Partial oxidation of methane to synthesis gas over MgO-supported Rh catalysts: the effect of precursor of MgO

Five magnesium-containing precursors were used to prepare magnesium oxides of different surface areas. With these oxides as supports, catalysts (1 wt.% Rh loading) with different Rh dispersions after reduction were prepared. At a T-furnace of 750 degrees C and 1 atm, all these catalysts provided a conversion >80% and selectivities of 95-96% to CO and 96-98% to H-2, at the high space velocity of 7.2 x 10(5) ml g(-1) h(-1), with very high stability. No significant deactivation of the catalyst was observed for up to 96 h of reaction. However, no notable effect of the precursor of MgO was noted and possible explanations are provided. Temperature-programmed reduction (TPR) experiments indicated the presence of up to three kinds of rhodium-containing species, Rh2O3, Rh2O3-interacting with the support, and MgRh2O4, in the oxidized MgO-supported Rh catalysts. The strong interactions between rhodium and magnesium oxides are suggested to be responsible for the high stability of the catalyst. It was found that the methane conversion increased with the amount of catalyst when it was below 5.0 mg, but remained almost unchanged when it was greater than 5.0 mg. The catalytic assays also provided some information about the reaction mechanism. (C) 2000 Elsevier Science B.V. All rights reserved.