138
6 Conversion of Methane to Aromatic Hydrocarbons
Si
O
O
O
O
O
Al
O
O
Na +
-
+ NH 4 Cl
NH 4
+
Si
O
O
O
O
O
Al
O
O
-
+ NaCl
H
Si
O
O
O
O
O
Al
O
O
NH 4
+
Si
O
O
O
O
O
Al
O
O
-
– NH 3
Si
O
O
O
O
O
Al
O
O
Na +
-
+ NH 4 Cl
NH 4
+
Si
O
O
O
O
O
Al
O
O
-
+ NaCl
(6.9)
Since the amount of Brønsted acid sites (acidic protons) in the zeolite depends
on the Si/Al ratio, the catalytic activities of H
+ -exchanged zeolites modified with
Mo species may be influenced by the Si/Al ratio. Liu et al. investigated the influence
of the Si/Al ratio of H-ZSM-5 modified with Mo (3 wt%, 0.32 mmol/g) on the
catalytic activity of the resulting zeolites in the MDA reaction [21, 30]; the results are
summarized in Table 6.4. For instance, the high catalytic performance was observed
for the 3 wt% Mo catalysts with a Si/Al ratio of approximately 20. The concentration
of acidic protons (Brønsted acid sites) in H-ZSM-5 can also be estimated from the
Si/Al ratio. As shown in Table 6.4, the conversion of methane remained relatively
constant at Si/Al ratios of up to 36.7 (0.43 mmol/g protons), i.e., when the acidic
proton concentration was greater than that of Mo (0.32 mmol/g). However, when the
concentration of acid protons was decreased below that of Mo via increasing the Si/Al
ratio, the catalytic activity for the formation of aromatic hydrocarbons decreased, as
shown in Table 6.4.
Sriglan et al. reported that the formation rate of aromatic hydrocarbons over Mo
(3.9 wt%)/H-ZSM-5 catalysts depended on their Si/Al ratio [31], with the aromatic
hydrocarbon formation rate increasing as the Si/Al ratio was increased from 14 to
28. However, hydrocarbon formation decreased when the Si/Al ratio was further
increased to 54. The results discussed above demonstrate that the Si/Al ratio of
Mo/H
+ -exchanged zeolite catalysts influences their catalytic activities in the MDA
reaction.
Similarly, Mátus et al. found that the catalytic activity of Mo-modified H-ZSM-5
depended on the concentration of Mo when the Si/Al ratio of the zeolite was held
6 Conversion of Methane to Aromatic Hydrocarbons
Si
O
O
O
O
O
Al
O
O
Na +
-
+ NH 4 Cl
NH 4
+
Si
O
O
O
O
O
Al
O
O
-
+ NaCl
H
Si
O
O
O
O
O
Al
O
O
NH 4
+
Si
O
O
O
O
O
Al
O
O
-
– NH 3
Si
O
O
O
O
O
Al
O
O
Na +
-
+ NH 4 Cl
NH 4
+
Si
O
O
O
O
O
Al
O
O
-
+ NaCl
(6.9)
Since the amount of Brønsted acid sites (acidic protons) in the zeolite depends
on the Si/Al ratio, the catalytic activities of H
+ -exchanged zeolites modified with
Mo species may be influenced by the Si/Al ratio. Liu et al. investigated the influence
of the Si/Al ratio of H-ZSM-5 modified with Mo (3 wt%, 0.32 mmol/g) on the
catalytic activity of the resulting zeolites in the MDA reaction [21, 30]; the results are
summarized in Table 6.4. For instance, the high catalytic performance was observed
for the 3 wt% Mo catalysts with a Si/Al ratio of approximately 20. The concentration
of acidic protons (Brønsted acid sites) in H-ZSM-5 can also be estimated from the
Si/Al ratio. As shown in Table 6.4, the conversion of methane remained relatively
constant at Si/Al ratios of up to 36.7 (0.43 mmol/g protons), i.e., when the acidic
proton concentration was greater than that of Mo (0.32 mmol/g). However, when the
concentration of acid protons was decreased below that of Mo via increasing the Si/Al
ratio, the catalytic activity for the formation of aromatic hydrocarbons decreased, as
shown in Table 6.4.
Sriglan et al. reported that the formation rate of aromatic hydrocarbons over Mo
(3.9 wt%)/H-ZSM-5 catalysts depended on their Si/Al ratio [31], with the aromatic
hydrocarbon formation rate increasing as the Si/Al ratio was increased from 14 to
28. However, hydrocarbon formation decreased when the Si/Al ratio was further
increased to 54. The results discussed above demonstrate that the Si/Al ratio of
Mo/H
+ -exchanged zeolite catalysts influences their catalytic activities in the MDA
reaction.
Similarly, Mátus et al. found that the catalytic activity of Mo-modified H-ZSM-5
depended on the concentration of Mo when the Si/Al ratio of the zeolite was held