Mesoporogen-free synthesis of hierarchical sodalite as a solid base catalyst from sub-molten salt-activated aluminosilicate

Abstract

A rapid and environmentally friendly approach to synthesize hierarchical sodalite from natural aluminosilicate mineral without the involvement of any mesoporogen or post-synthesis treatment was developed. This strategy involves three important steps: the first is the depolymerization of an aluminosilicate mineral into highly reactive silicon and aluminum species with ideal meso-scale structures through activation of a sub-molten salt. The second step is the hydrolysis and condensation of the activated aluminosilicate mineral into zeolitic precursors that also have a meso-scale structure. The third is the rapid zeolitization of the zeolitic precursors through the reversed crystal growth route at room temperature and ambient pressure to form hierarchical sodalite. The physicochemical properties of the as-synthesized sodalite were systematically characterized, and the formation mechanism of the hierarchical pore structure was discussed. When used as a solid base catalyst for Knoevenagel condensation, the as-synthesized sodalite and its potassium ion-exchanged product with hierarchical micro–meso–macroporous structure both exhibited high catalytic activity and product selectivity.