Cyclohexane transformations over metal oxide catalysts 1. Effect of the nature of metal and support on the catalytic activity in cyclohexane ring opening

Article abstract of DOI:10.1023/A:1015443307743

The activities of monometallic Pt-, Ru-, and Rh-containing catalysts supported on Al2O3, Al2O3-F, SiO2, WO3/ZrO2, and La2O3/ZrO2, in cyclohexane ring opening to form "-hexane were studied. The most active catalyst is Rh/Al2O3. Cyclohexane hydrogenolysis t

Full text of DOI:10.1023/A:1015443307743

Russian Chemical Bulletin, International Edition, Vol. 51, No. 2, pp. 249—254, February, 2002
249
Cyclohexane transformations over metal oxide catalysts
1
. Effect of the nature of metal and support on the catalytic activity in
cyclohexane ring opening
O. V. Masloboishchikova, T. V. Vasina, E. G. KhelkovskayaꢀSergeeva, L. M. Kustov, and P. Zeuthenb
a
a
a
a
aN. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
4
7 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5328. Eꢀmail: lmk@ioc.ac.ru
b
Haldor Topsoe А/S, DKꢀ2800 Lyngby, Denmark
The activities of monometallic Ptꢀ, Ruꢀ, and Rhꢀcontaining catalysts supported on Al O ,
2
3
Al O —F, SiO , WO /ZrO , and La О /ZrO , in cyclohexane ring opening to form nꢀhexane
2
3
2
3
2
2
3
2
were studied. The most active catalyst is Rh/Al O . Cyclohexane hydrogenolysis to nꢀhexane
2
3
also occurs over the Pt/Al O and Pt/La О /ZrO catalysts. Ring opening over the Ru catalysts
2
3
2
3
2
proceeds at significantly lower temperatures (210—230 °C) than over the Pt and Rh catalysts
350—400 °C), but the ruthenium systems are less selective for nꢀhexane formation than
Rh/Al O catalysts. The effects of acidꢀbasic properties of the support and the reaction condiꢀ
(
2
3
tions on the activities of the catalytic systems in cyclohexane ring opening was studied.
Key words: cyclohexane, methylcyclopentane, nꢀhexane, ring opening, hydrogenolysis,
dehydrogenation, isomerization, heterogeneous catalysis, platinum, rhodium, ruthenium.
Selective ring opening of naphtene hydrocarbons to
form normal and low branched paraffins improves the
quality of diesel fuel due to enhancement of the cetane
number of the fuel, whereas skeletal isomerization leads
to a marked improvements in quality of gasoil fractions.
Ring opening of cyclopropane, cyclobutane, and
oxides modified with SO42– or WO42– anions and exhibitꢀ
ing strong acid and superacid properties (Pt/WO /ZrO
3
2
and Pt/SO /ZrO ). When alkylcyclopentanes undergo
4
2
hydrogenolysis over electronꢀdeficient metal particles,
isoalkanes are formed along with nꢀalkanes С and С .
6
7
The type of cyclohexane or methylcyclohexane transꢀ
1
—5
9—11,14
cyclopentane hydrocarbons has been reported earlier.
formations over Ruꢀ and Irꢀcontaining catalysts
Ring opening of cyclohexane to form nꢀhexane was studꢀ
ied to a lesser extent.6
depends on the metal dispersion. When the dispersion is
low, cyclohexane hydrogenolysis (hydrocracking) to form
light alkanes, mainly methane, prevails, whereas dehyꢀ
drogenation to benzene is the main reaction over highly
dispersed catalysts.9
,7
Dehydrogenation, isomerization to methylcyclopenꢀ
tane (MCP), and hydrocracking to С —С hydrocarbons
1
5
are the main reactions of cyclohexane and its alkyl deꢀ
rivatives over oxide catalysts containing Pt, Rh, Ru, Ir,
The effects of the metal nature (Pt, Rh, Ru), acidꢀ
basic properties of the support (SiO , Al O , Al O —F,
Re, and U.1
,7—11
Under specific conditions, nꢀhexane
2
2
3
2
3
can be formed from cyclohexane over oxide catalysts conꢀ
taining Rh, Ru, Ni, and Pt.6
WO /ZrO , and La O /ZrO ), аnd the reaction condiꢀ
3 2 2 3 2
,7,12
tions on the activity and selectivity of the metal oxide
catalysts in the cyclohexane ring opening to form nꢀhexꢀ
ane were studied in this work.
