Cu/ZSM-5and K-promoted Co/MgO Catalysts For N₂O Decomposition

In recent years, the increase of atmosphere pollution from N2O compels the researchers giving an effective eliminating method to control the emission of N2O. Since the catalytic decomposition of N2O is direct and simple, the active catalyst that could be practically used for the N2O decomposition has drawn much attention in the world wide.The N2O decomposition catalyzed by Cu/HZSM-5(SiO2/Al2O3=25) was investigated in the thesis, and the optimal loading amount of Cu (7wt.%) was found out. It was found that adding proper amount of ammonia during the impregnation can significantly improve the activity of the catalyst. By means of UV-vis and XRD characterization, it was found that the number of the bis(μ-oxo)dicopper core [Cu2(μ-O)2]2+is increased in population due to the ammonia addition. Accordingly, the bis(μ-oxo)dicopper core [Cu2(u-O)2]2+was proposed to be highly active to the N2O decomposition.In this thesis, Co/MgO catalysts with different loadings of Co were prepared, and the optimal loading amount of Co (13wt.%) was found out. By means of Arrhenius plots, active sites catalyzing N2O decomposition on the different Co/MgO catalysts and the activation energy were estimated, with which the regulation of the catalytic activity changing with the cobalt loadings was well explained.It was found that the activity of Co/MgO catalyst can be effectively improved by doping the catalyst with alkali metals. The promotional effect for the alkali metals can be represented in the order K> Na> Li. The optimal ratio of K/Co for K doping the Co/MgO is K/Co=0.02. The activity of the0.02K-13%Co/MgO catalysts being prepared from different potassium precursors for the N2O decomposition are in the order of KNO3> K2CO3≈KOH≈CH3COOK≈K2C2O4≈K2SO4>KCl.The0.02K-13%Co/MgO catalyst obtained by calcination at500℃in air is the most active in all of the tested Co/MgO catalysts. It was found that the impregnation sequence of the MgO support with K and Co also affects the activity of the catalyst for the aimed reaction.H2-TPR and FT-IR characterization were used for studying the role of K in the catalyst for the reaction. The results reveal that the addition of K into Co/MgO can increase the number of active Co24sites in the catalyst, reduce the temperature of Co3+being converted to Co2+, and decrease the temperature of oxygen being released from the catalyst surface, which are the reasons why K effectively improves the activity of the catalyst for the N2O decomposition.