A series of ZnBr2 impregnated on rice husk ash silica catalysts were synthesised via the wet impregnation method for the CO2 cycloaddition to styrene oxide reaction. The X-ray diffraction (XRD) analysis indicates that the impregnation resulted in the deterioration of the silica’s pore channels. Catalyst with 0.5 w/w of Zn (0.5 wtZnBr2-SiO2) was highly active in the CO2 cycloaddition to styrene oxide. The conversion of styrene oxide (StO) was 89.1 , with the styrene carbonate (SC) selectivity of 92.1 under the optimum conditions (130°C, 60 bar, 3 h and solventless). Additionally, the universality of 0.5 wtZnBr2-SiO2 was also studied with other epoxides, and it shows good to excellent activity. The catalytic performance of the 0.5 wt ZnBr2-SiO2 remains constant after being reused three consecutive times. The activation energy of the reaction was determined to be 89.06 kJ/mol.
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