The cycloaddition reaction between carbon dioxide (CO2) and epoxides is an attractive example for the synthesis of value-added chemicals exploiting CO2 greenhouse emissions. In this study, we reported on the propylene carbonate (PC) production mediated by lanthanum oxide (La-O)/tetrabutyl ammonium bromide (TBAB) binary mixture. The effect of different reaction parameters including catalyst/co-catalyst loading, the amount of substrate, CO2 pressure, temperature, and reaction time were investigated. The binary catalytic system showed high catalytic conversion and selectivity. Catalyst reusability experiments indicated that the binary system was recyclable over five times without losing its activity/selectivity. In addition, a plausible reaction mechanism based on spectroscopic and kinetic measurements were presented, which was supported by density functional theory (DFT) calculations.