Generation of mesoporosity in H–Y zeolites by basic or acid/basic treatments: Towards a guideline of optimal Si/Al ratio and basic reagent

Abstract

We elaborate a post-modification method for faujasite zeolite to introduce additional mesopore volume, by desilication (if necessary combined with prior dealumination). CBV712 (Si/Al = 6), CBV720 (15), and CBV760 (28) were used as starting materials. We employ tetraalkylammonium hydroxide (TAAOH) as desilicating agent, varying its alkyl chain from C1 to C4. The different sizes of TAAOH show different modulating capacities in pore generation. Short alkyl chains generate a lot of mesopores, but also lead to extended amorphization. The opposite holds true for long alkyl chains. The desilication treatment was unsuccessful for CBV712, because of its too high Al content. CBV712, was therefore dealuminated by oxalic acid, to different extents, before applying TAAOH. This allowed us to identify the optimal Si/Al range for the desilication treatment, i.e. between 15 and 28. We also examined the accessibility of active sites in mesoporous zeolites by the sterically hindered base 2,4,6-tri-tert-butylpyridine (TTBPy).