130
6 Conversion of Methane to Aromatic Hydrocarbons
6 CH 4 + 9/2 O 2
C 6 H 6 + 9 H 2 O
(6.6)
Even at 623 K, the conversion of methane to benzene is thermodynamically
complete with 100% conversion, although the selectivity towards hydrocarbons is
low.
6.4 Zeolite-Based Catalysts for the Conversion of Methane
to Aromatic Hydrocarbons
Since the H-ZSM-5-supported MoO 3 zeolite catalyst for the MDA reaction was
reported in 1993, many catalysts based on the dispersion of metal ions on various supports, mainly zeolites, have been investigated. In the following sections, the
catalytic activities of various zeolite-based catalysts are surveyed.
6.4.1 Catalytic Activities of Mo Species Loaded
on H + -Exchanged Zeolites
The performances of a variety of catalysts in which Mo species are supported on various H
+ -exchanged zeolites have been examined at ~1000 K in a fixed-bed continuousflow reactor [5, 19–25]; data for these systems are shown in Tables 6.1 and 6.2. In
almost all cases, a methane pressure of 101 kPa was used. In these tables, the singlepass conversion of methane and the selectivities towards hydrocarbons (benzene,
toluene, naphthalene, C 2 hydrocarbons (C 2 H 4 + C 2 H 6 ), and coke) are summarized
under all reaction conditions, although in some cases, the amount of coke formed on
the surface of the catalyst was not provided. The selectivities were calculated on a
carbon basis.
The Mo/H-MCM-22 listed in Table 6.1 was prepared by impregnation with
ammonium heptamolybdate and then dried and calcined at 873 K. When the
reaction was carried out at 973 K, the Mo (6 wt%)/H-MCM-22 produced benzene
in 80.0% selectivity at 10.0% methane conversion. On the other hand, Mo (6
wt%)/H-ZSM-5 gave benzene with 57.8% selectivity at 10.6% methane conversion.
ZRP-1, which has a structure similar to pentasil-type zeolites, is a phosphorousand rare earth oxide-containing material [22]. This catalyst was prepared by
modifying a silica-rich H-ZSM-5 with phosphorous and rare earth oxides. The
Mo/H-ZRP-1 catalyst also selectively produced aromatic hydrocarbons, with a
(benzene + naphthalene) selectivity of 75.6% at 9.7% methane conversion.
Among the Mo-modified H
+ -exchanged zeolites shown in Table 6.1, H-MCM-36,
H-IM-5, and H-ITQ-2 also gave aromatic hydrocarbons with selectivities of 40–50%
at methane conversions of 6–11%, while USY, MFS-16, and mordenite showed
lower catalytic activities for the formation of aromatic hydrocarbons and produced
6 Conversion of Methane to Aromatic Hydrocarbons
6 CH 4 + 9/2 O 2
C 6 H 6 + 9 H 2 O
(6.6)
Even at 623 K, the conversion of methane to benzene is thermodynamically
complete with 100% conversion, although the selectivity towards hydrocarbons is
low.
6.4 Zeolite-Based Catalysts for the Conversion of Methane
to Aromatic Hydrocarbons
Since the H-ZSM-5-supported MoO 3 zeolite catalyst for the MDA reaction was
reported in 1993, many catalysts based on the dispersion of metal ions on various supports, mainly zeolites, have been investigated. In the following sections, the
catalytic activities of various zeolite-based catalysts are surveyed.
6.4.1 Catalytic Activities of Mo Species Loaded
on H + -Exchanged Zeolites
The performances of a variety of catalysts in which Mo species are supported on various H
+ -exchanged zeolites have been examined at ~1000 K in a fixed-bed continuousflow reactor [5, 19–25]; data for these systems are shown in Tables 6.1 and 6.2. In
almost all cases, a methane pressure of 101 kPa was used. In these tables, the singlepass conversion of methane and the selectivities towards hydrocarbons (benzene,
toluene, naphthalene, C 2 hydrocarbons (C 2 H 4 + C 2 H 6 ), and coke) are summarized
under all reaction conditions, although in some cases, the amount of coke formed on
the surface of the catalyst was not provided. The selectivities were calculated on a
carbon basis.
The Mo/H-MCM-22 listed in Table 6.1 was prepared by impregnation with
ammonium heptamolybdate and then dried and calcined at 873 K. When the
reaction was carried out at 973 K, the Mo (6 wt%)/H-MCM-22 produced benzene
in 80.0% selectivity at 10.0% methane conversion. On the other hand, Mo (6
wt%)/H-ZSM-5 gave benzene with 57.8% selectivity at 10.6% methane conversion.
ZRP-1, which has a structure similar to pentasil-type zeolites, is a phosphorousand rare earth oxide-containing material [22]. This catalyst was prepared by
modifying a silica-rich H-ZSM-5 with phosphorous and rare earth oxides. The
Mo/H-ZRP-1 catalyst also selectively produced aromatic hydrocarbons, with a
(benzene + naphthalene) selectivity of 75.6% at 9.7% methane conversion.
Among the Mo-modified H
+ -exchanged zeolites shown in Table 6.1, H-MCM-36,
H-IM-5, and H-ITQ-2 also gave aromatic hydrocarbons with selectivities of 40–50%
at methane conversions of 6–11%, while USY, MFS-16, and mordenite showed
lower catalytic activities for the formation of aromatic hydrocarbons and produced