TiO2/MCM-22催化合成对二甲苯的研究

Study on synthesis of p-xylene catalyzed by TiO2/MCM-22

以钛酸四丁酯为前驱体,乙醇为溶剂,通过浸渍法制备了一系列TiO2改性MCM-22微孔分子筛择形催化剂,在连续流动固定床反应器上考察了甲苯与碳酸二甲酯烷基化合成对二甲苯的择型催化性能。通过XRD、FT-IR、N2吸附-脱附、NH3-TPD、XPS、吡啶吸附FT-IR、UV-Vis等手段对催化剂进行表征,并考察了反应温度、空速对甲苯烷基化反应的影响。结果表明,制备的TiO2改性MCM-22催化剂在甲苯与碳酸二甲酯烷基化合成对二甲苯过程中不仅表现出优异的择型性能,而且还保持了较高的催化活性。这是由于钛酸四丁酯具有较大的分子尺寸,在浸渍过程中仅微孔分子筛外表面酸性位被有效覆盖,而分子筛孔内的酸性位并未受到影响。

A series of TiO2 modified MCM-22 catalysts are prepared by impregnation method with tetrabutyl titanate as the precursor and ethanol as the solvent. The shape-selective catalytic performances of the TiO2 modified MCM-22 catalysts in the synthesis of p-xylene via alkylation of toluene with dimethyl carbonate are investigated on a fixed bed reactor.The catalysts are characterized by means of XRD,FT-IR,N2 adsorption-desorption,NH3-TPD,XPS,FT-IR with pyridine adsorption and UV-Vis. Influences of temperature and velocity on the toluene alkylation are also studied. The results indicate that the TiO2 modified MCM-22 catalysts prepared by using tetrabutyl titanate as the precursor and ethanol as the solvent exhibit an excellent shape-selectivity along with a high catalytic activity in the synthesis of PX,which achieves a well coverage of the acid sites on the external surface of MCM-22 zeolite and preserve the acid sites in the pores of MCM-22 simultaneously because of the big molecular size of tetrabutyl titanate.