Organic-free modulation of the framework Al distribution in ZSM-5 zeolite by magnesium participated synthesis and its impact on the catalytic cracking reaction of alkanes

Al distribution engineering is an effective way to tune the catalytic performance of ZSM-5 zeolite. In the present work, a series of [Al, Mg]-ZSM-5 with different Mg contents were obtained by hydrothermal synthesis method. For comparison, Mg/ZSM-5 with a comparable Mg content were also prepared using the conventional impregnation method. Characterizations of XPS-sputtering, H2-TPR and Py-IR indicated the distribution and coordination structures of Mg in the samples obtained by the two preparation methods were quite different. Besides, the introduction of magnesium by hydrothermal synthesis well regulates the location of framework Al, which is not possible by the impregnation method. 27Al MAS NMR and UV–vis-DRS of Co2+-exchanged zeolites demonstrated [Al,1.0 Mg]-ZSM-5 has less aluminum in the channel intersections compared to conventional HZSM-5. Finally, the significantly lower content of "Al pairs" in [Al,1.0 Mg]-ZSM-5 inhibits the hydride transfer process, resulting in higher yields of propylene in n-octane and crude oil catalytic cracking reactions.