Si-29 MAS NMR, XRD and FESEM studies of rice husk silica for the synthesis of zeolites

We have used rice husk ash as a silica source for the synthesis of zeolites. Amorphous silica is a highly reactive silicon source, but not all silica which is amorphous to XRD is equally suitable. The local structure of amorphous silica was investigated by Si-29 magic-angle spinning nuclear magnetic resonance (MAS NMR) and field emission scanning electron microscopy (FESEM) in order to optimize the process. The results show that amorphous silica extracted by physical combustion with controlled temperature contains only *Si(OSi)(4) tetrahedral units and is the most reactive silica sourer in the synthesis of zeolite Y, compared to other silica samples prepared by chemical extraction and uncontrolled burning. The presence of crystalline cristobalite and trydimite phases and SiOH groups render the silica less active.