Abstract
A series of alpha-MoO3-TiO2 mixed oxides were prepared by calcining a mixture of the heteropolyacid H3PMo12O40 and TiO2 at temperatures ranging from 350 degrees C to 600 degrees C. The mixed oxides thus prepared were characterized and tested for the oxidation of cyclohexene by the oxidizing mixture H2O2/CO2. FTIR and XRD characterizations showed that the Keggin structure of H3PMo12O40 was preserved for calcination temperatures below 400 degrees C. Above 450 degrees C, Keggin's structure collapses. XRD analysis revealed that as the calcination temperature increased, more orthorhombic alpha-MoO3 was formed. Analysis of the reaction mixture by GC-MS showed that oxidation by the H2O2/CO2 mixture leads to 1,2-cyclohexanediol as the main product and to 2-cyclohexene-1-one and 2-cyclohexene-1-ol as minor products. Oxidation by H2O2/CO2 mixture proved to be more effective than H2O2 alone and CO2 alone. The conversion (69.4%) and the 1,2-cyclohexanediol selectivity (93.2%) obtained over alpha-MoO3-TiO2 mixed oxides, higher than that obtained with TiO2 monoxide and alpha-MoO3 monoxide, suggest a synergistic effect between TiO2 and alpha-MoO3. This efficient and stable catalyst after reuse can be developed for the synthesis of diols.