Wikipedia
Z-Stoff was a name for calcium permanganate or potassium permanganate mixed in water. It was normally used as a catalyst for T-Stoff ( high test peroxide) in military rocket programs by Nazi Germany during World War II.
Z-Stoff was used in the cold engine of the Messerschmitt Me 163 A airplane and in several early guided missiles, like the booster engine used with the Henschel Hs 293 anti-ship guided missile. T-Stoff decomposed by Z-Stoff was commonly used by World War II German military to generate steam for powering of fuel pumps in airplanes and rockets.
The reaction produces manganese dioxide, which tends to clog the steam generators. Later generations of the Walter Rocket used solid-state catalyst instead of its water solution.