N_2O在Cu_xFe_(1-x)Fe_2O_4和Ni_xFe_(1-x)Fe_2O_4复合氧化物催化剂上的分解反应

用共沉淀法制备了一组具有尖晶石结构的Cu-Fe和Ni-Fe复合氧化物,用于有氧条件下催化分解N2O,考察了催化剂组成对催化活性的影响.用N2物理吸附(BET)、X射线衍射(XRD)、H2程序升温还原(H2-TPR)等技术对催化剂进行了结构表征.结果表明:在不同组成的Cu-Fe、Ni-Fe系列复合氧化物催化剂中,Cu Fe2O4和Ni Fe2O4对于N2O分解反应的初活性较高,这是因为Cu Fe2O4和Ni Fe2O4的比表面积较高、晶粒较小,而且其表面氧物种与金属(Cu2+、Fe3+)的化学作用较弱,氧物种易脱除、脱氧量较高.相比较而言,Ni Fe2O4催化剂上的N2O分解活化能低于Cu Fe2O4,Ni Fe2O4的初活性优于Cu Fe2O4.500℃连续反应100 h,Cu Fe2O4上的N2O转化率降至84.9%,而Ni Fe2O4上的N2O转化率一直保持99%,Ni Fe2O4有较高的催化稳定性.

Catalytic Decomposition of N2O over CuxFe1-xFe2O4 and NixFe1-xFe2O4 Composite Oxides

A series of Cu-Fe and Ni-Fe composite oxides with spinel structure were prepared by a co-precipitation method for N2O decomposition in the presence of oxygen. The effect of composite oxides compositions on catalytic performance was investigated. These catalysts were characterized by means of nitrogen physisorption (BET), X-ray diffraction (XRD) and temperature-programmed reduction of hydrogen (H2-TPR) techniques. It is shown that CuFe2O4 and NiFe2O4 exhibited higher activity for N2O decomposition in Cu-Fe and Ni-Fe composite oxide families, respectively, due to their higher surface area, smaller crystallite, weaker interaction between oxygen species and surface active sites and larger amount of desorbed oxygen in reduction process. The kinetic data suggested that the apparent activation energy (Ea) of N2O decomposition reaction over NiFe2O4 catalyst is lower than that over CuFe2O4 catalyst, thus the catalytic activity of NiFe2O4 is higher than CuFe2O4. After reaction at 500 C for 100 h, the conversion of N2O over CuFe2O4 catalyst declined from 98.7% to 84.9%, whereas N2O conversion over NiFe2O4 always kept 99%. It can be concluded that NiFe2O4 is a stable catalyst in N2O decomposition reaction.