Novel activity of SnO2 for methanol conversion: Formation of methane, carbon dioxide, and hydrogen

Article abstract of DOI:10.1246/cl.2002.390

SnO₂ catalyzed methanol conversion to form methane, carbon dioxide and hydrogen selectively. It was suggested that formaldehyde was an intermediate to give methyl formate that readily decomposed into methane and carbon dioxide.

Full text of DOI:10.1246/cl.2002.390

390
Chemistry Letters 2002
Novel Activity of SnO2 for Methanol Conversion:
Formation of Methane, Carbon Dioxide, and Hydrogen
Tohru Mori, Shunichi Hoshino, Arthit Neramittagapong, Jun Kubo, and Yutaka Morikawaꢀ
Chemical Resources Laboratory, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama 226-8503
(Received December 14, 2001; CL-011261)
SnO2 catalyzed methanol conversion to form methane,
The reaction of methanol was carried out in a conventional
flow-type reaction system with a Pyrex glass reactor under
atmospheric pressure. The feed gas consisted of 25 vol% of
carbon dioxide and hydrogen selectively. It was suggested that
formaldehyde was an intermediate to give methyl formate that
readily decomposed into methane and carbon dioxide.
methanol and N2 balance. The total flow rate was 40 cm3 minÀ1
.
The catalysts were pretreated in an N2 stream at 450 ꢁC for 2 h
prior to the reaction. The feed and effluent gases were analyzed
with an on-line gas chromatograph (Shimadzu GC-7A) equipped
with a thermal conductivity detector and a flame ionization
detector using Porapak-T and Molecular Sieve 13X columns.
Table 1 summarizes the activities of various metal oxide
catalysts. The reactions over three SnO2 catalysts were not
different substantially and yielded methane, carbon dioxide, and
formaldehyde. Methane and carbon dioxide were formed in
approximately equal amount and their total selectivity was higher
than 80%. Small amounts of carbon monoxide and dimethyl ether
and a detectable amount of methyl formate were also formed. The
product distribution indicates that the reaction (1) takes place on
SnO2 selectively. The specific rates of methanol conversion were
4.65, 4.12, and 5.31 ꢀmol minÀ1 mÀ2 for SnO2-A, -B, and -C,
respectively, suggesting that the catalytic activity was indepen-
dent on the surface structure. The other oxides of metal
neighboring on a periodic table, PbO, Sb2O3, and Bi2O3, were
also tested for the reaction (not shown). However, these oxides
were reduced to metallic state during the reaction yielding carbon
dioxide and water at even relatively low temperature of 350 ꢁC,
and did not show any catalytic activity.
MgO and ZnO catalyzed the decomposition of methanol into
carbon monoxide and hydrogen. The major products over CeO2
were carbon monoxide and methane. The amount of carbon
monoxide was twice or more higher than that of methane. The
result suggests that carbon monoxide was formed by the
decomposition of methanol and a reverse water gas shift reaction
between carbon dioxide and hydrogen formed by the reaction (1).
La2O3 is known to have both acidic and basic properties,6 and
gave the decomposition and the dehydration products, carbon
monoxide and dimethyl ether. ZrO2 is relatively more acidic than
Methanol is one of the important feedstocks in chemical
industries. Methanol is decomposed into carbon monoxide and
hydrogen over metal catalysts,1 dehydrogenated into formalde-
hyde or methyl formate over Zn- or Cu-containing catalysts,2;3
and dehydrated into dimethyl ether and successively to hydro-
carbons over acid catalysts.4 Shido et al.5 reported that Mo dimer
oxycarbide species in NaY supercages catalyzed a conversion of
methanol into methane, carbon dioxide and hydrogen (eq 1).
However, the catalyst also promoted dehydration of methanol to
form dimethyl ether.
2CH3OH ! CH4 þ CO2 þ 2H2
ð1Þ
Recently, we found that SnO2 promoted the reaction (1)
selectively. The results are reported here.
Three kinds of SnO2 were employed as catalysts. SnO2-A
was prepared by decomposition of tin hydroxide. SnCl4Á5H2O
was dissolved in distilled water and an Na2CO3 solution was
added until pH value attained 4. The resultant precipitate was
washed until noClÀ ions were detected, driedovernight at110 ꢁC,
and then calcined at 450 ꢁC in air for 2 h. SnO2-B and SnO2-C
were purchased from Kanto Chemical Co. and Soekawa
Chemicals, respectively. MgO, ZnO, ZrO2, La2O3, and CeO2
were obtained by decomposition of magnesium carbonate, zinc
carbonate, zirconium hydroxide, lanthanum hydroxide, and
cerium hydroxide, respectively, in an N2 stream at 450 ꢁC for
2 h. The BET surface area of metal oxide was measured by N2
adsorption at liquid nitrogen temperature using a conventional
flow-type adsorption apparatus. Powder X-ray diffraction (XRD)
patterns of fresh and used catalyst were recorded with Rigaku
RAD-1VB.
Table 1. Catalytic reaction of methanol over various metal oxides at 375 ꢁC
Surface area
/m2gÀ1
Catalyst weight
/g
Conversion
/%
Selectivity/%
CH2O CO
Catalyst
CH4
CO2
MF
D
ME
SnO2-A
SnO2-B
SnO2-C
MgO
ZnO
CeO2
50
32
12
252
37
94
51
0.3
1.0
1.0
1.0
0.2
1.0
1.0
1.0
15.6
29.2
13.8
9.2
35.0
14.9
14.4
46.4
39.3
43.4
38.9
0
0.5
30.2
0
39.8
45.6
40.4
1.9
10.9
1.8
17.4
7.8
18.2
0.4
5.0
0.3
2.8
8.0
0.7
0.9
0.8
94.1
76.9
65.6
60.5
0.3
0
tr.
tr.
0
0
0
2.8
2.3
1.7
3.5
0.2
2.1
La2O3
ZrO2
3.7
0
0
0
36.9
91.6
141
tr.
MF, methyl formate and DME, dimethyl ether.
Copyright Ó 2002 The Chemical Society of Japan

