钴改性水滑石基LNT催化剂制备及其NO_x吸附-还原和碳烟催化氧化性能
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摘要
采用共沉淀法和浸渍法制备了贵金属负载的Co改性水滑石基LNT(leanNO_x trap)催化剂,通过多种实验手段表征其理化特性,并研究其NO_x吸附-还原性能及碳烟催化氧化性能.结果表明,Co的引入并不会破坏前驱体水滑石晶体结构,500℃焙烧后原本的水滑石结构被破坏,并出现明显的CoAl_2O_4尖晶石相.Co含量的上升会导致催化剂表面的Co—O吸附位增加,同时催化剂表面吸附的亚硝酸盐物种会逐渐向硝酸盐物种转化.此外,随着Co含量的增加,NO_x脱附峰温度向低温区域移动,脱附峰面积先增加后降低.Pt/BaO/Co_(2.7)Mg_(0.3)AlO催化剂在NO_x吸附-还原反应中对NO_x的净化效率达到89.6%,同时针对碳烟的催化氧化反应又表现出良好的催化性能.
A series of cobalt-doped hydrotalcite-based lean NO_x trap(LNT)catalysts with a well dispersed noblemetal were synthesized using the co-precipitation and impregnation methods.In addition to the physical-chemical properties,the performances of NO_x adsorption-reduction and soot oxidation of the prepared catalysts were also investigated using multiple experimental methods.The research results indicate that the addition of cobalt did not affect the original structure of hydrotalcite-like precursors.After calcination at 500 ℃,however,the structure of hydrotalcite precursors was destroyed,and the Co Al_2 O_4 spinel structure appeared.The increasing Co content would increase the Co—O adsorption sites on the LNT catalyst surface;meanwhile,the nitrite species on the catalyst surface were gradually transformed into nitrate species.Moreover,with the increase in Co loading,the peak temperature of NO_x desorption moved to the low temperature range,and the desorption capacity rose at first but then decreased.The Pt/BaO/Co_(2.7) Mg_(0.3) AlO catalyst achieved a NO_x reduction efficiency of 89.6%,and exhibited an excellent performance in the reaction of soot oxidation.
A series of cobalt-doped hydrotalcite-based lean NO_x trap(LNT)catalysts with a well dispersed noblemetal were synthesized using the co-precipitation and impregnation methods.In addition to the physical-chemical properties,the performances of NO_x adsorption-reduction and soot oxidation of the prepared catalysts were also investigated using multiple experimental methods.The research results indicate that the addition of cobalt did not affect the original structure of hydrotalcite-like precursors.After calcination at 500 ℃,however,the structure of hydrotalcite precursors was destroyed,and the Co Al_2 O_4 spinel structure appeared.The increasing Co content would increase the Co—O adsorption sites on the LNT catalyst surface;meanwhile,the nitrite species on the catalyst surface were gradually transformed into nitrate species.Moreover,with the increase in Co loading,the peak temperature of NO_x desorption moved to the low temperature range,and the desorption capacity rose at first but then decreased.The Pt/BaO/Co_(2.7) Mg_(0.3) AlO catalyst achieved a NO_x reduction efficiency of 89.6%,and exhibited an excellent performance in the reaction of soot oxidation.
引文
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[17]Yu J J,Cheng J,Ma C Y,et al.NOx decomposition,storage and reduction over novel mixed oxide catalysts derived from hydrotalcite-like compounds[J].Journal of Colloid&Interface Science,2009,333(2):423-430.
[18]Park Syungyong,Choi Byungchul,Kim Hwanam.Effective additives to improve hydrothermal aging of DME reforming catalyst in terms of hydrogen yield and de-NOx performance of RC+LNT combined system[J].Applied Catalysis A:General,2012,437/438:173-183.
[19]Park Syungyong,Kim Hwanam.Hydrogen production by steam reforming(SR)of DME over Cu catalysts and de-NOx performance of a combined system of SR+LNT[J].Catalysis Today,2011,164(1):240-245.
[20]Teraoka Y,Kanada K,Kagawa S.Synthesis of La-K-Mn-O perovskite-type oxides and their catalytic property for simultaneous removal of NOx and diesel soot particulates[J].Applied Catalysis B:Environmental,2001,34(1):73-78.
[2]Liu Zhiming,Woo S I.Recent advances in catalytic DeNOx science and technology[J].Catalysis Reviews,2006,48(1):43-89.
[3]Reichle W T.Synthesis of anionic clay minerals(mixed metal hydroxides,hydrotalcite)[J].Solid State Ionics,1986,22(1):135-141.
