A ＂Green＂ Cyclohexanone Oxidation Route Catalyzed byHollow Titanium Silicate Zeolite for Preparingε-Caprolactone, 6-Hydroxyhexanoic Acid and Adipic Acid

摘要

Hollow titanium silicalite (HTS) molecular sieve has been synthesized, and information on its structure, physico-chemical characterization, as well as surface property was investigated by a host of analytical methods, such as XRF, XRD, low-temperature N2 adsorption/desorption, TEM, FT-IR, UV-Vis, 29Si MAS NMR, and XPS techniques. The characterization results suggest that HTS zeolite has a special hollow crystal structure and its mesopore volume is larger than that of TS-1 zeolite. The titanium species in this zeolite are composed of the framework tetrahedral Ti (IV) ions and extra-framework octahedral Ti (IV) ions, which tend to disperse into its bulk phase. This zeolite material also has been applied to catalyze the cyclohexanone oxidation process, and the products are not completely consistent with those results obtained by using TS-1 zeolite, which might be caused by their difference in pore structure and pore volume, especially the mesopore volume. Cyclohexanone oxidation catalyzed by HTS zeolite is a representative consecutive reaction, the main target products of which are e-caprolactone, 6-hydroxyhexanoic acid and adipic acid. The effect of H2O2/cyclohexanone mole ratio on the cyclohexanone conversion, the total target product selectivity, the distribution of three target products selectivity and their variations along with reaction time is also researched and analyzed, which indicate that HTS zeolite shows a high performance for the Baeyer-Villiger reaction of cyclohexanone and catalytic oxidation of 6-hydroxyhexanoic acid under mild conditions, and the quantity of active surface titanium species as well as the pore structure and mesopore volume controlling the mass diffusion rate are the key factors determining the catalytic activity of HTS zeolite and product selectivity.