-Y, but not on Pt/ZSM-22, was not detected in any
of the experiments.
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Similar to the behavior observed for the C7 fraction,
cyclohexanes are more abundant than cyclopentanes in
the C8 fraction. Ethylcyclohexane, the monobranched six-
membered-ring component in this fraction, is the most im-
portant component formed; however, its relative impor-
tance decreases with the conversion, which is attributed
to secondary isomerization to dimethylcyclohexanes. On
the Pt/H-Y catalyst the 1,10-dimethyl-cyclohexane can be 12. Martens, J. A., and Jacobs, P. A., in “Theoretical Aspects of Hetero-
formed (Table 8) which was not produced on Pt/H-ZSM-22.
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New York, 1990.
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Approach, Ph.D. thesis, Vrije Universiteit Brussel, Belgium, 1998.
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Chem. B 102, 4588 (1998).
The isomerization and hydrocracking reaction pathways
of 1-cyclohexyloctane are strongly dependent on the pres-
ence of a long paraffin such as dodecane. Cyclopentane and
cyclohexane are too large for penetration into the ZSM-22
micropores. In the presence of dodecane fitting much bet-
ter in the pore, the reactions of the ring are suppressed and
the conversions occur preferentially in the long alkyl chain
of the naphthene molecule. In the presence of dodecane,
1-cyclohexyloctane undergoes first a ring contraction with
side chain elongation, favored by physisorption of the
long n-alkyl chain in the pore mouth. The nonyl chain
undergoes methyl branching with a peculiar selectivity
pattern that is imposed by key–lock physisorption. The
1-cyclopentyl-m-methyloctanes are sensitive to cracking
through -scission in the chain. In the absence of dode-
cane, the six-membered ring of 1-cyclohexyloctane can be
adsorbed in a pore mouth and undergo methyl branching.
Subsequent ring contractions and expansions result in
elongation of the short alkyl substituent and shortening of
the long one. These isomers lacking methyl branching on
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ACKNOWLEDGMENTS
Chon, S.-K. Lhm, and Y. S. Uh, Eds.), Studies in Surface Science and
Catalysis Vol. 105, p. 1285. Elsevier, Amsterdam, 1997.
J.A.M. acknowledges a Ph.D. fellowship to the Mexican Petroleum In- 27. Martens, J. A., Souverijns, W., Verrelst, W., Parton, R., Froment,
stitute. This research has been done as a part of the program Interuniversi-
taire attractiepolen, funded by the Belgian government, Diensten van de
G. F., and Jacobs, P. A., Angew. Chem., Int. Ed. Engl. 34 (22), 2528
(1995).