Cu-SAPO-44选择性催化丙烯还原NO性能研究

Selective catalytic reduction of nitric oxide with propylene over one-step synthesized Cu-SAPO-44 catalysts

以环己胺(CHA)和铜胺络合物(Cu-TEPA)为共模板剂,一步水热合成Cu-SAPO-44分子筛催化剂,用于贫燃条件下选择性催化丙烯还原NO(C_(3)H_(6)-SCR)。采用N_(2)吸附-脱附、X射线衍射(XRD)、透射电子显微镜(TEM)、紫外可见光谱(UV-vis)、NH_(3)程序升温脱附(NH_(3)-TPD)和H_(2)程序升温还原(H_(2)-TPR)等方法对催化剂进行表征。与纯SAPO-44相比,Cu-TEPA的引入显著增强了分子筛的C_(3)H_(6)-SCR催化活性。当Cu/Al=0.25时,Cu-SAPO-44催化剂有着最大的比表面积、丰富的酸性位和较多的孤立Cu^(2+)物种,具有最佳的脱硝性能。随着Cu-TEPA引入量的增加,铜物种会在分子筛表面聚集,生成相对较多无活性的CuO,从而降低了脱硝活性。原位红外光谱(In situ DRIFTS)研究表明,孤立的Cu^(2+)有助于NO和C_(3)H_(6)的吸附和活化,促进反应关键中间产物−NCO形成。50 h的持久性反应测试表明,Cu-SAPO-44催化剂始终保持>60%的NO_(x)转化率和>90%的N_(2)选择性,表现出良好的反应稳定性。

Cu-SAPO-44 zeolite catalysts were synthesized by one-step hydrothermal method using cyclohexylamine(CHA)and Cu-amine complex(Cu-TEPA)as co-template.They were used for selective catalytic reduction of nitric oxide with propylene(C_(3)H_(6)-SCR)under lean burning condition.These catalysts were characterized by N_(2) adsorption-desorption,X-ray diffraction(XRD),transmission electron microscopy(TEM),UV-vis spectroscopy(UV-vis),NH_(3) temperature-programmed desorption(NH_(3)-TPD)and H_(2) temperature-programmed reduction(H_(2)-TPR).Compared with pure SAPO-44,the introduction of Cu-TEPA significantly enhanced the catalytic activity of C_(3)H_(6)-SCR.When Cu/Al was 0.25,Cu-SAPO-44 catalyst had the largest specific surface area,abundant acidic sites and moderate isolated Cu^(2+)species,thus it had the best deNOx performance.With the increase of Cu-TEPA introduction,copper species would aggregate on the surface of the zeolite and form more inactive CuO,thus reducing the denitrification activity.In situ study by DRIFTS indicated that isolated Cu^(2+)could contribute to the adsorption and activation of NO and C_(3)H_(6),thus enhancing in the formation of−NCO,which was a key intermediate of the reaction.The Cu-SAPO-44 catalyst maintained more than 60%NOx conversion and more than 90%N_(2) selectivity in long term test of 50 h,showing appropriate reaction stability.