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甲烷氧化偶联Ti-La-Li系混合氧化物催化剂 总被引:4,自引:1,他引:3
研究了Ti-La-Li三元氧化物的组成、结构及其对甲烷氧化偶联反应的催化性能;用XRD、IR、XPS和SEM等方法对催化剂进行表征,结果表明:在LiTi_xLa_(1-x)O_2系列催化剂中,随x值的不同,可生成LaTi_(1-y)Li_yO_(3-λ)、Li_2TiO_3、La_(0.66)TiO_(2.993)、La_2O_3和Li_(1.33)Ti_(1.66)O_4几种物相,其中,钙钛矿到三元复合氧化物LaTi_(1-y)Li_yO_(3-λ)是甲烷氧化偶联反应的主要活性相,活性位Li~+-O~--Ti~(3+)的形成是活性提高的主要原因.Li_2TiO_3和La_(0.66)TiO_(2.993)是深度氧化活性相,而Li_(1.33)Ti_(1.66)O_4既无偶联活性,也无深度氧化活性. 相似文献
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甲烷氧化偶联La—Mn—Li系复合氧化物催化剂的研究 总被引:1,自引:0,他引:1
用XRD、IR、XPS和SEM等方法研究了混合氧化物LiLa_(1-x)Mn_xO_2的结构和它们对甲烷氧化偶联的催化性能。结果表明,随着MnO_2的变化,可形成一系列复合氧化物,其中三元复合氧化物La_2Mn_(1-y)Li_yO_4是甲烷氧化偶联的活性相,由于Li~+部分取代Mn~(2+)形成Li~+-O~--Mn(2+)缺陷簇,增加了活性氧种的浓度和再生速度是这种氧化物具有较高甲烷偶联活性的主要原因。脉冲实验证明,CH_4脱氢生成CH_3·偶联生成C_2H_6,进一步氧化脱氢生成C_2H_4都可在催化剂表面完成,而CO和CO_2是在气相反应中生成的。在780℃C_2收率可达23.9%。 相似文献
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甲烷氧化偶联反应近年来研究十分活跃。Lunsford等报道了载有碱金属的碱土氧化物是对此反应有效的催化剂,并提出晶格取代型活性中心[M~ O~-〕和表面活化、气相偶联的反应机理。Otsuka等系统地研究了稀土氧化物的甲烷氧化偶联活性,本文通过氧化镧中添加锂前后的对比,运用骤冷技术与ESR法研究了催化剂的表面活性氧,以低温TPD法研究了甲烷在催化剂表面上的吸附与活化,以及在甲烷氧化偶联中的催化行为。 相似文献
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自从1982年Keller首先报导了甲烷氧化偶联制乙烯、乙烷的催化反应以来,引起国内外广泛的重视,若甲烷的转化率C达35%,C_2的选择性S(C_2)达88%,乙烯/乙烷较大时,则甲烷氧化偶联催化过程可以工业化.当前国内外的工作重点是寻求甲烷转化率高,C_2选择性好的催化剂.Li和烯土复合氧化物催化剂引起人们注意,C_2的收率Y(C_2)可达24.6%,本文采用高温灼烧而成的Li-Nd-Mg复合氧化物,Y(C_2)可达31.3%. 实验部分Li-Nd-Mg复合氧化物由高温灼烧而成,实验采用小型固定床石英反应器,反应器的直 相似文献
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研究了铌掺杂的Li/MgO甲烷氧化偶联催化剂的反应性质及铌的助剂作用。铌的引入使得该催化剂上甲烷氧化偶联反应的活化温度降低50℃以上, 使此温度降到了催化剂中碳酸锂的熔点附近。试验观察到部分催化剂上甲烷氧化偶联反应的活性曲线在碳酸锂的熔点附近有一转折, 这一转折现象的出现与否及程度取决于制备条件。在碳酸锂的熔点附近, 含有铌的催化剂得到活化, 观察到无稀释气体时的反应引燃现象, 即温度增加几度活性便达到最大值。当在比碳酸锂熔点稍高的温度下且不稀释时反应, 含铌催化剂活性很高但很快失活, 在稍低于此熔点下则不失活, 但活性较低。这些试验结果表明, 含铌催化剂的活化与失活均与催化剂中的碳酸锂的相变化有关。试验还观察到了在稍高于碳酸锂的熔点下做寿命试验时, 甲烷氧化偶联反应的振荡现象。 相似文献
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《物理化学学报》2019,(9)
甲烷氧化偶联制乙烷、乙烯是一种最直接有效的甲烷转化工艺路线。催化剂的结构、碱性、活性组分的状态及分布和氧物种的性质是影响甲烷氧化偶联性能的重要因素,而这些因素与催化剂组成直接相关。以固体酸WO_3/TiO_2为载体,采用浸渍法制备出一系列负载Li、Mn活性组分的催化剂。利用电感耦合等离子体发射光谱(ICP-O_ES)、X射线衍射(XRD)、高分辨透射电镜(HRTEM)、CO_2程序升温脱附(CO_2-TPD)、O_2程序升温脱附(O_2-TPD)、H_2程序升温还原(H_2-TPR)、拉曼光谱(Raman)、X射线光电子能谱(XPS)和CH_4程序升温表面反应(CH_4-TPSR)等表征技术对催化剂进行了研究,发现Li的添加提高了C2选择性,并有效抑制了甲烷深度氧化形成CO_2的过程。XRD分析表明Li的添加不仅能够促进锐钛矿型二氧化钛向金红石型二氧化钛转化而且促使了高价锰离子的还原。XPS与CO_2-TPD分析表明Li的增加有利于增加催化剂表面的晶格氧含量和降低催化剂表面的碱性。O_2-TPD分析表明Li含量逐渐升高能够促使晶格氧的移动性增强,从而提高催化剂的反应性能。催化剂的性能受Mn物种的含量与价态的影响,过多的Mn物种对甲烷氧化偶联是不利的,易造成甲烷的深度氧化。同时,Li和Mn活性组分通过协同作用影响着催化剂的反应性能,能够形成新的活性物种MnTiO_3提高甲烷氧化偶联的低温活性。催化剂在n(Li):n(Mn)=2:1、反应温度750°C条件下,C2产率达16.3%,表现出最佳催化效果。 相似文献
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采用溶胶-凝胶法制备纳米钙钛矿型复合氧化物催化剂SrTi1-xLixO3-δ(x=0、0.025、0.050),用微型催化反应评价装置结合XRD、TEM、原位ESR和程序升温表面反应(TPSR)等方法,研究甲烷氧化偶联(OCM)纳米SrTi1-xLixO3-δ催化剂结构和催化性能。结果表明,B位掺杂适量的低价Li+离子可优化纳米SrTiO3催化剂低温(~650℃)甲烷氧化偶联催化性能,Li+掺杂量为0.025时获得最高的甲烷转化率和C2选择性。与柠檬酸法制相同组成的常规催化剂相比,SrTi0.975Li0.025O3-δ纳米催化剂具有较优良的低温OCM催化性能和相同温度下更高的C2选择性。SrTi0.975Li0.025O3-δ纳米催化剂优良的催化性能与其表面原子配位不饱和存在F中心相关。 相似文献
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甲烷在MnOx/SiO2催化剂上氧化偶联反应的研究 总被引:3,自引:1,他引:2
