Abstract: A composite active phase/support catalyst for purifying exhaust gases, the active phase of which comprises a solid solution of transition metals oxides with a spinel structure of the formula AB.sub.2 O.sub.4 wherein "A" comprises a combination of metals with their stoichiometric indexes being in the range Zn.sub.0.18-0.21 Cd.sub.0.18-0.21 Co.sub.0.18-0.63 Fe.sub.0.02-0.46 and "B" also comprises the combination of transition metals with their stoichiometric indexes being in the range Cu.sub.0.09-0.36 Ni.sub.0.09-0.11 Cr.sub.0.24-0.48 Fe.sub.0.28-0.34. The support comprises an oxide carrier coated with oxide layer having a spinel structure of the formula Cu.sub.0.33 Co.sub.0.33 Ni.sub.0.33 Al.sub.2 O.sub.4 whereas the amount of the active phase per support surface lies in the range 10-12 .mu.Moles of AB.sub.2 O.sub.4 per 1m.sup.2 of support surface.