Study On Mixed Oxide Catalysts For The Reduction Of NO_x By NH₃

The non vanadium based de-NO_x catalyst has attracted more attention in the removal of NO_x.In this research,Ce-Sn bi-metallic mixed oxide catalyst and Fe-Ni-Ti tri-metallic mixed oxide catalyst for the selective catalytic reduction of NO_x with NH₃（NH₃-SCR）have been inveatigated.The Ce-Sn catalyst prepared by the hydrothermal method was active.Over this catalyst 84%NO_x conversion was achieved between 300-450℃,and nearly 100%N₂ selectivity was obtained in temperature range studied.Ce-Sn catalyst also showed high resistance aganist H₂O and SO₂.The redox cycle(2Ce⁴⁺+Sn²⁺（?）2Ce³⁺+ Sn⁴⁺)existed over this catalyst.The strong interaction between Ce and Sn resulted in the improved redox property and increased Lewis acid sites,which contributed to the adsorption of NH₃.The adsorbed NO_x species did not participate in the reaction,while the ammonia adsorbed on Lewis acid was reactive.NH₃-SCR of NO_x over Ce-Sn catalyst mainly followed Eley-Rideal（E-R）mechanism.The Fe-Ni-Ti catalyst prepared by hydrothermal method also exhibited excellent NH₃-SCR activity,N₂ selectivity and high tolerance to H₂O and SO₂.Characterization results suggested the strong interaction between Fe,Ni and Ti led to an amorphous structure and large BET surface area.The redox property and surface acid were obviously enhanced.Dual redox cycle(Fe³⁺+ Ni²⁺（?）Fe²⁺+ Ni³⁺,Ti⁴⁺+ Ni²⁺（?）Ti³⁺+ Ni³)promoted electron transfer,which contributed to the adsorption and activation of NH₃.Asorbed NH₃ species and M-NO₂ species were reactive in the reduction of NO_x.The SCR reaction over Fe-Ni-Ti catalyst followed Eley-Rideal（E-R）and Langmiur-Hinshelwood（L-H）mechanism.