N₂O Catalytic Decomposition Over Mixed Oxides Derived From Hydrotalcite-like Compounds

We researched hydrotalcite-like precursors and its mixed oxides in this paper, and the mixed oxides had been applied to N₂O catalytic decomposition.Kept the atomic ratio of M²⁺/M³⁺ constant to 3,series of hydrotalcite-like precursors with different Co content Co_xMg_3-xAl-HT (x = 0, 0.5,1, 1.5, 2, 2.5, 3) and different Fe content Co_2.5Mg_0.5Fe_xAl_1-x-HT (x = 0, 0.1, 0.3, 0.5,0.7, 0.9, 1)were synthesized by co-precipitation methods. Mixed oxides derived from these precursors through calcination were applied to N₂O catalytic decomposition. XRD, BET, TG-DSC and TPR techniques were used to study the influences of Co content on composition and structure of precursors and corresponding mixed oxides.The performances of N₂O catalytic decomposition on Co_xMg_3-xAlO catalysts were investigated and the impacts of reaction conditions, such as N₂O concentration, space velocity, O2 and H₂O on catalytic activity were also studied in detail. The results show that complete layer structure of hydrotalcite was formed in all precursors. After calcination, the main phase of catalyst is Co-Al spinel. Moreover, Co introduction promotes the formation of spinel. Mg can improve thermal stability of catalysts in some degree. Co content has important influence on the thermal stability, surface area, reducibility and activity of catalyst. With increase of Co content, surface area of catalysts decreases, however, surface area is not an important factor in N₂O catalytic decomposition. Two-stage reduction was observed in TPR tests of all Co-containing catalysts. The reduction process of Co was followed as the route: Co3+→Co2+→Co. Co_2.5Mg_0.5AlO catalyst calcined at 500℃shows relatively good activity on N₂O decomposition. Catalytic activity decreases with increase of calcination temperatures. N₂O concentration, space velocity and O2 have a little impact on activity in some sense, while H₂O obviously influences the activity of N₂O catalytic decomposition.Research of Co_2.5Mg_0.5FexAl1-x-HT expressed that series of hydrotalcite-like precursors also show complete layer structure, After calcination, the main phase of catalyst is spinel,too.but the N₂O catalytic activity was low the Co_xMg_3-xAlO.Maybe the Fe decreases catalysts'thermal stability.Furthermore, we had Co_2.5Mg_0.5AlO supported on ceria /zirconia(Ce-Zr) to decompose N₂O with the H₂O in present.The results show that the Co_2.5Mg_0.5AlO/Ce-Zr influence by H₂O was smaller than Co_2.5Mg_0.5AlO on N₂O catalytic decomposition.