208
7 C–C Bond Formation via Carbocations in the Methane …
(7.60)
(7.61)
C
CH 3
H 3 C
H 2 + C 4 H 8
CH 4 + C 3 H 6
CH 3
H
Thus, the formation rates of H 2 and CH 4 are the rates of the C–H and C–C bond
cleavage reactions, respectively. The primary reaction rates over Ag- and Zn-ZSM-5
zeolites, together with those for H-ZSM-5, are summarized in Table 7.10. The rates of
the C–H bond cleavage reaction over Ag- and Zn-ZSM-5 zeolites are much faster than
that over H-ZSM-5. The rate of the C–C bond cleavage reaction (reaction (7.61)) over
Ag-ZSM-5 is evidently different from that over Zn-ZSM-5. Ag-ZSM-5 suppressed
this reaction (the formation of CH 4 ), as compared with H-ZSM-5, while Zn-ZSM-5
greatly enhanced it. The ratio of the CH 4 formation rates is Zn-ZSM-5/H-ZSM-5 =
81:5.
(3) n-Pentane cracking
In n-pentane cracking, the following four primary reactions occur.
(7.62)
(7.63)
(7.64)
(7.65)
CH 3 CH 2 CH 2 CH 2 CH 3
H 2 + C 5 H 10
CH 4 + C 4 H 8
C 2 H 6 + C 3 H 6
C 3 H 8 + C 2 H 4
The C–H bond cleavage reaction (reaction (7.62)) gives H 2 and C 5 H 10 . C 5 H 10 is
readily decomposed to lower alkenes and alkanes. The C–C bond cleavage reaction
gives CH 4 , C 2 H 6 , and C 3 H 8 as primary reaction products through reactions (7.63),
(7.64), and (7.65), respectively. The reaction rate for each of the above reactions
is summarized in Table 7.10. Over H-ZSM-5, the ratio of the C–H bond cleavage
reaction rate to that of the C–C bond cleavage reaction was 4:11. The rates of the
C–H bond cleavage reaction (reaction (7.62)) over the zeolites Ag- and Zn-ZSM-5
were about 20 times faster than the rate over H-ZSM-5. The formation rates of CH 4 ,
C 2 H 6 , and C 3 H 8 over Ag-ZSM-5 were almost comparable to those over H-ZSM-5.
However, the formation rates of these alkanes over Zn-ZSM-5 were almost three
times faster than over H-ZSM-5.
(4) iso-Pentane cracking
In iso-pentane cracking, the primary reactions can be accounted for by reactions
(7.66), (7.67), and (7.68) below.
7 C–C Bond Formation via Carbocations in the Methane …
(7.60)
(7.61)
C
CH 3
H 3 C
H 2 + C 4 H 8
CH 4 + C 3 H 6
CH 3
H
Thus, the formation rates of H 2 and CH 4 are the rates of the C–H and C–C bond
cleavage reactions, respectively. The primary reaction rates over Ag- and Zn-ZSM-5
zeolites, together with those for H-ZSM-5, are summarized in Table 7.10. The rates of
the C–H bond cleavage reaction over Ag- and Zn-ZSM-5 zeolites are much faster than
that over H-ZSM-5. The rate of the C–C bond cleavage reaction (reaction (7.61)) over
Ag-ZSM-5 is evidently different from that over Zn-ZSM-5. Ag-ZSM-5 suppressed
this reaction (the formation of CH 4 ), as compared with H-ZSM-5, while Zn-ZSM-5
greatly enhanced it. The ratio of the CH 4 formation rates is Zn-ZSM-5/H-ZSM-5 =
81:5.
(3) n-Pentane cracking
In n-pentane cracking, the following four primary reactions occur.
(7.62)
(7.63)
(7.64)
(7.65)
CH 3 CH 2 CH 2 CH 2 CH 3
H 2 + C 5 H 10
CH 4 + C 4 H 8
C 2 H 6 + C 3 H 6
C 3 H 8 + C 2 H 4
The C–H bond cleavage reaction (reaction (7.62)) gives H 2 and C 5 H 10 . C 5 H 10 is
readily decomposed to lower alkenes and alkanes. The C–C bond cleavage reaction
gives CH 4 , C 2 H 6 , and C 3 H 8 as primary reaction products through reactions (7.63),
(7.64), and (7.65), respectively. The reaction rate for each of the above reactions
is summarized in Table 7.10. Over H-ZSM-5, the ratio of the C–H bond cleavage
reaction rate to that of the C–C bond cleavage reaction was 4:11. The rates of the
C–H bond cleavage reaction (reaction (7.62)) over the zeolites Ag- and Zn-ZSM-5
were about 20 times faster than the rate over H-ZSM-5. The formation rates of CH 4 ,
C 2 H 6 , and C 3 H 8 over Ag-ZSM-5 were almost comparable to those over H-ZSM-5.
However, the formation rates of these alkanes over Zn-ZSM-5 were almost three
times faster than over H-ZSM-5.
(4) iso-Pentane cracking
In iso-pentane cracking, the primary reactions can be accounted for by reactions
(7.66), (7.67), and (7.68) below.