Fine Tuning of Hierarchical Zeolite Beta Acid Sites Strength

Abstract

Two different synthesis methods to obtain hierarchical Beta zeolite are investigated: direct synthesis using cetyltrimethylammonium bromide (CTAB) as a mesoporous template and post-synthesis desilication by etching with NaOH and TPAOH. The main focus of this study is to show the possibility of fine tuning of the acid site (OH) strength (Brønsted and Lewis acid sites) through wet impregnation of these hierarchical Beta zeolites with divalent metal cations (Mg2+, Co2+, Ni2+, Cu2+, and Zn2+), which are important for various applications. Fourier transform infrared spectroscopy (FTIR) and deuterated acetonitrile as the probe molecule were used as a powerful technique to analyze the quantity and number of Brønsted/Lewis acid sites in the modified zeolite Beta structure. Investigating the influence of different divalent metal cations with a comparable ionic radius on the acidity of the hierarchical Beta zeolites, the present research aims to shed light on the structure–activity relationship that determines their catalytic behavior, for the development of efficient and environmentally friendly catalysts for various industrial applications.

Keywords

• hierarchical zeolite Beta
• Brønsted acid site
• Lewis acid site
• FTIR spectroscopy