SiO_2–Al_2O_3 Composite Oxides with Hierarchical Pores as Solid Acid Catalysts for Tetrahydrofuran Polymerization

摘要

A series of SiO_2–Al_2O_3 composite oxides with different parameters of porous structure was synthesized via sol-gel process at a systematically varied pH (pH 2, 5, 7, 9, 11, 13), and characterized by trans- mission electron microscope, N_2 adsorption–desorption measurements, X-ray powder diffraction, Fourier transform infrared spectroscopy, temperature–programmed desorption of ammonia and IR spectra of pyridine adsorption. The catalytic performance of SiO_2–Al_2O_3 was investigated in the catalytic polymerization of tetrahydrofuran. All the SiO_2–Al_2O_3 oxides are characterized by similar acidity but different porous properties. In the pH range of 7 to 9, the hierarchical pore system composed of mesopores and macropores is formed. Due to an enhanced accessibility of acid sites and easier diffusion of reacting molecules, the samples containing a hierarchical pore system of the catalysts show the highest yield of polytetrahydrofuran (about 48%) and an improved number-average molecular weight (Mn).