Research On Thecatalyst Performance Of NOx-soot Simultaneous Removal Over La₂NiO₄ Perovskite-like Mixed Oxides

Owing to the great concerns of global gas pollution problem,marine diesel engine exhaust emission standard has been improved again and again all over the world.It is of great significance for us to pay more attention to the technologys of simultaneous NOx-soot removal.More and more reseachers focused on the typical K2NiF4structure perovskite-like oxidesfor its unique structural characteristics.In this paper,a series of nanometric perovskite-like catalystswereprepared bycitric acid complexation andlow-temperature combustion synthesis.The physico-chemical properties ofthe catalysts were characterized by XRD,BET,FT-IR,H2-TPR,O2-TPD,NO-TPD,Soot-TPR,XPS and catalytic activity measurements.Firstly,in order to investigate the partial substitution of La in the Aposition,different elements like Sr,K,Na and Ce were doped in La2NiO4 to synthesize a series catalyats:La_1.8Sr_0.2NiO₄,La_1.8K_0.2NiO₄,La_1.8Na_0.2NiO₄,La_1.8Ce_0.2NiO₄.The result revealed that all catalyst showed a typical K₂NiF₄ structure,K⁺?Sr²⁺?Na⁺were doped in the perovskite-like oxides successfully,no other phase occurred,trace amount of CeOxemerge upon La_1.8Ce_0.2NiO₄.According to the activity evaluation result,La_1.8Sr_0.2NiO₄ catalyst exhibited the best catalyticperformance with ignition temperature around 331°C and temperatures of the peak maxima of sootcombustion were found to be 473°C,but the conversion ratio of NO closed to40%at 470°C.Then,with the purpose of improving the performance of simultaneous NOx-soot removal for catalysts,a series of La_2-xSr_xNiO₄?x=0,0.2,0.5?catalysts were prepared.It revealed that perovskite-like oxides had a large capacity of strontium.With the Sr content increased,catalysts showed better simultaneous removal ability.La_1.5Sr₀₅NiO₄ catalyst exhibited the best catalyticperformance with Tiaround 300°C and Tm were found to be470°C,the conversion ratio of NO closed to 87%at 470°C.Finally,on the condition that Sr doping amount was kept at 0.2 to ensure the stabilization of perovskite-like structure,the partial substitution of Ni in the B position with noble metal element Pd were carried out.For the sake of studying the influence of trace Pd on catalyst performance,a series of La_1.8Sr_0.2Ni_1-yPd_yO₄?y=0,0.01,0.03,0.05?catalysts were prepared successfully.It found that substitutionof Ni by Pd is essential for promoting catalytic ability.With the Pd content increased,catalytic ability increased first then descreased.La_1.8Sr_0.2Ni_0.99Pd_0.01O₄ showed the best catalyticperformance for soot combustionwith Ti around 265°C and Tm were found to be 468°C and well performance for NO removal with its conversion ratio could close to 91%at 470°C.Morever,perovskite-like oxides had a low capacity of palladium,the catalytic abilityoccurred a bluff type fall when Pd doping amount was 0.5.