One-Pot Synthesis of Zeolitic Strong Solid Bases: A Family of Alkaline-Earth Metal-Containing Silicalite-1

Fabricating stable strong basic sites in well-preserved crystallized zeolitic frameworks still remains a difficult issue. Here, we reported a family of MFI-type metallosilicate zeolites, AeS-1 (Ae: alkaline-earth metal ions of Mg, Ca, Sr or Ba; S-1: silicalite-1) through a direct one-pot hydrothermal method involving the acidic co-hydrolysis/condensation of the silica precursor with the Ae salts. Step-by-step full characterizations were designed and conducted for in-depth discussion of the Ae status in AeS-1. Strong basicity (H-≈22.5-26.5) was detected in AeS-1. The basicity was further confirmed by CO₂ sorption measurements, ¹³C NMR spectra of chloroform-adsorbed samples, and ¹H→¹³C and ¹H→²⁹Si cross-polarization magic-angle spinning NMR spectra of ethyl cyanoacetate-adsorbed samples. The results of Knoevenagel condensations demonstrated the excellent solid base catalysis of AeS-1, which showed high activity, reusability, and shape-selectivity, all of which are explained by Ae-derived zeolitic intracrystalline strong basic sites. Basic instinct: A family of alkaline-earth metal-containing silicalite-1 zeolites was synthesized in a one-pot hydrothermal system involving an unusual acidic co-hydrolysis/condensation of the silica precursor with alkaline-earth salts. This generated a new type of strong zeolitic solid bases with superior basicity and well-preserved zeolite crystalline structure.