The Basicity of MO/ZrO2 Catalyst and Their Use in the Synthesis of 2-Ethyl-Hexyl Carbonate
|School||Harbin Engineering University|
|Keywords||di-2-ethyl-hexyl carbonate catalyst basicity activity|
In this paper, MgO/ZrO2, K2O/ZrO2, MgO/ZrO2-La2O3-x and K2O/ZrO2-La2O3-x (x=0.4%,0.5%,0.6%,0.7%和0.8%) catalysts, which were prepared by impregnation method and calcined at 500℃,600℃and 700℃. The catalysts were used for di-2-ethyl-hexyl carbonate synthesis from dimethyl carbonate (DMC) and 2-ethyl-hexanol. The structure of catalysts was characterized by XRD, Raman and the basicity was characterized by CO2-TPD.It can be concluded from the result of XRD that the tetragonal zirconia phases were detected for MgO/ZrO2. Mg2+ substituted for Zr4+ in zirconia lattice and the oxygen vacancies produced in the zirconium lattice to maintain neutrality. The oxygen vacancies reduced the repulsion between the local oxygen vacancies and oxygen vacancies, having a greate distortion in the coordination layers, so that the catalysts maintained tetragonal phase at room temperature. However, the peak of MgO was appeared at 700℃. This could be attributed to that the framewok of catalysts may change at 700℃, and the active component was precipitation. With the content of La increased in catalysts, the peak of MgO disppeared gradually. This could be attributed to that La can prevent MgO from appearing at higher tempreture. For K2O/ZrO2 and K2O/ZrO2-La2O3-x, it was observed that tetragonal and monoclinic zirconia phases were detected at every calcination temperature. And the tetragonal zirconia phases was predominant phases when La was increasing in the catalysts, it indicated that La had a stabilization impact on zirconia lattice of K20/Zr02-La203-x catalysts.It can be concluded from the result of Raman that only the tetragonal phase appeared at every calcination temperature. For MgO/ZrO2-La2O3-x catalysts, La had a stabilization impact on zirconia lattice on the phase of catalysts. For K2O/ZrO2-La2O3-x catalysts, the calcination had a little effect on the phase of catalysts. With the increasing of La, the tetragonal zirconia phases was predominant phases and monoclinic zirconia phases decreased. It indicated that La had a stabilization impact on zirconia lattice of K20/Zr02-La203-x catalysts, and this was consistent with the result of XRD.It can be concluded from the result of CO2-TPD that the desorption peaks displays three peaks:the bacisity of ZrO2 at low temperature, the basicity of MgO and the basicity of the ZrO2 at high temperarure. For the catalysts with the same content of La, the basicity of catalysts was highest at 600℃. MgO/ZrO2-La2O3-0.6% had the highest basicity for the catalysts calcined at the same temperature. For K2O/ZrO2 and K2O/ZrO2-La2O3-x, the desorption peaks displays two peaks. The peak at the high temperature was due to the basicity of K2O, and the other peak was due to ZrO2 at middle temperature.For MgO/ZrO2 and MgO/ZrO2-La2O3-x, MgO/ZrO2-La2O3-0.6% calcined at 873K had the highest activity and the yield was 44.94%. According to XRD and CO2-TPD, it can be concluded that the activity and basicity of catalysts have the same changing trend. For K2O/ZrO2 and K20/Zr02-La203-x, K2O/ZrO2-La2O3-0.6% calcined at 973K had the highest activity and thet yield was 81.18%. The activity of K2O/ZrO2 was higher than the activity of MgO/ZrO2, it was attributed to that the basicity of K2O/ZrO2 was strenger than the basicity of MgO/ZrO2.The synthesized samples were determined using FT-IR,1H-NMR, gas chromatography and MS experiments. The experimental results showed that the structure of the synthesized samples was di-2-ethyl-hexyl carbonate. The catalysts had high catalytic activity was also proved by the analysis of gas chromatography online tracking reaction. When the reaction was 1.5h, the di-2-ethyl-hexyl carbonate was produced. When the reaction was 3.5h, the intermediate product disappeared.