Dehydrogenation of methanol on low Cu and Re - Cu catalysts supported on sibunite

Article abstract of DOI:10.1023/A:1021303622225

The activity and selectivity of mono- and bimetallic catalysts containing copper and rhenium on sibunite were studied in the decomposition of methanol to methyl formate (MF), water, H₂, CO, and CO₂ at 200-400°C. Methane is also forme

Full text of DOI:10.1023/A:1021303622225

1698
Russian Chemical Bulletin, International Edition, Vol. 51, No. 9, pp. 1698—1701, September, 2002
Dehydrogenation of methanol on low Cu and Re—Cu catalysts
supported on sibunite
b
b
b
M. A. Ryashentseva,a E. V. Egorova, A. I. Trusov, and S. N. Antonyuk
ꢀ
aN. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5328. Eꢀmail: secretary@ioc.ac.ru
bM. V. Lomonosov Moscow State Academy of Fine Chemical Technology,
86 prosp. Vernadskogo, 117571 Moscow, Russian Federation.
Fax: +7 (095) 434 8711. Eꢀmail: nhsigt@unesco.mitht.rssi.ru
The activity and selectivity of monoꢀ and bimetallic catalysts containing copper and
rhenium on sibunite were studied in the decomposition of methanol to methyl formate (MF),
water, Н2, СО, and СО2 at 200—400 °С. Methane is also formed on rheniumꢀcontaining
catalysts at 300—400 °С. The dehydrogenating activity and selectivity to form MF are higher
on the copperꢀsibunite catalysts than on the rheniumꢀsibunite samples. The introduction of
0.25% Re into the 4% copperꢀcontaining catalyst enhances its total activity and stability.
Key words: supported monometallic copperꢀ and rheniumꢀcontaining catalysts, bimetalꢀ
lic rhenium,copperꢀcontaining catalysts, methanol, methyl formate, dehydrogenation, sibunite.
Catalytic dehydrogenation of methanol is a preꢀ
Experimental
parative method for the synthesis of methyl formate
(MF), which is a starting product for such valuable
compounds as formic and acetic acids, formamide,
and DMF.
The reaction was carried out in a flowꢀtype quartz reactor
(450×12 mm) at 150—400 °С and atmospheric pressure. The
weight of the catalyst sample was 0.7 g. Methanol (reagent
20
20
grade, nD 1.3288, d4 0.7912) was supplied to the reactor
using an automated plungerꢀtype dosing system with a space
velocity v = 7.5 h–1. The duration of each run was 30 min.
Liquid products were analyzed by an LKhMꢀ8MD chroꢀ
matograph with a thermal conductivity detector (column
2 m×3 mm packed with 10% Tweenꢀ60 on Polychromꢀ1). The
internal standard method was used to estimate the quantitative
composition of the liquid products with an accuracy of 4 rel.%.
Gaseous products were analyzed by gas adsorption chromatogꢀ
raphy on three packed columns using a thermal conductivity
detector. Column А (3 m×3 mm) was packed with the SKT
carbon, column B (1.7 m×3 mm) was packed with molecular
sieves 5 Å, and column C (2 m×3 mm) was packed with Polisorb.
Argon served as the carrier gas in column A, and helium was
used in columns B and C. The gas composition was determined
with an error not higher than 3 rel.%.
Sibunite was used as the support for the catalysts. Its filled
mass was 0.6 g cm–3, and the specific surface measured by
nitrogen adsorption was 680 m2 g–1 and that estimated by pheꢀ
nol adsorption was 230 m2 g–1. The granules were 2—3 mm in
size (see Ref. 5).
Samples of the monometallic copperꢀ and rheniumꢀconꢀ
taining catalysts were prepared by the impregnation of the supꢀ
port with aqueous solutions of copper salts and ammonium
perrhenate, respectively. The combined impregnation of sibunite
with aqueous solutions of the copper salts and ammonium
perrhenate was used to obtain bimetallic copperꢀrhenium cataꢀ
The copperꢀcontaining catalytic systems based on
aluminacalcium cements1 with an optimum content of
copper of 40 wt.% manifest a high activity in the dehyꢀ
drogenation of methanol to MF. However, at high temꢀ
peratures the catalyst activity decreases probably because
of sintering of copper.2 The system containing copper,
zinc, aluminum, and alkaline metal oxides is also an
active and selective catalyst for the synthesis of MF.3
The introduction of promoting additives, such as zircoꢀ
nium dioxide,4 into the copperꢀcontaining catalysts imꢀ
proves their timeꢀon stream behavior.
The nature of the support has a great effect on the
activity and selectivity of catalytic systems. A new class
of supports, viz., sibunites, is of considerable interest.
They are prepared by introducing the pyrolytic carbon
layer on the surface of technical carbon.5 The Cu(1%)/Sib
catalyst (Sib is sibunite) is active in the dehydrogenation
of isopropyl alcohol to acetone. The introduction of
1% rhenium into the same catalyst enhances its activity
and selectivity.6
In this work an attempt is made to develop a selective
low copper catalyst supported on sibunite for the dehyꢀ
drogenation of methanol to MF and to estimate the inꢀ
fluence of rhenium additives on its characteristics.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1559—1561, September, 2002.
1066ꢀ5285/02/5109ꢀ1698 $27.00 © 2002 Plenum Publishing Corporation