From the study of the mechanisms of hydrogenolysis
7
of cyclopentane and cyclohexane, it can be inferred that
Pt significantly differs from other VIII group metals in its
catalytic behavior. Whereas cyclohexane transforms to
nꢀhexane over the activated carbonꢀsupported Rh, Ru,
Ir, and Os catalysts, this reaction does not occur over
Pt/С, although the corresponding alkanes can be formed
Experimental
We used γꢀAl O , Al O —F (F content was 0.3 or 3.5 wt.%)
2
3
2
3
and SiO2 with the specific surface area (S ) of 250, 150—160,
and 300 m g , respectively, as the catalyst supports. The supꢀ
port 15% WO /ZrO was prepared according to the known proꢀ
cedure, and 3% La О /ZrO was prepared by impregnating
2 3 2
zirconium hydroxide with an aqueous solution of lanthanum
sp
from cyclopentane and С —С cycloalkanes.
2 –1
7
15
Isomerization to alkylcyclopentanes is the main pathꢀ
3
2
8
13
1
5
way of the cyclohexane and methylcyclohexane transꢀ
formations over bifunctional Pt catalysts containing metal
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 237—241, February, 2002.
066ꢀ5285/02/5102ꢀ249 $27.00 © 2002 Plenum Publishing Corporation
1

250
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 2, February, 2002
Masloboishchikova et al.
nitrate followed by calcination at 500 °C for 4 h. The metals (Pt,
Rh, and Ru) were introduced from dilute aqueous solutions of
Н PtCl , RhCl , and [Ru(NH ) ](NO ) , respectively, by imꢀ
pregnation of the support at 20 °C followed by evaporation on a
rotary evaporator. Then the samples were dried for 2 h at 130 °C.
the Pt/Al O catalyst without F (see Table 1). With inꢀ
2
3
creasing temperature and conversion of cyclohexane, the
selectivity for benzene decreases, while MCP and isoꢀ
hexanes appear in the reaction products. A pressure
increase at the constant temperature leads to a deꢀ
crease in both the cyclohexane conversion and selectivity
for benzene, and the nꢀhexane yield increases. The
nꢀC6H14 : iꢀC6H14 ratio in the products of cyclohexane
transformation varies from 5 to 13, and this is signifiꢀ
cantly higher than that found in MCP hydrogenolysis
under similar conditions (see Ref. 4). Hence, nꢀhexane
can be formed over Pt/Al O through the direct opening
2
6
3
3 6
3 3
Before runs, the catalysts were reduced in an H flow for 3 h at
2
4
50 °C. The concentrations of Pt, Ru, and Rh in the catalysts
were 1.0 wt.%.
The cyclohexane transformations were studied in a flow setup
at 180—400 °C and a pressure of 0.7—5.0 MPa. The catalyst
3
–1
volume was 1—3 cm , the cyclohexane feed rate was 1—2 h at
the molar ratio Н : С Н = (5—10) : 1. The reaction products
2
6
12
were analyzed by GLC without preliminary separation of gasꢀ
eous and liquid hydrocarbons on a column (l = 3 m) packed
with polymethylphenylsiloxane on Celite Cꢀ22. The selectivity
for each product was evaluated as the ratio of its yield to the
overall cyclohexane conversion.
2
3
of the cyclohexane ring.
As is known, treatment of the Al O surface with haꢀ
2
3
lides induces the appearance of proton acidity and, as a
result, the enhancement of catalytic activity in skeletal
isomerization. Cyclohexane is mainly dehydrogenated to
benzene over the Pt/Al O —F catalyst (3.5 wt.% F) at
Results and Discussion
2
3
3
20—420 °C and a pressure of 0.7 MPa (Fig. 1, a). Howꢀ
Pt catalysts. Dehydrogenation to benzene is the main
reaction involved in cyclohexane transformations in the
ever, as pressure is increased to 2.0 MPa, the product
distribution substantially changes: despite a decrease in
the molar ratio H : C H from 10 : 1 to 5 : 1, the benzene
presence of Pt/SiO at 340 °C and a pressure of 0.7 MPa
2
2
6
12
(
Table 1). In this case, cyclohexane does not undergo
yield is at most 6 wt.%, and simultaneously, the contribuꢀ
tion from isomerization of cyclohexane to MCP increases
(Fig. 1, b). With an increase in temperature from 350 to
400 °C, the MCP yield passes through a maximum, the
nꢀhexane yield increases up to 22.9 wt.%, and that of
isohexanes reaches 42.4 wt.% (see Fig. 1, b).
