One-pot engineering of mesoporosity and Al distribution in zeolite ZSM-5 for enhanced iso-butane cracking

Zeolites possessing desirable acidic sites, accessible pore structures and fast diffusion capacity are ideal solid acid catalysts. A one-pot strategy employing the pH-sensitive polyanionic material, sodium alginate, as a bifunctional soft template tunes the mesoporosity and framework aluminum sites in zeolite ZSM-5. Comprehensive physiochemical studies demonstrate that the hierarchical zeolite ZSM-5 possesses abundant intracrystalline mesopores and a high population of framework aluminum sites in straight and sinusoidal channels, slightly more of which exist as Al pairs. Iso -butane cracking was employed as a model reaction to investigate the catalytic behavior of the different zeolites ZSM-5 samples. The obtained data suggest that, compared with conventional zeolite HZSM-5 and microporous zeolite HZSM-5-SA, the hierarchical zeolite HZSM-5-SA-NaOH exhibits higher catalytic activity and stability, together with a higher ethylene yield. The significantly boosted catalytic performance arises from the improved accessibility of acidic sites, as well as the excellent mass transfer and diffusion properties.