不同形貌MnO_2及其负载Au催化剂的制备与CO和甲苯催化氧化性能研究
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摘要
以高锰酸钾和(或)硫酸锰为锰源,分别采用水热法和PVA保护的硼氢化钠还原法,制备了一维纳米棒状、线状和管状x Au/MnO_2(x为2%、4%、8%和10%)催化剂。一维棒状、线状和管状x Au/MnO_2中的MnO_2均为四方晶相α-MnO_2,其α-MnO_2样品的比表面积为48.4~114.0 m2/g。棒状4%Au/α-MnO_2的催化活性最好:在空速为20 000 m L/(g·h)的条件下,CO转化率达到50%和90%时的反应温度(T50%和T90%)分别为11.4和16.3℃;氧化甲苯的T50%和T90%分别为210和225℃。基于大量的表征结果和多组催化活性数据分析发现,棒状4%Au/α-MnO_2催化剂催化活性最好的主要原因是其低温还原性能最好、吸附氧物种浓度较高、催化剂上的Au纳米粒子高度分散、Au纳米粒子与α-MnO_2纳米棒之间有较强相互作用。
1-D nanosized rod-like, wire-like, and tubular α-MnO_2( x Au/α-MnO_2,x = 2%,4%,8%,10%) were prepared using the hydrothermal and PVA-protected Na BH4 reduction methods at different temperatures with KMn O4 and/or Mn SO4 as Mn source, respectively. It is shown that the α-MnO_2 in x Au/α-MnO_2 was tetragonal in crystal structure, surface area of α-MnO_2 nanorods, nanowires, and nanotubes was in the range of 48. 4-114. 0 m2/g. The4% Au/α-MnO_2 sample possessed the highest adsorbed oxygen species concentration and the best low-temperature reducibility, thus showing the highest catalytic activity: the T50%and T90%( temperatures required for achieving reactant conversions of 50% and 90%) were 11. 4 and 16. 3 ℃ for CO oxidation, and 210 and 225 ℃ for toluene oxidation at a space velocity of 20 000 m L/( g · h), respectively. Based on the characterization results and activity data, it is concluded that the better low-temperature reducibility, higher oxygen adspecies concentration, highly dispersed Au NPs, and stronger interaction between Au NPs and MnO_2 nanorods were the main factors influencing the catalytic performance of 4% Au/α-MnO_2.
1-D nanosized rod-like, wire-like, and tubular α-MnO_2( x Au/α-MnO_2,x = 2%,4%,8%,10%) were prepared using the hydrothermal and PVA-protected Na BH4 reduction methods at different temperatures with KMn O4 and/or Mn SO4 as Mn source, respectively. It is shown that the α-MnO_2 in x Au/α-MnO_2 was tetragonal in crystal structure, surface area of α-MnO_2 nanorods, nanowires, and nanotubes was in the range of 48. 4-114. 0 m2/g. The4% Au/α-MnO_2 sample possessed the highest adsorbed oxygen species concentration and the best low-temperature reducibility, thus showing the highest catalytic activity: the T50%and T90%( temperatures required for achieving reactant conversions of 50% and 90%) were 11. 4 and 16. 3 ℃ for CO oxidation, and 210 and 225 ℃ for toluene oxidation at a space velocity of 20 000 m L/( g · h), respectively. Based on the characterization results and activity data, it is concluded that the better low-temperature reducibility, higher oxygen adspecies concentration, highly dispersed Au NPs, and stronger interaction between Au NPs and MnO_2 nanorods were the main factors influencing the catalytic performance of 4% Au/α-MnO_2.
引文
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[3]YUAN C Z,GAO B,SU L H,et al.Interface synthesis of mesoporous Mn O2and its electrochemical capacitive behaviors[J].Journal of Colloid and Interface Science,2008,322:545-550.
[4]LIANG S H,TENG F,BULGAN G,et al.Effect of phase structure of Mn O2nanorod catalyst on the activity for CO oxidation[J].Journal of Physical Chemistry C,2008,112:5307-5315.
[5]HICKEY N,FORNASIERO P,KAPAR J,et al.Effects of the nature of the reducing agent on the transient redox behavior of NM/Ce0.68Zr0.32O2(NM=Pt,Pd,and Rh)[J].Journal of Catalysis,2001,200(1):181-193.
[6]FORNASIERO P,KAPAR J,SERGO V,et al.Redox behavior of high-surface-area Rh-,Pt-,and Pd-loaded Ce0.5Zr0.5O2mixed oxide[J].Journal of Catalysis,2001,202(1):56-59.
[7]THORM HLEN L P,SKOGLUNDH M,FRIDELL E,et al.Lowtemperature CO oxidation over platinum and cobalt oxide catalysts[J].Journal of Catalysis,1999,188(2):300-310.
[8]HOFLUND G B,GARDNER S D,SCHRYER D R,et al.Au/Mn Oxcatalytic performance characteristics for low-temperature carbon monoxide[J].Applied Catalysis B:Environmental,1995,B6(2):117-126.
[9]周仁贤,郑小明.Pt/Al2O3,Pd/Al2O3催化剂上CO氧化与表面氧脱出-恢复性能[J].催化学报,1995,16(4):324-327.ZHOU R X,ZHENG X M.Oxidation of CO and surface oxygen property on Pt/Al2O3and Pd/Al2O3[J].Chinese Journal of Catalysis,1995,16(4):324-327.
[10]SCHRYER D R,UPCHURCH B T,VAN NORMAN J D,et al.Effects of pretreatment conditions on a Pt/Sn O2catalyst for the oxidation of CO in CO2lasers[J].Journal of Catalysis,1990,122(1):193-197.
[11]SHEINTUCH M,SCHMIDT J,LECTHMAN Y,et al.Modelling catalyst-support interactions in carbon monoxide oxidation catalyzed by Pd/Sn O2[J].Applied Catalysis,1989,49(1):55-65.
[12]DONG G L,WANG J G,GAO Y B,et al.Preparation and characterization of Ce O2-Ti O2mixed oxides[J].Journal of Inorganic Materials,1999,14(6):873-880.
[13]ZHU H Q,QIN Z F,WANG J G,et al.Low temperature oxidation of CO over Pd/Ce O2-Ti O2catalysts with different pretreatments[J].Journal of Catalysis,2005,233(1):41-50.
[14]叶青,霍飞飞,闫立娜,等.α-Mn O2负载纳米Au催化剂低温催化氧化CO和苯的性能[J].物理化学学报,2011,27(12):2872-2880.YE Q,HUO F F,YAN L N,et al.Highly active Au/α-Mn O2catalysts for the low-temperature oxidation of carbon monoxide and benzene[J].Acta Physico-Chimica Sinica,2011,27(12):2872-2880.
[15]郝郑平,安立敦,王弘立.负载型金催化剂用于室温下CO的消除[J].环境污染与防治,1996(4):4-5.HAO Z P,AN L D,WANG H L.Supported gold catalyst for removing carbon monoxide at room temperature[J].Environmental Pollution&Control,1996(4):4-5.
[16]王芳.规整形貌Mn Ox的可控合成及其对甲苯氧化的催化性能研究[D].北京:北京工业大学,2012.