Changes in Fe-Mn-SO42-/ZrO2 catalyst formulations during activation have been observed. In air or an inert gas, the added salt, such as iron and/or manganese nitrate, decomposes over a temperature range of about 200-400 degrees C to produce nitric oxide, oxygen and iron and/or manganese oxide. The crystallization of zirconia occurs at 450 degrees C; when the sample contains sulfate the exothermic event occurs at a temperature that is about 200 degrees C higher. Heating in the presence of hydrogen causes the evolution of nitric oxide to occur over a narrow temperature range and at a lower temperature than when the sample is heated in helium or air. It appears that the nitrate ions associated with Fe, Mn and Zr decompose to produce nitric oxide, and presumably water, at different temperatures when the sample is heated in the presence of hydrogen. Heating samples of sulfated zirconia containing iron and/or manganese in hydrogen causes sulfur evolution at a lower temperature, and a significant fraction of it in the form of H2S.