Effect of alkali metal ion modification on the catalytic performance of nano-HZSM-5 zeolite in butene cracking

Nano-HZSM-5 was modified by different alkali metal ions; the effect of the modification on its acidity and catalytic performance in butene cracking was investigated by using NH₃-TPD characterization and catalytic evaluation in a small fixed-bed reactor. The results indicated that although the catalysts modified with various ions of Li, Na and K are different in their metal loading required to achieve the highest selectivity to ethylene and propylene, the best selectivity value obtained over all these modified catalysts is located in 50%~60%. The activity of the alkali modified catalysts decreases slowly with the extension of the reaction time on stream; however, the selectivity to ethylene and propylene does not increase accordingly. The conversions of different butene isomers over the zeolite catalysts are decreased in the sequence of butene-1 > trans-butene-2 > cis-butene-2 > iso-butene, which may reflect the order of their reactivity towards cracking.