Synthesis and catalytic properties of macroporous SiO2-coated CNT-sieve-composite-supported 12-tungstophosphoric acid catalysts with dual pore structure for the Baeyer–Villiger oxidation of cyclic ketones under microwave irradiation

Abstract

Carbon nanotube sieves (CNTs-S) with a flutelike shape were synthesized by cutting and perforating using a chemical oxidation etching method. Using the obtained CNTs-S as a hard template, SiO2-coated CNTs-S dual pore structures (CNTs-S@SiO2) were formed. Finally, tungstophosphoric acid was supported on CNTs, CNTs-S, and CNTs-S@SiO2 matrices by the incipient wetness method to obtain the corresponding supported catalysts PW12/CNTs, PW12/CNTs-S, and PW12/CNTs-S@SiO2. The results showed that obtained 30%PW12/CNTs-S and 30%PW12/CNTs-S@SiO2 catalysts in 30 wt% dipping solution had the best catalytic performance for Baeyer–Villiger oxidation of cyclic ketones by H2O2. The conversion of cyclohexanone was 94% and 91%, respectively, in 5 min under microwave irradiation. Cyclopentanone and adamantanone approached quantitative conversion and the selectivity of corresponding lactones reached 100%. The dual pore structure catalyst showed very excellent cyclic stability.