EFFECTS OF RHODIUM ADDITION ON METHANE OXIDATION BEHAVIOR OF ALUMINA-SUPPORTED NOBLE-METAL CATALYSTS

Laboratory methane oxidation experiments were conducted using a series of catalyst samples prepared by impregnating Ph-free noble metal catalysts (i.e., Pt/Pd, Pt or Pd) with various amounts of rhodium (0.0035, 0.005, and 0.014 wt.-% Rh). The addition of these small amounts of rhodium did not significantly change the temperature required for the onset of the methane oxidation. However, variable-composition experiments conducted at a temperature characteristic of warmed-up catalytic converters (ca. 550 degrees C) reveal that the rhodium addition tends to shift the optimum feedstream stoichiometry (at which a maximum methane conversion occurs) toward more reducing conditions. These Rh-induced effects on methane conversion behavior appear to be independent of how the rhodium is incorporated in the catalyst.