Preparation of α-MoO3 from H3PMo12O40 precursor: synthesis of 1,2-cyclohexanediol from cyclohexene over α-MoO3-TiO2 catalyst

Abstract

A series of α-MoO3-TiO2 mixed oxides were prepared by calcining a mixture of the heteropolyacid H3PMo12O40 and TiO2 at temperatures ranging from 350 °C to 600 °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 °C. Above 450 °C, Keggin’s structure collapses. XRD analysis revealed that as the calcination temperature increased, more orthorhombic α-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 α-MoO3-TiO2 mixed oxides, higher than that obtained with TiO2 monoxide and α-MoO3 monoxide, suggest a synergistic effect between TiO2 and α-MoO3. This efficient and stable catalyst after reuse can be developed for the synthesis of diols.