Nano Silica with High Surface Area from Rice Husk as a Support for 12-Tungstophosphoric Acid: An Efficient Nano Catalyst in Some Organic Reactions

Nano silica was prepared from rice husk with high surface area. X-ray diffraction (XRD) pattern showed that the amorphous form of silica was produced. Chemical composition of the nano silica was estimated by X-ray fluorescence spectroscopy and CHN analysis. The nano silica was used as a support for H3PW12O40. The nano silica and nano silica supported H3PW12O40 were characterized by inductively coupled plasma, XRD, transmission electron microscopy (TEM), N2 adsorption-desorption, and Fourier transform infrared spectroscopy. TEM images of nano silica as well as the supported catalyst displayed average size of 6 and 7 nm, respectively. The catalyst showed excellent activity in some important organic reactions including Biginelli, Hantzsch, Mannich, and Claisen-Schmidt reactions with good reusability. Catalytic activity of this nano catalyst is an improvement over the commercially available silica that is used to support H3PW12O40.