低温等离子体改性Mn-CeO_x催化剂强化甲硫醚催化氧化性能的机理
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摘要
为研究低温等离子改性催化剂的机理,利用介质阻挡放电产生低温等离子体改性Mn–CeO_x催化剂,并研究了不同放电功率和处理时间对催化剂物理结构及化学特性的影响。选取恶臭气体甲硫醚作为污染物对改性后的催化剂进行活性测试。结果发现,经过等离子体改性的催化剂活性提高,改性效果与放电功率和处理时间相关。同时选取催化剂进行XRD、BET、H_2–TPR和XPS表征测试,结果发现,等离子体改性后的催化剂比表面积增加,孔径增大;放电功率和放电时间都会对催化剂的表面物理结构、化学特性活性产生较大影响;表面活性氧以及Mn4+和Ce~(3+)含量增加,Mn和Ce相互作用增强。其中,Mn–Ce–20 W–60 min催化剂比表面积为66.92 m~2/g,孔容为0.172 cm~3/g,远大于未经处理的Mn–Ce催化剂,且具有较高的Mn4+和Ce~(3+)含量,与其他条件处理的催化剂相比,在催化氧化甲硫醚过程中催化活性最高。
In order to study the mechanism of nonthermal plasma(NTP) for modifying the catalyst, we applied nonthermal plasma to modify the Mn-CeOx catalyst in different modification conditions such as discharge power and treatment time for the oxidation of dimethyl sulfides(DMS), and studied the effects of discharge power and treatment time on the physical structure and chemical properties of the catalyst. And DMS was chosen as the pollutant in catalytic oxidation activity tests. The results showed that the catalytic activity increased after the nonthermal plasma treatment, and the modification effect was related to the discharge power and treatment time. To elucidate the plasma modification effect, XRD, BET, H_2-TPR, and XPS techniques were used for catalyst characterization, and it was found that the structural and morphological properties of the NTP-modified catalysts changed with higher surface areas and microspore volume. Both discharge power and treatment time had great influences on the surface physical structure and chemical properties of catalysts. The relative concentration of manganese and cerium ions in different valence on catalyst surface and oxidation states of surface species over catalysts also varied. High surface areas and microspore volume, high concentration of chemisorbed oxygen, Mn4+ and Ce~(3+), and the efficient synergetic catalytic effect between manganese ions and cerium ions played an important role in the higher activity of NTP-modified catalysts. The Mn-Ce-20 W-60 min catalyst possessed the highest BET surface area and pore volume of about 66.92 m~2/g and 0.172 cm~3/g, and showed the highest concentrations of chemisorbed oxygen Oα, Mn4+ and Ce~(3+) on the catalyst surface. Compared with other catalysts, the Mn-Ce-20 W-60 min catalyst showed the best catalytic activity for DMS oxidation.
In order to study the mechanism of nonthermal plasma(NTP) for modifying the catalyst, we applied nonthermal plasma to modify the Mn-CeOx catalyst in different modification conditions such as discharge power and treatment time for the oxidation of dimethyl sulfides(DMS), and studied the effects of discharge power and treatment time on the physical structure and chemical properties of the catalyst. And DMS was chosen as the pollutant in catalytic oxidation activity tests. The results showed that the catalytic activity increased after the nonthermal plasma treatment, and the modification effect was related to the discharge power and treatment time. To elucidate the plasma modification effect, XRD, BET, H_2-TPR, and XPS techniques were used for catalyst characterization, and it was found that the structural and morphological properties of the NTP-modified catalysts changed with higher surface areas and microspore volume. Both discharge power and treatment time had great influences on the surface physical structure and chemical properties of catalysts. The relative concentration of manganese and cerium ions in different valence on catalyst surface and oxidation states of surface species over catalysts also varied. High surface areas and microspore volume, high concentration of chemisorbed oxygen, Mn4+ and Ce~(3+), and the efficient synergetic catalytic effect between manganese ions and cerium ions played an important role in the higher activity of NTP-modified catalysts. The Mn-Ce-20 W-60 min catalyst possessed the highest BET surface area and pore volume of about 66.92 m~2/g and 0.172 cm~3/g, and showed the highest concentrations of chemisorbed oxygen Oα, Mn4+ and Ce~(3+) on the catalyst surface. Compared with other catalysts, the Mn-Ce-20 W-60 min catalyst showed the best catalytic activity for DMS oxidation.
引文
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[2]HONG S H,SHIN D C,LEE Y J,et al.Health risk assessment of volatile organic compounds in urban areas[J].Human&Ecological Risk Assessment,2017(2):1454-1465.
[3]邱坤赞,耿雪威,蔡宇翔,等.等离子体协同V2O5-WO3/TiO2催化降解恶臭气体的试验研究[J].浙江大学学报:工学版,2016,50(1):63-69.QIU Kunzan,GENG Xuewei,CAI Yuxiang,et al.Performance evaluation of hybrid system comprising plasma and V2O5-WO3/TiO2catalysts for odor gas decomposition[J].Journal of Zhejiang University:Engineering Science,2016,50(1):63-69.
