掺杂La或Si对Ag/Al_2O_3催化剂热稳定性和脱NO活性的影响

Effects of Doping La or Si on Thermal Stability and NO Removal Activity of Ag/Al_2O_3 Catalysts

利用 BET比表面测定和 X-射线衍射技术考察了掺杂 La或 Si的 Ag/ Al2 O3催化剂的热稳定性 ,并研究了富氧条件下 ,丙烯在这些催化剂上选择性还原 NO的活性 .结果表明 ,掺杂 L a或 Si能抑制 Al2 O3相变 ,使 γ- Al2 O3完全转化为 α- Al2 O3的温度升至 1 1 0 0℃以上 .相应地 ,延缓催化剂比表面下降 ,从活性角度来看 ,当焙烧温度为 1 1 0 0℃时 ,与掺杂 La或 Si相比 ,不掺杂 La或 Si的 Ag/ Al2 O3催化剂活性要低得多 ;当焙烧温度低于 1 0 0 0℃时 ,掺杂少量 L a(2 % La2 O3)对 Ag/ Al2 O3催化剂活性影响不大 ,但是 ,掺杂 Si(2 %或 8% Si O2 )或较高含量 La(8% La2 O3)会导致催化剂活性降低 .综合考虑热稳定性和富氧条件下的 NO还原活性 ,认为掺杂较低含量 La(2 % La2 O3)的 Ag/ Al2 O3催化剂性能最佳 .

Silver catalysts,supported on La or Si\|doped alumina,were prepared.Their thermal stability was assessed using BET surface area measurement and X\|ray diffraction techniques.And the selective catalytic reduction of NO by propene in the presence of excess oxygen was investigated over these catalysts.The results indicate that doping La or Si suppresses the phase transformation of alumina and makes the γ Al 2O 3 to α Al 2O 3 phase transformation temperature increase to above 1100℃,which,accordingly,retards the surface area loss of catalysts.As far as NO reduction activities are concerned,when the calcination temperature is 1100℃,the NO reduction activities of La or Si\|free Ag/Al 2O 3 catalysts are much lower than that of La or Si\|doped Ag/Al 2O 3 catalysts.When the calcination temperature is no more than 1000℃,doping 2% La 2O 3 almost does not affect NO reduction activity of Ag/Al 2O 3 catalyst.However,doping 2%～8% SiO 2 and 8% La 2O 3 leads to the decrease in the NO reduction activities over Ag/Al 2O 3 catalysts.Based on these results,the 2% La 2O 3\|doped Ag/Al 2O 3 catalyst is thought to be optimal when the thermal stability and NO reduction activity are comprehensively considered.