Hierarchy Brings Function: Mesoporous Clinoptilolite and L Zeolite Catalysts Synthesized by Tandem Acid–Base Treatments

Abstract

Hierarchical clinoptilolite and L zeolites are prepared using optimized tandem dealumination–desilication treatments. The main challenge in the postsynthetic modification of these zeolites is the high Al content, requiring a tailored dealumination prior to the desilication step. For natural clinoptilolite, sequential acid treatments using aqueous HCl solutions were applied, while for L a controlled dealumination using ammonium hexafluorosilicate is required. Subsequent desilication by NaOH treatment yields mesopore surfaces of up to 4-fold (clinoptilolite, 64 m2 g–1; L, 135 m2 g–1) relative to the parent zeolite (clinoptilolite, 15 m2 g–1; L, 45 m2 g–1). A thorough characterization sheds light on the composition, crystallinity, porosity, morphology, coordination, and acidity of the modified clinoptilolite and L zeolites. It is elaborated that, besides the degree of dealumination, the resulting Al distribution is a critical precondition for the following mesopore formation by desilication. Adsorption exper...