Mg掺杂改性γ-Fe_2O_3催化剂NH_3-SCR脱硝特性

Structural properties of Mg doped γ-Fe_2O_3 catalysts and their activities in the selective catalytic reduction with NH_3

采用共沉淀-微波热解法制备一系列不同Mg掺杂比的Fe_(1-x)Mg_xO_z(x=0,0.1,0.2,0.3)催化剂,研究Mg掺杂对γ-Fe_2O_3催化剂SCR脱硝活性的影响,并借助XRD,N_2吸附-脱附、SEM和EDS等手段对催化剂进行表征。Mg的最佳掺杂比为0.2,且Fe_(0.8)Mg_(0.2)O_z催化剂在325℃时脱硝效率可达99.1%,同时活性温度窗口为250~350℃。Fe_(0.8)Mg_(0.2)O_z催化剂主要活性组分为γ-Fe_2O_3,其中Mg以无定型状态存在,能够与晶格中的Fe相互作用形成良好的固溶体,其较大的比表面积(44.00 m^2/g)、比孔容(0.19 cm^3/g)为反应气体在催化剂表面吸附与活化提供了丰富的表面活性位;合理的孔结构分布、良好的孔间连通性则利于传质的快速进行。Fe_(0.8_Mg_(0.2)O_z催化剂最佳O_2体积分数为3%,推荐NH_3/NO为1;催化剂表面氧化能力的提高及反应物的快速吸附、活化有利于NH3-SCR反应的进行。

A series of magnetic iron-magnesium mixed oxide catalysts （Fe1-xMgxOz,where x =0,0.1,0.2,0.3） were synthesized via a novel co-precipitation method with microwave thermal treatment and their activities were tested on a quartz fixed-bed reactor.Physical properties of the catalysts were characterized by X-ray diffraction （XRD）,N2-ad-sorption-desorption,Scanning Electron Microscope （SEM） and Energy Dispersive Spectrometer （EDS）.Fe0.8 Mg0.2Oz with a wide temperature window of 250 ℃ to 350 ℃ was validated as the proper SCR catalyst,and the maximum NOx conversion of 99.1% was achieved at 325 ℃.Activity was strongly influenced by the γ-Fe2O3 crystalline phase,magnesium existed in an amorphous phase and interacted with iron oxide intensively to form solid solution.Optimum pore diameter distribution,appropriate surface area （44.00 m^2/g）,pore volume （0.19 cm^3/g） and abundant lattice oxygen could be guaranteed in Fe0.8 Mg0.2Oz catalyst,which was good for the diffusion process and enhanced the activity.The optimum O2 concentration of Fe0.8Mg0.2Oz catalyst was 3%,and recommended NH3/NO was 1.The improvement of oxidation ability on the surface of the catalyst and the rapid adsorption and activation of reactants were both in favor of NH3-SCR reaction.