Effect of alkaline-acid treatment on the physicochemical properties of ferrierite zeolite with application in the catalytic cracking reactions of n-hexane and UHMWPE

Abstract

This study investigates the effects of sequential alkaline-acid treatments on commercial ferrierite zeolite (Si/Al = 10) using different concentrations of NaOH (0.2 and 0.35 M) and temperatures (80 and 100 ºC), while maintaining a fixed concentration of oxalic acid (0.9 M). These zeolites were then evaluated for their textural properties and acidity in the cracking of n-hexane and ultra-high molecular weight polyethylene (UHMWPE). Chemical and textural properties were characterized by X-ray diffraction (XRD), energy dispersive X-ray (EDX) analyses, nitrogen adsorption–desorption using BET, t-plot and BJH methods, transmission electron microscopy (TEM), thermal analyses (TG/DTG), Fourier transform infrared spectroscopy (FT-IR), and ammonia temperature-programmed desorption (NH₃-TPD). Alkaline treatments caused Si leaching, reducing crystallinity and microporosity, while increasing mesoporosity and external surface area. Subsequent acid treatments restored crystallinity and microporosity by removing amorphous species and preserving mesoporosity. More severe alkaline treatment conditions (0.35 M and 100 ºC) generated more mesopores but significantly reduced microporosity and acidity, compromising the shape selectivity and active catalytic sites of ferrierite zeolite. Thus, the zeolite treated with 0.2 M NaOH and 0.9 M oxalic acid at 80 ºC exhibited the best balance between micro-mesoporosity and acidity, resulting in higher catalytic activity in the cracking of n-hexane and UHMWPE.