7.7 Unique Properties of Silver Cations …
199
In-ZSM-5 also gave benzene and toluene. The main product was propylene, with
singly
13 C-labeled propylene (
13 CC 2 H 6 ) being formed to varying extents. However, no multi
13 C-labeled propylene or other hydrocarbons were observed. The
13 CC 2 H 6 fraction of the produced propylene depended on the kind of metal cations,
clearly indicating that methane was activated on metal cations and/or metal cationic
species via Mechanism 2, not Mechanism 1. Furthermore, propylene was produced by both the reaction of CH 4 with C 2 H 4 and the direct conversion of C 2 H 4 via
oligomerization/cracking reactions.
When the zeolite In-ZSM-5 was used as a catalyst, singly
13 C-labeled toluene
(
13 CC 6 H 8 ) was also produced. The fraction of
13 C-labeled toluene (
13 CC 6 H 8 ) among
the total toluene was 54%. However, the
13 CC 5 H 6 fraction of benzene was 9%, which
was close to the percentage expected based on the natural abundance of
13 C atoms,
indicating that the benzene originated solely from C 2 H 4 , and was not produced by
the conversion of propylene.
To investigate the position of
13 C atom in the
13 CC 6 H 8 , its fragmentation MAS
spectrum was measured [90]. Two kinds of
13 C-labeled toluene were observed:
13 CH 3 –C 6 H 5 and CH 3 –
13 CC 5 H 5 . The fraction of
13 CH 3 –C 6 H 5 in the produced
toluene was 17%, while that of CH 3 -
13 CC 5 H 5 was 37% (54 – 17 = 37%).
13 CH 3 -
C 6 H 5 was produced by the reaction of
13 CH 4 with benzene. CH 3 -
13 CC 5 H 5 was
presumably formed by the reaction of
13 CC 2 H 6 with butanes (C 4 H 8 ) produced by
the dimerization of C 2 H 4 and/or by isomerization of
13 CH 3 –C 6 H 5 .
7.7.6.3 Reaction of
13 CH 4 with Benzene Using in-ZSM-5
According to Mechanism 2,
+ CH 3 carbenium ions should be also generated over
M-cation zeolites in addition to Ag-zeolites. To provide experimental evidence for
this, the reaction of
13 CH 4 with benzene was carried out for 1 min using In-ZSM-5
in a closed gas-circulation reactor. The reaction temperature was 673 K, and the
pressures of
13 CH 4 and benzene were 39.8 and 1.63 kPa, respectively. Under the
above reaction conditions, the conversion of benzene was 5.6%, and both toluene
and H 2 were reaction products. The mole fraction of singly
13 C-labeled toluene in the
total produced toluene was 97%, indicating that the
+ CH 3 carbenium ions generated
on In-ZSM-5 subsequently reacted with benzene to produce toluene. Therefore,
methane can be activated not only by Ag
+
n cationic clusters but also metal cations,
such as In cations, to generate
+ CH 3 carbenium ions via Mechanism 2 (reaction
(7.52)).
As described in Sect. 7.7.7.2, both
13 CH 3 –C 6 H 5 and CH 3 –
13 CC 5 H 5 were produced in the reaction of
13 CH 4 with C 2 H 4 over In-ZSM-5. To further investigate
the position of the
13 C atom in the singly
13 C-labeled toluene, the fragmentation
of toluene was analyzed using mass spectroscopy. The fragmentation spectrum of
the
13 C-labeled toluene is shown in Fig. 7.6 as Spectrum A, while that of
13 C-free
toluene (CH 3 –C 6 H 5 ) is shown as Spectrum B. In spectrum A, the main peak observed
199
In-ZSM-5 also gave benzene and toluene. The main product was propylene, with
singly
13 C-labeled propylene (
13 CC 2 H 6 ) being formed to varying extents. However, no multi
13 C-labeled propylene or other hydrocarbons were observed. The
13 CC 2 H 6 fraction of the produced propylene depended on the kind of metal cations,
clearly indicating that methane was activated on metal cations and/or metal cationic
species via Mechanism 2, not Mechanism 1. Furthermore, propylene was produced by both the reaction of CH 4 with C 2 H 4 and the direct conversion of C 2 H 4 via
oligomerization/cracking reactions.
When the zeolite In-ZSM-5 was used as a catalyst, singly
13 C-labeled toluene
(
13 CC 6 H 8 ) was also produced. The fraction of
13 C-labeled toluene (
13 CC 6 H 8 ) among
the total toluene was 54%. However, the
13 CC 5 H 6 fraction of benzene was 9%, which
was close to the percentage expected based on the natural abundance of
13 C atoms,
indicating that the benzene originated solely from C 2 H 4 , and was not produced by
the conversion of propylene.
To investigate the position of
13 C atom in the
13 CC 6 H 8 , its fragmentation MAS
spectrum was measured [90]. Two kinds of
13 C-labeled toluene were observed:
13 CH 3 –C 6 H 5 and CH 3 –
13 CC 5 H 5 . The fraction of
13 CH 3 –C 6 H 5 in the produced
toluene was 17%, while that of CH 3 -
13 CC 5 H 5 was 37% (54 – 17 = 37%).
13 CH 3 -
C 6 H 5 was produced by the reaction of
13 CH 4 with benzene. CH 3 -
13 CC 5 H 5 was
presumably formed by the reaction of
13 CC 2 H 6 with butanes (C 4 H 8 ) produced by
the dimerization of C 2 H 4 and/or by isomerization of
13 CH 3 –C 6 H 5 .
7.7.6.3 Reaction of
13 CH 4 with Benzene Using in-ZSM-5
According to Mechanism 2,
+ CH 3 carbenium ions should be also generated over
M-cation zeolites in addition to Ag-zeolites. To provide experimental evidence for
this, the reaction of
13 CH 4 with benzene was carried out for 1 min using In-ZSM-5
in a closed gas-circulation reactor. The reaction temperature was 673 K, and the
pressures of
13 CH 4 and benzene were 39.8 and 1.63 kPa, respectively. Under the
above reaction conditions, the conversion of benzene was 5.6%, and both toluene
and H 2 were reaction products. The mole fraction of singly
13 C-labeled toluene in the
total produced toluene was 97%, indicating that the
+ CH 3 carbenium ions generated
on In-ZSM-5 subsequently reacted with benzene to produce toluene. Therefore,
methane can be activated not only by Ag
+
n cationic clusters but also metal cations,
such as In cations, to generate
+ CH 3 carbenium ions via Mechanism 2 (reaction
(7.52)).
As described in Sect. 7.7.7.2, both
13 CH 3 –C 6 H 5 and CH 3 –
13 CC 5 H 5 were produced in the reaction of
13 CH 4 with C 2 H 4 over In-ZSM-5. To further investigate
the position of the
13 C atom in the singly
13 C-labeled toluene, the fragmentation
of toluene was analyzed using mass spectroscopy. The fragmentation spectrum of
the
13 C-labeled toluene is shown in Fig. 7.6 as Spectrum A, while that of
13 C-free
toluene (CH 3 –C 6 H 5 ) is shown as Spectrum B. In spectrum A, the main peak observed