本文研究了催化剂MnOx/SiO_2在改进为连续进料反应条件下的催化活性及其催化反应机理.实验结果表明;锰负载量升至10(Wt)%时,甲烷转化率和C_2选择性均最高;进一步增大锰负载量时,催化剂中Mn_3O_4晶相形成,此时催化活性开始下降,说明催化剂中形成的硅酸锰盐与甲烷氧化偶联反应直接关联.反应初期,催化反应活性较高,但C_2选择性较低,反应几小时后,活性有所下降,但C_2选择性提高,最后.活性和选择性趋近稳定.进一步研究表明:催化剂中Mn~(2+)配位环境从反应前的八面体中介场转变为四面体强场,而且催化剂中Mn~(2+)浓度增大约100倍,说明Mn~(2+)浓度提高有利C_2选择性提高.反应稳定后的催化剂表面观察到Carbide(282.9 eV)和CHx(a)(X=0-3)(284.5 eV)碳物种存在,说明甲烷在催化剂表面吸附并分解:CH_4(g)→CH_3(a)→一CH_2(a)→→→Carbide,并讨论了甲烷通过CHx(a)在催化剂表面上迁移,直接偶联生成乙烯(X=2)和乙烷(X=3)的可能性. 相似文献
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YUAN Song-Yue ZHAO Zhen Changchun institute of Applied Chemistry Academia Sinica Changchun. Jilin YU Zuo-LongChengdu Institute of Organic Chemistry Academia Sinica Chengdu Sichuan 《天然气化学杂志》1995,(4)
The correlations of the calcination temperature.structure and catalvtic activity of the LiLa_(0.5)Ti_(0.5)O_(2-(?)) catalvsts with main phase and major active phase of perovskite-type trmary complex oxide LaTi_(l-y)Li_yO_(3-λ)m the Oxidative coupling of methane(OCM)have been studied The surface and bulk structures of the catalysts were characterized by means of XRD,XPS. IR.BFT and so on. The results clearly indicated that the effect of calcination temperature on the activity for the oxidative coupling of methaneis twofold On one hand.high calcination temperature is favoragble for Lisubstitution for Ti~(3 )into the lattice of LaTiO_3 and the production of moreoxygen vacancies at which active oxygen species are formed However,excessivelv high calcmation temperature makes Li~ substitution for Ti~(3 )less due to a httle change of structure or phases of the catalvst On the otherhand,the conversion of CH_4 drops because of the decrease of surface area,when the calcination temperature is raised. 相似文献
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XU Yi-De** HUANG Bu-WenWEI Xin-Yun HUANG Jia-ShengState Key Laloratory of CatalysisDalian Institute of Chemical Physics Academia SmicaDalian Ijiaoning 《天然气化学杂志》1995,(2)
A comparative study of the role of lattice and gaseous oxygen in theoxidative coupling of methane over Na~ /Cao and Ca_xSr_(1-x)TiO_3 perovskiteoxide catalysts was performed by using a pulse reaction technique with CH_4,O_2 and mixtures of CH_4and O_2.It was found that there is an oxygen species onthe Surface of Cao which is active only for the total oxidation of methane at thereaction temperature.These oxygen species.once reacted with methane andconsumed,can be regenerated by the adsorption of oxygen molecules from thegas phase or by the migration of the lattice oxysen from the bulk onto thesurface.In contrast,no such oxygen species and no reaction can be detected bymethane pulsed over Ca_xSr_(1-x)TiO_3perovskite oxide catalysts.Na~ can heavilysuppress the non-selective oxygen species on the surface,and When 5mol%Na~ was incorporated onto the surface of Cao,the sample showed no reactivityto methane.When oxygen exists in the gas phase,or the pulse containsmethane and oxygen,the reaction over(Cao is mai 相似文献
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研究了不同碱金属离子对CaO的促进作用,发现以Na~+的添加效果最好。在此基础上,研究了不同含钠化合物对CaO的促进作用,并用脉冲反应技术研究Na~+/CaO催化剂表面氧物种的特性及其作用。CaO表面上存在非选择性氧化的氧物种。Na~+对CaO的修饰作用是抑制非选择性氧化。当表面上的非选择性氧化的氧物种消耗后,体相的晶格氧会向表面迁移,以补充消耗掉的表面氧物种。消耗掉的表面氧物种也可由气相氧补充。CH_4脉冲和混合气脉冲说明仅靠[Na~+O~-]中心不足以使甲烷转化成C_2产物,必须有气相氧的参与才能使甲烷转化成C_2产物。 相似文献
