Abstract: A catalyst for improving combustion of fluid fuels which comprises three layers. An inner or core layer of complex oxides of a mixture of Mn, Ni, Co and Cu; an intermediate layer containing alumina and silicate and optionally silicon carbide and an outer layer comprising a fired mixture of a Pt--Pd,Rh alloy on Al.sub.2 O.sub.3, Mo--Al.sub.2 O.sub.3, mixed oxides of La--Sr--Co and at least one of Vanadium oxide on alumina and Ag on Alumina. The catalyst can contact the fluid fuel in a storage tank, in a pipeline or in a combustion chamber. The invention also comprises combustion engines which incorporate the described catalyst.