| abstract |
NO x , where x is 1 and 2, in exhaust gases is reduced over heterogeneous catalysts with hydrocarbons, carbon monoxide, hydrogen or mixtures thereof in the presence of oxygen from 100 to 650° C. and an absolute pressure of from 0.5 to 50 bar by a process in which the heterogeneous catalysts used are bimodal or polymodal compounds of the general formula I n n A.sub.1-x M.sub.2 O.sub.4 (I), n n which, if required, are doped with rare earth metals, noble metal, titanium, vanadium, molybdenum, tungsten or mixtures thereof, and where n A is magnesium, calcium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, tin or mixtures thereof, n M is aluminum, gallium, indium, tin, chromium, manganese, iron, cobalt, nickel, copper, zinc or mixtures thereof and n x is from 0 to 0.99, n whose oxygen atoms are in a cubic close packed arrangement and A is present in the tetrahedral sites and M in the octahedral sites, it also being possible for A to occupy octahedral sites if an equivalent amount of M occupies tetrahedral sites. |