Heterogeneous catalysts for esterification reaction

Sodium silicate from rice husk ash was functionalized with different silylating agents to produce silica with -CH2-Cl (labelled as RHACCl), -CH2-NH2 (labelled as RHAPrNH2) and -CH2-SH (labelled as RHAPrSH) end groups via a novel one-pot synthesis. Saccharine (Sac) and Melamine (Mela) were immobilized onto RHACCl to form RHAC-Sac and RHAPrMela. The functionalized -CH2-SH group in RHAPrSH was oxidized to sulfonic acid, -CH2-SO3H (labelled as RHAPrSO3H) with hydrogen peroxide at room temperature. The catalysts showed good textural and structural properties. RHAC-Sac, RHAPrMela, RHAPrSO3H, RHA-Blank (as control) as well as homogenous Sac and homogenous Mela were used as catalysts in the esterification reaction. The catalytic activity was found to follow the sequence: RHAPrSO3H > RHAPrMela > homogenous Sac > RHAC-Sac > homogenous Mela > RHA-Blank. The catalysts were easily regenerated and could be reused several times without loss of catalytic activity.