The synthesis and characterization of Al-Beta and all-silica Beta formed in fluoride and caustic media.

Abstract

The influence of various parameters upon the synthesis of the BEA structure in fluoride and caustic media is investigated and results are compared and related to some previous studies in the literature. High crystalline, low faulted BEA structure has been made in an excess of fluoride (F−/SiO2 ratio of 1.5) across the entire gel Si/Al ratio range of 20 to ∞ using a fumed silica source and in the absence of seed crystals or stirring. Although, for gel Si/Al ratios >20, no aluminium was found in the products. The scope for further investigation of the effects of H2O content and stirring vs. non-stirring upon crystallinity and aluminium uptake, especially in conditions of lower fluoride concentration, is shown. Results from the caustic media syntheses agree with those from previous studies and it is found that the uptake of aluminium into the zeolite during synthesis is required for the formation of the BEA structure. Product characterization of Al-Beta confirms the framework incorporation of aluminium through increased d-spacings, the presence of tetrahedral coordinate aluminium and lowering of the FT-IR external asymmetric stretch and double bend vibration relative to an all-silica sample.