Comparison of flame-made rhodium on Al2O3 or Ce0.5Zr0.5O2 supports for the partial oxidation of methane

• We compare the effect of alumina and ceria–zirconia support on rhodium activity.
• Thermodynamic behavior is obtained at low rhodium loadings on alumina support.
• Higher oxygen concentrations affect the catalytic performance of rhodium.
• Oxygen spill-over from ceria–zirconia support to rhodium limits catalytic activity.
• Formation of metallic rhodium is enhanced on alumina support.

Catalytic partial oxidation of methane (CPOM) was investigated for rhodium supported on Al2O3 or on Ce0.5Zr0.5O2. The catalysts were synthesized by flame spray pyrolysis and characterized by nitrogen adsorption, transmission electron microscopy, X-ray diffraction, temperature-programmed reduction (TPR) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The Rh/Al2O3 catalysts exhibited an enhanced and stable CPOM activity compared to Rh/Ce0.5Zr0.5O2. Syngas formation was promoted for 0.5 wt% Rh on Al2O3 close to the calculated thermodynamic equilibrium, outperforming 1 wt% Rh/Ce0.5Zr0.5O2 in the temperature range 525–750 °C. A proposed mechanism of the effect of support on Rh activity is discussed in terms of oxygen transport capacity of the support materials. Further, high oxygen concentrations showed that Al2O3 is a better support compared to Ce0.5Zr0.5O2. This could be attributed to the fact that the Al2O3 support inhibits Rh oxidation and therefore allows the presence of Rh in its metallic state, which is preferable for high syngas formation. After thermal treatment of the catalysts, the catalytic effectiveness of Rh was more than 5 times higher for Al2O3 than for Ce0.5Zr0.5O2 supports.

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