Co-Mg/Al类水滑石衍生复合氧化物上N_2O催化分解

N_2O Catalytic Decomposition over Mixed Oxides Derived from Co-Mg/Al Hydrotalcite-like Compounds

恒定二价与三价阳离子比为3((nCo+nMg)/nAl=3),采用共沉淀法制备不同Co含量的系列类水滑石前驱物CoxMg3-xAl-HT(x=0,0.5,1,1.5,2,2.5,3),经焙烧得到其衍生复合氧化物催化剂CoxMg3-xAlO.采用XRD、BET、TG-DSC和TPR等表征手段考察了Co含量对材料前驱物及其衍生复合氧化物组成和结构等方面的影响,研究了系列CoxMg3-xAlO催化剂的催化N2O分解性能;同时探讨了反应条件,如N2O浓度、空速、O2和H2O等因素对催化剂活性的影响.结果表明,所有前驱物材料均能形成完整的层状水滑石结构;经高温焙烧后形成了以Co-Al尖晶石为主相的复合氧化物,且Co掺杂有助于尖晶石相的生成;Co含量对材料的热稳定性、比表面、可还原性和催化分解活性有显著的影响;含Co复合氧化物催化材料存在两个还原峰,还原过程为Co3+→Co2+→Co;Mg有助于提高催化剂的热稳定性;随着Co含量增加,催化剂比表面下降,但比表面不是影响催化剂活性的主要因素;500℃焙烧后的Co2.5Mg0.5AlO催化剂具有较好的N2O催化分解活性;提高前驱物的焙烧温度导致催化剂的活性下降;N2O浓度、空速及O2对催化剂活性的影响较小,而H2O则对催化剂的活性有较大的影响.

Kept the atomic ratios of M^2＋/M^3＋ 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： Co^3＋→CO^2＋→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.