hydrogenolysis and the yield of nꢀhexane was <1%. Over
the Pt/Al O —F catalyst (0.3 wt.% F) under similar condiꢀ
tions, cyclohexane is predominantly dehydrogenated to
benzene but the yields of nꢀhexane and MCP are one order
2
3
of magnitude higher than those over Pt/SiO . Less than 1%
2
of cyclohexane is hydrocracked to С —С hydrocarbons.
The introduction of 3.5 wt.% F in the Pt/Al O cataꢀ
1
5
2
3
At a low cyclohexane conversion (11.6%) only benꢀ
zene and a small amount of nꢀhexane are obtained over
lyst changes the pattern of cyclohexane transformation: at
the conversion of <15%, only MCP and benzene are
Table 1. Effect of reaction conditions on the conversion and selectivity of cyclohexane transformations
over the Ptꢀ and Rhꢀcontaining oxide catalysts (molar ratio Н : С Н = 10 : 1)
2
6
12
Catalyst
v
/
p
Т
X
(%)
Y
S (%))
vol
h–1 /MPa /°С
(wt.%)
С —С5 iꢀС Н nꢀС Н
MCP С Н
6 6
1
6
14
6
14
Pt/SiO2
1
1
0.7
0.7
340
340
38.9
37.6
0.4
3.2
—
0.5
—
0.8
1.0
8.5
0.2
4.3
98.8
85.9
Pt/Al O —F
2
3
(
0.3 wt.% F)
Pt/Al O
2
2
2
2
2
2
1
1
2
2
3
1
350
370
370
400
400
350
11.6
34.1
14.7
49.6
41.4
14.5
1.5
2.7
5.2
12.4
17.5
—
—
—
—
1.2
2.9
—
—
0.9
2.7
3.2
8.0
—
12.9
7.9
35.4
25.0
42.3
—
—
5.3
9.5
4.6
8.9
87.1
85.9
52.4
65.9
37.9
39.3
2
3
Pt/Al O —F
60.7
2
3
(
3.5 wt.% F)
Rh/SiO2
Rh/Al O
2
2
2
2
2
5
1
1
3
5
320
280
350
300
280
92.7
33.2
100
91.0
55.9
51.9
24.9
—
59.3
49.0
44.0
23.2
100
34.1
12.3
—
1.8
—
0.7
—
56.0
75.0
—
65.2
87.7
—
—
—
—
—
—
—
—
—
—
2
3
Note. The following designations were used here and in Tables 2, 3: vvol is the cyclohexane space feed rate,
X is the cyclohexane conversion, Y is the nꢀhexane yield, S is the selectivity for products.

Cyclohexane conversion on different catalysts
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 2, February, 2002
251
Y (wt.%)
X (%)
Y (wt.%)
X (%)
1
1
2
1
00
100
a
a
80
80
60
40
20
5
8
6
4
2
0
0
0
0
80
60
40
20
6
4
2
0
0
0
2
4
4
3
3
5
3
00
320
340
360
380
T/°C
3
00
340
380
T/°C
Y (wt.%)
X (%)
Y (wt.%)
00
X (%)
1
6
4
2
0
0
0
60
40
20
1
100
80
b
1
b
8
6
4
2
0
0
0
0
3
60
4
2
40
3
5
3
20
340
360
380
T/°C
X (%)
20
2
Y (wt.%)
1
3
50
370
390
T/°C
c
8
0
80
60
40
20
Fig. 1. Effect of reaction conditions on the cyclohexane converꢀ
sion (X ) (1) and yields (Y ) of benzene (2), nꢀhexane (3), isoꢀ
hexanes (4), and methylcyclopentane (5) over Pt/Al O —F
5
60
40
2
3
(
3.5 wt.% F): pressure 0.7 MPa (a), 2.0 MPa (b), molar ratio
Н2 : C H = 10 : 1 (a) and 5 : 1 (b), cyclohexane space feed
6
12
–
1
rate, 2 h
.
