INTERACTION OF C-2-C-6 HYDROCARBONS WITH SURFACES OF H-ZSM-5 AND GA-H-ZSM-5 ZEOLITES

The interactions of lower alkanes and alkenes with H-ZSM-5 and Ga-H-ZSM-5 were studied between 373 and 923 K applying carrier-gas free pulsing of the hydrocarbons (10(15)-10(17) molecules/pulse) by means of the Temporal Analysis of Products (TAP) method. Ethane was reversibly adsorbed on H-ZSM-5 below 673 K, interaction was not observed above 673 K. Ethane was adsorbed on the gallium species of Ga-H-ZSM-5 above 573 K, selective dehydrogenation to ethylene occurred at 873 K and above. At low pulse intensities, the adsorption of ethylene on H-ZSM-5 could be studied without interfering reactions like oligomerization, cyclization, or aromatization. At higher pulse intensities, ethylene was converted to benzene via the consecutive formation of butenes and C-6 alkenes. The existence of 1-hexene and 3-methyl-1-pentene as intermediates is not likely, since they were predominantly cracked, in comparison to 1,5-hexadiene, which showed a higher rate of aromatization.