Abstract: Synthesis of micro-mesoporous zeolites β/M (where β and M denote β zeolite and MCM-41 zeolite, respectively) combined with zeolites β and MCM-41 was achieved in the sodium hydroxide system using a two-step hydrothermal treatment method. Sodium aluminate and fume silica were used as the sources of aluminum and silicon, while tetraethylammonium hydroxide (TEAOH) and cetyltrimethylammonium bromide (CTAB) were used as templates for the formation of β crystal seeds and for self-assembling of β crystal seeds into mesoporous zeolites β/M, respectively. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and high resolution transmission electron microscope (HRTEM). Reaction time and particle size of β crystal seeds were found to play an important role in the synthesis of β/M zeolites. When β seeds crystallize in a short time, a pure phase (denoted βM) can result, whose mesoporous structure resembles MCM-41, while long crystallization times can result in a phase mixture of mesoporous βM and microporous β zeolite. Due to the insertion of the secondary building units of β zeolite into the mesoporous wall, the β/M micro-mesoporous combined zeolites showed enhanced toluene adsorption performance and hydrothermal stability.

Key words: Micro-mesoporous combined zeolite, Crystallization time, Grain size, Toluene adsorption, Automobile cold start emission control