The catalyst comprises a first catalyst from Pt, Pd, and Ir and their oxides, at 0.1-10 g/l catalyst supported on silica-boria-alumina composite oxides and zeolites with silica/alumina molar ratio >30. It may further comprise one of Au, Ag, Cu, Fe, Sb, Se, Te, and Ta and their oxides as a 2nd catalyst, at 0.01-5 g/l catalyst, and 2nd/1st catalyst support weight ratio <1. The catalyst is used for treating flue gases containing HCl, dioxins, and furans; eliminating pollutants in the gases by oxidative decomposition while suppressing secondary pollutant formation from gaseous precursors.