4
2
0
formed with the selectivity for MCP 1.5 times higher than
that for benzene (see Table 1). At pressures above 1 MPa,
the main reaction accompanying cyclohexane transforꢀ
mation over the catalyst becomes isomerization to MCP
followed by hydrogenolysis to isohexanes and nꢀhexane
rather than dehydrogenation to benzene (see Fig. 1, b).
In the presence of the Pt/WO /ZrO bifunctional sysꢀ
3
2
300
320
340
360
T/°C
Fig. 2. Dependence of the cyclohexane conversion (X ) (1) and
yields (Y) of alkanes С —С5 (2), nꢀhexane (3), isohexanes (4),
and methylcyclopentane (5) over the catalysts Pt/WO /ZrO
(a), Pt/La2O3/ZrO2 (b), and Rh/WO3/ZrO2 (c) on temperature
T ) (pressure 2.0 MPa, molar ratio Н : C H = 10 : 1, cycloꢀ
1
3
2
3
2
(
tem containing strong acid sites, cyclohexane predomiꢀ
nantly isomerizes to MCP (Fig. 2, a). At temperatures
2
6
12
–
1
hexane space feed rate, 2 h ).
>
350 °C, isohexanes and nꢀhexane are formed in small
quantities with total yields not exceeding 10 wt.% (Table 2,
Fig. 2, a).
sure, the cyclohexane conversion increases and selectivꢀ
ity for nꢀhexane decreases. Simultaneously, the yield
of the С —С hydrocarbons increases and formation
Selectivity for nꢀhexane is very high for the
Pt/La О /ZrO system possessing the basic properties
1
5
of isohexanes and benzene is detected (see Table 2,
2
3
2
(
see Table 2). With increasing temperature and presꢀ
Fig. 2, b).

252
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 2, February, 2002
Masloboishchikova et al.
Table 2. Effect of the acidꢀbasic properties of the support in Ptꢀ and Rhꢀcontaining catalysts on the
–
1
selectivity of cyclohexane transformations (molar ratio Н : С Н = 10 : 1, vvol = 2 h
)
2
6
12
Catalyst
p
Т
X
Y
S (%)
/
MPa /°С
(%)
(wt.%)
С —С5 iꢀС Н nꢀС Н
MCP
С Н
1
6
14
6
14
6
6
Pt/WO /ZrO
1
2
2
1
2
2
2
2
2
3
3
3
4
1
2
3
3
300
300
400
300
300
350
33.0
38.5
89.8
43.0
43.6
90.6
—
—
2.8
1.2
1.2
—
—
—
—
—
3.1
2.8
2.8
100
100
76.3
90.0
89.4
70.2
54.5
—
2.7
—
—
—
—
—
—
8.4
—
—
—
45.5
—
38.0
—
11.5
5.8
—
3
2
—
7.0
6.5
7.1
20.2
—
5.2
0.7
0.7
3.0
—
3.7
10.0
2.5
Rh/WO /ZrO
3
2
6.0
—
6.6
—
370* 67.9
Pt/La O /ZrO
2
370
400
370
380
400
380
280
280
280
300
18.7
66.6
19.8
36.5
83.3
57.5
33.8
41.7
47.9
100
18.0
29.4
17.1
25.9
43.4
38.5
21.3
30.0
34.1
—
—
96.3
44.1
88.6
71.0
52.1
67.0
63.0
71.9
71.2
—
2
3
5.2
11.4
9.9
10.7
13.2
—
—
—
—
7.7
31.5
19.8
37.0
28.1
28.8
100
Rh/La O /ZrO
2
—
—
—
—
—
—
—
—
2
3
*
Replacement of H for N (molar ratio N : C H = 10 : 1).