[4]SHEKHER G B,HYUN K K,PANDEY R A,et al.Review of biotreatment techniques for volatile sulfur compounds with an emphasis on dimethyl sulfide[J].Process Biochemistry,2014,49(9):1543-1554.
[5]SHAHZAD K M,RAZZAK S A,HOSSAIN M M,et al.Catalytic oxidation of volatile organic compounds(VOCs)-a review[J].Atmospheric Environment,2016(140):117-134.
[6]OJALA S,PITKAHO S,LAITINEN T,et al.Catalysis in VOC abatement[J].Topics in Catalysis,2011,54(16):1224-1256.
[7]CHU H,HAO G H,TSENG T K.The kinetics of catalytic in cineration of dimethyl sulfide and dimethyl disulfide over an MnO/Fe2O3catalyst[J].Journal of the Air&Waste Management Association,2001,51(4):574.
[8]HUANG H B,XU Y,FENG Q Y,et al.Low temperature catalytic oxidation of volatile organic compounds:a review[J].Catalysis Science&Technology,2015,5(5):2649-2669.
[9]TANG X L,NING P,LI K,et al.Mn Ox catalysts modified by nonthermal plasma for NO catalytic oxidation[J].Journal of Physical Chemistry C,2012,116(18):10017-10028.
[10]RAHEMI N,HAGHIGHI M,BABALUO A A,et al.Plasma assisted synthesis and physicochemi cal characterizations of Ni-Co/Al2O3nanocatalyst used in dry reforming of methane[J].Plasma Chemistry and Plasma Processing,2013,33(4):663-680.
[11]PAN Y X,LIU C J,SHI P,et al.Preparation and characterization of coke resistant Ni/SiO2 catalyst for carbon dioxide reforming of methane[J].Journal of Power Sources,2008,176(1):46-53.
[12]WANG Z J,LIU Y,SHI P,et al.Al-MCM-41 supported palladium catalyst for methane combustion:Effect of the preparation methodologies[J].Applied Catalysis B Environmental,2009,90(3/4):570-577.
[13]MAHMOOD A,SEONG I W.Enhancement of catalytic activity of Au/TiO2 by thermal and plasma treatment[J].Korean Journal of Chemical Engineering,2013,30(10):1876-1881.
[14]ZHU X L,HUO P P,ZHANG Y P,et al.Structure and reactivity of plasma treated Ni/Al2O3 catalyst for CO2 reforming of methane[J].Applied Catalysis B Environmental,2008,81(1):132-140.
[15]ZHANG H,CHU W,XU H Y,et al.Plasma-assisted preparation of Fe-Cu bimetal catalyst for higher alcohols synthesis from carbon monoxide hydrogenation[J].Fuel,2010,89(10):3127-3131.
[16]YAN X L,LIU Y,ZHAO B R,et al.Enhanced sulfur resistance of Ni/SiO2 catalyst for methanation via the plasma decomposition of nickel precursor[J].Physical Chemistry Chemical Physics,2013,15(29):12132-12138.
[17]TANG X L,GAO F Y,XIANG Y,et al.Low temperature catalytic oxidation of nitric oxide over the Mn-CoOx catalyst modified by nonthermal plasma[J].Catalysis Communications,2015(64):12-17.
[18]MASATO M,MASATOSHI U,DAISUKE K,et al.MnOx-CeO2binary oxides for catalytic NOx sorption at low temperatures:sorptive removal of NOx[J].Chemistry of Materials,2000,12(10):3158-3164.
[19]LIN F W,HE Y,WANG Z H,et al.Catalytic oxidation of NO by O2over CeO2-MnOx:SO2 poisoning mechanism[J].Rsc Advances,2016.6(37):31422-31430.
[20]LIAO Y N,FU M L,CHEN L M,et al.Catalytic oxidation of toluene over nano rod-structured Mn-Ce mixed oxides[J].Catalysis Today,2013,216(6):220-228.
[21]JEAN-CHARLES D,GONBEAU D,VINATIER P,Et al.Systematic XPS studies of metal oxides,hy droxides and peroxides[J].Physical Chemistry Chemical Physics,2000,2(6):1319-1324.
[22]LIU G,YUE R L,JIA Y,et al.Catalytic oxidation of benzene over Ce-Mn oxides synthesized by flame spray pyrolysis[J].Particuology,2013,11(4):454-459.
[23]WAN Y P,ZHAO W R,TANG Y,et al.Ni-Mn bi-metal oxide catalysts for the low temper ature SCR removal of NO with NH3[J].Applied Catalysis B Environmental,2014,148(6):114-122.
[24]TANG W X,WU Xi F,LIU G,et al.Preparation of hierarchical layer-stacking Mn-Ce composite oxide for catalytic total oxidation of VOCs[J].Journal of Rare Earths,2015,33(1):62-69.
[25]HE J,GUNUGUNURI K.Ceria-modified manganese oxide/titania materials for removal of elemental and oxidized mercury from flue gas[J].Journal of Physical Chemistry C,2011,115(49):24300-24309.