Study On Catalytic Decomposition Of N₂O Over Cobalt Based Catalysts And Bismuth Species Photocatalysts

Nitrous oxide?N₂O?is one of the greenhouse gases which destroy ozone layer,pollute the environment and do great harm to human health.More attentions have been attracted on abating N₂O emissions.The direct catalytic decomposition of N₂O is one of the most efficient and economic methods.In this work,cobalt-based spinel mixed with metal oxide catalysts and partially doped by metal and bismuth-based photocatalysts were prepared by coprecipitation method and hydrothermal method respectively.The catalytic decompositions of N₂O over these catalysts were performed in fixed bed microreactor and batch photocatalytic reactor respectively.The prepared catalysts were characterized by XRD,SEM,BET,H₂-TPR,O₂-TPD-TG,XPS,UV-vis DRS,PL and FTIR.Doping transition metals?Cr,Fe,Cu,Ni?could not improve the activity of cobalt-based spinel catalyst for N₂O catalytic decomposition and even increase the temperature of N₂O decomposition.However,both rare earth metals?La,Ce,Pr,Nd?and alkaline earth metals?Mg,Ca,Sr,Ba?could improve the activity,and alkaline earth metal Sr-doped catalysts have the best performance.The activity evaluation results exhibit that the Sr_0.7Co_2.3O₄ catalyst performes the best catalytic activity with low temperature for N₂O decomposition when compared with other catalysts.The temperatures of conversion of N₂O?10%,50%,95%?with Sr-doped catalysts are 314 ^oC,382 ^oC and 450 ^oC,which have decreased104 ^oC,107 ^oC and 205 ^oC respectively when compared with Co₃O₄.The redox properties of catalyst play an important role on catalytic activity according to the mechanism of N₂O decomposition.The results of characterization show that catalyst doping with Sr partially has more Co²⁺component which is beneficial to adsorption and activation of N₂O,and the amount of oxygen vacancies is increasing at the same time,which promote the recombination and desorption of atomic oxygen in the active sites,thus improve the catalytic activity.All of the semiconductor photocatalysts Bi₂WO₆,BiVO₄ and Bi₂MoO₆ prepared by hydrothermal methods show the properties of response of visible light and photocatalytic activity of N₂O decomposition.The effect of hydrothermal temperature on physical and chemical properties and photocatalysis were investigated.The results show that Bi₂WO₆ prepared under 180 ^oC could exhibite good photocatalytic activity and the conversion of N₂O is 27.1%after illuminating of visible light for 12 h.The characterization results show that the size of Bi₂WO₆-180^oC is 8.9 nm.According to the quantum size effect,when the particle size is less than 10 nm,the smaller the particle size is,the easier the photogenerated electrons migrates to the surface of catalys,which also inhibites the recombination of electron-hole and improve the photocatalytic activity.