[4]李倩.Co、Mn水滑石基复合氧化物催化剂上碳烟和NOx的催化消除[D].天津:天津大学化工学院,2010.Li Qian.Catalytic removal of soot and NOx over Co-or Mn-based hydrotalcite-derived complex oxides catalysts[D].Tianjin:School of Chemical Engineering and Technology,Tianjin University,2010(in Chinese).
[5]Wang Z,Shangguan W,Su J,et al.Catalytic oxidation of diesel soot on mixed oxides derived from hydrotalcites[J].Catalysis Letters,2006,112(3/4):149-154.
[6]刘钰,杨向光,张忠良,等.以水滑石为前体的Mg-Al-M复合氧化物对催化消除NOx的活性[J].催化学报,1999,20(4):450-454.Liu Yu,Yang Xiangguang,Zhang Zhongliang,et al.Synthesis and characterization of composite oxide MgAl-M from hydrotalcite and its catalytic activity for NOx removal[J].Chinese Journal of Catalysis,1999,20(4):450-454(in Chinese).
[7]Ni Z,Chen A,Fang C,et al.Enhanced NOx adsorption using calcined Zn/Mg/Ni/Al hydrotalcite-like compounds[J].Journal of Physics&Chemistry of Solids,2009,70(3):632-638.
[8]Yu Junjie,Tao Yanxin,Liu Changchun,et al.Novel NO trapping catalysts derived from Co-Mg/X-Al(X=Fe,Mn,Zr,La)hydrotalcite-like compounds[J].Environmental Science&Technology,2007,41(4):1399-1404.
[9]Yu J J,Jiang Z,Zhu L,et al.Adsorption/desorption studies of NOx on well-mixed oxides derived from CoMg/Al hydrotalcite-like compounds[J].Journal of Physical Chemistry B,2006,110(9):4291-4300.
[10]ObalováL,KaráskováK,JirátováK,et al.Effect of potassium in calcined Co-Mn-Al layered double hydroxide on the catalytic decomposition of N2O[J].Applied Catalysis B:Environmental,2009,90(1):132-140.
[11]Chmielarz L,Ku?trowski P,Rafalska-?asocha A,et al.Catalytic activity of Co-Mg-Al,Cu-Mg-Al and CuCo-Mg-Al mixed oxides derived from hydrotalcites in SCR of NO with ammonia[J].Applied Catalysis B:Environmental,2002,35(3):195-210.
[12]Shangguan W F,Teraoka Y,Kagawa S.Promotion effect of potassium on the catalytic property of Cu Fe2O4,for the simultaneous removal of NOx,and diesel soot particulate[J].Applied Catalysis B:Environmental,1998,16(2):149-154.
[13]Shangguan W F,Teraoka Y,Kagawa S.Simultaneous catalytic removal of NOx,and diesel soot particulates over ternary AB2O4,spinel-type oxides[J].Applied Catalysis B:Environmental,1996,8(2):217-227.
[14]Prinetto F,Ghiotti G,Nova I,et al.FT-IR and TPDinvestigation of the NOx storage properties of BaO/Al2O3and Pt-BaO/Al2O3 catalysts[J].Journal of Physical Chemistry B,2001,105(51):12732-12745.
[15]Sedlmair C,Seshan K,Jentys A,et al.Elementary steps of NOx,adsorption and surface reaction on a commercial storage-reduction catalyst[J].Journal of Catalysis,2003,214(2):308-316.
[16]Sundararajan R,Srinivasan V.Catalytic decomposition of nitrous oxide on CuxCo3-xO4spinels[J].Applied Catalysis,1991,73(2):165-171.
[17]Yu J J,Cheng J,Ma C Y,et al.NOx decomposition,storage and reduction over novel mixed oxide catalysts derived from hydrotalcite-like compounds[J].Journal of Colloid&Interface Science,2009,333(2):423-430.
[18]Park Syungyong,Choi Byungchul,Kim Hwanam.Effective additives to improve hydrothermal aging of DME reforming catalyst in terms of hydrogen yield and de-NOx performance of RC+LNT combined system[J].Applied Catalysis A:General,2012,437/438:173-183.
[19]Park Syungyong,Kim Hwanam.Hydrogen production by steam reforming(SR)of DME over Cu catalysts and de-NOx performance of a combined system of SR+LNT[J].Catalysis Today,2011,164(1):240-245.
[20]Teraoka Y,Kanada K,Kagawa S.Synthesis of La-K-Mn-O perovskite-type oxides and their catalytic property for simultaneous removal of NOx and diesel soot particulates[J].Applied Catalysis B:Environmental,2001,34(1):73-78.