Study on N
2O Catalytic Decomposition over Mixed Oxides Derived from Co-Mg/Al Hydrotalcite-like Compounds
Acta Phys. -Chim. Sin.
2007, 23 (02):
Kept the atomic ratios of M2+/M3+ at a constant of 3, series of hydrotalcite-like precursors with different Co contents CoxMg3-xAl-HT(x=0, 0.5, 1, 1.5, 2, 2.5, 3) were synthesized by co-precipitation methods. Mixed oxides CoxMg3-xAlO were derived from these precursors through calcination. 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 over CoxMg3-xAlO catalysts were investigated and the effect of reaction conditions, such as N2O concentration, space velocity, O2, and H2O, on catalytic activity were also studied in detail. The results showed that complete layer structure of hydrotalcite was formed in all precursors. After calcination, the main phase of the catalysts was Co-Al spinel. Moreover, Co introduction promoted the formation of spinel. Mg could improve thermal stability of the catalysts to some degree. Co content had important influence on the thermal stability, surface area, reducibility, and activity of the catalysts. With increase of Co content, surface area of the catalysts decreased, however, surface area was 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. Co2.5Mg0.5AlO catalyst calcined at 500 ℃ showed relatively good activity in N2O decomposition. Catalytic activity decreased with increase of calcination temperatures. N2O concentration, space velocity, and O2 had a little effect on activity in some sense, while H2O obviously influenced the activity of N2O catalytic decomposition.
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