Switching Between Oxidation Types Using Molybdenum Phosphate Catalysts for Paraffin Activation Using Doped Fe as Surface Acidity Modifier and MoOx as an Oxygen Insertion Tool

Abstract

A comparative study of the activation of n-hexane over 12-molybdophopshoric acid (H3PMo12O40 or HPA), Fe3+ doped HPA (Fe0.69H0.93PMo12O40) and an iron phosphate catalyst (P/Fe = 1.22) was carried out. The Fe doped HPA catalyst is thermally more stable and less acidic than the unmodified HPA catalyst. The HPA and the Fe doped HPA catalysts both catalytically produced 2,5-dimethyltetrahydrofuran and 2,5-hexadione (oxygenates), with the Fe doped HPA catalyst selectively producing more oxygenates than the HPA catalyst. The iron phosphate catalyst produced cis-2-hexene and 1-hexene but no oxygenates, which implies that the iron phosphate catalyst promotes dehydrogenation, but not oxygen insertion. At 360 °C, the HPA catalyst initiated benzene formation reactions. At isoconversion of ca. 8% under isothermal conditions, the iron phosphate catalyst gave the highest selectivity (72%) towards benzene, which may have formed through both catalytic and non-catalytic reactions. In contrast, the Fe doped HPA catalyst showed a lower benzene selectivity than the HPA catalyst with a corresponding increase in cyclic oxygenates.