Direct Synthesis Of Diethyl Carbonate From CO₂ And Ethanol Over Ce_xZr_1-xO₂ And CeO₂ Catalysts

Carbon dioxide, which is blamed for the global green house effect, has attracted researchers'attention for its utilization. The process for direct synthesis of diethyl carbonate (DEC) from CO2 and ethanol not only produces economic chemicals with high value, but also improves environment by using CO2 as recycled carbon resource. In this paper, direct synthesis of DEC from CO2 and ethanol over CexZr1-xO2 and CeO2 was studied.CexZr1-xO2 (x=0.07) and CeO2 were effective catalysts for direct synthesis of DEC from CO2 and ethanol. The catalysts were prepared by precipitation from ZrOCl2 and Ce(NO3)3 with NH3·H2O at a constant pH and were calcined at 800℃. When CO2 and ethanol were charged with 238mmol and 168mmol, respectively, for 2h at 140℃, 0.29mmol or 0.4mmol DEC with 95% DEC selectivity could be obtained using the catalyst of 0.1g Ce0.07Zr0.93O2 or 0.5g CeO2 with trace amount of aldehyde and acetal.The insertion of zirconium atoms into the CeO2 cubic fluorite structure should be conferred on the high thermal stability of the textural properties and formation of high surface area. The catalysts of CexZr1-xO2 could be stabilization of the fluorite structure and the smallest particles at x=0.5. The structures of CexZr1-xO2 were varied with the Ce/Zr ratio. The structural modification of zirconium-cerium was characterized mainly by XRD. For CexZr1-xO2, the phase was tetragonal with a little monoclinic at x<0.15, stable cubic with slight modification at 0.15≤x≤0.8 and cubic at x>0.8.The catalytic properties of CexZr1-xO2 were related to the structure and the acid and basic sites on the surface. At 0.15≤x≤0.8, the activities of the catalysts were decreased by the formation of the strong acid and basic sites on the surface due to metastable tetragonal phase. The activity of CeO2 with higher acidity was better than that of Ce0.07Zr0.93O2 with higher basicity.