Dehydrogenation of methanol on supported catalysts Russ.Chem.Bull., Int.Ed., Vol. 51, No. 9, September, 2002
1699
Table 1. Composition of products of methanol transformation on the sibuniteꢀsupported monoꢀ and bimetallic catalysts
(p = 0.1 MPa, v = 7.5 h–1
)
Catalyst
T/°С
Composition of products (mol.%)
X*
SMF**
МMF
MeОН
H2O
Н2
СО
СН4
СО2
%
Cu(1%)/Sib
200
225
250
300
400
200
225
250
300
400
200
250
300
400
200
250
300
400
200
250
300
400
200
250
300
0.4
0.8
1.0
0.5
0.2
Traces
0.2
0.4
0.7
0.4
0.6
1.3
1.2
0.1
0.2
0.6
1.1
0.4
97.7
96.1
95.7
96.8
92.3
99.4
98.7
97.6
95.6
79.6
98.4
95.7
94.1
97.0
99.2
97.2
92.3
73.9
98.8
95.6
88.1
72.0
98.9
96.6
92.9
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
1.4
2.7
3.0
2.2
6.7
0.4
0.9
1.7
3.0
14.8
1.0
2.6
3.0
2.3
0.6
2.0
3.7
14.5
0.9
3.3
8.8
20.1
0.5
1.9
3.0
—
Traces
0.1
0.3
0.6
—
Traces
0.1
0.4
4.5
Traces
0.4
1.4
0.5
Traces
0.2
—
—
—
—
—
0.3
0.2
Traces
Traces
—
Traces
Traces
0.1
2.3
3.9
4.3
3.2
7.7
0.6
1.3
2.4
4.4
20.4
1.6
4.3
5.9
3.0
0.8
2.8
7.7
26.1
1.2
4.4
11.9
28.0
1.1
3.4
7.1
34.8
41.0
46.5
31.3
5.2
Re(1%)/Sib
—
—
0
30.8
33.3
31.8
3.9
69.0
59.1
42.1
6.7
50.0
42.9
28.6
3.1
33.3
27.3
10.1
0
Traces
Traces
0.1
Traces
Traces
0.2
Traces
—
Traces
Traces
0.2
0.1
0.4
0.2
Cu(2%)/Sib
Re(2%)/Sib
Traces
Traces
Traces
0.1
Traces
Traces
Traces
Traces
0.1
0.1
0.1
0.1
0.1
Traces
Traces
0.1
Traces
Traces
Traces
0.2
0.4
Traces
0.1
2.7
10.6
Traces
0.3
2.0
6.6
0.1
0.6
3.0
Cu(1%)+
+Re(1%)/Sib
0.2
0.6
0.6
Traces
0.3
—
Traces
Traces
0.3
Traces
Traces
0.1
0.4
0.9
0.1
0.2
Cu(2%)+
+Re(2%)/Sib
59.2
35.1
12.5
0.6
0.4
0.1
0.1
0.5
* Total conversion of MeOH.
** Selectivity for MF formation.
lysts. The samples were dried at 120 °С and reduced in a hydroꢀ
gen flow at 400 °С.
The sibuniteꢀsupported monometallic catalysts containing
1, 2, and 4% Сu or 1 and 2% Re and bimetallic samples with
the Cu content from 1 to 4% and the Re content from 0.25 to
2% were used (Table 1).
The degree of methanol conversion was taken as a measure
of the catalytic activity. The selectivity to form MF (SMF) was
estimated from the content of MF in the reaction products.
The fraction of MF in the liquid products increases as
the temperature increases from 200 to 250—300 °C. Howꢀ
ever, side reactions resulting in the formation of CO and
CH4 begin to occur simultaneously. According to the
available data,7,8 MF formation on the copperꢀcontainꢀ
ing catalysts proceeds via dehydrogenation of methanol
2 MeOH → HCOOMe + 2 H2.
(1)
In addition, the following reactions can occur:
decarbonylation of the MF that formed1,9
HCOOMe → MeOH + CO,
Results and Discussion
(2)
(3)
Sibunite alone does not decompose methanol at
150—400 °С, and at temperatures >400 °С СО and Н2
are formed in the 1 : 2 molar ratio due to the thermal
decomposition.
Liquid products of methanol transformation formed
at 200—400 °С on monometallic catalysts containing
1% and 2% Cu or Re and on the corresponding bimetalꢀ
lic samples contain the unreacted alcohol, MF, and waꢀ
ter (see Table 1). Gaseous products contain hydrogen,
carbon monoxide, and carbon dioxide. At temperaꢀ
tures >300 °С methane is formed on the rheniumꢀconꢀ
taining samples.
decomposition of MF to CO and hydrogen10
HCOOMe → 2 CO + 2 H2,
decomposition of MF to carbon dioxide and methane8
HCOOMe → CO2 + CH4,
waterꢀgas shift reaction11
CO + H2O → CO2 + H2
(4)
(5)
(6)
and steam conversion of methanol12,13
MeOH + H2O → CO2 + 3 H2.

