Fe负载量对xFe/ZSM-5催化剂氨选择性催化还原NO的影响

采用旋转蒸发法,将过渡金属Fe负载到ZSM-5分子筛上,控制Fe负载量的变化,制备一系列xFe/ZSM-5(x为Fe负载量,x=0.1%(质量分数,下同)、0.7%、1.4%、2.1%,省略%)分子筛催化剂。对所制备xFe/ZSM-5的氨选择性催化还原(NH_3-SCR)NO活性进行评价,并通过不同表征技术对催化剂的结构和理化性质进行了测定。结果表明,Fe负载量对xFe/ZSM-5的NH_3-SCR活性影响较大。其中1.4Fe/ZSM-5取得最宽的活性温度窗口,在250～530℃的NH_3-SCR活性达到80%以上(以NO转化率计)。孤立Fe³⁺物种为xFe/ZSM-5催化剂低温段的主要活性物种,而低聚态Fe_2O_3物种会促进高温段NH_3的非选择性氧化,造成高温段NH_3-SCR活性下降;负载Fe物种后催化剂的强酸位数量减少,中酸位数量增加,中酸位有利于提高催化剂NH_3-SCR性能。

Effects of Fe loading quantity on the performance of xFe/ZSM-5 for the ammonia selective catalytic reduction of NO

The transition metal Fe was loaded on ZSM-5 molecular sieve by rotary evaporation method to prepared a series of xFe/ZSM-5 catalysts(x was Fe loading quantity,x=0.1%(mass ratio,the same below),0.7%,1.4%,2.1%,% omitted).The performances of xFe/ZSM-5 catalysts in NH3 selective catalytic reduction(NH3-SCR)of NO were investigated,and the structures and physicochemical properties of the catalysts samples were analyzed by different characterization techniques.The change of Fe loading quantity had a great influence on the NH3-SCR activity of xFe/ZSM-5.The sample with Fe loading quantity of 1.4% obtained the widest window range of activity temperature,with the NH3-SCR activity exceed 80%(accounted by NO conversion rate)in the range of 250-530 ℃.The isolated Fe^3+ was the main active species of xFe/ZSM-5 catalyst in the low temperature stage,while the oligomeric Fe2O3 species would promote the non-selective oxidation of NH3 in the high temperature stage,resulting in the decrease of NH3-SCR activity in the high temperature stage.After loading Fe species,the number of strongly acidic sites of the catalyst decreased,while the numbers of moderately acidic sites increased.The moderately acidic sites were beneficial to improve the NH3-SCR performance of the catalysts.