Hierarchical Zeolite Beta via Nanoparticle Assembly with a Cationic Polymer

Nanozeolite aggregates with secondary pores of tunable sizes were prepared by the flocculating action of a cationic polymer. Specifically, highly concentrated zeolite beta precursor gels were hydrothermally converted in the presence of the cationic polymer polydiallyldimethylammonium chloride (PDDA). Without polymer, highly crystalline zeolite beta in the form of nanosized particles was obtained from colloidal solutions at high yield. Upon addition of polymer, these nanoparticles were flocculated into self-sustaining, easily retrievable mesoporous aggregates in a one-step procedure at nearly 100% yield, showing interparticle pores with very high mesopore volumes and surface areas. The influence of the amount of polymer, its molecular weight as well as the nature of the silica precursor on pore characteristics, crystallinity, and morphology were studied with nitrogen sorption, mercury intrusion porosimetry and electron microscopy, respectively. Changing the polymer concentration is a powerful parameter to effectively tune the interstitial pore size between 40 and 400 nm by controlling the growth of the zeolite beta particles.