1700
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 9, September, 2002
Ryashentseva et al.
Table 3. Influence of the rhenium content in the sibuniteꢀ
supported copperꢀcontaining catalysts on the total conversion
(X (%)) and selectivity of methyl formate formation (SMF (%))
in the dehydrogenation of methanol* at 200 (I), 250 (II), and
300 °C (III)
Based on the thermodynamics of methanol dehydroꢀ
genation,14 equilibrium concentrations of MF are in the
range from 20 to 50%. Methanol and MF are capable of
forming intermediates, which are tightly bound to the
surface.15,16
The conversion of methanol to MF on the monomeꢀ
tallic copperꢀ and rheniumꢀcontaining sibuniteꢀsupported
catalysts increases as the temperature increases from 200
to 250—300 °С. Higher temperatures decrease the deꢀ
hydrogenating activity.
Initial
sample
C**
X
SMF
I
II
III
I
II
III
Cu(2%)/Sib
0
1.6
4.3
4.1
3.7
3.5
3.4
2.2
5.8
5.2
4.7
5.9
6.2
6.4
6.9
7.1
3.1
8.7
8.4
8.6
69.0 59.1 42.1
66.4 52.5 36.0
62.5 49.9 28.4
60.0 42.4 17.1
59.2 35.1 12.5
65.8 55.6 20.0
63.5 52.6 28.2
62.3 52.5 25.5
53.5 44.3 20.8
0.25 1.5
An increase in the rhenium content from 1 to 2%
increases SMF from 33.3 to 42.9% at 250 °С. A similar
increase in the copper content in the monometallic
sample increases the selectivity from 46.5 to 59.1%.
The decomposition of MF was studied on the
Cu(1%)/Sib and Re(1%)/Sib samples (Table 2). At 200 °С
the amount of methanol formed on the copperꢀcontainꢀ
ing sample is ∼3 times greater than that formed on the
rheniumꢀcontaining sample. On the Re(1%)/Sib cataꢀ
lyst the CO : H2 ratio is equal to 1, which corresponds to
the stoichiometry of reaction (3), whereas on the copꢀ
perꢀsibunite catalyst it is ∼2. The decomposition of
MF has previously been studied in detail13 on the
CuO/ZnO/Al2O3 catalyst. A kinetic analysis of this proꢀ
cess showed that the formation of CO was mainly caused
by reaction (3). According to the published results,13 the
data in Table 1 indicate that the change in the selectivity
of MF conversion is antiparallel to the conversion of
methanol, and this determines a low yield of MF.
Methanol dehydrogenation occurs as a successive reꢀ
action through stages (2) and (3).14 At high conversions
the selectivity with respect to MF decreases rapidly due
to the decomposition of MF in reaction (3). The kinetics
and mechanism of MF transformations on the copperꢀ
containing catalysts were considered in detail in several
works.15—17
0.5
1.0
2.0
0
0.25 1.5
0.5
1.0
1.4
1.3
1.1
1.3
Cu(4%)/Sib
2.7
2.3
* p = 0.1 MPa, v = 7.5 h–1
** Content of Re (wt.%).
.
