Methods and chemical compositions for treating a gas stream comprising non-halogenated and halogenated organic compounds while suppressing halogenation of the non-halogenated organic compounds with the oxidation products of the halogenated organic compounds in the gas stream are disclosed. The gas stream in the presence of oxygen is contacted with the catalyst compositions of the invention to oxidize the non-halogenated and the halogenated compounds to form water, carbon dioxide, and halogen molecules (Cl.sub.2, Br.sub.2, etc.) and/or halogen acids such as HCl, HBr, etc. An advantage of the present compositions and methods is that halogenation or of the treated emissions is suppressed over a process operating temperature range 400 to 550.degree. C.