a Brønsted and b Lewis acid amount at 200 ℃.

3.3 Catalytic performance

The cracking reaction of C4-olefin (OCC) to propylene in industries is an important application of ZSM-5 zeolites, and the conversion of C4-olefin and yield of propylene mostly depend on zeolites’ acidity, pore structure and catalytic stability [49]. In this study, we investigated the catalytic performance of four ZSM-5 samples for the OCC reaction. The conversion of C4-olefin and yield of propylene obtained under the catalysis of different ZSM-5 samples are shown in Fig. 11. At first, the C4-olefin’s conversion and yield of propylene under the catalysis by the four ZSM-5 samples had no obvious difference. However, the conversions of C4-olefin catalyzed by the ZSM-5-SD and ZSM-5-SS decreased faster than those by ZSM-5-RD and ZSM-5-RS after 16 h. And the conversions of C4-olefin by the ZSM-5-RD, ZSM-5-RS, ZSM-5-SD, and ZSM-5-SS were 65% 62%, 53% and 53% at 44 h, respectively. Besides, the yield of propylene catalyzed by ZSM-5-RD and ZSM-5-RS were higher markedly than those catalyzed by ZSM-5-SD and ZSM-5-SS after 30 h. This indicates that ZSM-5 samples prepared by RPB premix possess more active sites with weak Lewis acidity and medium-strong Brønsted acidity, less transfer limitation in micropore, and more excellent catalytic stability than those by STR premix.