The Decomposition Of N₂O Over Co₃O₄-based Composite Oxide Catalysts

N₂O with high global warming potential is one of the greenhouse gases restricted by the Kyoto Protocol,which can also continuously destroy the ozone layer.Among the technologies for reduction of N₂O emission,the catalytic decomposition is considered as the promising elimination method due to its low energy consumption and high efficiency.This thesis aims to the decomposition of N₂O over Co₃O₄-based composite oxide catalysts.The research contents and results are listed as follows:?1?The effects of preparation methods,Nd/Co molar ratio and alkali metal additives of Nd-Co₃O₄ series catalysts were investigated.The techniques such as XRD,BET,SEM,XPS,H₂-TPR,and O₂-TPD were used to characterize the physicochemical properties of catalysts.The result shows that the 0.01Nd-Co₃O₄ catalyst prepared by hydrothermal method exhibited a high activity.After the addition of Nd,the crystallite size became smaller and the specific surface area increased,which is responsible to the improvement of catalytic activity.The addition of K could increase the electron density of the metal atoms,reduce the electron binding energy,as well as enhance the reducing ability and the removal of surface oxygen species,thus improving the catalyst activity.The catalyst of0.02K/0.01Nd-Co₃O₄ displayed the best activity,water and oxygen resistance and stability.?2?Y-Co₃O₄ series catalysts were prepared and the effects of different preparation parameters on the catalytic performance of N₂O catalysts were studied.Meanwhile the physical and chemical properties of the catalysts were characterized.The result shows that the 0.03Y-Co₃O₄ catalyst prepared by hydrothermal method exhibited a high activity.After the addition of Y,the crystallite size became smaller and the specific surface area increased,which was favorable for the decomposition of N₂O.Compared with the Nd-Co₃O₄ catalyst,the specific surface area of the Y-Co₃O₄ catalyst increased to a greater extent,and the catalytic activity is higher.In addition,it is found that the Co²⁺active sites over K-modified catalyst increased and the Co-O bond was weakened,thus oxygen species can be removed more easily,which was beneficial to the catalytic decomposition of N₂O.The catalyst of 0.02K/0.03Y-Co₃O₄ showed the best activity,water and oxygen resistance and stability.?3?Compared with the traditional co-precipitation at 90?,the Y-Co₃O₄-boiling catalyst had higher catalytic activity.As the temperature increases,the rate of urea hydrolysis became faster,and more OH^–species were produced,then the nucleation rate increased.When the nucleation rate was close to or greater than the growth rate,the catalyst tended to form smaller crystallites,which was beneficial to enhance the catalytic activity.In addition,the K promoter further improved the catalytic performance of the Y-Co₃O₄-boiling catalyst.Even when oxygen and steam were simultaneously present,the K/Y-Co₃O₄-boiling catalyst still exhibited good catalytic stability.?4?A preliminary exploration for the coupling reaction of N₂O decomposition and ethylbenzene dehydrogenation on Co-Al catalyst was conducted.The effects of catalyst composition and K modification on ethylbenzene conversion and styrene selectivity were studied.It is found that the catalyst with CoCo_0.5Al_1.5O₄ exhibited higher catalytic performance.After K-modification,the conversion of ethylbenzene reached 40%,and styrene selectivity more than 90% at 500?.