Influence of alkalinity on the synthesis of hierarchical LTA zeolite by using bridged polysilsesquioxane

Abstract

The mechanism of formation of hierarchical LTA zeolite involved the methoxyl groups of bridged polysilsesquioxane hydrolyzing into hydroxyl groups. The covalent Si–O–Si bond between silicon hydroxyl in the above solution and other silica sources forms by dehydration, avoiding phase separation. The influence of alkalinity on the synthesis of hierarchical LTA zeolites was investigated by using bridged polysilsesquioxane. XRD patterns indicate the synthesis of sodalite at the same molar composition of the hierarchical LTA zeolites without bridged polysilsesquioxane. The characterization results from TG and DTG revealed that bridged polysilsesquioxane was successfully incorporated into the as-synthesized hierarchical LTA zeolite. N₂-adsorption/desorption results proved that mesopores and the porosities of the hierarchical LTA zeolites are adjustable by a change of alkalinity. SEM images indicated that the morphologies of the hierarchical LTA zeolites changed with increasing alkalinity. The hierarchical LTA zeolites showed faster initial exchange rates of Na⁺ to Mg²⁺ compared with conventional LTA.