Synthesis and Characterization of Pillared High Layer Charged Synthetic Saponite

Alumina pillared clays were prepared using synthetic saponites with different layer charges, and their cracking activities were characterized by cumene conversion reaction. It was found that the pillared saponite with super high layer charges (2.0) exhibited stable cracking activity in the thermal treatment temperature range from 500 to 700DGC. The BET surface areas of the pillared saponites (calcined at 500DGC for 2 h) with layer charges of 1.0, 1.5 and 2.0 were 360, 280 and 310 m2/g respectively, according to the N2 adsorption-desorption determinations at 77 K. A significant layer charge effect was found on the catalytic cracking activity of the pillared clays according to the model reaction, indicating that substitutions in the tetrahedral sheets played an important role in the development of surface Bronsted acidic sites of pillared clay. Because of strong Bronsted sites of pillared saponites, peaks centered at 432DGC were found in the spectra of the temperature programmed desorption of ammonia. The structure of pillared saponite with 2.0 layer charges, being the best solid acid catalyst in this study, was also characterized by 27A1 MAS NMR. A new peak centered at 1.9 ppm after pillaring was observed, which was ascribed mainly to the octahedral aluminum in the pillar.