2 2 2 6 12
Hence, depending on the acidꢀbasic properties of the
280 °C (pressure 1.0 MPa) is 24.9 wt.% at selectivity of
support and reaction conditions, cyclohexane transforms
over the Ptꢀcontaining catalysts through the following
pathways: dehydrogenation to benzene, isomerization to
MCP, opening of the cyclohexane ring to nꢀhexane, and
hydrogenolysis to С —С alkanes. When Pt is supported
75%, whereas cyclohexane transforms to С —С hydroꢀ
1
5
carbons at 350 °C with the 100% conversion and selectivꢀ
ity. The highest nꢀhexane yield (59.3 wt.%) was obtained
over Rh/Al O at 300 °C and 3.0 MPa. The yield of
2
3
isohexanes is at most 1.8 wt.%. Benzene and MCP are not
formed over the Rh/Al O and Rh/SiO catalysts under
1
5
on SiO or Al O , dehydrogenation of cyclohexane to
2
2
3
2
3
2
benzene prevails. Cyclohexane ring opening to form
conditions of our experiments (see Table 1).
nꢀhexane occurs over the Pt/Al O and Pt/La О /ZrO
The data of Table 2 and Fig. 2, c clarify the activity
and selectivity of the Rhꢀcontaining systems with the acid
(WO /ZrO ) and basic (La O /ZrO ) properties.
2
3
2
3
2
systems. The Broensted acid sites (Bꢀsites) likely parꢀ
ticipate in the formation of the isomerization prodꢀ
ucts (MCP, isohexanes) over the acid catalysts
3
2
2
3
2
Isomerization to MCP is the main pathway of cycloꢀ
hexane transformation over the Rh/WO /ZrO and
(
Pt/Al O —F, Pt/WO /ZrO ). Isohexanes found over
2 3 3 2
3
2
Pt/Al O seem to be the products of secondary reactions.
Pt/WO /ZrO catalysts. With an increase in temperature,
2
3
3 2
Rh catalysts. The Rh/Al O catalysts have been shown
the yield of MCP passes through a maximum, while the
2
3
earlier12 to be the most active and selective in cyclohexꢀ
ane ring opening to form nꢀhexane. As can be seen in
Table 1, cyclohexane hydrogenolysis over the Rh cataꢀ
lysts occurs at temperatures of 280—320 °C, that is,
yields of isohexanes, nꢀhexane, and alkanes С —С
1
5
steadily increase (see Fig. 2). At similar cyclohexane
conversions, the selectivity for MCP is lower over
Rh/WO /ZrO and those for isohexanes and nꢀhexane
3
2
5
0—100 °C lower than that over the Pt/Al O systems.
are substantially higher than over Pt/WO /ZrO (see
3 2
2
3
The reaction conditions strongly affect the pathway of the
cyclohexane transformation over Rh/Al O and Rh/SiO :
both selective ring opening to form nꢀhexane and comꢀ
Table 2). When N is used instead of H , the cyclohexane
2 2
conversion decreases and the MCP and benzene are the
transformation products. Hence, cyclohexane isomerizaꢀ
tion to MCP occurs predominantly over the Ptꢀ and
Rhꢀcontaining catalysts supported on the acid oxides
(Al O —F, WO /ZrO ). Isohexanes and nꢀhexane are proꢀ
2
3
2
plete hydrogenolysis to С —С hydrocarbons can take
1
5
place depending on the temperature and/or pressure. This
catalytic behavior is determined not only by the support
nature (Al O , SiO ) but also by the properties of supꢀ
2
3
3
2
duced upon the hydrogenolysis of MCP and cyclohexane
(see Table 2, Fig. 2).
On the contrary, the cyclohexane ring opening to
form nꢀhexane and the hydrogenolysis of cyclohexꢀ
2
3
2
1
6
ported Rh clusters, since this behavior is due to differꢀ
ences in the activation energies for cracking and ring openꢀ
ing. For example, the nꢀhexane yield over Rh/Al O at
2
3

Cyclohexane conversion on different catalysts
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 2, February, 2002
253
Table 3. Cyclohexane transformations over the Ru catalysts (moꢀ
benzene nor MCP were formed over Ru/Al O and
2 3
Ru/Al O —F under the above conditions.
2 3
–
1
lar ratio Н : С Н = 10 : 1, p = 1.0 MPa, vvol = 2 h
)
2
6
12
Summing up, the overall scheme of cyclohexane transꢀ
formations over the metal oxide catalysts can be preꢀ
sented as follows.
