NaOH改性MnO2/γ-Al2O3催化尿素醇解合成碳酸丙烯酯

Synthesis of propylene carbonate from urea and 1,2-propylene glycol over MnO_2/γ-Al_2O_3 catalyst modified by NaOH

采用超声浸渍法制备了MnO2/γ-Al2O3催化剂,并用碱和盐对其进行了改性。采用X射线衍射仪(XRD)、CO2-TPD对改性后的MnO2/γ-Al2O3催化剂进行了表征,研究了改性后催化剂在尿素醇解合成碳酸丙烯酯(PC)反应中的催化性能。研究结果表明,NaOH改性MnO2/γ-Al2O3催化剂具有最好的催化性能;同时催化剂的焙烧时间、焙烧温度以及NaOH改性量影响催化剂表面碱性活性中心的数量和强度,其中中强碱的增加是改性后催化剂活性提高的主要原因。在NaOH用量为MnO2质量的10%,400℃焙烧2h后,改性MnO2/γ-Al2O3催化剂表面的中强碱量最大,催化活性最高,PC收率与选择性分别达86.9%、91.8%。

MnO2/γ-Al2O3 catalyst was prepared by ultrasonic impregnation and modified by alkali or salt. The modified MnO2/γ-Al2O3 was characterized by X-ray diffraction （XRD）, temperature-programmed desorption of CO2（CO2-TPD）. Catalytic performances were investigated in urea alcoholysis to propylene carbonate （PC）. The activity of MnO2/γ-Al2O3 catalyst modified by NaOH was the best. At the same time, calcination temperature, calcination time and amount of NaOH affected the quantity and intensity of basic activity centers on the surface of the modified catalyst. The increase of moderately basic activity center was the main reason for the catalyst activity improvement after modification. When the MnO2/γ-Al2O3 catalyst was modified by 10% NaOH, and calcined at 400℃ for 2 h, the quantity of moderately basic activity center on the surface was the most, which led to the highest activity. Yield and selectivity of PC were up to 86.9% and 91.8%, respectively.