A comparative study of molybdenum and iron phosphate-based catalysts in n-hexane activation.
A comparative study of the activation of n-hexane over the 12-molybdophopshoric acid (H3PMo12O40 or HPA), its Fe3+ doped salt (Fe0.69H0.93PMo12O40 or Fe doped HPA) and the iron phosphate catalyst (P/Fe = 1.22) was carried out. It was found that the Fe doped HPA catalyst is thermally more stable and less acidic that the HPA catalyst. The HPA and the Fe doped HPA catalysts were more reactive that the iron phosphate catalyst. Both the HPA and Fe doped HPA catalytically produced 2,5- dimethyltetrahydrofuran and 2,5-hexadione (oxygenates), with the Fe doped HPA catalyst selectively producing more oxygenates than the HPA catalyst. This implied that the Fe3+ cation promoted the oxygen insertion reactions. The iron phosphate catalyst catalytically produced cis-2-hexene and 1- hexene but did not produce oxygenates, which means that the iron phosphate catalyst promotes oxidative dehydrogenation but does not promote oxygen insertion reactions. At 349 oC, the HPA catalyst played a role in initiating benzene formation. At isoconversion, the iron phosphate catalyst produced the highest yield of benzene (5.8 % at 8.1 % hexane conversion), which may have formed through both catalytic and non-catalytic reactions. The Fe doped HPA catalyst produced a lower benzene yield (1.4 % at 6 % hexane conversion) than the HPA catalyst (3.6 % at 8.3 % hexane conversion) at almost isoconversion and isothermal conditions.