Catalytic and electrocatalytic oxidation of propane on V-Mg-O and V-Mg-O (Ag) catalysts

Vanadium magnesium oxide catalysts prepared in this work were found active in selective oxidation of propane to propene. A selectivity as high as 79% was obtained at 10% conversion (813 K). No oxygenated or C₂ products were detected and the catalysts were found to undergo no change in activity over many weeks of operation. Under electrochemical pumping of oxygen (EOP) towards the catalyst (with oxygen present in the feed gas), both conversion and selectivity were found to increase slightly as external current increased, indicating the effect of electrical current can be exhibited by an oxide catalyst. However, in the absence of oxygen in the feed gas, EOP could lead to an even higher selectivity: 84 and 86.9% respectively for a 24 V-Mg-O and a 24 V-Mg-O (Ag) (1/2) catalyst. The overall results obtained suggest that electrochemically supplied oxygen is more selective towards C₃H₆. Mechanisms of both catalytic and electrocatalytic oxidation of propane were tentatively suggested, with surface oxygen ion vacancy identified as active surface species and the rate determining step involving heterolytic splitting of the C₃H₈ molecule to form a surface bonded C₃H ₇ ^– ion and a surface hydroxyl ion. The higher selectivity towards C₃H₆ in case of EOP was explained on this basis. While mixing with Ag powder was found to improve significantly the electrocatalytic performance of vanadium magnesium oxide, its role appears to be non-chemical: it simply gives rise to a larger area of the gas/catalyst/Ag electrode interface.