7.7 Unique Properties of Silver Cations …
203
Fig. 7.7 Conversion of CH 4
() and C 2 H 4 (◯) in the
reaction of a CH 4 –C 2 H 4
mixture as a function of the
running time over In-ZSM-5
(Reprinted with permission
from ref [90]. Copyright
2020 American Chemical
Society). Reaction
conditions: 673 K, CH 4 =
C 2 H 4 = 33.8 kPa, W /F:
3.8 g h mol −1
As mentioned before, the carbenium ions also gored over H-zeolites and superacid
catalysts.
In this section, the differences between the catalytic properties of Ag-zeolites
and Zn-zeolites are focused upon and compared with the catalytic properties of
H-zeolites.
7.7.7.1 Primary Reactions of Lower Alkanes Over H-Zeolites
Based on the mechanism of alkane activation in superacid solutions, the Haag-Dessau
mechanism was proposed in 1994. The mechanism involves penta-coordinated carbonium ions as a reaction intermediate in the reactions of lower alkanes, such as
iso-butane, over H-zeolites [32, 33] as shown in reaction (7.53).
C
R 2
H
R 3
R 1
H + +
+
R 3
H
C
R 2
H
R 1
C
R 2
H
R 1
+ R 3 H
H
H
C
R 2
R 3
R 1
+
C
R 2
R 3
R 1
+ H 2
+
+
(7.53)