| Summary: | The immobilization of three homogeneous catalysts namely; sulfonic acid,
1,1,3,3-tetramethyl guanidine and 1,5,7-triazabicyclo[4.4.0]dec-5-ene guanidine was
carried out on silica from rice husk ash. Sodium silicate from the rice husk ash was
immobilised with 3-(mercaptopropyl)trimethoxysilane. This was further oxidised to
sulfonic acid in a simple one pot method. The solid acid catalyst was denoted as
RHAPrSO3H. Analysis of the catalyst by nitrogen adsorption-desorption using
Brunauer, Emmet and Teller (BET) method showed its surface area to be 340 m2g-1
with average pore volume of 0.24 cc g-1 and pore diameter of 2.9 nm. Acidity tests
by cation exchange capacity and pyridine FT-IR adsorption, revealed the presence of
acid sites on the catalyst surface. Similarly, the 29Si MAS NMR of RHAPrSO3H
revealed the presence of Q4, Q3, T3, T2 and T1 silicon centres, while only Q4 and Q3
silicon centres were present in RHASiO2. The catalyst was used in the acetalization
reaction of glycerol with benzaldehyde. Under the best reaction conditions of 120 °C
temperature, 2:1 molar ratio of glycerol: benzaldehyde, 0.15g mass of catalyst and 8
h reaction time, significant conversion was achieved with high selectivity towards
five member ring isomer.
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