Applicability of UV-VIS spectroscopy for monitoring surface reactions of hydrocarbons in acidic zeolites has been demonstrated by the examples propene/HNaY, cyclohexene/HZSM-5 and neopentane/HNaM. In all cases the presence of alkenyl carbenium ions could be proved, undergoing oligomerization or transformation to poly-enylic carbocations with time of contact or elevated temperatures. At temperatures above 400 K the oligomers are decomposed. In order to get more detailed knowledge on the structure of the carbenium ions involved, complementary UV-VIS and IR studies are proposed.
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