负载型La_(0.8)Sr_(0.2)CoO_3燃烧催化剂的载体效应

Effects of Support on the Performance of Combustion Catalyst La_(o.8) Sr_(0.2) CoO_3/γ-Al_2O_3

负载型 L a0 .8Sr0 .2 Co O3/γ- Al2 O3(L SC/γ- A )催化剂 ,由于钴离子在不太高的温度下易和载体γ- Al2 O3作用形成 Co Al2 O4尖晶石或类尖晶石 ,因而不能有效地成为 CO、 HC化合物完全氧化的催化剂 .采用 XRD、 BET、DTA、 TG和二甲苯完全氧化催化活性测试等手段 ,研究了 Co Al2 O4的形成过程 .可以认为这是一个放热、释氧而失重的过程 ,并伴有晶胞的稍微增大 .若在γ- Al2 O3表面涂敷一层以 Mg Al2 O4为主相的覆盖层 ,将有助于阻挡Co2 +离子进入 γ- Al2 O3的晶格 ,使涂层表面有效地生长出 L SC活性组分 ,提高其完全氧化的催化活性 .

Supported combustion catalyst La 0.8 Sr 0.2 CoO 3(LSC)/γ Al 2O 3 is expected to possess relatively high activity for the oxidation of carbon monoxide and many hydrocarbons. Cobalt ions can easily react with γ Al 2O 3 at not very high temperature (about 470 ℃) to form spinel or spinel like CoAl 2O 4, which decreases the activity of the combustion catalyst. In this work, the formation of spinel or spinel like CoAl 2O 4 was investigated using XRD, DTA, TG, BET and the catalytic activity for xylene complete oxidation was examined. The formation of CoAl 2O 4 is an exothermic and weight loss reaction and in this process the crystal cell is enlarged slightly which results in small shifts of d hkl towards lower values. When MgAl 2O 4 layer was covered on the surface of γ Al 2O 3 by impregnation, the entering of Co 2+ ions into γ Al 2O 3 lattice was restrained, then LSC was formed on the surface of MgAl 2O 4, which leads to good catalytic activity of xylene complete oxidation.