Mn、W掺杂菱铁矿催化剂对柴油机尾气SCR脱硝性能的影响

EFFECT OF SCR DENITRIFICATION PERFORMANCE WITH Mn AND W DOPED SIDERITE CATALYST FOR DIESEL ENGINE EXHAUST

对菱铁矿掺杂Mn、W等过渡金属元素制备催化剂用于柴油机尾气SCR脱硝。500℃煅烧菱铁矿催化剂在30000h^-1高空速下虽具较高SCR脱硝效率,但活性温度窗口较窄,仅在240~330℃内脱硝效率在90%以上,与柴油机尾气温度(200~400℃)有较大差距,故采用混合搅拌法对菱铁矿催化剂掺杂Mn改性提高其低温活性,掺杂W改性提高其高温活性,从而拓宽活性温度窗口。实验结果表明:单独掺杂3%Mn和3%W时,催化剂温度窗口分别拓宽至180~330℃和240~390℃。同时掺杂Mn和W,掺杂M0.01W0.03-菱铁矿催化剂在210~390℃内脱硝效率超过90%,基本符合柴油机尾气排放温度,可适用于柴油机尾气脱硝。运用BET、XRD和NH3-TPD等方法对催化剂进行表征发现,掺杂后的催化剂比表面积更大、表面结晶更弱、吸附位酸性更强,有利于提高柴油机尾气的SCR脱硝活性。

Catalysts prepared by doping Mn, W transition metals to siderite were used for SCR NO x removal of diesel exhaust in this paper.Although the siderite catalyst calcined at 500 ℃ had high de-NO x efficiency under a gas hourly space velocity of 30000 h ^-1 , the active temperature window was as narrow as 240~330 ℃, which had obvious difference from the range of diesel exhaust temperature, 200~400 ℃.Therefore, Mn was doped to siderite catalyst with mixing stirring method to improve its low-temperature activity, and W was doped to improve its high-temperature activity, thus the active temperature window was broadened.The experimental results showed that the active temperature windows of modified siderite catalysts were 180~ 330 ℃ and 240~390 ℃ by doped with 3%Mn and 3%W,namely.Furthermore,1%Mn^3%W doped catalyst kept its efficiency more than 90% in temperature range of 210~390 ℃, which was almost the same as the temperature range of diesel engine exhaust.The composition and structure of catalysts were characterized by BET, XRD and NH 3-TPD.The results showed that the doped catalyst had larger specific surface area, weaker surface crystal, and more acidic of adsorption sites, which was conducive to improve the catalytic activity of diesel exhaust NO x removal.