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V. R. Choudhary V. H. Rane S. T. Chaudhari 《Reaction Kinetics and Catalysis Letters》1998,63(2):371-377
Pulse reaction of methane in the presence and absence of free (or gaseous) oxygen and that of ethane and ethylene in the absence
of free oxygen over Li−MgO, La−MgO and Sm−MgO (Li or La or Sm/Mg ratio=0.1) have been investigated for elucidating the role
of lattice and free oxygen in oxidative coupling of methane (OCM) over these catalysts. No significant role is played by the
lattice oxygen from these catalysts in the OCM process. The presence of free oxygen is essential for all these catalysts to
be active and selective in OCM process. However, lattice oxygen plays some role in ethane conversion but a very significant
role in ethylene conversion over these catalysts. 相似文献
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Screening of MgO——and Ce02-Based Catalysts for Carbon Dioxide Oxidative Coupling of Methane to C2+ Hydrocarbons 下载免费PDF全文
The catalyst screening tests for carbon dioxide oxidative coupling of methane (CO2-OCM)have been investigated over ternary and binary metal oxide catalysts.The catalysts are prepared by doping MgO-and CeO2-based solids with oxides from alkali(Li2O),alkaline earth (CaO),and transition metal groups (WO3 or MnO).The presence of the peroxide (O2^2-)active sites on the Li2O2,revealed by Raman spectroscopy,may be the key factor in the enhanced performance of some of the Li2O/MgO catalysts.The high reducibility of the CeO2 catalyst,an important factor in the CO2-OCM catalyst activity,may be enhanced by the presence of manganese oxide species. The manganese oxide species increases oxygen mobitity and oxygen vacancies in the CeO2 catalyst.raman and Fourier Transform Infra Red (FT-IR)spectroscopies revealed the presence of lattice vibrations of metal-oxygen bondings and active sites in which the peaks carresponding to the buld crystalline structures of Li2O,CaO,WO2 and MnO are detected.The performance of 5%MnO/15?O/CeO2 catalyst is the most potential among the CeO2-based catalysts,although lower than the 2%Li2O/MgO catalyst.The 2%Li2O/MgO catalyst showed the most promising C2 hydrocarbons selectivity and yield at 98.0%and 5.7%,respectively. 相似文献
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Screening of MgO- and CeO_2-Based Catalysts for Carbon Dioxide Oxidative Coupling of Methane to C_(2+) Hydrocarbons 总被引:1,自引:0,他引:1
The catalyst screening tests for carbon dioxide oxidative coupling of methane (CO2-OCM) have been investigated over ternary and binary metal oxide catalysts. The catalysts are prepared by doping MgO- and CeO2-based solids with oxides from alkali (Li2O), alkaline earth (CaO), and transition metal groups (WO3 or MnO). The presence of the peroxide (O2-2) active sites on the Li2O2, revealed by Raman spectroscopy, may be the key factor in the enhanced performance of some of the Li2O/MgO catalysts. The high reducibility of the CeO2 catalyst, an important factor in the CO2-OCM catalyst activity, may 相似文献