A green route to synthesize HZSM-5 zeolites for the coreaction of n-heptane and methanol to light olefins

H-form HZSM-5 zeolites are important industrial materials. However, their direct synthesis remains challenging since they have to be synthesized in the presence of a Na alkaline solvent. Herein, we report that ammonia hydroxide can serve as an alkaline source for the direct synthesis of HZSM-5 zeolites by steam-assisted crystallization (SAC) and dynamic agitation crystallization (DAC). We demonstrated that the mass transfer of silicon and aluminum sources is crucial for the crystallization process; therefore, the crystallization rate of HZSM-5 by DAC is considerably faster than that by SAC. The catalytic performances of the coreaction of n-heptane and methanol show that the cracking products of n-heptane participate in the dual-cycle reactions of methanol, leading to an enhanced yield of light olefins but a reduced catalyst lifetime because of an accelerated coking rate. This study contributes a green route to the synthesis of HZSM-5 zeolites and provides insight for improving the yield of light olefins.