Partial Oxidation of Ethane by Reductively Activated Oxygen over Iron Phosphate Catalyst

Abstract

The catalytic oxidation of ethane was carried out at 573–773 Kover iron phosphate catalyst. The oxidation of ethane by oxygenproduced only ethylene and carbon oxides. The co-feed of hydrogenwith oxygen remarkably accelerated the conversion of ethane.Ethanol and acetaldehyde were newly formed by co-feedinghydrogen. The partial oxidation of ethane to ethanol andacetaldehyde can also be achieved by using nitrous oxide as anoxidant. The co-feed of hydrogen with nitrous oxide increasedthe conversion of ethane and the yield to C2oxygenates. Theinvestigation on the reaction paths suggests that ethanol is theprimary product in the oxidation of ethane with hydrogen–oxygengas mixture and with nitrous oxide. Acetaldehyde and ethyleneare produced through further oxidation and dehydration ofethanol, respectively. The highest yield obtained for C2oxygenates was 4.4% (ethanol, 1.4%; acetaldehyde, 3.0%) at 673 K. The kinetic and mechanistic studies suggest that the oxidationof ethane proceeds by a similar reaction mechanism to the oneproposed for the oxidation of methane. Oxygen is activated bythe electrons and protons derived from hydrogen on the catalystsurface, generating a new oxygen species, probably adsorbedperoxide species, effective for the selective oxidation ofethane to ethanol. The same oxygen species can be generatedfrom nitrous oxide by its reductive activation. Both kineticresults and isotopic effects on the conversion of ethane suggestthat the dissociation of the C–H bond of ethane proceeds notablyfaster than the formation of the active oxygen species. Incontrast with ethane, the rate of activation of methane wascomparable to that of the generation of the active oxygen species.