Hierarchical ZSM-5 zeolites were prepared by alkali treatment (desilication) at two temperatures, two reaction times, and two NaOH concentrations. A 23 factorial design was used to study the effect of these variables on the crystallinity, microporosity, and mesoporosity of the zeolite due to the desilication treatment. The factorial design analysis showed that the temperature, reaction time and NaOH concentration and the second order interaction between temperature and time have statistically significant effect on the micropore volume. On mesopore volumes (Vmeso) and areas (Smeso), the reaction time and NaOH concentration factors have statistically significant effects. In the case of mesopore volumes, the second order reaction time and NaOH concentration interaction factor are also significant. On the other hand, only the alkali concentration affected, negatively, the relative crystallinity. Two hierarchical ZSM-5 zeolites with the highest relative crystallinity and mesoporosity were selected and further characterized by inductively coupled plasma (ICP) analysis, 29Si nuclear magnetic resonance (NMR), 27Al NMR, Fourier transform infrared (FTIR) spectroscopy in the OH stretch region and pyridine adsorbed FTIR spectroscopy. NMR and FTIR results showed that the alkali treatment selectively removed silica from the zeolite framework, decreasing the SAR (silica-to-alumina ratio) values, while decreasing Brønsted acid site concentrations and increasing Lewis acid sites concentrations.

Alumina supported niobium oxide was prepared by chemical vapor deposition (CVD) of NbCl5. The alumina was calcined and pretreated at differents temperatures in order to vary the density of OH groups on the surface which was determined by thermogravimetric analysis. A good correlation was found between the amount of anchored niobium and the total number of anionic sites (oxide and hydroxyl groups) on the surface of the alumina. The infrared spectra on the OH stretching region indicate that OH groups coordinated to at least one tetrahedral aluminum were more reactive towards NbCl5.