When the reaction temperature increases from 200 to
300 °С, the dehydrogenating activity of the monometalꢀ
lic samples containing 2 and 4% Cu changes insignifiꢀ
cantly. The introduction of Re (from 0.25 to 1%) into
the Cu(4%)/Sib sample enhances the total conversion of
methanol at 300 °С almost threefold, whereas an increase
in selectivity is insignificant. The Cu(4%)+Re(0.25%)
sample on sibunite exhibits the highest dehydrogenating
activity.
It can be assumed that at high temperatures copper
sintering occurs more intensely on the samples without a
rhenium additive. The timeꢀon stream behavior of these
two samples was studied for 24 h of the continuous opꢀ
eration at 250 °С and v = 7.5 h–1. On the monometallic
Cu(4%)/Sib sample the total conversion of methanol
after operation for 1 h was 11%. It decreased to 8% after
24 h on stream, and the selectivity of MF formation
decreased from 55 to 49%. The total conversion of methaꢀ
nol on the Cu(4%)+Re(0.25%)/Sib sample was twice as
high (∼23%) and remained virtually unchanged. The seꢀ
lectivity for MF formation (41 2%) also remained unꢀ
changed.
Bimetallic samples containing 1 or 2% Cu and Re
exhibit similar dehydrogenating activities at 200 and
250 °С (see Table 1). The data on the influence of the
rhenium additives to the copperꢀcontaining catalysts on
their dehydrogenating activity are presented in Table 3.
The strong interaction of the metal with the oxide
support suppressing the reduction of the metal on the
surface can be observed in conventional supported cataꢀ
lysts.18—20 In metalꢀcarbon catalysts, unlike metalꢀoxide
catalysts, there is no strong interaction of the metal with
the support, and that facilitates the reduction of the acꢀ
tive component on the surface.20
Thus, our study shows that the introduction of rheꢀ
nium into the copperꢀsibunite catalyst enhances its acꢀ
tivity in methanol dehydrogenation and timeꢀon stream
behavior. These properties are characteristic of rheniumꢀ
containing catalytic systems.21
Table 2. Decomposition of methyl formate on the sibuniteꢀ
supported monometallic catalysts (p = 0.1 MPa, v = 7.5 h–1
)
Cataꢀ
lyst
Т/°С
Composition of products (mol.%)
НСООMe MeОН Н2О Н2 СО СО2
Cu(1%)/Sib 200
83.8
92.2
93.7
95.3
94.1
92.6
6.4
3.1
2.5
2.0
1.9
1.4
0.1
0.2
0.3
0.2
0.6
0.9
3.0
1.3
1.0
0.2
1.2
2.5
6.3
3.0
2.4
0.2
1.2
2.4
0.4
0.2
0.1
2.2
1.0
0.3
225
250
Re(1%)/Sib 200
225
250

Dehydrogenation of methanol on supported catalysts Russ.Chem.Bull., Int.Ed., Vol. 51, No. 9, September, 2002
1701
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Received June 20, 2001;
in revised form November 14, 2001