Liquid phase oxidation of cyclohexane over mesoporous cobalt silicates molecular sieves synthesized in strong acidic media by assembly of preformed CoS-1 precursors with triblock copolymer

Abstract

Cobalt–incorporated mesoporous silica materials [MCoS(n), n = Si/Co = 20; 60] have been successfully prepared in strong acidic media by assembly of preformed CoS-1 precursors with triblock copolymer of the Pluronic type (P123) by a two steps procedure. They were characterized by various techniques including XRD, BET, FT-IR spectroscopy and diffuse reflectance UV–Vis (DRUV–Vis). The results show that the calcined MCoS materials contain Co(II) ions in tetrahedral environments under low and high Co content and the mesoporous walls contain the MFI structure building units. Liquid phase oxidation of cyclohexane using TBHP as oxidant was investigated on MCoS(n). The major products detected are cyclohexanone and cyclohexanol in all cases. The MCoS(n) catalysts are more active when water free TBHP was used and the conversion of cyclohexane increases when cyclohexane to TBHP molar ratio increases from 1:1 to 1:2, while the cyclohexanol selectivity decreases, which is ascribed to a further oxidation of cyclohexanol to cyclohexanone. The catalytic activity of MCoS(n) materials is enhanced as the cobalt content increases. It is worth noting that MCoS(20)is more active than Co-SBA15(20). The most active catalyst MCoS(20) acts as truly heterogeneous catalyst and was very stable after four runs.