Synthesis of hierarchical ZSM-5 aggregates by an alkali-treated seeds method with cetyltrimethylammonium bromide for the methanol to gasoline reaction

Abstract

A series of hierarchical ZSM-5 aggregates with a relatively low SiO2/Al2O3 ratio (~ 50) were successfully synthesized using alkali-treated commercial ZSM-5 as seeds and cetyltrimethylammonium bromide (CTAB) as mesogenous template. The effect of the amounts of CTAB on the physicochemical and catalytic properties of the synthesized catalysts was characterized by XRD, FE-SEM, FE-TEM, N2 physical adsorption, ICP-OES, NH3-TPD, Py-IR and TGA. Moreover, the possible formation mechanism of the hierarchical ZSM-5 aggregates was studied. The results indicated that the mesoporosity of the hierarchical ZSM-5 aggregates was greatly enhanced with the addition of CTAB. The primary crystal size of the ZSM-5 aggregates significantly decreased owing to the protective effect of CTAB, which inhibits the further crystal growth. The hierarchical ZSM-5 aggregates prepared with addition of a suitable amount of CTAB showed large specific surface areas and large external surface areas, abundant intercrystalline mesopores and appropriate concentration of acid sites, which resulted in excellent catalytic performance in the methanol to gasoline reaction. The stability of the catalyst was remarkably improved and the gasoline yield was given a rise of 10% compared with the catalyst prepared in the absence of CTAB.