Properties and Functions of Hierarchical Ferrierite Zeolites Obtained by Sequential Post-Synthesis Treatments

A post-synthesis route involving a sequence of up to three treatments in aqueous NaAlO2, HCl, and NaOH solutions, was designed to prepare a variety of complex hierarchical ferrierite zeolites, that is, microporous materials with auxiliary mesoporosity. The precise effect of each step on the composition, structure, morphology, porosity, and acidity of the samples was assessed by means of a multitechnique approach, including inductively coupled plasma-optical emissions spectrometry (ICP-OES), N2 sorption at 77 K, Ar sorption at 87 K, transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD), liquid and solid-state nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), and temperature-programmed desorption of ammonia (NH3-TPD). NaAlO2 desilicates a portion of the zeolite crystal by alkaline attack, although most of the extracted silicon is retained in the solid forming nanocrystals because of Al(OH)3 precipitation on the zeolite surface...