Influence of Al³⁺ on polymorph A enrichment in the crystallization of beta zeolite

Using tetraethylammonium hydroxide as the organic structure-directing agent and in the presence of fluoride, polymorph A-enriched silica beta zeolite was synthesized under concentrated hydrothermal conditions. The introduction of Al species into the same starting mixture resulted in a decrease in the degree of enrichment of polymorph A in beta zeolite and an Al-incorporated beta zeolite resulted. The crystallized polymorph A-enriched silica beta zeolite and the Al-incorporated beta zeolite and their crystallization processes were investigated by X-ray diffractometry, elemental analysis, thermogravimetric analysis-differential thermal analysis, nitrogen adsorption, scanning electron microscopy, and solid-state magic angle spinning nuclear magnetic resonance. The introduction of Al species accelerated crystallization and reduced the crystal size of Al-incorporated beta zeolite. The intermediate of five-coordinated Al species accounted for a decrease in the degree of enrichment of polymorph A in the crystallization of Al-incorporated beta zeolite.