Catalyst
Т
X
SnꢀC6H14 Yield of products (wt.%)
/
°С (%)
(%)
С —С iꢀС Н nꢀС Н
1
5
6
14
6
14
Ru/Al O
200
11.9 66
29.4 53
0
5.5 65
30.9 44
4.1
—
0.3
—
—
—
7.8
15.7
—
3.6
13.6
—
2
3
2
2
10
30 100
13.4
100
1.9
17.3
100
Ru/Al O —F 190
2
3
(
3.5 wt.% F) 210
2
30 100
0
—
ane to С —С alkanes prevail over the basic catalysts
1
5
(
Rh/La O /ZrO and Pt/La O /ZrO ). The nꢀhexane
2 3 2 2 3 2
yield over Rh/La O /ZrO reaches 34.1 wt.% with selecꢀ
2
3
2
tivity of 71.2%.
It has been shown earlier13 that the Bꢀsites and metalꢀ
lic particles participate in cyclohexane ring opening over
bifunctional catalysts and this process involves alkylꢀ
cyclopentanes. When the support has no Bꢀsites,7,12 ring
opening occurs through the С—С bond rupture over the
metal (Pt, Rh, Ru) and nꢀhexane and alkanes with lower
molecular weights are formed.
A preferable reaction path depends on the metal naꢀ
ture, acidꢀbasic properties of the support, and the reacꢀ
tion conditions.
Dehydrogenation of cyclohexane to benzene occurs
over Pt/SiO and Pt/Al O , and cyclohexane ring openꢀ
Considerable differences in selectivity of Ptꢀ and
Rhꢀcontaining catalysts on the acid and basic supports
can be due not only to the support properties but also the
different dispersion of the metal particles. The difference
in sizes of the metal particles causes a change in the metal
charge during the formation of specific active sites at the
metal—support interface.16 For example, a bifunctional
site, a positively charged adduct of the metal particle
with a proton, can be formed upon interaction beꢀ
2
2
3
ing to form nꢀhexane, whilst to a lesser extent, takes place
over Pt/Al O . Depending on the reaction conditions,
2
3
dehydrogenation of cyclohexane to benzene or its isomerꢀ
ization to MCP followed by С cycle opening and forꢀ
5
mation of a mixture of hexane isomers prevails over
Pt/Al O —F.
2
3
The catalysts containing Pt and Rh on the solid
superacid WO /ZrO , are characterized by the high yield
3
2
1
6,17
tween the Rh (or Pt) small particles and Bꢀsites.
and selectivity to MCP. When the basic support is used
(La О /ZrO ), a high selectivity in cyclohexane ring openꢀ
These sites are capable of catalyzing С—С bond hydroꢀ
genolysis.
2
3
2
ing to form nꢀhexane was found. The opening of the С6
ring to form nꢀhexane and hydrogenolysis to С —С alꢀ
Ru catalysts. The Ru systems are active in cyclohexꢀ
ane hydrogenolysis at lower temperatures than the Rh
and Pt catalysts (cf. the data of Tables 1—3). The
hydrogenolysis of cyclohexane to form nꢀhexane and alꢀ
kanes with lower molecular weights is the main pathꢀ
1
5
kanes are the main reactions over the Rh/Al O , Rh/SiO ,
2
3
2
and Ru catalysts.
In terms of the maximal yield of nꢀhexane formed
upon cyclohexane ring opening, the catalysts studied can
way of cyclohexane transformation over Ru/Al O and
be arranged in the following sequence: Rh/Al O >
2 3
2
3
Ru/Al O —F (see Table 3).
> Rh/SiO2 > Pt/La О /ZrO > Rh/La O /ZrO >>
2 3 2 2 3 2
2
3
The cyclohexane conversion at temperatures of
>> Pt/Al O ≈ Ru/Al O .
2 3 2 3
2
10—230 °C over the Ru catalysts varies from 30 to 100%,
The most active and selective catalyst in this reaction
is Rh/Al O .
whereas the Pt and Rhꢀcontaining catalysts are inactive
in fact. The yield of nꢀhexane and selectivity of its formaꢀ
tion strongly depend on the reaction temperature. When
the temperature increases from 190—200 to 230 °C the
selectivity drops from 65% to 0. The maximal yield of
nꢀhexane over Ru/Al O was 15.7 wt.% at the selectivity
of 53%. The yield of С —С hydrocarbons changes in
parallel to the cyclohexane conversion, and only С —С
alkanes, mainly methane, are formed at 230 °C. Neither
2
3
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Received July 26, 2001;
in revised form October 11, 2001