Methane partial oxidation over NiO/MgO solid solution catalysts

Abstract

The following issues regarding the partial oxidation of methane to synthesis gas, over NiO/MgO solid solution catalysts, at a very high space velocity of the feed gas (CH 4/O 2=2/1, GHSV=720 000 cm 3/g h), were investigated: (i) the effect of the solid solution formation between NiO and MgO on the reaction; (ii)the effect of the composition of the catalyst; and (iii) the reaction mechanism. It was found that the mechanical mixtures of NiO and MgO have low activity and selectivity; however, their activity and selectivity became higher with increasing calcination time, due to the formation of a NiO–MgO solid solution. In contrast, the solid solution catalysts prepared via impregnation provided high activity and selectivity, as well as high stability over a large range of NiO concentrations. However, the activity was low for too low concentrations of NiO in NiO/MgO and the catalyst was no longer stable for too high concentrations of NiO. By comparing, under the same reaction conditions, the rate of partial oxidation of methane for CH 4/O 2=2/1 to that of the reforming reaction of a mixture CH 4/H 2O/CO 2 obtained from the former by complete combustion, one could conclude that the pyrolysis mechanism was dominant at 700°C and 750°C, but at 850°C, the combustion reforming mechanism also played a part.