TiO2／Al2O3负载量对气相酯交换合成碳酸甲丙酯的影响

采用XRD、N2 physical adsorption、XPS、NH3-TPD和吡啶吸附IR等技术,对碳酸二甲酯和丙醇气固相合成碳酸甲丙酯的TiO2/Al2O3催化剂进行了表征.实验结果表明,TiO2/Al2O3表面的Lewis酸中心是反应的催化活性位,酸性主要来源于Al2O3,TiO2起修饰作用,有利于选择性生成碳酸甲丙酯.随着Ti负载量的增加,TiO2在Al2O3表面由高度分散状态向晶态转变,其比表面积逐渐降低,但是TiO2/Al2O3的表面酸性质没有受到显著影响,L酸量先是增加,而后略有下降.当Ti负载量为5%时,DMC的转化率及MPC的选择性分别达到54.3%和88.1%.

Effect of TiO2/Al2O3 Loadings on Synthesis of Methyl Propyl Carbonate by Gas-phase Transesterification

The TiO2/Al2O3 catalysts with variant loadings for the synthesis of methyl propyl carbonate (MPC) via the gas-phase transesterification of dimethyl carbonate (DMC) with propanol were characterized by means of XRD, N2 physical adsorption, XPS, NH3-TPD and FT-IR of adsorbed pyridine. Experimental results indicated that the Lewis acidic centers on the surface of TiO2/Al2O3 were the catalysis active sites for the reaction, which attributed mainly to Al2O3. TiO2 as a modified component favored the selective formation of MPC. As the Ti loadings increased, the dispersion of TiO2 on the surface of Al2O3 changed from monolayer to crystal phase and the BET surface areas of TiO2/Al2O3 decreased. The surface acidity of TiO2/Al2O3 was not remarkably influenced while the Lewis acidic amount increased firstly and then decreased slightly. When the Ti loading was 5%, the reaction reached a maximum with the conversion of DMC, the selectivity of MPC of 54.3% and 88.1%, respectively.