Studies on the catalyst preparation methods and kinetic behavior of supported cobalt catalysts for the complete oxidation of cyclohexane

摘要

Low cost dispersed supported cobalt oxide nanocatalysts on activated carbon (AC) were prepared by two different methods: (1) combined impregnation and deposition–precipitation (IMP-DP) and (2) heterogeneous deposition–precipitation (HDP). XRD, TEM, FESEM, BET and Boehm techniques were used for the characterization of the support and the catalysts. Characterization analyses indicated the negative effect of the wet impregnation method on the IMP-DP technique for the preparation of catalysts for the total oxidation of cyclohexane in air. The catalysts prepared by HDP and IMP-DP methods were found to have significant differences in oxidation activity, morphology, particle size, and shape of active sites. The HDP preparation method resulted in dispersed catalysts with particle sizes less than 15 nm, which were smaller than those prepared by the IMP-DP method. The morphology of cobalt oxide on activated carbon indicated “lamellar” and “sphere” shapes for catalysts prepared by the IMP-DP and HDP method, respectively. Higher removal efficiencies for cyclohexane were obtained for catalysts synthesized by HDP compared with those prepared by the IMP-DP method. The Eley–Rideal rate expression was found to be appropriate to describe the kinetics of cyclohexane oxidation over the range of experimental conditions employed in this study.