the metal oxide and the support material 6 5 grams of powder are charged into a vertically arranged quartz reactor diameter 20 mm height about 500 mm in the middle of which there is arranged a gas permeable frit for exposure of the sample the bed depth is about 15 mm around the quartz reactor there is arranged a furnace which heats a length of about 100 mm of the middle part of the reactor to temperatures of up to 550 u00b0 c through the catalyst there is passed at a space velocity of about 10 000 per hour a gas mixture comprising 1000 ppm of no 1000 ppm of propene 10 of oxygen and the remainder argon as a carrier gas downstream of the reactor the no concentration is measured using a gas detector with any no 2 formed being reduced to no in a converter prior to detection simultaneously oxidation of hydyrocarbons to co 2 is observed by measurement of the co 2 content by means of the gas detector the study on this catalyst indicated as in the case of all the catalysts of the invention a high stability it is favorable that in the temperature range indicated which corresponds approximately to the temperatures which can occur in the waste gas stream of an exhaust of an internal combustion engine the degree of reduction is significantly higher than for the pure spinel in contrast a pure h mordenite leads under comparable conditions to no significant no x.