The Study On Catalytic Reduction Of NO By CO Over NiO/CeO₂ Catalyst

CO and NOx releasing from automobile emissions are the main pollutants in theatmosphere, and abatement the pollution of these exhausts have attracted much attention allover the world. Catalytic reduction of NO by CO is considered to be one of the mostimportant approach for the control of this exhaust gas. Because most of employed noblecatalysts (TWC) are facing some disadvantages such as high cost and low anti-oxidationcapability, studies with non-noble catalysts to substitute for noble catalysts have been ahotspot research in recent years.A catalyst, nickel as active component and CeO₂ as carrier, was synthesized byimpregnation method and tested in the catalytic removal reaction of NO and COsimultaneously. The effects of the nature of support, the preparation method of support andoxygen on the catalytic activity over NiO/CeO₂ were investigated. The XRD, H₂-TPR, TPDand TPSR techniques were adopted to characterize the structure properties of the catalyst, theredox interplay of the NiO and CeO₂ and the mechanism of the NO/CO reaction. Some usefulresults are shown as follows:(1) The nature of support and the preparation method of support have close relation withthe catalytic activity. Comparing with the activity of NiO/γ-Al₂O₃, NiO/TiO₂, and NiO/CeO₂catalysts, NiO/CeO₂ showed the highest light-off conversions of NO and CO and lowesttemperature of total conversion. Three kind of CeO₂ prepared by (â…°) homogeneousprecipitation (HP), (â…±) precipitation (PC), and (â…²) direct decomposition (DP) method wereused as the carrier of NiO. Through the activity comparison of NiO/CeO₂(HP), NiO/CeO₂(PC)and NiO/CeO₂(DP), CeO₂(HP) optimized as the preferable carrier for active component (at aspace velocity of 120 000h^-1, the coversion of NO is 50ï¼…at 170℃over NiO/CeO₂(HP)catalyst, and the complete conversion of NO and CO occurred at 210℃).(2) The addition of a small amount of O₂ has no much effect on the NO and COcoversion of the catalyst (at a space velocity of 120 000h(-1), the coversion of NO is 25ï¼…at 170℃, and the complete conversion of NO and CO occurred at 210℃).(3) Analylizing from the XRD patterns of NiO/CeO₂(HP), it is possible that certainamounts of Ni²⁺ ions have incorporated into the ceria lattice and the other nickel of additionremain on the catalyst in the form of NiO crystallites; The interaction between the NiO and CeO₂ was studied by H₂-TPR measurement, it is revealed that the new active oxygen formedby their interplay would be the reason of the high activity of NiO/CeO₂ catalyst.(4) Based on the TPSR and TPD results, a reaction model for NO/CO interaction overNiO/CeO₂ has been proposed: (â…°) CO reduces surface oxygen to create vacant sites; (â…±) on thevacant sites, NO dissociates to produce N₂; and (â…²) the oxygen originated from NOdissociation is removed by CO to regenerate the active sites and made the reaction proceedfurther. So the reductant of CO pre-reducing the surface of the catalyst is the critical step forthis catalytic reaction.