Silica beta synthesized under alkaline conditions

Abstract

Zeolite β is an important material in catalysis, however the material with molar ration of silicon and aluminum more than 200 is difficult to synthesize. Typically, the pure silica β and heteroatom zeolite β are prepared at near neutral pH using HF as the mineralization agent. However, the HF is highly toxic and corrosive, and the zeolites formed are usually more than 10 μm. In this paper, alkaline and fluorine-containing salts was applied, and pure silica β was hydrothermally synthesized from a basic precursor. The silica resource and alkali metal cations in the precursor would influence the crystallization process, tetraethyl orthosilicate and sodium cations are preferred. The pure silica β is plate-like, the crystals formed on the third day are about 50 × 300 × 300 nm, which keep growing with the time, and pure silica zeolite β with uniform size of about 200 × 700 × 700 nm are synthesized in a week. More importantly, the pure silica β is defects-free, and it's highly hydrophobic.