Chapter 7
C–C Bond Formation via Carbocations
in the Methane Conversion Under
Non-oxidative Conditions
7.1 Introduction
Chapter 6 discussed the conversion of methane to aromatic hydrocarbons such as
benzene, which is a thermodynamically unfavorable reaction under non-oxidative
reaction conditions. However, Olah et al. reported that even under such circumstances, superacids such as FSO 3 H–SbF 5 catalyze the poly-condensation of methane
to produce higher molecular weight alkanes, such as ethane (C 2 H 6 ) and propane
(C 3 H 8 ) at approximately 400 K [1]. They also demonstrated the reaction of alkenes
such as C 2 H 4 (ethylene) with methane to produce alkanes such as C 3 H 8 via superacid
catalysis. Therefore, superacid catalysts do not produce alkenes during the conversion of alkanes such as methane, but instead are selective towards carbon–carbon
(C–C) bond formation at lower reaction temperatures than heterogeneous catalysts
such as zeolites.
In 1982, Sommer et al. reported the alkylation of CH 4 , C 2 H 6 , C 3 H 8 , and n-C 4 H 10
(n-butane) with C 2 H 4 to produce various alkanes in an HF-containing TaF 5 solution
[2]. Furthermore, in 1997 Choudhary et al. reported that an H-galloaluminosilicate
zeolite could heterogeneously catalyze the reaction of CH 4 with lower alkenes such
as C 2 H 4 and C 3 H 6 to produce mainly aromatic hydrocarbons around 800 K [3].
In 2002, Baba et al. have found that Ag
+ -exchanged zeolites (Ag-zeolites) produce
propylene (C 3 H 6 ) and hydrogen (H 2 ) via the reaction of CH 4 with C 2 H 4 . Thus, in
this reaction, propylene and hydrogen are produced, while superacid catalysts give
C 3 H 8 rather than C 3 H 6 [4].
CH 4 + CH 2 =CH 2
CH 3 CH=CH 2 + H 2
(7.1)
These results suggest that the reaction of methane with alkenes can be a useful way
to produce higher molecular weight hydrocarbons (higher hydrocarbons), and thus,
another method of CH 4 utilization to provide useful raw materials, in addition to the
polycondensation of methane via the methane dehydroaromatization (MDA) reaction mentioned in Chapter 6. Furthermore, as discussed in Chapter 1, the reactions
© Springer Nature Singapore Pte Ltd. 2020
T. Baba and A. Miyaji, Catalysis and the Mechanism of Methane Conversion to Chemicals,
https://doi.org/10.1007/978-981-15-4132-2_7
165
C–C Bond Formation via Carbocations
in the Methane Conversion Under
Non-oxidative Conditions
7.1 Introduction
Chapter 6 discussed the conversion of methane to aromatic hydrocarbons such as
benzene, which is a thermodynamically unfavorable reaction under non-oxidative
reaction conditions. However, Olah et al. reported that even under such circumstances, superacids such as FSO 3 H–SbF 5 catalyze the poly-condensation of methane
to produce higher molecular weight alkanes, such as ethane (C 2 H 6 ) and propane
(C 3 H 8 ) at approximately 400 K [1]. They also demonstrated the reaction of alkenes
such as C 2 H 4 (ethylene) with methane to produce alkanes such as C 3 H 8 via superacid
catalysis. Therefore, superacid catalysts do not produce alkenes during the conversion of alkanes such as methane, but instead are selective towards carbon–carbon
(C–C) bond formation at lower reaction temperatures than heterogeneous catalysts
such as zeolites.
In 1982, Sommer et al. reported the alkylation of CH 4 , C 2 H 6 , C 3 H 8 , and n-C 4 H 10
(n-butane) with C 2 H 4 to produce various alkanes in an HF-containing TaF 5 solution
[2]. Furthermore, in 1997 Choudhary et al. reported that an H-galloaluminosilicate
zeolite could heterogeneously catalyze the reaction of CH 4 with lower alkenes such
as C 2 H 4 and C 3 H 6 to produce mainly aromatic hydrocarbons around 800 K [3].
In 2002, Baba et al. have found that Ag
+ -exchanged zeolites (Ag-zeolites) produce
propylene (C 3 H 6 ) and hydrogen (H 2 ) via the reaction of CH 4 with C 2 H 4 . Thus, in
this reaction, propylene and hydrogen are produced, while superacid catalysts give
C 3 H 8 rather than C 3 H 6 [4].
CH 4 + CH 2 =CH 2
CH 3 CH=CH 2 + H 2
(7.1)
These results suggest that the reaction of methane with alkenes can be a useful way
to produce higher molecular weight hydrocarbons (higher hydrocarbons), and thus,
another method of CH 4 utilization to provide useful raw materials, in addition to the
polycondensation of methane via the methane dehydroaromatization (MDA) reaction mentioned in Chapter 6. Furthermore, as discussed in Chapter 1, the reactions
© Springer Nature Singapore Pte Ltd. 2020
T. Baba and A. Miyaji, Catalysis and the Mechanism of Methane Conversion to Chemicals,
https://doi.org/10.1007/978-981-15-4132-2_7
165