Incorporation of Keggin-based H(3)PW(7)Mo(5)O(40) into bentonite: synthesis, characterization and catalytic applications

The Keggin-based molybdo-substituted tungstophosphoric acid, H(3)[PW(7)Mo(5)O(40)]·12H(2)O, 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 H(3)[PW(7)Mo(5)O(40)]·12H(2)O was impregnated with bentonite clay. In addition, the PW(7)Mo(5)/bentonite catalyst can be conveniently recovered and reused numerous times without demonstrating a significant loss in activity.