Chemistry Letters 2002
391
above oxides and catalyzed the dehydration into dimethyl ether
preferentially.
Figure 1 shows the results of the reaction over SnO2-A at
various temperatures. The catalytic activity did not change
appreciably throughout the reaction and no difference was
observed between the XRDpatterns of fresh and used catalysts.
The values of selectivity to methane and carbon dioxide increased
with increasing reaction temperature, while the selectivity to
formaldehyde decreased from 24.7% at 350 ꢁC to 11.1% at
400 ꢁC.
Figure 2. Change in conversion and product selectivity
as a function of W=F in the reaction of methanol over
SnO2-B at 375 ꢁC; conversion of methanol (l), and
selectivities to methane (ꢂ), carbon dioxide (Ã),
formaldehyde (4), carbon monoxide (}), and dimethyl
ether (5).
Figure 1. Reaction of methanol over SnO2-A at various
temperatures; conversion of methanol (l) and selectiv-
ities to methane (ꢂ), carbon dioxide (Ã), formaldehyde
(4), carbon monoxide (}), and dimethly ether (5). The
amount of catalyst was 0.3 g.
Figure 2 shows the effect of contact time (W=F) on the
conversion and selectivity in the reaction over SnO2-B at 375 ꢁC.
The conversion increased up to 50% with W=F linearly.
Formation of methane and carbon monoxide in an equal amount
was observed again at any conversion level and increased with
W=F, while the selectivity to formaldehyde decreased. The
results indicate that the reaction (1) takes place over the SnO2
catalyst through the dehydrogenation of methanol to formalde-
hyde and subsequent reaction to form methane and carbon
dioxide.
Scheme 1 summarizes the reaction pathway deduced from
the results mentioned above. Since methane and carbon dioxide
are formed in the same amount by the reaction, they seem to be
formed via decomposition of methyl formate species adsorbed on
SnO2 catalyst. Methanol is dehydrogenated to formaldehyde over
SnO2 catalyst and formaldehyde reacts subsequently with
methanol to form methyl formate, as proposed for the
dehydrogenation of methanol over Cu catalyst.7 Methyl formate
was formed in very small amounts as seen in Table 1. It is
assumed that the methyl formate species formed on SnO2 is
Scheme 1.
unstable under the reaction conditions and is readily decomposed
into methane and carbon dioxide.
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