Heterogeneously catalysed partial oxidation of cyclohexane in supercritical carbon dioxide Original Research Article

Heterogeneously catalysed partial oxidation of cyclohexane to cyclohexanol and cyclohexanone in supercritical carbon dioxide was investigated realising batch experiments and continuous runs within the temperature range from 353 to 673 K at pressures between 80 and 160 bar. Before catalytic runs, phase behaviour of the reaction mixture was studied by means of a high-pressure optical cell and the results indicate that: (i) the system is supercritical at the applied reaction conditions; and (ii) results agree well to estimated values using the Peng–Robinson equation of state. Mainly two classes of catalysts were tested in oxidation runs: (i) conventional metal oxide catalysts (active metals Co, Mn, Fe) on alumina or silica as well as microporous (MOR, AlPO-31) and mesoporous materials (Al-MCM-41) as supports; and (ii) organometallic complexes (salenes) of those metals immobilised on mesoporous molecular sieve (MCM-41) or microporous material (EMT). In general, the use of supported metal oxides leads to higher yields for target products cyclohexanone and cyclohexanol compared to the immobilised complexes. Maximum selectivity for these products reached 26% (-one) respective 16% (-ol) at 10% conversion.