Preparation of Y zeolite composites with adjustable, highly dispersed intra-crystal mesoporosity: Effect of lactic acid treatment in CTAB-assisted two-step approach

Abstract

Series of meso/microporous zeolite Y composites with adjustable hierarchy factors (HF) from 0.04 to 0.16, are prepared from commercial NaY zeolite (Si/Al = 2.5) by the two-step method with first lactic acid leaching and then CTAB-assisted ammonia treatment. The essential effect of lactic acid on the formation of diverse mesoporous domains in microporous crystals are systematically investigated. A possible scheme is proposed. The lactic acid leaching process is found to be very crucial to controllably remove the framework aluminum and regulate the amount/size of intra-crystal amorphous silicon-rich domains, which then evolve to mesostructures within the microporous crystals via structural re-arrangement/dissolution-reassembly process during the CTAB-assisted ammonia treatment. Varying the lactic acid concentrations would result in different crystallinity preservations and diverse proportions/dispersity of mesoporous regions, and thus well tune the HF values of the final composites. The zeolite Y composites with moderate mesoporosities allow much better performances in the acetalization reactions of cyclohexanone with pentaerythritol due to the improved diffusion ability of large sized guest molecules, whereas accompanying loss of acidity would depress reactivities of the treated samples for dehydration of small isopropanol.