The oxidative dehydrogenation of n-octane to styrene using catalysts derived from hydrotalcite-like precursors Original Research Article

A number of hydrotalcite-like compounds containing Mg and V were prepared with different Mg/V ratios, ranging from 1:1 to 4:1. The effect of variations in synthesis procedures, such as preparing the compounds under inert gas, hydrothermal treatments at different temperatures and different precipitating agents were examined. These compounds were characterised by ICP-OES, powder XRD (including, in part, in situ powder XRD under H2, air and N2), Raman (incl. in situ), IR, XPS and SEM. They were then investigated as catalysts for the aerobic oxidation of n-octane under varying conditions of GHSV, temperature and feed/air ratio. Styrene was found to be the dominant organic product and a maximum selectivity of 19%, corresponding to a yield of 14%, was obtained with a catalyst with a Mg/V ratio of 2.3. The mechanism appears to involve olefin formation, followed by cyclisation to form ethyl benzene, which is further dehydrogenated to form styrene. Catalysts where the precursors have more amorphous structures were found to be superior to those obtained from highly crystalline precursors, and catalysts derived from sodium salts were superior to those obtained from potassium salts.