焙烧温度对TiO_2/γ-Al_2O_3催化剂气相酯交换合成碳酸甲丙酯性能的影响

Effect of Calcination Temperature on TiO_2/γ-Al_2O_3 Catalyst in Sythesis of Methyl Propyl Carbonate by Gas-Phase Transesterification

在连续流动气固相反应条件下,考察了焙烧温度对TiO2/γ-Al2O3催化剂催化碳酸二甲酯(DMC)和丙醇气相酯交换合成碳酸甲丙酯(MPC)反应的影响,并采用X射线衍射、傅里叶变换红外光谱、氨程序升温脱附、X射线光电子能谱等技术对TiO2/γ-Al2O3催化剂进行了表征。实验结果表明,在500℃下焙烧的Ti质量分数为5%的TiO2/γ-Al2O3催化剂对DMC和丙醇气相酯交换合成MPC反应的活性最好,DMC转化率可达54%,MPC选择性为90%。表征结果显示,Ti主要以Ti4+的形式存在于TiO2/γ-Al2O3催化剂表面;随焙烧温度的升高,TiO2/γ-Al2O3催化剂中的一水软铝石逐渐转化为γ-Al2O3,同时,钛酸四丁酯分解,TiO2含量增加,有利于提高TiO2/γ-Al2O3催化剂的活性;TiO2/γ-Al2O3催化剂的酸强度随焙烧温度的升高而减弱。

Effect of calcination temperature on activity of TiO2/γ-Al2O3 catalyst in synthesis of methyl propyl carbonate （MPC） by gas - phase transesterification of dimethyl carbonate （DMC） and propanol was studied. The catalyst was characterized by means of XRD, FFIR, NH3 TPD and XPS. Under optimal conditions： TiO2 mass fraction in TiO2/γ-Al2O3 catalyst 5% and the calcination temperature 500 ℃, conversion of DMC and selectivity to MPC were 54% and 90%, respectively. XPS results show that Ti exists in form of Ti^4＋ on surface of the catalyst. Boehmite in the catalyst is gradually transforming into γ-Al2O3 with rise of calcination temperature and at same time tetrabutyl titanate is decomposing into TiO2, so catalyst activity improves. However, acidic strength of catalyst lowers along with rise of calcination temperature.