Continuous solid solutions constructed from two isostructural octahedron-based molecular sieves: preparation, acidity regulation and catalytic application in Strecker reactions

Abstract

Strecker reactions have an important application in the preparation of α-amino acids and biologically active molecules in homogeneous acid- or base-catalyzed systems. As novel solid acid catalysts, Al_xGa_1−x-PKU-1 (x = 0–1) solid solutions constructed by two octahedron-based molecular sieves were prepared by using a molten boric acid method and exhibited a continuously-adjustable acidity in heterogeneously-catalyzed Strecker reactions under mild conditions. Al_xGa_1−x-PKU-1 accommodated a large number of Brønsted acid sites in the framework, and the acidic density and strength were enhanced with the successive incorporation of Al atoms, thus the catalytic activity became superior in the formation of α-aminonitriles. Three-fold coordinated boron atoms, despite the electron-deficient configuration, seemed unable to behave as Lewis acid centers probably due to steric hindrance against the adsorption of large organic substrates. This work illustrates, for the first time, possible application in Strecker reactions using zeolite-like solid solutions, and will potentially provide an effective method and a beneficial reference to control surface acidity for porous materials.