Synthesis of beta nanozeolite aggregates with hierarchical pores via steam-assisted conversion of dry gel and their catalytic properties for Friedel-Crafts acylation

Abstract

Modulation of the porosity and acidity of zeolites is a very attractive subject for designing highly efficient solid-acid catalysts. In this work, Beta nanozeolite aggregates with hierarchical porous structure were synthesized via steam-assisted conversion (SAC) of dry gel in presence of seeds and a cationic polymer of polydiallyldimethylammonium chloride (PDAD). The influence of various synthesis parameters, such as the alkalinity, the contents of PDAD and zeolite seeds, and the crystallization conditions (temperature, water/dry gel ratio and time) on the formation of Beta zeolites was studied by combining a variety of characterization techniques. The SAC-synthesized Beta zeolites (S-Beta) are assembled from ultra-small nanocrystals around 10 nm to form self-sustaining micron-sized zeolitic aggregates, and possess abundant interconnected mesopores and relatively mild acidity. Compared with the conventional Beta zeolite, S-Beta aggregates show much higher catalytic activity for the Friedel-Crafts acylation of anisole with acetic anhydride. The excellent catalytic performance of S-Beta should be mainly attributed to the enhanced mass transport ability for reagents as well as the mild acidity that can avoid the rapid deactivation of the catalyst under the test conditions.