Desilication of ferrierite zeolite for porosity generation and improved effectiveness in polyethylene pyrolysis

Desilication of the medium-pore ferrierite zeolite in sodium hydroxide solutions was conducted to modify the porous structure and to create structural defects, resulting in enhanced accessibility and ultimately improved catalytic performance. Commercial H-ferrierite (Si/Al = 29) with the characteristic plate-like morphology was used as starting material. The attack by NaOH induces deaggregation, exfoliation, fracture, and ultimately perforation of the ferrierite crystals, resulting in mesoporosity of combined inter- and intracrystalline nature. The parent and treated samples were characterized by ICP-OES, XRD, N2 adsorption, SEM, TEM, 27Al and 29Si MAS-NMR, FTIR, and NH3-TPD. Optimization of the treatment conditions (NaOH concentration, temperature, and time) is required to introduce substantial mesoporosity without significantly altering the micropore structure due to excessive Si leaching. Compared to other frameworks (e.g. MFI, MTW, MOR, and BEA), FER requires harsher conditions to extract silicon leading to mesoporosity. Under optimal conditions, the mesopore surface area of the NaOH-treated ferrierite increased by a factor of 3–4 with respect to the parent zeolite, while mostly preserving the native crystallinity and acidity. The ability of NaOH to induce porosity changes in FER largely exceeds conventional dealumination post-treatments. The benefit of the introduced porosity was demonstrated in the catalytic pyrolysis of low-density polyethylene.