Crystallization of high silica BEA by dry gel conversion

Abstract

Zeolite with BEA structure was prepared using a new crystallization method called ‘Dry Gel Conversion Technique’. This dry gel conversion technique is a convenient method to prepare zeolites and enables one to synthesize zeolite BEA with SiO 2/Al 2O 3 ratios from 30 to infinity using tetraethylammonium hydroxide (TEAOH) as a structure directing agent. Zeolite BEA with SiO 2/Al 2O 3 ratios from 30 to 730 were rapidly crystallized in 3 and 12 h, respectively. The 27Al NMR spectrum for BEA with SiO 2/Al 2O 3 ratio of 30 confirmed the absence of octahedrally coordinated aluminum. The crystallization rates were higher for BEA with low SiO 2/Al 2O 3 ratios than for those with high SiO 2/Al 2O 3 ratios. BEA crystallized by this method had uniform particles of about 60 nm. Higher Na + ion concentrations in the gel promoted the formation of high silica BEA. Elimination of occluded TEA cations took place at lower temperatures (around 623 K) in high silica BEA than that in BEA with low SiO 2/Al 2O 3 ratios (around 900 K). This method also allowed to synthesize BEA in the form of self-bonded pellets.