The utilization of rice husk silica as a catalyst: Review and recent progress

In this review article, we report the recent development and utilization of silica from rice husk (RH) for the immobilization of transition metals and organic moieties. Silicon precursor was obtained in the form of sodium silicate and as rice husk ash (RHA). Sodium silicate was obtained by direct silica extraction from rice husk via a solvent extraction method while rice husk ash was obtained by pyrolyzing the RH in the range of 500–800 °C for 5–6 h. Transition metals were immobilized into the silica matrix via the sol–gel technique while the organic moieties were incorporated using a grafting method. 3-(Chloropropyl)triethoxy-silane (CPTES) was used as a bridge to link the organic moieties to the silica matrix. All the catalysts exhibited good physical and catalytic potential in various reactions.

In this review work, rice husk silica was used to incorporate and immobilize transition and non-transition metals and organic ligands to transform it into heterogeneous catalysts. The catalysts showed good physico-chemical properties and high catalytic yield in oxidation, esterification, Friedel–Crafts, photocatalysis and aminolysis reactions.Figure optionsDownload high-quality image (189 K)Download as PowerPoint slideHighlights
► Inorganic silica was obtained from rice husk by burning and solvent extraction.
► The silica was used as a support for metals and used as heterogeneous catalysts.
► The catalysts were used in liquid phase organic reactions.
► Surface structures of the catalysts were correlated to their catalytic activity.
► Reaction mechanisms were proposed based on reactivity and physical properties.