Incorporation of Keggin-based H3PW7Mo5O40 into bentonite: synthesis, characterization and catalytic applications

Abstract

The Keggin-based molybdo-substituted tungstophosphoric acid, H₃[PW₇Mo₅O₄₀]·12H₂O, were synthesized and incorporated with a bentonite clay by using a wetness impregnation method. The catalysts were characterized using several methods, such as inductively coupled plasma-atomic emission spectroscopy (ICP-AES), Fourier transform infrared spectroscopy (FT-IR), X-ray diffractometry (XRD), scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM-EDS), transmission electron microscopy (TEM), and thermogravimetric and differential thermal analysis (TG-DTA). This extremely active catalytic system provides a green strategy for the synthesis of 1,8-dioxo-octahydroxanthene and 1,8-dioxo-decahydroacridine derivatives under solvent free conditions at 80 °C with a good reaction mass efficiency, effective mass yield, and excellent atom economy. Both the surface acidity and catalytic activity sharply increased after H₃[PW₇Mo₅O₄₀]·12H₂O was impregnated with bentonite clay. In addition, the PW₇Mo₅/bentonite catalyst can be conveniently recovered and reused numerous times without demonstrating a significant loss in activity.