Wikipedia
Hopcalite
Hopcalite is a mixture of copper and manganese oxides used as catalyst to convert carbon monoxide into carbon dioxide when exposed to the oxygen in air. A variety of composition for are known, "Hopcalite II" is approximately 3:1 manganese dioxide : copper oxide. Hopcalite I is a mixture of 50% MnO, 30% CuO, 15% "CoO", and 5% AgO.